Room: Track 3
Purpose: While proton therapy is rapidly becoming a routine radiotherapy modality, its biggest advantage, the Bragg peak, is also a major disadvantage: Delivering the Bragg peak to the tumour, while maximizing tumour control and minimizing damage to healthy bystander tissue, makes it impossible to directly verifying the conformity of the proton beam with the tumour during treatment. While some methods allow to measure the range of the protons indirectly, e.g. PET, prompt gamma emission, they are often time consuming and rely on comparing the results with a Monte-Carlo simulation or calibration. We established a novel technique that measures the range of the proton beam directly.
Methods: During proton therapy, secondary particles are produced, some of which are gamma-rays. Most gamma-ray radiation is promptly emitted by tissue. However, if a carefully chosen metal hadron-tumour-marker (HTM) is administered close to the tumor, some protons will undergo nuclear reactions with the marker to produce beta-delayed characteristic gamma-rays via different reaction channels. As these channels are chosen to have different energy dependencies, the ratio of the different channels as measured in a gamma energy spectrum is a direct measure of the proton energy at the HTM. The subsequent conversion to range is very precise due to the proximity of the HTM to the Bragg peak.
Results: The method has been demonstrated with LaBr detectors at the proton therapy facility at TRIUMF to yield a range-verification uncertainty as low as 0.5 mm. A repeat of the experiment with HPGe detectors with superior energy resolution was carried out, which will give even smaller range uncertainties. Data analysis is currently underway.
Conclusion: Using our sub-millimeter range-verification technique, we have successfully measured delayed gamma radiation from various HTMs. This technique is a promising new method to significantly reduce uncertainties in proton therapy and thus increase the therapeutic index.
Funding Support, Disclosures, and Conflict of Interest: We acknowledge the support of the CIHR, NSERC and SSHRC (under Award No. NFRFE-2018-00691). TRIUMF receives federal funding via a contribution agreement with the National Research Council of Canada.