Room: AAPM ePoster Library
Purpose: The purpose of this study is to introduce the novel methods of 3D dosimetry from 2D measurements using phosphor screen for helical tomotherapy.
Methods: The transparent cylindrical phantom was designed with phosphor screen to see the radiation incident in axial 2D planar. The virtual target was planned to be treated by treatment planning system (TPS) of tomotherapy. The cylindrical phantom was placed on the tomotherapy table and irradiated as calculations of the TPS. During the irradiation the table did not move to stick the phantom placing in the center of the gantry. Every frame with time stamp, acquired by CCD camera was reconstructed to 3D and the doses were measured in voxel by voxel. The dose distributions from the fluorescent images were compared with the calculated dose distribution from the TPS.
Results: The dose rate affected to the pixel values rather than the radiation energies. The curve for dose rate versus pixel value was not saturated at the maximum dose rate. The discrepancies between calculation and measurement in the low dose region were larger than high dose region. It seems that the phosphor screen is sensitive for the scattered radiation and we need to improve the linearity correction methods.
Conclusion: The phosphor screen is easy to use and reusable for dosimeter in radiotherapy. The characteristic of the screen is feasible to apply to the therapeutic radiation when it is properly calibrated. The 3D dosimetry using the phosphor screen and the CCD camera is respected to be useful to verify the dose distribution of the tomotherapy.
Funding Support, Disclosures, and Conflict of Interest: This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (NRF-2013R1A1A2012013).