SU-E-T-595: A Study of Sequential and Simultaneously Integrated Boost IMRT Methods in Head and Neck Cancer.

PURPOSE The purpose of this study was to obtain the characteristics of the sequential (SqB) and simultaneous integrated boost (SIB) IMRT methods in head and neck cancer using HART (Histogram Analysis in Radiation Therapy) program. METHODS Ten SqB and seventeen SIB IMRT cases were studied retrospectively. A cumulative mean dose of 71.3 Gy was prescribed sequentially, and a mean dose of 66.2 Gy for SIB method. Homogeneity (HI), radiation conformality indices (RCI) and quality factor (QF) were calculated from dose-volume histograms (DVHs). In order to estimate the radiobiological outcomes of NTCP, DVH statistics for the critical and hot spots were utilized with Poisson statistics and JT Lyman models in HART. RESULTS HI, RCI, and QF were 1.11±0.02, 0.97±0.01, 1.00±0.02 in SIB method; and 1.10±0.01, 0.98±0.01, and 0.93±0.03 in SqB method, respectively. Critical spots for parotids, larynx, and esophagus were 0.75±0.03, 0.06±0.02, and 0.34±0.02 in SqB method, and 0.29±0.07, <0.01, and 0.22±0.06 in SIB method, respectively. Hot spots for parotids, larynx, and esophagus were 0.34±0.03, 0.54±0.02, and <0.01, respectively in SqB method whereas 0.10±0.05, <0.01, and 0.05±0.03 in SIB method, respectively. NTCP estimates for parotids, larynx, and esophagus were 0.45±0.14, 0.03±0.01, and 0.17±0.09 in SqB method, and 0.09±0.04, <0.01, and 0.18±0.04 in SIB method, respectively. CONCLUSION For both boost methods mean HIs were comparable while mean RCI was better with SqB than SIB method. QF was significantly better in SIB than in SqB. Critical spots and hot spots were reduced in SIB method. Both SqB and SIB methods yielded similar NTCP for larynx and esophagus. Although better parotid sparing with SIB method than SqB was observed; due to the differences in tumors, stages and doses more patient data and detailed analyses should be followed for comparison. The radiobiological outcome-related analysis using DVHs can be utilized to evaluate different treatment planning techniques.