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Purpose: To evaluate the optimization strategies for midline and peripheral tumours for IMRT and RapidArc treatments using phantom and its clinical validation by comparing with different plans. Methods: Homogeneous phantom was CT scanned and PTV was delineated for two different positions (midline and periphery). Two organs at risk with different shapes (organ at risk 1, organ at risk 2) were created. Planning was done for IMRT and RapidArc with OAR‐1, placed at distance of 0.5cm and 2cm. Also OAR‐2, placed at a distance of 1cm and 2.5cm from the border of PTV along the central axis. The phantom study was clinically verified by comparing different treatment plans. Results: Dose homogeneity was almost similar for tumours in the midline where OARˈs are far. RapidArc plans show superior dose homogeneity, when the target is situated at the periphery and OARˈs are very near to PTV (homogeneity index 2.67 for RapidArc and homogeneity index 4.03 for IMRT). Target coverage was better for all RapidArc plans with maximum conformity index 1.01. The sparing of OAR in terms of the maximum dose was better in RapidArc. A considerable reduction in OAR mean dose (12.37% for OAR‐1 and 10.23% for OAR‐2) was observed with RapidArc technique for peripheral tumors. For healthy tissue no significant changes were observed in terms of the mean dose and integral dose. But RapidArc plans show a reduction in the volume of the healthy tissue irradiation above V10Gy for targets at the periphery and OAR near. Conclusions: Either IMRT or RapidArc can be chosen for tumours in the mid line. Particularly Rapid Arc treatment can be recommended for tumours which are situated at the periphery and organs at risk in close proximity. The clinical validation with different treatment plans well supported the phantom study.

Purpose: To assess the potential of cone beam CT (CBCT) derived adaptive RapidArc treatment for esophageal cancers in reducing the dose to organs at risk (OAR). Methods: Five patients with esophageal cancer were CT scanned in free breathing pattern. The PTV is generated by adding a 3D margin of 1 cm to the CTV as per ICRU 62 recommendations. The double arc RapidArc plan (Clin_RA) was generated for the PTV. Patients were setup using lasers and tattoos and kV‐CBCT scan was acquired daily during first week of therapy, then weekly. Setup errors > 5 mm only were corrected. These images were exported to the Eclipse TPS. The adaptive CTV which includes tumor and involved nodes was delineated in each CBCT image set for the length of PTV. The composite CTV from first week CBCTs was generated using Boolean union operator and 5 mm margin was added circumferentially to generate adaptive PTV (PTV1). Adaptive RapidArc plan (Adap_RA) was generated. NTCP and DVH of the OARs of the two plans were compared. Similarly, PTV2 is generated from weekly CBCTs. PTV2 was evaluated for the coverage of 95% isodose of Adap_RA plan. Results: The PTV1 and PTV2 volumes covered by 95% isodose in adaptive plans were 93.16±1.8% and 94.66±1.45% respectively. The lung V10Gy, V20Gy and mean dose in Adap_RA plan was reduced by 17.36% (p=0.001), 34.86% (p=0.002) and 16.74% (p<0.001) respectively in comparison with Clin_RA. The Adap_RA plan reduces the heart D35% and mean dose by 17.03% (p=0.002) and 17.04% (p=0.002). No significant reduction in spinal cord and liver doses were observed. NTCP for the lung (0.42% vs. 0.08%) and heart (1.41% vs. 0.092%) was reduced significantly in adaptive plans. Conclusions: The adaptive re‐planning strategy based on the first week CBCT dataset significantly reduces the doses and NTCP to OARˈs.