Thomas S D, Mackenzie M, Field G C, Syme A M, Fallone B G
Department of Medical Physics, Cross Cancer Institute, University of Alberta, 11560 University Avenue, Edmonton, Alberta T6G 1Z2, Canada.
Med Phys. 2005 Dec;32(12):3793-800. doi: 10.1118/1.2134929.
We performed two-dimensional treatment verifications for ten patients planned and treated with helical tomotherapy. The treatment verification consisted of a film measurement as well as point dose measurements made with an ion chamber. The agreement between the calculated and the measured film dose distributions was evaluated with the gamma index calculated for three sets of criteria (2 mm and 2%, 4 mm and 3%, and 3 mm and 5%) as recommended in the literature. Good agreement was found between measured and calculated distributions without any need of normalization of the dose data but with dose map registration using reference marks. In this case, 69.8 +/- 17.2%, 92.6 +/- 9.0%, and 93.4 +/- 8.5% passed the 2 mm and 2%, 4 mm and 3%, and 3 mm and 5% criteria, respectively. Agreement was excellent when both normalization and manual registration of the dose maps was employed. In this case 91.2 +/- 5.6%, 99.0 +/- 1.4%, and 99.5 +/- 0.8% passed the 2 mm and 2%, 4 mm and 3%, and 3 mm and 5% criteria, respectively. The mean percent discrepancy for the point dose measurements was -0.5 +/- 1.1%, -2.4 +/- 3.7%, -1.1 +/- 7.3% for the high dose, low dose, and critical structure point, respectively. Three criteria for a satisfactory treatment verification in the high dose regions of a plan were established. For the un-normalized reference mark registered data 80% of pixels must pass the 3 mm and 5% criteria. For the normalized and manually registered data, 80% must pass the 2 mm and 2% criteria, and the point dose measurement must be within 2% of the calculated dose. All low dose region/critical structure point dose measurements were evaluated on a patient by patient basis. The criteria we recommend can be useful for the routine evaluation of treatment plans for tomotherapy systems.
我们对10例采用螺旋断层放射治疗计划并接受治疗的患者进行了二维治疗验证。治疗验证包括胶片测量以及用离子室进行的点剂量测量。根据文献推荐，针对三组标准（2毫米和2%、4毫米和3%、3毫米和5%）计算伽马指数，评估计算所得与测量所得胶片剂量分布之间的一致性。测量分布与计算分布之间发现了良好的一致性，无需对剂量数据进行归一化处理，但需使用参考标记进行剂量图配准。在这种情况下，分别有69.8±17.2%、92.6±9.0%和93.4±8.5%通过了2毫米和2%、4毫米和3%、3毫米和5%的标准。当采用剂量图的归一化和手动配准两者时，一致性极佳。在这种情况下，分别有91.2±5.6%、99.0±1.4%和99.5±0.8%通过了2毫米和2%、4毫米和3%、3毫米和5%的标准。高剂量、低剂量和关键结构点的点剂量测量的平均百分比差异分别为-0.5±1.1%、-2.4±3.7%、-1.1±7.3%。制定了计划高剂量区域中令人满意的治疗验证的三项标准。对于未归一化的参考标记配准数据，80%的像素必须通过3毫米和5%的标准。对于归一化和手动配准的数据，80%必须通过2毫米和2%的标准，并且点剂量测量必须在计算剂量的2%以内。所有低剂量区域/关键结构点剂量测量均逐例患者进行评估。我们推荐的标准可用于断层放射治疗系统治疗计划的常规评估。
