Room: ePoster Forums
Purpose: The total dose distribution of the proton pencil beam scanning (PBS) is constructed by individually delivered Bragg peaks and its uniformity depends directly on the accuracy of the delivery (i.e., the beam energy and the spot location). This study suggests a novel approach that allows us to directly confirm in the layer-by-layer energy delivered for patient-specific QA. The acrylic-disk radiation sensor (ADRS) of 20-layers was constructed and its dosimetric properties were performed to evaluate the suitability of the new QA system. We compared the measured range using the multilayer ADRS to those calculated by the treatment planning system (TPS) for each scan layer.
Methods: The measurements were obtained from a clinical proton pencil beams. The multilayer ADRS is a series of transmitter disk with 150 mm diameter surrounded by thin optical fiber. This disk is an ultraviolet-transparent methyl methacrylate polymer and shows water equivalency. It is now improved the efficiency of the measurement by arranging the ADRS of 20-layers and fabricating black plastic cases that allow for flexibility in placement of the solid slabs phantom, including in the extra room. It is also designed with a 1 mm thick disk to obtain the high spatial resolution. We investigated the feasibility of the multilayer ADRS to verify the layer-by-layer energy along the scan path for patients treated with PBS in three different sites (prostate, head & neck, and lung).
Results: To evaluate the patient-specific energy, the calculated range by TPS and results measured by multilayer ADRS showed significant differences in the energy of each layer depending on the treatment site. Therefore, the patient-specific energy calculated by the TPS must be compared and verified by the measured value prior to treatment.
Conclusion: In this study, we believe that the multilayer ADRS has considerable potential to verify the energy for PBS.