Newer radiation treatments--brachytherapy and conformal radiotherapy--were discussed at a symposium at the 1996 meeting of the American Society for Therapeutic Radiology and Oncology (ASTRO) in Los Angeles.
Kent Wallner, MD, of Memorial Sloan-Kettering who has been implanting radioactive seeds for eight years, reported that tumor control rates with implantation are quite similar to the rates achieved with radical prostatectomy--at least over a 6-year period following the therapy. "Of course, these results need to be verified, but I think that radioactive seed implantation will very soon begin playing a more prominent role in the treatment of prostate cancer," he said.
The treatment has a number of advantages. It can be performed on an outpatient basis; it allows most men to go back to work within a few days; and it appears to preserve potency. All of the men under age 60 who were able to achieve erection before seed implantation remained potent 5 years after treatment, while 80% of those over 60 retained their ability to have erections.
Three-Dimensional Conformal Radiotherapy
Gerald E. Hanks, MD, chairman of radiation oncology at Fox Chase Cancer Center in Philadelphia, described the results of a study in which 233 men were treated with three-dimensional conformal radiotherapy (3D-CRT). The success rate at five years, as measured by a stable PSA level, was comparable to that of men treated with surgery at Johns Hopkins and M. D. Anderson. The 3D-CRT caused fewer side effects and preserved sexual function better than traditional radiation therapy, Dr. Hanks said.
Dr. Zvi Fuks, chairman of radiation oncology at Memorial Sloan-Kettering, who conducted the 3D-CRT study along with Dr. Hanks, discussed the possibility of increasing the dose of radiation by 10%. "The increase may be possible because 3D-CRT gives greater protection to healthy tissue," noted Dr. Fuks.
Dr Malcolm Bagshaw, professor emeritus at Stanford University School of Medicine, who pioneered the use of external-beam and linear accelerator treatment, observed that "the standard dose of 70 Gy is really quite a high dose in its own right. It is possible to increase the dose, but to what extent we don't really know yet. It would be important to increase the dose as high as can be achieved without increasing unwanted side effects. I think that for the time being, when a dose of 70 Gy is exceeded, it should be achieved in a clinical trial by people who are treating with a well-developed protocol and escalating the dose very cautiously.
Improvements in Traditional Radiotherapy
"We're seeing an absolute technical explosion in the development of linear accelerators, computer control of linear accelerators, better ways to plan the treatment and better ways to calculate the dosage," noted Dr. Bagshaw. Treating prostate cancer patients who are considered good candidates for radical surgery with external-beam radiation instead, is yielding the same long-term survival (15 years and longer) as surgery, he said.
Traditional radiotherapy may also have new applications. A pair of studies determined that traditional therapy could be effective for early-stage disease. The Cleveland Clinic study of 400 men with early-stage prostate cancer indicated that regardless of whether surgery or radiation was chosen, the same percentage in each group were recurrence free after 5 years. At the University of Michigan, Ann Arbor, 93 men who were candidates for prostate surgery were treated with traditional therapy instead. Five years after treatment, almost 99% showed signs of recurrence, a rate identical to that following surgery.