Breast radiation dose estimates compared to measured doses from involved field radiotherapy (IFRT) or mantle fields for early stage Hodgkin lymphoma (ESHL)

Abstract

18503 Background Breast cancer risk after mantle irradiation has prompted concern regarding the use of IFRT for ESHL. As breast cancer risk is radiation dose related, reliable estimates of breast radiation dose from IFRT might aid individual patient risk assessment. However, estimates of breast dose from radiation scatter/leakage beyond the involved field, using standard computer algorithms, are of uncertain accuracy. The aims of this study were to compare computer estimates with measured breast dose, and to compare breast dose from mantle and neck IFRT. Methods A phantom with breast tissue equivalent was used to determine breast dose using computerized treatment planning (CMS XiO), and to perform measurements within the phantom breast tissue using thermoluminescent dosimetry (TLD). These measurements were made for mantle fields and (neck) IFRT. Results Computer estimates and TLD measurements of breast dose in centigray (cGY) are shown for IFRT and mantle treatment, for a prescribed dose of 3000cGy, using 6MV X-rays from a Varian 21eX linear accelerator. Conclusions Breast dose from neck IFRT was lower than from mantle treatment by an order of magnitude, but being well outside the treatment field, was not accurately estimated by our computer algorithm. Work in progress will examine breast dose from mediastinal IFRT and involved node irradiation. Modifications to the planning algorithm may improve accuracy of dose estimates at a distance from the primary field, allowing routine breast dose estimates for patients. Ultimately, utilisation of dose-risk data may allow risk modelling and risk-benefit analysis of IFRT for ESHL in individual patients. [Table: see text] No significant financial relationships to disclose.