Comparative study of different radiation therapy techniques in large volume head and neck tumors

Abstract

The most used methods for head and neck cancer treatment are surgery, chemotherapy and radiotherapy. The radiation therapy aims to deliver a prescribed dose to target volumes, to kill the tumour cells, with a good protection of organs at risk OAR. More than half of all patients assessed to receive radiotherapy during their treatment. Radical radiation therapy is indicated either in the primary treatment of head and neck cancer with concurrent chemotherapy for locally advanced disease or in the postoperative setting with or without concurrent chemotherapy. Radiation therapy for advanced head and neck cancer has developed from the three dimensional conformal radiotherapy 3DCRT to intensity modulated radiation therapy IMRT and Volumetric modulated arc therapy VMAT. The aim of present work is to compare treatment planning for a large volume head and neck cancer patients using IMRT and VMAT techniques to evaluate and find out optimal technique for treating large volume head and neck tumor. Eleven patients with advanced head and neck tumors that previously treated were selected for the planning study. The patients are planned using the two different techniques (IMRT and VMAT) and optimized to evaluate highly conformal target coverage and sparing OAR. Standard fractionation is 33 fractions with 5 fractions weekly, the prescribed doses70Gy, 59.4Gy and 54Gy for the high, intermediate and low risk targets by simultaneous integrated boost. Evaluation of plan was depend on target dose coverage, homogeneity, conformity and gradient, dose statistics of the OARs, total monitor units and the remaining volume at risk RVR. The study showed that the two techniques are equal for target dose conformity index (0.94), and comparable in homogeneity index (0.91,0.93) for VMAT and IMRT respectively, while VMAT is more superior clearly in CN and GI (0.76, 44) than (0.68, 55) for IMRT. Furthermore VMAT has an advantage over IMRT in the most of OAR For the total monitor unit, IMRT is considered as a second choice, which gives more than three times monitor units for VMAT. However for low dose effect RVR, VMAT has the upper hand, that the average volume of RVR that received 15Gy, 10Gy and 5Gy are (4327, 5281 and 6703cc) and 1019cGy mean dose in VMAT techniques, while in IMRT are (4435, 5311 and 6543cc) and 1051cGy mean dose. Finally Results of the dosimetric comparison between both techniques showed that VMAT had a priority than IMRT in a lot of comparison points especially the time on the machine, that make VMAT is the first choice in the treatment plan selection.