Department of Radiation Oncology, Universitätsklinikum Erlangen, Friedrich-Alexander-Universität Erlangen-Nürnberg, Universitätsstraße 27, 91054, Erlangen, Germany.
Strahlenther Onkol. 2020 Jul;196(7):647-656. doi: 10.1007/s00066-020-01596-x. Epub 2020 Mar 10.
To investigate the dosimetric influence of daily interfractional (inter) setup errors and intrafractional (intra) target motion on the planning target volume (PTV) and the possibility of an offline adaptive radiotherapy (ART) method to correct larger patient positioning uncertainties in image-guided radiotherapy for prostate cancer (PCa).
A CTV (clinical target volume)-to-PTV margin ranging from 15 mm in LR (left-right) and SI (superior-inferior) and 5-10 mm in AP (anterior-posterior) direction was applied to all patients. The dosimetric influence of this margin was retrospectively calculated by analysing systematic and random components of inter and intra errors of 31 consecutive intermediate- and high-risk localized PCa patients using daily cone beam computed tomography and kV/kV (kilo-Voltage) imaging. For each patient inter variation was assessed by observing the first 4 treatment days, which led to an offline ART-based treatment plan in case of larger variations.
Systematic inter uncertainties were larger (1.12 in LR, 2.28 in SI and 1.48 mm in AP) than intra systematic errors (0.44 in LR, 0.69 in SI and 0.80 mm in AP). Same findings for the random error in SI direction with 3.19 (inter) and 2.30 mm (intra), whereas in LR and AP results were alike with 1.89 (inter) and 1.91 mm (intra) and 2.10 (inter) and 2.27 mm (intra), respectively. The calculated margin revealed dimensions of 4-5 mm in LR, 8-9 mm in SI and 6-7 mm in AP direction. Treatment plans which had to be adapted showed smaller variations with 1.12 (LR) and 1.72 mm (SI) for Σ and 4.17 (LR) and 3.75 mm (SI) for σ compared to initial plans with 1.77 and 2.62 mm for Σ and 4.46 and 5.39 mm for σ in LR and SI, respectively.
The currently clinically used margin of 15 mm in LR and SI and 5-10 mm in AP direction includes inter and intra uncertainties. The results show that offline ART is feasible which becomes a necessity with further reductions in PTV margins.
研究每日分次间（inter）摆位误差和分次内（intra）靶区运动对计划靶区（PTV）的剂量学影响，以及在图像引导放疗前列腺癌（PCa）中对较大的患者定位不确定性进行离线自适应放疗（ART）的可能性。
对所有患者采用CTV（临床靶区）-PTV 边界为 15mm（左右）和 5-10mm（前后），SI（上下）。通过分析 31 例中高危局限性 PCa 患者的每日锥形束 CT 和 kV/kV（千伏）成像的分次间和分次内误差的系统和随机分量，回顾性计算该边界的剂量学影响。对于每个患者，观察前 4 天的治疗情况来评估分次间的变化，如果变化较大，则采用离线基于 ART 的治疗计划。
系统性分次间不确定性（LR 为 1.12，SI 为 2.28，AP 为 1.48mm）大于系统性分次内误差（LR 为 0.44，SI 为 0.69，AP 为 0.80mm）。在 SI 方向的随机误差也有同样的发现，分别为 3.19（分次间）和 2.30mm（分次内），而在 LR 和 AP 方向，结果分别为 1.89（分次间）和 1.91mm（分次内）和 2.10（分次间）和 2.27mm（分次内）。计算出的边界在 LR 方向为 4-5mm，SI 方向为 8-9mm，AP 方向为 6-7mm。需要调整的治疗计划显示出较小的变化，Σ的变化为 1.12（LR）和 1.72mm（SI），σ的变化为 4.17（LR）和 3.75mm（SI），而初始计划的 Σ 为 1.77 和 2.62mm，SI 为 4.46 和 5.39mm。
目前临床上在 LR 和 SI 方向使用 15mm 的边界，AP 方向使用 5-10mm 的边界，包括分次间和分次内的不确定性。结果表明，离线 ART 是可行的，随着 PTV 边界的进一步缩小，它将成为必要的手段。
