Steggerda Marcel J, van der Poel Henk G, Moonen Luc M F
Department of Radiation Oncology, The Netherlands Cancer Institute, Antoni van Leeuwenhoek Hospital, Amsterdam, The Netherlands.
Brachytherapy. 2010 Oct-Dec;9(4):319-27. doi: 10.1016/j.brachy.2009.07.010. Epub 2010 Aug 6.
Reduction of the number of implantation needles for prostate brachytherapy will shorten the duration of implantation procedures and possibly reduce trauma-related morbidity. The purpose of this study was to investigate possibilities for the minimization of the number of needles and to investigate the consequences for the dose distribution.
A planning study for six different prostate volumes was performed. The number of needles was minimized by changing fixed 1cm interseed spacing to free interseed spacing within the needles and by increasing the seed activity. Dose-volume parameters of prostate and organs at risk (OAR) bladder, rectum, and urethra were determined. For plans with different needle and seed configurations, the sensitivity for random seed placement inaccuracies was tested. Dose distributions of realized implants based on fixed (n=21) and free interseed spacing (n=21) were compared.
The average number of needles (±1 standard deviation) could be reduced from 18.8±3.6 to 12.7±2.9 (-33%) when changing from fixed interseed spacing to free interseed spacing and subsequently to 7.3±1.0 (-42%) by increasing the seed strength from 0.57U to 1.14U. These needle reductions resulted in increased dose inhomogeneity within the prostate and increased sensitivity of dose-volume parameters of the OAR for random geometrical inaccuracies. Introduction of free interseed spacing in our clinic resulted in very satisfactory dose coverage of the prostate (D(90)=172±17Gy), while the average number of needles was reduced by 30%.
Substantial reduction of the number of implantation needles is possible without compromising adequate dose coverage of the prostate. However, the chance of an unpredicted high dose to the OAR increases as fewer needles are used.
减少前列腺近距离放射治疗中植入针的数量将缩短植入过程的持续时间，并可能降低与创伤相关的发病率。本研究的目的是探讨将针的数量减至最少的可能性，并研究其对剂量分布的影响。
对六个不同前列腺体积进行了计划研究。通过将针内固定的1厘米种子间距改为自由种子间距并增加种子活度，使针的数量减至最少。确定了前列腺及危及器官（膀胱、直肠和尿道）的剂量体积参数。对于具有不同针和种子配置的计划，测试了随机种子放置不准确的敏感性。比较了基于固定（n = 21）和自由种子间距（n = 21）的实际植入的剂量分布。
当从固定种子间距改为自由种子间距，随后将种子强度从0.57U增加到1.14U时，针的平均数量（±1标准差）可从18.8±3.6减少到12.7±2.9（-33%），进而减少到7.3±1.0（-42%）。这些针数量的减少导致前列腺内剂量不均匀性增加，以及危及器官的剂量体积参数对随机几何误差的敏感性增加。在我们的临床中引入自由种子间距导致前列腺的剂量覆盖非常令人满意（D(90)=172±17Gy），而针的平均数量减少了30%。
在不影响前列腺充分剂量覆盖的情况下，可大幅减少植入针的数量。然而，使用的针越少，危及器官出现意外高剂量的可能性就越大。
