Radiotherapy 101

Okay, so here is the standard but crucial caveat. This is not medical advice. No really it is not. Cancers vary hugely from case to case due to factors that are mostly entirely beyond the patient's control for example staging (how advanced the cancer is), position (obviously some areas are worse than others), tumour genetics (different tumour types respond differently to the same treatment), comorbidities ... . So noone can issue general advice. Whether any method is better than any other method, or even possible for a particular case, is IMPOSSIBLE to know without a patient's details, test results and scan data. If someone/a-website tells you differently, or issues blanket advice, do yourself a favour and ignore it. If you know this but still want guidance I wouldd advise visiting CRUK or Macmillan. Neither are perfect, but they are the best I know and will point you in the correct direction (which is probably your local doctor). 

So with the caveat firmly in place, lets start easy. Tumor tissue is bad. Normal tisue is good. Given you are mostly made of normal tissues, hopefully, this is obvious. Told you I would start easy. In the rare cases, where a tumour is obviously distinct, entirely seperate and accessible, treatment can be as simple as just cutting it off. Though "just cutting it" is a bit unfair to surgeons as the procedure might be a complex multiple hour intensely difficult operation. Still, you get the point.

Rarely are tumours so isolated. Alas, often advanced tumours might have "invaded" nearby vital structures or spread out ("metastasized") to form more cancers at distant sites. Both of these scenarios can render surgery impossible as the "collateral damage" in removing the cancer would be too much. Often the next best option available is radiotherapy.

Radiotherapy1 works by using beams of radiation to kill the tumour within the patient rather than by actually cutting open the patient to remove it. It has three major advantages over surgery.

  1. You avoid surgical trama ie the aforementioned collateral damage done by cutting into the patient to remove the tumour. 
  2. You can overlap multiple treatment beams which means you can use weak individual beams, to minimize the harm to sensitive but healthy surrounding tissue, but have all the beams overlap in the tumour region giving a highly localized  damaging effect around the tumour. 
  3. Generally, but not always, tumour tissue (really cells but lets stick to using "tissue" which is just a lump of cells anyway2) are worse at recovering from radiation than normal tissue. Hence, deliver the radiation in fractions seperated by an appropriate healing window and you will often find that the tumour is more damaged by the radiation than the normal tissue.
What I just explained pretty much covers all of radiotherapy from 1910's "röntgenotherapy" to today's cutting edge Ion Therapy. Despite all the complexity of modern radiotherapy technology, radiotherapy is still basically just a simple geometry and relative toxicity problem. 

If you only want the basic theory stop here. If you want to hear about daily practice read part two.


  1. Strictly I'm only talking about external beam radiotherapy (EBR) with modern linear accelerators (linacs) here. There are other types but linac EBR is the majority so I think it is an acceptable omission. 
  2. I wrote this whole thing trying to avoid as much field-specific medical physics nomenclature as possible so layfolk understand it.