Department of Physics, University of Bologna, Viale Berti Pichat 6/2, 40127 Bologna, Italy.
Radiat Oncol. 2012 Apr 2;7:56. doi: 10.1186/1748-717X-7-56.
Intensity-modulated radiotherapy (IMRT) enables a better conformality to the target while sparing the surrounding normal tissues and potentially allows to increase the dose to the target, if this is precisely and accurately determined. The goal of this work is to determine inter-fraction setup errors and prostate motion in IMRT for localized prostate cancer, guided by daily kilovoltage cone beam computed tomography (kVCBCT).
Systematic and random components of the shifts were retrospectively evaluated by comparing two matching modalities (automatic bone and manual soft-tissue) between each of the 641 daily kVCBCTs (18 patients) and the planning kVCT. A simulated Adaptive Radiation Therapy (ART) protocol using the average of the first 5 kVCBCTs was tested by non-parametric bootstrapping procedure.
Shifts were < 1 mm in left-right (LR) and in supero-inferior (SI) direction. In antero-posterior (AP) direction systematic prostate motion (2.7 ± 0.7 mm) gave the major contribution to the variability of results; the averages of the absolute total shifts were significantly larger in anterior (6.3 ± 0.2 mm) than in posterior (3.9 mm ± 0.2 mm) direction. The ART protocol would reduce margins in LR, SI and anterior but not in posterior direction.
The online soft-tissue correction based on daily kVCBCT during IMRT of prostate cancer is fast and efficient. The large random movements of prostate respect to bony anatomy, especially in the AP direction, where anisotropic margins are needed, suggest that daily kVCBCT is at the present time preferable for high dose and high gradients IMRT prostate treatments.
调强放疗（IMRT）能够更好地使靶区适形，同时保护周围正常组织，并在精确和准确确定的情况下，潜在地增加靶区剂量。这项工作的目的是通过每日千伏锥形束计算机断层摄影术（kVCBCT）来确定局部前列腺癌的分次间摆位误差和前列腺运动。
通过比较 18 名患者的 641 次每日 kVCBCT 与计划千伏 CT 之间的两种匹配方式（自动骨和手动软组织），回顾性评估了移位的系统和随机分量。使用前 5 次 kVCBCT 的平均值的模拟自适应放疗（ART）方案通过非参数自举程序进行了测试。
左右（LR）和上下（SI）方向的移位小于 1 毫米。在前后（AP）方向，前列腺的系统性运动（2.7 ± 0.7 毫米）是导致结果变异性的主要原因；前向（6.3 ± 0.2 毫米）的绝对总移位平均值明显大于后向（3.9 毫米±0.2 毫米）。ART 方案将减少 LR、SI 和前向的边缘，但不会减少后向的边缘。
在前列腺癌的调强放疗中，基于每日 kVCBCT 的在线软组织校正快速有效。前列腺相对于骨骼解剖结构的较大随机运动，尤其是在 AP 方向，需要各向异性边缘，这表明目前每日 kVCBCT 更适合高剂量和高梯度的前列腺 IMRT 治疗。
