Rectal Sparing by Balloon Catheter Immobilization during Intensity Modulated Radiation Therapy for Prostate Cancer

攝護腺癌強度調控放射線治療時使用直腸擴張氣球定位對於減少直腸劑量之影響

蔡巧琳(Chiao-Ling Tsai) ； 吳簡坤(Jian-Kuen Wu) ； 王駿瑋(Chun-Wei Wang) ； 傳筱如(Hsiao-Ju Fu) ； 成佳憲(Jason Chia-Hsien Cheng) ； 賴明坤(Ming-Kuen Lai)

《放射治療與腫瘤學》 14卷1期 (2007/03) Pp. 1-10

https://doi.org/10.6316/TRO/200714(1)1

摘要

目的：逐步增加攝護腺癌的放射線劑量對於其預後有顯著的改善。要達到一個最理想的治療計畫，其劑量分布受限於周圍的正常組織。本研究的目的在探討攝護腺癌強度調控放射線治療(IMRT)時，使用直腸擴張氣球定位對於減少直腸劑量之影響。
材料與方法：自2005年6月至8月，共有11位攝護腺癌的病患在第一次定位時，分別接受有置放直腸擴張氣球（氣球內打入60ml的空氣）及沒有置放直腸擴張氣球的電腦斷層(CT)定位。並且在IMRT療程結束時再接受一次有置放直腸擴張氣球的電腦斷層定位。由TMS Helax電腦治療計劃系統設計出靜態式(step-and-shoot)五方向共平面的IMRT治療計畫。分別為有置放直腸擴張氣球及沒有置放直腸擴張氣球製作兩個不同的IMRT治療計畫。臨床目標區域(CTV)的給予劑量都是78 Gy分39次每次2 Gy。CTV是根據病患所屬的危險群分類而訂定。計畫目標區域(PTV)95%以上的體積也要達到78Gy。按照累加的體積直方圖(DVH)分析出CTV、PTV、直腸及膀胱所接受的劑量。分次治療間攝護腺的位移誤差的測量是比較在兩次不同的CT，最靠近恥骨頂端的那一張CT影像上恥骨緣到攝護腺前緣及攝護腺後緣到骨的距離。用成對樣本t檢定評估劑量分布差異及分次治療間攝護腺的位移誤差。
結果：本研究中屬於TlcN0M0有4位病患、T2bN0M0有4位病患，T3bN0M0有2位病患，而T4N0M0有1位病患。CTV只包含攝護腺的有8位病患，包含攝護腺及兩側儲精囊的有3位病患。CTV所接受最低劑量的平均值為79Gy。平均的多葉準直儀移動片段(segment)的數量在有置放及沒有置放直腸擴張氣球的治療計畫分別為43及42(P=0.7)。有放置直腸擴張氣球的治療計畫在直腸接受高劑量的體積上有顯著的降低，≧65 Gy為13%及17% (P=0.007)；≧70 Gy為9%及13% (P=0.005。接受≧65 Gy的膀胱體積在兩個治療計畫中並沒有顯著差異（18%及16%，P=0.07）。攝護腺的位移誤差在治療之前及治療結束時是相似的，恥骨緣到攝護腺前緣的距離為0.90cm及0.96cm (P=06)，攝護腺後緣到　骨的距離為3.69cm及3.73cm(P=0.8)。每一位病患都能容忍在整個IMRT的療程中每天被放置直腸擴張氣球。沒有病患發生第三級或以上的急性反應。
結論：攝護腺癌IMRT時，每天使用直腸擴張氣球定位是一個可行與重複性高的步驟。此方法可以顯著減少直腸接受高劑量的體積。病患的接受度很好且不會造成攝護腺明顯的位移誤差。

關鍵字

直腸擴張氣球 ； 攝護腺癌 ； 強度調控放射線治療 ； 位移誤差

並列摘要

Purpose: Escalating radiotherapy dose results in a substantial improvement in prostate cancer outcome. Obtaining an optimal plan and acceptable dose distribution would be limited by normal critical structures. Our study is to evaluate the effect of rectal balloon immobilization in reducing rectal dose during daily treatment of prostate cancer with intensity modulated radiation therapy (IMRT).
Materials and Methods: From June 2005 to August 2005, 11 patients with prostate cancer underwent computed tomography (CT) simulations with and without rectal balloon (filled with 60ml air) before and at the end of IMRT course. TMS Helax treatment planning system was used to generate step-and-shoot five coplanar-field IMRT plans. Plans were separately designed with and without a rectal balloon. The prescription dose to clinical target volume (CTV) was 78 Gy in 39 fractions of 2 Gy each. CTV was determined according to the patients' risk category. The dose to 95% of planning target volume (PTV) was 78 Gy. Cumulative dose-volume histograms (DVHs) were analyzed for the CTV, PTV, rectum, and bladder. Inter-fractional prostate displacement was measured on two separate CT images with the distance between pubic bone rim/sacrum and anterior/posterior borders of prostate, respectively, at the cranial level of pubic symphysis. To assess the dosimetric difference and inter-fractional variation of balloon setup, the paired Student t-test was used.
Results: Patients included in this study had the TNM stage distribution of T1cN0M0 in 4 patients, T2bN0M0 in 4 patients, T3bN0M0 in 2 patients, and T4N0M0 in 1 patient. CTV was prostate alone in 8 patients and prostate plus bilateral seminal vesicles in 3 patients. Minimum dose to CTV with and without a rectal balloon were both 79 Gy in average. Average segment number in plans with and without a rectal balloon were 43 and 42 (P=0.7), respectively. Plans with a rectal balloon showed a significant reduction in rectal volume fraction at 65 Gy (13% vs 17%, P=0.007), and at 70 Gy (9% vs 13%, P=0.005). Plans with a rectal balloon did not show difference in bladder volume fraction at 65 Gy (18% vs 16%, P=0.07). Inter-fractional prostate positions before and at the end of IMRT were similar in the distance from pubic bone to anterior border (0.90cm vs 0.96cm, P=0.6), and posterior border of prostate to sacrum (3.69cm vs 3.73cm, P=0.8). All patients tolerated their whole IMRT course with daily placement of rectal balloon. There was no grade Ⅲ acute toxicity.
Conclusion: Rectal balloon immobilization during daily fractionated IMRT for prostate cancer is a feasible and reproducible procedure. It would be beneficial to reduce high dose to the rectum. The effect of prostate immobilization is acceptable with minimal inter-fractional setup variation.

並列關鍵字

Rectal balloon ； Prostate cancer ； Intensity modulated radiation therapy ； Inter-fractional displacement