Dose Agreement Analysis of Treatment Planning System-Calculated Doses and Markus Chamber-Measured Doses in the Near-Surface Region for Breast Cancer Patients' Conformal Treatment Plans

BACKGROUND: Surface/skin dose measurement is one of the most challenging tasks for clinical dosimetry in radiotherapy and comparison with almost all the commercially available treatment planning systems (TPSs) brings a significant variation with the measured dose. AIMS AND OBJECTIVES: In the current study, doses calculated from the TPS in the near-surface region for conformal plans (both three-dimensional conformal radiotherapy [3DCRT] and intensity-modulated radiotherapy [IMRT]) of 35 breast cancer patients were evaluated and compared with the doses measured with Markus chamber. MATERIALS AND METHODS: The computed tomography (CT) images of a solid water slab phantom with a Markus chamber (at different depths ranging from 1 mm to 5 mm from the surface) were taken and imported into the TPS. All the conformal treatment plans made in TPS were executed on a linear accelerator and dose agreements between TPS calculated and chamber measured doses were analysed. RESULTS: Results showed that this TPS underestimated the calculated doses in the superficial region by up to 26% and 21%, respectively, with respect to mean and maximum dose values obtained within the effective volume of the chamber used. CONCLUSION: The uncertainty of doses in the superficial region should be kept in mind when evaluating treatment plans for superficial tumours in TPS.