By Durado Brooks, MD, MPH

Thousands of men are diagnosed with prostate cancer each month. These men and their loved ones often turn to the internet to learn about their disease and treatment options, and these searches may lead to medical centers offering proton beam therapy.  These centers espouse the benefits of this treatment approach, and some include glowing testimonials from men who have undergone the treatment.

So is proton therapy the "magic bullet" for prostate cancer? 

The difference between proton therapy and traditional radiation

Proton therapy is a type of radiation treatment. Traditional radiation therapy has been used to treat cancers for a century using radioactive energy rays called "photons."  When radiation is directed at a cancerous tumor inside the body the rays must pass through normal, healthy tissue in order to reach the cancer cells. In doing so, photons often cause harm to these healthy cells in their quest to get to the tumor. 

In the case of prostate cancer, the radiation beams must pass through the skin, the bladder and the rectum on the way to the prostate gland, and once they reach the gland they encounter normal prostate cells and the nerves that control penile erections.  Damage to these tissues can lead to the complications that often accompany radiation treatment for prostate cancer, including bladder problems, rectal leakage or bleeding, and difficulty with erections.

Proton therapy is a new way to deliver radiation to tumors using tiny, sub-atomic particles (protons) instead of the photons used in conventional radiation treatment. Proton therapy uses new technology to accelerate atoms to 93,000 miles per second, separating the protons from the atom. While moving at this high-speed, the particles are "fired" at the patient's tumor. These charged particles deliver a very high dose of radiation to the cancer but release very little radiation to the normal tissue in their path.  In theory, this approach minimizes damage to healthy organs and structures surrounding the cancer. 

Benefits in prostate cancer uncertain

Proton therapy has been proven beneficial for tumors surrounded by sensitive structures such as the eye, brain, and spinal cord, where the potential for radiation damage is very high. Proton therapy also offers a distinct benefit in many childhood cancers due to the high risk of long-term side effects in children who receive standard radiation treatment.

In contrast, most studies of proton therapy for prostate cancer suggest that this new approach may be just as good as standard photon radiation treatment at controlling the growth and spread of the cancer, but there is no evidence that proton treatment does a better job of curing the cancer.

And in spite of the theory that protons cause less damage to normal tissue, there is at present no convincing evidence that urinary (bladder problems), gastrointestinal (rectal leakage or bleeding), or sexual (erectile dysfunction),  complication rates are lower following proton therapy. A few studies suggest that rates of some side effects might even be higher. 

Proton therapy popular and profitable

The lack of evidence has not slowed the rapid increase in the use of proton treatment for prostate cancer. One recent study documented a 67% increase in the number of cases of proton treatment for prostate cancer billed to Medicare between 2006 and 2009.  This rate of growth is particularly noteworthy given the limited access to proton therapy: there are at present only 10 proton beam centers operating in the United States, and each center treats only a few hundred cancer patients each year.

 The small number of centers reflects the complexity and cost ($100-$225 million) of building and maintaining the facilities. While equipment needed for standard radiation treatment can usually be added to an existing hospital or treatment facility, delivering proton beam therapy requires constructing a specialized building and installing complicated and expensive equipment to speed up atoms to what's needed to separate the proton and fire it at the tumor.  (Although it should be noted that more prostate cancer patients are being treated with proton therapy because new centers are opening, and increased outreach to patients is resulting in some centers extending hours to treat them.)

With this limited availability and no evidence that proton therapy is better, why is use of the procedure rising at such a feverish pace? Financial incentives may be playing a role. Proton beam therapy for prostate cancer is reimbursed at a much higher rate than traditional radiation treatment for the same condition. Medicare pays about $19,000 for a full dose of standard radiation therapy for prostate cancer, but it pays nearly double for proton therapy - more than $32,000. 

Prostate cancer has become far and away the most common condition for which a Medicare beneficiary receives proton beam therapy, accounting for 2 of every 3 claims and 80% of Medicare spending on the procedure.  So while the cost to build a treatment center is high, proton therapy presents a lucrative opportunity for those who are willing to make the investment.  Established facilities in the US report annual revenue approaching $50 million.  This profit potential is leading to a veritable "arms race" in the field, with the number of facilities in the US expected to double in the next few years.

Given the rising cost of US healthcare it is increasingly important to prove through studies that paying more is associated with better outcomes.  A great deal of research is currently underway to determine whether proton beam therapy for prostate cancer can fulfill the hope of saving livings while limiting side effects and complications.  However, men who are choosing treatment today should be aware that proton therapy's hoped-for benefits have not yet been proven.  Meanwhile these men (as well as Medicare and other insurers) should reasonably ask, "Does it make sense to get the same results yet pay twice as much?"

Dr. Brooks is director of prostate and colorectal cancers for the American Cancer Society.