Volumetric Modulated Arc Therapy Enabled Total Body Irradiation (VMAT-TBI): Six-year Clinical Experience and Treatment Outcomes

Abstract Background Total body irradiation is an important part of the conditioning regimens frequently used to prepare patients for allogeneic hematopoietic stem cell transplantation (SCT). Volumetric modulated arc therapy enabled total body irradiation (VMAT-TBI), an alternative to conventional TBI (cTBI), is a novel radiotherapy treatment technique that has been implemented and investigated in our institution. Objectives The purpose of this study is to 1) report our six-year clinical experience in terms of treatment planning strategy and delivery time, and 2) evaluate the clinical outcomes and toxicities in our cohort of patients treated with VMAT-TBI. Study Design This is a retrospective single center study. Forty-four patients at our institution received VMAT-TBI and chemotherapy conditioning followed by allogeneic stem cell transplant between 2014 and 2020. Thirty-two patients (73%) received standard-dose TBI (12-13.2 Gy in 6-8 fractions twice daily) while twelve (27%) received low-dose TBI (2-4 Gy in one fraction). Treatment planning, delivery, and treatment outcome data including overall survival (OS), relapse free survival (RFS), and toxicities were analyzed. Results The developed VMAT-TBI planning strategy consistently generated plans satisfying our dose constraints, with planning target volume (PTV) coverage >90%, mean lung dose (MLD) ∼50-75% of prescription dose, and minimal hotspots in critical organs. Most of the treatment deliveries were Conclusions VMAT-TBI provides a safe alternative to cTBI. The dose modulation capability of VMAT-TBI may lead to new treatment strategies, such as simultaneous boost and further critical organ sparing, for better malignant cell eradication, immune suppression, and lower toxicities.