本研究發展基於碘化鈉偵檢器之瞬發加馬輻射量測系統用以進行質子射程驗證，偵檢器系統由兩吋碘化鈉偵檢器及兩毫米縫隙之鉛準直儀構成，並以30 MeV, 1.5 nA 質子束照射聚乙烯及壓克力樹脂，量測瞬發加馬輻射隨深度之強度變化，藉以推估質子射程。此研究首要目標在於確認偵檢系統特性，經由實驗得知系統無感時間為1028 ns，藉由基準切割法了解堆積訊號比率為3 %，證明在此照射環境下偵檢器系統可有效運作。以高斯能譜訊號展延(GEB)方法將模擬能譜擬合實驗能譜，其結果提供瞬發加馬輻射於特定深度下的產量，並可得知系統對4.4 MeV光子的偵檢效率為7.1 × 10^(-6)。理論上在給定的一個質子能量Ep下，一個靶材深度d的瞬發加馬輻射產量(yield)為質子數量n(Ep)與反應巨觀截面Σ(E_p)之乘積。實驗中即使用步進馬達移動靶材以取樣並繪製在10公厘靶材深度內4.4 MeV 與6.13 MeV瞬發加馬輻射隨深度之強度變化。實驗結果顯示每一深度之取樣時間需大於1秒鐘，即大於9.375×10^9 個質子入射進靶材才可使此碘化鈉偵檢系統量測到足夠強之訊號並有效辨識瞬發加馬輻射峰值位置與獲取足夠的空間解析度。
本研究也建立一個數值模型以計算瞬發加馬輻射隨深度之強度變化。藉由讀入蒙地卡羅模擬所得之30 MeV質子束入射靶材後隨深度的能量及數量分佈，並導入瞬發加馬輻射產量截面資料庫進行計算，結果顯示在聚乙烯靶材4.4 MeV峰值位置為5.7 mm與實驗量測到之峰值位置5.5 mm有0.2 mm的差異。使用壓克力樹脂時，數值計算的4.4 MeV峰值位置為4 mm與實驗量測到之峰值位置4.8 mm有0.8 mm的差異。此峰值位置差異推測為截面資料庫不完全所導致。
本研究發展出一套碘化鈉偵檢系統可有效量測瞬發加馬輻射產量隨深度之強度變化，具備用於質子治療時驗證質子射程的潛力。

This study focuses on developing a NaI-based prompt gamma-ray detection system for proton range verification. This system is composed of a 2-inches NaI detector and a slit collimator with a width of 2 mm. When 30-MeV proton beam irradiates a PE or a PMMA phantom, the intensity distribution of prompt gamma emissions along the proton path can be acquired by moving the phantom and be used to estimate the proton range subsequently. One major purpose is to characterized this NaI-based system, from which the deadtime ~ 1028 ns that gives the signal missing rate ~ 0.05 % and the pile-up signal ratio ~ 3% is identified at the proton current ~ 1.5 nA; in this way, the used NaI-detection system can efficiently acquire prompt gamma signals at a current level < 5 nA generally applied in proton therapy without significant data loss. The Gaussian energy broadening fitting was utilized to evaluate the absolute prompt gamma yield at a specific depth; as a result, the detection efficiency is 7.1×10^(-6) for 4.4 MeV photons. In principle, the prompt gamma yield at a specific depth d is determined from the product of proton number n(Ep) and macroscopic cross section Σ(E_p) at a proton energy Ep. By using a stepping motor to move the PE or PMMA phantom, intensities of 4.4-MeV and 6.13-MeV prompt gamma-ray emissions are scanned and recorded within the depth of 10 mm. At the proton current ~ 1.5 nA, results show that the measuring time at a specific depth d should be > 1 seconds, such that > 9.375×10^9 protons can generate 4.4–MeV gamma-rays to a level capable of clearly identifying the peak of the gamma-ray distribution in a PE or a PMMA phantom. By incorporating the number and energy distributions of protons acquired with Monte Carlo simulation and the prompt gamma yield cross section, an analytical mode is developed to calculate the intensity distribution of prompt gamma-rays along the proton penetrating depth in a target. For 30-MeV protons, the calculated emission peak of 4.4 MeV gamma rays locating at 5.7 mm in a PE target is reasonably close to the experimental result at 5.5 mm. For a PMMA target irradiated with 30-MeV protons, the calculated emission peak at 4.8 mm shows a greater discrepancy with respect to the experimental one of 4 mm. Nevertheless, results shown in the thesis demonstrate that a NaI-based prompt gamma-ray detection system can effectively resolve the variation of prompt gamma yield along the proton path and is expected to be further developed in the application of proton range verification.

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