Radiotherapy is one of the two main treatment modalities aimed at curing prostate cancer. It can be delivered either as external beam radiation or interstitial brachytherapy (radioactive seeds implanted into the prostate). This article will focus mainly on external beam treatment, which is also very effective for improving symptoms if the tumour has spread to other organs (mainly bones).
How it works
Radiotherapy uses high-energy x-rays to destroy tumour cells. A machine called a linear accelerator rotates around the patient lying on the treatment couch, delivering high-dose radiation to the tumour from different angles while reducing the dose to surrounding tissues. Treatment is given in daily sessions from Monday to Friday for four to eight weeks.
Nowadays, we seldom use gamma rays produced by cobalt machines in the curative setting, although they remain an effective choice in palliative treatment. Photons (either x-rays or gamma rays) attack DNA — the major carrier of genetic information in cells (both normal and cancerous). The cells then die after losing their ability to grow and divide.
Radiotherapy or surgery?
Radiotherapy is suitable for patients of all ages, PSA levels, Gleason scores obtained from the biopsy and disease stages. Based on these factors, patients are divided into low-, intermediate- or high-risk groups for both local and distant spread — this will largely influence the choice of treatment.
Choosing between surgery and radiotherapy can be very difficult. In general, both provide the same long-term results and efficacy, but they have different side effects. Before deciding, it’s important to fully understand the pros and cons associated with each option.
Surgery — a single procedure with acceptable acute and long-term side effects — has an edge in younger patients, those with earlier-stage disease and those in the lower-risk group, but in patients over 70 years old with other medical problems, the complications of surgery are increased. If your Gleason score is 8 or higher, there’s a good chance that the tumour isn’t confined to the prostate alone. In this case, surgery might be complemented with radiotherapy and/or hormonal treatment, taking into account the side effects of all these modalities. Whenever possible, it’s preferable to choose one method that will effectively control the disease.
If radical prostatectomy fails to remove all the cancerous tissue or if the tumour recurs in the same area where the prostate was, radiotherapy can be used, but success with this approach has been limited. Three recent clinical trials showed benefits for immediate radiotherapy post radical prostatectomy in patients whose surgical margins were involved by cancer, or whose tumours extended outside the capsule or to the seminal vesicles. Those studies showed improvement in local control but not overall survival (even though there was a trend towards better survival). While the surgical options are limited if radiotherapy fails to control the cancer, newer approaches are on the horizon.
With hormonal therapy
If used together with radiotherapy, for intermediate- or high-risk patients, hormonal treatment will start two to four months prior to radiation. For intermediate-risk patients, the hormonal treatment will continue until the last day of radiation. Men in the high-risk category might need prolonged hormonal therapy, up to three years.
Preparation
After a biopsy confirms the diagnosis, further tests will be done to determine if the cancer has spread outside the prostate gland: blood work, a bone scan and, depending on the disease stage, computerized tomodensitometry (CT scan) of the abdomen and pelvis. Once the results are available, the radiation oncologist will discuss details about the treatment, as well as the possible need for hormonal treatment in conjunction with radiotherapy.
At the next visit, the patient will undergo a simulation; a special CT scan helps the radiation oncologist delineate the prostate, as well as other areas at risk for eventual spread of disease. At the same time, we perform an “urethrogram” to visualize the lower part of the prostate gland. This is a painless test in which a contrast dye is inserted through a tiny catheter in the penis, with no undesirable side effects reported except for mild burning. Patients might also have an ultrasound done after the CT scan to further image the prostate (this will help later on with the daily set-up for treatment).
The radiation oncologist and team then have a lot of “homework” to do to outline the prostate, bladder and rectum on the CT scan. A series of computer-assisted calculations help us determine the precise, safe level of radiation to the prostate gland that will minimize the dose to nearby organs and subsequent side effects.
Later, the patient will undergo another simulation to place the markings on his skin, and final x-rays that will be used for his daily set-up.
Procedures
The prostate isn’t stationary — depending on the fullness of the bladder or rectum, it moves up and down, back and forth daily. Many centres give patients special instructions for the simulations as well as the treatments, including emptying the bladder then drinking two large glasses of water a half-hour beforehand, and taking a laxative (e.g. milk of magnesia) to keep the rectum empty. Some centres use “fiducial markers,” small non-radioactive gold seeds inserted in the prostate to help adjust the beams. Other centres use ultrasound to position the radiation beams, and some use Cone Beam CT to image the target daily and readjust the beams. All these techniques increase the accuracy and reproducibility of the radiation treatments.
Treatment techniques include:
- 3D conformal radiotherapy, used in most centres — the radiation dose is shaped (conforms) to the target volume
- IMRT (Intensity Modulated Radiation Therapy) — each of the beams is subdivided into small “beamlets” of different intensity, in order to deliver high doses to the prostate and spare as much as possible the surrounding normal tissues
- CyberKnife® (investigational) — the treatment is delivered over a period of five days instead of four to eight weeks; some patients might not be eligible
A linear accelerator machine operated by radiotherapists delivers the treatment, which lasts only two to three minutes. During the rest of the session (up to 15 minutes), radiotherapists position the patient on the machine, do an ultrasound, plain films or Cone Beam CT to visualize the prostate and adjust the treatment fields, and make sure that all parameters determined for the procedure are in order. Special shields are used to spare radiation to the bladder and rectum, the two neighbouring organs.
Follow-up
The radiation oncologist sees the patient on a weekly basis during the therapy, and again four to six weeks later to assess his response and deal with any side effects that have developed. The radiation oncologist and the urologist who made the initial diagnosis share future follow-ups. Visits are usually scheduled every three months for the first year, every six months for the next four years and yearly after that. A PSA blood test one week before each appointment, together with a digital rectal examination, will be used to evaluate the response to treatment and long-term control.
Into the future
Research is ongoing on treatments that we hope will continue to expand our options and improve patient outcomes, including:
- boosting the radiation dose
- combining hormonal and radiation therapy in intermediate-risk patients
- IMRT
- hypofractionation (using shorter treatment time, i.e. four-and-a-half weeks, but with a higher dose per fraction, resulting in more killing of cells)
- chemotherapy in conjunction with hormones and radiotherapy for high-risk patients
- novel approaches like high dose rate brachytherapy as the sole treatment (monotherapy): instead of radioactive seeds, radiation is delivered through a number of small catheters that are placed in the prostate and removed following the treatment. Low- or intermediate-risk patients, with prostates smaller than 50 cc in size, are candidates for this approach; for high-risk patients, it is used to boost the external beam radiotherapy.
Radiotherapy is an effective treatment for prostate cancer, with a good cure rate and acceptable side-effect profile. Before deciding on any therapy, it’s important to have a frank discussion with your doctors about all the available options so that together, you can choose the one that’s best for you.
Dr. Boris Bahoric is a Radiation Oncologist at the Jewish General Hospital and Assistant Professor in the Department of Oncology at McGill University in Montreal, Québec.
