Conformal proton beam therapy of prostate cancer — update on the loma linda university medical center experience
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The ability to eradicate localized prostate cancer is dependent upon the radiation dose which can be delivered to the prostate. This dose is often limited by the tolerance of normal organs (rectum, bladder). Conformal beam therapy takes advantage of the unique depth dose characteristics of heavy charged particles (the Bragg Peak) to escalate the radiation dose delivered to the prostate while minimizing treatment-related toxicity.
643 patients with localized prostate cancer were treated with protons alone or a combination of protons and photons. All treatment was planned on a 3-D planning system and all received doses between 74–75 CGE (Cobalt Gray Equivalent) at 1.8–2.0 CGE/day. Patients were evaluated for toxicity and response to treatment.
Five-year actuarial clinical and biochemical disease-free survival rates for the entire group are 89 and 79% respectively. A statistically significant difference in biochemical disease-free survival was seen between patients in the “early” (T1b-2b, PSA<15) and “advanced” (T1b-2b, PSA>15 or T2c-T4, PSA<50) subgroups (89% vs. 68% at 4.5 years, p<0.001). A PSA nadir of less than 0.51 ng/ml predicted for the highest chance of freedom from biochemical recurrence. Minimal radiation proctitis was seen in 21% of patients; toxicity of greater serverity was seen in less than 1%.
Conformal proton beamt therapy produced high rates of response and minimal toxicity. A phase III dose escalation trial is in progress to help define the optimum radiation dose for the treatment of early stage prostate cancer.
Key WordsRadiotherapy Proton Prostate PSA Prognostic factors
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