Hypofractionated Radiotherapy for Hematologic Malignancies during the COVID-19 Pandemic and Beyond.

PURPOSE: Radiotherapy is integral in the management of hematological malignancies (HM). Standard radiotherapy dose fractionation regimens range between 20 and 50 Gy in 10-25 fractions over 2-5 weeks. This study presents the outcomes of patients with HM treated with hypofractionation radiotherapy (HFRT) during the COVID-19 pandemic. METHODS: Patients (n = 36) were treated with HFRT between January 2020 and September 2022. The outcomes measured were the overall response rate (ORR), freedom from local progression (FFLP), and overall survival (OS). RESULTS: The median follow-up was 13.2 months. Thirty-three patients (92%) had non-Hodgkin (NHL) or Hodgkin lymphoma (HL). Eighteen patients (50%) had aggressive and nine (25%) had indolent NHL. Nineteen patients (53%) presented with stage I/II and fifteen (42%) with stage III/IV disease. Twenty-five (69.4%) and eleven (30%) received consolidative and definitive RT, respectively. Twenty patients (56%) received treatment to the neck and/or thorax and nine (25%) to the abdomen or pelvis. The total dose ranged from 18 to 42.5 Gy in 6-17 fractions/2.67-5 Gy per fraction. The median dose in 2 Gy fractions for an alpha/beta (α/ß) ratio of 10 amounted to 39 Gy (SD ± 13.86) and 43.6 Gy (SD ± 12) for an α/ß of 3. The most commonly used fractionation scheme was 39 Gy in 13 fractions. ORR was 94.4% for the entire cohort, and 100, 94.4, and 83.3% for indolent NHL, aggressive NHL, and HL patients. The two-year FFLP was 76% (95% CI: 34-93%) for the entire cohort and 100, 87 (95% CI: 56.4-96.5%), and 42% (95% CI: 1.1-84.3%) for the indolent NHL, aggressive NHL, and HL patients. Two-year OS for the entire cohort was 80% (95% CI: 59.9-90.5%) and 100, 66.1 (95% CI: 36.4-84.4%), and 100% for the indolent NHL, aggressive NHL, and HL patients. Only one patient presented with grade two pulmonary toxicity. CONCLUSIONS: HFRT in HM provides excellent local control to be validated in a larger prospective study.

C-X-C Motif Chemokine Receptor 4-Targeted Radioligand Therapy in Hematological Malignancies-Myeloablative Effects, Antilymphoma Activity, and Safety Profile.

BACKGROUND: After C-X-C motif chemokine receptor 4 (CXCR4)-directed radioligand therapy (RLT), lymphoma patients are scheduled for conditioning therapy (CON) followed by hematopoietic stem cell transplantation (HSCT). We aimed to determine whether CXCR4-RLT can achieve bone marrow ablation and direct antilymphoma activity independent from CON/HSCT and also evaluated the safety profile of this theranostic approach in an acute setting. PATIENTS AND METHODS: After CXCR4-directed 68 Ga-pentixafor PET/CT, 21 heavily pretreated patients with hematological malignancies underwent CXCR4-directed RLT using 90 Y-pentixather. The extent of myeloablative efficacy was determined by investigating hematologic laboratory parameters before RLT (day -1), at the day of RLT (day 0), 2 days after RLT (day 2), and before CON (median day 10). Serving as surrogate marker of antilymphoma activity, lactate dehydrogenase (LDH) levels were also assessed until CON. We also screened for laboratory-defined tumor lysis syndrome after the Cairo-Bishop definition and recorded acute laboratory adverse events using the Common Terminology Criteria for Adverse Events version 5.0. RESULTS: After RLT, we observed a significant decline of leukocyte levels by 79.4% ± 18.7% till CON (granulocytes, drop by 70.3% ± 21%; platelets, reduction by 43.1% ± 36%; P ≤ 0.0005 vs day 0, respectively). After RLT, LDH levels already reached a peak at day 2, which was followed by a rapid decline thereafter (peak vs day of CON, P = 0.0006), indicating that 90 Y-pentixather exhibits direct antilymphoma activity. At day of CON, LDH levels were also significantly lower when compared with day -1 ( P = 0.04), suggestive for durable response mediated by RLT. No patient fulfilled the criteria of tumor lysis syndrome, whereas 25 laboratory adverse events attributable to CXCR4-directed treatment were identified (≥grade 3 in 2/25 [8%]). During further treatment course, all patients (100%) received HSCT. CONCLUSIONS: CXCR4-directed RLT causes effective myeloablation, which allows for HSCT. In addition, it also exerts direct antilymphoma activity independent of subsequent therapeutic steps, whereas safety profile was acceptable.

Is oligometastatic disease an applicable and useful concept in haematologic malignancies? A narrative review of radiation therapy standards, modern techniques, and innovations.

PURPOSE: Haematologic malignancies are particular in that they can generally be cured, even when distant metastases are present at diagnosis, unlike solid malignancies. Systemic treatments, including chemotherapy, targeted therapies, and immunotherapy, are the standard of care with excellent results. The considerable progress made in the management of these diseases in the last 20years has redefined the role of radiation therapy as minor in many clinical situations. We propose a literature review of data, showing that radiation therapy still has a role in curative, salvage, and palliative therapy situations. MATERIAL AND METHODS: A document and literature search was carried out in the following databases: Medline and ClinicalTrial.gov, for the terms "radiotherapy", "haematologic malignancies", "Hodgkin lymphoma", "non-Hodgkin lymphoma", "CAR T cells", "multiple myeloma", "solitary plasmocytoma", "intensity-modulated radiotherapy", "extracranial stereotactic body radiation therapy" and "proton therapy references". RESULTS: Haemopathological malignancies include a wide range of diseases and radiation therapy indications have been assessed over the past 20years. Currently, radiation therapy is indicated for localized disease (solitary plasmocytoma), as an adjuvant (Hodgkin lymphoma), in palliative settings, or after systemic treatment in relapsed patients (chimeric antigen receptor [CAR] T-cells) with a low recurrence burden, which can therefore be considered "oligorecurrence". Radiation therapy, through total body irradiation, has important indications, thanks to its immunomodulatory and/or myeloablative effects. Moreover, recent technological developments have made possible significant improvement in safety, contributing to radiation therapy being positioned in the treatment strategy of several indications. CONCLUSIONS: Given the effectiveness of systemic treatments in hematologic malignancies, the oligometastasis stage is of little importance. A curative intent after local radiation therapy, even advanced stage, is possible, both with residual disease for advanced Hodgkin lymphoma, aggressive non-Hodgkin lymphoma, or solitary plasmocytoma, and even without evidence of disease after chemotherapy for Hodgkin or non-Hodgkin lymphoma. The role of new treatments, such as CAR T cells, allows us to consider radiation therapy after systemic treatment of relapsed diseases with low volume recurrence, which can be considered oligorecurrence.

Assessment of Lymphoma and Other Hematologic Malignancies Training Needs Among Radiation Oncology Residents: a Brief Report.

The role of radiation therapy (RT) varies across hematologic malignancies (HM). Radiation oncology (RO) resident comfort with specific aspects of HM patient management is unknown. The International Lymphoma RO Group (ILROG) assessed resident HM training opportunities and interest in an HM away elective. RO residents (PGY2-5) in the Association of Residents in RO (ARRO) database (n = 572) were emailed an anonymous, web-based survey in January 2019 including binary, Likert-type scale (1 = not at all, 5 = extremely, reported as median [interquartile range]), and multiple-choice questions. Of 134 resident respondents (23%), 86 (64%) were PGY4/5 residents and 36 (27%) were in larger programs (≥ 13 residents). Residents reported having specialized HM faculty (112, 84%) and a dedicated HM rotation (95, 71%). Residents reported "moderate" preparedness to advocate for RT in multidisciplinary conferences (3 [2-3]); make HM-related clinical decisions (3 [2-4]); and critique treatment planning (3 [2-4]). They reported feeling "moderately" to "quite" prepared to contour HM cases (3.5 [3-4]) and "quite" prepared to utilize the PET-CT five-point scale (4 [3-5]). Overall, residents reported feeling "moderately" prepared to treat HM patients (3 [2-3]); 24 residents (23%) felt "quite" or "extremely" prepared. Sixty-six residents (49%) were potentially interested in an HM away elective, commonly to increase comfort with treating HM patients (65%). Therefore, HM training is an important component of RO residency, yet a minority of surveyed trainees felt quite or extremely well prepared to treat HM patients. Programs should explore alternative and additional educational opportunities to increase resident comfort with treating HM patients.

Outcomes of allogeneic haematopoietic stem cell transplantation with intensity-modulated total body irradiation by helical tomotherapy: a 2-year prospective follow-up study.

BACKGROUND AND OBJECTIVES: Intensity-modulated radiation therapy (IMRT) helps achieve good radiation dose conformity and precise dose evaluation. We conducted a single-centre prospective study to assess the safety and feasibility of total body irradiation with IMRT (IMRT-TBI) using helical tomotherapy in allogeneic haematopoietic stem cell transplantation (allo-HSCT). PATIENTS AND METHODS: Thirty-nine adult patients with haematological malignancy (acute lymphoblastic leukaemia [n = 21], chronic myeloid leukaemia [n = 6], mixed phenotype acute leukaemia [n = 5], acute myeloid leukaemia [n = 4], and malignant lymphoma [n = 3]) who received 12 Gy IMRT-TBI were enrolled with a median follow-up of 934.5 (range, 617-1254) d. At the time of transplantation, 33 patients (85%) achieved complete remission. The conditioning regimen used IMRT-TBI (12 Gy in 6 fractions twice daily, for 3 d) and cyclophosphamide (60 mg/kg/d, for 2 d), seven patients were combined with cytarabine, and five with etoposide. We set dose constraints for the lungs, kidneys and lens as the organs at risk. RESULTS: The mean doses for the lungs and kidneys were 7.50 and 9.11 Gy, respectively. The mean maximum dose for the lens (right/left) was 5.75/5.87 Gy. The 2-year overall survival (OS), disease-free survival (DFS), cumulative incidence of relapse (CIR) and non-relapse mortality (NRM) were 69, 64, 18 and 18%, respectively. Thirty-six patients developed early adverse events (AEs) (including four patients with Grade 3/4 toxicities), most of which were reversible oral mucositis and may partially have been related to IMRT-TBI. However, the incidence of toxicity was comparable to conventional TBI-based conditioning transplantation. None of the patients developed primary graft failure, or Grade III-IV acute graft-versus-host disease (GVHD). In late complications, chronic kidney disease was observed in six patients, a lower incidence compared to conventional TBI-based conditioning transplantation. No radiation pneumonitis or cataracts were observed in any of the patients. CONCLUSIONS: IMRT-TBI is safe and feasible for haematological malignancies with acceptable clinical outcomes.KEY MESSAGESIMRT-TBI-helical tomotherapy aids in accurate dose calculation and conformity.It could be used without any considerable increase in the rate of TBI-related AEs.Allo-HSCT with IMRT-TBI may be an alternative to conventional TBI for clinical use.

Growth and Nutritional Outcomes in Children Post-Haematopoietic Stem Cell Transplant without Exposure to Total Body Irradiation.

AIMS: Poor growth in childhood cancer survivors who undergo haematopoietic stem cell transplant (HSCT) without exposure to radiation is reported anecdotally, although literature to support this is limited. The aims of this study were to assess the change in height standard deviation score (SDS) and the final adult height (FAH) in children who underwent chemotherapy-only conditioned HSCT and to identify predictors of poor growth. MATERIALS AND METHODS: We conducted a retrospective hospital medical record review (1984-2010) of children (1-10 years) who underwent chemotherapy-only conditioned HSCT, noting anthropology measurements at cancer diagnosis, HSCT, 10 years old and FAH. RESULTS: The median age at HSCT of the 53 patients was 4.5 years, 75% had a haematological malignancy and 25% a solid tumour. Half of the cohort underwent allogenic HSCT and most (89%) conditioned with busulphan. The mean change in height SDS from primary cancer diagnosis to FAH was -1.21 (±1.18 SD), equivalent to 7-8.5 cm loss, with a mean FAH of -0.91 SDS (±1.10 SD). The greatest height loss occurred between diagnosis and HSCT (-0.77 SDS, 95% confidence interval -1.42, -0.12, P = 0.01), with no catch-up growth seen by FAH. Patients with solid tumours had the greatest height loss. Overall body mass index SDS did not change significantly over time, or by cancer type. CONCLUSIONS: Chemotherapy-only conditioned HSCT during childhood can impact FAH, with the greatest height loss occurring prior to HSCT and no catch-up growth after treatment finishes. Children transplanted for a solid tumour malignancy seem to be more at risk, possibly due to intensive treatment regimens, both pre-transplant and during conditioning.

Increased risk of breast cancer-specific mortality among cancer survivors who developed breast cancer as a second malignancy.

BACKGROUND: Cancer survivors who develop breast cancer as a second malignancy (BCa-2) are common. Yet, little is known about the prognosis of BCa-2 compared to first primary breast cancer (BCa-1). METHODS: Using the Surveillance, Epidemiology, and End Results database, we conducted a population-based cohort study including 883,881 patients with BCa-1 and 36,313 patients with BCa-2 during 1990-2015. Compared with patients with BCa-1, we calculated hazard ratios (HRs) of breast cancer-specific mortality among patients with BCa-2, using multivariable Cox regression. RESULTS: During the follow-up (median 5.5 years), 114,964 and 3829 breast cancer-specific deaths were identified among BCa-1 and BCa-2 patients, respectively. Patients with BCa-2 had more favorable tumor characteristics and received less intensive treatment e.g., surgery and chemo-/radio-therapy, compared to patients with BCa-1. When adjusting for demographic factors, patients with BCa-2 were at similar risk of breast cancer-specific mortality (HR 1.00, 95% CI 0.97-1.03) compared to patients with BCa-1. However, when additionally controlling for tumor characteristics and treatment modes, BCa-2 patients were at an increased risk of breast cancer-specific mortality (HR 1.11, 95% CI 1.08-1.15). The risk elevation was particularly greater when the first malignancy was lung, bladder, ovarian or blood malignancy (HRs 1.16-1.85), or when the first malignancy was treated with chemotherapy and radiotherapy (HR 1.44, 95% CI 1.28-1.63). CONCLUSIONS: Overall, patients with BCa-2 have worse breast cancer-specific survival, compared with their BCa-1 counterparts, although the risk elevation is mild. High-risk subgroups based on first malignancy's characteristics may be considered for active clinical management.

Preservation of fertility in teenagers and young adults treated for haematological malignancies.

As survival rates in teenagers and young adults diagnosed with haematological malignancies now exceed 70%, it is important that long-term quality of life, including measures to protect future fertility, are considered and discussed with patients and their families. Although discussion on the effect of planned cancer treatment on fertility is standard of care, knowledge of potential fertility treatment options and when they should be offered in haematological malignancies is not always so clear. In each case, the advice on the appropriate preservation of fertility depends upon a complex interplay of factors, weighing out the risk of future infertility against the risk of fertility preservation treatment, and recommendations must be made on a case-by-case basis. The aim of this Review is to evaluate the gonadotoxicity of treatments of prevalent haematological malignancies in teenagers and young adults, and provide an evidence-based framework to help with fertility discussion and management at the time of diagnosis, relapse or resistant disease, and in long-term follow-up settings.

Total Body Irradiation and Risk of Breast Cancer After Blood or Marrow Transplantation: A Blood or Marrow Transplantation Survivor Study Report.

PURPOSE: To examine the association between total body irradiation (TBI) and subsequent breast cancer in women treated with blood or marrow transplantation (BMT) for hematologic malignancies. PATIENTS AND METHODS: Participants were drawn from the BMT Survivor Study (BMTSS), a retrospective cohort study that included patients who underwent transplantation between 1974 and 2014 and survived for ≥ 2 years after BMT. Patients with pre-BMT chest radiation or a history of breast cancer were excluded. Participants completed the BMTSS survey, which included details regarding breast cancer diagnosis. Subsequent breast cancer was confirmed by pathology report review or physician notes. Cox proportional hazards models assessed the association between TBI and subsequent breast cancer. Standardized incidence ratios were calculated to determine the excess risk of subsequent breast cancer compared with that in the general population. RESULTS: A total of 1,464 female BMT survivors (allogeneic: n = 788; autologous: n = 676) participated, with a median follow-up of 9.3 years from BMT. TBI was used in 660 patients (46%). Thirty-seven women developed subsequent breast cancer (allogeneic: n = 19; autologous: n = 18). Multivariable analysis revealed that exposure to TBI was associated with an increased risk of subsequent breast cancer among allogeneic BMT survivors (hazard ratio [HR], 3.7 [95% CI, 1.2 to 11.8]; P = .03) and autologous BMT survivors (HR, 2.6 [95% CI, 1.0 to 6.8]; P = .048). Pre-BMT exposure to alkylating agents was associated with an increased risk of subsequent breast cancer among autologous BMT survivors (HR, 3.3 [95% CI, 1.0 to 9.0]; P = .05). Compared with that in the general population, exposure to TBI at age < 30 years was associated with a 4.4-fold higher risk of subsequent breast cancer in allogeneic BMT survivors and a 4.6-fold higher risk in autologous BMT survivors. CONCLUSION: The association between TBI and subsequent breast cancer, especially among those exposed at a young age, as well as pre-BMT exposure to alkylating agents, should inform breast cancer screening for early detection.

ILROG emergency guidelines for radiation therapy of hematological malignancies during the COVID-19 pandemic.

The International Lymphoma Radiation Oncology Group (ILROG) guidelines for using radiation therapy (RT) in hematological malignancies are widely used in many countries. The emergency situation created by the COVID-19 pandemic may result in limitations of treatment resources. Furthermore, in recognition of the need to also reduce the exposure of patients and staff to potential infection with COVID-19, the ILROG task force has made recommendations for alternative radiation treatment schemes. The emphasis is on maintaining clinical efficacy and safety by increasing the dose per fraction while reducing the number of daily treatments. The guidance is informed by adhering to acceptable radiobiological parameters and clinical tolerability. The options for delaying or omitting RT in some hematological categories are also discussed.

Advances in Precision Oncology: Targeted Thorium-227 Conjugates As a New Modality in Targeted Alpha Therapy.

Targeted α therapy (TAT) offers the potential for the targeted delivery of potent α-particle-emitting radionuclides that emit high linear energy transfer radiation. This leads to a densely ionizing radiation track over a short path. Localized radiation induces cytotoxic, difficult-to-repair, clustered DNA double-strand breaks (DSBs). To date, radium-223 (223Ra) is the only TAT approved for the treatment of patients with metastatic castration-resistant prostate cancer. Thorium-227 (227Th), the progenitor nuclide of 223Ra, offers promise as a wider-ranging alternative due to the availability of efficient chelators, such as octadentate 3,2-hydroxypyridinone (3,2-HOPO). The 3,2-HOPO chelator can be readily conjugated to a range of targeting moieties, enabling the generation of new targeted thorium-227 conjugates (TTCs). This review provides a comprehensive overview of the advances in the preclinical development of TTCs for hematological cancers, including CD22-positive B cell cancers and CD33-positive leukemia, as well as for solid tumors overexpressing renal cell cancer antigen CD70, membrane-anchored glycoprotein mesothelin in mesothelioma, prostate-specific membrane antigen in prostate cancer, and fibroblast growth factor receptor 2. As the mechanism of action for TTCs is linked to the formation of DSBs, the authors also report data supporting combinations of TTCs with inhibitors of the DNA damage response pathways, including those of the ataxia telangiectasia and Rad3-related protein, and poly-ADP ribose polymerase. Finally, emerging evidence suggests that TTCs induce immunogenic cell death through the release of danger-associated molecular patterns. Based on encouraging preclinical data, clinical studies have been initiated to investigate the safety and tolerability of TTCs in patients with various cancers.

Targeted Alpha-Particle Therapy for Hematologic Malignancies.

The short range and high linear energy transfer of α-particles offer the potential for efficient tumor killing while sparing normal bystander cells. Hematologic malignancies are ideally suited to targeted α-particle therapy (TAT) due to easy accessibility of malignant cells in blood, bone marrow, lymph nodes, and spleen as well as their radiosensitivity. Most clinical trials using α-particle therapy for hematologic malignancies have focused on acute myeloid leukemia (AML); however, preclinical studies have shown activity against other diseases such as non-Hodgkin's lymphoma and multiple myeloma. To date, the short-lived radionuclide bismuth-213 (213Bi) and its parent actinium-225 (225Ac) have been used clinically, but trials with astatinie-211 (211At) have recently begun, and thorium-227 (227Th) has shown promising preclinical results. Lintuzumab is a humanized monoclonal antibody that targets the cell surface antigen CD33, which is expressed on the vast majority of AML cells. Initial studies showed that 213Bi-labeled lintuzumab had antileukemic activity and could produce remissions after partial cytoreduction with cytarabine. An initial phase I trial demonstrated that a single infusion of 225Ac-lintuzumab could be given safely at doses upto 111 kBq/kg with antileukemic activity across all dose levels. A second phase I study showed that fractionated-dose 225Ac-lintuzumab could be safely combined with low-dose cytarabine and produced objective responses in 28% of older patients with untreated AML. In a phase II study, treatment with 225Ac-lintuzumab monotherapy for a similar patient population resulted in remission in 69% of patients receiving two fractions of 74 kBq/kg and 22% of patients receiving two 55.5-kBq/kg fractions. Additionally, TAT may be useful in intensifying antileukemic therapy prior to hematopoietic cell transplantation, and pretargeting strategies offer the possibility for improved tumor-to-normal organ dose ratios.

Temporal Trends of Resident Experience in External Beam Radiation Therapy Cases: Analysis of ACGME Case Logs from 2007 to 2018.

PURPOSE: We sought to characterize temporal trends of radiation oncology resident-reported external beam radiation therapy (EBRT) case experience with respect to various disease sites, including trends in stereotactic radiosurgery and stereotactic body radiation therapy cases. METHODS AND MATERIALS: Summarized, deidentified case logs for graduating radiation oncology residents between 2007 and 2018 were obtained from the Accreditation Council for Graduate Medical Education national summary data report. Mean number of cumulative cases and standard deviations per graduating resident by year were evaluated. Cases were subdivided into 12 disease-site categories using the Accreditation Council for Graduate Medical Education classification. Analysis of variance was used to determine significant differences, and strength of association was evaluated using Pearson correlation. RESULTS: The number of graduating residents per year increased by 66% from 114 in 2007 to 189 in 2018 (P < .001, r = 0.88). The overall mean number of EBRT cases per graduating resident decreased by 13.2% from 521.9 in 2007 to 478.5 in 2018, with a decrease in the ratio of nonmetastatic to metastatic cases per graduating resident. There was significant variation among the disease categories analyzed; however, the largest proportionate decreases were seen in hematologic, lung, and genitourinary malignancies. Stereotactic radiosurgery volume per graduating resident increased from an average of 27.9 cases in 2007 to 50.3 in 2018 (P < .001, r = 0.96). Stereotactic body radiation therapy volume per graduating resident increased as well, from a mean of 6 cases in 2007 to 55.6 cases in 2018 (P < .001, r = 0.99). CONCLUSIONS: We report a longitudinal summary of resident-reported experience in EBRT cases. These findings have implications for future efforts to optimize residency training programs and requirements.

Hematologic Malignancies.

Radiation therapy plays a critical role in the management of a wide range of hematologic malignancies. The optimal radiation dose and target volume, and safe and effective ways of integrating radiation with systemic agents, vary depending on the histologic subtypes, stage at presentation, patient performance status, response to systemic therapy if given, treatment intent, and patient preferences. Limiting doses to surrounding organs without sacrificing disease control is of paramount importance. Reducing radiation doses and treatment volume in selected cases, and the use of advanced radiotherapy technology, can improve the therapeutic ratio of patients receiving radiation therapy for hematologic malignancies.

Organ sparing of linac-based targeted marrow irradiation over total body irradiation.

PURPOSE: Targeted marrow irradiation (TMI) is an alternative conditioning regimen to total body irradiation (TBI) before bone marrow transplantation in hematologic malignancies. Intensity-modulation methods of external beam radiation therapy are intended to permit significant organ sparing while maintaining adequate target coverage, improving the therapeutic ratio. This study directly compares the dose distributions to targets and organs at risk from TMI and TBI, both modalities conducted by general-use medical linacs at our institution. METHODS: TMI treatments were planned for 10 patients using multi-isocentric feathered volumetric arc therapy (VMAT) plans, delivered by 6 MV photon beams of Elekta Synergy linacs. The computed tomography (CT) datasets used to obtain these plans were also used to generate dose distributions of TBI treatments given in the AP/PA extended-field method. We compared dose distributions normalized to the same prescription for both plan types. The generalized equivalent uniform dose (gEUD) of Niemierko for organs and target volumes was used to quantify effective whole structure dose and dose savings. RESULTS: For the clinical target volume (CTV), no significant differences were found in mean dose or gEUD, although the radical dose homogeneity index (minimum dose divided by maximum dose) was 31.7% lower (P = 0.002) and the standard deviation of dose was 28.0% greater (P = 0.027) in the TMI plans than in the TBI plans. For the TMI plans, gEUD to the lungs, brain, kidneys, and liver was significantly lower (P < 0.001) by 47.8%, 33.3%, 55.4%, and 51.0%, respectively. CONCLUSION: TMI is capable of maintaining CTV coverage as compared to that achieved in TBI, while significantly sparing organs at risk. Improvement on sparing organs at risk permits a higher prescribed dose to the target or the maximum number of times marrow conditioning may be delivered to a patient while maintaining similar typical tissue complication rates.