Martin Jarad M, Brett Richard, Blyth Jemma, Morrison Stewart, Bryant Daniel, Plank Ashley, Cheuk Robyn, Fay Michael, Dickie Graeme, Yaxley John
Division of Oncology, Cancer Care Services, Royal Brisbane and Women's Hospital, Brisbane, Queensland, Australia.
Brachytherapy. 2011 Nov-Dec;10(6):474-8. doi: 10.1016/j.brachy.2010.10.003. Epub 2010 Nov 26.
The sequencing of external beam radiotherapy (EBRT) and a high-dose-rate brachytherapy (HDRB) boost is often interchangeable in clinical practice. When given before EBRT, HDRB could induce volume alterations in the prostate, which may have significant implications for EBRT dosimetry. We aimed to assess the influence of HDRB on prostate volume and, hence, prostate dosing via subsequent EBRT.
Fifteen men had both pre- and post-HDRB CT performed followed by EBRT. After deidentification, the clinical target volume (CTV) was defined on each CT by a single-blinded observer. Volumes were compared for the pre- and post-HDRB scans in each patient. Radiotherapy planning was performed using the prebrachytherapy volumes aiming for the planning target volume (PTV) to be covered by 43.7Gy. After soft-tissue coregistration, this plan was also applied to the postbrachytherapy volumes.
Median volume increase was 35.4% for the CTV after HDRB. No patient experienced a decrease in CTV volume (range, 0-79% volume increase; p-value<0.001). Median volume increase was 26.1% for the PTVs, with no volume decrease observed (range, 8-56%; p<0.001). PTV proportion achieving dose target (V43.7Gy) decreased by median of 7% (range, 0-21.5%; p=0.004). The minimum dose to the PTV (D(100)%) decreased by a median of 6Gy (range, 0.5-16Gy; p<0.001).
Insertion of HDRB catheters exerts substantial acute volumetric distortion on the prostate. EBRT planning performed on the basis of pre-HDRB imaging only inherently risks underdosing tumor. Planning adjustments based on repeat CT, or dedicated post-HDBT planning, is warranted for men managed with HDRB before EBRT.
在临床实践中，外照射放疗（EBRT）与高剂量率近距离放疗（HDRB）增敏的顺序通常是可互换的。在EBRT之前进行HDRB时，可能会引起前列腺体积变化，这可能对EBRT剂量测定有重大影响。我们旨在评估HDRB对前列腺体积的影响，以及由此对后续EBRT前列腺剂量的影响。
15名男性在HDRB前后均进行了CT扫描，随后接受EBRT。在去识别后，由一名单盲观察者在每次CT上定义临床靶区（CTV）。比较每位患者HDRB前后扫描的体积。使用近距离放疗前的体积进行放射治疗计划，目标是计划靶区（PTV）接受43.7Gy的照射。在软组织配准后，该计划也应用于近距离放疗后的体积。
HDRB后CTV的中位体积增加35.4%。没有患者的CTV体积减小（范围为0 - 79%体积增加；p值<0.001）。PTV的中位体积增加26.1%，未观察到体积减小（范围为8 - 56%；p<0.001）。达到剂量目标（V43.7Gy）的PTV比例中位数下降7%（范围为0 - 21.5%；p = 0.004）。PTV的最小剂量（D(100)%）中位数下降6Gy（范围为0.5 - 16Gy；p<0.001）。
插入HDRB导管会对前列腺产生显著的急性体积变形。仅基于HDRB前成像进行的EBRT计划存在肿瘤剂量不足的固有风险。对于在EBRT前接受HDRB治疗的男性，基于重复CT进行计划调整或进行专门的HDBT后计划是必要的。
