Smith Ryan L, Panettieri Vanessa, Lancaster Craig, Mason Natasha, Franich Rick D, Millar Jeremy L
William Buckland Radiation Oncology, The Alfred Hospital, Commercial Road, Melbourne, 3004, Australia,
Australas Phys Eng Sci Med. 2015 Mar;38(1):55-61. doi: 10.1007/s13246-014-0317-2. Epub 2014 Dec 7.
To investigate how the dwell time deviation constraint (DTDC) parameter, applied to inverse planning by simulated annealing (IPSA) optimisation limits large dwell times from occurring in each catheter and to characterise the effect on the resulting dosimetry for prostate high dose rate (HDR) brachytherapy treatment plans. An unconstrained IPSA optimised treatment plan, using the Oncentra Brachytherapy treatment planning system (version 4.3, Nucletron an Elekta company, Elekta AB, Stockholm, Sweden), was generated for 20 consecutive HDR prostate brachytherapy patients, with the DTDC set to zero. Successive constrained optimisation plans were also created for each patient by increasing the DTDC parameter by 0.2, up to a maximum value of 1.0. We defined a "plan modulation index", to characterise the change of dwell time modulation as the DTDC parameter was increased. We calculated the dose volume histogram indices for the PTV (D90, V100, V150, V200%) and urethra (D10%) to characterise the effect on the resulting dosimetry. The average PTV D90% decreases as the DTDC is applied, on average by only 1.5 %, for a DTDC = 0.4. The measures of high dose regions in the PTV, V150 and V200%, increase on average by less than 5 and 2 % respectively. The net effect of DTDC on the modulation of dwell times has been characterised by the introduction of the plan modulation index. DTDC applied during IPSA optimisation of HDR prostate brachytherapy plans reduce the occurrence of large isolated dwell times within individual catheters. The mechanism by which DTDC works has been described and its effect on the modulation of dwell times has been characterised. The authors recommend using a DTDC parameter no greater than 0.4 to obtain a plan with dwell time modulation comparable to a geometric optimised plan. This yielded on average a 1.5 % decrease in PTV coverage and an acceptable increase in V150%, without compromising the urethral dose.
研究应用于模拟退火逆向计划（IPSA）优化的驻留时间偏差约束（DTDC）参数如何限制每个导管中出现过长的驻留时间，并描述其对前列腺高剂量率（HDR）近距离放射治疗计划的剂量学结果的影响。使用Oncentra Brachytherapy治疗计划系统（版本4.3，Nucletron公司，隶属于Elekta公司，瑞典斯德哥尔摩Elekta AB），为20例连续的HDR前列腺近距离放射治疗患者生成了一个无约束的IPSA优化治疗计划，其中DTDC设置为零。通过将DTDC参数每次增加0.2直至最大值1.0，还为每位患者创建了连续的约束优化计划。我们定义了一个“计划调制指数”，以描述随着DTDC参数增加驻留时间调制的变化。我们计算了计划靶体积（PTV）（D90、V100、V150、V200%）和尿道（D10%）的剂量体积直方图指数，以描述对剂量学结果的影响。当应用DTDC时，平均PTV D90%会降低，对于DTDC = 0.4，平均仅降低1.5%。PTV中高剂量区域的测量值V150和V200%平均分别增加不到5%和2%。通过引入计划调制指数来描述DTDC对驻留时间调制的净效应。在HDR前列腺近距离放射治疗计划的IPSA优化过程中应用DTDC可减少单个导管内出现过长孤立驻留时间的情况。已经描述了DTDC的作用机制，并对其对驻留时间调制的影响进行了描述。作者建议使用不大于0.4的DTDC参数，以获得与几何优化计划相当的驻留时间调制计划。这平均使PTV覆盖率降低1.5%，V150%有可接受的增加，同时不影响尿道剂量。
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