SU-E-T-647：计算机化非共面调强放疗射束角度优化中的计划质量高度依赖于射束方向搜索空间的范围。

SU-E-T-647: Plan Quality in Computerized Non-Coplanar IMRT Beam Angle Optimization is Highly Dependent on the Extent of the Beam direction Search Space.

作者信息

Voet P, Rossi L, Breedveld S, Aluwini S, Heijmen B

出版信息

Med Phys. 2012 Jun;39(6Part20):3855. doi: 10.1118/1.4735736.

DOI:10.1118/1.4735736

PMID:28517519

Abstract

PURPOSE

To investigate the relationship between plan quality and the extent of the beam direction search space in computerized beam angle selection for generating optimal (non-coplanar) IMRT plans for prostate SBRT with dose distributions simulating HDR brachytherapy.

METHODS

iCycle (1) was used to investigate the relationship between plan quality and the extent of the set of beam directions available for plan generation. For a group of 10 prostate patients, optimal plans were generated for 5 direction search spaces. For coplanar treatments (CP set), 72 orientations were available for selection (separation 5°). The fully non-coplanar set (F-NCP) included the CP directions plus 430 directions spread over the sphere. The CK set contained the directions available at the robotic Cyberknife unit. CK+ and CK++ were extensions of CK to investigate some of its characteristics. Generated plans were in accordance with our clinical SBRT protocol for Cyberknife treatment, delivering 4 fractions of 9.5 Gy. Adequate PTV coverage had the highest priority. Reduction of rectum dose was the highest OAR priority.

RESULTS

The mean PTV coverage (V95) of all SBRT plans was 99% ï,± 0.9% (1 SD). F-NCP plans had most favorable OAR dose parameters, while for coplanar plans OAR doses were highest. Compared to coplanar treatment, rectum Dmean/V60 were 25% / 37% and 19% / 21% lower in F-NCP and CK plans. Higher rectum dose for the Cyberknife set compared to F-NCP was not caused by a lack of posterior beams for Cyberknife. For all search spaces, reduction in OAR dose only leveled off with > 20 beams in the plans (for CP, rectum V60 in 25 beam plans was reduced by 64% compared to 11 beams). In the non-coplanar set-ups, there was a preference for beams with a (large) lateral component.

CONCLUSIONS

Plan quality clearly improved with the extent of the beam direction search space (coplanar worst), and the number of beam directions in the plan (25 clearly better than 11).(1) Breedveld S, Storchi P, Voet P, Heijmen B, Med Phys 2012; DOI: 10.1118/1.3676689.

摘要

目的

在为前列腺立体定向体部放疗（SBRT）生成模拟高剂量率近距离放疗剂量分布的最佳（非共面）调强放疗（IMRT）计划的计算机化射束角度选择中，研究计划质量与射束方向搜索空间范围之间的关系。

方法

使用iCycle(1)来研究计划质量与可用于计划生成的射束方向集范围之间的关系。对于一组10例前列腺癌患者，针对5个方向搜索空间生成了最佳计划。对于共面治疗（CP组），有72个方向可供选择（间隔5°）。完全非共面集（F-NCP）包括CP方向加上分布在球面上的430个方向。CK组包含机器人赛博刀设备可用的方向。CK+和CK++是CK的扩展，用于研究其一些特性。生成的计划符合我们用于赛博刀治疗的临床SBRT方案，给予4次分割，每次9.5 Gy。充分的靶区适形度具有最高优先级。降低直肠剂量是危及器官（OAR）的最高优先级。

结果

所有SBRT计划的平均靶区适形度（V95）为99%±0.9%（1个标准差）。F-NCP计划具有最有利的OAR剂量参数，而共面计划的OAR剂量最高。与共面治疗相比，F-NCP和CK计划中的直肠平均剂量/Dmean/V60分别低25%/37%和19%/21%。赛博刀组与F-NCP相比直肠剂量较高，并非由于赛博刀缺乏后向射束。对于所有搜索空间，只有当计划中的射束数>20时，OAR剂量的降低才趋于平稳（对于CP，25束射束计划中的直肠V60与11束射束相比降低了64%）。在非共面设置中，倾向于具有（大的）侧向分量的射束。