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

Jihyung Yoon, David Heins, Xiaodong Zhao, Mary Sanders, Rui Zhang

Research output: Contribution to journalArticlepeer-review

13 Scopus citations

Abstract

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 with standard and flattening-filter-free 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 K OBOF and in-beam out-of-field (IBOF) correction factor K IBOF, 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-1 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.

Original languageEnglish
Pages (from-to)9039-9053
Number of pages15
JournalPhysics in medicine and biology
Volume62
Issue number23
DOIs
StatePublished - Nov 13 2017

Keywords

  • flattening-filter-free
  • intensity modulated radiation therapy
  • mixed beam therapy
  • out-of-field dose
  • post-mastectomy radiotherapy
  • tomotherapy
  • volumetric modulated arc therapy

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