胸腔部位放射治療之能量選擇－物理考量

利用高能放射線以治療胸腔內惡性腫瘤，例如肺癌、食道癌、胸腺癌、及Hodgkin氏病等均是從事放射腫瘤工作者時常會遇到之挑戰。由於胸腔內不同組織的密度變化太大，可能會因此影響放射線在肺臟內的物理特性，甚至影響放射線能量之選擇。本文以物理實驗方法、測試鈷六十、六、及十百萬伏特X光三種能暈，在模擬胸腔組識假體內之半影區、深度劑量、及照野內外緣等變化，用以探求上述疑問。本實驗以驗證軟片分別置於假體深度2、4、6、8及10公分處來記錄放射線的變化。在半影區的變化方面，從均質假體換成模擬肺臟密度假體，鈷六十、6-、及10-MVX光分別變寬了-5.4%～-30.9%、-9.7~28.3%、及-2.7~91.8%。相同條伴下，加入模擬縱隔腔之部份對於半影區的影響並不大。在肺臟內深度劑量方面，鈷六十、6-及10-MVX光會比均質假體增加-l.0%~23.0%、0.5~14.0%、及0.5~7.5%。以物理觀點而言，能量愈高（如-10-MVX）在肺臟內的半影區會寬於平常在均質假體所測量之數據，臨床若要使用必須留有較寬之安全邊緣。而能量愈低者（如鈷-60或6-MVX光）雖程度上較輕微，但肺臟內的深度劑量卻遠比未校正之計算為高。

關鍵字

放射治療；半影區；肺臟；高能光子

並列摘要

Radiotherapy have an important role for treating the intra-thoracic malignant disease. The depth dose distribution and the width of the penumbra within the lung tissue are quite different from ordinary soft tissue owing to the entity of extra low density of the lung parenchyma. This experiment was designed to study three most popular energies which including Co-60, 6-, and 10-MV X-rays. Film dosimetry method had been used with different phantoms. There are three different kinds of phantom to simulate unit-density soft tissue, chest wall with lung, & chest wall with lung and mediastinum, respectively. The definition of penumbra is 20% to 80% dosage of the dose profile in the central plane. We used Kodak V films for recording the different layers of depth in test phantom, that were 2,4,6,8,& 10 cm, respectively. Comparing the size of penumbra between unit-density and lung-density phantom, the Co-60, 6-, and 10-MV X-rays increased -5.4% to -30.9%, -9.7% to 28.3%, and -2.7% to 91.8%, respectively. In the same condition, there is not too much different with and without the part of mediastinum simulator. The depth dose of lung parenchyma will increase -1.0% to 23.0% for Co-60, 0.5% to 14.0% for 6-MV X-rays, and 0.5% to 7.5% for 10-MV X-rays. In physical point of view, when the energies getting higher (ex. 10-MVX), the size of penumbra within the lung will be more widened than ordinary data. Clinically, if we wanted to use these kinds of energy, we must reserve a larger safe margin around the tumor. Although the lower energy (ex. Co-60) does not have above problem, but the absorbed dose within the lung will get higher than expected if correction does not apply to the calculation.

並列關鍵字

Radiotherapy ； Penumbra ； Lung ； High-energy photon

國際替代計量

胸腔部位放射治療之能量選擇－物理考量

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