The Science of Proton Therapy

Both standard photon (X-ray) radiation therapy and proton therapy attack tumors by interfering with the DNA of the cancer cells, preventing them from dividing and growing.  The difference between the two therapies is that protons can be more precisely targeted to the tumor, allowing patients to receive higher, more effective doses, and reducing damage to healthy tissue near the tumor. Research shows proton therapy can cause fewer short- and long-term side effects than standard radiation therapy, reduce the occurrence of secondary tumors1 and improve quality of life for patients.2,3

X-rays are electronic waves that penetrate tissue, gradually losing energy as they move along. To penetrate deeply enough in the body to reach most tumors, higher doses of radiation must be used. With X-ray therapy, however, the highest radiation dose occurs shortly after entering the body meaning that much of the radiation is deposited in the healthy tissue in front of the tumor.  When the X-ray exits the tumor, it continues to affect healthy tissue as it leaves the body. That can cause a variety of short- and long-term side effects, some of which can seriously affect quality of life and health.

With X-ray radiation therapy (black line), the radiation dose peaks soon after entering the body and often, long before reaching the tumor, gradually decreases.  Healthy tissue surrounding the tumor receives much of the dose.  With proton therapy (blue lines), treatment conforms more closely to the tumor, so that less radiation is deposited in the healthy tissue in front of the tumor compared to X-ray therapy, and almost none is deposited in the healthy tissue behind the tumor.

Protons are large particles that can be manipulated to release their energy at a precise point. The more energy, the deeper the protons can penetrate into the body.  The amount of proton energy is calculated to release the proton radiation precisely at the tumor site. The peak of this radiation dose (called the Bragg Peak) is designed to conform to the back of the tumor. Immediately after that point, the radiation dose falls to zero. Less of the radiation affects the healthy tissue in front of the tumor, and virtually none of it affects the healthy tissue behind the tumor.  That results in much less damage to healthy tissue or nearby organs and structures. It also means that a higher dose often can be delivered, leading to more effective treatment.

There are generally fewer side effects with proton therapy both in the short and long term.  For example:

  • More than half of men who receive X-ray therapy for prostate cancer experience short-term side effects such as diarrhea and painful urination, compared with virtually no side effects reported by patients who undergo proton therapy.4
  • While 15 percent of people who have X-ray therapy for head and neck cancer become blind, only 2 percent who undergo proton therapy experience that side effect.4
  • And 28.5 percent of children who have X-ray therapy to treat tumors in the brain or spine experience a 10-point IQ drop, compared to less than 2 percent of those who undergo proton therapy.4 Proton therapy also lessens the probability of secondary tumors occurring later in life, a significant problem for children who are cancer survivors.5

Web site:  www.procure.com

Media Contact:
Andrea Johnson, PCI
312/558-1770
ajohnson@pcipr.com

Footnotes: 
  1. Cox et al. Proton Therapy with Concurrent Chemotherapy can Reduce Toxicity and Allow Higher Radiation Doses in Advanced Non-Small Cell Lung Cancer. ASCO Annual meeting 2008.
  2. S. Ternier, Ph.D. Proton Therapy White Paper. On file.
  3. MacDonald S., DeLaney T. and Loeffler J. Proton Beam Radiation Therapy. Radiation Oncology 2006, 24:199-208.
  4. Metz J. Reduced Normal Tissue Toxicity with Proton Therapy. OncoLink 4.24.2002.
  5. Miralbell et al. Potential Reduction of the Incidence of Radiation-Induced Second Cancers by Using Proton Beam in the Treatment of Pediatric Tumors. Int J. Radiat. Oncol. Biol. Phys. 2002;54(3) 824-829