Quality assurance of rapidarc treatments with FFF

Abstract

Introduction With a maximum dose rate of 1400 MU/min X6FFF (Flattening Filter Free) is a major device for the development of hypofractionated stereotactic treatments. But the use of such a dose rate requires specific quality controls. The purpose of this study is to evaluate the feasibility of these controls and the validation of X6FFF RapidArc treatment delivery. Material and methods First of all, simple fields (square, rectangular and MLC) were analyzed. Absolute dose measures at the isocenter were performed with a 0.125 cc ionization chamber and a cylindrical water equivalent phantom. Planar dose distribution at the isocenter was verified with portal imager (aS1000) and EpiQA software (Epidos, Brastislavia). In this case, the analysis was performed using GAI (3%–3 mm) and smoothing detector response to adjust the resolution to the TPS dose calculation (2.5 mm/pixel). Then, 20 patients (10 prostates, 5 livers and 5 lungs), previously treated in X6 RapidArc, were replanned in X6FFF with Eclipse TPS (PRO v10 and AAA v10). They were checked on TrueBeam Novalis linear accelerator using the same devices as for simple fields. Results The variation of the correction factor for recombination between 1400 and 600 MU/min is less than 0.5%. For simple fields, GAI is 95.45%. The difference in absolute dose for 20 RapidArc plans is 1.7 ± 2.51% (mean ± 1 SD). This value is 1.23 ± 1.29% for prostate, 1.95 ± 2.59% for liver, 2.15 ± 3.74% for lung. As regards the comparison of dose distribution the overall GAI is 99.26 ± 0.75% (99.12 ± 0.76% for prostate, 99.27 ± 0.69% for liver et 99.46 ± 0.83% for lung). Conclusion RapidArc treatment delivery in X6FFF is dosimetrically acceptable and comparable to those obtained in X6. With a maximum dose rate of 1400 MU/min X6FFF (Flattening Filter Free) is a major device for the development of hypofractionated stereotactic treatments. But the use of such a dose rate requires specific quality controls. The purpose of this study is to evaluate the feasibility of these controls and the validation of X6FFF RapidArc treatment delivery. First of all, simple fields (square, rectangular and MLC) were analyzed. Absolute dose measures at the isocenter were performed with a 0.125 cc ionization chamber and a cylindrical water equivalent phantom. Planar dose distribution at the isocenter was verified with portal imager (aS1000) and EpiQA software (Epidos, Brastislavia). In this case, the analysis was performed using GAI (3%–3 mm) and smoothing detector response to adjust the resolution to the TPS dose calculation (2.5 mm/pixel). Then, 20 patients (10 prostates, 5 livers and 5 lungs), previously treated in X6 RapidArc, were replanned in X6FFF with Eclipse TPS (PRO v10 and AAA v10). They were checked on TrueBeam Novalis linear accelerator using the same devices as for simple fields. The variation of the correction factor for recombination between 1400 and 600 MU/min is less than 0.5%. For simple fields, GAI is 95.45%. The difference in absolute dose for 20 RapidArc plans is 1.7 ± 2.51% (mean ± 1 SD). This value is 1.23 ± 1.29% for prostate, 1.95 ± 2.59% for liver, 2.15 ± 3.74% for lung. As regards the comparison of dose distribution the overall GAI is 99.26 ± 0.75% (99.12 ± 0.76% for prostate, 99.27 ± 0.69% for liver et 99.46 ± 0.83% for lung). RapidArc treatment delivery in X6FFF is dosimetrically acceptable and comparable to those obtained in X6.