不同调强放疗输送技术的生物学效应：静态调强、动态调强和螺旋断层放疗。

Biological effect of different IMRT delivery techniques: SMLC, DMLC, and helical tomotherapy.

机构信息

Department of Radiation Oncology, Karmanos Cancer Center, Wayne State University School of Medicine, Detroit, Michigan 48201, USA.

出版信息

Med Phys. 2010 Feb;37(2):762-70. doi: 10.1118/1.3284369.

DOI:10.1118/1.3284369

PMID:20229886

Abstract

PURPOSE

Intensity-modulated radiotherapy (IMRT) is delivered using a variety of techniques with differing temporal dose characteristics. Spatial dose metrics are generally used to evaluate treatment plan quality. However, the use of this information alone neglects the effects of the significant differences in dose delivery duration and dose accumulation patterns, both of which can impact cell survival. This study uses the linear-quadratic model with dose protraction corrections to evaluate the biological effectiveness of different IMRT delivery techniques, including fixed gantry IMRT in SMLC (step-and-shoot) and DMLC (sliding window) modes and a rotational IMRT technique (helical tomotherapy) for the treatment of prostate and head/neck sites.

METHODS

The temporal dose pattern was measured using a small volume ion chamber (A1SL--0.057 cm3) to calculate the protraction factor, and biological equivalent dose (BED) was calculated for a range of repair half-times and alpha/beta ratios. The treatment BED is compared to an ideal delivery of the target prescription dose, in which dose is delivered instantaneously (G(t0) = 1), to evaluate loss in biological effectiveness due to protraction in delivery. In the case of a conventional prescription, the loss in biological effectiveness was further evaluated using published tumor control probability (TCP) data.

RESULTS

With SMLC and DMLC IMRT delivery, for both prostate and head/neck, the expected additional loss in BED is about 1% compared to 3D CRT, which corresponds to a predicted 2%-3% reduction in TCP. For tomotherapy, the prostate BED loss is smaller in comparison to 3D CRT; hence, the authors expect a TCP increase of the order of 2%-3%. The aforementioned differences are due to the dose accumulation time.

CONCLUSIONS

While it is theoretically possible to compensate for changes in biologically effective dose, this would be hindered by large uncertainties in parameters used for such calculations; therefore, it is advantageous to irradiate target volume elements as rapidly as possible. The results of this study indicate that temporal dose delivery pattern is an important component in determining the biological effects of IMRT treatment.

摘要

目的

调强放疗（IMRT）采用多种技术进行治疗，这些技术的剂量具有不同的时间特征。空间剂量指标通常用于评估治疗计划的质量。然而，仅使用这种信息会忽略剂量传递持续时间和剂量积累模式的显著差异的影响，这两者都可能影响细胞存活。本研究使用带有剂量迁延修正的线性二次模型来评估不同调强放疗传递技术的生物学效应，包括固定机架的调强放疗在静态调强（SMLC）模式下的步进-射击（step-and-shoot）和动态调强（DMLC）模式下的滑动窗口（sliding window）以及旋转调强放疗技术（螺旋断层放疗）在前列腺和头颈部的治疗。

方法

使用小体积电离室（A1SL--0.057 cm3）测量时间剂量模式，以计算迁延因子，并计算一系列修复半衰期和α/β比值的生物等效剂量（BED）。将治疗 BED 与目标处方剂量的理想传递进行比较，其中剂量瞬间传递（G(t0) = 1），以评估由于传递迁延导致的生物学效应丧失。对于常规处方，进一步使用已发表的肿瘤控制概率（TCP）数据评估生物效应丧失。