與光子療法相比，質子束能向目標提供更好的劑量分佈，同時將目標周圍的正常組織的劑 量最小化，在遠端邊緣以外的劑量沉積非常低，盡可能地降低對正常組織的損害。但是，質子射束在射程終點有較大的劑量梯度，這可能造成治療時的劑量分布不確定性。因此，需要在治療計劃中盡可能準確地預測質子束在人體中的劑量分佈，並在治療過程中對其進行良好的監控，例如透過檢測二次粒子來進行體內治療監測。通過質子與目標原子核（例 如 12C,14N 和 16O）的非彈性碰撞核反應，可能產生正子核種，或由被激發靶原子核發出瞬發伽馬射線。從患者體內發出的這些正子核種和瞬發伽馬射線與質子劑量空間分佈具有相關性。本研究採用基於 Geant4 10.4.p02 的 PTSim 套件進行碳，水，PE 和 PMMA 的相關研究，並利用林口長庚醫院質子治療中心真實治療機台的輻射相空間數據為射源，評估不同能量質子造成的正子核種及瞬發伽馬分佈，以驗證質子射程。本研究中偵測的伽馬能譜範圍是 0 – 10 MeV。並發現正子核種、瞬發伽馬及質子劑量三者分布有良好的相關性。瞬發伽馬和質子射程之間的差異為 1.5 – 3.3 mm，正子核種與質子射程之間的差異為 7.2 – 10.5 mm。此外，本研究模擬的正子核種分布與在長庚醫院測得由 130 MeV 質子照射 PMMA所得的互毀光子信號具有一致性。同時，本研究認為 PTSim用於模擬組織中的核相互作用 和正子核種分布上是一種功能強大且合適的工具。;Proton beam offers a better dose distribution to the target while minimizing the dose to the normal tissue surrounding the target, as the dose deposited beyond the distal edge is very low and the damage to the normal tissue will be minimized in comparison with the photon therapy. However, the end of range is where the beam features its sharpest dose gradient could be the uncertainties that are encountered in a patient. Therefore, the dose distribution of protons beam in the human body needs to be predicted as accurate as possible in the treatment planning and well monitored in the delivery process. In vivo treatment monitoring can be performed by detecting the secondary particles. Through the non-elastic nuclear interaction of protons with the target nuclei such as 12C, 14N, and 16O will produce positron emitters and prompt gammas. These positron emitters and prompt gammas rays emitted from the patient body are strongly associated with the dose distribution of the proton beam. In this thesis, simulations of carbon, water, PE, and PMMA irradiated with phase space data-carrying CGMH proton beam characteristics are studied. The PTSim based on Geant4 10.4 patch 2 was applied for those various targets to evaluate the positron emitter and prompt gamma distributions from different proton energies to verify the proton range. To validate our simulation system we compare the depth dose distribution from simulation with the measurement at CGMH under the same condition. The gamma energies detected in this study were in the range of 0 – 10 MeV. There is a good relation between positron emitter and prompt gamma distribution with the dose distribution. Differences between ranges of prompt gamma and proton are 1.5 –3.3 mm and positron emitter with proton are 7.2 – 10.5 mm. The range verification by comparing the measurement data of coincidence 511 keV gammas obtained at CGMH and simulation result of positron emitter distributions in PMMA by 130 MeV protons shows the good agreement. Also, PTSim is a powerful and suitable tool for the simulation of nuclear interactions and positron emitters in tissue.
