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6. Side effects from external beam radiotherapy.

Everything is funny as long as it is happening to somebody else.
(Will Rogers)

This web page describes the type of side effects that can arise from external beam radiotherapy. They primarily affect the rectum, bladder and urethra and they also affect sexual function. Some of the side effects occur during or shortly after radiotherapy but generally these are not too severe and clear up after a few weeks. Longer term side effects may not emerge for months or even years after treatment but it is only in a small minority of a few percent that the effects are sufficiently serious to need significant medical treatment.

Side effects (referred to as toxicity) that occur during or shortly after the radiotherapy treatment are known somewhat misleadingly as 'acute' side effects. Side effects that develop due to the radiation damage over a longer time scale (typically six months to a year) are known as 'late' side effects.

The US Radiation Therapy Oncology Group (RTOG) have devised a grading scheme for side effects but, for simplicity, we will simply divide them into mild and moderate to severe and these will be discussed below.

There have been numerous papers published on side effects and these all show that side effects are reduced by using 3-D CRT or IMRT compared with earlier radiotherapy techniques. There is a good deal of variation between the results of the different trials and, for the moderate to severe side effects, this is partly due to statistical uncertainty because the actual numbers experiencing the more serious side effects are small. The figures below are an amalgam of figures from several reports and should be treated as a guide rather than as an accurate statistical analysis.

The mild early (acute) side effects are simply an increased urgency to urinate and/or a stinging sensation when urinating. With 3-D conformal radiotherapy or IMRT at doses between 70 and 80 Gray, these mild effects occur in about 40% of men. About 30% experience nothing at all. Of the remainder, the urinary side effects may be a little more severe in terms of the urinary urgency, stinging or very weak flow. However, even these moderate side effects are generally temporary and can be alleviated by medication. Only very rarely (less than about 0.5%) do more serious problems like urinary retention occur which might necessitate the temporary use of a catheter.

Late urinary side effects are also quite rare. About 75% of men will not experience any late side effects and about 15% will experience only mild problems in terms of continuing urinary urgency (i.e. having to go to the toilet more than twice as often as previously). Most of the remainder will experience a frequent need to urinate (every hour or so) and they may experience pain or stinging when urinating. Medication is needed to deal with these problems. A very small minority (under 1%) will experience more serious problems like urinary retention, blood in the urine and so on. This unlucky small minority may require major medical intervention to deal with their problems.

About 75% of men experience no early rectal side effects. About 20% experience either some rectal discomfort or a tendency to diarrhoea. The remainder may suffer from more severe diarrhoea or abdominal pains and will need some medication to deal with the problems. Rectal bleeding at an early stage is extremely unlikely.

About 90% of men will experience no late rectal side. Of the remainder, most will experience a continuing problem of diarrhea but an unfortunate small minority of between 1% and 2% will experience more serious problems like rectal bleeding. These few may need more serious medical treatment like surgery to deal with or alleviate the problems. It has also been reported that the use of a hyperbaric chamber to breathe an enriched oxygen air supply for a period can also reduce or halt rectal bleeding. The occurrence of rectal bleeding is certainly a function of the dose and treatment at 80 Gy or thereabouts is likely to lead to about a doubling of rectal bleeding cases compared to 70 Gy treatments but the incidence is still reasonably low. Nevertheless, it does emphasise the increasing importance of more accurate targeting methods like IMRT at higher doses. There seems to be a rule of thumb that no more than about 20% of the rectum in the neighbourhood of the prostate should be subject to high levels of radiation of around 90% of the prostate dose.

It has also been shown that a history of diabetes has a significant impact on the likelihood of rectal bleeding - Akimoto et al (2004). It is also likely that other factors - like a large prostate - that make it difficult to avoid subjecting the rectum to high doses of radiation will also influence the occurrence of rectal bleeding.

Since radiotherapy is usually given in conjunction with hormone therapies, the side effects from the two therapies become entangled. The comments below apply to EBRT alone or to the period after hormone therapy ceases.

The impact of radiotherapy on sexual function seems less well documented than urinary and rectal side effects. The most immediate effect that develops over a few months to a year is that orgasms become largely 'dry'. A small amount of ejaculatory fluid may continue to be produced probably by the Cowper glands that are not irradiated. These glands are normally responsible for the production of a small amount of pre-ejaculatory fluid. From postings in internet newsgroups, opinions about the 'quality' of dry orgasms are variable but most seem to feel that they do not diminish sexual pleasure too much.

In the longer term, the radiation is thought to damage the nerves that control erections. These run down either side of the prostate. However, because prostate cancer affects mainly older men, it is difficult to distinguish between effects due to general ageing and those due to the radiation. However, for men in their sixties who were potent at the start of their treatment, about half will retain their potency at three years after treatment. For younger men, the figure is probably higher. Because the radiation damages rather than destroys the nerves responsible for erections, drugs like Viagra and Cialis can help to mitigate against 'creeping' impotence'.

The likelihood of developing side effects may well be linked to other things like overall health and diet. Keeping fit and eating well are worthwhile in their own right but they assume even greater importance in responding to medical illnesses and their treatment.

Akimoto T., Muramatsu H., Takahashi M. et al (2004)
Rectal bleeding after hypofractionated radiotherapy for prostate cancer: correlation between clinical and dosimetric parameters and the incidence of grade 2 or worse rectal bleeding.
Int. J. Radiation Oncology, Vol.60, Issue 4, pp.1033-1039.