Real-time verification of proton dose delivery

描述（由申请人提供）：在质子治疗过程中，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-原子核的相互作用可以留下一个完整的原子核，处于激发态，快速衰减，通常是通过发射一种特征伽马射线，这种现象被称为“瞬发”。这种伽马辐射只发生在质子-核相互作用（因而剂量沉积）发生的地方，而且辐射的能谱取决于被照射组织的特定原子组成。我们假设，通过适当测量质子剂量传递过程中发生的提示伽马射线发射，可以验证剂量传递和被照射组织的组成。这项研究的长期目标是开发一种临床可行的快速伽马成像（PGI）系统，能够测量患者体内辐照组织的组成和密度。本提案的具体目的是：(1)确定质子处理库内伽马射线探测器的响应；(2)确定所提出的PGI方法的图像重建的固有分辨率。为了实现上述目标，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提示发射所需的屏蔽水平和探测器定时响应。利用蒙特卡罗模型计算即时发射探测过程，以确定伽玛射线探测器的有限能量和空间分辨率对采用所提出的PGI方法重建的图像分辨率的影响。基于这些研究的结果，我们将确定测量质子束放疗期间发射的提示伽马射线能谱的总体可行性，以及用所提出的PGI方法重建辐照组织的组成和密度图像的可行性。在质子治疗期间，成像和跟踪组织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辐照组织在治疗过程中停止能力的变化。从测量中获得的停止功率值将允许更准确地计算质子束范围和治疗过程中患者体内的剂量递送，从而提高质子治疗递送的准确性。其次，PGI将提供一种直接的方法来评估辐照组织的变化，如肿瘤缺氧或健康组织在治疗过程中的元素组成，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。

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.