••• Chapter 49^ Radiation Therapy, Chemotherapy, Immunotherapy, and Tumor Markers^489
❍ What three main biologic processes are involved in the “dose-rate effect”?
(1) Repair of sublethal damage that occurs when radiation is delivered slowly. As the dose rate diminishes, repair
of sublethal damage occurs.
(2) Cellular proliferation occurs during protracted radiation exposure if the dose rate is low enough.
(3) Redistribution and accumulation of cells throughout the proliferative cycle. A low-dose rate limits cellular
proliferation allowing cells to accumulate in the radiosensitive G2 phase, ultimately leading to greater cell
killing.
❍ What are some advantages of low-dose rate remote afterloading brachytherapy for interstitial and
intracavitary applications?
The advantages include reduced radiation exposure to hospital health-care providers, improved control of isodose
distributions, and no need for shielded rooms.
❍ What are some advantages of high-dose rate afterloading brachytherapy, what number of fractional doses
are used on average and what is the approximate dose per fraction?
On average, high-dose remote afterloading brachytherapy employs five fractional doses with the dose per fraction
ranging between 500 and 800 cGy to point A.
❍ What are some advantages of high-dose rate remove afterloading brachytherapy for interstitial and
intracavitary applications?
(1) The radiation exposure to hospital health-care providers is essentially eliminated.
(2) There are no complications from prolonged bed rest since patient mobilization time is significantly shortened.
(3) Treatment is done on an outpatient basis, eliminating the need for general anesthesia.
(4) Treatment planning and dosimetry are more exact.
❍ What factors predispose a patient to radiation injury?
The patient’s nutritional status, prior collagen-vascular disease, superimposed infection, and physical or chemical
trauma.
❍ What doses of radiation will cause skin erythema?
In general, single doses between 600 and 750 cGy will produce erythema. Dry desquamation appears with doses
5000 cGy and skin ulceration with ulcers over 6500 cGy.
❍ What are some common gastrointestinal complaints following abdominal or pelvic irradiation?
Adverse side effects include watery diarrhea, abdominal cramping, increased peristalsis, decreased absorption, and
transit time. If the rectum is included in the radiation field, rectal discomfort and tenesmus, and bleeding may be
experienced.
❍ At what doses of radiation are bowel mucosal ulcerations, fibrosis, stenosis, and fistula formation
encountered?
These adverse changes are seen when the small and large bowel are exposed to doses of 6000 cGy or more.