Evaluation of Surface Dose for Intensity Modulated Radiotherapy of Head and Neck Cancer Using Thermoluminescent Dosimeters

Abstract

Accurate estimation of the surface dose in radiotherapy of patients with head and neck cancer is very important in terms of treatment. The aim of this study is to evaluate the surface dose for intensity-modulated radiotherapy (IMRT) of head and neck cancer using thermoluminescent dosimeters (TLDs). In addition, it is aimed to examine the surface dose estimates of the treatment planning system (TPS) for different grid sizes. Before the computed tomography (CT) images were taken for 15 head and neck cancer patients, 5 different points determined in the neck region were marked in a way that would not cause artifacts. IMRT plans are created for 1.5 and 2.5 mm grid sizes. Surface doses were obtained for TPS calculations and TLD measurements at 5 different points in the neck region. Surface doses obtained from TLD measurements and TPS calculations with different grid sizes were compared. All patients received 3-stage adaptive radiotherapy (ART) and the surface dose comparison was repeated for each plan. According to plan 0, the height of TLD measurements for the 1.5 and 2.5 mm grid size were 4.06% and 7.87%, respectively. In Plan 1, the difference between TPS and TLD doses was 4.00% and 8.15% for grid size 1.5mm and 2.5mm, respectively (p=0.00 and p=0.00). For dose measurements from Plan 2, the difference between TPS and TLD doses was 4.07% and 9.96% for grid size 1.5mm and 2.5mm, respectively (p=0.00 and p=0.00). Surface doses obtained in TLD measurements for all treatment plans were higher than in TPS dose calculations. Accurate estimation of the surface dose in head and neck cancer radiotherapy is very important for treatment. Surface doses calculated with TPS are usually lower than the prescribed dose. Therefore, during the evaluation of radiotherapy plans, it should be considered that TPS underestimates the surface dose. This ratio can be determined by dosimetric measurements. Thermoluminescent dosimeters are suitable equipment for this process.