Department of Radiation Oncology, Universitätsklinikum Erlangen, Friedrich-Alexander-Universität Erlangen-Nürnberg, Universitätsstraße 27, 91054, Erlangen, Germany.
Comprehensive Cancer Center Erlangen-EMN, Erlangen, Germany.
Radiat Oncol. 2023 Sep 22;18(1):158. doi: 10.1186/s13014-023-02325-1.
The goal of this study was to obtain maximum allowed shift deviations from planning position in six degrees of freedom (DOF), that can serve as threshold values in surface guided radiation therapy (SGRT) of breast cancer patients.
The robustness of conformal treatment plans of 50 breast cancer patients against 6DOF shifts was investigated. For that, new dose distributions were calculated on shifted computed tomography scans and evaluated with respect to target volume and spinal cord dose. Maximum allowed shift values were identified by imposing dose constraints on the target volume dose coverage for 1DOF, and consecutively, for 6DOF shifts using an iterative approach and random sampling.
Substantial decreases in target dose coverage and increases of spinal cord dose were observed. Treatment plans showed highly differing robustness for different DOFs or treated area. The sensitivity was particularly high if clavicular lymph nodes were irradiated, for shifts in lateral, vertical, roll or yaw direction, and showed partly pronounced asymmetries. Threshold values showed similar properties with an absolute value range of 0.8 mm to 5 mm and 1.4° to 5°.
The robustness analysis emphasized the necessity of taking differences between DOFs and asymmetrical sensitivities into account when evaluating the dosimetric impact of position deviations. It also highlighted the importance of rotational shifts, especially if clavicular lymph nodes were irradiated. A practical approach of determining 6DOF shift limits was introduced and a set of threshold values applicable for SGRT based patient motion control was identified.
本研究的目的是获得在六自由度（6DOF）中允许的最大偏移偏差，以便作为乳腺癌患者表面引导放射治疗（SGRT）的阈值。
研究了 50 例乳腺癌患者的适形治疗计划对 6DOF 偏移的稳健性。为此，在移位的 CT 扫描上计算了新的剂量分布，并根据靶区和脊髓剂量进行了评估。通过对靶区剂量覆盖施加 1DOF 的剂量限制，然后使用迭代方法和随机抽样对 6DOF 偏移进行连续限制，从而确定最大允许偏移值。
观察到靶区剂量覆盖显著降低，脊髓剂量增加。对于不同的 DOF 或治疗区域，治疗计划的稳健性差异很大。如果锁骨淋巴结被照射，对于侧向、垂直、滚动或偏航方向的偏移，以及部分明显的不对称性，灵敏度特别高。阈值具有相似的特性，绝对值范围为 0.8mm 至 5mm，1.4°至 5°。
稳健性分析强调了在评估位置偏差对剂量学影响时，考虑 DOF 之间的差异和不对称敏感性的必要性。它还强调了旋转偏移的重要性，特别是如果锁骨淋巴结被照射。介绍了一种确定 6DOF 偏移限制的实用方法，并确定了一组适用于基于 SGRT 的患者运动控制的阈值。
