Yu Jen, Zhang Xiaodong, Liao Li, Li Heng, Zhu Ronald, Park Peter C, Sahoo Narayan, Gillin Michael, Li Yupeng, Chang Joe Y, Komaki Ritsuko, Lin Steven H
Proton Therapy Center and Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030 and Maryland Proton Treatment Center, Department of Radiation Oncology, University of Maryland School of Medicine, Baltimore Maryland 21201.
Proton Therapy Center and Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030.
Med Phys. 2016 Mar;43(3):1111-8. doi: 10.1118/1.4940789.
To develop methods for evaluation and mitigation of dosimetric impact due to respiratory and diaphragmatic motion during free breathing in treatment of distal esophageal cancers using intensity-modulated proton therapy (IMPT).
This was a retrospective study on 11 patients with distal esophageal cancer. For each patient, four-dimensional computed tomography (4D CT) data were acquired, and a nominal dose was calculated on the average phase of the 4D CT. The changes of water equivalent thickness (ΔWET) to cover the treatment volume from the peak of inspiration to the valley of expiration were calculated for a full range of beam angle rotation. Two IMPT plans were calculated: one at beam angles corresponding to small ΔWET and one at beam angles corresponding to large ΔWET. Four patients were selected for the calculation of 4D-robustness-optimized IMPT plans due to large motion-induced dose errors generated in conventional IMPT. To quantitatively evaluate motion-induced dose deviation, the authors calculated the lowest dose received by 95% (D95) of the internal clinical target volume for the nominal dose, the D95 calculated on the maximum inhale and exhale phases of 4D CT DCT0 andDCT50 , the 4D composite dose, and the 4D dynamic dose for a single fraction.
The dose deviation increased with the average ΔWET of the implemented beams, ΔWETave. When ΔWETave was less than 5 mm, the dose error was less than 1 cobalt gray equivalent based on DCT0 and DCT50 . The dose deviation determined on the basis of DCT0 and DCT50 was proportionally larger than that determined on the basis of the 4D composite dose. The 4D-robustness-optimized IMPT plans notably reduced the overall dose deviation of multiple fractions and the dose deviation caused by the interplay effect in a single fraction.
In IMPT for distal esophageal cancer, ΔWET analysis can be used to select the beam angles that are least affected by respiratory and diaphragmatic motion. To further reduce dose deviation, the 4D-robustness optimization can be implemented for IMPT planning. Calculation of DCT0 and DCT50 is a conservative method to estimate the motion-induced dose errors.
开发在使用强度调制质子治疗（IMPT）治疗远端食管癌的自由呼吸过程中，评估和减轻呼吸及膈肌运动引起的剂量学影响的方法。
这是一项对11例远端食管癌患者的回顾性研究。对于每位患者，获取了四维计算机断层扫描（4D CT）数据，并在4D CT的平均相位上计算了标称剂量。计算了在整个射束角度旋转范围内，从吸气峰值到呼气谷值覆盖治疗体积的水等效厚度变化（ΔWET）。计算了两个IMPT计划：一个在对应小ΔWET的射束角度，另一个在对应大ΔWET的射束角度。由于传统IMPT中产生的大运动诱导剂量误差，选择了4例患者来计算4D稳健性优化的IMPT计划。为了定量评估运动诱导的剂量偏差，作者计算了标称剂量下内部临床靶体积95%所接受的最低剂量（D95）、在4D CT的最大吸气和呼气相位DCT0和DCT50上计算的D95、4D复合剂量以及单次分割的4D动态剂量。
剂量偏差随着所实施射束的平均ΔWET（ΔWETave）增加而增大。当ΔWETave小于5毫米时，基于DCT0和DCT50的剂量误差小于1钴灰当量。基于DCT0和DCT50确定的剂量偏差比基于4D复合剂量确定的剂量偏差成比例地更大。4D稳健性优化的IMPT计划显著降低了多个分割的总体剂量偏差以及单次分割中相互作用效应引起的剂量偏差。
在远端食管癌的IMPT中，ΔWET分析可用于选择受呼吸和膈肌运动影响最小的射束角度。为了进一步降低剂量偏差，可对IMPT计划实施4D稳健性优化。计算DCT0和DCT50是估计运动诱导剂量误差的保守方法。
