Piermattei A, Azario L, Delle Canne S, Rossi G, Sanità di Toppi G, Palazzoni G, Valentini V, Ausili Cefaro G, Cellini N
Istituto di Fisica, Servizio di Fisica Sanitaria, Università Cattolica S. Cuore (UCSC), Roma.
Radiol Med. 1997 May;93(5):600-6.
The calculated absorbed dose values to the reference point of the breast tangential irradiation, obtained by 2-dimensional (2D) Treatment Planning Systems (TPS), were compared with the measured absorbed dose values obtained with a ionization chamber in an anthropomorphic phantom treated with two opposed photon beams of 60Co, 6 MV and 10 MV. This comparison was aimed at assessing the 2D algorithm dose overestimation due to the effect of missing tissue in the irradiated field. The ratio between the computed dose, Dc, and the measured dose, Dm, reached 1.08 for 60Co beams and 1.04 for X-ray beams of linacs. The Clarkson method gives an adequate correction factor for the calculated absorbed dose value in the reference point. The portal films of some patients were studied to estimate the correction factor for the treatment time or monitor units evaluated by TPS using tomographic breast central plane. The values of the correction factors reached 1.10 for 60Co photon beams and 1.04 for X-ray beams. The measurements were carried out with TLDs positioned in the central plane of the breast, covered by a special bolus, of a second anthropomorphic phantom. The dose homogeneity as well as the accuracy of the relative computed dose values in the breast phantom irradiated with 10 MV X-ray beams were assessed.
将二维（2D）治疗计划系统（TPS）获得的乳腺切线照射参考点的计算吸收剂量值，与在一个用60Co、6MV和10MV的两个对置光子束治疗的人体模型中，使用电离室获得的测量吸收剂量值进行比较。该比较旨在评估由于照射野中组织缺失效应导致的二维算法剂量高估情况。对于60Co束，计算剂量Dc与测量剂量Dm的比值达到1.08，对于直线加速器的X射线束则为1.04。克拉克森方法为参考点处计算的吸收剂量值提供了一个合适的校正因子。研究了一些患者的射野片，以估计通过断层乳腺中心平面由TPS评估的治疗时间或监测单位的校正因子。对于60Co光子束，校正因子的值达到1.10，对于X射线束则为1.04。测量是在第二个人体模型的乳腺中心平面内放置热释光剂量计进行的，该平面由特殊的填充材料覆盖。评估了用10MV X射线束照射的乳腺模型中的剂量均匀性以及相对计算剂量值的准确性。
