3 years ago

Measurement and modeling of out-of-field doses from various advanced post-mastectomy radiotherapy techniques.

Jihyung Yoon, Rui Zhang, Mary Sanders, Xiaodong Zhao, David Heins
More and more advanced radiotherapy techniques have been adopted for post-mastectomy radiotherapies (PMRT). Patient dose reconstruction is challenging for these advanced techniques because they increase the low out-of-field dose area while the accuracy of out-of-field dose calculations by current commercial treatment planning systems (TPSs) is poor. We aim to measure and model the out-of-field radiation doses from various advanced PMRT techniques. PMRT treatment plans for an anthropomorphic phantom were generated, including volumetric modulated arc therapy (VMAT) with standard and flattening-filter-free (FFF) photon beams, mixed beam therapy, 4-field intensity modulated radiation therapy (IMRT), and Tomotherapy. We measured doses in the phantom where the TPS calculated doses were lower than 5% of the prescription dose using thermoluminescent dosimeters (TLD). The TLD measurements were corrected by two additional energy correction factors, namely out-of-beam out-of-field (OBOF) correction factor KOBOF and in-beam out-of-field (IBOF) correction factor KIBOF, which were determined by separate measurements using an ion chamber and TLD. A simple analytical model was developed to predict out-of-field dose as a function of distance from the field edge for each PMRT technique. The root mean square discrepancies between measured and calculated out-of-field doses were within 0.66 cGy/Gy for all techniques. The IBOF doses were highly scattered and should be evaluated case by case. One can easily combine the measured out-of-field dose here with the in-field dose calculated by the local TPS to reconstruct organ doses for a specific PMRT patient if the same treatment apparatus and technique were used.

Publisher URL: http://doi.org/10.1088/1361-6560/aa94b5

DOI: 10.1088/1361-6560/aa94b5

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