Mount Vernon Centre for Cancer Treatment, Middlesex, UK.
Radiother Oncol. 2009 Nov;93(2):253-8. doi: 10.1016/j.radonc.2009.09.015. Epub 2009 Oct 23.
Fractionated high dose-rate (HDR) brachytherapy in the treatment of prostate cancer relies on reproducible catheter positions for each fraction to ensure adequate tumour coverage while minimising dose to normal tissues. Peri-prostatic oedema may cause caudal displacement of the catheters relative to the prostate gland between fractions. This can be corrected for by changing source dwell positions or by physical re-advancement of catheters before treatment.
Data for 20 consecutive monotherapy patients receiving three HDR fractions of 10.5 Gy per fraction over 2 days were analysed retrospectively. Pre-treatment CT scans were used to assess the effect of catheter movement between fractions on implant quality, with and without movement correction. Implant quality was evaluated using dosimetric parameters.
Compared to the first fraction (f1) the mean inter-fraction caudal movement relative to the prostate base was 7.9 mm (f2) (range 0-21 mm) and 3.9 mm (f3) (range 0-25.5 mm). PTV D90% was reduced without movement correction by a mean of 27.8% (f2) and 32.3% (f3), compared with 5.3% and 5.1%, respectively, with catheter movement correction. Dose to 2 cc of the rectum increased by a mean of 0.69 (f2) and 0.76 Gy (f3) compared with an increase of 0.03 and 0.04 Gy, respectively, with correction. The urethra V12 also increased by a mean of 0.36 (f2) and 0.39 Gy (f3) compared with 0.06 and 0.16 Gy, respectively, with correction.
Inter-fraction correction for catheter movement using pre-treatment imaging is critical to maintain the quality of an implant. Without movement correction there is significant risk of tumour under-dosage and normal tissue over-dosage. The findings of this study justify additional imaging between fractions in order to carry out correction.
在前列腺癌的分次高剂量率（HDR）近距离治疗中，为了确保肿瘤得到充分覆盖，同时使正常组织的剂量最小化，需要对每次治疗的导管位置进行重复。前列腺周围水肿可能会导致导管在分次之间相对于前列腺发生尾向移位。可以通过改变源驻留位置或在治疗前通过物理方式重新推进导管来纠正这种移位。
回顾性分析了 20 例连续接受单药治疗的患者的资料，这些患者在 2 天内接受了 3 次每次 10.5 Gy 的 HDR 治疗。使用治疗前 CT 扫描来评估导管在分次间移动对植入物质量的影响，有无移动校正。使用剂量学参数来评估植入物质量。
与第一次治疗（f1）相比，前列腺基部的导管在分次间的平均尾向移动距离为 7.9mm（f2）（范围 0-21mm）和 3.9mm（f3）（范围 0-25.5mm）。不进行运动校正时，与 f1 相比，PTV D90%分别减少了 27.8%（f2）和 32.3%（f3），而进行导管运动校正时分别减少了 5.3%和 5.1%。与校正相比，直肠 2cc 体积的剂量增加了 0.69（f2）和 0.76Gy（f3），而校正分别增加了 0.03 和 0.04Gy。尿道 V12 也分别增加了 0.36（f2）和 0.39Gy（f3），而校正分别增加了 0.06 和 0.16Gy。
使用治疗前成像对导管运动进行分次校正对于保持植入物的质量至关重要。如果不进行运动校正，肿瘤会存在剂量不足的风险，而正常组织会存在剂量过大的风险。本研究的结果证明，为了进行校正，需要在分次之间进行额外的成像。
