Hyde D, Teke T, Mestrovic A, Gete E, Schmid M
British Columbia Cancer Agency- Centre for Southern Interior, Kelowna, BC, Canada.
British Columbia Cancer Agency-Vancouver Center, Vancouver, BC, Canada.
Med Phys. 2012 Jul;39(7Part2):4620. doi: 10.1118/1.4740090.
Stereotactic Body Radiation Therapy (SBRT) requires the delivery of a high biologically effective dose in only a few fractions. These large doses per fraction can necessitate long treatment times. The Varian Truebeam is capable of RapidArc delivery and also has the optional Flattening Filter Free (FFF) modes which greatly increase the dose rate. We have commissioned the 6MV FFF beam (1400 MU/min) for RapidArc lung SBRT, and verified heterogeneous dose calculations with Monte Carlo (MC).
The standard commissioning data was acquired for Varian's Analytical Anisotropic Algorithm (AAA) beam model. Measurements were acquired with the IBA Blue Phantom, using the CC13 and CC01 ion chambers and PTW diode. MLC-defined fields were also acquired for model verification. The Dosimetric Leaf Gap (DLG) was measured and then optimized using RapidArc lung SBRT plans, matching Eclipse with ion chamber measurements. Heterogeneous dose calculations were independently verified using MC.
There were some discrepancies regarding leaf transmission and penumbra, but the AAA model was generally well within 2% and 2 mm. A nominal DLG value of 1.6 mm was chosen. A representative lung SBRT case utilizing FFF RapidArc was calculated with MC. For the high dose region, 99% matched Eclipse within 3% and 3 mm. The mean dose difference of the PTV was 0.7%.
Although we have observed some minor infield discrepancies between the AAA and Monte Carlo calculations in heterogeneous media, the Eclipse AAA is reasonably accurate for complex FFF, RapidArc, SBRT lung planning.
立体定向体部放射治疗（SBRT）需要在仅几次分割中给予高生物等效剂量。这些每次分割的大剂量可能需要较长的治疗时间。瓦里安Truebeam能够进行容积弧形调强放疗（RapidArc），并且还具有可选的无均整器（FFF）模式，可大大提高剂量率。我们已将6MV FFF束（1400MU/分钟）用于肺部SBRT的RapidArc治疗，并使用蒙特卡罗（MC）方法验证了非均匀剂量计算。
获取了瓦里安分析各向异性算法（AAA）束模型的标准调试数据。使用IBA Blue Phantom，CC13和CC01电离室以及PTW二极管进行测量。还获取了多叶准直器（MLC）定义的射野用于模型验证。测量剂量学叶片间距（DLG），然后使用肺部SBRT的RapidArc计划进行优化，使Eclipse与电离室测量结果匹配。使用MC独立验证非均匀剂量计算。
在叶片透射和半影方面存在一些差异，但AAA模型总体上在2%和2mm以内。选择标称DLG值为1.6mm。使用MC计算了一个利用FFF RapidArc的代表性肺部SBRT病例。对于高剂量区域，99%在3%和3mm范围内与Eclipse匹配。计划靶体积（PTV）的平均剂量差异为0.7%。
尽管我们在非均匀介质中观察到AAA与蒙特卡罗计算之间存在一些较小的野内差异，但Eclipse AAA对于复杂的FFF、RapidArc肺部SBRT计划而言相当准确。
