| Radiation
Biology |
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;
1. Radiation.
2. Hypovascular-hypocellular-hypoxic tissue.
3. Tissue breakdown occurs.
4. A Non-healing wound forms. |
| Treatment |
·
Surgical Debridement
·
Hyperbaric Oxygen Therapy (HBO) |
| Mechanism
of action of HBO |
HBO
helps to reverse the process of the 3H’s (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. |
| Stage
I |
·
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 |
| 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 a Stage II Responder.
·
If the wound dehisces exposing bone once again, the patient is termed
a Stage II Nonresponder and is advanced to Stage III. |
| 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.
·
To 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
2006
The Cochrane Collaboration.
Marchetta
et al compared the outcomes of head and neck reconstructions
between DXT recipients and non-recipients.
* DXT treated patients had a 30% infection rate and 43% complication
rateo
* 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. |
