These new facilities will cost £250m (€318m) and will deliver a treatment that uses high-energy proton particle beams to destroy cancer cells.
Despite the heavy investment, the NHS believes that they will save money in the long term. By 2014, it's estimated that it would be paying out £30m (€38m) a year for patients to travel overseas for the treatment.
But just what is this type of treatment and will it be introduced here in Ireland?
Unlike traditional radiotherapy, which uses X-rays, proton therapy extracts protons from the centre of the atom and these are then aimed at the cancerous tissue.
Radiation oncologist Dr William Hartsell is the Medical Director of Chicago's ProCure Centre, one of an American chain of private clinics that specialise in proton therapy.
"What's happening inside the tumour is basically the same with traditional radiotherapy and proton therapy," he says. "In that context, the proton therapy is slightly more effective but not by much.
"What we do see, though, with proton therapy is that there is not as much collateral damage to the tissue around the cancerous tissue and that is its huge benefit."
This is because the protons release their energy when they stop at their target rather than when they are travelling through tissue.
It's particularly important for cancers which are located in sensitive areas such as the front of the skull and the nose and throat areas. It's also a reason why proton therapy is used more for rarer tumours.
Proton therapy is also used in clinics like ProCure for certain types of paediatric brain cancer.
"How I got into proton therapy is that I had treated a lot of children over the years and it is a therapy that is best used in children," says Dr Hartsell, who has been a radiation oncologist for 25 years, including a couple of years working in the Irish health system.
"We know that radiation therapy is effective in killing cancer cells, but it kills normal cells too. With proton therapy, much more of that normal tissue is kept and we can avoid a lot of the side-effects."
Proton therapy has been used by some Irish patients under the Treatment Abroad Scheme.
The HSE told Health & Living that: "Where the number of patients referred abroad for treatment is less than five, the Treatment Abroad Scheme does not release information in respect of them to protect patient confidentiality."
One person who availed of the treatment overseas is Megan Malone, who underwent it at Massachusetts General Hospital last year and whose story was documented in the media.
It was reported in the news at the time that the HSE paid for the six-week proton therapy as it's a treatment that was deemed medically necessary but was unavailable in Ireland. Megan returned home with her family to Cork last September and while she still undergoes MRI testing, her cancer has now gone.
Situations like Megan's are unusual and with less than five patients going abroad for proton therapy, there are no plans to provide the treatment in Ireland.
A spokesperson for the National Cancer Control Programme (NCCP) says: "The simple answer is that we won't be proposing it in Ireland. The cost of providing the treatment here would be too high given the number -- understood to be below five -- referred for it."
A proton therapy facility here would cost in the region of €100m due to the level of technology used.
The fact that two facilities will be situated in the UK will be of benefit to Irish patients who may need treatment overseas as they will have a shorter distance to travel.
While proton therapy isn't seen as financially viable in Ireland, there has been a significant upgrading of radiation oncology services.
Two new radiation oncology centres were opened at Beaumont and St James's Hospitals this year and new technologies, including the Rapid Arc treatment technology, have been made available.
According to the NCCP, this technology "allows precise delivery of the radiotherapy dose to the target area.
"It is designed to reduce the dose to nearby tissues and reduce the probability of side-effects when compared with standard radiotherapy."
There are 31 proton therapy facilities worldwide -- 10 in the US, eight in Japan and the remainder are located around Europe.
They are expensive to build. Dr Hartsell reports that the Chicago ProCure Centre cost $135m and that a facility with "all the bells and whistles" at the University of Pennsylvania cost $200m.
But Dr Hartsell believes that a proton therapy facility may eventually be built in Ireland.
"If you look at the population in Ireland at the moment and the anticipated increase in population and in cancer cases, I think the cost equation of paying for individual treatments abroad versus paying for a facility may change.
"I think I'd be surprised if by 2020 there isn't a proton therapy facility in Ireland."