||Radiotherapy causes chemical changes to bones and tissues. This can result in damage to the protein structure, lipids and DNA damage. Damage to the blood vessel lining with obliteration of the vessels may also be responsible for delayed necrosis following radiation.
|Effects of Radiation on Blood vessels
- Swelling, degeneration and necrosis of the blood vessels with resulting thickening of the vessel wall.
- Most damage to arterioles and small blood vessels.
|Effects of Radiation on soft tissues
- Skin thinning occurs in the chronic stages.
- Skin is prone to ulceration with minor trauma.
- Poor wound healing through wounds incised in previously irradiated skin.
- May directly affect the lining of the intestinal and urinary tracts producing radiation gastroenteritis and cystitis respectively.
|Effects of Radiation on Bones
- Bones are more dense than soft tissue and absorb a larger proportion of the incident radiation than do soft tissues.
- Affects vascular and cellular bone components.
- High dose radiation leads to bone death by damaging blood vessels passing between periosteum and the surface of the bone.
- Upsets bone metabolism leading to osteonecrosis.
- Usual sites of bone necrosis:
- Jaw (soft tissue tumours of head and neck)
- Ribs and sternum (breast cancer)
- Skull (brain tumours and soft tissue tumours of scalp)
- Vertebral column (spinal cord tumour)
|Pathophysiology of ORN
||1983 Definition of ORN (Marx)
The sequence of events is as follows;
- Hypovascular-hypocellular-hypoxic tissue.
- Tissue breakdown occurs.
- A Non-healing wound forms.
- Surgical Debridement
- Hyperbaric Oxygen Therapy (HBO)
|Mechanism of action of HBO
||HBO helps to reverse the process of the 3Hs (Hypovascularity – Hypoperfusion – Hypoxia).
One of the stimuli for angiogenesis (new blood vessel growth) is the oxygen concentration gradient. Blood vessels grow from an area of high oxygen concentration to an area of low oxygen concentration.
HBO greatly increases the oxygen concentration gradient so that the area surrounding the hypoxic tissue has a very high oxygen concentration. Once new blood vessels form the hypoperfusion and therefore the hypoxia is reversed. Once the hypoxia is reversed the tissue then has the propensity to heal
|Treatment Protocol for ORN in 3 stages
||30/10 Protocol. Published in 1983 and developed at the USAF Wilford Hall Medical Center and the University of Miami.
Each HBO session comprises of 90min 100% Oxygen at 2.4 ata with appropriate air breaks. In total a session takes approximately 2 hours.
- Initial trial of 30 HBO sessions
- Only use antibiotics if evidence of soft tissue infection.
- No surgery or debridement other than irrigation and removal of sequested, mobile bone fragments.
- After 30 Rx examine bone for response
- If the tissue is assessed as responding, the softened bone is removed and the patient allowed to undergo an additional 10 sessions of HBO.
- If the wound responds with complete healing without further treatment the patient is termed a Stage I Responder.
- If the exposed bone shows no sign of response after 30 sessions of HBO the patient is termed a Stage I Nonresponder and advanced to Stage II
- Patient already received 30 sessions of HBO.
- Surgical removal of exposed bone –using a saline cooled saw rather than a heat generating burr.
- Following surgery the patient will complete the final 10 sessions of HBO.
- If the patient heals without further bone exposure, the patient is termed aStage II Responder.
- If the wound dehisces exposing bone once again, the patient is termed aStage II Nonresponder and is advanced to Stage III
- Patients who have failed to respond to Stage I or II.
- Patients who initially present with an orocutaneous fistula, a pathologic fracture, or radiographically evident ostolysis to the inferior mandibular border.
- Too great a quantity of nonviable bone to repond to HBO alone or combined with limited surgical debridement.
- Patient has already received 30 sessions of HBO
- The patient then undergoes transoral resection of the involved portion of the mandible and an excision of any necrotic soft tissue.
- The patient then undergoes the final 10 sessions of HBO.
- Most patients undergo bony reconstruction of the jaw at three months.
|Evidence for HBO
- Cochrane review : Bennett MH,Feldmeier et al. Hyperbaric Oxygen Therapy for late radiation tissue injury – The Cochrane Collaboration.
- Marchetta et alcompared the outcomes of head and neck reconstructions between DXT recipients and non-recipients.
- DXT treated patients had a 30% infection rate and 43% complication ratio
- Non-recipients had a 22% infection rate and 10% complication rate
- Greenwood and Gilchrist (1973) described the use of HBO in post-irradiated head and neck surgery, finding that HBO improved wound healing.
- Neovius et al reviewed the literature and reported unanimously positive evaluations of the use of HBO in irradiated head and neck wounds.
- They also performed their own retrospective study and found an 80% healing rate in HBO treated patients vs 58% in the reference group.
- Prior to the use of HBO in previously irradiated mandible reconstructions the complication rate was as high as 70%, with 25% failure rate
- Marx employed pre- and post-operative HBO.
- Reported a surgical success rate of 94%
- Using a similar HBO protocol for patients undergoing tooth extractions from previously irradiated mandibles, there was a reduction in the incidence of ORN from 29.9% in the non-HBO group to 5.4% in the HBO group.