- 期刊
放射治療周邊固定器材輻射穿透性影響之研究
The Study of Dose Penetration Influence Due to Immobilization Accessory in Radiation Therapy
摘要
利用輻射線做為癌症病患的放射治療已經行之有年，我們在治療病人之前都必須知道高能光子射束所經過的身體，組織或器官及外加固定病患裝置器材的厚度以便去推估輻射改變的量，進而補足因病人體厚所造成的劑量衰減；尤其放射治療的技術及做法隨著設備及治療計劃系統的改良日益精進；從早期的2D到3D、順形放射治療及現被大家普遍接受的強度調控放射治療，由於危急器官的劑量相對降低而得以提高病灶接受的劑量；因此，病人每天擺設的位置精準度就顯得非常重要。由於用於固定病患的配件的種類繁多，這些配件對放射線的阻擋性如何及其對劑量的影響便是本篇主要探討的目的。 以SAD100公分，厚度5公分的條件，照野開10公分×10公分，加速器設定100mu取得一個讀值，之後再把要測量的周邊固定用配件放置到固態假體上，此時要讓加速器的中心射束軸通過要測量的部位，而同樣設定100mu，再將此兩個值，以有放置固定用配件的讀值放在分子，我們定義劑量的阻擋因子（衰減值）為：衰減值＝［1-（加固定器材後的微電量儀的讀值／沒加固定器材的微電量儀的讀值）］×100%。 結果從低能量到高能量，因為加了實心的枕墊，輻射劑量被阻擋5.3%到3.4%，而頭頸部的托盤碳纖維材質部份的阻擋量，依能量由低到高依序是2.3%到1.7%；而輻射線如果經過頭頸部托盤的鈕釦，則劑量的阻擋以能量由低到高依序為14.3%到9.7%；對於胸腹部固定托盤架的碳纖部分及其他配件的劑量阻擋以能量由低到高依序則有1.7%到5.1%的變化；對於自製木質頭頸部的延伸凸型板對光子射束能量低到高的阻擋性依序是2.4到1.7%。 經由此篇的研究及量測，讓我們更了解到在放射治療中所使用到的病患固定配件所造成輻射劑量衰減的情形。實驗的結果讓我們有足夠的資料去修正因使用病患固定配件而造成劑量的不足。因此，放射治療科對所使用的固定配件應當都要去量測其對輻射劑量的影響以便讓病人得到正確的劑量。
並列摘要
Radiation has been used to treat cancer patient for almost half century. Owing to the great achievement of computerized treatment planning system and innovative skill of dose delivery technique, the development of radiation therapy craftsmanship is changing with each passing day. Therefore, the patient treatment setup need to be more precise when patient is treated by using IMRT technique instead of 3D or conformal therapy. The purpose of this study is to measure the dose influence under diversity patient immobilization accessories. Various patient support devices were measured their penetration influence under Elekta linear accelerator with triple photon energy, 4 MV, 6 MV, 10 MV. Those devices include: head and neck patient holder tray and various set of pillows, pelvis holder, linear accelerator patient treatment supporter and home made salient wooden head and neck board. The measurement was carried out by setting the chamber center at Source to Axis distance 100 cm and embedded chamber 5 cm depth in solid water phantom with field side 10 cm by 10 cm. The penetration factor was defined as: penetration factor=[1-(electron meter reading with immobilization device/open field reading)]×100%. The results of these immobilization devices penetration influences showed from 5.3% to 3.4% in head and neck solid pillow with low to high energy respectively. Other support device penetration factor varied from 2.3% to 5.1% especially grow up to 10% when beam penetrate through tighten button of the holder. This study show how photon beams influenced by the immobilization device; therefore, penetration influence must be taken into consideration at treatment planning procedure. For those patients without using treatment planning, dose modification has to be done by manual when useful treat beam penetrate supporting device during the treatment.