Department of Radiation Oncology, Stanford University, Stanford, CA, USA.
Int J Radiat Oncol Biol Phys. 2012 Apr 1;82(5):2025-32. doi: 10.1016/j.ijrobp.2011.03.004. Epub 2011 Apr 29.
To determine whether normal tissue complication probability (NTCP) analyses of the human spinal cord by use of the Lyman-Kutcher-Burman (LKB) model, supplemented by linear-quadratic modeling to account for the effect of fractionation, predict the risk of myelopathy from stereotactic radiosurgery (SRS).
From November 2001 to July 2008, 24 spinal hemangioblastomas in 17 patients were treated with SRS. Of the tumors, 17 received 1 fraction with a median dose of 20 Gy (range, 18-30 Gy) and 7 received 20 to 25 Gy in 2 or 3 sessions, with cord maximum doses of 22.7 Gy (range, 17.8-30.9 Gy) and 22.0 Gy (range, 20.2-26.6 Gy), respectively. By use of conventional values for α/β, volume parameter n, 50% complication probability dose TD(50), and inverse slope parameter m, a computationally simplified implementation of the LKB model was used to calculate the biologically equivalent uniform dose and NTCP for each treatment. Exploratory calculations were performed with alternate values of α/β and n.
In this study 1 case (4%) of myelopathy occurred. The LKB model using radiobiological parameters from Emami and the logistic model with parameters from Schultheiss overestimated complication rates, predicting 13 complications (54%) and 18 complications (75%), respectively. An increase in the volume parameter (n), to assume greater parallel organization, improved the predictive value of the models. Maximum-likelihood LKB fitting of α/β and n yielded better predictions (0.7 complications), with n = 0.023 and α/β = 17.8 Gy.
The spinal cord tolerance to the dosimetry of SRS is higher than predicted by the LKB model using any set of accepted parameters. Only a high α/β value in the LKB model and only a large volume effect in the logistic model with Schultheiss data could explain the low number of complications observed. This finding emphasizes that radiobiological models traditionally used to estimate spinal cord NTCP may not apply to the dosimetry of SRS. Further research with additional NTCP models is needed.
利用 Lyman-Kutcher-Burman（LKB）模型对人体脊髓进行正常组织并发症概率（NTCP）分析，并结合线性二次模型来考虑分割效应，从而预测立体定向放射外科（SRS）后发生脊髓病的风险。
2001 年 11 月至 2008 年 7 月，对 17 例患者的 24 个脊髓血管母细胞瘤采用 SRS 治疗。其中，17 个肿瘤单次分割剂量中位数为 20 Gy（范围：18-30 Gy），7 个肿瘤 2 或 3 次分割，剂量分别为 20-25 Gy，脊髓最大剂量为 22.7 Gy（范围：17.8-30.9 Gy）和 22.0 Gy（范围：20.2-26.6 Gy）。利用常规的 α/β、体积参数 n、50%并发症概率剂量 TD(50)和逆斜率参数 m 值，采用计算上简化的 LKB 模型来计算每个治疗的生物等效均匀剂量和 NTCP。对 α/β 和 n 的替代值进行了探索性计算。
本研究中，1 例（4%）发生了脊髓病。采用 Emami 的放射生物学参数的 LKB 模型和采用 Schultheiss 参数的逻辑模型分别预测了 13 例并发症（54%）和 18 例并发症（75%），均过高地估计了并发症发生率。增加体积参数（n），假设存在更大的平行组织，可改善模型的预测价值。采用最大似然法对 LKB 模型进行 α/β 和 n 的拟合，得到了更好的预测结果（0.7 例并发症），其中 n = 0.023，α/β = 17.8 Gy。
SRS 的脊髓剂量学耐受度高于使用任何一组公认参数的 LKB 模型所预测的结果。只有 LKB 模型中的高 α/β 值和 Schultheiss 数据的逻辑模型中的大体积效应才能解释观察到的低并发症发生率。这一发现强调了传统上用于估计脊髓 NTCP 的放射生物学模型可能不适用于 SRS 的剂量学。需要进行更多的研究，使用额外的 NTCP 模型。
