Proton therapy: a less toxic radiotherapy
radiotherapy Cancer proton therapy

Proton therapy: a less toxic radiotherapy

Dr. Talia Henkle
Dr. Talia Henkle

In 10 seconds? Proton therapy is a type of cancer radiation therapy (radiotherapy) that can be a safer alternative to traditional X-ray radiation. At this stage, however, proton therapy is pricey and frequently difficult to access.

Tell me more about it! Radiotherapy is a cancer treatment strategy that uses high-energy beams to damage and eventually kill cancer cells directly. X-rays have been the mainstay of radiation therapy since its inception. In 1988, proton beams entered the cancer treatment stage as a promising upgrade to conventional radiation therapy due to their better safety profile and are now recommended by experts for the treatment of over 40 different types of cancer.

So, what’s the difference? First, let me tell you about traditional radiotherapy. X-rays are weightless beams of energy that can be concentrated and targeted to tumors. While X-rays are great in that they can blast internal tumors without the need for surgery, they have seriously toxic downsides. After the X-rays reach their target, they will diffuse outwardly in all directions, damaging the healthy tissues around the target area. This can be dangerous when tumors are in sensitive areas (such as near the eyes, brainstem, or liver), and can even cause new cancers to form down the line!

OK, and what is proton therapy? Protons are the dense, positively charged components of atoms. Protons can be stripped from hydrogen atoms and accelerated in sophisticated machines to form high-energy beams that can be targeted to damage cancer cells.

So, why are protons less toxic? X-rays and proton beams have similar cancer-killing potential. The difference lies in the side effects. Unlike X-rays, protons have mass, which changes their physical properties. Instead of irradiating outwardly in all directions after hitting their target, protons are deposited at their calculated depth (i.e. in the tumor), sparing the surrounding tissues from their cell-killing potential.

Proton therapy can significantly protect healthy tissue from ionizing radiation Source: LaRiviere MJ, et al. Hematol Oncol Clin North Am; 2019:33(6)

That sounds good! But does it really make that much of a difference in practice? These days, proton therapy is touted most for pediatric and young adult patients–who are at the highest risk for developing long-term health issues (including other cancers!) from off-target X-ray radiation effects that can permanently damage developing tissues. It’s also useful for cancers in delicate areas. For example, X-ray irradiation of liver cancers may be administered at sub-optimal doses to avoid causing liver failure–which may not control the cancer. With proton therapy, however, the full dose can be administered to the tumor without fear of damaging the liver.

So, is proton therapy the current go-to? Not so fast. The machinery needed to perform proton therapy is extremely pricey–think $100-300 million to build 5 treatment rooms. These costs make the treatment very expensive, limit the number of centers that can be built, and make insurance companies less willing to finance proton therapy treatment (the main barrier to its wider usage today). But innovative business models and philanthropic efforts are underway to hopefully make proton therapy more affordable and accessible to everyone who will benefit.

The FLASH effect

Multiple cancer studies in mice have shown that quickly shooting ultra-high dose proton beams at tumors can simultaneously treat tumors and keep healthy tissues safer when compared with typical proton therapy treatment doses.

This is exciting! But before this strategy can be tested in humans, the existing machinery needs to be modified and clinical trials in patients need to be conducted to see if it can live up to the hype!

Dr. Talia Henkle has distilled 4 research papers saving you 14 hours of reading time.

The Science Integrity Check of this 3-min Science Digest was performed by Flávia Oliveira Geraldes.

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