Physical and Radiobiological Evaluation of Accelerated Intensity Modulated Radiotherapy for Locally Advanced Head and Neck Cancer and Comparison with Short-Term Clinical Outcomes

Abstract

Objective: The present study aims to evaluate the accelerated intensity modulated radiotherapy (IMRT) of head<br />and neck (HandN) treatments using physical indices and radiobiological models with its clinical correlation using<br />histogram analysis in radiation therapy (HART). The radiobiological evaluation in terms of tumor control probability<br />(TCP) and normal tissue complication probability (NTCP) indices were compared with acute toxicity. Materials and<br />Methods: A total of twenty patients with stage III and IV of HandN cases treated with accelerated IMRT using 6MV<br />photons were chosen for the study. Using HART software, physical indices of the IMRT plans have been defined by<br />universal plan indices (UPI's) which summarize the various recognized plan indices. The overall quality factor (QF)<br />of a plan was determined by a linear combination of all indices in UPI set. The clinical outcomes in terms of the acute<br />toxicity like dysphagia and xerostomia were compared with NTCP values of the OAR calculated from HART software.<br />Results: The mean QF and the mean Poisson TCP index was found to be 0.993±0.02 and 0.86 ±0.02 respectively. The<br />mean JT Lyman NTCP index for bilateral parotid, constrictors, and larynx were found to be 0.23±0.14, 0.30±0.17 and<br />0.22±0.15 respectively. The acute toxicities in terms of severity of xerostomia and dysphagia have shown a moderate<br />correlation with NTCP values of bilateral parotids, constrictors, and larynx, respectively. Conclusion: The mean<br />QF based on UPI was found to be close to unity, which correlates with being a better IMRT plan. The present study<br />suggested the existence of a moderate correlation between the calculated NTCP values and their respective severities<br />of the organ at risk (OAR's). Accelerated IMRT with chemotherapy is a clinically feasible option in the treatment<br />of locally advanced head and neck squamous cell carcinoma (HNSCC) with encouraging initial tumor response and<br />acceptable acute toxicities.