Affiliation:
1. Department of Radiation Oncology Shanghai Concord Medical Cancer center Shanghai China
2. Proton & Heavy Ion Medical Research Center, State Key Laboratory of Radiation Medicine and Protection Soochow University Soochow Jiangsu China
Abstract
AbstractPurposeThis paper describes the implementation of an instantaneous low‐dose‐rate total body irradiation (TBI) technique using block‐filtered 6 MV X‐rays with a linear accelerator (LINAC) to reduce pulmonary toxicity.MethodsIn the absence of dedicated TBI‐specific meter‐set dose rates in LINAC and sufficient treatment room size, a 2‐cm‐thick transmission block was used together with a 200‐cm source‐to‐surface distance (SSD) to reduce the instantaneous dose rates of 6 MV x‐rays down to 10 cGy/min, thus alteration to the beam properties. A TBI‐specific dose calculation model was built with data acquired at the treatment planning system (TPS)‐permitted maximum 140‐cm SSD and was validated in phantoms at a 180‐cm SSD. As for planning strategies, we adopted large anterior‐to‐posterior/posterior‐to‐anterior (AP/PA) open fields with multi‐leaf collimator shielding for lungs to achieve target coverage, lung protection, and efficient dose delivery. A custom‐designed sliding couch (Patent No. ZL202123085880.1) was manufactured to support patients during treatment. Measures to control the quality and safety of TBI treatment include machine interlocks, pretreatment checklists, and in‐vivo dose monitoring.ResultsThe instantaneous dose rate of block‐filtered 6MV X‐ray was reduced to approximately 7.0 cGy/min at 12.5–7.5 cm depth with a 185–200 cm SSD. The dose calculated by TPS differs from the measurements by 0.15%–1.55% in the homogeneous phantom and 1.2%–4.85% in the CIRS thorax phantom. The open‐field TBI technique achieved V90% (PTV) ≈ 96.8% and MLD = 6.6 Gy with 1‐h planning and 50‐min beam delivery in a single fraction. From February 2021 to July 2023, 30 patients received TBI treatments in our center, and in‐vivo monitoring results differed from TPS calculations by −1.49%–2.10%. After 6–12 months of follow‐ups, all the patients treated in our center showed no pulmonary toxicities of grade 2 or higher.ConclusionA low instantaneous dose rate TBI technique can be implemented in the clinic.