Radiation Medicine Program, Princess Margaret Hospital, University Health Network, Toronto, Ontario M5G 2M9, Canada.
Med Phys. 2010 Feb;37(2):505-15. doi: 10.1118/1.3276775.
To evaluate the utility of a new complexity metric, the modulation complexity score (MCS), in the treatment planning and quality assurance processes and to evaluate the relationship of the metric with deliverability.
A multisite (breast, rectum, prostate, prostate bed, lung, and head and neck) and site-specific (lung) dosimetric evaluation has been completed. The MCS was calculated for each beam and the overall treatment plan. A 2D diode array (MapCHECK, Sun Nuclear, Melbourne, FL) was used to acquire measurements for each beam. The measured and planned dose (PINNACLE3, Phillips, Madison, WI) was evaluated using different percent differences and distance to agreement (DTA) criteria (3%/ 3 mm and 2%/ 1 mm) and the relationship between the dosimetric results and complexity (as measured by the MCS or simple beam parameters) assessed.
For the multisite analysis (243 plans total), the mean MCS scores for each treatment site were breast (0.92), rectum (0.858), prostate (0.837), prostate bed (0.652), lung (0.631), and head and neck (0.356). The MCS allowed for compilation of treatment site-specific statistics, which is useful for comparing different techniques, as well as for comparison of individual treatment plans with the typical complexity levels. For the six plans selected for dosimetry, the average diode percent pass rate was 98.7% (minimum of 96%) for 3%/3 mm evaluation criteria. The average difference in absolute dose measurement between the planned and measured dose was 1.7 cGy. The detailed lung analysis also showed excellent agreement between the measured and planned dose, as all beams had a diode percentage pass rate for 3%/3 mm criteria of greater than 95.9%, with an average pass rate of 99.0%. The average absolute maximum dose difference for the lung plans was 0.7 cGy. There was no direct correlation between the MCS and simple beam parameters which could be used as a surrogate for complexity level (i.e., number of segments or MU). An evaluation criterion of 2%/ 1 mm reliably allowed for the identification of beams that are dosimetrically robust. In this study we defined a robust beam or plan as one that maintained a diode percentage pass rate greater than 90% at 2%/ 1 mm, indicating delivery that was deemed accurate when compared to the planned dose, even under stricter evaluation criterion. MCS and MU threshold criteria were determined by defining a required specificity of 1.0. A MCS threshold of 0.8 allowed for identification of robust deliverability with a sensitivity of 0.36. In contrast, MU had a lower sensitivity of 0.23 for a threshold of 50 MU.
The MCS allows for a quantitative assessment of plan complexity, on a fixed scale, that can be applied to all treatment sites and can provide more information related to dose delivery than simple beam parameters. This could prove useful throughout the entire treatment planning and QA process.
评估一种新的复杂度度量——调制复杂度评分（MCS）在治疗计划和质量保证过程中的效用，并评估该度量与可交付性的关系。
已完成多站点（乳房、直肠、前列腺、前列腺床、肺和头颈部）和站点特异性（肺）剂量学评估。为每个射束和整个治疗计划计算了 MCS。使用二维二极管阵列（MapCHECK，Sun Nuclear，佛罗里达州墨尔本）获取每个射束的测量值。使用不同的百分比差异和距离符合度（DTA）标准（3%/3mm 和 2%/1mm）评估测量和计划的剂量（PINNACLE3，Phillips，威斯康星州麦迪逊），并评估剂量学结果与复杂性（由 MCS 或简单射束参数测量）之间的关系。
对于多站点分析（总共 243 个计划），每个治疗部位的平均 MCS 评分分别为乳房（0.92）、直肠（0.858）、前列腺（0.837）、前列腺床（0.652）、肺（0.631）和头颈部（0.356）。MCS 允许对特定于治疗部位的统计数据进行编译，这对于比较不同的技术以及比较单个治疗计划与典型的复杂度水平都很有用。对于选择进行剂量学评估的六个计划，对于 3%/3mm 评估标准，二极管百分通过率的平均值为 98.7%（最低为 96%）。计划剂量与测量剂量之间的绝对剂量差异平均值为 1.7cGy。详细的肺部分析也显示出测量剂量与计划剂量之间极好的一致性，因为所有射束的 3%/3mm 标准的二极管百分通过率均大于 95.9%，平均通过率为 99.0%。肺部计划的平均绝对最大剂量差异为 0.7cGy。MCS 与简单射束参数之间没有直接的相关性，这些参数可以作为复杂度水平的替代指标（即，段数或 MU 的数量）。2%/1mm 的评估标准可以可靠地识别出在剂量学上稳健的射束。在这项研究中，我们将稳健的射束或计划定义为在 2%/1mm 时保持二极管百分通过率大于 90%的射束或计划，这表明与计划剂量相比，即使在更严格的评估标准下，也可以实现被认为是准确的交付。通过定义特定性为 1.0 来确定 MCS 和 MU 的阈值标准。MCS 阈值为 0.8 可以识别出具有 0.36 灵敏度的稳健可交付性。相比之下，MU 的阈值为 50MU 时，灵敏度为 0.23。
MCS 允许对计划复杂度进行定量评估，其在固定范围内，可以应用于所有治疗部位，并可以提供比简单射束参数更多的与剂量传递相关的信息。这在整个治疗计划和 QA 过程中可能会很有用。
