Is proton therapy for prostate cancer better than traditional radiation therapy?

Proton therapy for prostate cancer (or proton beam therapy for prostate cancer, as it is sometimes called) is a type of external radiation treatment that uses nuclear technology to deliver fast-moving ions into cancer tumors. Some claim it is more precise than traditional external beam radiation and may reduce the risk of incontinence and impotence, which are side effects of proton therapy for prostate cancer.

This form of radiation treatment has increased in popularity since it was first introduced in the United States at Loma Linda University Medical Center. Their web site makes many claims, but 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 a treatment option worth exploring.

How proton therapy 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. One trial only studied a model in 3 men, and 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%).

Slater et al reported on an early study of 1,255 men treated between 1991 and 1997 that overall biochemical disease-free survival rate with proton therapy was 73%, and was 90% in men who had a pre-treatment PSA ≤4.0. This rate was 87% in patients with post-treatment PSA nadirs ≤0.50. 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 proton radiation therapy demonstrated disease-free survival rates comparable with other forms of local therapy.

A small but growing number of medical centers in the United States now offer proton beam therapy for prostate cancer. While it is growing in popularity, it tends to be more expensive than traditional forms of radiation therapy.

The procedure

The actual procedure that a man undergoes for receiving proton therapy for prostate cancer 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. During the treatment, a man must lie still (to avoid having the radiation go to the wrong place). Before treatment, CT or MRI tests are used to target the tumor’s location and plot the course for proton beam therapy.

Proton therapy for prostate cancer may be used alone, or it is sometimes combined with surgery for prostate cancer (such as radical prostatectomy), radiation therapy, and/or chemotherapy.

7/09

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References:

Cancer.Net. Explaining Proton Therapy. http://www.cancer.net/patient/Library/Cancer.Net+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.