Koeck Julia, Kromer Katharina, Lohr Frank, Baack Tobias, Siebenlist Kerstin, Mai Sabine, Büttner Sylvia, Fleckenstein Jens, Wenz Frederik
Department of Radiation Oncology, University Medical Center Mannheim, University of Heidelberg, Theodor-Kutzer-Ufer 1-3, 68135, Mannheim, Germany.
Unita Operativa di Radioterapia, Dipartimento di Oncologia, Az. Ospedaliero-Universitaria di Modena, Modena, Italy.
Strahlenther Onkol. 2017 Jul;193(7):578-588. doi: 10.1007/s00066-017-1107-z. Epub 2017 Feb 20.
This treatment planning study analyzes dose coverage and dose to organs at risk (OAR) in intensity-modulated radiotherapy (IMRT) of rectal cancer and compares prone vs. supine positioning as well as the effect of dose optimization for the small bowel (SB) by additional dose constraints in the inverse planning process.
Based on the CT datasets of ten male patients in both prone and supine position, a total of four different IMRT plans were created for each patient. OAR were defined as the SB, bladder, and femoral heads. In half of the plans, two additional SB cost functions were used in the inverse planning process.
There was a statistically significant dose reduction for the SB in prone position of up to 41% in the high and intermediate dose region, compared with the supine position. Furthermore, the femoral heads showed a significant dose reduction in prone position in the low dose region. Regarding the additional active SB constraints, the dose in the high dose region of the SB was significantly reduced by up to 14% with the additional cost functions. There were no significant differences in the dose distribution of the planning target volume (PTV) and the bladder.
Prone positioning can significantly reduce dose to the SB in IMRT for rectal cancer and therefore should not only be used in 3D conformal radiotherapy but also in IMRT of rectal cancer. Further protection of the SB can be achieved by additional dose constraints in inverse planning without jeopardizing the homogeneity of the PTV.
本治疗计划研究分析了直肠癌调强放射治疗（IMRT）中靶区剂量覆盖情况及危及器官（OAR）的受量，并比较了俯卧位与仰卧位的差异，以及在逆向计划过程中通过额外的剂量限制对小肠（SB）进行剂量优化的效果。
基于10名男性患者俯卧位和仰卧位的CT数据集，为每位患者共创建了四种不同的IMRT计划。将OAR定义为小肠、膀胱和股骨头。在一半的计划中，逆向计划过程中使用了两个额外的小肠代价函数。
与仰卧位相比，俯卧位时小肠在高剂量和中剂量区域的受量有统计学意义的显著降低，降幅高达41%。此外，股骨头在低剂量区域俯卧位时受量也显著降低。关于额外的主动小肠限制，使用额外的代价函数后，小肠高剂量区域的受量显著降低，降幅高达14%。计划靶区（PTV）和膀胱的剂量分布无显著差异。
俯卧位可显著降低直肠癌IMRT中对小肠的剂量，因此不仅应在三维适形放疗中使用，也应在直肠癌IMRT中应用。在逆向计划中通过额外的剂量限制可进一步保护小肠，而不影响PTV的均匀性。
