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Hypofractionated proton beam scanning radiotherapy for prostate cancer

Reporter: J. Taylor Whaley, MD
The Abramson Cancer Center of the University of Pennsylvania
Last Modified: May 14, 2011

Presenter: Herbst M, Wilms M, Dohr D, Hillbrand M.
Presenter's Affiliation: Renecker Proton Therapy Center, Munich, Germany

Background

• Prostate cancer is the most common non-skin cancer found in men, with approximately 200,000 cases occurring per year in the United States.
• The optimal radiation dose fractionation schedule for localized prostate cancer is unclear.
• Much interest has been given to hypofractionated radiation in recent years due to the potential advantages, including convenience for patients with shorter treatment duration, increased treatment capacity within a cancer center, and decreased costs to the healthcare system.
• From the perspective of prostate cancer radiation biology, hypofractionation could offer an increased therapeutic benefit, which could improve tumor control.
• However, despite the potential advantages, three randomized trials have failed to demonstrate these benefits, although each has its short-comings. Currently, several randomized trials are ongoing to evaluate hypofractioned radiation with photon and proton treatment.
• With increasing availability of protons around the world, hypofractionated radiation with proton therapy has been an area of interest.
• The purpose of this study was to validate dose escalation in prostate cancer treatment with proton beam scanning technique.

Materials and Methods

• 127 patients with prostate were treated with proton beam therapy from November 2009 to 2011 at the Rinecker Proton Therapy Center in Munich, Germany.
• 108 of the patients were treated in the definitive setting and 17 were treated in the post-operative setting. High risk patients composed 25% of the patient population and were treated with neoadjuvant and concurrent hormone ablation.
• PSA prior to radiation ranged from 0.1 to 948 mg/ml. Mean was 21.6 mg/ml.
• Treatment volumes included prostate and seminal vesicles in low risk patients. Regional lymphatics, up to the level of the common iliac nodes, were treated in high risk patients.
• Median dose prescription was 63 Gy (RBE) (range- 54 to 70 Gy) with a fractionation schedule dictated by protocol. Protocol for fractionation called for 3 Gy per fraction to the prostate and 2.5 Gy to the regional lymphatics delivered daily.
• Patients were treated with opposed lateral proton beams only.
• Treatment set-up included a daily rectal balloon as well as gold fiducials.
• Follow up was restricted to less than 1 year.

Results

• Toxicity was recorded in the acute setting, at 3 months, and at 6 months follow up.

• PSA evaluation occurred at 3 month follow up visit. Range was 0.01 to 130 ng/mL (mean of 6.56). No further follow up was available.

Author's Conclusions

• In patients with prostate cancer, hypofractionated proton beam scanning radiotherapy offers a viable option with dosimetric advantages of proton therapy and convenience advantages to patients.
• The hypofractionated treatment was well tolerated despite dose elevation to 63 Gy. Acute toxicity in this cohort of patients was acceptable.
• The acute side effects decreased within 4 to 5 weeks following treatment. At 3 and 6 months of follow up, no GI or GU side effects of grade 2 or greater were reported.
• The acute decrease in PSA seen after 3 months was an impressive decline.
• Further follow up is required to evaluate the local and biochemical control as well as any potential late side effects of hypofractionated proton therapy.

Clinical Implications

• The authors present their experience with hypofractionated proton radiotherapy for prostate cancer, and the presentation is certainly a valuable contribution to the literature.
• In this cohort of patients, the acute toxicity was acceptable and comparable to toxicity seen in previous trials for standard fractionation as well as photon treatment.
• Although the acute decline in PSA is indeed striking, much longer follow up is required to evaluate the effectiveness of the treatment due to the indolent nature of prostate cancer.
• Information on late effects and long term outcomes associated with this treatment remains unavailable and will certainly contribute to the literature when longer follow-up permits analysis of quality of life and disease control following hypofractionated proton beam radiotherapy.
• Certainly, prospective randomized trials are preferred to further evaluate the role of proton therapy in prostate cancer.