CyberKnife Radiotherapy Treatment For Prostate Cancer
The CyberKnife is a type of radiotherapy which is ground-breaking in terms of the treatment programme. By delivering a much higher dose using highly accurate technology, the CyberKnife reduces the number of treatment sessions required from 37 down to just five. There is no knife, no incisions and it is not a form of surgery. The CyberKnife system is composed of several parts – treatment is delivered by a linear accelerator (Linac). The Linac is mounted on a robotic arm, which is able to move freely around the patient and deliver treatment from all angles. The patient lies on a couch which itself can be programmed and adjusted to allow the beams to reach the tumour from many angles and in an optimal way.
The system also includes two x-ray machines located above the patient. These machines take images of the patient every 15 seconds and by doing so, can detect tiny movements. This is very important for prostate cancer patients, because the prostate itself can move, even though this may not be evident externally. If movement exceeds tiny margins, the robot and Linac automatically stops and treatment is re-planned to exactly match the changed location of the prostate.(needs to be re-phrased as the treatment is not re-planned but re-started when the robot locks on the prostate by adjusting for any movement).
What is different about the CyberKnife?
The key difference is the degree of accuracy achieved by the CyberKnife, as a result of x-rays being taken every 15 seconds. For prostate cancer patients, this is important because the prostate moves internally, even when the patient remains absolutely still.
“The imaging we have from treatment so far has shown exactly how much the prostate can move without any external signs of movement, such as when gas passes through the rectum or as the bladder fills,” says Dr El-Modir
When using traditional radiotherapy (even the most advanced Linac machines), oncologists plan treatments using margins of 5–15mm, to allow for natural movement and slight inaccuracy. The margins with CyberKnife are much smaller: just 0–2mm. Because of this confidence in accuracy, the CyberKnife can safely deliver much higher doses of radiotherapy in each session. This very high dose, delivered with such precision, is known medically as stereotactic therapy. With the CyberKnife the number of treatment sessions is just five, compared with 37 required for standard prostate cancer radiotherapy.
Who is suitable for treatment with the CyberKnife?
CyberKnife is suitable for the following patients with prostate cancer:
- Localised prostate cancer (T1 or T2).
- Gleason score up to seven and PSA less than 20.
- No severe urinary symptoms or previous TURP (you will need to be able to manage without going to the toilet for 30 minutes to one hour during treatment). If you are unsure how severe your urinary symptoms are, try this IPSS symptom score. Men scoring more than 20 would be considered severe and not suitable for CyberKnife treatment.
- Small to medium size of prostate.
CyberKnife is not suitable if:
- you have artificial hips on both sides, but may be possible if on one side only;
- you have any medical condition or an implant that prohibits having a MRI scan.
What does CyberKnife treatment involve for a patient?
Implanting gold markers
The first step is to implant what is known as Fiducial markers into your prostate. These markers are made of gold and are the size of a grain of rice. They are implanted using a needle under ultrasound guidance via the perineum or rectum. You may experience a little discomfort, but this is normally mild. There follows a wait of seven to ten days for any minor swelling to settle down and any movement to settle.
Before your treatment, you will have a CT and MRI scan. CT scans are always used for radiotherapy planning and this is combined with MRI, because MRI provides a better definition of the outline of the prostate. The two are then fused together, along with the location of the markers which have been implanted into your prostate. The markers work on the same principle as the ‘lock on’ process used by airline pilots to ensure they are following a route. X-rays taken every 15 seconds during treatment will check whether the actual location of the gold markers matches their location in your pre-treatment treatment mapping. So any changes, even very small ones, are quickly identified and if there is movement, the robot will stop treatment and correct for the movement.
Where would I have my radiotherapy for prostate cancer?
Some patients have their five sessions within one week, others on alternative days across two weeks. Each session takes 30 minutes to an hour. Patients lie on the couch while the robotic arm moves around them, delivering treatment. You are not enclosed within the machine, as is necessary during an MRI scan, so there is no difficulty with claustrophobia. However, staff will help the patient to prepare for the experience of the robot moving around them, often getting quite close. The advantage of the constant process of imaging during treatment is that if you do move, or need to take a short break, this can be accommodated.
How effective is the CyberKnife and what are the possible side-effects and complications?
Several clinical studies have shown that CyberKnife is as effective as standard radiotherapy. CyberKnife is one of the recommended treatment options for the treatment of localised prostate cancer by the American Society of Radiation Oncology (ASTRO). Read the results of a study in full.
Possible side effects during treatment
Mild to moderate urinary problems and mild fatigue for 1–2 months; about 1% of patients need catheterization for urinary retention; resume normal activity immediately after treatment.
Possible long-term side effects
Despite receiving high doses of radiation, long-term urinary effects are not common and rectal injury is rare; 20–30% patients develop erectile dysfunction.