Room: AAPM ePoster Library
Purpose: Plastic scintillation detectors (PSDs) have interesting dosimetric properties, including small size and energy independence. These advantages make them well suited for VMAT patient-specific QA, either alone or in conjunction with a detector matrix. This work aims to determine if the HYPERSCINT scintillation dosimetry research platform (Medscint inc., Quebec city, Canada) can replace the classic ion chamber in a clinical patient-specific QA workflow.
Methods: A custom made, 3D-printed detector holder for the Delta4 Phantom+ diode matrix (Scandidos, Uppsala, Sweden) was designed to accustomed both a A1SL ionization chamber (Standard Imaging, Middleton, WI) and a HYPERSCINT PSD probe. A total of 36 prostate plans (without pelvic nodes) and 47 palliative plans were selected for the study. Plans were delivered on the Phantom+ using a VersaHD linear accelerator and measured simultaneously on both detectors. Difference between planned and measured dose (corrected for daily linac output) were computed for both the chamber and the PSD and the results from both detectors were compared for consistency.
Results: Dose difference between the measured and planned dose for the ionization chamber was (0.3±0.2)% (average ±1 standard deviation) for the prostate cases and (0.0±0.5)% for the palliative cases. For the HYPERSCINT these values stand as (0.9±0.3)% for the prostate cases and (0.5±0.7)% for the palliative cases. When comparing pairs of measurements (ion chamber vs PSD), it was found that the PSD overestimated the ion chamber dose by (0.6±0.2)% for the prostates cases and (0.5±0.4) % for the palliative cases.
Conclusion: Albeit a systematic offset of about 0.5% between the ion chamber and the PSD measured doses, the latter detector shows enough accuracy to consider replacing the ion chamber in VMAT patient-specific QAs. The causes underlying this 0.5% offset are currently under investigation.