Proton therapy for prostate cancer – Better than regular radiation?

Are those ads that claim that proton therapy for prostate cancer is better really true?

What we do know is that this type of external radiation treatment uses nuclear technology to deliver fast-moving ions into cancer tumors. It’s also called proton beam therapy for prostate cancer.

Some claim that proton therapy for prostate cancer is more precise than traditional external beam radiation and may reduce the risk of incontinence and impotence.

Growing in the US

This form of radiation treatment has increased in popularity since it was first introduced in the United States at Loma Linda University Medical Center.

Despite all the claims, there have only been limited clinical studies comparing proton beam therapy for prostate cancer to traditional forms of external beam radiation.

What is needed is a large, randomized clinical trial comparing proton therapy for prostate cancer to treatments such as radical prostatectomy, IMRT, and standard 3D conformal radiation.

Until that happens, we cannot know for sure if proton therapy for prostate cancer is better than other forms of radiation therapy.

But it is certainly a treatment option worth exploring, particularly as more therapy centers are opening across the U.S.

How proton therapy for prostate cancer differs

Proton beams do not release energy before and after they reach the desired area of the prostate. It is believed that this may cause less damage to healthy tissues.

Another claimed advantage is that doctors can deliver more radiation to the site of the tumor.

Some investigators have also claimed that proton therapy for prostate cancer offers less chance of developing secondary cancers, but we must stress that the clinical data on this is very sparse.

Clinical evidence

One trial studied a model in 3 men, but that is not enough to be conclusive. Other investigators (Nieder et al) have suggested that the estimated risk of men developing secondary cancers (such as bladder cancer and rectal cancer) following external beam radiotherapy, brachytherapy, and external beam radiotherapy/brachytherapy is low (less than 2%).

In a study (Slater et al) of 1,255 men treated between 1991 and 1997, it was reported that:

  • Overall biochemical disease-free survival rate with proton therapy was 73%
  • In men who had a pre-treatment PSA ≤ 4.0 it was 90%
  • In men with post-treatment PSA nadirs ≤ 0.50 it was 87% (nadir is the absolute lowest level PSA drops after treatment)
  • Rates dropped with rises in initial and nadir PSA values
  • Long-term survival outcomes were comparable with those reported for other curative treatments

The authors concluded that disease-free survival rates were comparable to other forms of local therapy.

The procedure

It is similar to traditional external beam radiation. One difference is that a special machine (commonly referred to as a synchrotron or cyclotron) is used to speed up the protons.

The speed determines how the protons travel to a specific depth in a man’s body.

Like all radiation, during treatment, a man must lie still. Before treatment, CT or MRI tests are used to target the tumor’s location and plot the course for proton beam therapy.

It may be used alone, or can be combined with surgery for prostate cancer, such as:

Prostate cancer questions and answers


Cancer.Net. Explaining Proton Therapy.
+Features/Treatments,+Tests,+and+Procedures/Explaining+Proton+Therapy. Accessed July 21, 2009.

Fontenot JD, Lee AK, Newhauser WD. Risk of secondary malignant neoplasms from proton therapy and intensity-modulated x-ray therapy for early-stage prostate cancer. Int J Radiat Oncol Biol Phys. 2009;74(2):616-22.

Nieder AM, Porter MP, Soloway MS. Radiation therapy for prostate cancer increases subsequent risk of bladder and rectal cancer: a population based cohort study. J Urol. 2008;180(5):2005-9; discussion 2009-10. Epub 2008 Sep 17.

Nguyen PL, Trofimov A, Zietman AL. Proton-beam vs intensity-modulated radiation therapy. Which is best for treating prostate cancer? Oncology.2008;22(7):748-54; discussion 754, 757.

Slater JD, Rossi CJ, Yonemoto LT, Bush DA., Jabola RB. Proton therapy for prostate cancer: the initial Loma Linda University experience. Int J Radiat Oncol Biol Phys. 2004 59(2): 348-352.

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