SU‐E‐J‐158: Experimental Investigation of Proton Radiography Based On Time‐Resolved Dose Measurements

Purpose: To use proton radiography for i) in‐vivo range verification of the brain fields of medulloblastoma patients in order to reduce the exit dose to the cranial skin and thus the risk of permanent alopecia; ii) for performing patient specific optimization of the calibration from CT‐Hounsfield units to proton relative stopping power in order to minimize uncertainties of proton rang Methods: We developed and tested a prototype proton radiography system based on a single‐plane scintillation screen coupled with a fast CCD camera (1ms sampling rate, 0.29×0.29 mm 2 pixel size, 30×30 cm 2 field of view). The method is based on the principle that, for passively scattered beams, the radiological depth of any point in the plateau of a spread‐out Bragg‐Peak (SOBP) can be inferred from the time‐pattern of the dose rate measurements. We performed detector characterization measurements using complex‐shape homogeneous phantoms and an Alderson phanto Results: Detector characterization tests confirmed the robustness of the technique. The results of the phantom measurements are encouraging in terms of achievable accuracy of the water equivalent thickness. A technique to minimize the degradation of spatial resolution due to multiple Coulomb scattering is discussed. Our novel radiographic technique is rapid (100 ms) and simultaneous over the whole field. The dose required to produce one radiograph, with the current settings, is ∼3 cG Conclusion: The results obtained with this simple and innovative radiography method are promising and motivate further development of technique. The system requires only a single‐plane 2D dosimeter and it uses the clinical beam for a fraction of second with low dose to the patient