Chapter 18 Total Body Irradiation
History of Total Body Irradiation
Only a decade after Roentgen described the “x ray,” German biophysical engineer Friedrich J. Dessauer1,2 first described a “new technique of radiotherapy” that involved homogenous irradiation of the entire body. In his initial report describing the technique in 1905, he proposed irradiating a supine patient using three simultaneously active, low-voltage roentgen-ray sources (Fig. 18-1). In 1907, Aladár Elfer,3 a medical professor in Hungary, reported his experience using a TBI technique that spared the head in three patients with leukemia. Although there is a paucity of data regarding the early use of the technique, some have speculated that untoward hematologic toxicity probably limited its application.4
Figure 18-1 Diagram demonstrating the total body irradiation technique proposed by Dessauer in 1905.
Reprinted from Wetterer J (ed): Handbuch der Röntgentherapie nebst Anhang. Die Radium Therapie. Leipzig, Otto Nemnich, 1908.
Early success using TBI to treat hematopoietic and lymphoid malignant tumors in Europe (there named the Teschendorf method) prompted development of the technique in the United States.5–7 Arthur C. Heublein, in collaboration with Gioacchino Failla, is credited with the development of the first TBI unit in North America, located at Memorial Hospital in New York City. In the United States, the technique became known as “Heublein therapy.”8 A specially constructed treatment ward was designed to treat four patients at extended distance (5 to 7 m) simultaneously at an exposure rate of 0.7 roentgen (R)/hour, for about 20 hours/day, typically over 1 to 2 weeks, using a 185-kV x-ray tube at 3 mA, with a 2-mm copper filter. The goal was to deliver 25% of the erythema dose (750 R).
Remarkably, in Heublein’s initial report, no hematopoietic toxicity was noted with this treatment schedule. Seven of 12 patients (58%) with advanced lymphomas and leukemias and 2 of 8 patients (25%) with metastatic breast, melanoma, and kidney cancers were noted to demonstrate some form of improvement after treatment.9,10 A later report of the experience with 270 cancer patients from Memorial Hospital treated with TBI between 1931 and 1940 confirmed that the technique was more successful in patients with hematopoietic and lymphoid cancers compared with those with carcinomas or sarcomas, for whom it was ineffective. The authors emphasized that the technique was safe if doses were prescribed cautiously. They did not recommend exposures greater than 300 R and noted hematopoietic and gastrointestinal toxicity with exposures as low as 50 to 100 R.8
In the early 1940s, World War II prompted an initiative to develop nuclear weapons, called the Manhattan Project. Part of this endeavor sponsored research into the human biologic response to ionizing radiation, including TBI. The military’s interest in TBI was primarily to help understand human tolerance for radiation exposure during occupational duties and warfare and to develop radiation biodosimetric assays. Several research studies coordinated through the Manhattan Project were initiated in patients with advanced cancers,11–13 as well as patients with benign diseases.13 For example, studies of dose escalation, radiation biologic dosimetry, and cognitive and psychomotor function were carried out at the M.D. Anderson Hospital for Cancer Research.14 A detailed report of 30 patients treated at the maximum exposure level (200 R) in the initial study concluded that side effects primarily consisted of nausea, vomiting, and myelosuppression, and that intervention was necessary in 10% of patients treated with this dose of TBI.15 At Baylor University College of Medicine, studies using 25 to 250 R of TBI with 250 kV to 2 MV photons were performed to find a biologic dosimeter, as well as to study acute effects of radiotherapy.16 The Sloan-Kettering Institute for Cancer Research also participated in similar studies of at least 20 patients, although the results were never published. The military conducted similar studies at the Naval Hospital in Bethesda, Maryland, and reported palliation of patients with radiosensitive diseases treated with fractionated TBI.17 
The most recent research study of TBI sponsored by the U.S. Department of Defense was at the University of Cincinnati. It focused on identifying biochemical markers in the urine that predicted response to TBI. Later, studies of the neuropsychiatric effects of TBI were initiated. Ultimately, only results regarding the palliation of advanced cancers were reported.18 Patients with advanced metastatic radioresistant malignant tumors, for whom chemotherapy was unavailable, were often treated with TBI in the absence of any clear anticipated benefit. Patients treated with TBI in this manner were included in research studies, often without consenting to participate. The ethics of this practice was called into question by a report written in 1995 by the U.S. Department of Energy’s Advisory Committee on Human Radiation Experiments,19 which may have contributed to the public’s general uneasiness regarding radiation.20
TBI was not only used in malignant diseases, but it was considered the critical immunomodulator in the first successful solid organ transplant. In 1959, a kidney was successfully transplanted between dizygotic twins after TBI at exposures of up to 450 R (given to the recipient).21 Around the same time in France, successful kidney transplants after TBI were being reported.22,23 Of the first seven patients who underwent kidney transplant following TBI and/or pharmacologic immunomodulation worldwide between 1959 and 1962, the two who did not experience kidney failure were treated with TBI alone (without chemical immunosuppression) before transplant, and each survived for more than 20 years after transplant.21,22,23 However, successful preclinical studies with pharmacologic therapy prompted the use of chemical immunosuppressants (corticosteroids, 6-mercaptopurine, and azathioprine) for solid organ transplantation after 1963.24
With an increased understanding of the human response to TBI and a rapidly growing body of preclinical in vivo studies of TBI, therapeutic protocols were developed to maximize benefit in patients with malignant diseases. In 1957, Nobel laureate E. Donnall Thomas25,26 first reported the use of bone marrow infusion in humans following whole body irradiation or chemotherapy, and less than 1 year later he published his experience in using TBI with exposures up to 600 R followed by bone marrow transplantation. In the series of the first five patients with leukemia treated with TBI, who then received intravenous infusion of normal donor marrow, Thomas and colleagues26 noted the difficulty of acute myelosuppression and resultant hemorrhage and infection during the period leading up to engraftment. The report also commented that low dose rates (delivery over 2 to 3 days) appeared preferable to higher dose rates, for metabolic and immunologic reasons. In addition, patients receiving 200 to 300 R fared better than those receiving 400 to 600 R. The problem of delivering an adequately homogenous dose was raised, and suggestions about using higher-energy photons were proposed. Thomas and associates27 later reported on syngeneic bone marrow transplantation in two children after 850 to 1140 R was delivered in a single fraction over 22 to 25 hours, using cobalt-60 (60Co) sources. The authors concluded that 1000 R of TBI did not produce “troublesome” acute radiation sickness, did produce remission of leukemia, but did not cure the disease. The first report of successful cure of a patient with leukemia with allogeneic transplantation after TBI was reported in 1969. The technique involved opposed 60Co sources, which operated at 5.8 R/minute, to a total exposure of 1620 R, calculated to be 954 rad at midline. With appropriate supportive care, no major acute radiation sickness was noted, but the patient died of overwhelming cytomegalovirus infection, without evidence of leukemia.28
Over the next several years, techniques of combining chemotherapy and TBI were developed and refined, with promising results.29,30 Success in the treatment of advanced leukemias and severe aplastic anemia was achieved. Departure from the use of TBI alone was primarily fostered by the development of more effective cytotoxic chemotherapeutics and immunologic therapies, which when combined with TBI, yielded fewer leukemic recurrences.29 Although the use of TBI without HSCT has largely been abandoned, primarily for fear of inducing secondary malignant tumors and limiting later therapeutic options, some question the validity of this fear, and still contend that very low dose TBI (1.5 to 2 Gy in 10 to 20 fractions over several weeks) is a viable option for initial therapy in advanced indolent lymphomas.31 Figure 18-2 demonstrates how the use of TBI during HSCT has remained constant or increased over the past few years.32
Hematopoietic Stem Cell Transplant
Hematopoietic stem cell transplant (HSCT) has evolved into a highly complex clinical discipline, firmly rooted in immune system and cancer biology, the details of which are beyond the scope of this chapter. When HSCT was initially performed (see History of Total Body Irradiation), bone marrow was extracted from the donor, filtered, and infused intravenously into the recipient. Later, peripheral blood stem cells, instead of bone marrow, were collected from the donor as an alternative to bone marrow grafting. For this reason, “bone marrow transplants” are now more appropriately termed “hematopoietic stem cell transplants” because the critical component of the graft is the hematopoietic stem cell (HSC), independent of the source. The peripheral blood stem cells are often “mobilized” from the donor using hematopoietic growth-stimulating factors and are removed from the donor by apheresis. In addition, recent success using HSCs derived from human umbilical cord blood has been described. Depending on the source of HSCs, various postcollection processing measures (e.g., cell selection and depletion) may be undertaken to optimize the outcome of the transplant.
When transplant occurs between different individuals, the hematopoietic graft is said to be an allogeneic graft. This is in contradistinction to reinfusion of native HSCs back into the donor in an autologous transplant, more appropriately termed an autoplant, because nothing is being transferred between different individuals.33 A rare but alternative situation is when an organ from a genetically identical twin of a patient is transplanted (syngeneic transplant). Of these three methods of HSCT, autologous and syngeneic transplantations are generally associated with less risk because issues related to immunocompatibility are minimized. Allogeneic transplantations require the “matching” of donor and recipient and are typically carried out through identification of human leukocyte antigen (HLA) compatibility. The donor may be related to the recipient or may be identified through registries of volunteers, such as the National Marrow Donor Program.
Before undergoing HSCT, most patients will require intensive antineoplastic and/or immunomodulatory therapy, often referred to as conditioning, in preparation for HSCT. Conditioning can involve cytotoxic chemotherapy, immunomodulators, antibody therapy, or radiation therapy. The nature of the conditioning regimen can be referred to as of high or reduced intensity or as myeloablative, submyeloablative, or nonmyeloablative, to carry out conventional or mini-(ature) transplants.33 Although agreed-on formal definitions of these regimens do not exist,34 the goal of high-intensity/myeloablative/conventional transplant is to completely eliminate the recipient’s native HSC compartment, which necessitates HSCT (autologous or allogeneic) for survival. High-intensity/myeloablative/conventional transplants may or may not involve TBI to high doses (>5 Gy in a single fraction, >8 Gy in multiple fractions). Reduced-intensity/nonmyeloablative/mini-transplant conditioning regimens are often used for older patients or those with medical problems, for whom a high-intensity/myeloablative/conventional transplant would cause excessive morbidity or mortality, and may or may not involve TBI to lower doses. During and immediately after conditioning, the transplant recipient is at significant risk for infections and other hematologic complications. For this reason, the supportive care of HSCT recipients is complex and should only be undertaken in specialized facilities. Nonetheless, some groups have developed reduced-intensity and myeloablative HSCT regimens, including TBI, which have been safely undertaken on an outpatient basis.35,36
According to data summarized by the Center for International Blood and Marrow Transplant Research (CIBMTR) in 2006, the diseases most commonly treated with HSCT in North America are (in decreasing order of frequency) multiple myeloma (MM), non-Hodgkin’s lymphoma (NHL), acute myelogenous leukemia (AML), Hodgkin’s disease (HD), acute lymphoid leukemia (ALL), myelodysplastic and myeloproliferative syndrome (MDS), chronic myelogenous leukemia (CML), aplastic anemia (AA), and various other leukemias, cancers, and nonmalignant diseases.37 The 2009 National Comprehensive Cancer Network (NCCN) guidelines for therapy indicate that allogeneic or autologous HSCT may be a treatment option for testicular cancer, AML, MM, MDS, CML, HD, and NHL, depending on the clinical situation. HSCT with or without TBI-based conditioning has also been described in the treatment of solid tumors, including breast cancer, germ cell tumors, renal cell carcinoma, melanoma, neuroblastoma, and other pediatric cancers. Detailed discussion of these diseases and their management is beyond the scope of this chapter, and the reader is referred to other appropriate chapters in this text and other texts for further review.38–41 The role of TBI in nonmalignant diseases will be discussed further in subsequent sections of this chapter.
Radiobiology
Preclinical studies have helped define some of the fundamental radiobiologic properties of the normal lymphocytes. The D0 (see Chapter 5) of normal lymphocytes has been reported to be 0.5 to 1.4 Gy,42–45 depending on the in vitro or in vivo model used to calculate this parameter. This D0 suggests that normal lymphocyte cells are very sensitive to ionizing radiation. A very small shoulder on the radiation cell survival curve has been noted,46,47 suggesting little repair between fractions of radiation. Clinical data have revealed similar findings in patients undergoing hyperfractionated TBI, with lymphocyte survival demonstrating an effective D0 of 3.8 Gy, according to one study.48 Other radiobiologic phenomena have been ill defined in other normal hematopoietic cells. Radiobiologically relevant levels of hypoxia are unlikely in the hematopoietic compartment. Repopulation is not likely to influence hematopoietic cell survival, given the short duration of most TBI regimens (1 to 5 days), although given the variable life span of leukocytes (days to years), it may be of some relevance. Redistribution would appear to be of significance, given the time scale for TBI; however, this has been difficult to assess.49
The radiobiology of malignant hematopoietic cells has been described. The D0 of leukemic cells generally ranges from 0.8 to 1.5 Gy; however, compared with normal hematopoietic cells, a wider range of radiosensitivities have been described.50,61 Many have cited the technical nuances and variations in assay technique for this great range.49,62 Similar to normal hematopoietic cells, their malignant counterparts are thought to demonstrate little sublethal damage repair,63,64,65–67 although split-dose-rate and low-dose-rate experiments have demonstrated the capacity of leukemic cells to repair radiation-induced damage.55–59,68,69 Generally, leukemic cells are thought to have a cell survival curve with a minimal shoulder or no shoulder, although this varies across cell types and cell lines.47,51–54 For example, Cosset and colleagues62,70 summarized preclinical and clinical findings, concluding that AML demonstrates little repair, whereas CML does demonstrate repair; ALL, myeloma, and lymphomas have not been well studied but appear to demonstrate a wide range of repair capacity. Similar to normal hematopoietic cells, reoxygenation is unlikely to be radiobiologically relevant to malignant hematopoietic cells during TBI. Redistribution and repopulation, however, may be relevant but have not been systematically studied. 
In vivo preclinical research laid the foundation for the first successful HSCT in humans. Studies in rats,71 dogs,72 and nonhuman primates73 demonstrated that reconstitution of the hematopoietic system was possible after TBI with supralethal doses of radiation. Later work in animals revealed that delivering TBI in several fractions required a higher total dose relative to the biologically isoeffective dose given in a single fraction.74–76 Another model demonstrated no significant difference in the effect of a low-dose-rate (0.04 Gy/minute), single-fraction of TBI compared with a hyperfractionated course of TBI given three times a day to the same total dose.77
Although the hematopoietic system is the target of TBI, normal tissues effectively limit the dose that can be safely delivered. The sparing of normal tissues with fractionated TBI was proposed by Peters and colleagues63,64 and was subsequently supported by preclinical data in mice78,79 and dogs80 that showed that less lung injury occurred with fractionated TBI regimens.
Immediate Toxicity and Management in Total Body Irradiation
Although a good deal of what has been learned about the acute in vivo biologic effects of TBI has been derived from laboratory-based animal studies, whole body irradiation also has been studied in people exposed during accidental or wartime nuclear events.81,82 These large-scale studies are valuable because they deal with apparently normal subjects; however, the retrospective nature limits the quality of the data. The reader is referred to several excellent texts for a review of acute and fatal radiation syndromes (gastrointestinal, hematopoietic, and cerebrovascular syndromes) that can be caused by TBI in an uncontrolled setting.83–85
Acute side effects of therapeutic TBI can be difficult to distinguish from other HSCT-related morbidities. However, Chaillet and colleagues86 conducted an informative prospective clinical study of the symptoms and signs that occur in patients after TBI, before the initiation of any other HSCT-related therapy. Thirty-one patients, 4.5 to 55 years of age, were treated using parallel-opposed anteroposterior 18-MV photons from a linear accelerator. Shielding was used to limit the lung dose to 8 Gy. A total dose of 10 Gy was given as a “single dose” as six discrete fractions of 1.6 Gy each given over 15 minutes, with a 30-minute break between fractions, for a mean dose rate of 0.04 Gy/minute and an instantaneous dose rate of 0.11 to 0.12 Gy/minute. Symptoms and signs were assessed regularly during the 4-hour TBI and for 20 hours after the completion of TBI. Antiemetics, but no chemotherapy or steroids, were given before the start of TBI. Table 18-1 displays the symptoms and signs experienced by patients during the 4 hours of TBI and within 24 hours of starting TBI. 
The results of a similar study conducted by Buchali and colleagues87 of patients who were treated with a fractionated course of TBI delivered mostly to a total dose of 12 Gy using 2 Gy per fraction, twice daily, 8 hours apart, with lung doses limited to 10 Gy, are also summarized in Table 18-1.
A prospective clinical study showed that fractionation of TBI can reduce acute nausea, vomiting, mucositis, diarrhea, and parotitis, although the differences were not statistically significant. Late cutaneous eruptions were more common in patients undergoing fractionated TBI, although the numbers were not statistically significant. The same study, which randomized patients to either high- or low-dose-rate TBI, revealed no differences in the acute toxicities mentioned when comparing dose rate.88 Another randomized controlled trial (RCT) reported that fractionating TBI revealed “no apparent difference in acute toxicity” compared with single-fraction TBI, with both regimens being “well-tolerated.”89
Older studies cite nausea and vomiting as frequent side effects of TBI. These symptoms have been substantially minimized with the advent of more effective antiemetics, such as the 5-hydroxytryptamine (serotonin) receptor-3 (5-HT3) antagonists. Several small but high-quality controlled clinical studies support the prophylactic use of 5-HT3 antagonists to reduce nausea and vomiting during TBI90–94; they are summarized in web-only Table 18-2, available 
on the Expert Consult website. The use of corticosteroids in conjunction with 5-HT3 antagonists is supported by a trial listed in Table 18-2. However, given the toxicity associated with this approach, consensus regarding routine administration in conjunction with TBI is lacking.95–97 Of note, less nausea and vomiting have been noted in myeloablative conditioning regimens involving TBI compared with those that use chemotherapy alone, even with modern antiemetics.98
TABLE 18-2 Randomized Controlled Trials of Prophylactic Antiemetics in Patients Undergoing Total Body Irradiation
Oral mucositis is a side effect of TBI in up to 75% of patients undergoing myeloablative TBI, causing mouth pain and odynophagia and necessitating intensive supportive care such as total parenteral nutrition and opioid analgesics.99 In one study, intensive dental hygiene conferred a reduction in the rate of moderate and severe mucositis, although the authors thought the rate to be clinically insignificant.100 Topical oral agents, such as chlorhexidine digluconate and neutral calcium phosphate in conjunction with topical fluoride treatments can decrease pain duration and severity of oral mucositis, as well as pain and need for opioid analgesics.101–103 Similarly, prophylactic oral sucralfate and clarithromycin have reduced moderate and severe oral mucositis rates.104,105 One study showed that when given prophylactically, amifostine limited the duration of mucositis, with an associated decrease in the rate of moderate and severe infections, with no effect on HSCT outcome.106
In one study, researchers noted that short-term intravenous recombinant granulocyte-macrophage colony–stimulating factor decreased rates of moderate to severe mucositis,107 but in another study, they found no effect when this agent was delivered topically.108 Recently, Spielberger and associates109 reported the results of a trial of the recombinant human keratinocyte growth factor palifermin, given before and after conditioning with 12 Gy of fractionated TBI. Palifermin reduced the rate and duration of moderate and severe mucositis by 35% and 3 days, respectively, and decreased mouth and throat pain, as reflected in reduced morphine usage and decreased need for total parenteral nutrition (by 24%). This study dealt only with patients undergoing autologous HSCT; however, in the setting of TBI for allogeneic HSCT, palifermin may also confer a protective effect on the mucosa, although this has not been studied in an RCT.110
Skin erythema may also be noted toward the end of a course of TBI; desquamation is rare. Hyperpigmentation may be noted in the long term. Alopecia typically occurs 7 to 14 days after TBI is complete, and hair typically returns 3 to 6 months after treatment.111 Changes in the color or texture of regrown hair have been noted by some. Of note, myeloablative conditioning regimens using chemotherapy alone have noted a significantly higher incidence of permanent alopecia.112
Later Toxicity and Its Management in Total Body Irradiation
Hematopoietic Toxicity
As previously mentioned (see the previous section on Radiobiology), the hematopoietic system is particularly sensitive to TBI, and lymphopenia is often seen with doses of 0.5 Gy and can be seen with doses of 0.3 Gy. Lymphopenia is typically followed by neutropenia, thrombocytopenia, and finally anemia. Soon after a TBI dose of 4 to 6 Gy has been given, lymphocytosis can be seen, but it typically is followed by neutropenia within 1 week. Three to 4 weeks after TBI, neutrophils fall to their minimum113 (Fig. 18-3). Regeneration of the HSC compartment depends on the total dose used because higher doses cause more rapid myelosuppression of greater duration. Administration of hematopoietic growth factors after TBI have the theoretical potential to alter hematopoietic system reconstitution, although reports in the setting of allogeneic HSCT have demonstrated an increased risk of GVHD and compromised survival114 and, therefore, routine use is controversial.115,116 Of note, hematopoietic growth factors have only been used in the period following TBI, given the concerns raised by a trial in lung cancer, where growth factors increased pulmonary toxicity and thrombocytopenia when given concurrently with chemoradiation therapy.117
Oral Toxicity
As noted before, the salivary glands frequently are affected by TBI. Although acute parotitis is typically self-limited and can be managed with anti-inflammatory medicines, long-term salivary gland dysfunction can result in xerostomia, which may lead to dental caries. In a study of children who underwent allogeneic HSCT, the risk of developing impaired salivary function was 22% in those who received TBI as part of conditioning versus 1% in those who did not.118 Studies have shown that salivary flow can improve up to 1 year after the completion of TBI.119 Fractionating TBI was shown to reduce salivary dysfunction by 54% in one study.120
Myeloablative conditioning regimens with and without TBI have been associated with abnormalities in tooth development in children.120–122 In one series, myeloablative conditioning regimens using chemotherapy alone were associated with significantly higher rates of tooth developmental abnormalities than those involving TBI, although rates of salivary gland dysfunction were highest amongst the patients treated with single-fraction TBI.123 Because of the increased risk of oral pathology associated with TBI, careful pretransplant evaluation by a dental specialist is recommended to minimize the risk of serious morbidity.124 Pilocarpine has been noted to help relieve symptoms of xerostomia in patients treated with TBI.125
Pulmonary Toxicity
The major dose-limiting toxicity of TBI is pneumonopathy (restrictive or obstructive lung disease), which can manifest early as pneumonitis and/or later as pulmonary fibrosis. In the setting of HSCT, radiation pneumonopathy can be difficult to distinguish from other causes of lung pathology; moreover, lung damage is likely multifactorial, with the risk of acute lung complications estimated to be 30% to 60%, depending on factors such as infection, conditioning regimen, GVHD, age, and diagnosis.126 Likewise, late pneumonopathy occurs in 10% to 26% of patients and is associated with underlying lung dysfunction, type of conditioning regimen, acute and chronic GVHD and prophylaxis, donor and recipient age and immunocompatibility, stage of disease, and genetic predisposition.127 TBI has been shown to be a risk factor for idiopathic pneumonia syndrome,128 as well as for diffuse alveolar hemorrhage.129 Although rates of pneumonopathy in patients receiving TBI vary widely (10% to 84%),130 some series have reported pneumonitis in up to 20% of HSCT patients who never received TBI.131 In the modern era, with appropriate TBI techniques, the risk of pneumonopathy in patients treated with TBI may not be increased at all.132 Nevertheless, the significance of the problem is clear, given that mortality related to interstitial pneumonitis in patients treated with TBI can be 60% to 80%.131,133,134
Several TBI-specific factors (e.g., total dose, fractionation, dose rate, and use of lung shielding) have been shown to have a significant bearing on the development of pulmonary complications. The total dose used during TBI has frequently been cited as a major factor influencing lung complications.130,135,136 In two prospective RCTs using 12 Gy versus 15.75 Gy, higher rates of mortality were noted within the first 6 months in patients treated with 15.75 Gy, although pulmonary complications were not specifically cited as the excess cause of deaths.137–139,140 In a retrospective dosimetric study, a mean lung dose of more than 9.4 Gy was found to be an independent predictor for lethal pulmonary complications in patients receiving TBI to a total dose of 10 Gy in three daily fractions, at 0.055 Gy/minute using parallel opposed lateral fields.141 Two RCTs have demonstrated that fractionated TBI can reduce pneumonitis compared with single-fraction TBI, although only one study showed differences that were statistically significant.89,142,143 A retrospective study found no difference in pneumonitis rates when comparing a single fraction of 6 Gy and three daily fractions of 3.33 Gy, suggesting that total doses of less than 10 Gy may not require fractionation to prevent toxicity, although no randomized data support this.144 The necessity of hyperfractionation to prevent lung toxicity is unclear: A comparison of two prospective single-arm trials at the same institution revealed that conventional fractionation given with anteroposterior fields and lung blocks to a total dose of 12 Gy in daily 3-Gy fractions may not be any different than hyperfractionated TBI given twice daily with 1.7 Gy per fraction to a total dose of 10.2 Gy over 3 days, using parallel opposed lateral fields and no blocks.145
Sampath and colleagues146 recently reviewed 26 studies involving 1096 patients to create a dose-response model for predicting the risk of pneumonitis from TBI while taking other factors into consideration. Although unable to estimate the risk of pneumonitis for hyperfractionated regimens, they were able to determine the effect of fractionation and cyclophosphamide and busulfan on the risk of developing pneumonitis, in a dose-response model, as seen in Figure 18-4.
Pneumonitis rates were not significantly different in a trial that randomized patients to high- or low-dose-rate TBI.88 However, there is an abundance of retrospective clinical data suggesting that lowering the dose rate (<0.025 to 0.09 Gy/minute) does decrease the likelihood of pulmonary complications,130,136,140,147,148 especially if TBI is delivered as a single fraction.149 If TBI is fractionated, some report that a low dose rate (<0.069 Gy/minute) is not necessary,134 whereas others found a beneficial effect.150,151 Studies of patients receiving fractionated TBI with lung shielding have demonstrated a reduction in pneumonopathy.152,153 however, one RCT found no difference in pneumonopathy rates if the shielding allowed a lung dose of either 6 or 8 Gy in a single fraction.154
Pulmonary function tests (PFTs) (e.g., spirometry and diffusion capacity) are often helpful in the assessment of patients with pulmonary symptoms or radiographic abnormalities. Studies of pulmonary function tests in patients treated with HSCT have demonstrated a deleterious effect on spirometry and diffusion capacity, which often resolves in the absence of other complicating factors155–157 and is related to the TBI dose.158 A retrospective study found that lung shielding had a small but significantly beneficial effect on pulmonary function tests 1 year after HSCT, especially in patients with abnormal function before HSCT.159 In one study, busulfan and not TBI, was associated with a negative effect on PFTs.160 There is no evidence that PFTs improve pulmonary outcome after HSCT in adulthood, and for this reason they are not recommended.161 However, some groups recommend baseline PFTs as part of long-term follow-up care for children treated with TBI.162 Counseling regarding smoking cessation is of critical importance for all patients, especially those who are at increased risk of developing lung injury. In the event of acute pneumonitis, high-dose steroids (30 to 60 mg of prednisone/day) typically alleviate symptoms within 24 to 48 hours.
Cardiovascular Toxicity
Cardiovascular toxicity in adults as a result of HSCT has been relatively rare, given the stringent selection criteria for patients treated with this aggressive therapeutic modality. Nevertheless, in adult patients who survived autologous or allogeneic HSCT, cardiac events were responsible for 2.4% and 3% of deaths, respectively; this finding represents a greater than expected occurrence.163,164 Most of the recent literature has identified no association between TBI and the development of cardiovascular disease in adults.165,166 In several detailed prospective analyses using plasma cardiac troponin and brain natriuretic peptide levels, electrocardiography and echocardiography revealed no evidence of cardiac dysfunction in previously healthy individuals treated with TBI.167,168 However, a prospective study of children who underwent allogeneic HSCT found a 12% and 26% cumulative incidence of abnormalities in ejection fraction (<30%) on echocardiography before HSCT and 5 years after HSCT, respectively. This study revealed that TBI was associated with abnormalities in cardiac function on univariate analysis but not multivariate analysis; the 5-year cumulative incidence of cardiac abnormality was 26% or 2% in children treated with TBI, with or without prior anthracycline therapy, respectively.169 Recent data from large studies of survivors of childhood cancer suggest that the risk of cardiac mortality is significantly elevated for children who receive heart doses of 5 Gy, although it should be noted that anthracycline doses of over 360 mg/m2 similarly increased the risk.170 Importantly, the rate of death from recurrence or progression of cancer exceeds the rate of death from cardiac disease by an approximate factor of 7.171 The reason for excess late cardiovascular toxicity in TBI in children is probably because of the association of TBI with the premature development of cardiovascular disease risk factors (e.g., hypertension, dyslipidemia, diabetes) that result in deleterious consequences rather than direct radiation cardiotoxicity.172,173 Therefore it appears prudent to screen patients who have undergone HSCT for cardiovascular disease for risk factors, whether or not treatment involved TBI, to minimize late morbidity and mortality.
Hepatic Toxicity
Hepatotoxicity from TBI manifests primarily as veno-occlusive disease (VOD), also known as sinusoidal obstructive syndrome (SOS), of the liver. This clinicopathologic phenomenon was first described in 1977 by Shulman and colleagues,174 who noted the onset of weight gain from ascites, painful hepatomegaly, and jaundice from centrilobular liver acinus necrosis 1 to 4 weeks after HSCT. Overall, up to 70% of patients who undergo HSCT can be affected by VOD. TBI, along with many other risk factors, has been implicated in the development of VOD.175 An RCT and a meta-analysis found that patients treated with busulfan instead of TBI were significantly more likely to develop VOD.176,177 Two RCTs have concluded that fractionated TBI reduces the incidence of VOD compared with single-dose TBI.142,143 Another RCT found no difference in the rate of VOD when the dose rate was either 0.06 Gy/minute or 0.15 Gy/minute,88 although a retrospective study of single-dose TBI found that dose rates of 0.07 Gy/minute were associated with less VOD than dose rates of 0.18 to 1.2 Gy/minute.178 A TBI dose greater than 13.2 Gy has been reported to be associated with higher rates of VOD on univariate analysis,179 although a dose greater than 12 Gy was not associated with VOD in another retrospective study.180 Lawton and associates181 reported a nonstatistically significant 10% decrease in the rate of fatal VOD in patients treated with TBI as part of HSCT when a 10% attenuation liver block was employed. Ursodeoxycholic acid was effective in preventing VOD in an RCT of patients undergoing TBI followed by HSCT,182 although another RCT did not support this finding.183 Reduced-intensity conditioning regimens may also prevent VOD. Treatment of VOD can include the fibrinolytic antithrombotic agent defibrotide; decompressing the sinusoids by a transjugular intrahepatic portosystemic shunt and liver transplantation is another, more invasive option for the management of severe disease.184
Visual Toxicity
Cataracts are one of the most common complications of TBI. Patients may present with painless vision loss and may be noted to have opacification of the lens on examination. In one series of patients treated with TBI in one or two fractions, severe visual impairment was noted in about half of patients.185 This problem has been noted to arise in a large proportion of patients treated with TBI, depending on the total dose, use of fractionation, and the dose rate. When considering risk factors associated with HSCT, steroid use,186–188 prior cranial irradiation,189,190 and the development of GVHD188 have been shown to predispose to cataractogenesis, whereas heparin use appears to be protective.191 Delivering TBI in a single fraction is the single biggest risk factor for developing a cataract after HSCT.191–196 High-dose-rate (>0.035 to 0.048 Gy/minute) TBI also appears to increase the risk of cataract formation.189,191,194,197 A prospective study that randomized patients to high- or low-dose-rate TBI found that the incidence of cataract 5 years after treatment was 12% and 34% in the low- and high-dose-rate arms, respectively, with 13% and 39% of the cataracts, respectively, occurring in patients who received fractionated or single-dose TBI.198 Kal199 and van Kempen-Harteveld200 recently reviewed the subject of TBI-induced cataracts and concluded that a biologically equivalent dose of 40 Gy yields a 10% chance of developing cataracts, using linear-quadratic modeling that included corrections for dose rate, with an α/β of 0.65 for late effects on the lens. On the basis of this, they suggest considering lens shielding for single-fraction TBI regimens,199 although this is controversial in the setting of malignant disease.200 Given the frequency of cataracts occurring after TBI, patients should be monitored for the development of this complication.201 Management of cataracts that impair vision or degrade quality of life may involve phacoemulsification and extraction; recent data suggest that these procedures are safe, with an adverse event rate of 0.1% for experienced surgeons,202 and effective, with a 90% chance of 20/40 vision postoperatively.203
Renal Toxicity
Kidney dysfunction occurs in approximately 17% of survivors of HSCT204 and can manifest in a number of ways, with the most to least frequent syndromes being idiopathic chronic kidney disease, nephrotic syndrome, thrombotic microangiopathy (thrombotic thrombocytopenic purpura and hemolytic uremic syndrome), and acute renal failure.205 The syndrome most associated with TBI is thrombotic microangiopathy, which can manifest as nephritis, hypertension, proteinuria, and/or anemia 6 to 12 months after HSCT. HSCT-related risk factors for nephropathy can include GVHD, infections with cytomegalovirus or BK virus, nephrotoxic medications such as cytotoxic chemotherapeutic agents (cytarabine, cyclophosphamide, ifosfamide, cisplatin, retinoic acid, carmustine, actinomycin D, melphalan), antibiotics (acyclovir, ganciclovir, foscarnet, vancomycin, amphotericin, aminoglycosides), and immunosuppressants (cyclosporine, tacrolimus, methotrexate). The larger and more contemporary studies of chronic kidney disease after HSCT have not demonstrated an association with TBI.206–210
Total dose has been implicated as the most important factor in predicting renal morbidity from TBI; a retrospective study found that GVHD and high-dose TBI (13.5 Gy) were associated with elevated serum creatinine levels.211 A prospective evaluation of renal function using radioisotopes found that early nephropathy was associated with age of less than 40 years, use of kidney blocks (possibly related to nephrotoxic contrast media given during simulation), and nephrotoxic drug use, whereas late nephropathy was associated with nephrotoxic drug use but not TBI dose.212 The benefit of kidney shielding has been assessed in two retrospective studies, both of which demonstrated significant improvement in long-term kidney function, with no evidence of dysfunction when the hyperfractionated dose was limited to 9.8 to 10 Gy.213,214 Two recent dose-effect modeling studies have demonstrated that nephropathy is unlikely after a biologically equivalent total dose of 16 Gy (calculated using a linear quadratic model, with corrections for dose rate and an α/β of 2.5 Gy) and that fractionating TBI and delivery of a low dose rate (<0.10 Gy/minute) prevent kidney dysfunction.199,215 Monitoring blood chemistry and counts, as well as blood pressure and urine studies, is advised given the prevalence of kidney disease after HSCT.
Although no therapies have been proven to treat HSCT-related nephropathy, medication therapies (antihypertensives, corticosteroids), plasma exchange, hemodialysis, and renal transplant are possible options for management.205 The angiotensin-converting enzyme inhibitor captopril prevents chronic nephropathy in patients with diabetes216 and may reduce the risk of radiation nephropathy from TBI in preclinical studies.217,218 A small RCT in which captopril was given to mitigate chronic renal failure in patients undergoing 12 Gy of fractionated TBI (with a kidney dose of 9.8 Gy) before HSCT revealed less nephropathy; however, the results were not statistically significant.219
Endocrine Toxicity
Hypothyroidism is the most common endocrinopathy after HSCT.220 Most cases are overt and primary in nature, but subclinical and autoimmune thyroid dysfunction have also been noted. Hypothyroidism has been reported in up to 90% of patients after TBI delivered with a single dose of 10 Gy221 and in up to 15% of patients treated with hyperfractionated TBI to 15 Gy.222 These findings demonstrate the benefit of fractionation in avoiding this complication. One of the largest studies with a lengthy follow-up of children treated with or without TBI before HSCT revealed that TBI was not a risk factor for developing hypothyroidism when compared with equivalent conditioning with busulfan. In this study, the risk of hypothyroidism was higher in children undergoing HSCT before 10 years of age, and the risk continued to increase until 28 years after HSCT.223 A recent study demonstrated that reduced-intensity conditioning with lower doses of radiation during TBI was not associated with lower rates of hypothyroidism,224 suggesting that there is no dose threshold effect. Nevertheless, this complication should be monitored with assessment of thyroid hormones and can be easily managed with thyroid hormone replacement and monitoring.
Gonadal and reproductive endocrine functions can be altered by HSCT and TBI, as reviewed by Chemaitilly and Sklar.220 In males, Leydig cell function is typically preserved, given the dose of radiation delivered during full-dose TBI.225 However, in patients who have received prior testicular radiation or who will have a testicular boost during conditioning, Leydig cell function may be threatened. Germ cells are typically thought to be exquisitely sensitive to radiation. A recent study demonstrated that fertility is significantly reduced among boys treated with a radiation dose of more than 7.5 Gy to the gonads, although it should be kept in mind that other antineoplastics, such as alkylating agents, also profoundly reduce fertility.226 Although there have been case reports of men being treated with TBI and later having children, most men are rendered sterile by HSCT with full-dose TBI; most will experience azoospermia with reduced-dose TBI, but some may also be rendered sterile. With this in mind, male patients should be counseled regarding gamete cryopreservation before initiation of therapy. Likewise, postpubertal women are likely to experience ovarian failure as a result of intensive conditioning, including TBI, and should be counseled about this before treatment. However, about half of prepubertal girls who are treated with fractionated TBI will experience normal reproductive development.227 As reviewed by Schmidt and colleagues,228 several fertility-preserving options may be available to women who wish to bear children after HSCT.
Hypothalamic-pituitary function appears to be unaffected by TBI of adults to doses of 12 Gy.229 However, if additional brain radiotherapy has been or will be delivered, this complication could be encountered. Growth dysfunction may be caused by TBI through a variety of mechanisms, including growth hormone deficiency and skeletal dysplasia; other factors, including GVHD, liver dysfunction, and busulfan-based conditioning, may also contribute. Younger patients are more likely to be affected by growth impairment. In addition, children treated with single-fraction TBI (as opposed to fractionated TBI) are more likely to experience growth impairment.230 Growth hormone replacement therapy has been recommended to correct this deficiency,231 although RCTs have not shown proven benefit232 and treatment is associated with several significant toxicities.
Bone Toxicity
Bone health is another concern in patients that have undergone HSCT. Although TBI has been shown to be a risk factor for avascular necrosis of bone,233 a prospective study found no association between bone metabolism and conditioning with TBI; corticosteroid use is probably the major factor in HSCT causing bone health problems.234 Monitoring bone health with growth assessments, biochemical hormone assessments, and dual-energy x-ray absorptiometry (DEXA) scans is appropriate, and consideration of counseling, weight-bearing exercise, and use of calcium and vitamin D supplementation or antiresorptive agents (bisphosphonates) should be given in patients with evidence of abnormalities.
Nervous System Toxicity
Mild to moderate neurocognitive impairment has been noted in up to 60% of adults undergoing HSCT with TBI.235 However, these findings have not been consistent, because several studies have documented no impairment at all.236,237 TBI-based conditioning (compared with non–TBI-based conditioning) has not been associated with neurocognitive impairment in adults who received full-dose238 or reduced-intensity conditioning.239 Children treated with TBI may experience mild neuropsychologic effects.240 The effects are more prominent in young children,241 especially those under 3 years of age.242 Similar to adults, no difference in neurocognitive function has been associated with TBI and non–TBI-based conditioning regimens in older children.243 However, in young children, TBI-based regimens appear to exert more of a negative effect than non–TBI-based regimens.244 The magnitude of the deficit has been described as statistically, but not clinically, significant (i.e., a deficit of 3 points in IQ) in recent investigations.245
Beyond generally mild cognitive effects of TBI on the nervous system, other types of toxicity are rare. Myelopathy is uncommon, but it has been reported to occur with TBI in conjunction with involved radiation therapy fields, even at cumulative doses considered to be “tolerable” (e.g., 45 Gy).246 Similarly, severe and fatal neurologic toxicity was reported in a series of children treated with TBI and was generally associated with prior whole brain radiotherapy to 18 Gy; therefore the cumulative radiation dose in this approach must be considered carefully.247 Other neurologic toxicity has not been associated with TBI in adults248 or children.249
Risk of Secondary Malignant Tumors
Beyond organ-specific toxicities, the risk of developing secondary malignant neoplasms is increased in patients who have undergone HSCT. Typically, three groups of secondary malignant neoplasms after HSCT are described, and they follow a distinct pattern of development250 (Fig. 18-5): myelodysplastic disease (MDS) and acute myelogenous leukemia (AML), posttransplant lymphoproliferative disorder (PTLD), and solid tumors.251 There are multiple risk factors that may predispose to development of a secondary malignant tumor after HSCT, including, but not limited to, genetic aberrations, therapy given before HSCT, conditioning regimen, graft source and processing, posttransplantation immunosuppression, and GVHD38; only the association of TBI with secondary malignant neoplasms will be discussed here.
Secondary MDS or AML after HSCT has been reported to occur at rates between 1.1% at 20 months and 24.3% at 43 months. The World Health Organization classifies secondary MDS and AML as alkylating-agent and/or radiation-related disease, typically occurring 4 to 7 years after treatment, or topoisomerase-II inhibitor–related disease, typically occurring 6 months to 5 years after treatment.252 Several studies have attempted to quantify the risk of developing secondary MDS or AML after undergoing TBI, with conflicting results. Studies from research groups from Minnesota,253 Newcastle,254 the City of Hope,255 and France256 have demonstrated no increase in rates of MDS or AML after myeloablative HSCT using TBI. Other studies from Nebraska,257 the European Group for Bone Marrow Transplantation (EBMT),258 Paris,259 Barcelona,260 and France261 have found weak associations of borderline or no statistical significance. One study found an association of secondary MDS or AML with TBI on multivariate analysis when TBI was used with etoposide and cyclophosphamide.262 A recent, detailed study of this subject found that among 4000 patients treated with autologous HSCT for lymphoma, 57 developed MDS or AML, with a cumulative incidence rate of 3.7%, 7 years after HSCT. A case-control analysis revealed a weak association of TBI and the subsequent development of MDS or AML that was not statistically significant. In a small subgroup analysis, a TBI dose of 13.2 Gy was associated with MDS or AML, but the authors cautioned that this group of patients may have shared other non–TBI-related factors that could have contributed to leukemogenesis. Older age also appeared to increase the risk.263 The dose threshold effect was not supported by a more recent study that found no differences in the rate of MDS or AML after TBI, whether 12 or 14 Gy of TBI was given.264
The association of TBI with the subsequent development of a PTLD has been described in several studies. Because it is thought to result from immune system dysfunction, PTLD occurs primarily in patients following allogeneic, not autologous, HSCT. The cumulative incidence of PTLD at 12 years varied by the number of risk factors the patient had, and ranged from 0.2% to 8.1%.265 Small early studies from Seattle251 and the CIBMTR266 suggested an association between TBI use during HSCT and subsequent development of a PTLD. However, later research from Minnesota,253 Vancouver,267 and Nebraska268 suggested no association between TBI and PTLD. A follow-up study from the CIBMTR, the largest and most comprehensive study available, involving 26,000 patients who underwent allogeneic HSCT over a 30-year period, clearly demonstrated no association between PTLD and TBI, in contrast to their previous findings.265
The risk of solid tumors after HSCT involving TBI has been studied extensively.269–279 The largest and most recently updated analysis from the CIMBTR suggests that among patients who undergo allogeneic HSCT, the cumulative incidence of developing a solid malignant tumor (including carcinomas in situ that are not of the skin) is 1%, 2.2%, and 3.3% at 10, 15, and 20 years after transplant, respectively, based on the competing risk analysis method.280 The number of secondary solid tumors was double what would have been expected in this population; significantly higher rates of oral cavity and pharyngeal, liver, central nervous system, thyroid, bone, and soft tissue cancers and melanomas were observed. TBI was found to be a risk factor for developing a secondary solid tumor, with the risk increased in those who survived more than 5 years from the HSCT and in those less than 30 years old at the time of HSCT. Although an earlier study found that TBI doses of less than 10 Gy were associated with fewer secondary solid tumors,269 this dose association was not maintained in the subsequent analysis.280 There was no difference in the rate of secondary solid tumors in patients treated with fractionated or single-dose TBI. There was no increased risk of squamous cell carcinomas in patients treated with TBI and no increased risk of secondary solid tumors in patients treated with TBI after age 30. Chronic GVHD and male sex were associated with the development of secondary solid tumors and squamous cell carcinoma, respectively.280
Given the increased risk of secondary malignant neoplasms after TBI, careful surveillance of long-term survivors is a desirable (but not yet proven effective) strategy for minimizing secondary morbidity and mortality. Guidelines published by the American Cancer Society,281 the National Comprehensive Cancer Network (NCCN) (www.nccn.org), and the Children’s Oncology Group162 provide important references regarding assessing patients at higher risk of developing a secondary solid tumor.
Physical Principles of Total Body Irradiation
Although irradiating the entire body may seem like a simple exercise, TBI is a highly specialized technique fraught with unique challenges. Nevertheless, the physical aspects of TBI have not changed significantly over the last three decades. The American Association of Physicists in Medicine (AAPM) Report 17, Task Group 29, “The Physical Aspects of Total and Half Body Photon Irradiation,” is still considered the authoritative reference for methodology and recommendations regarding the physical aspects of TBI.282 More recently, the American College of Radiology created a practice guideline for TBI treatment delivery.283 The reader is referred to these resources and others284 for detailed information on this subject.
