Dosimetric evaluation of carcinoma nasopharynx using Volumetric Modulated Arc Therapy (VMAT): An institutional experience from Western India

Abstract— Treatment of nasopharyngeal carcinoma is done by advanced radiotherapy techniques like VMAT (Volumetric Modulated Arc Therapy) where dose to critical organs around tumour is of concern. Present study aimed to describe radiation dose to critical organs in nasopharyngeal cancer patients using VMAT technique. Study was conducted on 10 carcinoma nasopharynx patients treated by VMAT technique at a super-specialty cancer institute in Rajasthan. The structures were contoured using RTOG (Radiation Therapy Oncology Group) guidelines and dose prescription to PTV (Planning Target Volume) was such that 95% iso-dose covered 100% of PTV. Constraints to the OARs (Organs at risk) were as per QUANTEC (Quantitative Analysis of Normal Tissue Effects in the Clinic). VMAT planning was done by double arc using Eclipse (v 10.0.42) treatment planning system. Mean dose to brain stem, spinal cord and optic chiasma were 51.79 Gy, 45.92 Gy and 18.8 Gy respectively. Mean dose to left and right temporal lobes was 22.7Gy and 24.3Gy. Dose to right and left eye were 20.6 Gy and 19.2 Gy while dose to right and left lenses were 5.9Gy and 5.8 Gy respectively. Dose to brain stem, spinal cord, optic chiasma, eyes, lens and temporal lobes were below the dose constraints. VMAT is an effective way to deliver maximum radiation to tumour tissue while providing better sparing of normal tissue and less doses to OARs in carcinoma nasopharynx.