Establishment of a Novel Method for Dose Distribution Verification in Stereotactic Radiosurgery (SRS) Using General
Shunta Hirano1, Takaaki Ito2, Yuya Yanagi3
1Department of Medical Physics, Graduate School of Medical Sciences, Kindai University, Osaka, JPN.
None:
Stereotactic radiosurgery (SRS) involves steep dose gradients and small irradiation fields, which makes ensuring irradiation accuracy extremely important. While general semiconductor array detectors are reusable and cost-effective, their wide detector spacing results in insufficient spatial resolution. The aim of this study is to establish a novel patient-specific quality assurance (PSQA) method for single-isocenter multiple-target SRS volumetric modulated arc therapy (SIMT-SRS-VMAT) that can evaluate dose distribution with the same accuracy as radiochromic film by virtually narrowing the detector spacing by combining measurement with a general semiconductor array detector and translational movement of the treatment couch. Single-field plans with a single target and SIMT-SRS-VMAT plans with two targets were created for 1 cm lesions. Measurements using MapCHECK2 (Sun Nuclear, Melbourne, FL, USA) were combined with couch movement to synthesize measurement data at virtual detector spacings of 5, 4, 3, 2, and 1 mm. Root mean square error (RMSE) was used to evaluate profile shape accuracy, and γ analysis was used to evaluate dose distribution agreement. At virtual detector spacings of 10 mm, 5 mm, 4 mm, 3 mm, 2 mm, 1 mm, and with radiochromic film, the RMSE values in SIMT-SRS-VMAT were 8.02% ± 0.34%, 2.16% ± 0.07%, 1.60% ± 0.08%, 1.48% ± 0.17%, 1.32% ± 0.10%, 1.38% ± 0.03%, and 1.25% ± 0.02%, respectively. The RMSE decreased as the detector spacing narrowed, resulting in profile shapes comparable to those obtained with radiochromic film. In γ analysis, setting the virtual detector spacing to 5 mm enabled analysis covering the entire dose range, and the γ pass rate was comparable to EBT4 (Ashland Inc., Wayne, NJ, USA) for all tolerances. This study established a novel method of verification of dose distribution with the same accuracy as film, combining measurement with a general semiconductor array detector and translational movement of the treatment couch. With this approach, specialized high-resolution SRS array detectors and disposable radiochromic film are not needed, making SRS PSQA less costly and manpower-intensive.
