There are many situations where combinations of treatments for prostate cancer are recommended. For example, patients with very large prostate glands may require hormone treatment before a seed implant can be performed. Three to four months of hormone therapy will usually shrink the prostate by 40 to 50 percent, often making these difficult glands amenable to a seed implant.
Patients with a high PSA, a high Gleason score or advanced cancer found on staging studies will often benefit from hormone therapy administered prior to, during or even after external beam radiation. In this case, the hormone treatment shrinks the cancer, making it easier for the radiation therapy to kill the remaining cancer cells.
About half of the patients being considered for a seed implant are advised to receive this therapy in combination with external beam radiation. In this case, the treatment is not doubled, but rather, a reduced-dose of external radiation is combined with a reduced-dose seed implant. The external radiation is used to destroy cancer cells that may be in the tissues around the prostate or in the lymph nodes. The goal of the reduced-dose seed implant is to destroy the remaining cancer cells that are still present in the prostate after completion of the reduced-dose external beam radiation.
Patients who undergo radical prostatectomy may be at risk for a recurrence of their prostate cancer in the surgical area if the pathologist finds that the cancer has extended outside of the prostate gland. For example, if there is involvement of the seminal vesicles, neuro-vascular bundle, or lymph nodes, external beam radiation may be advised to destroy any remaining cancer cells. There are some situations where combinations of three treatments are advised. Some patients receive both hormone therapy and external radiation after a radical prostatectomy.
External Beam Radiation and Radioactive Seed Implants
Some patients may benefit from the combination of external beam radiation and seed implant therapy. In this case a reduced-dose of external radiation (five weeks) and a reduced-dose implant is used. The goal of the 5 weeks of external radiation is to kill any cancer cells that are outside the prostate in the surrounding fat and muscle, nerve bundle area (neuro-vascular bundle), seminal vesicles or lymph nodes. Some or all of these areas may need to be targeted with the external radiation depending on the risk factors in your particular case. In general, patients with a PSA less than >10, a Gleason score 7 or higher, a sizeable tumor felt on digital rectal exam (DRE), extensive cancer seen on the biopsy material (i.e., the majority of the biopsy cores involved), or cancer seen outside the prostate on an MRI, are more likely to be advised to undergo combination therapy.
Studies have shown that five weeks of external radiation (45 Gy) is usually sufficient to destroy small amounts of cancer. Surgical studies have shown that about half of patients do have "small fingers" of malignant cells outside the prostate, and that the risk factors for extra-prostatic cancer are those described above. Therefore, your treatment will be custom tailored based on which risk factors you have. For example, if you have a PSA of 9 and a Gleason score of 7, the external beam radiation treatment might be limited to the prostatic region. On the other hand, if you have a Gleason score of 8, and a PSA of 15, it is likely that whole pelvic radiation will be recommended.
The Timing of the Therapy
Please keep in mind that the five weeks of external radiation is also treating the prostate. Therefore, the seed implant dose must be reduced to take into account the 45 Gy that you have already received to the prostate. In most cases, the external radiation is given first. After a two to six week break, the seed implant is performed.
The five weeks of external beam radiation is extremely well tolerated. Just as the urinary and rectal symptoms are getting started, the treatment ends. By the time that the implant is performed, these side effects will have mostly or completely resolved. The side effects of the seed implant are virtually identical to those observed when seeds alone are performed.
The long-term complications of combination therapy are similar to those of prostate seed implant monotherapy. With combination therapy, we do observe rectal bleeding more frequently than with monotherapy. Erectile dysfunction may occur more often. As described above, these two problems can usually be managed successfully with medications.
You will be scheduled to have a CT scan of the prostate so that computerized dose calculations can be performed. This will allow your radiation oncologist to evaluate the actual dose delivered to the prostate gland as a result of the implant. These calculations are called post-implant dosimetry. The post-implant CT scan does not involve the injection of any dyes or contrast. You will not be required to drink any barium or use any laxatives or enemas. This test only takes about five minutes.
As part of your follow-up care, you will be instructed to see both your urologist and radiation oncologist. They will help you to get through the side effects as comfortably as possible. After three months they will perform routine DREs. The first PSA will be drawn about three months after the implant. Bone scans, CT scans, and MRI scans are not part of the routine follow-up. They may be ordered if your PSA rises.