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

Rekha Reddy Buchapudi,Ganesh Narayanasamy,Varatharaj Chandraraj,Anil Kumar M R,Ravikumar Manickam,Tanvir Pasha C R,Anil Pyakuryal

doi:10.31557/apjcp.2019.20.8.2463

Abstract

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

Highlights

The main objective of the radiotherapy delivery is to give the maximum dose to the tumor cells and the minimum possible dose to the organ at risk (OAR)
The present study suggested the existence of a moderate correlation between the calculated normal tissue complication probability (NTCP) values and their respective severities of the organ at risk (OAR’s)
The dose distributions of intensity modulated radiotherapy (IMRT) plans are much Heterogeneous when compared to 3D conformal radiation therapy (3DCRT), which leads to a challenging process, in particular, to head and neck (HandN) cancer treatment

Summary

Introduction

The main objective of the radiotherapy delivery is to give the maximum dose to the tumor cells and the minimum possible dose to the organ at risk (OAR). The advancement in imaging and modern, sophisticated techniques have increased the complexity of treatment planning while achieving the above objectives It leads to results in maximum dose to the tumor and dose reduction to the normal structures surrounding the target (Kataria et al, 2012). A more practical approach of analyzing radiotherapy plans is to utilize the UPI set and the overall quality factor (QF) of the treatment as discussed in the literature (Pyakuryal et al, 2010) The biological models such as tumor control probability (TCP) based on the Poisson statistics model and normal tissue complication probability (NTCP) based on the Lyman-Kutcher-Burman model, were efficient to estimate the radiobiological outcomes of the treatments by taking into account of the dose-volume effects in the organs.

Materials and Methods

Results

Discussion