Department of Medical Physics in Radiation Oncology, German Cancer Research Center, Heidelberg, Germany.
Med Phys. 2013 Jan;40(1):011716. doi: 10.1118/1.4771932.
Various strategies to select beneficial beam ensembles for intensity-modulated radiation therapy (IMRT) have been suggested over the years. These beam angle selection (BAS) strategies are usually evaluated against reference configurations applying equispaced coplanar beams but they are not compared to one another. Here, the authors present a meta analysis of four BAS strategies that incorporates fluence optimization (FO) into BAS by combinatorial optimization (CO) and one BAS strategy that decouples FO from BAS, i.e., spherical cluster analysis (SCA). The underlying parameters of the BAS process are investigated and the dosimetric benefits of the BAS strategies are quantified.
For three intracranial lesions in proximity to organs at risk (OARs) the authors compare treatment plans applying equispaced coplanar beam ensembles with treatment plans using five different BAS strategies, i.e., four CO techniques and SCA, to establish coplanar and noncoplanar beam ensembles. Treatment plans applying 5, 7, 9, and 11 beams are investigated. For the CO strategies the authors perform BAS runs with a 5°, 10°, 15°, and 20° angular resolution, which corresponds to a minimum of 18 coplanar and a maximum of 1400 noncoplanar candidate beams. In total 272 treatment plans with different BAS settings are generated for every patient. The quality of the treatment plans is compared based on the protection of OARs yet integral dose, target homogeneity, and target conformity are also considered.
It is possible to reduce the average mean and maximum doses in OARs by more than 4 Gy (1 Gy) with optimized noncoplanar (coplanar) beam ensembles found with BAS by CO or SCA. For BAS including FO by CO, the individual algorithm used and the angular resolution in the space of candidate beams does not have a crucial impact on the quality of the resulting treatment plans. All CO algorithms yield similar target conformity and slightly improved target homogeneity in comparison to equispaced coplanar setups. Furthermore, optimized coplanar (noncoplanar) beam ensembles enabled more than a 6% (5%) reduction of the integral dose. For SCA, however, integral dose was increased and target conformity was decreased in comparison to equispaced coplanar setups-especially for a small number of beams.
Both BAS strategies incorporating FO by CO and independent BAS strategies excluding FO provide dose savings in OARs for optimized coplanar and especially noncoplanar beam ensembles; they should not be neglected in the clinic.
多年来，人们提出了各种选择调强放射治疗（IMRT）有益射束组合的策略。这些射束角度选择（BAS）策略通常是针对应用等间隔共面射束的参考配置进行评估的，但它们彼此之间并没有进行比较。在这里，作者对四种通过组合优化（CO）将剂量优化（FO）纳入 BAS 的 BAS 策略和一种将 FO 与 BAS 解耦的 BAS 策略，即球形聚类分析（SCA）进行了荟萃分析。研究了 BAS 过程的基本参数，并量化了 BAS 策略的剂量学优势。
对于三个靠近危及器官（OARs）的颅内病变，作者比较了应用等间隔共面射束组合的治疗计划和应用五种不同 BAS 策略的治疗计划，即四种 CO 技术和 SCA，以建立共面和非共面射束组合。研究了 5、7、9 和 11 束的治疗计划。对于 CO 策略，作者以 5°、10°、15°和 20°的角度分辨率进行 BAS 运行，这对应于至少 18 个共面和最多 1400 个非共面候选射束。对于每个患者，总共生成了 272 个具有不同 BAS 设置的治疗计划。根据保护 OARs 的情况来比较治疗计划的质量，但也考虑了整体剂量、靶区均匀性和靶区适形性。
通过 BAS 由 CO 或 SCA 找到的优化非共面（共面）射束组合，可以将 OARs 的平均平均剂量和最大剂量降低超过 4 Gy（1 Gy）。对于包括 CO 中 FO 的 BAS，所使用的单个算法和候选射束空间中的角度分辨率对治疗计划的质量没有关键影响。与等间隔共面设置相比，所有 CO 算法都产生了类似的靶区适形性和略有改善的靶区均匀性。此外，优化的共面（非共面）射束组合使整体剂量降低了超过 6%（5%）。然而，对于 SCA，与等间隔共面设置相比，整体剂量增加，靶区适形性降低，尤其是对于较少的射束。
包含 CO 中 FO 的两种 BAS 策略和不包含 FO 的独立 BAS 策略都为优化的共面和特别是非共面射束组合的 OARs 提供了剂量节省；在临床上不应忽视它们。
