Department of Radiation Oncology, MD Anderson Cancer Center Orlando, Orlando, Florida, USA.
Int J Radiat Oncol Biol Phys. 2012 Dec 1;84(5):1220-5. doi: 10.1016/j.ijrobp.2012.01.046. Epub 2012 Apr 6.
To determine the daily and cumulative dosimetric effects of intrafraction prostate motion on step-and-shoot (SNS) intensity-modulated radiation therapy (IMRT) plans, to evaluate the correlation of dosimetric effect with motion-based metrics, and to compare on a fraction-by-fraction basis the dosimetric effect induced in SNS and helical tomotherapy plans.
Intrafraction prostate motion data from 486 fractions and 15 patients were available. A motion-encoded dose calculation technique was used to determine the variation of the clinical target volume (CTV) D(95%) values with respect to the static plan for SNS plans. The motion data were analyzed separately, and the correlation coefficients between various motion-based metrics and the dosimetric effect were determined. The dosimetric impact was compared with that incurred during another IMRT technique to assess correlation across different delivery techniques.
The mean (±1 standard deviation [SD]) change in D(95%) in the CTV over all 486 fractions was 0.2 ± 0.5%. After the delivery of five and 12 fractions, the mean (±1 SD) changes over the 15 patients in CTV D(95%) were 0.0 ± 0.2% and 0.1 ± 0.2%, respectively. The correlation coefficients between the CTV D(95%) changes and the evaluated motion metrics were, in general, poor and ranged from r = -0.2 to r = -0.39. Dosimetric effects introduced by identical motion in SNS and helical tomotherapy IMRT techniques were poorly correlated with a correlation coefficient of r = 0.32 for the CTV.
The dosimetric impact of intrafraction prostate motion on the CTV is, in general, small. In only 4% of all fractions did the dosimetric consequence exceed 1% in the CTV. As expected, the cumulative effect was further reduced with fractionation. The poor correlations between the calculated motion parameters and the subsequent dosimetric effect implies that motion-based thresholds are of limited value in predicting the dosimetric impact of intrafraction motion. The dosimetric effects between the two evaluated delivery techniques were poorly correlated.
确定分次内前列腺运动对步进式（SNS）强度调制放射治疗（IMRT）计划的日剂量和累积剂量的影响，评估剂量效应与运动指标的相关性，并逐部分比较 SNS 和螺旋断层放疗计划引起的剂量效应。
有 486 个分次和 15 个患者的分次内前列腺运动数据。使用运动编码剂量计算技术来确定 SNS 计划的临床靶区（CTV）D95%值相对于静态计划的变化。单独分析运动数据，并确定各种运动指标与剂量效应之间的相关系数。比较剂量效应与另一种 IMRT 技术引起的剂量效应，以评估不同递送技术之间的相关性。
在所有 486 个分次中，CTV 的 D95%的平均（±1 标准差[SD]）变化为 0.2 ± 0.5%。在 15 个患者中，在进行 5 次和 12 次治疗后，CTV D95%的平均（±1 SD）变化分别为 0.0 ± 0.2%和 0.1 ± 0.2%。CTV D95%变化与评估的运动指标之间的相关系数通常较差，范围从 r = -0.2 到 r = -0.39。SNS 和螺旋断层放疗 IMRT 技术中相同运动引起的剂量效应相关性较差，CTV 的相关系数为 r = 0.32。
分次内前列腺运动对 CTV 的剂量影响通常较小。只有 4%的分次中 CTV 的剂量后果超过 1%。如预期的那样，随着分次的进行，累积效应进一步降低。计算的运动参数与随后的剂量效应之间的相关性较差表明，基于运动的阈值在预测分次内运动的剂量效应方面具有一定的局限性。两种评估的递送技术之间的剂量效应相关性较差。
