三維近接放射治療在子宮頸癌的發展應用

The development and application of 3D brachytherapy in the treatment of cervical cancer

近接放射治療是子宮頸癌治療中重要的一環。傳統二維近接治療使用A點（約是子宮頸口往上往外2cm位置，A點劑量應等於給予的處方劑量，通常是80–90Gy）；ICRU 38號報告的直腸點／膀胱點（代表直腸／膀胱的劑量，各應小於75/80 Gy）等概念進行計畫的設計與評估，有其不足之處。逐漸盛行的三維近接治療，則遵循歐洲放射腫瘤學會(GEC-ESTRO)以及美國近接治療學會(ABS)指引的原則，以三維影像為基礎，進行臨床靶區(clinical target volume)以及正常器官的圈畫，並在考量生物等效劑量轉換的前提下，設計出同時符合靶區目標劑量以及正常器官耐受劑量條件的理想計畫。劑量學的研究顯示，傳統計畫有腫瘤涵蓋不足、正常器官保護不足等問題，在三維計畫中有顯著的進步。眾多的臨床研究證實，與歷史資料相比，三維近接治療能減少65%局部腫瘤復發，以及減少50–60%第三級以上之腸胃道及膀胱晚期副作用。雖然三維近接治療仍有一些待解決的問題，隨著觀念和技術持續的進步，終將成為近接治療的主流。

Brachytherapy plays an important role in the treatment of cervical cancer. Conventional 2-D brachytherapy treatment plan, which is designed and evaluated using the concept of point A and rectal/bladder point defined in ICRU report 38, has its limitation. The increasingly used 3-D brachytherapy is usually based on the GEC-ESTRO guideline proposed by European Society of Therapeutic Radiation Oncology and the ABS guideline, proposed by American Brachytherapy Society. The contouring of CTVs and normal organs is based on 3-D image. Taking biological effective dose into account, an ideal plan is made to satisfy both the prescribed dose to target volumes and the normal organ tolerance. Dosimetry studies have revealed that inadequate coverage of tumor and unacceptably high doses to normal organs the major problems in conventional brachytherapy are substantially improved in 3D brachytherapy. Numerous clinical studies have confirmed that with 3D brachytherapy, the local tumor recurrence is reduced by 65% and grade 3 or greater late GI/bladder toxicities are reduced by 50–60%. Despite several uncertainties and challenges in 3D brachytherapy, as the concept and technology continuously evolve, it will become the standard of care in the near future.