A dosimetric comparison of treatment plans by using two different algorithms with VMAT technique for prostate patients

In this study, it was aimed to compare the performance of two different algorithms on the VMAT technique. Twenty patients with prostate cancer were selected for comparison. Tomography images were scanned with a 3mm slices. Target volume PTV and at-risk organs (OAR) as bladder, rectum, right -left femur heads were defined. Doses of target volumes were prescribed as 70 Gy in 35 fractions for all treatment plans. In Varian technique patient plans are prepared using 6 MV energy, AAA algorithm, and double arc VMAT technique with the Eclipse Treatment Planning System (TPS), then in Electa for same patients, treatment plans using 6 mV energy, the Monte Carlo algorithm and VMAT technique are made with the Monaco TPS. Dose distributions were obtained for each patient. These two different algorithms were compared in terms of critical organ dose values, target volume maximum dose values, HI, CI and MU values of PTV. Plans were normalized to cover 95% of the target volume. CI and HI values in Varian Rapidarc are 1.01±0.02 (1), 0.08±0,01 (0.08), respectively. For Elekta-VMAT CI and HI values are 0.96±0.02 (0,95) and 0.1±0.02 (0.09), respectively. Consequently RapidArc gave better result for CI and HI values. The monitor unit value of RapidArc 761,35 ± 94,29 was observed to be lower than that of Elekta-VMAT monitor unit 922,15 ± 93,4. In terms of bladder and rectum doses Elekta-VMAT technique give lower results than results of RapidArc technique. There was no significiant difference (p>0.05) in the calculation of PTV Dmax and bladder 50% for each machine. When the critical organ doses were considered, the Elekta-VMAT technique has statistically significant lower values for bladder and rectum doses than those values of the RapidArc technique. For right and left femurs, the RapidArc technique showes better results. RapidArc MU values are lower than MU values of Elekta-VMAT, so treatment duration was shorter in RapidArc. Clinically both VMAT-techniques for each machine were equally effective in producing acceptable plans. As a result it can be said that these two techniques produce equivalent results by practice