Intensity-Modulated Radiotherapy Versus 3-D Tangential Therapy in the Treatment of Left Breast Cancer: A Comparative Planning Study

強度調控與三度空間相切照野對於左側乳癌放射治療的治療計劃與劑量分析比較

陳邦瑜(Pang-Yu Chen) ； 施文彬(Wen-Pin Shih) ； 梁基安(Ji-An Liang) ； 楊世能(Shih-Neng Yang) ； 蕭安成(An-Cheng Shiau) ； 陳尚文(Shang-Wen Chen) ； 林芳仁(Fang-Jun Lin)

《放射治療與腫瘤學》 12卷4期 (2005/12) Pp. 267-275

https://doi.org/10.6316/TRO/200512(4)267

摘要

目的：乳房保留手術後合併輔助性放射治療已是早期乳癌的標準治療程序。然而因存活時間延長，有些研究顯示左側乳癌病人放療後有較高的心臟副作用機會。針對左側乳癌，本篇研究設計三種強度調控放射治療計劃，並與三度空間相切照野治療計劃作比較，評估不同的治療技術對腫瘤範圍的涵蓋及心臟保護效應的差異性。
材料與方法：本研究搜集十位左側乳癌病人，之前以三度空間相切照野治療，總劑量是50Gy，治療次數是25次。所有病人經乳房保留手術後，接受電腦斷層攝影治療規劃。每位病人接受四種治療計劃的分析，評估其計畫治療體積(PTV)以及重要器官(OAR)的劑量－體積分布圖(DVH)。使用的治療計畫系統是Eclipse Version 7.1，治療射束是6MV的X射線，劑量給予方式是step and shoot。四種治療計畫如下：(1)3-D tangential field (3D)，(2)2-field tangential IMRT plan(2T)，(3)2-field optimized IMRT plan(2O)，and (4)4-field IMRT technique(4I)。統計分析不同計劃間DVH的差異性是根據Student's t-test。
結果：四種治療方式皆能達到類似的PTV體積之涵蓋均勻度。當計算3D、2T、2O和4I四種計劃中介於治療劑量95-107%之PTV之體積比率(V(下標 95-107%))時，其平均值分別是96.1%、97.4%、96.0%和97.6%。而在計算心臟體積比率接受大於95/80%治療劑量方面，其平均值分別為3.4/7.4%、2.5/5.8%、1.7/4.5%和1.2/2.9%。另外肺部體積接受大於20Gy的平均值分別是19.6%、17.5%、23.9%和19.3%。4I治療計劃顯著降低心臟的高劑量區，然而卻相對增加對側乳房的劑量。此外，結果顯示使用IMRT治療計劃並不會增加肺部大於20Gy的照射體積或平均劑量。
結論：對於左側乳癌接受術後放射治療的病人，須評估心臟接受較高放射劑量後的副作用機會，而強度調控放射治療(IMRT)提供另一種選擇。本篇研究顯示4-field IMRT技術可達到與相切照野相同的計畫治療體積之涵蓋均勻度，並得到較佳的心臟保護效應。

關鍵字

乳癌 ； 強度調控放射治療 ； 心臟致死率 ； 心臟劑量

並列摘要

Purpose: Adjuvant radiotherapy is a part of the routine care of patients with early breast cancer. However, a subset of patients with left breast cancer has been shown to be at significant risk of cardiac mortality after longer relapse-free survival. This planning study was designed to assess the efficacy of target coverage and cardiac sparing by three intensity-modulated radiotherapy (IMRT) techniques compared to three-dimensional tangential radiotherapy.
Materials and Methods: Treatment planning study was performed retrospectively on 10 selected left-sided breast cancer patients previously treated by three-dimensional tangential radiotherapy with the prescribed dose of 50 Gy in 25 fractions. All patients underwent CT scan following their breast conserving surgery. For each patient, plans were generated and compared using dose volume histograms for planning target volume (PTV) and organs at risk (OAR). Treatment planning was performed using a commercial IMRT system (Eclipse Version 7.1), and the beam fluency was delivered using a step and shoot window leaf sequence and 6-MV beams. Four different radiation techniques were analyzed: (1) 3-dimensional tangential plan (3D), (2) 2-field tangential IMRT plan (2T), (3) 2-field optimized IMRT plan (2O), and (4) 4-field IMRT plan (4I). Doses to the PTV and each OAR were compared using a paired Student's t-test.
Results: PTV homogeneity was similar for the four techniques. For all patients, the average part of the PTV receiving a dose between 95 and 107% of the prescribed dose was 96.1%, 97.4%, 96.0% and 97.6% for the 3D, 2T, 2O and 4I plans, respectively. The mean proportion of the heart receiving more than 95/80% of the prescribed dose was 3.4/7.4% for 3D, 2.5/5.8% for 2T, 1.7/4.5% for 2O and 1.2/2.9% for 4I techniques, while the mean proportion of lung receiving more than 20 Gy was 19.6%, 17.5%, 23.9% and 19.3% for the four plans, respectively. When compared to 3D plans, the 41 plans significantly reduced the high dose irradiation volume of heart; however, the irradiated doses to the contralateral breast were increased. The use of IMRT techniques did not increase either V20 Gy of lung or the mean left lung doses.
Conclusion: Left breast cancer patients undergoing adjuvant irradiation in which the heart receiving higher dose should be considered for alternation to IMRT plan. Better cardiac sparing effect is achievable with the use of 4-field IMRT technique without compromising target coverage.

並列關鍵字

Breast cancer ； Intensity-modulated radiotherapy ； Cardiac mortality ； Cardiac dose