以曲棍球棒形的照野照射顱脊軸之劑量術與臨床應用

傳統的腦脊髓軸放射線治療通常使用多重照野的照射方式，且用移動照野交接處(moving junctions)的方法避免在脊髓上劑量過高。但也可使用單一的「曲棍球棒」(hockey stick)形大照野以避免小照野交接處劑量過高的問題。台北榮總以人形假體及鈷六十遠距離治療機(AECL ELDORADO 70)來做曲棍球棒形照野的劑量術。測量時亦用到了Kodak XV-2驗證片及氟化鋰(LIF)片。實驗時將假體置於地板，SSD拉長至180cm，在假體所臥之平面大小為85x25cm平方公分。假體之頭部轉向左邊及右邊各照3分鐘。測量結果，除了眼睛晶狀體之劑量稍高（中央照野之20至25%）外，其餘在腦部及脊髓之劑量分佈仍算均勻，頭尾端之劑量在中央照野的74%以上。本研究於臨床應用顯示治療效果良好，目前未見嚴重併發症。曲棍球棒形照野提供了腦脊髓照射的另一個選擇。

關鍵字

腦脊髓放射治療學；劑量學

並列摘要

Conventional cranio-spinal axis irradiation usually involves multiple fields with moving junctions to avoid overlapping over the spinal cord. In this study a single long ”hockey stick” portal was used to prevent the risk of dose inhomogeneity during irradiation. A Rando phantom and a telecobalt machine (AECL ELDORADO 70) were used to simulate the actual treatment arrangement for dosimetry study. The Rando phantom was put in a prone position on the floor with the maximal dimensions of 85 x 25 cm^2 in field size. The source-skin distance was 180 cm. The hockey stick portal was repeatedly irradiated with the head rotated to the right and the left alternatively. Film dosimetry and thermoluminescent dosimetry (TLD) were used to measure the radiation doses at different depths along the cranio-spinal axis. TLD revealed that the hockey stick portal can provide a uniform distribution of radiation exposure to the brain and the spinal cord. The measured doses to critical organs such as the lens were around 26%, the ovary between 15 to 50%, and the thyroid around 37%, relative to the central axis dose (100%). This technique has been applied to treat medulloblastoma, germinoma and ependymoma in our center since 1989. The preliminary result shows that hockey stick portal is clinically feasible. Compared with the conventional technique, it can obtain similar treatment result without increasing local recurrence and morbidity.

並列關鍵字

Therapeutic radiology, brain ； therapeutic radiology, spine ； dosimetry

延伸閱讀

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國際替代計量

以曲棍球棒形的照野照射顱脊軸之劑量術與臨床應用

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