A comparison of 4 rotational techniques for cranial stereotactic radiosurgery according to the position and the target number

Introduction In order to select the best one according to the number and the position of the lesions we compare in this study dynamic conformal arc (DCA), coplanar VMAT (RAC), noncoplanar VMAT (RANC) and entire arc VMAT with table rotations of 10° and 350° (RAT). Material and methods 5 single lesions (case 1), 5 multiple lesions (case 2) and 5 single lesions close to organs at risk (case 3) were analyzed. Each technique was evaluated in regard to conformity and homogeneity indexes for PTV (CI = [[(PTV covered by prescription isodose)tˆ2/(V*PTV*V_(prescription isodose)) and HI=(D_max- D_min)/D_mean), the healthy brain tissue dose (V10Gy), Dmax (OAR) and the number of monitor units (MU). Results For case 1, HI and CI are better for RANC (HI: 0.17 RANC – 0.22 RAT – 0.23 RAC _0.27 DCA and CI: 0.86 RAT – 0.85 RANC _0.83 RAC – 0.76 DCA) but DCA reduces brain tissue V10Gy (11.97 cc DCA – 14.51 cc RANC – 15.9 cc RAT – 18.34 cc RAC) and MU (3092 DCA – 4573 RAC – 4639 RANC – 5250 RAT). In case 2, HI is similar for VMAT (0.17 RANC and RAT – 0.18 RAC – 0.22 DCA) and CI is top with RAT (0.72 RAT – 0.68 RAC – 0.67 RANC – 0.65 DCA). The healthy brain is as well protected with DCA as with RANC (10.5 DCA and RANC – 15.08 RAT – 18.12 RAC) but MU decrease with RANC (4250 RANC – 4802 RAT – 4841 RAC – 7908 DCA). For case 3, RAT improves HI and CI (HI: 0.27 RAT – 0.3 RANC – 0.31 RAC – 0.57DCA and CI: 0.74 RAT – 0.65 RAC – 0.59 RANC _0.5 DCA) and spares brain tissue and OAR (V10Gy: 1.31 RAT – 1.56 RAC – 2 RANC – 2.31 DCA and Dmax (OAR): 12.17 RAT – 12.59 RAC – 12.77 RANC – 14.15 Gy DCA). The MU numbers decrease with DCA (2184 DCA – 3533 RANC – 3714 RAT – 3840 RAC). Conclusion For simple case 1, DCA provide better plan considering low doses to healthy brain. For case 2, RANC is the best compromise ‘‘PTV cover- brain protection”. For case 3, results are significantly better with RAT.