IMRT Planning Using 5, 7 and 9 Radiation Field Directions for Nasopharyngeal Cancer Cases

Abstract

Nasopharyngeal carcinoma (NPC) is one of the deadliest cancers in the world. In treating NPC, Intensity Modulated Radiation Therapy (IMRT) uses radiation fields from several directions to kill cancer cells and shrink tumours. IMRT requires accurate planning using the Treatment Planning System (TPS) to avoid organs at risk (OARs) around the nasopharyngeal cavity. The purpose of this study is to analyse the results of different number of radiation field directions in treatment planning for nasopharyngeal cancer using IMRT. The study focuses on the distribution of dose in the target tumour and organs at risk around the target. The treatment planning parameters are Dose Volume Histogram (DVH), Conformity Index (CI), Homogeneity Index (HI), dose at organs at risk (OARs) and beam on time (BOT). This study used TPS Monaco with the Monte Carlo algorithm and the inverse planning method. Based on DVH, CI, HI and BOT parameters, the results of this study indicate that the most optimal number of radiation field directions to give prescribed doses was 9 radiation field directions. There was no significant difference in the average dose received by OARs in planning with 7 and 9 radiation field directions. In the planning using 5 field directions, some of the OARs received doses above the tolerance limit. While in the planning using 7 and 9 field directions, most of the OARs received doses below the tolerated doses which met the permitted treatment requirements.