Delayed Radiation Injury
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What is a Delayed Radiation Injury?
Radiation therapy is a vital part of oncology therapy. It is frequently employed to decrease and eliminate tumors, particularly those that may be difficult to access or treat surgically. It is used in prostate cancer, gynecologic cancers, bowel cancers, and many others. As radiation therapy uses focused radiation beams to destroy tumors, a side effect is that it exposes the tissues along the path of the radiation beam. It is these healthy tissues in the path of the beam that may develop a radiation injury, and a delayed radiation injury is defined as occurring greater than 6 months (although some sources will go down to 3 months) after radiation exposure.
What happens to tissues in a Delayed Radiation Injury?
The exposure of healthy tissues to radiation leads to DNA injury, lipid (fat molecules) damage, and protein breakdown. A delayed radiation injury is a consequence of these injuries over time. Affected tissues and organs become hypocellular (decreased amount of healthy cells), hypovascular (loss of healthy blood vessels), and hypoxic (receiving inadequate oxygen). This damage typically presents as troubling symptoms that affect the quality of life of patients. Symptoms depend on the location of the injury but can include things like blood/clots in the urine and increased need for urination (bladder injury) or blood in bowel movements and bowel irritability (bowel injury).
What therapies can cause a Delayed Radiation Injury?
Radiation therapy for the following oncologic treatments may lead to a delayed radiation injury:
Radiation therapy of the prostate
Radiation therapy of the cervix or uterus
Radiation therapy of the small or large bowel
Radiation therapy of the brain
Radiation therapy of the oropharyngeal area (mouth/tongue/throat)
Where can a Delayed Radiation Injury occur?
Depending on which organ is irradiated, the following surrounding tissues may be exposed to radiation and subsequently suffer a delayed radiation injury leading to some of the following conditions:
Radiation cystitis (Injury of the bladder)
Radiation proctitis (Injury of the rectum)
Radiation enteritis (Injury of the intestines)
Osteoradionecrosis of the jaw (Injury of the jawbone)
Radionecrosis of the brain (Injury and breakdown of brain tissue)
Other locations of injury
How are Delayed Radiation Injuries treated with Hyperbaric Oxygen Therapy?
As described, some of the hallmarks of a delayed radiation injury are tissues that are hypovascular and hypoxic meaning they have a damaged blood supply and insufficient oxygen delivery. The blood vessels that do exist often develop fibrosis, a process in which the walls are thickened and the room for blood flow is reduced. Hyperbaric oxygen therapy helps treat delayed radiation injuries in three ways. It helps promote a process called angiogenesis (‘blood vessel growth’) to promote new blood vessels to develop in the damaged tissues. Secondly studies have demonstrated that it can reduce the amount of fibrosis in blood vessels to limit this damaging complication. Finally, it mobilizes progenitor cells (‘stem cells’) through its effect on the hematologic system which are an important component of the tissue repair pathways in our body.
What is the goal of Hyperbaric Oxygen Therapy for Delayed Radiation Injuries?
Hyperbaric oxygen therapy is used in delayed radiation injuries to help the tissues heal with the goal to reduce or eliminate the troubling symptoms patients experience that affect their quality of life. In studies looking at radiation cystitis (bladder injury), patients who received hyperbaric oxygen therapy had more than double the decrease in their symptom scores compared with those who received medical management alone (17.8 point decrease in symptom severity score in hyperbaric patients vs 7.7 point decrease in medically treated patients, determined using EPIC symptom scoring tool with a maximum of 60 possible points).