放射治療(俗稱電療)的進步，在這幾年由報章雜誌的報導頻率，便可見一般。治療的機器，過去刻板印象中的鈷60，早已被直線加速器所取代。直線加速器可提供較高能量的放射線，可穿透較深的組織，且對體表的傷害較低。然而隨著科技的進展，機器的精細及治療計畫的複雜程度，皆非10年前所能比擬。廠商們也根據不同原理，設計出各有特色的治療機器，希望能提供患者最好的治療效果。

經過加裝相關設備，傳統的直線加速器也可施行大多數的特殊的放射治療。例如在射束出口加上多葉準直儀，及有合適的治療計畫系統，便能進行強度調控(IMRT)的治療。所謂強度調控，意指在同一照野下，有不同的放射線強度。這種治療方式，對於深度不一或是形狀不規則的腫瘤，有較好的包覆性，且對正常組織傷害較小，腫瘤內的劑量分布也較為均勻。而影像導引放射治療，可藉由再次的影像確定治療位置及範圍，減少治療的誤差。

然而傳統機器較不適用於單次高劑量的治療，例如放射手術。長時間的治療，若無很好的固定方法，會引起相當大的誤差，所以伽瑪刀便利用腦部手術定位的頭架固定方式，來達到最佳的固定效果。伽瑪刀使用二百多顆固定角度的鈷60射源，其射束集中至一點，治療時將病灶移到劑量集中點，便可在短時間給予相當高的劑量。而好的病患固定系統加上固定角度的射源，給予伽瑪刀在各種腦部放射治療機器中，最小的治療誤差。但是其高劑量區成一圓球形，若腫瘤形狀為不規則形，便需要利用多個中心點的圓球劑量分布來組成治療所需形狀，這種治療方式導致伽瑪刀常是劑量分布最不均勻的治療方式。另一方面，伽瑪刀因其設計為頭盔式的射源，故僅能運用於腦部或頭部治療，而射束大小也限制其適合病灶約在3公分左右。運用跟伽瑪刀相似的原則，傳統的直線加速器若加上相關配備也可施行放射手術治療，其劑量分布甚至優於伽瑪刀，但是因機器上的限制，其準確度稍差，但多還在2mm之內。

為進一步改善傳統直線加速器治療機用於放射手術的缺點，諾力刀使用較精細的機器使誤差降低到1mm左右，高劑量輸出來減少治療時間，而微細多葉準直儀使利用單一中心點治療不規則形狀的腫瘤成為可能，進而有很好的劑量分布，而非頭架的固定方式可運用於多次治療，以減少高劑量單一次照射所可能引發的副作用。若運用於顱外的治療，諾力刀可運用互成直角的兩個X光射源做影像導引的放射治療(IGRT)，來校正治療的位置。然而其影像導引僅用於治療前的定位，但並無法即時修正位置，故在諾力刀的治療中，選擇好的固定系統仍然相當重要。
目前僅有電腦刀可在治療中監測病患位置。電腦刀同樣利用兩個X光射源做影像導引的根據，在治療中會再擷取影像作為定位的修正參考，每次治療可能會照數十到上百張X光，稍增加低劑量的輻射曝露，也會因多次再對位而使治療時間延長。電腦刀利用機器手臂控制小型直線加速器的位置，在空間中運用類似伽瑪刀的圓錐狀射束，可從上百個不同角度來做治療。因其可選擇角度眾多，對正常組織有不錯的閃避能力，但是其射束形狀及強度固定，所以劑量均勻性稍差。

而螺旋刀是運用電腦斷層的概念，將高能的放射線束用來治療及造影。螺旋刀的治療是將射束如同螺旋般繞病患治療，利用快速多葉準直儀控制劑量的給予，這種繞轉的治療方式，可在同平面上產生相當好的高劑量分布曲線，但是同時也有較廣泛的低劑量區域，而且並沒辦法進行非同平面的治療。在影像導引方面，不同於諾力刀及電腦刀利用骨骼來定位，螺旋刀可在每次取像中直接看見腫瘤所在位置，以減少治療誤差。但因其治療計畫需時甚久，現仍無法根據斷層所顯示腫瘤變化更改治療參數，且因其機械結構關係，並不能像諾力刀或電腦刀輕易修正病患位置。

整體而言，現今的放射治療技術已較過去有長足的進步，一般的治療機器誤差多在5mm以內，而上述介紹的機器誤差皆在2mm以內，能夠符合高精確程度治療的需求。但是腫瘤治療並不是僅有好的機器便可，一個好的治療團隊，包括內外科、診斷科、放射治療科，及物理師平時對這些機器的保養及品質管控，才能確保治療的品質，否則號稱最準確的伽瑪刀治療後發現位置有明顯誤差，也偶有所聞。選擇治療機器前，尤其是高劑量少次數精密治療，多聽多看才能確保自身的權益。

Since Cobalt-60 unit was well known as a machine for radiotherapy, same concept was remained in general population.    However, linac accelerator provides x-ray with engery higher than gamma ray from Cobalt-60 unitand this higher energy x-ray penetrates into deeper tissues and protects dmages in the superficial tissues.  With the advance of technology, a varity of machines with unique characteristics were designed by different vendors to fit the needs of clinical application..

Conventional linac accelerator (Linacs) can perform most of the routine radiation therapy techniques.. For example, with add-on Multi-leaf collimator (MLC) and appropriate treatment planning system (TPS), most of the Linacs can deliver Intensity Modulated Radiation Therapy (IMRT) IMRT means we are able to have different radiation intensity at different regions insdie the one treatment field.  IMRT technique has the adventage of beter conformity  for irregular tumor shape as compared to conventional three-dimensional radiation therapy (3D CRT). The dose distribution inside the tumor is also more uniform However, the conventional linac accelerator is not suitable for high-dose single fraction treatment such as radiosurgery (SRS) for brain tumor, due to its larger MLC width and limited angles for non-coplaner treatment .A good fixation system is also required to reducethe setup error in SRS. Thus, gamma knife utilizes the head frame used for brain surgery as a fixation tool to achieve the best fixation. Gamma knife uses over 200 Cobalt-60 sources from fixed but different angles  to focus on the same spot, and tumor is moved tothis focus spot to receive fairly high dose  radiation in a short period of time. The fixation system and fixed-angle sources design in Gamma knife provides best fixation and least setup errors among all types of equipment for SRS of brain. However, the high-dose area forms in round shape and multiple centers are required for  an irregular tumor. Thoverlap of doses from multiple centers causes the most inhomogenous dose distribution as compared to other techniques. The distribution of radioactive sources is in helmet shape in Gamma Knife, which made it can be only used on brain or head treatment. The size of the radiation source limits the size of suitable tumor to around 3cm as well.  SRS can be performed by conventional Linacs with ancillary devices  and  the dose distribution is comparable to Gamma Knife; but the accuracy of whole system is within 2mm which is slightly inferior to Gamma Knife. In order to improve the machine accuracy, Novalis uses more sophiscated devices to improve the accuracy to be less than 1mm. Novalis has high dose rate to decrease the treatment time, micro multileaf collimator to shape irregular tumor with one single focus center , and frameless fixation for fractionated treatment to minimize the possible side effect from a single, high dose treatment. For extra-cranial treatment, Novalis provided two orthogonal x-ray images as pre-treatment image-guided radiation therapy (IGRT) verification. However,  this IGRT technique can be only used before treatment, and not able to correct setup error instantly during the radiotherapy. Therefore, the choice of fixation device on Novalis machine still plays an important role.

Currently, only cyberknife can detect the setup error of the patients during the treatment. Cyberknife also use two x-ray images as IGRT reference, and performs repeated x-ray images as setup localization. It may take ten to hundreds x-ray images in every treatment; this increases radiation exposure and also increases the treatment time. Cyberknife utilizes robotic arm to control the location of the mini Linacs;  it can perform the treatment from hundreds of angles, thus it provides relatively good normal organ sparing. However, its beam shape and intensity is fixed and the dose homogeneity is relatively worse due to the overlapping of fixed beam shape..

Tomotherapy borrows the concept of tomography (CT) in diagnostic radiology, and uses high-energy radiation beam for treatment and imaging. Tomotherapy perform the radiation therapy in spiral direction around the patient and use fast multileaf collimator to control the given dose. This kind of spiral treatment can have very good dose distribution in coplanar direction, but it has more low dose region and is not able to perform non-coplanar treatment. In the aspect of IGRT, Tomotherapy can visualize the location of tumors after IGRT and minimize treatment error. However, the treatment planning time is long, Tomotherapy  can’t change treatment parameters according to changes of tumor . Due to its mechanical limitation, it can’t easily correct patient position like Novalis or Cyberknife.

In general, the radiation therapy technique evolved rapidly and most of the machines have the error less than 5mm and the machine we described above could achieve error within 2mm and fit the need of high precision treatment. However, asuccessful cancer treatment not only lies on a good machine, but more importantly needs a strong team including  surgeon, medical oncologist, radiation oncologist, radiologist and many specialitist, The medical physicist plays important role in performing the quality assurance of whole treatment system, and assuring the treatment quality. Before making a choice on treatment machine and technique, we recommend you to search and learn more information, so that the possibility for you to have the most appropriate treatment will be maximized..

1. RapidArc is a volumetric arc therapy that delivers a precisely sculpted 3D dose distribution with a single 360-degree rotation of the linear accelerator gantry.
2. Volumetric modulated arc therapy differs from existing techniques like helical IMRT or intensity-modulated arc therapy (IMAT), because it delivers dose to the whole volume, rather than slice by slice. The treatment planning algorithm ensures the treatment precision and spares normal healthy tissue.

1. A single arc can deliver essentially similar dose distributions compared with IMRT plans that incorporate as many as 36 fields, in other words, RapidArc can improve treatment quality because it has more angle to modulate the dose distribution.
2. RapidArc delivers treatments two to eight times faster than our fastest dynamic treatments today and increases precision. It takes less than two minutes to finish one treatment – can reduce dose error caused by tumors that move during treatment as the patient breathes in and out.
3. As compared with IMRT, volumetric arc therapy can use less radiation output to match with the same prescribed dose. It can reduce scattered dose to the patient.

• ExacTrac has two x-ray tubes on the floor which are perpendicular to each other. It performs localization correction in two minutes.
• X-ray IGRT images are verified automatically and patient setup, including corrections with 6 degree freedom, is accurately adjusted for streamlined workflow and throughput.
• Compared with traditional linac, the Novalis Radiosurgery System can perform:
• Imaged Guided Radiotherapy (IGRT) – inclusive of x-ray and infrared imaged guided radiotherapy.
• Stereotactic Radiosurgery (SRS) – cranial and extra-cranial stereotactic radiosurgery.
• Stereotactic Radiotherapy (SRT) – fractionated stereotactic radiotherapy.
• Intensity-Modulated Radiosurgery (IMRS)

• Fully automated real-time imaging system enables clinicians to pinpoint tumor sites, adjust positioning, and complete a treatment all within the standard timeslot
• On-Board Imager operates along three axes of motion for optimum positioning
• High precision image tracker shows internal anatomic landmarks and tracks motion
• Toolkit includes radiographic 2D imaging, and fluoroscopic and 3D cone-beam CT for fine tuning patient positioning just prior to treatment
• Volumetric cone-beam CT provides a high-quality 3D image to help distinguish tumors from surrounding soft tissue and improve tumor targeting

• Real-time Position Management™ (RPM) system

• Real-time Position Management™ (RPM) system