Verification and Evaluation of Radiation Doses received by organs at risk in (3D-CRT) and IMRT technique for breast cancer

Abstract

External beam radiotherapy can be delivered more precisely by using three Dimensional Conformal Radiotherapy (3D-CRT) technique, which is a traditional method used for whole breast radiotherapy. 3D-CRT includes standard wedged tangents (two opposed wedged tangential photon beams), which is based on three Dimensional images (3D) from a special computed tomography (CT scan). Overseas notification form advent of CT scans and more powerful computers have improved dose calculation algorithms and Multi-leaf Collimators (MLCs). Consequently, 3D-CRT is able to shape the Radiotherapy Beam (RTB) closely to match the target shape and volume. Intensity Modulated Radiation Therapy (IMRT) technique has the ability to improve sparing of normal tissues and treatment results of radiotherapy (RT). RT is a standard adjuvant therapy in conservative treatment of breast cancer (BC). The IMRT technique is used for many treatment sites, allowing for improved normal tissue sparing, more conformal dose distributions and prevention of secondary cancer. The purpose of this study is to verify and evaluate between the outcome of Radiation Treatment Plans (RTP) of left-sided whole breast irradiation of IMRT technique, and 3D-CRT technique to organs at risk (OAR) that are proximal to the target volume during breast radiotherapy. These include left lung, right lung, heart, and spinal cord by different numbers of beam in left sided breast at Zhianawa cancer center (ZCC) - Sulaimany-KR-Iraq. A second aim is to establish a guideline for breast cancer radiotherapy planning at ZCC. Thirteen patients with left-sided, breast carcinoma who had received radiotherapy were selected for this study. The dose prescriptions for the patients were different according to each patient's cancer stage, using 6, 18 MV photons. The clinical target volume [CTV] was contoured as a target volume and the contralateral breast, left lung, right lung, heart, and spinal cord tissues as OAR. The two different planning techniques were analyzed for 13 patients with left-sided breast conserving surgery. Plans were compared on the basis of planning target volume (PTV) dose conformity index (CI), homogeneity index (HI) and the volumes of normal tissues treated based on dose-volume histograms (DVHs). DVHs were calculated for the PTV, heart, left lung, right lung, spinal cord and soft tissue surrounding the breast PTV (VOB) volume. IMRT techniques slightly improved homogeneity ( HI) than 3D (0.16.04 vs. 0.22, p<0.068). However, there was no significant difference between IMRT and 3D-CRT plans regarding CI. No significant difference was noted in CI by 3D and IMRT as both showed similarity, p< 0.190 ); IMRT technique benefited patients more than 3D-CRT by reducing the high-dose (40.05 Gy) volume for the heart. The heart's mean dose was significantly lower in 3D compared to IMRT (3.58 Gy vs. 10.07Gy, respectively; p < 0.0001). Both the mean dose of the left lung and right lung, were significantly lower for 3D compared to IMRT (10.18Gy vs. 14.26Gy and 0.34 vs. 4.17 respectively; p < 0.001), and p< 0.0001. Cord Max. Cord Max dose was significantly lower in 3D compared to IMRT (6.83Gy % vs. 20.89 Gy%, p < 0.0001). IMRT plans improved by increasing low-dose volume (Lift lung, and Spinal cord soft tissue surrounding the breast) compared with 3D-CRT plans (P<0.0001) but with Right lung P<0.575. However, 3D-CRT plans were improved by increasing low-dose volume (heart) compared with IMRT plans (P<0.230)