The examination of tumor volume and critic organs dose distribution due to lost weight in head and neck cancers using adaptive radiotherapy technique

Radiotherapy is the main treatment modality in head and neck cancer. Technological developments enabled giving maximum radiation dose to tumor while providing maximum protection of normal tissues. As a consequence cure rates increased and side effects decreased. Many head and neck cancer patients have marked anatomic changes during 6-7 weeks of radiotherapy due to tumor shrinkage and weight loss. The purpose of this study is to examine the effects of anatomic changes that have occurred after significant weight loss on dose distribution and to show advantages of adaptive radiation therapy technique. In this study 5 head and neck cancer patients treated with chemoradiotherapy who have more than 10% weight loss have been analysed. Computed tomography images were performed before treatment and after third week. Target volumes and critical organs in CT slices have been determined manually. In treatment planning, 9 field IMRT technique have been performed and target volumes and critical organs doses have been evaluated with dose volume histograms. Adaptive and non-adaptive radiation therapy plannings have been compared dosimetrically. As a result, an average 3.3% and 5% better dose distribution was achived in target volumes with adaptive radiation therapy. Furthermore in critical organs significant reduction in maximum and mean doses were obtained. Maxiumum dose reduction in spinal cord and brain stem occurred as 10.9% and 10.4% respectively. Right and left cochlea mean doses decreased as 12.4% and 13.3% respectively; right and left parotis mean doses decreased as 10.3% and 14.4% respectively. According to these results, it has been shown that adaptive radiotherapy is better technique because of better dose distribution and protection of normal organs at risk. Key Words: Adaptive radiotherapy, Head and neck cancer