Low D A, Mutic S, Dempsey J F, Gerber R L, Bosch W R, Perez C A, Purdy J A
Mallinckrodt Institute of Radiology, Division of Radiation Oncology, St. Louis, MO 63110, USA.
Radiother Oncol. 1998 Dec;49(3):305-16. doi: 10.1016/s0167-8140(98)00125-x.
The accuracy of dose calculation and delivery of a commercial serial tomotherapy treatment planning and delivery system (Peacock. NOMOS Corporation) was experimentally determined.
External beam fluence distributions were optimized and delivered to test treatment plan target volumes, including three with cylindrical targets with diameters ranging from 2.0 to 6.2 cm and lengths of 0.9 through 4.8 cm, one using three cylindrical targets and two using C-shaped targets surrounding a critical structure, each with different dose distribution optimization criteria. Computer overlays of film-measured and calculated planar dose distributions were used to assess the dose calculation and delivery spatial accuracy. A 0.125 cm3 ionization chamber was used to conduct absolute point dosimetry verification. Thermoluminescent dosimetry chips, a small-volume ionization chamber and radiochromic film were used as independent checks of the ion chamber measurements.
Spatial localization accuracy was found to be better than +/-2.0 mm in the transverse axes (with one exception of 3.0 mm) and +/-1.5 mm in the longitudinal axis. Dosimetric verification using single slice delivery versions of the plans showed that the relative dose distribution was accurate to +/-2% within and outside the target volumes (in high dose and low dose gradient regions) with a mean and standard deviation for all points of -0.05% and 1.1%, respectively. The absolute dose per monitor unit was found to vary by +/-3.5% of the mean value due to the lack of consideration for leakage radiation and the limited scattered radiation integration in the dose calculation algorithm. To deliver the prescribed dose, adjustment of the monitor units by the measured ratio would be required.
The treatment planning and delivery system offered suitably accurate spatial registration and dose delivery of serial tomotherapy generated dose distributions. The quantitative dose comparisons were made as far as possible from abutment regions and examination of the dosimetry of these regions will also be important. Because of the variability in the dose per monitor unit and the complex nature of the calculation and delivery of serial tomotherapy, patient-specific quality assurance procedures will include a measurement of the delivered target dose.
通过实验确定了一种商用连续断层放射治疗计划与实施系统（孔雀系统，NOMOS公司）的剂量计算与投送准确性。
对外照射注量分布进行优化并投送至测试治疗计划靶区，包括三个直径范围为2.0至6.2厘米、长度为0.9至4.8厘米的圆柱形靶区，一个使用三个圆柱形靶区，两个使用围绕关键结构的C形靶区，每个靶区具有不同的剂量分布优化标准。利用胶片测量和计算的平面剂量分布的计算机叠加图来评估剂量计算和投送的空间准确性。使用一个0.125立方厘米的电离室进行绝对点剂量测定验证。热释光剂量测定芯片、小体积电离室和放射变色胶片用作电离室测量的独立对照。
发现横向轴上的空间定位准确性优于±2.0毫米（有一个例外为3.0毫米），纵向轴上优于±1.5毫米。使用计划的单切片投送版本进行的剂量测定验证表明，在靶区内和靶区外（高剂量和低剂量梯度区域），相对剂量分布精确到±2%，所有点的平均值和标准差分别为-0.05%和1.1%。由于剂量计算算法中未考虑泄漏辐射且散射辐射积分有限，发现每个监测单位的绝对剂量相对于平均值变化±3.5%。为了投送规定剂量，需要根据测量比例调整监测单位。
该治疗计划与实施系统为连续断层放射治疗产生的剂量分布提供了足够准确的空间配准和剂量投送。尽可能从毗邻区域进行了定量剂量比较，对这些区域的剂量测定进行检查也很重要。由于每个监测单位剂量的变异性以及连续断层放射治疗计算和投送的复杂性，针对患者的质量保证程序将包括对投送的靶区剂量进行测量。
