Total body irradiation (TBI) in combination with chemotherapy is widely used as a conditioning regimen in pediatric and adult hematopoietic stem cell transplantation (HSCT). The combination of TBI with chemotherapy has demonstrated superior survival outcomes in patients with acute lymphoblastic and myeloid leukemia when compared with conditioning regimens based only on chemotherapy. The clinical application of intensity-modulated radiation therapy (IMRT)-based methods (volumetric modulated arc therapy (VMAT) and TomoTherapy) seems to be promising and has been actively used worldwide. The optimized conformal total body irradiation (OC-TBI) method described in this study provides selected dose reduction for organs at risk with respect to the most significant toxicity (lungs, kidneys, lenses). This study included 220 pediatric patients who received OC-TBI with subsequent chemotherapy and allogenic HSCT with TCRαβ/CD19 depletion. A group of 151 patients received OC-TBI using TomoTherapy, and 40 patients received OC-TBI using the Elekta Synergy™ linac with an Agility-MLC (Elekta, Crawley, UK) using volumetric modulated arc therapy (VMAT). Twenty-nine patients received OC-TBI with supplemental simultaneous boost to bone marrow—(SIB to BM) up to 15 Gy: 28 patients (pts)—TomoTherapy; one patient—VMAT. The follow-up duration ranged from 0.3 to 6.4 years (median follow-up, 2.8 years). Overall survival (OS) for all the patients was 63% (95% CI: 56–70), and event-free survival (EFS) was 58% (95% CI: 51–65). The cumulative incidence of transplant-related mortality (TRM) was 10.7% (95% CI: 2.2–16) for all patients. The incidence of early TRM (<100 days) was 5.0% (95% CI: 1.5–8.9), and that of late TRM (>100 days) was 5.7 (95% CI: 1.7–10.2). The main causes of death for all the patients were relapse and infection. The concept of OC-TBI using IMRT VMAT and helical treatment delivery on a TomoTherapy treatment unit provides maximum control of the dose distribution in extended targets with simultaneous dose reduction for organs at risk. This method demonstrated a low incidence of severe side effects after radiation therapy and predictable treatment effectiveness. Our initial experience demonstrates that OC-TBI appears to be a promising technique for the treatment of pediatric patients.

This study presents the experience of one center in the development and implementation of two different methods of totalbody irradiation (ТОТ) based on radiation therapy with intensity modulation, namely, Helical TomoTherapy (HT) and Volumetric Modulated Arc Therapy (VMAT), implemented on the classic linear accelerator Elekta Synergy. The aim of the work is the comparison of two TBI methods, as well as a description of the process of introducing these methods into the routine practice of the radiotherapy department. The study was approved by the Independent Ethics Committee of the Dmitry Rogachev Nationa Medical Research Center of Pediatric Hematology, Oncology and Immunology. Prescribed total doses: PTV – 12.0 Gy with a single fraction of 2.0 Gy twice per a day, at least 95% of PTV should have received a dose of 11.4 Gy, the volume of each lung receiving 8.0 Gy should not exceed 40%, the average dose in each of the kidneys should not exceed 9.0 Gy, the dose in the anterior segment of the eye should be reduced as much as possible while maintaining the dose in surrounding part of PTV. In total, from July 2014 to December 2018, 156 patients received TBI, 128 of which on TomoTherapy and 28 on Elekta. The use of a standardized approach to TBI from July 2015 to December 2018 made it possible to introduce TBI into the routine practice of the radiotherapy department. A standardized approach to TBI was implemented with the irradiation of 17 on Elekta and 91 on TomoTherapy. It allowed us toobtain uniform reproducible results in terms of dosimetric criteria. The volume of lungs receiving a dose of 8.0 Gy did not exceed 40% for TomoTherapy and for Elekta, the average dose in the kidneys did not exceed 8.0 Gy for both modalities. In the standardized versions of TBI, 10.0 Gy cover at least 95% of the ribs volume, in accordance with the prescription. In both cases, the quality of PTV coverage met the prescribed criteria, namely, at least 95 percent of the volume of PTV received at least 95% of the prescribed dose (11.4 Gy). The minimum dose in the lungs was 6.2 ± 0.2 Gy and 5.1 ± 0.4 Gy, for TomoTherapy and Elekta respectively. The presence or absence of the clinical significance of this criterion is to be assessed. The developed TBI methods allow to deliver the prescribed dose to the target while maintaining the specified dose levels in the organs at risk. However, TomoTherapy plans have better target coverage and homogeneity than VMAT-based plans for Elekta. The use of a standardized approach makes it possible to quantify treatment plans for these techniques.

Purpose: Combination of total body irradiation (TBI) with chemotherapy is widely used technique for conditioning before hematopoietic stem cell transplantation for patient with hematological malignancies worldwide. Total body irradiation for patients with high height has to be divided into two parts: irradiation of upper part of the patient’s body (including head, body and part of legs) and irradiation of lower part of the patient’s body (including leg). There is an area in which the fields overlap each other – the junction area. The aim of this work is the development and verification of simple junction technique that would provide the dose distribution in the junction area from 90 to 125 % of prescribed dose. Material and methods: Total body irradiation was performed on the Tomotherapy machine using helical geometry of the beam delivery. Distribution of the dose in junction area was investigated. Simple solution was proposed: during the optimization of the radiotherapy plan certain margin should be maintained between upper and lower targets while dose distribution in junction area satisfies the uniformity requirements for the given irradiation geometry. The dimension of the margin was determined experimentally using a CheesePhantom and radiochromic EBT-2 films. The uniformity of dose distribution in the junction area was monitored by in vivo measurements using radiochromic EBT-2 films located on the skin surface of patients. Results: The dimension of the margin at which the dose in the junction area is within the range of 90 to 125 % of the prescribed dose was determined experimentally and amounted to 5.25 cm. The values of the measured dose were in the range from 97 to 105 %. In total 18 in vivo measurements of the junction area were performed. According to the results of in vivo dosimetry, the values of the doses measured in the junction area were in the range from 93 ± 3 % to 108 ± 4 %. Conclusion:The developed planning method with the selected plan geometry ensures satisfactory heterogeneity of the dose distribution in the area of field junction between the upper and lower irradiation regions, despite of the existing uncertainty of patient positioning. Results were confirmed by in vivo measurements. The obtained data can be used for total body irradiation of the patients using Helical Tomotherapy.