Poster - Thur Eve - 66: A planning comparison between RapidArc and intensity modulated radiotherapy for head and neck cancer.

Volumetric modulated arc therapy (VMAT) has recently been used to improve the dose distribution and efficiency of treatment delivery over the standard intensity-modulated radiotherapy (IMRT) technique. This study compares the dosimetry between RapidArc plan and standard IMRT plan for head and neck cancer. Three head and neck patients treated clinically with sliding window intensity-modulated radiotherapy (IMRT) technique at Grand River Regional Cancer Center were selected randomly and re-planned using RapidArc technique with 6 MV photon beams generated by a Varian 21EX linac with 120-leaf multileaf collimator. Three dose prescriptions were used to deliver 70 Gy, 63 Gy and 58.1 Gy to the regions of the primary tumors, intermediate-risk nodes and low-risk nodal level, respectively, in 35 fractions. Dosimetric comparison based on the dose-volume histogram, target coverage, organ at risk (OAR) dose sparing were studied between the RapidArc plan and IMRT plan. RapidArc technique from Varian Medical Systems showed superior target coverage, better OAR sparing, fewer monitor units per fraction with less treatment time over IMRT technique for head and neck cancers. The average homogeneity index, defined as the difference between the percentage dose covering 5% and 95% of the PTV, is 9.5 for RapidArc plan and 10.5 for IMRT plan. All RapidArc plans met the dose objectives for the primary OAR: spinal cord, brainstem, brain etc. Both parotid mean dose and D50% are lower for RapidArc plan than those of the IMRT plan. The technique is currently being used clinically at our cancer center.