Department of Physics, Florida Atlantic University, Boca Raton, Florida, USA.
South Florida Proton Therapy Institute, Delray Beach, Florida, USA.
J Appl Clin Med Phys. 2023 Apr;24(4):e13880. doi: 10.1002/acm2.13880. Epub 2023 Jan 18.
The multi-leaf collimator (MLC)-equipped CyberKnife M6 radiosurgery system (CKM6) (Accuray Inc., Sunnyvale, CA) has been increasingly employed for stereotactic radiosurgery (SRS) to treat relatively small lesions. However, achieving an accurate dose distribution in such cases is usually challenging due to the combination of numerous small fields ≤ (30 × 30) mm . In this study, we developed a new Monte Carlo (MC) dose model for the CKM6 system using the EGSnrc to investigate dose variations in the small fields. The dose model was verified for the static MLC fields ranging from (53.8 × 53.9) to (7.6 × 7.7) mm at 800 mm source to axis distance in a water phantom, based on the computed doses of Accuray Precision (Accuray Inc.) treatment planning system (TPS). We achieved a statistical uncertainty of ≤4% by simulating 30-50 million incident particles/histories. Then, the treatment plans were created for the same fields in the TPS, and the corresponding measurements were performed with MapCHECK2 (Sun Nuclear Corporation), a standard device for patient-specific quality assurance (PSQA). Results of the MC simulations, TPS, and MapCHECK2 measurements were inter-compared. An overall difference in dosimetric parameters such as profiles, tissue maximum ratio (TMR), and output factors (OF) between the MC simulations and the TPS results was found ≤3% for (53.8 × 53.9-15.4 × 15.4) mm MLC fields, and it rose to 4.5% for the smallest (7.6 mm × 7.7 mm) MLC field. The MapCHECK2 results showed a deviation ranging from -1.5% to + 4.5% compared to the TPS results, whereas the deviation was within ±2.5% compared with the MC results. Overall, our MC dose model for the CKM6 system showed better agreement with measurements and it could serve as a secondary dose verification tool for the patient-specific QA in small fields.
多叶准直器（MLC）配备的 CyberKnife M6 放射外科系统（CKM6）（Accuray Inc.，加利福尼亚州森尼韦尔）已越来越多地用于立体定向放射外科（SRS）治疗相对较小的病变。然而，由于许多≤（30×30）mm 的小射野的组合，在这种情况下实现精确的剂量分布通常具有挑战性。在这项研究中，我们使用 EGSnrc 为 CKM6 系统开发了一种新的蒙特卡罗（MC）剂量模型，以研究小射野中的剂量变化。基于 Accuray Precision（Accuray Inc.）治疗计划系统（TPS）的计算剂量，在水模体中，在 800mm 源轴距离处，从（53.8×53.9）到（7.6×7.7）mm 范围验证了静态 MLC 射野的剂量模型。通过模拟 3000 万至 5000 万入射粒子/历史，实现了≤4%的统计不确定性。然后，在 TPS 中为相同的射野创建治疗计划，并使用 MapCHECK2（Sun Nuclear Corporation）进行相应的测量，MapCHECK2 是用于患者特定质量保证（PSQA）的标准设备。比较 MC 模拟、TPS 和 MapCHECK2 测量的结果。MC 模拟和 TPS 结果之间的剂量学参数（如轮廓、组织最大比（TMR）和输出因子（OF））的总体差异在（53.8×53.9-15.4×15.4）mm MLC 射野中≤3%，在最小的（7.6mm×7.7mm）MLC 射野中上升到 4.5%。与 TPS 结果相比，MapCHECK2 结果显示偏差范围在-1.5%至+4.5%之间，而与 MC 结果相比，偏差在±2.5%范围内。总体而言，我们为 CKM6 系统开发的 MC 剂量模型与测量结果具有更好的一致性，它可以作为小射野患者特定 QA 的辅助剂量验证工具。
