Statistical process control for IMRT dosimetric verification
Statistical process control for IMRT dosimetric verification
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DOI：
10.1118/1.2975144
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发表时间：
2008-10-01
期刊：
影响因子：
3.8
通讯作者：
Sharpe, Michael B.
中科院分区：
文献类型：
--
作者：
Breen, Stephen L.;Moseley, Douglas J.;Sharpe, Michael B.
患者特异性测量通常用于验证调强放疗（IMRT）的剂量学。为了评估我们的IMRT过程的剂量学性能，我们使用统计过程控制（SPC）概念来分析330个头颈部（H&N）治疗计划的测量结果。本工作的目的是：(i)审查一系列连续头颈部治疗计划的剂量测量，以便更好地了解适当的剂量耐受量；（ii）用SPC分析结果，制定测量差异的行动水平；（iii）对临床环境中描述IMRT剂量学所需的测量次数进行估计；（iv）用SPC评估我们的规划系统中的新梁模型。H&N IMRT病例使用PINNACLE3治疗计划系统6.2b或7.6c版本（Philips Medical Systems, Madison， WI）进行计划，并在Varian （Palo Alto， CA）或Elekta （Crawley， UK）直线发电机上进行治疗。作为常规质量保证的一部分，在20厘米直径的圆柱形幻影上重新计算计划，并在高剂量体积（最高剂量的PTV）和低剂量体积（脊髓器官危险，OR）下进行离子室测量。计划剂量和测量剂量之间的差异记录为计划剂量的百分比。随着时间的推移，差异是稳定的。使用PINNACLE(3) 6.2b和Varian直线机的测量结果显示，PTVs的平均差异为0.6% (n=149，范围-4.3%至6.6%)，而OR测量结果显示更大的系统差异（平均4.5%，范围-4.5%至16.3%），这是由于MLC模型在早期版本的规划系统中众所周知的局限性。使用PINNACLE(3) 7.6c和Varian直线机测量显示，PTVs （n=160，范围为-3.0%至5.0%）和ORs（范围为- 5.0%至4.4%）的平均差异为0.2%。PTV数据的能力指数（规格范围与数据范围的比值）为1.3，表明几乎所有测量值都在+/- 5%以内。我们使用SPC工具在规划系统中评估了一种新的光束模型，尽管测量次数较少（n=25），但ptv和or的系统差异分别为-0.6%和0.4%。对这一系列H&N IMRT测量的分析表明，我们的IMRT剂量法随着时间的推移是稳定的，并且在可接受的耐受范围内。这些数据为在规划系统中评估梁模型的变化提供了有用的信息。通过在传统的质量控制程序中加入统计过程控制，IMRT得到了加强。(C) 2008年美国医学物理学家协会。
Patient-specific measurements are typically used to validate the dosimetry of intensity-modulated radiotherapy (IMRT). To evaluate the dosimetric performance over time of our IMRT process, we have used statistical process control (SPC) concepts to analyze the measurements from 330 head and neck (H&N) treatment plans. The objectives of the present work are to: (i) Review the dosimetric measurements of a large series of consecutive head and neck treatment plans to better understand appropriate dosimetric tolerances; (ii) analyze the results with SPC to develop action levels for measured discrepancies; (iii) develop estimates for the number of measurements that are required to describe IMRT dosimetry in the clinical setting; and (iv) evaluate with SPC a new beam model in our planning system. H&N IMRT cases were planned with the PINNACLE3 treatment planning system versions 6.2b or 7.6c (Philips Medical Systems, Madison, WI) and treated on Varian (Palo Alto, CA) or Elekta (Crawley, UK) linacs. As part of regular quality assurance, plans were recalculated on a 20-cm-diam cylindrical phantom, and ion chamber measurements were made in high-dose volumes (the PTV with highest dose) and in low-dose volumes (spinal cord organ-at-risk, OR). Differences between the planned and measured doses were recorded as a percentage of the planned dose. Differences were stable over time. Measurements with PINNACLE(3) 6.2b and Varian linacs showed a mean difference of 0.6% for PTVs (n=149, range, -4.3% to 6.6%), while OR measurements showed a larger systematic discrepancy (mean 4.5%, range -4.5% to 16.3%) that was due to well-known limitations of the MLC model in the earlier version of the planning system. Measurements with PINNACLE(3) 7.6c and Varian linacs demonstrated a mean difference of 0.2% for PTVs (n=160, range, -3.0%, to 5.0%) and -1.0% for ORs (range -5.8% to 4.4%). The capability index (ratio of specification range to range of the data) was 1.3 for the PTV data, indicating that almost all measurements were within +/- 5%. We have used SPC tools to evaluate a new beam model in our planning system to produce a systematic difference of -0.6% for PTVs and 0.4% for ORs, although the number of measurements is smaller (n=25). Analysis of this large series of H&N IMRT measurements demonstrated that our IMRT dosimetry was stable over time and within accepted tolerances. These data provide useful information for assessing alterations to beam models in the planning system. IMRT is enhanced by the addition of statistical process control to traditional quality control procedures. (C) 2008 American Association of Physicists in Medicine.