ESTRO 2024 - Abstract Book

S3253

Physics - Detectors, dose measurement and phantoms

ESTRO 2024

a part of the SINFONIA project on the risk appraisal for detrimental effects of radiation exposure during the management of cancer patients.

Results:

The results indicate that out-of-field doses depend on the distance from the isocenter for both forms of treatment. When considering out-of-field proton, photon and neutron equivalent doses, it becomes evident that near the target, the proton equivalent doses are higher than neutron equivalent dose. It is worth noting that in proton beam therapy the secondary photons are considered negligible due to their minimal values. For the proton plans, the comparison of the out-of-field total equivalent dose (proton + neutron components) shows that out-of-field neutron doses are lower than the proton doses in organs close to the target. For organs farther away, the neutron equivalent doses dominate the total organ dose, but the absolute values are low. The range of the out of-field doses in selected organs for both VMAT and proton plan is presented in Table 1. The results show that the maximum total out-of-field doses in proton therapy are 87 mSv/Gy(RBE), 73 mSv/Gy(RBE), 31 mSv/Gy(RBE), and 26 mSv/Gy(RBE) in the lungs, thyroid, spinal cord, and esophagus, respectively, whereas, for the same organs, the maximum out-of-field values from VMAT are 430 mSv/Gy, 160 mSv/Gy, 380 mSv/Gy, and 210 mSv/Gy, respectively. The minimum out-of-field doses are for distant organs like the prostate with values of 37 mSv/Gy for VMAT and 0.10 mSv/Gy(RBE) for the proton plan.

Conclusion:

In this study, individual out-of-field organ doses were calculated for cHL VMAT and proton treatments. The findings indicate that VMAT may lead to higher out-of-field doses than proton therapy, even when accounting for the increased effectiveness of secondary neutrons. This indicates that it is necessary to evaluate doses from secondary radiation affecting healthy organs beyond the treatment field edges for a full assessment of the long-term implications from both photon and proton therapy.

Keywords: Secondary dose, photon therapy, proton therapy