Evaluation of thE dosimEtric and radiobiological impacts on prostatE cancEr patiEnts of daily imagE-guidEd volumEtric modulatEd arc thErapy

弧旋刀影像導引放射治療對攝護腺癌之劑量學及輻射生物效應評估

陳俊佑(Chun-You Chen) ； 余孝緯(Hsiao Wei Yu) ； 陳秋萍(Chiu-Ping Chen) ； 林其嶪(Chi-Yeh Lin) ； 周志成(Chih-Cheng Chou) ； 陳梓欣(Tzu-Hsin Chen) ； 陳薏茹(Yi-Ju Chen) ； 王豪(Hao Wang) ； 李俊毅(Chun-I Li) ； 蔡佳宜(Chia-Yi Tsai) ； 陳加惠(Chia-Hui Chen) ； 吳思遠(Szu-Yuan Wu)

《放射治療與腫瘤學》 22卷4期 (2015/12) Pp. 285-296

https://doi.org/10.6316/TRO/201522(4)285

摘要

目的：對於治療攝護腺癌的病患，使用影像導引放射治療被認為可以降低副作用並改善預後。本研究利用治療計劃系統模擬有無影像導引下之劑量分布，以評估兩者劑量學上的差異。材料與方法：我們蒐集了10個使用弧旋刀治療攝護腺癌病患，每個病患的計劃靶體積都是以臨床標靶體積向各個方向增加5 mm所得到的，我們依照每日治療前執行影像導引所得到的擺位誤差移動這些病人的原始治療計畫中照射之中心點以模擬沒有影像導引下的劑量分布，接著以劑量學指標（dosimetric index）比較原劑量分布與模擬無影像導引劑量分布之差異，最後計算等價均勻劑量（equivalent uniform dose）以及正常組織併發症機率（normal tissue complicationprobability）以評估於生物效應上之影響。結果：擺位的系統誤差（Σ）以及隨機誤差（σ）於左右（LR）、上下（SI）、前後（AP）方向各為0Σ LR= 1.4 mm, σ LR= 1.95 mm, Σ SI= 3.22 mm, σ SI= 2.46 mm, Σ AP= 3.17 mm以及σ AP=2.79 mm。在模擬無影像導引的情況下，臨床標靶體積的劑量覆蓋率較差（V100%: 99.99% vs.92.37%, p ＜ 0.05 and V95%: 100% vs. 99.46%, p ＜ 0.05）且等價均勻劑量亦較低（76.8 Gy vs. 75.4Gy, p ＜ 0.05）。直腸以及膀胱的劑量學指標、等價均勻劑量以及正常組織併發症機率皆無明顯差異。結論：在以攝護腺加5 mm作為計畫標靶體積的狀況下，使用弧旋刀搭配影像導引治療攝護腺癌可以降低擺位誤差，並避免因誤差造成臨床標靶體積劑量低於預期之情況，不過對於直腸及膀胱之劑量和生物效應，並無明顯差異。

關鍵字

弧旋刀 ； 錐狀射束電腦斷層掃描 ； 等價均勻劑量 ； 正常組織併發症機率

並列摘要

Purpose: Image-guided radiation therapy (IGRT) was suggested to improve outcomes and reduce toxicity for localized prostate cancer treatment. We generated virtual treatment plans to evaluate the dosimetric impacts with and without IGRT. Materials and Methods: Daily position setup errors from 10 patients treated with volumetric modulated arc therapy (VMAT) were acquired with cone-beam computed tomography (CBCT). A margin of 5 mm was added to the clinical target volume (CTV) to generate a planned target volume (PTV). We shifted the isocenters in the planning system with errors, fraction by fraction, to simulate the situation without IGRT. Dosimetric indices were compared between the initial plans (pretreatment CT plans) and the shifted plans. Radiobiological evaluations of an equivalent uniform dose (EUD) and normal tissue complication probability (NTCP) were also performed. Results : The system errors (Σ) and random errors (σ) in the left-right (LR), superiorinferior (SI), and anterior-posterior (AP) directions were Σ LR=1.4 mm, σ LR= 1.95 mm, Σ SI =3.22 mm, σ SI = 2.46 mm, Σ AP=3.17 mm and σ AP = 2.79 mm. Coverage of the CTV for 100% and 95% of the prescribed doses were lower in the shifted plans (V100%: 99.99% vs. 92.37%, p ＜ 0.05 and V95%: 100% vs. 99.46%, p ＜ 0.05). There was no difference in the dosimetric indices for the bladder and rectum. The EUD value of the CTV was also lower in the shifted plan (76.8 Gy vs. 75.4 Gy, p ＜ 0.05). The EUD and NTCP for the bladder and rectum did not statistically differ. Conclusions: Using CBCT-acquired VMAT for treating prostate cancer not only shortened the treatment time but also decreased the setup uncertainty. In the setting of reducing the PTV margin to 5 mm, the dose to the prostate was compromised without IGRT but the estimated toxicity to the rectum and bladder exhibited no difference.

並列關鍵字

Volumetric modulated arc therapy (VMAT) ； Cone-beam computed tomography (CBCT) ； Equivalent uniform dose (EUD) ； Normal tissue complication probability (NTCP)