SEATTLE--A mixture of neutron radiation with conventional photon radiation, using a custom tailored pelvic template for each patient, appears to provide more effective therapy for prostate cancer than photon radiation alone (eg, external beam or I-125), while reducing the complications caused by neutron radiation alone, said Jeffrey Forman, MD, of Wayne State University, Detroit.
Dr. Forman discussed the technique, called three-dimensional conformal fast neutron irradiation, at the Pacific Northwest Cancer Foundation Meeting on Transperineal Brachytherapy for Early Stage Prostate Cancer.
He has been studying neutron radiation for prostate cancer treatment because, he said, "radiobiologic principles would suggest that a slowly proliferating tumor, like prostate cancer, would be advantageously treated by high LET (linear energy transfer) radiation."
This has indeed proved to be the case, with 70% vs 58% local control of the tumor, and 53% vs 29% 10-year survival in favor of neutron/photon irradiation vs conventional external photon beam therapy alone (RTOG 77-04).
However, pelvic neutron irradiation has a high rate of complications, including rectal toxicity, bladder complications, and hip stiffness, progressing to pelvic bone necrosis in some patients. To address this problem, researchers have applied 3D conformal irradiation techniques to neutron therapy (see below).
In this technique, the neutron beams are directed more precisely to the confined area of the tumor, thus sparing adjacent radiosensitive structures such as the bladder and rectal tissue.