Follow-Up Data from UCSF Suggests Cyberknife Monotherapy Results Improved Slightly Over Time

Original Study Compared Stereotactic Monotherapy, Boost and Brachytherapy

by John Otrompke

(c) 2011 John Otrompke

Follow-up analysis from a small study comparing boost and monotherapy with the Cyberknife and brachytherapy for prostate cancer suggests that some monotherapy results have improved since publication, a researcher from the University of California at San Francisco said.

In the original study, published last year in the International Journal of Radiation Oncology, Biology and Physics, 20 of 38 patients were treated by the Cyberknife with stereotactic radiotherapy as a monotherapy, while 18 received the Cyberknife treatment as a boost (following external beam radiation and hormone therapy). 

The article, ‘Stereotactic Body Radiotherapy as Monotherapy or Post-External Beam Radiotherapy Boost for Prostate Cancer: Technique, Early Toxicity, and PSA Response’ (Jabbari, et al), which was published December 21, 2010, reported results at a minimum follow-up of 12 months.

In the time since publication (nearly a year), PSA nadirs for those treated with Cyberknife monotherapy have come down to more closely approach the lower level achieved with patients who received Cyberknife therapy as a boost. PSA nadir for those who received boost therapy was 0.3 nanograms per milliliter upon follow-up analysis, compared to about 0.5 at the time of the original publication,according to Alexander R. Gottschalk, MD, PhD, associate professor in radiation oncology at the University of California at San Francisco, a co-author on the study.

The nadir for those treated with both external beam radiation and the Cyberknife remains at 0.1, he added.

To date, Gottschalk has treated about 110 patients with stereotactic therapy, about half with monotherapy, and half as a boost, he said. In the study, which was not randomized, sicker patients received Cyberknife as a boost, Gottschalk explained.

“Patients who got Cyberknife treatment as a boost also received hormonal therapy, because in general they had more advanced disease, which required more aggressive therapy,” he said. “I try to choose whether they should get monotherapy or boost therapy depending on their prostate cancer characteristics,” he added.

Those who received Cyberknife as a monotherapy received 9.5 Gray for four fractions, while those who received a boost received the same dose for two fractions. When stereotactic therapy was used as a boost, the patients got 25 fractions of conventional radiation with two fractions of SBRT.

At the time of the study, researchers compared the PSA nadir achieved with both forms of Cyberknife treated with that experienced in a similar group of 44 patients who received brachytherapy, or high dose rate radiation with temporary radioactive “seeds,” according to the study.

Those in the monotherapy cohort had a median PSA nadir of 0.47 in the originally-published data, compared to 0.1 in the cohort which received boost therapy. 

For those who received brachytherapy, the nadir was 0.09, with a median follow-up of 48.6 months, the study indicated.

There are two types of brachytherapy: a permanent implant, and high dose rate radiation, in which a patient usually stays in the hospital for about 24 hours, Gottschalk noted.

Follow-up data indicated that grade three gastro-intestinal side effects remained the same and late grade three gastro-urinary toxicities remained similar.

In the original study, 42% of patients who received monotherapy with the Cyberknife had acute Grade 2 toxicity, compared to 11% of those who received Cyberknife as a boost, at a median follow-up of 18.3 months.

While Gottschalk still reported no early-occurring grade three gastrointestinal toxicities, about four out of 110 patients have reported a late-occurring grade three gastro-urinary toxicity, requiring a catheterization, he said.

In the original study, two patients experienced a late-occurring grade three gastro-urinary toxicity. Biochemical and clinical data show that no patients have progressed, Gottschalk added.