Mavroidis Panayiotis, Katsilieri Zaira, Kefala Vasiliki, Milickovic Natasa, Papanikolaou Nikos, Karabis Andreas, Zamboglou Nikolaos, Baltas Dimos
Department of Medical Radiation Physics, Karolinska Institutet and Stockholm University, Sweden.
Department of Medical Physics & Engineering, Strahlenklinik, Klinikum Offenbach GmbH, Germany.
J Contemp Brachytherapy. 2010 Sep;2(3):117-128. doi: 10.5114/jcb.2010.16923. Epub 2010 Oct 13.
One of the issues that a planner is often facing in HDR brachytherapy is the selective existence of high dose volumes around some few dominating dwell positions. If there is no information available about its necessity (e.g. location of a GTV), then it is reasonable to investigate whether this can be avoided. This effect can be eliminated by limiting the free modulation of the dwell times. HIPO, an inverse treatment plan optimization algorithm, offers this option. In treatment plan optimization there are various methods that try to regularize the variation of dose non-uniformity using purely dosimetric measures. However, although these methods can help in finding a good dose distribution they do not provide any information regarding the expected treatment outcome as described by radiobiology based indices.
The quality of 12 clinical HDR brachytherapy implants for prostate utilizing HIPO and modulation restriction (MR) has been compared to alternative plans with HIPO and free modulation (without MR). All common dose-volume indices for the prostate and the organs at risk have been considered together with radiobiological measures. The clinical effectiveness of the different dose distributions was investigated by calculating the response probabilities of the tumors and organs-at-risk (OARs) involved in these prostate cancer cases. The radiobiological models used are the Poisson and the relative seriality models. Furthermore, the complication-free tumor control probability, and the biologically effective uniform dose ([Formula: see text]) were used for treatment plan evaluation and comparison.
Our results demonstrate that HIPO with a modulation restriction value of 0.1-0.2 delivers high quality plans which are practically equivalent to those achieved with free modulation regarding the clinically used dosimetric indices. In the comparison, many of the dosimetric and radiobiological indices showed significantly different results. The modulation restricted clinical plans demonstrated a lower total dwell time by a mean of 1.4% that was proved to be statistically significant ( = 0.002). The HIPO with MR treatment plans produced a higher by 0.5%, which stemmed from a better sparing of the OARs by 1.0%.
Both the dosimetric and radiobiological comparison shows that the modulation restricted optimization gives on average similar results with the optimization without modulation restriction in the examined clinical cases. Concluding, based on our results, it appears that the applied dwell time regularization technique is expected to introduce a minor improvement in the effectiveness of the optimized HDR dose distributions.
在高剂量率近距离放射治疗中，计划者经常面临的一个问题是在少数几个主要驻留位置周围选择性地存在高剂量体积。如果没有关于其必要性的可用信息（例如靶区的位置），那么研究是否可以避免这种情况是合理的。通过限制驻留时间的自由调制可以消除这种影响。HIPO是一种逆向治疗计划优化算法，提供了此选项。在治疗计划优化中，有各种方法试图使用纯剂量学措施来规范剂量不均匀性的变化。然而，尽管这些方法有助于找到良好的剂量分布，但它们没有提供任何关于基于放射生物学指标所描述的预期治疗结果的信息。
将利用HIPO和调制限制（MR）的12例前列腺临床高剂量率近距离放射治疗植入的质量与采用HIPO和自由调制（无MR）的替代计划进行了比较。考虑了前列腺和危及器官的所有常见剂量体积指标以及放射生物学指标。通过计算这些前列腺癌病例中涉及的肿瘤和危及器官（OARs）的反应概率，研究了不同剂量分布的临床有效性。所使用的放射生物学模型是泊松模型和相对序列性模型。此外，无并发症肿瘤控制概率和生物学等效均匀剂量（[公式：见正文]）用于治疗计划的评估和比较。
我们的结果表明，调制限制值为0.1 - 0.2的HIPO可提供高质量的计划，就临床使用的剂量学指标而言，实际上与自由调制所实现的计划相当。在比较中，许多剂量学和放射生物学指标显示出显著不同的结果。调制限制的临床计划的总驻留时间平均降低了1.4%，这被证明具有统计学意义（ = 0.002）。采用MR的HIPO治疗计划使[指标]提高了0.5%，这源于对OARs更好的保护，保护程度提高了1.0%。
剂量学和放射生物学比较均表明，在检查的临床病例中，调制限制优化平均给出的结果与无调制限制优化的结果相似。总之，根据我们的结果，似乎所应用的驻留时间正则化技术有望在优化的高剂量率近距离放射治疗剂量分布的有效性方面带来微小的改善。
