# Multi-isocentric volumetric arc-based total body irradiation: radiation dose impact on oncological outcomes in patients receiving allogeneic hematopoietic cell transplantation

## TL;DR

This study compares the effectiveness of different radiation doses in preparing patients for a type of cell transplant, finding that a higher dose may improve survival.

## Contribution

The study evaluates oncological outcomes of 12 Gy versus 8 Gy total body irradiation in allogeneic hematopoietic cell transplantation.

## Key findings

- Higher dose (12 Gy) showed better overall survival compared to 8 Gy.
- Toxicities were similar between the two dose groups.
- All patients receiving 12 Gy achieved engraftment, while one graft failure occurred in the 8 Gy group.

## Abstract

Total body irradiation (TBI) is an important component of conditioning schedules. Data comparing different radiotherapy (RT) regimens in allogeneic hematopoietic cell transplantation (allo-HCT) remain limited. We aimed to evaluate the oncological outcomes of patients receiving different RT doses.

All patients treated with multi-isocentric volumetric arc-based total body irradiation (VMAT-TBI) at a dose of ≥8 Grays (Gy) between 2021 and 2023 were included in this retrospective analysis. The RT regimens were either 8 Gy delivered in 4 bi-daily fractions (fx) or 12 Gy in 6 bi-daily fx. We evaluated the overall survival (OS), relapse-free survival (RFS), engraftment, and toxicities in both groups.

Forty-two patients met the inclusion criteria, including 24 treated with a 12 Gy regimen. Hazard ratio for OS after adjusting for age, Charlson Comorbidity Index (CCI), Disease Risk Index (DRI), disease status and total conditioning score (TCI) for survival was 0.02 (0.00, 0.48. p=0.01) in favor of a higher dose. The median RFS in the 12 Gy cohort was not achieved, and it was 11.8 months in the 8 Gy group. Toxicities were comparable between the groups. Two treatment-related deaths occurred in the 8 Gy arm. All patients in the 12 Gy arm achieved engraftment, whereas one graft failure was observed in the 8 Gy arm.

In patients receiving modern TBI before allo-HCT with high-quality dose distribution, 12 Gy appears to be more effective than 8 Gy. However, this concerns a single-center cohort with TBI dose allocation according to estimated patient fragility before transplant. Therefore, randomized trials are required to determine the optimal RT dose.