Grogg Kira, Alpert Nathaniel M, Zhu Xuping, Min Chul Hee, Testa Mauro, Winey Brian, Normandin Marc D, Shih Helen A, Paganetti Harald, Bortfeld Thomas, El Fakhri Georges
Center for Advanced Radiological Sciences, Nuclear Medicine and Molecular Imaging, Radiology Department, Massachusetts General Hospital, Boston, Massachusetts.
Department of Radiological Science, College of Health Science, Yonsei University, Wonju, Kangwon, Korea.
Int J Radiat Oncol Biol Phys. 2015 Jun 1;92(2):453-9. doi: 10.1016/j.ijrobp.2015.01.023. Epub 2015 Mar 25.
This work was a proof-of-principle study for the evaluation of oxygen-15 ((15)O) production as an imaging target through the use of positron emission tomography (PET), to improve verification of proton treatment plans and to study the effects of perfusion.
Dynamic PET measurements of irradiation-produced isotopes were made for a phantom and rabbit thigh muscles. The rabbit muscle was irradiated and imaged under both live and dead conditions. A differential equation was fitted to phantom and in vivo data, yielding estimates of (15)O production and clearance rates, which were compared to live versus dead rates for the rabbit and to Monte Carlo predictions.
PET clearance rates agreed with decay constants of the dominant radionuclide species in 3 different phantom materials. In 2 oxygen-rich materials, the ratio of (15)O production rates agreed with the expected ratio. In the dead rabbit thighs, the dynamic PET concentration histories were accurately described using (15)O decay constant, whereas the live thigh activity decayed faster. Most importantly, the (15)O production rates agreed within 2% (P>.5) between conditions.
We developed a new method for quantitative measurement of (15)O production and clearance rates in the period immediately following proton therapy. Measurements in the phantom and rabbits were well described in terms of (15)O production and clearance rates, plus a correction for other isotopes. These proof-of-principle results support the feasibility of detailed verification of proton therapy treatment delivery. In addition, (15)O clearance rates may be useful in monitoring permeability changes due to therapy.
本研究是一项原理验证性研究，旨在通过正电子发射断层扫描（PET）评估氧-15（¹⁵O）生成作为成像靶点，以改进质子治疗计划的验证并研究灌注效应。
对一个模型和兔大腿肌肉进行了辐照产生的同位素的动态PET测量。在活体和死亡状态下对兔肌肉进行辐照和成像。将一个微分方程拟合到模型和体内数据，得出¹⁵O生成率和清除率的估计值，并将其与兔的活体与死亡比率以及蒙特卡罗预测值进行比较。
PET清除率与3种不同模型材料中主要放射性核素种类的衰变常数相符。在2种富氧材料中，¹⁵O生成率的比率与预期比率相符。在死亡的兔大腿中，使用¹⁵O衰变常数准确描述了动态PET浓度变化过程，而活体大腿的放射性活度衰减得更快。最重要的是，不同条件下的¹⁵O生成率在2%以内相符（P>0.5）。
我们开发了一种新方法，用于在质子治疗后立即定量测量¹⁵O的生成率和清除率。根据¹⁵O的生成率和清除率以及对其他同位素的校正，对模型和兔的测量结果进行了很好的描述。这些原理验证结果支持了详细验证质子治疗输送的可行性。此外，¹⁵O清除率可能有助于监测治疗引起的通透性变化。
