An undiscussed danger of radiation therapy to the head is increased risk of stroke. A study of head and neck cancer patients who received radiation therapy found that stroke rates were five times greater than expected. This elevated stroke risk was found many years after administration of radiation. The average time between radiation treatment and stroke was 10.9 years, but the increased risk of stroke persisted for 15 years after radiation therapy.
Late side effects occur months to years after finishing radiation. They can include: lymphedema of the arm; weakening of bone; fibrosis of the lung; accelerated atherosclerosis of the heart; and, secondary malignancies. Radiation can also affect salivary function, thyroid function and gonadal function long term.
Pelvis. Radiation therapy aimed at the pelvis may cause these side effects:
- Rectal bleeding
- Bladder irritation
In addition, radiation therapy to the pelvis can cause different symptoms for men and women.
- Sexual problems, such as erectile dysfunction, which is the inability to get or maintain an erection
- Lowered sperm counts and reduced sperm activity from radiation therapy to the testes or prostate. This may affect the ability to father a child.
- Changes in menstruation, such as stopping menstruating
- Symptoms of menopause, such as vaginal itching, burning, and dryness
- Infertility, which is the inability to conceive a child or maintain a pregnancy, if both ovaries receive radiation.
 Abayomi OK. Neck irradiation, carotid injury and its consequences. Oral Oncol. 2004 Oct;40(9):872-8.
 Dorresteijn LD, Kappelle AC, Boogerd W, et al. Increased risk of ischemic stroke after radiotherapy on the neck in patients younger than 60 years. J Clin Oncol. 2002 Jan 1;20(1):282-8.