Real-time verification of proton dose delivery

描述(申请人提供)：在质子治疗治疗期间，质子与患者组织内原子的原子核和束缚电子相互作用。质子与原子核的相互作用可能会留下一个处于激发能量状态的完整原子核，这种能量状态会迅速衰减，通常是通过发射一种特有的伽马射线，这种现象被称为“快速发射”。这种伽马辐射只发生在质子-原子核相互作用(从而发生剂量沉积)的地方，发射的能谱取决于受照射组织的特定原子组成。我们假设，通过适当地测量质子剂量传递过程中发生的即时伽马射线发射，可以验证剂量传递和受照组织的成分。这项研究的长期目标是开发一种临床上可行的即时伽玛成像(PGI)系统，能够测量患者体内照射的组织的成分和密度。这项建议的具体目标是(1)确定质子处理库内伽马射线探测器的响应，以及(2)确定所提议的PGI方法的图像重建的固有分辨率。为了实现所述目标，将进行测量和蒙特卡罗计算，以确定隔离和测量质子束发射过程中的瞬发辐射所需的屏蔽水平和探测器定时响应。根据蒙特卡罗模型对快速发射探测过程的计算将被用来确定伽马射线探测器的有限能量和空间分辨率对用建议的PGI方法重建的图像的分辨率的影响。根据这些研究的结果，我们将确定测量质子束放射治疗过程中发射的瞬发伽马射线能谱以及重建经建议的PGI方法照射的组织的成分和密度图像的总体可行性。一种成像和跟踪质子治疗期间照射组织的元素组成和密度变化的方法的意义是多方面的。首先，这种方法可以直接测量照射组织在治疗过程中的阻止能力的变化。通过测量获得的停止功率值将允许更准确地计算治疗过程中患者体内的质子射程和剂量传输，从而提高质子治疗传输的准确性。其次，PGI将提供一种直接方法来评估照射组织的变化，如肿瘤缺氧或治疗过程中健康组织的元素组成，这些变化可能与肿瘤反应和/或正常组织并发症的发生有关。 公共卫生相关性：这项拟议的研究旨在开发新的方法来测量和成像体内质子放射治疗期间照射的组织的原子组成，使我们能够研究这些组织的生物学变化和反应。这将提供一种手段，在治疗过程中每天测量和跟踪这些组织中元素组成的变化。这种能力将允许监测患者对质子放射治疗的反应(通过测量的组织成分变化)，从而为肿瘤学家提供一种手段，根据他们的测量反应改变和调整针对每个患者的治疗方案。

DESCRIPTION (provided by applicant): During proton therapy treatment, protons interact with both the nucleus and bound electrons of atoms within patient tissue. Proton-nucleus interactions can leave behind an intact atomic nucleus in an excited energy state that quickly decays, frequently through emission of a characteristic gamma-ray, a phenomenon known as "prompt emission". This gamma emission occurs only where proton-nucleus interactions (and thus dose deposition) occur and the energy spectrum of the emission is dependent on the specific atomic composition of the irradiated tissue. We hypothesize that by properly measuring the prompt gamma-ray emission that occurs during proton dose delivery, the dose delivery and the composition of tissue irradiated can be verified. The long term goal of this research is to develop a clinically viable Prompt Gamma Imaging (PGI) system capable of measuring both the composition and density of tissues irradiated within the patient. The specific aims of this proposal are (1) to determine the response of gamma-ray detectors within a proton treatment vault and (2) to determine the inherent resolution of image reconstruction for the proposed PGI method. To achieve the stated aims, both measurements and Monte Carlo calculations will be made to determine the shielding levels and detector timing response required to isolate and measure prompt emission during proton beam delivery. Calculations of the prompt emission detection process from a Monte Carlo model will be used to determine the effects of the finite energy and spatial resolution of the gamma-ray detectors on the resolution of images reconstructed with the proposed PGI method. Based on the results of these studies, we will determine the overall feasibility of measuring the prompt gamma-ray spectra emitted during proton beam radiotherapy and for reconstructing images of the composition and density of tissues irradiated with the proposed PGI method. The significance of a method to image and track changes to the elemental composition and densities of tissues irradiated during proton therapy is multi-fold. First, such a method could allow for the direct measurement of changes to the stopping powers for irradiated tissues over the course of treatment. The stopping power values obtained from measurements would allow for more accurate calculation of proton beam range and dose delivery within the patient over the course of treatment, thus improving accuracy of the proton treatment delivery. Second, PGI would provide a direct method to evaluate changes in irradiated tissues, such as tumor hypoxia or the elemental composition of healthy tissues over the treatment course that could be correlated to tumor response and/or the onset of normal tissue complications. PUBLIC HEALTH RELEVANCE: The proposed research aims to develop novel methods to measure and image the atomic composition of tissues irradiated during proton radiotherapy in-vivo, allowing us to study biological changes and response of these tissues. This would provide a means to measure and track changes to elemental composition in these tissues on a daily basis over the course of treatment. Such capabilities would allow for the monitoring of a patient's response to proton radiotherapy (via measured changes to tissue composition), thus providing a means for the oncologists to change and adapt treatment delivery for each patient individually based on their measured response.