SU-E-T-301: Evaluation of Simultaneously Integrated Boost (SIB) and Sequential IMRT Boost (SqIB) Treatments of Head and Neck Cancer Using Empirical Radiobiological Modeling

Purpose: To evaluate and compare normal tissue complication probabilities (NTCP) in SIB (simultaneous integrated boost) and SqIB (sequential IMRT boost) IMRT methods in head and neck cancer using the radiobiological modeling of HART program (Histogram Analysis in Radiation Therapy; J Appl Clin Med Phys 11(1): 3013, 2010). Methods: Of the 40 SIB IMRT cases identified in a 2‐year follow up study, 14 SIB (Rx range: 66–70Gy) cases that developed dysphagia(N=11) or xerostomia(N=10) or both types of complications(N=9) were studied. Similarly 10 SqIB cases (Rx=73.5Gy) was studied previously. The TCP and NTCPs were calculated from the dose‐volume histogram (DVH) statistics using the Poisson Statistics (PS) and JT Lyman models respectively. Values for the volume parameter (n), slope parameter (m), tumor control dose (TCD=63.8Gy) and tolerance dose (TD50,5 = 46 and 47 Gy for bilateral parotids and esophagus, respectively) were selected from Luxton et al. (Phys. Med. Biol. 53, 23–36, 2008). Results: In the SIB method (N=14; Student's t‐test), TCP of tumor was estimated to be 0.78±0.02; while NTCP for parotids and esophagus were 0.16±0.10, and 0.20±0.06 respectively. The corresponding numbers in the SqIB method (N=10) were 0.83±0.02; 0.45±0.14 and 0.17±0.09 respectively. Conclusion: In a 2‐year follow up study with SIB treatments, the estimated values of NTCP of esophagus correlated with the severity of dysphagia. In addition, the hot spots were also reduced and better parotid sparing was found in SIB method than in SqIB method which may partially be related to smaller prescription doses. However JT Lyman model provided better correlation between severity of xerostomia and NTCP of parotids; and PS models for tumor progression free survivability in SqIB treatments. These findings are not in direct comparison due to the differences in tumors and stages. This novel methodology of radiobiological outcome‐related analysis can be utilized to evaluate different treatment plan techniques.