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In Vivo Emission-Guided Registration of Target Volume and Bragg Peak in Proton Therapy

H Lin1*, K Chuang2 , H Chang3 , T Chao4 , M Jan5 , (1) Medical Physics Research Center, Institute for Radiological Research, Taoyuan, TAO, (2) National Tsing-Hua University, ,,(3) Institute of Nuclear Energy Research, Atomic Energy Council, Taoyuan, ,(4) Chang Gung University, Taoyuan, ,(5) Chang Gung University, Taoyuan,


(Sunday, 7/14/2019)  

Room: ePoster Forums

Purpose: Bragg peak (BP) of a high energy proton beam can be used in radiotherapy to deliver most dose to the target while spare the normal tissues. The BP needs to be accurately monitored as its high dose might be wrongly deposited and causes an overdose in the healthy organs.

Methods: In this study, we propose a technique to verify the registration between the BP location and the target volume prior to therapy. The target volume is located by an emission scan with a pre-injected radionuclide Tc-99m just before proton treatment using a dual mode gamma camera that can switch between the “Prompt gamma(PG)-based� and “SPECT-based� collimator. If the BP and the target volume coincide then there is no setup error and the treatment can be started. A validated GATE Monte Carlo code was employed to simulate the spot-scanning proton therapy. A cylindrical polymethylmethacrylate (PMMA) phantom with a spherical tumor and Zubal phantom with an embedded brain tumor were performed for the study.

Results: The detection ability of the SPECT-based camera was dependent on the tumor size and tumor-to-background (TB) ratio. The TB ratio must be greater than 4 for a tumor to be detected. For those detected tumors, the location errors are within 0.5 mm for the weighted center of tumors. Both the PG-based collimator and SPECT-based collimator can achieve reasonable accuracy and good response to the phantom shift. For Zubal phantom, a linear relationship between the detected shifts of the weighted center of tumors and simulated tumor shifts was presented.

Conclusion: We conclude that the combination of emission scan and PG imaging using a dual mode gamma camera can be used to verify the treatment planning system and to monitor the range in proton therapy. It will play a valuable role in quality assurance of proton therapy.


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