SU‐E‐T‐449: Optimization and Evaluation: IMRT of Sinoâ,<nasal Carcinoma in Reference to ICRU 83

Abstract

Purpose:Estimating the potential radiobiological advantage using the sub‐volume concept (ICRU 83)in plan optimization and evaluation of IMRT for sino‐nasal carcinoma.Methods:Ten patients planned with IMRT were selected retrospectively. Two plans were generated for each patient with 7 coplanar field arrangements. The PTV was prescribed 60Gy/30# with an unedited expansion from CTV (CC=5mm, ML=4mm and AP=4mm) and the in‐air PTV filled with a virtual bolus 1cm thick. Proximity structures were defined as per the guidelines. Plan1 was optimized and evaluated based on ICRU 50/62, whereas plan2 was based incorporating the ICRU 83 approach. The dosimetric parameters, including CI, HI, MU were compared and radiobiological metrics estimated using the Biosuite software (NTCP‐LKB model & EUD). The paired T‐test was used to assess the statistical significance of differences of similar parameters between the plans.Results:The mean±sd of PTV was 230.21±88.13cc, where as the sub‐volume PTV was 3.09±1.47cc. PTV dosimetric parameters i.e., D2%, D98%, D95%, D50%, etc., CI and HI were similar for both plans, but OAR and PRV showed reduction in D2%, Dmax, Dmean for plan2 compared with plan1. D2% of optic chiasm 53.66±0.90 vs. 52.47±0.89, p = 0.004; left optic nerve 54.91±1.54 vs. 53.67±1.56, p = 0.001; left retina 54.00±1.34 vs. 51.82±2.52, p = 0.005 for plan1 and plan2 respectively while Dmax, Dmean for other OARs and PRVs demonstrated a similar trend. NTCP for optic chiasm was 7.71±2.86 vs. 5.62±2.24, p = 0.005 without fractionation effect, whereas it was 4.42±2.11 vs. 2.80±1.46, p = 0.006 with fractionation effect for plan1 and plan2 respectively. Similar trend were observed for other OARs and EUDs.7% increase in MU for plan2 was observed.Conclusion:Incorporating the sub volume concept of ICRU 83 in IMRT optimization and evaluation may Resultin reduction of doses to OAR and lower / safer NTCP without compromising TCP.The authors are acknowledging Dr. Julien Uzan and Professor Alan Nahum, Clatterbridge Cancer Centre, Wirral, UK for guidance and sharing the Biosuite software for radiobiological evaluation.