Mahmoudzadeh Houra, Lee Jenny, Chan Timothy C Y, Purdie Thomas G
Mechanical and Industrial Engineering Department, University of Toronto, Toronto, Ontario M5S 3G8, Canada.
Radiation Medicine Program, UHN Princess Margaret Cancer Centre, Toronto, Ontario M5G 2M9, Canada.
Med Phys. 2015 May;42(5):2212-22. doi: 10.1118/1.4916092.
In left-sided tangential breast intensity modulated radiation therapy (IMRT), the heart may enter the radiation field and receive excessive radiation while the patient is breathing. The patient's breathing pattern is often irregular and unpredictable. We verify the clinical applicability of a heart-sparing robust optimization approach for breast IMRT. We compare robust optimized plans with clinical plans at free-breathing and clinical plans at deep inspiration breath-hold (DIBH) using active breathing control (ABC).
Eight patients were included in the study with each patient simulated using 4D-CT. The 4D-CT image acquisition generated ten breathing phase datasets. An average scan was constructed using all the phase datasets. Two of the eight patients were also imaged at breath-hold using ABC. The 4D-CT datasets were used to calculate the accumulated dose for robust optimized and clinical plans based on deformable registration. We generated a set of simulated breathing probability mass functions, which represent the fraction of time patients spend in different breathing phases. The robust optimization method was applied to each patient using a set of dose-influence matrices extracted from the 4D-CT data and a model of the breathing motion uncertainty. The goal of the optimization models was to minimize the dose to the heart while ensuring dose constraints on the target were achieved under breathing motion uncertainty.
Robust optimized plans were improved or equivalent to the clinical plans in terms of heart sparing for all patients studied. The robust method reduced the accumulated heart dose (D10cc) by up to 801 cGy compared to the clinical method while also improving the coverage of the accumulated whole breast target volume. On average, the robust method reduced the heart dose (D10cc) by 364 cGy and improved the optBreast dose (D99%) by 477 cGy. In addition, the robust method had smaller deviations from the planned dose to the accumulated dose. The deviation of the accumulated dose from the planned dose for the optBreast (D99%) was 12 cGy for robust versus 445 cGy for clinical. The deviation for the heart (D10cc) was 41 cGy for robust and 320 cGy for clinical.
The robust optimization approach can reduce heart dose compared to the clinical method at free-breathing and can potentially reduce the need for breath-hold techniques.
在左侧乳腺切线调强放射治疗（IMRT）中，患者呼吸时心脏可能进入辐射野并接受过量辐射。患者的呼吸模式通常不规则且不可预测。我们验证了一种用于乳腺IMRT的心脏保护稳健优化方法的临床适用性。我们将稳健优化计划与自由呼吸时的临床计划以及使用主动呼吸控制（ABC）的深吸气屏气（DIBH）时的临床计划进行比较。
本研究纳入8例患者，每例患者均使用4D-CT进行模拟。4D-CT图像采集生成了10个呼吸相位数据集。使用所有相位数据集构建平均扫描图像。8例患者中的2例还使用ABC在屏气状态下进行了成像。基于可变形配准，使用4D-CT数据集计算稳健优化计划和临床计划的累积剂量。我们生成了一组模拟呼吸概率质量函数，其代表患者在不同呼吸相位所花费的时间比例。使用从4D-CT数据中提取的一组剂量影响矩阵和呼吸运动不确定性模型，对每位患者应用稳健优化方法。优化模型的目标是在呼吸运动不确定性下，在确保达到靶区剂量约束的同时，将心脏剂量降至最低。
对于所有研究患者，在心脏保护方面，稳健优化计划优于或等同于临床计划。与临床方法相比，稳健方法将累积心脏剂量（D10cc）降低了多达801 cGy，同时还提高了累积全乳靶区体积的覆盖范围。平均而言，稳健方法将心脏剂量（D10cc）降低了364 cGy，将优化乳腺剂量（D99%）提高了477 cGy。此外，稳健方法从计划剂量到累积剂量的偏差较小。稳健方法的优化乳腺（D99%）累积剂量与计划剂量的偏差为12 cGy，而临床方法为445 cGy。心脏（D10cc）的偏差稳健方法为41 cGy，临床方法为320 cGy。
与自由呼吸时的临床方法相比，稳健优化方法可降低心脏剂量，并可能减少屏气技术的需求。
