非共面 CyberKnife 和等中心调强体部放射治疗前列腺癌时靶区正常组织界面附近的剂量梯度。
Dose gradient near target-normal structure interface for nonisocentric CyberKnife and isocentric intensity-modulated body radiotherapy for prostate cancer.
机构信息
Department of Radiation Oncology, University of California, San Francisco, School of Medicine, San Francisco, CA 94143-1708, USA.
出版信息
Int J Radiat Oncol Biol Phys. 2010 Sep 1;78(1):58-63. doi: 10.1016/j.ijrobp.2009.07.1752. Epub 2010 Feb 3.
PURPOSE
The treatment planning quality between nonisocentric CyberKnife (CK) and isocentric intensity modulation treatment was studied for hypofractionated prostate body radiotherapy. In particular, the dose gradient across the target and the critical structures such as the rectum and bladder was characterized.
METHODS AND MATERIALS
In the present study, patients treated with CK underwent repeat planning for nine fixed-field intensity-modulated radiotherapy (IMRT) using identical contour sets and dose-volume constraints. To calculate the dose falloff, the clinical target volume contours were expanded 30 mm anteriorly and posteriorly and 50 mm uniformly in other directions for all patients in the CK and IMRT plans.
RESULTS
We found that all the plans satisfied the dose-volume constraints, with the CK plans showing significantly better conformity than the IMRT plans at a relative greater dose inhomogeneity. The rectal and bladder volumes receiving a low dose were also lower for CK than for IMRT. The average conformity index, the ratio of the prescription isodose volume and clinical target volume, was 1.18 +/- 0.08 for the CK plans vs. 1.44 +/- 0.11 for the IMRT plans. The average homogeneity index, the ratio of the maximal dose and the prescribed dose to the clinical target volume, was 1.45 +/- 0.12 for the CK plans vs. 1.28 +/- 0.06 for the IMRT plans. The average percentage of dose falloff was 2.9% +/- 0.8%/mm for CK and 3.1% +/- 1.0%/mm for IMRT in the anterior direction, 3.8% +/- 1.6%/mm for CK and 3.2% +/- 1.9%/mm for IMRT in the posterior direction, and 3.6% +/- 0.4% for CK and 3.6% +/- 0.4% for IMRT in all directions.
CONCLUSION
Nonisocentric CK was as capable of producing equivalent fast dose falloff as high-number fixed-field IMRT delivery.
目的
研究非共面 CyberKnife（CK）和共面调强治疗在前列腺体部分分割放疗中的治疗计划质量。特别是，研究了靶区和直肠、膀胱等关键结构的剂量梯度。
方法和材料
在本研究中，接受 CK 治疗的患者接受了 9 次固定野调强放疗（IMRT）的重复计划，使用相同的轮廓集和剂量-体积限制。为了计算剂量下降，所有 CK 和 IMRT 计划中的临床靶区轮廓均在前、后方向扩展 30mm，在其他方向均匀扩展 50mm。
结果
我们发现所有计划都满足了剂量-体积限制，CK 计划的适形性明显优于 IMRT 计划，在相对较大的剂量不均匀性下更是如此。CK 计划中直肠和膀胱接受低剂量的体积也低于 IMRT 计划。CK 计划的平均适形性指数（即处方等剂量体积与临床靶区体积的比值）为 1.18 +/- 0.08，IMRT 计划为 1.44 +/- 0.11。CK 计划的平均均匀性指数（即最大剂量与临床靶区体积的比值）为 1.45 +/- 0.12，IMRT 计划为 1.28 +/- 0.06。CK 计划在前后方向的剂量下降平均百分比为 2.9% +/- 0.8%/mm，IMRT 计划为 3.1% +/- 1.0%/mm；CK 计划在前后方向的剂量下降平均百分比为 3.8% +/- 1.6%/mm，IMRT 计划为 3.2% +/- 1.9%/mm；CK 计划在所有方向的剂量下降平均百分比为 3.6% +/- 0.4%，IMRT 计划为 3.6% +/- 0.4%。
结论
非共面 CK 能够产生与高剂量固定野 IMRT 相当的快速剂量下降。
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