Department of Radiology, Ujitakeda Hospital, Uji-city, Kyoto, Japan.
Anticancer Res. 2013 Jun;33(6):2453-6.
To evaluate an appropriate planning target volume (PTV) margin in for one to three vertebral metastases using megavolt computed tomography (MVCT) images during the course of image-guided and stereotactic intensity-modulated radiotherapy (IGRT-IMRT) by use of helical tomotherapy.
A total of 25 lesions in 24 patients with vertebral metastases who received IGRT-IMRT were analyzed. MVCT images were acquired before and after radiation therapy. Intra-fractional movement and PTV margin were calculated by comparing treatment planning images and these 310 MVCT images for right-left (RL), superior-inferior (SI), and anteroposterior (AP) dimensions. Five patients were treated by 35 Gy/5 fractions, 17 by 30 Gy/5 fractions, one by 25 Gy/5 fractions, and one by 60 Gy/30 fractions. A margin to compensate for these variations was calculated with the formula of vanHerk's equation.
The intra-fractional motion was 0.02 (-1.3 to 1.4) ± 0.34 mm in the RL direction, -0.09 (-1.8 to 0.28) ± 0.44 mm in the SI direction, and 0.20 (-1.8 to 1.8) ± 0.36 mm in the AP direction. The required PTV margin was 0.98 mm in the RL direction, 0.69 mm in the SI direction, and 1.26 mm in the AP direction. No patient showed a deviation greater than 2 mm.
The PTV margin in hypofractionated IGRT-IMRT, using helical tomotherapy for a few vertebral metastases, was 2 mm or less and our tentative PTV margin of 5 mm was sufficient and reducible.
使用螺旋断层放疗（Helical Tomotherapy），通过图像引导和立体定向调强放疗（IGRT-IMRT），在治疗过程中，评估一个至三个椎体转移瘤的合适计划靶区（PTV）边界。
分析了 24 例椎体转移瘤患者的 25 个病灶，这些患者均接受了 IGRT-IMRT 治疗。在放疗前后采集了 MVCT 图像。通过比较治疗计划图像和这 310 个 MVCT 图像，计算了右-左（RL）、上-下（SI）和前-后（AP）三个方向的分次内运动和 PTV 边界。5 例患者接受 35 Gy/5 次分割，17 例患者接受 30 Gy/5 次分割，1 例患者接受 25 Gy/5 次分割，1 例患者接受 60 Gy/30 次分割。使用 van Herk 方程公式计算了补偿这些变化的边界。
RL 方向的分次内运动为 0.02（-1.3 至 1.4）±0.34mm，SI 方向为-0.09（-1.8 至 0.28）±0.44mm，AP 方向为 0.20（-1.8 至 1.8）±0.36mm。所需的 PTV 边界在 RL 方向为 0.98mm，SI 方向为 0.69mm，AP 方向为 1.26mm。没有患者的偏差大于 2mm。
对于少数椎体转移瘤的短分割 IGRT-IMRT，使用螺旋断层放疗，PTV 边界为 2mm 或更小，我们暂定的 5mm PTV 边界是足够的，并且可以缩小。
