Medical Physics Laboratory, Medical School, National and Kapodistrian University of Athens, 75 Mikras Asias, 11527 Athens, Greece.
Radiotherapy and radiosurgery department, Iatropolis Clinic, 54 Ethnikis Antistaseos, 15231 Athens, Greece.
Phys Med Biol. 2022 Jun 24;67(13). doi: 10.1088/1361-6560/ac783b.
The diversity in technical configuration between clinically available radiosurgery systems, results in accordingly diverse treatment times for the same physical dose prescription, spanning from several min to more than 1 h. This, combined with evidence supporting the impact of dose delivery temporal pattern on the bio-effectiveness of low-LET radiation treatments, challenges the 'acute exposure' assumption adopted clinically to estimate the biological outcome of a given treatment scheme under the concept of biologically effective dose (BED).: In this work, the treatment plans of 30 patients underwent CyberKnife radiosurgery for vestibular schwannoma (VS), prescribing a marginal dose of 13 Gy to the tumor, were retrospectively reviewed and the corresponding dose distributions were resolved in the temporal domain. For this purpose, the dose delivery timeline for each treatment was calculated based on relevant treatment plan data and technical specifications of the CyberKnife system, while dosimetry data were independently acquired on a CT-based digital model of each patient using an in-house developed dose calculation algorithm.: Results showed that CyberKnife delivers highly inhomogeneous dose rate distributions in the temporo-spatial domain. This influences the delivered BED levels due to alterations in the sublethal damage repair (SLR) occurring within the treatment session. Using a BED framework involving SLR effects, it was shown that each physical dose iso-surface is associated with a BEDrange. For the patient cohort studied, a typical range of 2%, with respect to the mean BEDvalue was found at 1.: The marginal BEDdelivered to the tumor by the prescription dose iso-surface deteriorates with treatment time, involving both beam-on time and beam-off gaps. For treatment time,, between 21 and 50 min, this can be expressed byBEDslr(Gy2.47)=-0.35±2.8%∙Tmin+(76.74±0.4%).Compared to the acute exposure approach, a BED 'loss' of 21% is associated with the delivery of 13 Gy to the VS-tumor in 35 min.
临床可用的放射外科系统在技术配置方面存在差异，因此对于相同的物理剂量处方，治疗时间也相应地有所不同，从几分钟到 1 个多小时不等。这一点，再加上有证据表明低 LET 辐射治疗的剂量传递时间模式对生物效应有影响，这就对临床上采用“急性暴露”假设来估计特定治疗方案的生物学结果提出了挑战，这种假设是基于生物有效剂量（BED）的概念。在这项工作中，回顾性地审查了 30 名接受 CyberKnife 放射外科治疗前庭神经鞘瘤（VS）的患者的治疗计划，为肿瘤规定了 13 Gy 的边缘剂量，并在时间域中解决了相应的剂量分布。为此，根据相关的治疗计划数据和 CyberKnife 系统的技术规格，计算了每个治疗的剂量传递时间线，同时使用自主开发的剂量计算算法，在每个患者的基于 CT 的数字模型上独立获取剂量数据。结果表明，CyberKnife 在时-空域中提供高度不均匀的剂量率分布。这会影响 BED 水平，因为在治疗过程中会发生亚致死损伤修复（SLR）的改变。使用涉及 SLR 效应的 BED 框架，表明每个物理剂量等剂量面都与 BED 范围相关。对于所研究的患者队列，发现典型的范围为 2%，相对于平均 BED 值。通过处方剂量等剂量面输送到肿瘤的边缘 BED 随着治疗时间的延长而恶化，包括照射时间和照射间隙。对于治疗时间 tmin 在 21 到 50 分钟之间，可以表示为 BEDslr（Gy2.47）=-0.35±2.8%×Tmin+（76.74±0.4%）。与急性暴露方法相比，将 13 Gy 输送到 VS 肿瘤需要 35 分钟，这与 BED 损失 21%相关。
