Prostate Cancer, Radiation, and Rectal Side Effects

 

Beam radiation is an accepted whole-gland treatment for prostate cancer. It is also called radical radiation or radical radiotherapy. Radiation is often prescribed for men who can’t have or don’t want surgery (radical prostatectomy). Many improvements in the technology, and refinements in the dosage, have occurred over the last two decades in a concerted effort to improve cancer control yet decrease the risks of side effects. Today, there are several different types of radical radiation:

  • Conventional external beam radiation therapy (EBRT)
  • Intensity modulated radiation therapy (IMRT)
  • Conformal beam radiation
  • Stereotactic radiation
  • Proton beam

Side effects of prostate cancer radiation, if they occur, are usually temporary. They can include fatigue, bladder/urinary dysfunction, sexual dysfunction, and rectal or bowel problems. Because of the “scatter effect” of all radiation, including proton beam, longer term side effects include a small, increased risk of of future secondary cancers (bladder or rectal). Prostate cancer radiation also eliminates the option of treating recurrence or other pelvic cancers with any more radiation.

Cancer destruction by thermal ablation (e.g. cryo, HIFU or focal laser), is immediately effective against prostate cancer. However, radiation is not! Over time, it has a cumulative effect on the genetic mechanisms that allow cancer cells to reproduce themselves, so they gradually die off. Beam radiation is delivered daily over a period of weeks so the cancer cells are continually exposed to radiation. Radiation exposure can cause delayed side effects due to its gradual damage to healthy tissues.  I recently read two reports concerning rectal problems that can show up weeks, even months, after radiation.

A 1999 study compared conventional EBRT vs. conformal radiation to measure which caused more late onset (>3 months) side effects of rectal inflammation and bleeding.[i] (Note: conformal radiation is intended to “shape” the most intense dosage to strike the prostate with less scatter effect to the bladder and rectum.) Conformal radiation had fewer side effects, but the rates were still rather high:

 

Grade 1 problems Grade 2 problems (worse)
EBRT 56% 15%
Conformal 37% 5%

 

A much more recent study tracked the incidence of adverse rectal events, especially rectal bleeding, following proton beam therapy.[ii] It was a fairly large study with 1285 consecutive patients.  Grade 1 rectal bleeding occurred in 217 patients (16.9%), Grade 2 in 14.5%, and Grade 3 in 11 (0.9%). It should be noted that men on blood thinners were at greater risk for developing rectal bleeding, as were those receiving investigational (higher) doses of radiation that affected the rectal wall.

There will always be a place for radiation as a potentially curative treatment for prostate cancer. What’s important, as with any treatment modality, is the two-pronged question: How effective is the treatment, and what are the side effect risks? The 1999 study reported that with a median follow-up period of 3.6 years, the cancer control rates were 83% for EBRT and 78% for conformal. This suggests that even though the conformal group had fewer rectal side effects, almost 1 in 4 patients (22%) were at risk for recurrence.

 

Patients should be fully informed by their doctors regarding the cost/benefits ratio of the treatments they are considering. It is to be hoped that improvements in targeting radiation to the cancer while protecting nearby healthy structures will continue to be made.

 


[i] Dearnaley D, Khoo V, Norman A et al. Comparison of radiation side-effects of conformal and conventional radiotherapy in prostate cancer: a randomized trial. Lancet 1999 Jan; 353(9149):267-72.

[ii] Colaco RJ, Hoppe BS, Flampouri S et al. Rectal toxicity after proton therapy for prostate cancer: An analysis of outcomes of prospective studies conducted at the University of Florida Proton Therapy Institute. Int J Radiat Oncol Biol Phys. 2014 Nov 5. pii: S0360-3016(14)04060-7.

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