Prostate Cancer Radiotherapy
External Beam Radiotherapy
Some of the newest advances in radiotherapy are in the field of external beam radiotherapy. The advantage of external beam radiotherapy is that it has the longest track record out of all forms of radiotherapy, and it does not require any invasive procedures or operations.
External beam radiotherapy (EBRT) is given in a way almost unrecognisable compared to 5 or 10 years ago (indeed it seems as if major advances occur every 6-12 months which decrease the risk of side-effects and/or increase cure rates). EBRT is very much technology and engineering-based, and there have been remarkable advances in recent years. The benefits to cancer patients are far-reaching, and prostate cancer patients in particular have been shown to benefit.
Prostate cancer EBRT is given typically over 8 or more weeks, 5 days a week. Each treatment takes about 15 minutes, and is just like having an x-ray.
There are several critical aspects of prostate cancer EBRT. These should be some of the questions you ask your treating radiation oncologist. If you read (and understand!) the following, you are lucky. It is rare that patients are given the opportunity to learn about all of these issues.
1. Marking the prostate with seeds ("Fiducial markers") or doing cone beam imaging
If possible, patients should consider having seeds (which are non-radioactive) put into the prostate before radiotherapy. Why? At simulation (i.e. the preparation scans done before EBRT) the prostate is outlined by the doctor, and the outline is overlaid against the hip and pelvic bones, and skin. Then each day during radiotherapy, patients are usually only set up to treat the prostate based on lining up to the bones and skin. This assumes that the prostate has not moved at all in relation to the bones and skin. However we know that the prostate moves every day because of differences in how full the bladder or bowel are. Thus it is quite possible (and has been demonstrated in studies) that many daily treatments not only miss parts of the prostate, they also treat normal body parts (such as rectum and bladder) unneccesarily. It makes far more sense to set the daily treatment up to where the prostate really is that day! This way we are much more likely to hit the prostate (potentially increasing cure) and avoid normal tissue (thus possibly decreasing side-effects). By putting seeds into the prostate, one can actually set up each day to the seeds, and be reassured that the prostate is getting the expected treatment. This should also decrease side-effects. If your centre does not have fiducial markers you should seriously consider finding a centre that does. An alternative method, which may be even better than fiducial markers, is the use of "cone beam" imaging. Cone beam may be better because not only does it show where the prostate is, it also shows the rectum and bladder (which of course we do not want to treat). More on cone beam imaging can be found here.
2. Voluming the prostate with MRI and CT
Once the seeds are in place, simulation occurs. Simulation is the process by which we put "volumes" on (i.e. outline in 3 dimensions) the prostate and cancer. In the past (and at many departments even today), patients were only volumed with x-ray or CT scans. CT-simulation is excellent for most cancer types. However the problem is that x-rays or CTs do not clearly show the prostate, and it is often impossible to tell prostate apart from normal tissues such as muscle, bladder and rectum. CTs are also fairly poor at showing cancer cells inside and outside the prostate. With the advent of MRI scans, the prostate can be very well seen, and cancer cells in surrounding fat, seminal vesicles, or lymph nodes are much better seen. For this reason, all patients having prostate cancer radiotherapy should seriously consider MRIs and CTs for voluming (this is called MRI-CT fusion). It is expected that using MRI-CT fusion increases likely cure and decreases side-effects. If you are not offered MRI-CT fusion, you should seriously consider finding a centre that does.
3. Considering lymph node treatment
Many patients with intermediate and high risk prostate cancer are at risk of lymph node spread. Particularly high risk patients should have a discussion with their radiation oncologist about lymph node treatment pros and cons. Studies have shown higher cure rates with lymph node treatment, at the expense of increased risks of side-effects. In Australia, many radiation oncologists do not offer lymph node treatment, however in other countries such as the USA, it is recommended for many patients. You should ask your radiation oncologist exactly what the risk of lymph node involvement is, and if it is high (say more than 15%), whether you will be offered the choice of lymph node radiotherapy.
4. Giving radiotherapy more slowly
In the past, patients were usually treated with radiotherapy by giving 2 Gy per day (Gy is the measurement of dose). This is given for, say, 37 treatments, to give a total dose of 74Gy (2 Gy x 37 = 74Gy). Some studies show that by giving the radiation more slowly (at 1.8 Gy per day instead of 2.0 Gy per day), that the risk of serious long term side-effects of radiotherapy may be halved. These studies are not conclusive, however potentially halving serious side-effects is a very important advance in treatment. It is interesting that few radiation oncologists in Australia give 1.8 Gy per day, but in the USA it is given much more commonly. In Australia, one reason doctors give two Gy per day because it shortens the treatment time (and often departments have limited radiotherapy resources and are trying to treat patients as quickly as possible). The other reason that doctors do not give 1.8Gy per day is that doctors may not believe that it makes any difference. However the only two good quality studies that looked at the issue of treating at 1.8 Gy per day instead of 2.0 Gy per day found that treating at 1.8 Gy per day at least halved side-effects, yet was just as effective at curing patients (to view the 2 study reports click here and here). Despite the fact that there are only two studies, this issue remains controversial.
5. Dose-escalation
In the past, prostate cancer patients were given quite low doses of radiation, which are now considered to be too low to maximize the chance of cure. Studies have shown that instead of between 60 and 70 Gy of radiation, most patients should probably be getting between 73.8 and 81Gy. With the advances in EBRT, these higher doses may be given with the same or less side-effects that occurred with the lower doses in the past. There are many radiation centres in Australia that do not treat patients to the best dose (which for many patients is at least 73.8Gy).
6. 3D conformal and intensity-modulated radiotherapy (IMRT)
Modern computing and engineering now allows us to treat the prostate cancer and miss most normal tissues. Old techniques (such as the "4 field box") should be avoided, as studies show much worse side-effects with these. The 4 field technique means that the cancer is treated from 4 angles, and the intersection (which is where the high dose region occurs) is in a box-like shape, thus treating unneccesarily large amounts of normal tissues. Prof Shakespeare believes that as a minimum, 6 field radiotherapy should be standard, and in many cases IMRT should be considered. These techniques decrease the amount of normal tissue treated significantly.
7. Daily x-rays during treatment
Prof Shakespeare's own research shows that every patient should have an x-ray every single day of radiotherapy treatment, to ensure that the prostate is being treated. We know that the prostate moves, so there is no point "treating blindly" without checking the prostate's position. In many radiation centres, x-rays are only done once a week or less: this seems a very poor option, since every day, patients positions change. It has been very well documented that if you do not do a check x-ray every single day, you may well be missing your prostate. As mentioned previously, the prostate position can be best seen if patients have seeds ("Fiducial markers") inserted before treatment or cone beam imaging. Unfortunately, most radiation departments do not use fiducial markers or cone beam, and instead x-ray patients' bones. This is all very well, except that we might treat the correct bone area every day, but the prostate might be partly missed. There seems to be little point doing daily x-rays of the bones when the prostate could be a centimetre or more away. This is why one of the best ways of ensuring the prostate is actually being treated is to do daily x-rays (also known as electronic portal imaging or on-board imaging) of fiducial markers which are inserted in the prostate, or doing cone beam imaging which identifies prostate, rectum and bladder.
