Detector Development for Prompt Gamma Imaging in Proton Therapy Online Monitoring

Proton therapy allows for accurate positioning of target tumors by accurate dose delivery at the Bragg peak. But a 10~15 mm proton range deflection could be caused by uncertainties including CT image artifacts and treatment setup errors. Prompt gamma imaging (PGI) offers a reliable real-time monitoring for proton range inside the patient and more accurate spatial information of the Bragg peak. In this work, we report the detector development for a prompt gamma imaging system. A detector based on a 12 × 12 BGO block and an 8 × 8 SiPM array was designed. Since 2~8 MeV high energy of prompt gamma may cause complicated interaction inside scintillation crystal and saturation of SiPMs, positioning performance and response linearity of the detector were evaluated. The proposed detector was tested under high energy sources, such as
²²
Na,
⁸⁸
Y and
²³²
Th. Flood maps at 511 keV and 1.275 MeV of
²²
Na, 898 keV and 1.836 MeV of
⁸⁸
Y and 2.6 MeV of
²³²
Th were generated. Root mean squared (RMS) metric were defined to assess the detector's positioning performance quantitively. Detector response linearity at different energy were evaluated. The detector demonstrates better crystal identification at higher energy. Energy resolution of 36.21% ± 5.16% (511 keV), 28.24% ± 3.86% (898 keV), 20.56% ± 2.46% (1.275 MeV), 17.48% ± 2.63% (1.836 MeV) and 17.08 ± 3.08% (2.6 MeV) were reached respectively. Moreover, mean linearity of peak positions within 144 single crystals was 0.9997 ± 0.00046 which is a clear demonstration of good detector response linearity. The result shows that the detector performed well on positioning, energy resolving and response linearity. Decreased RMS value and energy resolution implies even better positioning performance and energy resolving ability at 2~8 MeV.