Park Justin C, Li Jonathan G, Arhjoul Lahcen, Yan Guanghua, Lu Bo, Fan Qiyong, Liu Chihray
Department of Radiation Oncology, University of Florida, Gainesville, Florida 32610-0385.
Med Phys. 2015 Apr;42(4):1836-50. doi: 10.1118/1.4914858.
The use of sophisticated dose calculation procedure in modern radiation therapy treatment planning is inevitable in order to account for complex treatment fields created by multileaf collimators (MLCs). As a consequence, independent volumetric dose verification is time consuming, which affects the efficiency of clinical workflow. In this study, the authors present an efficient adaptive beamlet-based finite-size pencil beam (AB-FSPB) dose calculation algorithm that minimizes the computational procedure while preserving the accuracy.
The computational time of finite-size pencil beam (FSPB) algorithm is proportional to the number of infinitesimal and identical beamlets that constitute an arbitrary field shape. In AB-FSPB, dose distribution from each beamlet is mathematically modeled such that the sizes of beamlets to represent an arbitrary field shape no longer need to be infinitesimal nor identical. As a result, it is possible to represent an arbitrary field shape with combinations of different sized and minimal number of beamlets. In addition, the authors included the model parameters to consider MLC for its rounded edge and transmission.
Root mean square error (RMSE) between treatment planning system and conventional FSPB on a 10 × 10 cm(2) square field using 10 × 10, 2.5 × 2.5, and 0.5 × 0.5 cm(2) beamlet sizes were 4.90%, 3.19%, and 2.87%, respectively, compared with RMSE of 1.10%, 1.11%, and 1.14% for AB-FSPB. This finding holds true for a larger square field size of 25 × 25 cm(2), where RMSE for 25 × 25, 2.5 × 2.5, and 0.5 × 0.5 cm(2) beamlet sizes were 5.41%, 4.76%, and 3.54% in FSPB, respectively, compared with RMSE of 0.86%, 0.83%, and 0.88% for AB-FSPB. It was found that AB-FSPB could successfully account for the MLC transmissions without major discrepancy. The algorithm was also graphical processing unit (GPU) compatible to maximize its computational speed. For an intensity modulated radiation therapy (∼12 segments) and a volumetric modulated arc therapy fields (∼90 control points) with a 3D grid size of 2.0 × 2.0 × 2.0 mm(3), dose was computed within 3-5 and 10-15 s timeframe, respectively.
The authors have developed an efficient adaptive beamlet-based pencil beam dose calculation algorithm. The fast computation nature along with GPU compatibility has shown better performance than conventional FSPB. This enables the implementation of AB-FSPB in the clinical environment for independent volumetric dose verification.
在现代放射治疗治疗计划中，使用复杂的剂量计算程序是不可避免的，以便考虑多叶准直器（MLC）产生的复杂治疗野。因此，独立的体积剂量验证耗时较长，这影响了临床工作流程的效率。在本研究中，作者提出了一种高效的基于自适应子束的有限尺寸笔形束（AB-FSPB）剂量计算算法，该算法在保持准确性的同时最大限度地减少了计算过程。
有限尺寸笔形束（FSPB）算法的计算时间与构成任意野形状的无限小且相同的子束数量成正比。在AB-FSPB中，对每个子束的剂量分布进行数学建模，使得代表任意野形状的子束尺寸不再需要无限小或相同。结果，可以用不同尺寸且数量最少的子束组合来表示任意野形状。此外，作者纳入了模型参数以考虑MLC的圆角边缘和透射。
在10×10 cm²方形野上，使用10×10、2.5×2.5和0.5×0.5 cm²子束尺寸时，治疗计划系统与传统FSPB之间的均方根误差（RMSE）分别为4.90%、3.19%和2.87%，而AB-FSPB的RMSE分别为1.10%、1.11%和1.14%。对于25×25 cm²的更大方形野尺寸，这一发现同样成立，其中FSPB中25×25、2.5×2.5和0.5×0.5 cm²子束尺寸的RMSE分别为5.41%、4.76%和3.54%，而AB-FSPB的RMSE分别为0.86%、0.83%和0.88%。发现AB-FSPB能够成功考虑MLC的透射且无重大差异。该算法还与图形处理单元（GPU）兼容，以最大限度地提高其计算速度。对于强度调制放射治疗（约12个射野分段）和容积调强弧形治疗野（约90个控制点），3D网格尺寸为2.0×2.0×2.0 mm³，剂量分别在3 - 5秒和10 - 15秒内计算完成。
作者开发了一种高效的基于自适应子束的笔形束剂量计算算法。其快速计算特性以及与GPU的兼容性显示出比传统FSPB更好的性能。这使得AB-FSPB能够在临床环境中用于独立的体积剂量验证。
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