Author: Nguyen Phuong Dang, Mason Hazlett, Lijun Ma, Yutaka Natsuaki, William T. Watkins, Zhengzheng Xu, Timothy Pok Chi Yeung 👨🔬
Affiliation: Reflexion Medical Inc,, Radiation Oncology, Keck School of Medicine of USC, RefleXion Medical, Department of Radiation Oncology, City of Hope National Medical Center 🌍
Purpose: This is the first study reporting the beam dosimetric parameter cross-checks of Reflexion linac using different water phantom systems and detectors. The difference in measurements using different water phantoms and detectors was evaluated.
Methods: The measurements were performed at 85cm nominal source-to-surface distance. The reference beams of 2x10cm2 and 1x10cm2 field size (FS) were used for percentage depth dose (PDD) measurements, while in-plane and cross-plane profiles were acquired using 2x40cm2 FS at 10cm depth. The IBA Helix Phantom and PTW MP3-T were used as the water phantoms and Edge diode detector (0.019cm3) and A1SL ion chamber (0.053cm3) were selected as the detectors. The IBA phantom used continuous beam scan with 0.5mm resolution. The MP3-T phantom allowed stepwise scanning with 2mm step size and 0.5s measurement time. Beam profiles were compared with the beam model in treatment planning system (TPS) using 1mm/1% criteria. PDD10 derived from point measurements (Dose@10cm/Dose@1.5cm) using different detectors and MP3-T phantom were reported.
Results: The beam profiles acquired from IBA and MP3-T phantoms agreed with the TPS model (1%/1mm). PDD10 of 2x10cm2 FS acquired by IBA and MP3-T were 57.2% and 56.7%, respectively (TPS: 57.6%). Point-based PDD10 of 2x10 cm2 beam with A1SL and Edge were 57.8% and 57.0%, respectively. PDD10 of 1x10 cm2 beam measured with A1SL and Edge were 55.5% and 55.1%, respectively (TPS: 55.2%).
Conclusion: The dosimetric parameters from water phantom systems and solid water agreed with the beam model in TPS. However, consistent difference in PDD10 between IBA and PTW MP3-T phantoms was observed. The result of further investigation will be presented at the time of the conference.