Siebert Frank-André, Kohr Peter, Kovács György
Clinic of Radiotherapy, Interdisciplinary Brachytherapy Center, University Hospital of Schleswig-Holstein, Campus Kiel, Arnold-Heller-Strasse 9, 24105 Kiel, Germany.
Strahlenther Onkol. 2006 Feb;182(2):96-101. doi: 10.1007/s00066-006-1465-4.
The objective of this investigation was a direct comparison of the dosimetry of CT-based and radiograph- based postplanning procedures for seed implants.
CT- and radiograph-based postplans were carried out for eight iodine-125 ((125)I) seed implant patients with a commercial treatment-planning system (TPS). To assess a direct comparison of the dosimetric indices (D90, V100, V400), the radiograph-based seed coordinates were transformed to the coordinate system of the CT postplan. Afterwards, the CT-based seed positions were replaced by the radiograph-based coordinates in the TPS and the dose distribution was recalculated.
The computations demonstrated that the radiograph-based dosimetric values for the prostate (D(p)90, V(p)100, and V(p)400) were on average lower than the values of the CT postplan. Normalized to the CT postplan the following mean values were found: D(p)90: 90.6% (standard deviation [SD]: 9.0%), V(p)100: 86.1% (SD: 14.7%), and V(p)400: 79.4% (SD: 14.4%). For three out of the eight patients the D(p)90 decreased to 90% of the initial CT postplan values. The reason for this dosimetric difference is supposed to be evoked by an error of the reconstruction software used. It was detected that the TPS algorithm assigned some sources to wrong coordinates, partly out of the prostate gland.
The radiograph-based postplanning technique of the investigated TPS should only be used in combination with CT postplanning. Furthermore, complex testing procedures of reconstruction algorithms are recommended to minimize calculation errors.
本研究的目的是直接比较基于CT和基于X线片的粒子植入术后计划程序的剂量学。
使用商用治疗计划系统（TPS）对8例碘-125（¹²⁵I）粒子植入患者进行基于CT和X线片的术后计划。为了直接比较剂量学指标（D90、V100、V400），将基于X线片的粒子坐标转换为CT术后计划的坐标系。然后，在TPS中用基于X线片的坐标替换基于CT的粒子位置，并重新计算剂量分布。
计算表明，基于X线片的前列腺剂量学值（D(p)90、V(p)100和V(p)400）平均低于CT术后计划的值。以CT术后计划为标准，得到以下平均值：D(p)90：90.6%（标准差[SD]：9.0%），V(p)100：86.1%（SD：14.7%），V(p)400：79.4%（SD：14.4%）。8例患者中有3例的D(p)90降至初始CT术后计划值的90%。这种剂量学差异的原因被认为是由所用重建软件的误差引起的。检测发现TPS算法将一些源分配到错误的坐标，部分超出前列腺。
所研究的TPS基于X线片的术后计划技术应仅与CT术后计划联合使用。此外，建议对重建算法进行复杂的测试程序，以尽量减少计算误差。
