Maintain Efficacy and Spare Toxicity: Traditional and New Radiation-Based Conditioning Regimens in Hematopoietic Stem Cell Transplantation

Novelty in total body irradiation (TBI) as part of pre-transplant conditioning regimens lacked until recently, despite the developments in the field of allogeneic stem cell transplants. Long-term toxicities have been one of the major concerns associated with TBI in this setting, although the impact of TBI is not so easy to discriminate from that of chemotherapy, especially in the adult population. More recently, lower-intensity TBI and different approaches to irradiation (namely, total marrow irradiation, TMI, and total marrow and lymphoid irradiation, TMLI) were implemented to keep the benefits of irradiation and limit potential harm. TMI/TMLI is an alternative to TBI that delivers more selective irradiation, with healthy tissues being better spared and the control of the radiation dose delivery. In this review, we discussed the potential radiation-associated long-term toxicities and their management, summarized the evidence regarding the current indications of traditional TBI, and focused on the technological advances in radiotherapy that have resulted in the development of TMLI. Finally, considering the most recent published trials, we postulate how the role of radiotherapy in the setting of allografting might change in the future.

Allogeneic stem cell transplant outcomes between TBI-containing reduced intensity and myeloablative conditioning regimens for ALL in complete remission

Total-body irradiation (TBI)-based conditioning regimen is preferred in acute lymphoblastic leukemia (ALL). We retrospectively evaluated allogeneic stem cell transplant (alloSCT) outcomes of 86 adult ALL patients in complete remission (CR) who received TBI-containing reduced intensity (RIC) (Flu/Mel/TBI = 31) and myeloablative conditioning (MAC) (VP16/TBI = 47; CY/TBI = 8) between January 2005 and December 2019. All patients received peripheral blood allografts. Patients in the RIC group were older than the MAC group (61 years old versus 36 years, p < .001). Donor was 8/8 HLA-matched in 83% and unrelated in 65% of patients. Three-year survival was 56.04% for RIC and 69.9% for MAC (HR 0.64; p = .19). Propensity score-based multivariable Cox analyses (PSCA) did not demonstrate any difference in grade III-IV acute graft versus host disease (GVHD) (SHR 1.23, p = .91), chronic GVHD (SHR 0.92, p = .88), survival (HR 0.94, p = .92), and relapse-free survival (HR 0.66, p = .47) between both groups, while relapse rate was lower (SHR 0.21, p = .02) for MAC compared to RIC. Our study did not demonstrate any difference in survival for TBI-containing RIC and MAC alloSCT for adult ALL in CR.

Delayed renal injury in survivors of hematologic acute radiation syndrome

PURPOSE

A mass casualty disaster involving radiological or nuclear agents continues to be a public health concern which requires consideration of both acute and late tissue toxicities in exposed victims. With the advent of advanced treatment options for the mitigation of hematological injuries, there are likely to be survivors of total body irradiation (TBI) exposures as high as 8-10 Gy. These survivors are at risk for a range of delayed multi-organ morbidities including progressive renal failure.

MATERIAL AND METHODS

Here, we established the WAG/RijCmcr rat as an effective model for the evaluation of medical countermeasures (MCM) for acute hematologic radiation syndrome (H-ARS). The LD50/30 dose for adult and pediatric WAG/RijCmcr rats was determined for both sexes. We then confirmed the FDA-approved MCM pegfilgrastim (peg-GCSF, Neulasta®) mitigates H-ARS in adult male and female rats. Finally, we evaluated survival and renal dysfunction up to 300 d post-TBI in male and female adult rats.

RESULTS

In the WAG/RijCmcr rat model, 87.5% and 100% of adult rats succumb to lethal hematopoietic acute radiation syndrome (H-ARS) at TBI doses of 8 and 8.5 Gy, respectively. A single dose of the hematopoietic growth factor peg-GCSF administered at 24 h post-TBI improved survival during H-ARS. Peg-GCSF treatment improved 30 d survival from 12.5% to 83% at 8 Gy and from 0% to 63% at 8.5 Gy. We then followed survivors of H-ARS through day 300. Rats exposed to TBI doses greater than 8 Gy had a 26% reduction in survival over days 30-300 compared to rats exposed to 7.75 Gy TBI. Concurrent with the reduction in long-term survival, a dose-dependent impairment of renal function as assessed by blood urea nitrogen (BUN) and urine protein to urine creatinine ratio (UP:UC) was observed.

CONCLUSION

Together, these data show survivors of H-ARS are at risk for the development of delayed renal toxicity and emphasize the need for the development of medical countermeasures for delayed renal injury.

Long-term follow up of patients with hematological malignancies treated with total body irradiation using intensity modulated radiation therapy

BACKGROUND

With the advent of modern radiation treatment technologies such as intensity modulated radiation therapy (IMRT), there has been increasing interest in its use for total body irradiation (TBI) conditioning regimens for hematopoietic cell transplantation (HCT) to achieve lower doses to critical organs such as the lungs and kidneys. Although this has been reported on in early studies, long-term safety and efficacy data is limited.

METHODS

We performed a single institution matched-pair retrospective analysis of patients treated with IMRT TBI and standard TBI between 2010 and 2020 to provide data on long-term outcomes. Patients with hematologic malignancies, who could not tolerate standing for traditional TBI or who received prior radiation received IMRT TBI. Patients were matched based on age, diagnosis, disease status, and year of transplant, and were matched 2:1 to the standard TBI and IMRT TBI cohorts. Patient and treatment characteristics, toxicity, graft-versus-host disease (GVHD), dosimetry, and outcomes were evaluated for each cohort.

RESULTS

A total of 13 patients met inclusion criteria for the IMRT cohort, leading to 26 patients in the standard TBI cohort. There was no significant difference in relevant clinical factors between the cohorts. Reasons for using IMRT over conventional TBI included being unable to stand (n=5), prior radiation (n=5), and pediatric patient requiring anesthesia (n=3). Among living patients, median follow-up for all patients was 5.1 years in the IMRT TBI cohort and 5.5 years in the standard TBI cohort. The 5-yr estimate of OS was 68% in the IMRT TBI cohort and 60% in the standard TBI cohort (p=0.706). The 5-yr estimate of RFS was 54% in the IMRT TBI cohort and 60% in the standard TBI cohort (p=0.529). There was no clinically significant pneumonitis, nephritis, hypothyroidism, or cataracts reported in the IMRT TBI cohort. 41.7% of patients in the IMRT TBI cohort and 79.2% of patients in the standard TBI cohort experienced Grade II-IV acute GVHD (p=0.023).

CONCLUSIONS

IMRT TBI appears to lead to favorable long-term outcome and dosimetry, and therefore potentially improved long-term toxicity profile compared to conventional TBI. IMRT TBI warrants further investigation as part of larger prospective trials.

New strategy of a lung compensating technique with STR for total body irradiation

Purpose

To determine the thickness of a soft variable shape tungsten rubber (STR) as a lung compensating filter in total body irradiation.

Methods

A tough water (TW) phantom and tough lung (TL) phantom were used as water and lung‐equivalent phantoms. The TW with a thickness of 3 cm simulating the thoracic wall was used (upper layer). The TW or TL with a thickness from 1 to 15 cm (1 cm increments) was placed beneath the upper layer (middle layer). The TW with a thickness of 5 cm simulating the mediastinum was placed beneath the middle layer (lower layer), and a farmer ionization chamber was placed beneath this layer. The relative doses of a 10 MV X‐rays were then measured. The TL was compensated in 1 mm increments from 1 to 11 mm of the STR, and the thickness of the STR at the same dose of TW (water equivalent) was obtained.

Results

The compensating ability of STR increased as the thickness of the TL increased, and an STR with a thickness of 1 mm reduced the dose by 2%–4%, depending on the thickness of lung. The STR thickness as an equivalent dose of TW per cm of TL was approximately linear, and the thickness was 0.62 mm/cm of TL.

Conclusion

The STR can be used as a lung compensating filter for a water equivalent dose with 0.62 mm of STR per cm of lung.

Abnormal sensation during total body irradiation: a prospective observational study

Light flash and odor during radiotherapy are well-known phenomena. Two prospective observational studies have indicated that 55% of patients observed a light flash during irradiation of the retina and 27% of patients sensed an odor during radiotherapy for the nasal cavity. A prospective observational study was performed in all patients at our hospital who received total body irradiation (TBI) between January 2019 to October 2021. Light flash and odor during TBI were examined using the same method as that used in previous studies. A total of 32 patients received TBI during the study period. The patients had a median age of 41 (18-60) years, and included 20 males and 12 females. A survey checklist showed that 14 patients (44%) sensed light and 14 patients (44%) sensed odor during TBI,. The color of the light during irradiation was yellow in six cases, white in four cases, and blue in four cases. The intensity of the light was 2-5 (median 3, 1 is very weak, 5 is very strong) and the time over which the light flash was felt was 4-60 s (median 10 s). Two patients each sensed smells of plastic, ozone and bleach, and others sensed one smell each. The intensity of the odor was 1-4 (median 3, 1 is very weak, 5 is very strong) and the time over which the odor was sensed was 1-25 s (median 3 s). We conclude that light flashes and odors are each sensed by 44% of patients during TBI. Various types of light flashes and odors were reported in this study.

Thyroid function disorders and secondary cancer following haematopoietic stem cell transplantation in pediatrics: State of the art and practical recommendations for a risk-based follow-up

Thyroid disorders (TD) represent a remarkable share of all the late morbidities experienced following pediatric haematopoietic stem cell transplantation (HSCT), with long-term reported occurrence often exceeding 70%. In addition, the data collected on wide cohorts of survivors assessed longitudinally outlined a progressive increase in the cumulative incidence of TD as far as 30 years following transplantation. Accordingly, a life-long monitoring of thyroid health is warranted among patients exposed to HSCT in childhood, in order to early detect TD and undertake a prompt dedicated treatment. Although several national and international consortia have provided recommendations for the early detection of thyroid disorders among childhood cancer survivors exposed to radiotherapy and alkylating agents, no guidelines specifically and thoroughly focused on HSCT-related TD have been published to date. As stem cell transplantation has become the standard-of-care in a growing body of non-oncological conditions, this urge has become pivotal. To highlight the challenging issues specifically involving this cohort of patients and to provide clinicians with the proposal of a practical follow-up protocol, we reviewed published literature in the light of the shared experience of a multidisciplinary team of pediatric oncologists, transplantologists, pathologists and endocrinologists involved in the long-term care of HSCT survivors. As a final result, we hereby present the proposals of a practical and customized risk-based approach to tailor thyroid health follow-up based on HSCT-related detrimental factors.

Acute Lymphoblastic Leukaemia in the Youngest: Haematopoietic Stem Cell Transplantation and Beyond

The ALL SCTped 2012 FORUM (For Omitting Radiation Under Majority age) trial compared outcomes for children ≥4 years of age transplanted for acute lymphoblastic leukaemia (ALL) who were randomised to myeloablation with a total body irradiation (TBI)-based or chemotherapy-based conditioning regimen. The TBI-based preparation was associated with a lower rate of relapse compared with chemoconditioning. Nevertheless, the age considered suitable for TBI was progressively raised over time to spare the most fragile youngest patients from irradiation-related complications. The best approach to use for children <4 years of age remains unclear. Children diagnosed with ALL in their first year of life, defined as infants, have a remarkably poorer prognosis compared with older children. This is largely explained by the biology of their ALL, with infants often carrying a KMT2A gene rearrangement, as well as by their fragility. In contrast, the clinical presentations and biological features of ALL in children >1 year but <4 years often resemble those presented by older children. In this review, we explore the state of the art regarding haematopoietic stem cell transplantation (HSCT) in children <4 years, the preparative regimens available, and new developments in the field that may influence treatment decisions.

Total Body Irradiation in Haematopoietic Stem Cell Transplantation for Paediatric Acute Lymphoblastic Leukaemia: Review of the Literature and Future Directions

Total body irradiation (TBI) has been a pivotal component of the conditioning regimen for allogeneic myeloablative haematopoietic stem cell transplantation (HSCT) in very-high-risk acute lymphoblastic leukaemia (ALL) for decades, especially in children and young adults. The myeloablative conditioning regimen has two aims: (1) to eradicate leukaemic cells, and (2) to prevent rejection of the graft through suppression of the recipient's immune system. Radiotherapy has the advantage of achieving an adequate dose effect in sanctuary sites and in areas with poor blood supply. However, radiotherapy is subject to radiobiological trade-offs between ALL cell destruction, immune and haematopoietic stem cell survival, and various adverse effects in normal tissue. To diminish toxicity, a shift from single-fraction to fractionated TBI has taken place. However, HSCT and TBI are still associated with multiple late sequelae, leaving room for improvement. This review discusses the past developments of TBI and considerations for dose, fractionation and dose-rate, as well as issues regarding TBI setup performance, limitations and possibilities for improvement. TBI is typically delivered using conventional irradiation techniques and centres have locally developed heterogeneous treatment methods and ways to achieve reduced doses in several organs. There are, however, limitations in options to shield organs at risk without compromising the anti-leukaemic and immunosuppressive effects of conventional TBI. Technological improvements in radiotherapy planning and delivery with highly conformal TBI or total marrow irradiation (TMI), and total marrow and lymphoid irradiation (TMLI) have opened the way to investigate the potential reduction of radiotherapy-related toxicities without jeopardising efficacy. The demonstration of the superiority of TBI compared with chemotherapy-only conditioning regimens for event-free and overall survival in the randomised For Omitting Radiation Under Majority age (FORUM) trial in children with high-risk ALL makes exploration of the optimal use of TBI delivery mandatory. Standardisation and comprehensive reporting of conventional TBI techniques as well as cooperation between radiotherapy centres may help to increase the ratio between treatment outcomes and toxicity, and future studies must determine potential added benefit of innovative conformal techniques to ultimately improve quality of life for paediatric ALL patients receiving TBI-conditioned HSCT.

"Longitudinal Fecal Microbiome Study of Total Body Irradiated Mice Treated With Radiation Mitigators Identifies Bacterial Associations With Survival"

Total body irradiation (TBI) has been demonstrated to alter the intestinal microbiome, but the effects of successful small molecule ionizing radiation mitigators on the intestinal microbiome are not well-known. Our survival experiments examined the effects of anti-cell death radiation mitigators on and in conjunction with the host's microbiota. Mice received 9.25 Gy TBI and then were administered radiation mitigators 24 hours later. Passed stool were collected pre-irradiation, then on days 1, 3, 5, 7, 10, 14, 21, and 30 post-irradiation for 16S rRNA gene (V4 region) sequencing. The Cox proportional hazards (CPH) model was fit with taxonomic composition (time varying covariates) and treatment as predictors. In the first experiment, mice were administered drugs for "granulocyte stimulation and anti-apoptosis" in four protocol combinations: JP4-039 (anti-apoptosis), granulocyte colony-stimulating factor (G-CSF, granulopoietic precursor cell stimulator), both mitigators, and control. Survival improved relative to control (30.0%) for G-CSF (80%, p-value = 0.025), G-CSF/JP4-039 (70%, p-value = 0.084), but not for JP4-039 (50.0%). In the second experiment, mice were administered mitigation drugs "inhibiting programmed cell death" pathways: JP4-039 (anti-apoptosis), necrostatin-1 (anti-necroptosis), and baicalein (anti-ferroptosis), in eight combinations. The survival of JP4-039/baicalein (60.0%, p-value = 0.010) and JP4-039/baicalein/necrostatin-1 (60.0%, p-value = 0.06) treatment combinations were significantly different from the control (26.7%). The JP4-039/necrostatin-1 (46.7%) and baicalein/necrostatin-1 (40.0%) and singlet treatment combinations (26.7%) were not significantly different from the control. Despite differences between the baseline microbiota compositions of the two experiments, consistent changes in composition after irradiation were found: Lactobacillus decreased post-irradiation, relative to baseline. By day 7, microbiota perturbations had incompletely reversed, and no drug-specific differences were identifiable. The CPH model identified Lactobacillus and members of Ruminococcaceae, including Ruminococcus, as protective and Akkermansia as deleterious. By day 30, the microbiota of surviving mice had not returned to baseline, but the differences between experiments suggest the resultant microbiota composition of the survivors are stochastic or batch specific in nature, rather than a requirement for survival. In conclusion, the study determined that key taxa identified in fecal samples, when applied towards the prediction of TBI survival, improves the survival model relative to treatment information alone.

Study of feasible and safe condition for total body irradiation using cardiac implantable electronic devices

Cardiac implantable electronic devices (CIEDs) were believed to have a tolerance dose and that direct irradiation has to be avoided. Thus, no clinical guidelines have mentioned the feasibility of total body irradiation (TBI) with a CIED directly. The purpose of this work was to study a feasible and safe condition for TBI using a CIED. Eighteen CIEDs were directly irradiated by a 6-MV X-ray beam, where a non-neutron producible beam was employed for the removal of any neutron contribution to CIED malfunction. Irradiation up to 10 Gy in accumulated dose was conducted with a 100-cGy/min dose rate, followed by up to 20 Gy at 200 cGy/min. An irradiation test of whether inappropriate ventricular shock therapy was triggered or not was also performed by using a 6-MV beam of 5, 10, 20 and 40 cGy/min to two CIEDs. No malfunction was observed during irradiation up to 20 Gy at 100 and 200 cGy/min without activation of shock therapy. These results were compared with typical TBI, suggesting that a CIED in TBI will not encounter malfunction because the prescribed dose and the dose rate required for TBI are much safer than those used in this experiment. Several inappropriate shock therapies were, however, observed even at 10 cGy/min if activated. The present result suggested that TBI was feasible and safe if a non-neutron producible beam was employed at low dose-rate without activation of shock therapy, where it was not inconsistent with clinical and non-clinical data in the literature. The feasibility of TBI while using a CIED was discussed for the first time.

Dosimetric evaluation of ovaries and pelvic bones associated with clinical outcomes in patients receiving total body irradiation with ovarian shielding

Total body irradiation (TBI) with ovarian shielding is expected to preserve fertility among hematopoietic stem cell transplant (HSCT) patients with myeloablative TBI-based regimens. However, the radiation dose to the ovaries that preserves ovarian function in TBI remains poorly understood. Furthermore, it is uncertain whether the dose to the shielded organs is associated with relapse risk. Here, we retrospectively evaluated the relationship between fertility and the dose to the ovaries, and between relapse risk and the dose to the pelvic bones. A total of 20 patients (median age, 23 years) with standard-risk hematologic diseases were included. Median follow-up duration was 31.9 months. The TBI prescribed dose was 12 Gy in six fractions for three days. Patients' ovaries were shielded with cylinder-type lead blocks. The dose-volume parameters (D98% and Dmean) in the ovaries and the pelvic bones were extracted from the dose-volume histogram (DVH). The mean ovary Dmean for all patients was 2.4 Gy, and 18 patients recovered menstruation (90%). The mean ovary Dmean for patients with menstrual recovery and without recovery were 2.4 Gy and 2.4 Gy, respectively, with no significant difference (P = 0.998). Hematological relapse was observed in five patients. The mean pelvis Dmean and pelvis D98% for relapse and non-relapse patients were 11.6 Gy and 11.7 Gy and 5.6 Gy and 5.3 Gy, respectively. Both parameters showed no significant difference (P = 0.827, 0.807). In conclusion, TBI with ovarian shielding reduced the radiation dose to the ovaries to 2.4 Gy, and preserved fertility without increasing the risk of relapse.

RRx-001 Radioprotection: Enhancement of Survival and Hematopoietic Recovery in Gamma-Irradiated Mice

The present studies evaluate the in vivo prophylactic radioprotective effects of 1-bromoacetyl-3, 3-dinitroazetidine (RRx-001), a phase III anticancer agent that inhibits c-myc and downregulates CD-47, after total body irradiation (TBI), in lethally and sublethally irradiated CD2F1 male mice. A single dose of RRx-001 was administered by intraperitoneal (IP) injection 24 h prior to a lethal or sublethal radiation dose. When irradiated with 9.35 Gy, the dose lethal to 70% of untreated mice at 30 days (LD_70/30), only 33% of mice receiving RRx-001 (10 mg/kg) 24 h prior to total body irradiation (TBI) died by day 30, compared to 67% in vehicle-treated mice. The same pretreatment dose of RRx-001 resulted in a significant dose reduction factor of 1.07. In sublethally TBI mice, bone marrow cellularity was increased at day 14 in the RRx-001-treated mice compared to irradiated vehicle-treated animals. In addition, significantly higher numbers of lymphocytes, platelets, percent hematocrit and percent reticulocytes were observed on days 7 and/or 14 in RRx-001-treated mice. These experiments provide proof of principle that systemic administration of RRx-001 prior to TBI significantly improves overall survival and bone marrow regeneration.

Total Body Irradiation for Hematopoietic Stem Cell Transplantation: What Can We Agree on?

Total body irradiation (TBI), used as part of the conditioning regimen prior to allogeneic and autologous hematopoietic cell transplantation, is the delivery of a relatively homogeneous dose of radiation to the entire body. TBI has a dual role, being cytotoxic and immunosuppressive. This allows it to eliminate disease and create “space” in the marrow while also impairing the immune system from rejecting the foreign donor cells being transplanted. Advantages that TBI may have over chemotherapy alone are that it may achieve greater tumour cytotoxicity and better tissue penetration than chemotherapy as its delivery is independent of vascular supply and physiologic barriers such as renal and hepatic function. Therefore, the so-called “sanctuary” sites such as the central nervous system (CNS), testes, and orbits or other sites with limited blood supply are not off-limits to radiation. Nevertheless, TBI is hampered by challenging logistics of administration, coordination between hematology and radiation oncology departments, increased rates of acute treatment-related morbidity and mortality along with late toxicity to other tissues. Newer technologies and a better understanding of the biology and physics of TBI has allowed the field to develop novel delivery systems which may help to deliver radiation more safely while maintaining its efficacy. However, continued research and collaboration are needed to determine the best approaches for the use of TBI in the future.

Automatic treatment planning for VMAT-based total body irradiation using Eclipse scripting

The purpose of this work is to establish an automated approach for a multiple isocenter volumetric arc therapy (VMAT)‐based TBI treatment planning approach. Five anonymized full‐body CT imaging sets were used. A script was developed to automate and standardize the treatment planning process using the Varian Eclipse v15.6 Scripting API. The script generates two treatment plans: a head‐first VMAT‐based plan for upper body coverage using four isocenters and a total of eight full arcs; and a feet‐first AP/PA plan with three isocenters that covers the lower extremities of the patient. PTV was the entire body cropped 5 mm from the patient surface and extended 3 mm into the lungs and kidneys. Two plans were generated for each case: one to a total dose of 1200 cGy in 8 fractions and a second one to a total dose of 1320 cGy in 8 fractions. Plans were calculated using the AAA algorithm and 6 MV photon energy. One plan was created and delivered to an anthropomorphic phantom containing 12 OSLDs for in‐vivo dose verification. For the plans prescribed to 1200 cGy total dose the following dosimetric results were achieved: median PTV V100% = 94.5%; median PTV D98% = 89.9%; median lungs Dmean = 763 cGy; median left kidney Dmean = 1058 cGy; and median right kidney Dmean = 1051 cGy. For the plans prescribed to 1320 cGy total dose the following dosimetric results were achieved: median PTV V100% = 95.0%; median PTV D98% = 88.7%; median lungs Dmean = 798 cGy; median left kidney Dmean = 1059 cGy; and median right kidney Dmean = 1064 cGy. Maximum dose objective was met for all cases. The dose deviation between the treatment planning dose and the dose measured by the OSLDs was within ±4%. In summary, we have demonstrated that scripting can produce high‐quality plans based on predefined dose objectives and can decrease planning time by automatic target and optimization contours generation, plan creation, field and isocenter placement, and optimization objectives setup.

Total body irradiation models in NHPs - consideration of animal sex and provision of supportive care to advance model development

PURPOSE

Harmonized animal models are an indispensable tool for the development of safe and effective medical countermeasures (MCMs) against radiation injury, and rhesus macaques (referred herein as NHPs) play a critical role in FDA approval of radiation medical countermeasures for acute and delayed radiation syndromes. Reliance on such models requires that they be well characterized, which consists, in part, of a reproducible dose to mortality response relationship (DRR). However, data describing the DRR for both male and female NHPs from the same study are scarce. Furthermore, the level of supportive care and the use of blood transfusions may shift the DRR, yet such information can be difficult to compare across publications. To address these knowledge gaps, the DRRs of two different NHP total body irradiation (TBI) models are compared in this paper, one which is reliant on the use of male animals provided blood transfusions, and the other which incorporates both sexes wherein animals are not provided transfusions.

MATERIALS AND METHODS

Studies were conducted using NHPs (Macacca mulatta) receiving TBI, with survival reported over a 60 days. Two primary studies, incorporating both male and female animals not receiving blood transfusions as a provision of supportive care, were compared to two previously published studies, which incorporated only male animals provided blood transfusions as a part of the supportive care regimen. Criterion for euthanasia, and all other provisions of supportive care were comparable. Linear probit plots estimating the lethal dose (LD) and upper and lower limits of the 95% confidence interval (CI) for 10, 30, 50, 70 and 90% mortality, were compared between individual studies and the two models presented.

RESULTS

Comparison of probit estimates reveals two important findings. (1) Females have higher mortality than males at identical radiation doses, and (2) blood transfusions increased survival of male animals at lower doses but not at high doses of radiation exposure.

CONCLUSIONS

The use of single sex animal models may lead to an incomplete understanding of potential sex differences in the dose to mortality response of the TBI model. Consistent use of both sexes and type of supportive care will improve the transferability and reliability of NHP-TBI models currently in use, assist in the selection of radiation doses for single dose lethality studies, and allow investigators to determine the effectiveness of a particular MCM.

Developing and comparing models of hematopoietic-acute radiation syndrome in Göttingen and Sinclair minipigs

PURPOSE

Current animal models of hematopoietic-acute radiation syndrome (H-ARS) are resource intensive and have limited translation to humans, thereby inhibiting the development of effective medical countermeasures (MCM)s for radiation exposure.

MATERIALS AND METHODS

To improve the MCM pipeline, we developed models of H-ARS in male Göttingen and Sinclair minipigs. Weight matched Göttingens and Sinclairs received total body irradiation (TBI; 1.50-2.10 Gy and 1.94-2.90 Gy, respectively), were observed for up to 45 days with blood collections for clinical pathology analysis, and were examined during gross necropsy.

RESULTS

The lethal dose for 50% of the population over the course of 45 days (LD_50/45) with 'field' supportive care (primarily antibiotics and hydration support) and implanted vascular access ports was 1.89 and 2.53 Gy for Göttingens and Sinclairs, respectively. Both minipig strains exhibited prototypical H-ARS characteristics, experiencing thrombocytopenia and neutropenia, and nadirs approximately 14 days following irradiation, slightly varying with dose. Both strains experienced increased bruising, petechia, and signs of internal hemorrhage in the lungs, GI, heart, and skin. All observations were noted to correlate with dose more closely in Sinclairs than in Göttingens.

CONCLUSION

The results of this study provide a template for future MCM development in an alternate species, and support further development of the Göttingen and Sinclair minipig H-ARS models.

Technical Note: Quality assurance and relative dosimetry testing of a 60 Co total body irradiator using optical imaging

PURPOSE

The aim of this study was to create an optical imaging-based system for quality assurance (QA) testing of a dedicated Co-60 total body irradiation (TBI) machine. Our goal is to streamline the QA process by minimizing the amount time necessary for tests such as verification of dose rate and field homogeneity.

METHODS

Plastic scintillating rods were placed directly on the patient treatment couch of a dedicated TBI ⁶⁰ Co irradiator. A tripod-mounted intensified camera was placed directly adjacent to the couch. Images were acquired over a 30-s period once the cobalt source was fully exposed. Real-time image filtering was used; cumulative images were flatfield corrected as well as background and darkfield subtracted. Scintillators were used to measure light-radiation field correspondence, dose rate, field homogeneity, and symmetry. Dose rate effects were measured by modifying the height of the treatment couch and scintillator response was compared to ionization chamber (IC) measurements. Optically stimulated luminesce detector (OSLD) used as reference dosimeters during field symmetry and homogeneity testing.

RESULTS

The scintillator-based system accurately reported changes in dose rate. When comparing normalized output values for IC vs scintillators over a range of source-to-surface distances, a linear relationship (R²  = 0.99) was observed. Normalized scintillator signal matched OSLD measurements with <1.5% difference during field homogeneity and symmetry testing. Beam symmetry across both axes of the field was within 2%. The light field was found to correspond to 90 ± 3% of the isodose maximum along the longitudinal and latitudinal axis, respectively. Scintillator imaging output results using a single image stack requiring no postexposure processing (needed for OSLD) or repeat manual measurements (needed for IC).

CONCLUSION

Imaging of scintillation light emission from plastic rods is a viable and efficient method for carrying out TBI ⁶⁰ Co irradiator QA. We have shown that this technique can accurately measure field homogeneity, symmetry, light-radiation field correspondence, and dose rate effects.

Therapeutic potential of natural plant products and their metabolites in preventing radiation enteropathy resulting from abdominal or pelvic irradiation

Radiation-induced gastrointestinal injury or radiation enteropathy is an imminent risk during radiation therapy of abdominal or pelvic tumors. Despite remarkable technological advancements in image-guided radiation delivery techniques, the risk of intestinal injury after radiotherapy for abdominal or pelvic cancers has not been completely eliminated. The irradiated intestine undergoes varying degrees of adverse structural and functional changes, which can result in transient or long-term complications. The risk of development of enteropathy depends on dose, fractionation, and quality of radiation. Moreover, the patients' medical condition, age, inter-individual sensitivity to radiation and size of the treatment area are also risk factors of radiation enteropathy. Therefore, strategies are needed to prevent radiotherapy-induced undesirable alteration in the gastrointestinal tract. Many natural plant products, by virtue of their plethora of biological activities, alleviate the adverse effects of radiation-induced injury. The current review discusses potential roles and possible mechanisms of natural plant products in suppressing radiation enteropathy. Natural plant products have the potential to suppress intestinal radiation toxicity.

Thyroid nodules and long-term follow-up among childhood cancer survivors who underwent hematopoietic stem cell transplantation

Thyroid nodules have been observed in childhood cancer survivors (CCS) treated with chemotherapy and radiotherapy. We report four patients with thyroid nodules identified during the long-term follow-up of children who underwent hematopoietic stem cell transplantation (HSCT). The thyroid nodules were diagnosed as adenomatous goiter in all four patients. The interval between the primary cancer diagnosis and the occurrence of the thyroid nodules was more than 10 yr. Furthermore, all four patients underwent HSCT in conditioning with total body irradiation (TBI) before the age of 10 yr. Two of four patients commenced treatment with levothyroxine due to elevated TSH levels. Only two patients showed elevated thyroglobulin levels (> 70 µg/L). In conclusion, we suggest that CCS who have undergone HSCT in conditioning with TBI more than 10 yr previously should be followed up carefully for thyroid nodules using ultrasound.

Volumetric modulated arc therapy for total body irradiation: A feasibility study using Pinnacle3 treatment planning system and Elekta Agility™ linac

A study was undertaken to explore the use of volumetric modulated arc therapy (VMAT) for total body irradiation (TBI). Five patient plans were created in Pinnacle3 using nine 6 MV photon dynamic arcs. A dose of 12 Gy in six fractions was prescribed. The planning target volume (PTV) was split into four subsections for the head, chest, abdomen, and pelvis. The head and chest beams were optimized together, followed by the abdomen and pelvis beams. The last stage of the planning process involved turning all beams on and performing a final optimization to achieve a clinically acceptable plan. Beam isocenters were shifted by 3 or 5 mm in the left-right, anterior-posterior, and superior-inferior directions to simulate the effect of setup errors on the dose distribution. Treatment plan verification consisted of ArcCheck measurements compared to calculated doses using a global 3%/3 mm gamma analysis. All five patient plans achieved the planning aim of delivering 12 Gy to at least 90% of the target. The mean dose in the PTV was 12.7 Gy. Mean lung dose was restricted to 8 Gy, and a dose reduction of up to 40% for organs such as the liver and kidneys proved feasible. The VMAT technique was found to be sensitive to patient setup errors particularly in the superior-inferior direction. The dose predicted by the planning system agreed with measured doses and had an average pass rate of 99.2% for all arcs. VMAT was found to be a viable treatment technique for total body irradiation.

Local Tumor Control and Normal Tissue Toxicity of Pulsed Low-Dose Rate Radiotherapy for Recurrent Lung Cancer: An In Vivo Animal Study

OBJECTIVES

This study investigates (1) local tumor control and (2) normal tissue toxicity of pulsed low-dose rate radiotherapy (PLDR) for recurrent lung cancer.

METHODS

For study 1, nude mice were implanted with A549 tumors and divided into the following 3 groups: (1) control (n = 10), (2) conventional radiotherapy (RT; n = 10), and (3) PLDR (n = 10). Tumor-bearing mice received 2 Gy daily dose for 2 consecutive days. Weekly magnetic resonance imaging was used for tumor growth monitoring. For study 2, 20 mice received 8 Gy total body irradiation either continuously (n = 10) or 40 × 0.2 Gy pulses with 3-minute intervals (n = 10).

RESULTS

For study 1, both conventional RT and PLDR significantly inhibited the growth of A549 xenografts compared with the control group (>35% difference in the mean tumor volume; P < .05). The PLDR results were slightly better than conventional RT (8% difference in the mean tumor volume; P > .05). For study 2, the average weight was 20.94 ± 1.68 g and 25.69 ± 1.27 g and the survival time was 8 days and 12 days for mice treated with conventional RT and PLDR (P < .05), respectively.

CONCLUSION

This study showed that PLDR could control A549 tumors as effectively as conventional RT, and PLDR induced much less normal tissue toxicity than conventional RT. Thus, PLDR would be a good modality for recurrent lung cancers.

ADVANCES IN KNOWLEDGE

This article reports our results of an in vivo animal investigation of PLDR for the treatment of recurrent cancers, which may not be eligible for treatment because of the dose limitations on nearby healthy organs that have been irradiated in previous treatments. This was the first in vivo study to quantify the tumor control and normal tissue toxicities of PLDR using mice with implanted tumors, and our findings provided evidence to support the clinical trials that employ PLDR treatment techniques.

Modelling hematological parameters after total body irradiation

PURPOSE

The time- and dose-dependent reconstitution of hematopoiesis after radiation exposure is strongly related to the stem cell population and can be used to predict hematological parameters. These parameters allow further insight into the hematopoietic system and might lead to the development of novel stem cell transplantation models.

MATERIALS AND METHODS

CD4-/- C57Bl/6 mice, transgenic for human CD4 and HLA-DR3, were irradiated in a single (3, 6, 8 and 12 Gy) and fractionated (6 × 1 Gy, 6 × 1.5 Gy, 6 × 2 Gy; twice daily) dose regimen. Blood was analyzed weekly for red blood cells (RBC), hemoglobin concentration (Hb), hematocrit (HCT) and white blood cells (WBC). Organ and tissue damage after irradiation were examined by histopathology.

RESULTS

The recovery curves for RBC, Hb, HCT and WBC showed the same velocity (< 1 week) for all radiation doses (3-12 Gy) starting at different, dose-dependent times. The only dose-dependent parameter was defined by the beginning of the recovery process (dose-dependent shift) and higher doses were related to a later recovery of the hematopoietic system. The RBC, Hb and HCT recovery was followed by a saturation curve reaching a final concentration independent of the radiation dose. Histological analysis of the bone marrow in the single dose cohort showed a dose-dependent reduction of the cellularity in the bone marrow cavities. The fractioned radiation dose cohort resulted in a regeneration of all bone marrow cavities.

CONCLUSION

Specific functions were developed to describe the reconstitution of hematological parameters after total body irradiation.