Hopewell John W, Millar William T, Lindquist Christer, Nordström Håkan, Lidberg Pär, Gårding Jonas
Green Templeton College and Particle Therapy Cancer Research Institute, University of Oxford, Oxford, UK.
Beatson Oncology Centre, Gartnavel Hospital, Glasgow, UK.
J Radiosurg SBRT. 2013;2(4):257-271.
In the application of stereotactic radiosurgery, using the Gamma Knife, there are large variations in the overall treatment time for the same prescription dose, given in a single treatment session, for different patients. This is due to not only changes in the activity of the Cobolt-60 sources, but also to variations in the number of iso-centers used, the collimator size for a particular iso-center, and the time gap between the different iso-centers. Although frequently viewed as a single dose treatment the concept of biologically effective dose (BED), incorporating concurrent fast and a slow components of repair of sublethal damage, would imply potential variations in BED because of the influence of these different variables associated with treatment. This was investigated in 26 patients, treated for Vestibular Schwannomas, using the Series B Gamma-Knife, between 1999 and 2005. The iso-center number varied between 2 and 13, and the overall treatment time from 25.4-129.58 min. The prescription doses varied from 10-14 Gy. To obtain physical dose and dose-rates from each iso-center, in a number of locations in the region of interest, a prototype version of the Leksell GammaPlan was used. For an individual patient, BED values varied by up to 15% for a given physical iso-dose. This was due to variation in the dose prescription at different locations on that iso-dose. Between patients there was a decline in the range of BED values as the overall treatment time increased. This increased treatment time was partly a function of the slow decline in the activity of the sources with time but predominantly due to changes in the number of iso-centers used. Thus, variations in BED values did not correlate with prescription dose but was modified by the overall treatment time.
在立体定向放射外科手术中，使用伽玛刀时，对于相同的处方剂量，在单次治疗中，不同患者的总体治疗时间存在很大差异。这不仅是由于钴 - 60源活性的变化，还由于所使用的等中心数量、特定等中心的准直器尺寸以及不同等中心之间的时间间隔的变化。尽管通常被视为单次剂量治疗，但考虑到亚致死性损伤修复的快速和缓慢成分的生物有效剂量（BED）概念，由于与治疗相关的这些不同变量的影响，BED可能存在潜在差异。在1999年至2005年期间，对26例接受前庭神经鞘瘤治疗的患者使用B型伽玛刀进行了此项研究。等中心数量在2至13之间变化，总体治疗时间为25.4 - 129.58分钟。处方剂量从10 - 14 Gy不等。为了在感兴趣区域的多个位置获得每个等中心的物理剂量和剂量率，使用了Leksell GammaPlan的原型版本。对于个体患者，对于给定的物理等剂量，BED值变化高达15%。这是由于该等剂量不同位置处的剂量处方变化所致。在患者之间，随着总体治疗时间的增加，BED值的范围有所下降。这种治疗时间的增加部分是由于源活性随时间的缓慢下降，但主要是由于所使用的等中心数量的变化。因此，BED值的变化与处方剂量无关，但受总体治疗时间的影响。
