Radiation therapy uses high-energy x-rays, either beamed from a machine or emitted by radioactive seeds implanted in the prostate, to kill cancer cells. When prostate cancer is localised, radiation therapy can serve as an alternative to surgery. External beam radiation therapy is also commonly used to treat regional disease — cancers that have spread too widely in the pelvis to be removed surgically, but have not spread to the lymph nodes. In men with advanced disease, radiation therapy can also help shrink tumours and relieve pain.
Nevertheless, radiation that kills cancerous cells can also damage or kill healthy cells, resulting in increased risk for urinary or sexual dysfunction. Depending on the type of radiation used, up to one-half of patients may become impotent within two years of having radiation therapy. In addition, about 15% to 30% of men who have radiation therapy have urinary burning, urinary bleeding, frequent urination, rectal bleeding, rectal discomfort or diarrhoea during or shortly after the treatment.
External Beam Radiation Therapy
External beam radiation therapy generally requires treatment five days a week for six or seven weeks. The treatment causes no pain and each session lasts just a few minutes. The primary target is the prostate gland itself. If the tumor is large, hormonal therapy may be started at the time of radiation therapy in many cases and continued for several years. In addition, the seminal vesicles may be irradiated, since prostate cancer commonly spreads to this location.
Radiation can also be delivered to the prostate from dozens of tiny radioactive seeds that are implanted directly into the prostate gland. This approach, known as interstitial implantation or brachytherapy, has the advantage of delivering a high dose of radiation to tissues in the immediate area, while minimising damage to healthy tissues such as the rectum and bladder.
As practiced today, internal radiation therapy relies on ultrasound or CT to guide the placement of thin-walled needles through the skin of the perineum. Seeds made of radioactive palladium or iodine are delivered through the needles into the prostate, according to customised patterns developed using sophisticated computer programs — to conform to the shape and size of the individual’s prostate.
Refer to “Prostate Brachytherapy” page for more information.
Conformal Radiation Therapy
Three-dimensional conformal radiation therapy (3D-CRT) uses sophisticated computer software to precisely shape the distribution of radiation beams to the shape of the diseased prostate, thereby minimizing damage to normal tissue in the vicinity of treatment.
Using high-quality imaging techniques such as computed tomography (CT) or magnetic resonance imaging (MRI), plus powerful workstation computers, doctors are now able to visualize radiation therapy targets and aim radiation more directly at the tumor and cancerous tissues — while sparing critical adjacent normal structures.
More recent advances include IMRT and VMA which enable more precise delivery of radiation to the prostate with less radiation to the adjacent tissues, resulting in less toxicity and enabling higher doses to be used (~75g) with better long-term results.