English

Abstract

BACKGROUND Intensity modulated radiation therapy (IMRT) has become the standard treatment in head & neck cancer (HNC). Anatomic changes during IMRT can have impact on dose coverage and organs at risk (OAR) doses. These changes can be compensated by modifying the plan during treatment. The purpose of this study is to evaluate the impact of anatomical variations during IMRT on target volumes, OAR and dose volume histogram (DVH) in locally advanced HNC patients. METHODS Twenty-four HNC patients undergoing definitive chemoradiotherapy were planned with initial plan. Repeated computerised tomography (CT) scans were performed at 2nd week (repeat CT1) and 4th week (repeat CT2). Previous plan was transferred to new CT for dosimetric analysis. Patient received remaining fractions with adaptive plan if needed based on triggers (1. more than 5 % deviation in OAR doses 2. If PTV dose did not conform to ICRU83). Plan 1 was generated by replanning on repeat CT and plan 2 was by superimposition of previous plan. DVH of both plans were compared for volumetric and dosimetric parameters in patients who required re-planning. RESULTS Fifty-eight percent of patients required adaptive plan. Seventy-one percent required re-plan at the end of 4th week and 28.5 % at 2nd week. Parotid glands and gross tumour volume (GTV) node reduction were significant in patients who required re-plan compared to patients who did not require re-plan. Patients with significant GTV node reduction experienced grade III/IV mucositis. Patients with significant GTV node and parotid glands reduction experienced grade III/IV dermatitis. CONCLUSIONS More than half of HNC patients required re-planning. Most of them required replanning at 4th week. GTV node and parotid glands reduction can predict the requirement of re-plan, risk of grade III/IV dermatitis. GTV node reduction can predict the risk of grade III/IV mucositis. KEYWORDS IMRT, Adaptive Radiotherapy, Anatomical Variations in Head and Neck Cancer, Implementation of Adaptive Plan