頭頸部腫瘤於左右兩側照野時，劑量分佈不均勻度的分析及簡易套裝組織補償器的運用

Assessment of Dose Nonuniformity under Bilateral Opposed Fields for Head and Neck Tumor and Introduction of a Simple Application Model of Tissue Compensator

陳尚文(Shang-Wen Chen) ； 林芳仁(Fang-Jen Lin) ； 涂振邦(Chen-Pang Tu) ； 蕭安成(An-Cheng Shiau) ； 吳學鼎(Hsieh-Ting Wu) ； 梁基安(Ji-An Liang) ； 楊世能(Shih-Neng Yang)

《放射治療與腫瘤學》 5卷3期 (1998/09) Pp. 157-162

https://doi.org/10.6316/TRO/199805(3)157

摘要

目的：左右兩側照野的放射治療在頭頸部腫瘤的治療上相當普遍。因頭部與前緣的治療深度有差異，所以評估計劃目標體積內劑量分佈不均勻的現象，並發展一種簡易的套裝組織補償器的運用方式，以改善治療時的不均勻度。
材料與方法：首先分析12例因頭頸部腫瘤而接受左右兩側照野之病人，其中舌癌4例，下咽癌4例，鼻咽癌4例。這些病人的頭部及頸部寬度以電腦斷層攝影分析，其中頸部寬度的參考點定在照野的中心(field center)，而頸部寬度的參考點定在頸椎C3及C4交界處之治療截面向前延伸離頸部前緣2CM（參考點A）及3cm（參考點B）。於模擬攝影時將照野中頸部寬度明顯減少區域標示於片子上，經由電腦斷層攝影分析標示區的頸部落差情況，以標示區各截面之脊椎骨椎體前緣當作三角型的底邊的參考線，可量出每個案例頸部三角型區域的角度θ以θ之平均值裂作了幾套單一斜度的組織補償器。
結果：若以照野的中心為基準，前頸部劑量過高的情況如下，參考點A高出治療中心之處方劑量(prescribed dose)的平均值分別是舌癌13.7%(10.0~16.6%)，下咽癌7.4%(5.8~9.9%)，鼻咽癌為13.6%(12.4~14.4%)；而頸部參考點B高出治療中心點之處方劑量的平均值分別舌癌11.7%(9.5~14.7%)，下咽癌5.4%(4.0~6.7%)，鼻咽癌為10.1%(7.4~13.1%)。病人頸部標示區不同截面不θ角度數都落在35至55度之間，若以5度為間隔單位，其中有9例θ角平均值為45度，2例平均值為50度，1例平均值為40度。而個別使用了單一斜度（分別為40,45及50度）的套裝組織補償器後，發現頸部劑量過高的情況已有很大的改善。
結論：頭頸部腫瘤當進行大範圍的左右兩側照野時，必須評估照野內前頸部治療劑量是否較中心點給予劑量為高。如果無法針對每一個案製作一個組織補償器，本文所介紹之簡易的套裝組織補償器的運用方式，作為改善前頸療劑量不均勻的一種參考。

關鍵字

放射治療 ； 劑量分佈不均勻 ； 組織補償器

並列摘要

Purpose: For the radiotherapy of many head and neck tumors, bilateral parallel opposed fields have been used for initial treatment. Because the thickness of head and anterior portion of neck may be different, our study is to evaluate the dose nonuniformity within target volume and to introduce a simple application model of tissue compensator to improve the dose nonuniformity for the bilateral treatment.
Materials and methods: We analyzed the data of twelve cases with head and neck tumors (4 tongue cancers, 4 hypopharyngeal cancers, and the rest are nasopharyngeal cancer). They received bilateral parallel opposed fields or initial treatment. The thickness of head and neck was estimated from CT scan, the reference point of the thickness of head was defined at field center, and the reference points of the thickness of were defined at cross-section of C3-C4 interface, 2 cm from anterior margin of neck (reference point A), 3 cm anterior margin (reference point B). During simulation, the area with significant deficit was delineated, and was analyzed on CT scan. If the line along the anterior border of vertebral body was defined as the base of a triangle, we can find the base angle θ of anterior neck. Following measurcment and analysis of angle θ of different sections on CT scan, several sets of compensator were made.
Results: If the given dose was normalized at the center of radiation field, the average percentage of overdose of anterior neck was as following: reference point A, 13.7% (10.0~166.6) for tongue cancer, 7.4% (5.8~9.9) for hypopharyngeal cancer, 13.6% (12.4~14.4) for nasopharyngeal cancer; reference point B, 11.7% (9.5~14.7), 5.4% (4.0~6.7), and 10.1% (7.4~13.1) respectively. The degree of angle θ at different cross-sections of anterior neck were all within the range of 35° to 55°. With the interval of 5 degree as a unit, the mean degree of angle θ is 45°for 9cases, 50°for 2 cases, and 40°for one case. After the application of compensator with simple slope(40°, 45°, and 50°), the overdose of anterior neck has been substantially improved.
Conclusion: When bilateral parallel opposed fields are used for the initial treatment of head neck tumors, the dose nonuniformity of anterior portion of neck should be assessed. If significant overdose was noted and it is impossible to make tissue compensator case by case, the simple application model of tissue compensator for anterior neck can be considered.

並列關鍵字

Radiotherapy ； Dose nonuniformity ； Tissue compensator