Fast Neutron Radiotherapy Promising for Prostate Cancer

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Tushar Kumar, MD
Tushar Kumar, MD

SAN DIEGO—Experience with the world's largest series of patients treated with Fast Neutron Radiotherapy (FNRT) for localized prostate cancer (PCa) suggests that this approach is associated with excellent long-term outcomes with a good safety profile, according to data presented at the 52nd annual meeting of the American Society for Radiation Oncology.

“Fast Neutron Therapy is very powerful and radiobiologically very advantageous to the patient,” said lead researcher Tushar Kumar, MD, a radiation oncologist at Wayne State University in Detroit.  “Without the use of this current technology, there were substantial side-effects in earlier worldwide trials. Fast Neutron Therapy is particle radiotherapy, and it is different than traditional photon therapy. It is biologically more effective at treating certain types of cancers. ”

Dr. Kumar, who presented new study data at the meeting, said FNRT is not new, having been in use since 1938. It gained popularity in the 1980s, when 10 centers were using it, but today only four centers are using it. Dr. Kumar said he believes it is time to re-evaluate what he considers an important therapy.

“In the 1990s, there were two major randomized studies published with Fast Neutron Therapy and at least one the studies showed large toxicity,” Dr. Kumar said. “The problem with that study is that the techniques were not advanced. They were treating large fields, using inappropriate blocking, so the results of the study were not promising.”

Those hurdles have been overcome and the technology has become much more refined, he said. FNRT is associated with substantially less toxicity, thanks in part to the use of computed tomography guided therapy.

Dr. Kumar and his colleagues have treated 1,006 patients with a combination of photon radiotherapy and FNRT, the largest such series ever. The investigators categorized 21% of patients as low risk, 40% as intermediate risk, and 39% as high risk. They defined low risk as a PSA of 10 ng/mL or less, a Gleason score 2-6, and stage T1-T2a disease; intermediate risk as a PSA of 10.1-20 and/or a Gleason score of 7, and/or stage T2b disease); and high risk as a PSA above 20 and/or a Gleason score of 8-10, and/or stage T2c disease or greater. The median age of the study population was 67 years. The median follow-up was seven years and the median pre-treatment PSA level was 8.6. The cohort was 64% Caucasian and 36% African American. At the time of analysis, 59.7% of patients were still alive.

In addition, 4% of low-risk patients, 10% of intermediate-risk patients, and 35% of high-risk patients received androgen deprivation therapy after their radiation treatment.

 

The 10-year biochemical progression-free survival (BPFS) rate in the low-, intermediate-, and high-risk patients was 93.6%, 80.3%, and 61.7%, respectively. The 15-year BPFS was 88.1%, 80.3%, and 56.6%, respectively. The 10-year overall survival (OS) rate was 73%, 56.3%, and 52.7%, respectively. The 15-year OS rate was 44.2%, 13.2%, and 18.7%. 

ADT use correlated with improved OS in the low- and intermediate-risk groups, but not in the high-risk patients. OS was significantly longer for Caucasian men compared versus African-American men among the high-risk patients only, with no differences noted in BPFS.

“We found that you can use Fast Neutron Radiotherapy safely and minimize toxicity,” Dr. Kumar told Renal & Urology News. “We found that the patients do live a long time with prostate cancer, and when they do, they have minimal toxicity with neutrons. I think we can treat higher grade cancers more effectively and make the patients live longer.”

His team observed low rates of genitourinary (GU) and gastrointestinal (GI) toxicities. The three-month GU toxicity rates were 15% (Grade 1), 3% (Grade 2) and 0.5% (Grade 3). At six months, the GU toxicity rates were 14%, 3%, and 0.2%, respectively. The three-month GI toxicity rates were 17% (Grade 1), 2% (Grade 2), and 0.1% (Grade 3). At six months, the rates were 12%, 4%, and 0%, respectively.

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