- 期刊
質子治療機－質子射束輸出系統特性之分析與比較
The Analysis and Study of Dose Delivery System of Proton Facility
摘要
現今質子治療機加速系統採兩種方式，一爲迴旋加速器，另一爲同步輻射加速器，以迴旋加速器加速質子的優點爲質子在迴旋加速器由圓心逐漸往外加速到達足夠能量後，再由切線方向射出進入射束導引裝置到達機頭，此質子流供應是源源不絕，而同步輻射加速器是由加速器系統內圈或是由外圈先由小型直線加速器質子束，再一束束注入同步輻射加速器內加速，同步輻射加速器源頭由小型直線加速器，一束一束的注入；所以相對質子離子切線脫離同步加速迴圈時也是一束一束的射出；所以迴旋加速器的質子輸出是連續性，而同步輻射加速器質子束的輸出是不連續的質子團狀態輸出；此兩種質子輸出會經過質子射束傳輸系統後導引到機頭，然後再由機頭的開口(nozzle)射出進入病人體力達到治療病人的目的，250MeV質子將近可以在一秒鐘內繞著像頭髮那麼小的直徑做280億圈的圓周運動，是要讓高速運動的質子轉向及控制它精準的打在幾公分長寬的腫瘤內，著實是一件非常困難的事；現今質子治療機已經可以很精準控制質子行徑方向和落在腫瘤定點；本文即是要探討現今使用的質子治療機射束輸出系統種類，以及能夠在臨床提供何種治療模式。
並列摘要
Radiotherapy using protons has been around as a curative instrument in the treatment of cancer since the mid 1950's. After the potential advantages of protons for clinical use were pointed out by Robert Wilson in 1946, 1 a number of research institutes developed proton delivery systems, the first patients being treated at the Lawrence Berkeley Laboratory in 1954. Since then, more than 36 000 have been treated world wide, in 26 different centers. 2 The most prevalent method for the delivery of proton therapy is still that developed for many of the early patient treatments, the so-called passive scattering approach, 3, 4 an approach which has also been used at PSI for the irradiation of more than 4000 uveal melonoma patients. In 1980, however, Kanai et al.5 proposed to scan a narrow pencil beam in three-dimensions through the target volume. This idea was taken over and developed at PSI from the late 1980's onwards, and in December 1996, the first patient was treated using the so-called spot scanning method, 6 As protons are charged particles, a narrow proton pencil beam can be magnetically scanned within the patient under computer control. This, together with a step-wise and orthogonal motion of the patient couch, obviates the need for scattering elements or field specific hardware to broaden and conform the field laterally. In depth, the near mono-energetic Bragg peaks are shifted through the mechanical insertion of thin polyethylene plates immediately before the patient. With these three steering elements, individual and narrow Bragg peaks can be delivered in three dimensions throughout the target volume. A unique feature of this system is that the pencil beams are scanned on a Cartesian grid. That is, all pencil beams incident on the patient are parallel to one another along the incident field direction. 7 Thus, the delivery geometry can be considered to have an infinite source-toskin distance. During delivery, the position and dose of each Bragg peak is controlled through the use of a fast monitoring system and two functionally redundant computers. As the proton beam is switched off between the delivery of individual pencil beam positions, this approach is similar in concept to the step-and-shoot method for IMRT, but with each ”segment” being a narrow proton pencil beam.