Author: Wen C. Hsi, Kayla Schneider 👨🔬
Affiliation: Department of Radiation Oncology, University of Arkansas for Medical Sciences (UAMS), Department of Radiation Oncology, University of Arkansas for Medical Sciences 🌍
Purpose:
Measurement-based patient-specific quality-assurance (PSQA) conducted with a 2D dosimeter to verify delivered dose of each field over 3 measurement-depths is time-consuming with limited sensitivity for detecting errors of delivered spot-locations. Incorporating commercial independent dose calculation (IDC), which utilizes the planned spot patterns of all fields, enables IDC-based patient-specific QA (PSQA) to efficiently and sensitively verify 3D dose delivery within the patient’s geometry. We evaluated myQAiON_PT for Monte-Carlo-based IDC and delivery-logfile of each field after the implementation and commissioning for IDC-based PSQA.
Methods:
The reconstructed 3D dose-distributions of the IDC of each patient and logfile of each field were compared with corresponding planned dose-distribution. This study included 25 out of 260 patients acquired in myQAiON_PT, with five patients selected per site (brain, head-and-neck, breast, lung, and abdomen.) Gamma comparisons were performed for 2D measurement-based or 3D IDC-based PSQA with 3mm-3% criteria. We used failing cases with passing rate of Gamma-index < 95% to investigate the root-cause of failure.
Results:
2D Gamma-index passing-rate exceeded 99% for measurement-based PSQA on all sites while 3D Gamma-index passing-rate exceeded 95% for all IDC-based PSQA except one failed lung-case with a passing-rate of 90.5%. Lung and breast sites had lower passing-rates than other sites, with lung having the highest variability. The root cause of the failure was strongly related to differences in the assignment of proton-relative-stopping power (PRSP) from CT-HU in Monte-Carlo dose-engines used for planning and myQAiON_PT system, while no significant error was observed spot position on this lung-case.
Conclusion:
MyQAiON_PT provides effective and accurate IDC-based PSQA for all 5 sites. With acquired 260 data of patients treated in our first-year operation, we will further analyze an additional 30 failing-cases for the root-causes of various failure modes, including the resolution for known root-cause of lung failing-case.