Abstract
Background and purpose: To introduce a standard linac with true attachment free, rapid arc and dose-drop scheme for positioning related dose deviation control based total body irradiation(TBI).Materials/Methods: One eight years old girl diagnosed with acute lymphocytic leukemia underwent TBI in 2020. Target volumes and organs at risk were contoured after CT simulation. Total sixteen ARC and four AP-PA from five isocenters were designed. A dose-drop scheme on both sides of adjacent region were performed to reduce positioning-related dose deviation. A series of quality assurance before radiotherapy and real-time dose monitoring during radiotherapy were carried out.Results: The average on board imaging (OBI) time of per fraction was 40.3 min, the average beam on time of per fraction was 37.2 min, the average time to change from head first to feet first position was 18.4 min. The average mean lung dose was 9.89 Gy, the maximum lens dose was 7.60 Gy, the mean PTV_total dose was 12.17Gy, 98.23% PTV_total volume was covered by 90% of the prescription dose. The maximum dose (Dmax) of PTV_total was 13.65Gy. Dmean and V10.8 of PTV_total are only slightly different(0.49% - 1.89% and 0.26% - 1.04% respectively) even with an error of 5 - 20mm longitudinal misalignments. Gamma passing rate(3mm/ 3% Gamma criteria) are between 93.5% and 100%. Real-time dose monitoring showed an overall deviation of -3.9%±5.51%.Conclusions: Standard linac, rapid arc and dose-drop for positioning-related dose deviation control based total body irradiation is feasible, accurate, and reliable. It is worthy of clinical application.
First Experience of Standard Linac, Rapid Arc and Dose-drop Scheme Based Total Body Irradiation
