Of these 2 kinds of radiation therapies, external–beam therapy uses a machine. This machine is of a large build; it also makes high decibel sounds while it is operated. The good thing is this equipment works without touching your body. But you will see it moving around you and emits high–intensity radiations from several dimensions.  
 
Radiation therapies deliver high-intensity x – rays. Such rays are from linear accelerator – also known as linac. Doctors administer such powerful rays through a customised dosage plan. Such plans aid in mapping tissues requiring cancer treatment. 
 
In case of radiation therapy done with internalised approach involves placing one or more sources of radiations in humans. Sources of powerful rays are solid or liquid in nature. Brachytherapy is the name of treatment offered with a solid source to generate rays. Your radiation therapists / oncologists will put a ribbon or capsule which houses a source of rays. Placement site nears the site of tumor(s).  
 
Both forms of radiation therapies are localised – as they gain access to the site affected by cancer. In other words, there is relatively lesser risk of rays damaging healthy or normal tissues. Of the two types of radiotherapy, internal approach has the source providing powerful rays for a predetermined duration.  
 
However, radiation therapy offered through liquid-based radiation sources are labelled as systemic therapy. In such cases, rays successfully breach tissues and blood, to reach all through your body. Upon placement, rays continue to identify ad well as destroy cancer-causing cellular forms. 
An advancement in radiation-based treatment is the volumetric–modulated–arc therapy – in short, VMA therapy. Here, the machine called linear accelerator (linac) rotates at multiple axes – gaining access to many parts of the patient’s body. This machine enables radiations to enter into the body through many angles. 
 
One of the very modern developments is machines – i.e., linear accelerators – are attached with an accessory called as collimator. This accessory saves your body like a protective cover; multi-leaf collimators are known to have 100+ sheaths for added protection. Each of these sheaths aid blocking a part of the radiations from hitting where they are not needed.  
 
This is a reason why areas exposed to linear accelerators are marked with high level of precision; this helps avoid needless spillage of x-rays to unaffected sites or organs of your system. You need to note that prior formats of linear accelerators did not come with a collimator. During those times, shields are made with hand-made settings; these are employed to reduce risks associated with needless exposure on powerful rays. 
 
Lastly, radiotherapy for treating cancers that use external–beam technology forms part of highly focused pathway. Owing to this, this approach is taken for cancers identified in an individual organ or tissue. Example: people identified with lung tumors are exposed to radiotherapy onto the chest. By this way, rays are not let to damage any other site or parts of the body.