Abstract：
To recalculate biological effective dose values (BED) for radio-surgical treatments of acoustic neuroma from a previous study. BEDs values were previously overestimated by only using beam-on times in calculations, so excluding the important beam-off-times (when deoxyribonucleic acid repair continues) which contribute to the overall treatment time. Simple BED estimations using a mono-exponential approximation may not always be appropriate but if used should include overall treatment time.
Time intervals between isocenters were estimated. These were especially important for the Gamma Knife Model 4C cases since manual changes significantly increase overall treatment times. Individual treatment parameters, such as iso-center number, beam-on-time, and beam-off-time, were then used to calculate BED values using a more appropriate bi-exponential model that includes fast and slow components of DNA damage repair over a wider time range.
The revised BED estimates differed significantly from previously published values. The overestimates of BED, obtained using beam-on-time only, varied from 0%-40.3%. BED subclasses, each with a BED range of 5 Gy2.47, indicated that revised values were consistently reduced when compared with originally quoted values, especially for 4C compared with Perfexion cases. Furthermore, subdivision of 4C cases by collimator number further emphasized the impact of scheduled gap times on BED. Further analysis demonstrated important limitations of the mono-exponential model. Target volume was a major confounding factor in the interpretation of the results of this study.
BED values should be estimated by including beam-on and beam-off times. Suggestions are provided for more accurate BED estimations in future studies.
Time intervals between isocenters were estimated. These were especially important for the Gamma Knife Model 4C cases since manual changes significantly increase overall treatment times. Individual treatment parameters, such as iso-center number, beam-on-time, and beam-off-time, were then used to calculate BED values using a more appropriate bi-exponential model that includes fast and slow components of DNA damage repair over a wider time range.
The revised BED estimates differed significantly from previously published values. The overestimates of BED, obtained using beam-on-time only, varied from 0%-40.3%. BED subclasses, each with a BED range of 5 Gy2.47, indicated that revised values were consistently reduced when compared with originally quoted values, especially for 4C compared with Perfexion cases. Furthermore, subdivision of 4C cases by collimator number further emphasized the impact of scheduled gap times on BED. Further analysis demonstrated important limitations of the mono-exponential model. Target volume was a major confounding factor in the interpretation of the results of this study.
BED values should be estimated by including beam-on and beam-off times. Suggestions are provided for more accurate BED estimations in future studies.
摘要：
目的：从先前的研究中重新计算用于放射外科（SRS）治疗听神经瘤的生物有效剂量值（BED）。以前仅在计算中使用开束时间来高估BED值，因此，排除了重要的束关闭时间（当DNA修复继续），这有助于整个治疗时间。使用单指数近似的简单BED估计可能并不总是合适的，但如果使用，应包括总体治疗时间。
方法：估计等中心之间的时间间隔。这些对于伽玛刀4C型病例尤其重要,因为手动改变显著增加总体治疗时间。个别治疗参数，如等中心号码，然后使用更合适的双指数模型计算BED值，该模型包括在更宽的时间范围内DNA损伤修复的快速和慢速成分。
结果：修订后的BED估计值与先前公布的值有显著差异。床的高估，仅使用波束接通时间获得，从0-40.3%不等。BED子类，每个BED范围为5Gy2.47，表明与原始引用值相比，修订值始终降低，尤其是4C与Perfexion病例相比。此外，通过准直器数量细分4C例，进一步强调了预定间隙时间对BED的影响。进一步的分析表明了单指数模型的重要局限性。目标体积是解释本研究结果的主要混杂因素。
结论：BED值应该通过包括波束开启和波束关闭时间来估计。为未来研究中更准确的BED估计提供了建议。
方法：估计等中心之间的时间间隔。这些对于伽玛刀4C型病例尤其重要,因为手动改变显著增加总体治疗时间。个别治疗参数，如等中心号码，然后使用更合适的双指数模型计算BED值，该模型包括在更宽的时间范围内DNA损伤修复的快速和慢速成分。
结果：修订后的BED估计值与先前公布的值有显著差异。床的高估，仅使用波束接通时间获得，从0-40.3%不等。BED子类，每个BED范围为5Gy2.47，表明与原始引用值相比，修订值始终降低，尤其是4C与Perfexion病例相比。此外，通过准直器数量细分4C例，进一步强调了预定间隙时间对BED的影响。进一步的分析表明了单指数模型的重要局限性。目标体积是解释本研究结果的主要混杂因素。
结论：BED值应该通过包括波束开启和波束关闭时间来估计。为未来研究中更准确的BED估计提供了建议。
