Exhibit Hall | Forum 5
Purpose: To verify the relative range-shifts of therapeutic proton beam by measuring prompt gamma (PG) distribution in spot scanning proton therapy.
Methods: Gamma electron vertex imaging (GEVI) system which consists of an electron converter, two hodoscopes, and a calorimeter was utilized for PG measurement. In GEVI, PGs Compton-scatter in the electron converter and the Compton-recoiled electrons are traced by the hodoscopes and the calorimeter. Spot scanning proton beams, extracted from 230-MeV cyclotron, were irradiated into a homogeneous slab phantom and an anthropomorphic head phantom, respectively. The treatment plans of 100 cGy/field were established and one of fields in each plan were monitored. The proton beam range was shifted by blocking the exit of beam nozzle with range-shifting plates and by moving the phantom, respectively. The range-shift was introduced in global and local regions, and its magnitude was varied from 1 mm to 10 mm. The measured PG profiles were analyzed by the 99% confidence intervals and the statistical hypothesis tests, each being used to evaluate range-shift detection accuracy and sensitivity, respectively.
Results: The results of confidence intervals showed that the measured range-shifts accurately indicate the true shift values. The overall accuracy was 0.70 mm for all investigated range-shift scenarios. The results of one-sample t-tests confirmed that all the range-shifts were significantly different from zero, which means that the GEVI system can sensitively detect the range-shift up to 1 mm. Furthermore, the results of ANOVAs proved that most of the different range-shifts can be clearly distinguishable from each other.
Conclusion: In the present study, the performance of the GEVI system to detect the proton range-shifts was evaluated. Our results showed a remarkable performance, showing high range-shift detection accuracy and sensitivity.
Funding Support, Disclosures, and Conflict of Interest: This research was supported by the National Cancer Center Grants (NCC-2110390-2), Korea.