title: Dosimetric effects of air pocket sizes in MammoSite treatment as accelerated partial breast irradiation for early breast cancer.
abstract: MammoSite Brachytherapy System had been used as one of the Accelerated Partial Breast Irradiation (APBI) techniques since 2002. The clinical results from several clinical institutions had shown comparable treatment efficacy, cosmesis, and toxicity, to other APBI techniques. During MammoSite treatment, air cavities had been one of the primary issues causing treatment cancellation or delay. With the tolerance of the air volume less than 10% of the total Planning Target Volume (PTV) been set, there is still no data available to show the actual dose delivered to the breast tissue with the existence of the air pocket. In this paper, Monte Carlo N-Particle version 5 (MCNP5) was used to model a hypothesis MammoSite phantom with different sizes of air pockets, and compared to the calculation results from the treatment planning system (TPS) without heterogeneous corrections. It was found that without heterogeneous corrections, the difference between the TPS and MCNP5 calculations in the air cavity surface doses and PTV point doses can be up to 2.02% and 3.61%, respectively, with the balloon and air pocket size combinations calculated in this paper. Based on the distance from the point of interest to the balloon surface, an approximate dose can be calculated using the linear relationship found in this study. These equations provide a quick and simple way to predict the actual dose delivered to the breast soft tissue located within the PTV. With the equation applied to the dose from the TPS, the dose error caused by the air pocket during MammoSite treatment can be reduced to the minimum.
authors.affiliation: Department of Radiation Oncology, University of Utah, Salt Lake City, UT 84108, USA. y.jessica.huang@hci.utah.edu
authors.forename: Y Jessica
authors.initials: YJ
authors.lastname: Huang
authors.forename: Melissa
authors.initials: M
authors.lastname: Blough
mesh_terms: D000388:Air; D000465:Algorithms; D001918:Brachytherapy / Q000009:adverse effects / Q000295:instrumentation; D001940:Breast / Q000473:pathology / Q000528:radiation effects*; D001943:Breast Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D055088:Early Detection of Cancer; D005260:Female; D006801:Humans; D008954:Models, Biological; D009010:Monte Carlo Method; D009367:Neoplasm Staging; D019047:Phantoms, Imaging; D011832:Radiation Injuries / Q000517:prevention & control; D011874:Radiometry; D011879:Radiotherapy Dosage