High-dose IMRT proven effective in treating prostate cancer

September 28, 2006

After nearly a decade of intensity-modulated radiation therapy barriers to its adoption remain, ranging from the high cost of technology to fundamental changes in the practice of medicine. Now, a study conducted at Memorial Sloan-Kettering Cancer Center may help overcome those obstacles, as it establishes IMRT as an indispensable weapon against at least one form of cancer.

After nearly a decade of intensity-modulated radiation therapy barriers to its adoption remain, ranging from the high cost of technology to fundamental changes in the practice of medicine. Now, a study conducted at Memorial Sloan-Kettering Cancer Center may help overcome those obstacles, as it establishes IMRT as an indispensable weapon against at least one form of cancer.

A study of men treated with IMRT for prostate cancer at Sloan-Kettering found that the majority remained alive with no evidence of disease after an average follow-up period of eight years. Results from this study, the first large-scale effort addressing long-term outcomes for prostate cancer patients using IMRT, will be published in the October issue of the Journal of Urology.

"Our results suggest that IMRT should be the treatment of choice for delivering high-dose external beam radiotherapy for patients with localized prostate cancer," said Dr. Michael J. Zelefsky, chief of the brachytherapy service at Sloan-Kettering. "We were able to show long-term safety and long-term efficacy in a very diverse group of prostate cancer patients that we followed - many for as long as 10 years."

The 561 prostate cancer patients with a median age of 68 were classified into prognostic risk groups as defined by National Comprehensive Cancer Network guidelines. These are based on clinical characteristics including age, T stage, Gleason score, PSA (prostate specific antigen) level, and pretreatment with neoadjuvant androgen deprivation.

After an average of eight years, 89% of the men in the favorable risk group were disease-free. The high-dose radiotherapy was also curative for 78% of the intermediate, and 67% of the unfavorable group who survived after an average period of eight years. None of the men in any group developed secondary cancers as a result of the radiation therapy.

The success was achieved despite the presence of an aggressive form of the disease in some patients, indicated by high Gleason scores and high PSA levels.

IMRT, an improved form of 3D conformal radiation therapy, uses enhanced planning treatment software that precisely targets the prostate, allowing the beam of radiation to deliver a high dose to the tumor target, while sparing the adjacent bladder and rectum from exposure to the higher amounts of radiation.

The precision of this technique may be why the eight-year results show that all patients maintained urinary continence, and only 1.6% of the 561 patients experienced rectal bleeding, according to Zelefsky. Of the men who were potent prior to IMRT, however, erectile dysfunction developed in 49%.

"This study confirms that we can improve patients' quality of life by reducing the side effects of radiotherapy while maintaining disease-free survival," said Dr. Zelefsky. "But there is still room for improvement. We are incorporating image-guided approaches that may continue the excellent tumor control but further limit the area we are irradiating and reduce side effects."