Cilla S, Grimaldi L, D'Onofrio G, Viola P, Craus M, Azario L, Fidanzio A, Stimato G, Di Gesù C, Macchia G, Deodato F, Morganti A G, Piermattei A
U.O. di Fisica Sanitaria, Università Cattolica S. Cuore, Campobasso, Italy.
Phys Med. 2007 Mar;23(1):25-32. doi: 10.1016/j.ejmp.2006.12.001. Epub 2007 Mar 30.
A 2D array (PTW, type 10024), equipped with 729 vented plane parallel ion-chambers, has been calibrated as a detector for the in vivo comparison between measured and predicted portal doses for head-neck tumors. The comparison of absolute portal doses measured to ones predicted by a commercial treatment planning system within the field of view of the CT scanner, can help the delivered dose verification during different treatment fractions, in particular when the patient's present weight loss. This paper reports the preliminary results of the comparison of the portal doses measured by a PTW 2D array during several radiotherapy fractions and the predicted portal doses for seven patients undergoing head-neck tumor radiotherapy. The gamma index analysis supplied an agreement of more than 95% of the dose-point P(gamma)>95% within acceptance criteria, in terms of dose difference, DeltaD(max), and distance-agreement, Deltad(max), equal to 5% and 4mm, respectively. After the third week, one patient showed a decrease of P(gamma) values due to the markedly reduced patient's thickness. Even if the spatial resolution of the 2D array was 1cm, there were two advantages in the use of this 2D array as a portal dose device for IMRT quality control. The first one was the use of a stable and efficient absolute dosimeter for in vivo verification, although its construction and behavior for other gantry angles need to be tested, and the second one was the time efficiency in verifying the correct dose delivery in several fractions of the therapy. This study presents acceptance criteria for the comparison of TPS-predicted portal dose images with in vivo 2D ion-chamber measurements for IMRT. In particular, portal dose measurements offer clues for additional studies as to which indicators can signal the need for replanning during treatment.
一个配备729个通风平面平行电离室的二维阵列（PTW，型号10024）已被校准为用于体内比较头颈部肿瘤测量和预测的射野剂量的探测器。在CT扫描仪视野范围内，将测量的绝对射野剂量与商业治疗计划系统预测的剂量进行比较，有助于在不同治疗分次期间进行输送剂量验证，特别是当患者出现体重减轻时。本文报告了在几个放疗分次期间用PTW二维阵列测量的射野剂量与7名头颈部肿瘤放疗患者预测的射野剂量比较的初步结果。伽马指数分析在剂量差异ΔD(max)和距离一致性Δd(max)分别等于5%和4mm的验收标准内，提供了超过95%的剂量点P(伽马)>95%的一致性。第三周后，一名患者由于其厚度明显减小，P(伽马)值下降。即使二维阵列空间分辨率为1cm，但将该二维阵列用作调强放疗质量控制的射野剂量装置仍有两个优点。第一个优点是使用稳定且高效的绝对剂量计进行体内验证，尽管其在其他机架角度的结构和性能需要测试；第二个优点是在验证治疗的几个分次中剂量输送是否正确时具有时间效率。本研究提出了调强放疗中TPS预测的射野剂量图像与体内二维电离室测量结果比较的验收标准。特别是，射野剂量测量为关于哪些指标可表明治疗期间需要重新计划的进一步研究提供了线索。
