What is a Linear Accelerator


Medical Linear Accelerator (LINAC) is a machine used for delivering radiotherapy in cancer treatment. It delivers high-energy x-rays to the region of the patient’s tumor. This treatment can be designed in such a way that it destroys the cancer cells while sparing the surrounding normal tissue.

The LINAC is used to treat cancer of almost all body sites, either by using conventional techniques, Intensity-Modulated Radiation Therapy (IMRT), Image Guided Radiation Therapy (IGRT), Stereotactic Radiosurgery (SRS) and Stereotactic Body Radio Therapy (SBRT).

In Nepal, there are 6 radiotherapy machines, and three of them are conventional cobalt machines. (Bhaktapur, Bharatpur and Bir Hospital)

Advantages of a Linear Accelerator over the Cobalt machine ?


2D – vs – 3D

Linear Accelerators work on a different mechanism and also these days come with 3-Dimentional Planning System making them more precise, thus tumors can be treated precisely without much toxicity to surrounding tissue. Multileaf collimators (MLC) are computerized thin blocks that are attached to LINAC treatment head, that shapes the radiation beam according to geometry of tumor.

In Cobalt machine, 2-Dimentional planning is done imagining the tumor to be in the center of the drawn rectangle, which can be readily missed.


Cobalt machines work with a Cobalt-60 radioactive source, and can be very dangerous if it gets leaked or lost. Whereas Linear Accelerators do not have radioactive isotopes. It works with x-rays and the radiation is only ‘on’ when the machine is on. Because of this, personnel safety is also maintained.

No need of Source Change

Cobalt-60 is an radioactive isotope and has to be changed every 5 to 10 years because it gets depleted with time. In LINAC, there is no radioactive source so there is no concern of source change.


Burden of cancer patients needing radiotherapy is increasing day by day. Usually Cobalt machine can treat around 40-50 patients daily. Each treatment would take about 10-15 minutes. The advantage of LINAC is that the treatment time significantly decreases to less than 5 minutes, thus decreasing the patient’s time in the radiation bunker significantly.

Clinically Better

Because of high energy x-ray, the penetration of the LINAC is more as compared to Cobalt thus treating deep seated tumors can be done with confidence, sparing the overlying skin and the other normal tissue.

Is LINAC necessary?

LINAC is very necessary if cancer treatment has to be done properly. There are a few cobalt machines in Nepal and most of the developed countries have replaced it with LINACs many years back.

Radiotherapy is under-utilized around the world and varies widely among countries. Published peer-review literature has suggested that more than half of all cancer patients should have radiotherapy included as part of their treatment regimen. In under-developed or developing economies, radiotherapy is provided to no more than 25% of cancer patients.

IAEA recommends that each radiotherapy machine should treat on average up to 500 patients per year. It is also suggested that with current cancer incidence in the Low and Mid-Income countries, from 1–3 radiotherapy machines per one million population would be needed. That would mean in Nepal, we need atleast 30 Linear Accelerators.