Lin Teh, Wang Lu, Charlie Ma C-M
Department of Radiation Oncology, Fox Chase Cancer Center, Temple University, Philadelphia, Pennsylvania, USA.
J Med Phys. 2022 Jan-Mar;47(1):99-104. doi: 10.4103/jmp.jmp_123_21. Epub 2022 Mar 31.
To provide accurate and fast 3-D dose verification for hypofractionated stereotactic radiotherapy (SRT/SBRT) of small and multi targets calculated with a Varian Eclipse treatment planning system (TPS) delivered on a Varian accelerator. Ten brain and lung hypofractionated SRT/SBRT linac-based and CyberKnife plans were generated by the Eclipse system for delivery on the accelerator with the Millenium-120 leaf multileaf collimator (MLC) and Multiplan for the CyberKnife machine. These clinical SRT/SBRT plans required accurate quality assurance measurements to obtain absolute point dose and 3-D dose distributions due to the low number of fractions and high fraction doses. For small-field and multi-target plans, the EGS4/MCSIM code was used to calculate the dose distribution. A 0.125 cc ion chamber, a 0.016 cc pin-point chamber and Kodak EDR2 film were used for the measurements and the results were compared with Monte Carlo (MC) calculations. The dosimetry for small-field and multi-target treatment plans is challenging due to the comparable range of secondary electrons and the field sizes defined by SRT/SBRT MLC segments. Our MC simulations can accurately reproduce the linac dose distributions (within 1%/1 mm) three dimensionally. For the clinical SRT/SBRT plans investigated in this work, the MC doses agreed within 3% with ion chamber measurements and within 2%/2 mm with film measurements. The doses calculated by the Eclipse AAA algorithm and Multiplan differed by no more than 5% from MC calculations for small (4-40 cc) Planning Target Volumes (PTVs). MC dose calculation provides accurate and fast 3-D dose verification for hypofractionated SRT for small and multi-target treatment plans generated by a Varian Eclipse TPS on a Varian accelerator and Multiplan treatment planning on the CyberKnife System.
为使用瓦里安加速器上搭载的瓦里安Eclipse治疗计划系统（TPS）计算的小体积和多靶点的大分割立体定向放射治疗（SRT/SBRT）提供准确且快速的三维剂量验证。Eclipse系统生成了十个基于直线加速器和射波刀的脑和肺大分割SRT/SBRT计划，用于在加速器上使用Millenium - 120叶片多叶准直器（MLC）以及射波刀机器的Multiplan进行治疗。由于分次剂量少且单次剂量高，这些临床SRT/SBRT计划需要精确的质量保证测量来获取绝对点剂量和三维剂量分布。对于小射野和多靶点计划，使用EGS4/MCSIM代码计算剂量分布。使用一个0.125 cc的电离室、一个0.016 cc的针点电离室和柯达EDR2胶片进行测量，并将结果与蒙特卡罗（MC）计算结果进行比较。由于二次电子的射程与SRT/SBRT MLC段定义的射野大小相当，小射野和多靶点治疗计划的剂量测定具有挑战性。我们的MC模拟能够在三维空间中准确再现直线加速器剂量分布（在1%/1 mm范围内）。对于本研究中调查的临床SRT/SBRT计划，MC剂量与电离室测量结果的一致性在3%以内，与胶片测量结果的一致性在2%/2 mm以内。对于小体积（4 - 40 cc）的计划靶区（PTV），由Eclipse AAA算法和Multiplan计算的剂量与MC计算结果的差异不超过5%。MC剂量计算为瓦里安Eclipse TPS在瓦里安加速器上生成的小体积和多靶点治疗计划以及射波刀系统上的Multiplan治疗计划的大分割SRT提供了准确且快速的三维剂量验证。
