中心窄屏蔽鉛合金擋塊與分次多葉式準直儀對射束中心軸下劑量的評估與探討

Dose Evaluation and Comparison under Cerrobend Central Block with Fraction Multi-leaf Collimator

陳文凱(Wen-Kai Chen) ； 康誠麟(Chen-Lin Kang) ； 廖宗義(Tzung-Yi Liao) ； 阮國榮(Kuo-Jung Juan) ； 藍仁鴻(Jen-Hong Lan) ； 黃英彥(Ying-Yen Huang)

《中華放射線技術學雜誌》 32卷2期 (2008/12) Pp. 191-198

https://doi.org/10.30045/CJRT.200812.0007

摘要

放射治療當中，常會以鉛合金擋塊或是多葉式準直儀(Multi-leaf Collimators; MLC)作爲屏蔽物，阻擋會受到照射的危急器官或正常組織。本研究目的，即是在比較臨床上，使用中心窄屏蔽鉛合金擋塊(Cerrobend central block)與分次多葉式準直儀對照野中心窄屏蔽擋塊下方危急器官劑量的影響。選用配置在Varian 2100 C/D (MLC)型，直線加速器上的多葉式準直儀與傳統鉛擋塊比較在於：不同光子能量（6MV與15MV）；不同照野（10×10平方公分與20×20平方公分）；不同深度（4 cm、6 cm與11 cm）；不同擋塊尺寸（2 cm與4 cm）組合下，測量中心窄屏蔽鉛合金擋塊與分次多葉式準直儀二者下方劑量的差異。由研究結果得知，照野中心窄屏蔽擋塊下方的劑量值，會隨著深度增加與照野變大及擋塊尺寸較小有明顯增加的現象。而分次多葉式準直儀較中心窄屏蔽鉛合金擋塊增加較少，即散射輻射對照野中心窄屏蔽擋塊下方危急器官劑量影響較少。當使用照野中心窄屏蔽擋塊保護危急器官時，會因額外的散射劑量增加危急器官劑量。照野中心窄屏蔽擋塊下方的劑量值並非只有預估穿透量5%以下的輻射劑量，在某些條件下其劑量值有時可高達20%以上。由研究測量結果，分次多葉式準直儀較中心窄屏蔽鉛合金擋塊有較好的阻擋效果，所以在臨床上是值得運用及參考。

關鍵字

中心窄屏蔽鉛合金擋塊 ； 分次多葉式準直儀 ； 散射劑量

並列摘要

During the radiotherapy almost use Cerrobend block or multi-leaf collimator (MLC) shielding to protect critical organ or normal tissue. The experiment evaluated compare with critical organ dose will be effect by use narrow shielding Cerrobend central block and fraction MLC. MLC and Cerrobend central block which choose to use an allocation a type linear accelerator at the Varian 2100 C/D (MLC) to compare: The different energy (6 MV and 15 MV); field size (10×10cm^2 and 20×20cm^2); depth (4 cm、6 cm and 11 cm); block size (2 cm and 4 cm) combination bottom, measure the Cerrobend central block and fraction MLC two under difference for measuring. The results show the dose under central block increase with depth, field size and block size. Moreover the fraction MLC scatters radiation to critical organ increase less than the Cerrobend block. Applying narrow shielding central block to protect critical organ on clinical treatment has been suggested that one should take into the account the extra scattered radiation to the under block critical organ dose. While the dose under central block is not only 5% transmits dose. Instead, under block will be higher than 5% and could be as high as 20% or more on some clinical conditions. The final conclusion revealed the fraction MLC was able to decrease the critical organ scatters radiation.

並列關鍵字

Cerrobend central block ； fraction multi-leaf collimator ； scatters radiation