Planning and Dosimetry Study of Dynamic Intensity-Modulated Radiotherapy and Volumetric-Modulated Arc Therapy for Carcinomas of the Pharynx Using 6MV Flattening Filter and Flattening Filter-free Beams.

Abstract

Objective: This study aims to methodically explore and evaluate the effectiveness of volumetric-modulated arc therapy (VMAT) and intensity modulated radiotherapy (IMRT) with both flattened and unflattened 6MV beams for treating pharyngeal carcinomas.

Materials and methods: Twenty patients who had previously undergone treatment for advanced pharyngeal cancer were randomly chosen. They were replanned using a fixed nine-field dynamic IMRT and VMAT with RapidArc using both 6MV flattened and unflattened beams. A total of 80 similar treatment plans were generated for the TrueBeam SVC setup. These plans were assessed for target coverage, maximum and mean doses to the organs at risk, monitor unit (MU), beam-on time, dose to healthy tissue, and other indicators of dose quality.

Results: Target coverage was nearly identical across all the techniques. VMAT (6FF and 6FFF) achieved equivalent or superior target coverage while plans give better sparing of mean doses of parotid glands, esophagus, larynx, and maximum dose of the spinal cord while maintaining equivalent maximum dose of the brainstem. The MUs required for VMAT plans were about 4-5 times less than that of IMRT plans, additionally, the 6MV plan shows 20%-30% lesser MU than 6FFF plans in both techniques.

Conclusions: VMAT-6FFF shows fewer hot spots in the planning target volume (PTV) high-risk volume and equivalent or higher hot spots in the PTV intermediate-risk and PTV low-risk volumes. In terms of treatment time, VMAT 6FF has fewer MUs than VMAT 6 FFF. Hence, it shows that VMAT 6FF has less treatment time.