Tomsk Regional Oncology Centre, 115, Lenin Avenue, Tomsk 634050, Russia; Tomsk Polytechnic University, 30, Lenin Avenue, Tomsk 634050, Russia.
Tomsk Polytechnic University, 30, Lenin Avenue, Tomsk 634050, Russia.
Phys Med. 2019 Jun;62:41-46. doi: 10.1016/j.ejmp.2019.04.017. Epub 2019 May 6.
Stereotactic body radiation therapy is widely used for the hypofractionated treatment of prostate cancer. The range of total doses used in different clinical trials varies from 33.5 to 50 Gy delivered in 4 or 5 fractions. The choice of an optimal total dose value and fractionation regimen for a particular patient can be carried out using the integral radiobiological criteria, namely tumour control probability (TCP) and normal tissue complication probability (NTCP). In this study, we have investigated the dependence of simulated TCP/NTCP values on total dose in the range of 30-40 Gy delivered in 4 or 5 fractions for patients with low-risk prostate cancer in order to find the optimal total dose value and fractionation regimen.
The anatomic data (DICOM CT images) of 12 patients with low-risk prostate cancer, who were treated at Tomsk Regional Oncology Centre, were used for the calculation. Dosimetric treatment plans for all patients were simulated using VMAT with 2 arcs in the Monaco treatment planning system v5.10 (Elekta Instrument AB, Stockholm) with a total dose equal to 36.25 Gy. The dosimetric plans were rescaled in the dose range of 30-40 Gy. The TCP and NTCP values were calculated based on differential dose volume histograms using the Niemierko model for both TCP and NTCP, and the Källman-s model for NTCP calculations. The TCP calculation was carried out using the uncertainty of well-known tumour radiobiological parameters values, including α/β value. NTCP was calculated for an anterior rectal wall, which was the most irradiated organ at risk due to its close contact with the planning target volume.
The TCP and NTCP calculations for VMAT of the prostate cancer have shown that the optimal total dose ranges were equal to 32-34 Gy delivered in 4 fractions or 35-38 Gy delivered in 5 fractions. At doses lower than the optimal ones, the TCP values were lower than 95%, while TCP uncertainties were significant (as low as 80%). This fact might bring unexpectedly poor treatment results. At doses higher than optimal ones, the probability of toxicity to the anterior rectal wall became significant.
The optimization of radiation therapy regimen based on TCP/NTCP criteria could help to determine an optimal total dose and a number of fractions for a particular patient depending on patient-specific anatomic features and planned dose distribution.
立体定向体部放射治疗（Stereotactic Body Radiation Therapy，SBRT）被广泛应用于前列腺癌的分割治疗。在不同的临床试验中，所使用的总剂量范围从 33.5 到 50Gy，采用 4 或 5 次分割。为特定患者选择最佳的总剂量值和分割方案，可以使用整体放射生物学标准，即肿瘤控制概率（Tumor Control Probability，TCP）和正常组织并发症概率（Normal Tissue Complication Probability，NTCP）来实现。在这项研究中，我们针对低危前列腺癌患者，调查了在 30-40Gy 范围内，采用 4 或 5 次分割时，总剂量与模拟 TCP/NTCP 值之间的相关性，以确定最佳的总剂量值和分割方案。
使用来自托木斯克地区肿瘤中心的 12 例低危前列腺癌患者的解剖数据（DICOM CT 图像）进行计算。使用 Monaco 治疗计划系统 v5.10（Elekta Instrument AB，斯德哥尔摩）中的 2 个弧进行所有患者的容积旋转调强放射治疗（Volumetric Modulated Arc Therapy，VMAT）模拟，总剂量等于 36.25Gy。将剂量计划在 30-40Gy 的剂量范围内进行缩放。基于差分剂量体积直方图，使用 Niemierko 模型计算 TCP 和 NTCP 值，使用 Källman-s 模型计算 NTCP 值。TCP 计算是基于已知肿瘤放射生物学参数值的不确定性进行的，包括 α/β 值。计算 NTCP 时，考虑了最接近计划靶区的高危器官——前直肠壁。
VMAT 治疗前列腺癌的 TCP 和 NTCP 计算表明，最佳总剂量范围等于 32-34Gy 时采用 4 次分割，或 35-38Gy 时采用 5 次分割。低于最佳剂量时，TCP 值低于 95%，而 TCP 不确定性较大（低至 80%）。这一事实可能会带来出乎意料的治疗效果不佳。高于最佳剂量时，前直肠壁的毒性发生概率显著增加。
基于 TCP/NTCP 标准的放射治疗方案优化，有助于根据患者特定的解剖特征和计划的剂量分布，为特定患者确定最佳总剂量和分割次数。
