Determination of dose distributions for IMRT and conformal radiotherapy applications in breast cancer cases: A film-based phantom study

Radiotherapy treatment planning for breast cancer is challenging given the large-concave shaped target volume surrounded by lung and heart, breast- lung density differences and respiratory movement. Furthermore, it is difficult to obtain the steep dose gradient between target and organs at risk (OAR) while achieving dose homogeneity in the target volume. This experimental study compares planned and measured dose distributions for 3 dimensional conformal radiotherapy (3DCRT), Field in Field (FinF) and Intensity-Modulated Radiation Therapy (IMRT) techniques for breast cancer radiotherapy in order to investigate if the planned dose was applied precisely. Breast shaped phantom (BSP) was fabricated with bolus material and EBT2 films were placed into sagittal and transverse planes which intersect with the isocenter. BSP was placed on Alderson rando phantom, then planning computerized tomography (CT) images were obtained, target-normal tissues were delineated on these images. Treatment planning was performed for 3DCRT, FinF and IMRT techniques, followed by the irradiation with films for each calculated plan. Among applied techniques, the maximum and minimum dose differences for measured and calculated doses were 4.5 % and 0.05 % for FinF and IMRT techniques, respectively. Measured doses were higher than calculated doses for 66.6% of all points; however 93% of total points had a difference less than 3 %. Dose differences were minimum on X and Y axes that intersect with the isocenter and were directly correlated with the distance from the isocenter. There was no relation between dose differences and directions on axes. As a conclusion, TPS modeled the dose distributions adequately. However, the best modeling was for the IMRT technique. It could be related to the lung segment on beam path smaller in IMRT when compared to 3DCRT and FinF techniques.