高能光子射束下直線加速器治療床及固定模具對淺層劑量的影響

The ImpacT of LInac couch and ImmobILIzaTIon devIce on

趙曉玲(Hsiao-Ling Chao) ； 鄭秀成(Shiu-Chen Jeng) ； 吳簡坤(Jian-Kuen Wu) ； 許雅娟(Ya-Chuan Hsu) ； 曾鑠鑠(Shou-Shou Tseng) ； 黃國明(Kuo-Ming Huang) ； 吳筱菁(Hsiao-Ching Wu) ； 成佳憲(Chia-Hsien Cheng)

《放射治療與腫瘤學》 13卷3期 (2006/09) Pp. 217-223

https://doi.org/10.6316/TRO/200613(3)217

摘要

目的：臨床上當病患接受放射線治療時，支撐及固定病灶範圍所選用的材料是很重要的。治療時若使用後前向射束照野時，光子射束必須經過直線加速器的治療床及固定模具。當高能光子射束 穿過治療床及固定模具而衰減時，會造成皮膚免除效應降低。本研究是在呈現高能光子射束穿過丙烯樹酯治療床及固定模具後， 在治療物淺層劑量的變化情形。
材料與方法：測量時光子射束是以180度的後前向射束照野垂直入射，再以治療床及真空墊不同的擺設方式分別用4種不同的照野大小進行量測， 分別為10×10 ㎝2、15×15 ㎝2、20×20 ㎝2及25 ×25 ㎝2。
結果：真空墊的厚度愈厚時淺層劑量愈大，且當照野面積愈小時，淺層劑量增加的程度相對地愈大。治療床對劑量也有顯著的影響，尤其是淺層劑量，隨照野面積的減小影響愈大。10×10 ㎝2照野淺層劑量為未有治療床及真空墊時同照野的191%；在25×25 ㎝2照野時為161%。
討論：故因治療床及使用固定模具造成淺層劑量的增加， 此類設定對於放射治療後對皮膚所造成的可能傷害， 在臨床上治療設計應予於考量。

並列摘要

Purpose : Clinically it is important for patients to have the supporting and the immobilization during radiotherapy. When using a posterior-anterior beam, radiation normally passes through the treatment couch insert of the linear accelerator and the immobilization devices. With high energy photon beam
attenuated by the couch insert and immobilization devices, the skin sparing effect will be reduced.
This study is to investigate the dosimetric changes in the Superficial layer dose of the treated object after high energy photon beam passes through the treatment couch (Perspex) insert and immobilization devices.
Materials and Methods : The gantry angle was set as 180°, so that the posterior-anterior photon beam incidents to the couch insert. Measurements were taken for the different combinations of the couch insert and vacuums with 4 beam sizes: 10 × 10 cm2, 15 × 15 cm2, 20 × 20 cm2, and 25 × 25 cm2 .
Results : The thicker the vacuum, the larger increase in the Superficial layer dose. The proportion of Superficial layer dose increase was relative larger with smaller field size. There was significant influence of the dose from the couch insert. The magnitude of the influence was relative larger with
smaller field size. The Superficial layer dose with couch insert was 191% of the one with none of each other at the 10 × 10 cm2 field size. The Superficial layer dose with couch insert was 161% of the one with none of them at the 25 × 25 cm2 field size.
Conclusion : The uses of the couch inert and immobilization devices cause the increased Superficial layer dose. Special considerations need to be taken in these conditions for the possible radiation related skin injury. The impact should be incorporated into the treatment design.