Lee Tsair-Fwu, Fang Fu-Min, Chao Pei-Ju, Su T-J, Wang Luke K, Leung Stephen W
National Kaohsiung University of Applied Sciences, Kaohsiung, Taiwan, ROC.
Radiother Oncol. 2008 Oct;89(1):89-96. doi: 10.1016/j.radonc.2008.05.010. Epub 2008 Jun 2.
The study evaluates and quantifies the potential dosimetric gains of helical tomotherapy (HT) versus step-and-shoot intensity-modulated radiotherapy (SaS-IMRT) for nasopharyngeal carcinoma (NPC).
Twenty consecutive NPC patients curatively treated by HT were examined. Each case was planned by HT and SaS-IMRT (ADAC Pinnacle(3)) planning system, respectively. Dose plans were compared using dose volume histograms (DVH), conformity index (CI), homogeneity index (HI), and minimal dose to 1cc (D(min_1cc)) of the planned target volume (PTV) and a comprehensive quality index (CQI) of ten organs at risk (OARs). The prescribed dose/fractionation was 72Gy to the PTV, 64.8Gy to the elective PTV, and 54Gy to the clinically negative neck region. The plan of 54Gy to the PTV (PTV(54)) was used to evaluate the CI and HI in the target. The cumulative doses of the three PTV plans to the OARs were calculated.
We observed the HT plans significantly improved the CI (improvement ratio: 11.9+/-5.5%) and HI (improvement ratio: 8.8+/-1.5%) of the PTV(54) compared with SaS-IMRT plans. In addition, the mean/maximal dose of most of the OARs except chiasm was significantly reduced in HT plans, with the CQI of 0.92+/-0.08. A negative result of HT in chiasm was observed but only significantly revealed in cases without skull base infiltration.
A dosimetric gain in CI and HI of PTV and sparing of OARs was significantly obtained in HT versus SaS-IMRT plans in NPC patients. Whether such dosimetric superiority in HT could transfer into clinical advantages needs further investigation.
本研究评估并量化螺旋断层放射治疗（HT）与静态调强放射治疗（SaS-IMRT）相比，在鼻咽癌（NPC）治疗中潜在的剂量学获益。
对连续20例接受HT根治性治疗的NPC患者进行检查。每例患者分别采用HT和SaS-IMRT（ADAC Pinnacle(3)）计划系统进行计划制定。使用剂量体积直方图（DVH）、适形指数（CI）、均匀性指数（HI）、计划靶区（PTV）的1cc最小剂量（D(min_1cc)）以及十个危及器官（OARs）的综合质量指数（CQI）对剂量计划进行比较。PTV的处方剂量/分割为72Gy，选择性PTV为64.8Gy，临床阴性颈部区域为54Gy。采用PTV为54Gy的计划（PTV(54)）评估靶区内的CI和HI。计算三个PTV计划对OARs的累积剂量。
我们观察到，与SaS-IMRT计划相比，HT计划显著改善了PTV(54)的CI（改善率：11.9±5.5%）和HI（改善率：8.8±1.5%）。此外，除视交叉外，HT计划中大多数OARs的平均/最大剂量显著降低，CQI为0.92±0.08。观察到HT对视交叉有不良结果，但仅在无颅底浸润的病例中显著显现。
在NPC患者中，HT计划与SaS-IMRT计划相比，在PTV的CI和HI方面显著获得剂量学获益，且对OARs有保护作用。HT的这种剂量学优势是否能转化为临床优势尚需进一步研究。
