Risk factors

An important risk factor associated with osteoradionecrosis is the total radiation dose. Several authors found a total radiation dose greater than 6570 Gy as increasing the risk of osteoradionecrosis , - . Bedwinek found no osteoradionecrosis when the dose was less than 60 Gy, and 9% for doses greater than 70 Gy. Morrish37 found 0% incidence less than 65 Gy, 27.6% (dentulous patients) and 6.6% (edentulous patients) for 65 to 75 Gy, and 84.6% (dentulous patients) and 50% (edentulous patients) for doses greater than 75 Gy. Murray25 found an incidence of 14% for 50-60 Gy, 23.2% for 60-70 Gy, 19.5% for 70-80 Gy and 28.6% for doses greater than 80 Gy.

Volume of mandible irradiated is also a risk factor of osteoradionecrosis11'13'32'33'35'36'39'40. For Beumer32, for doses above 65 Gy, the risk of osteoradionecrosis increases significantly with the volume of the mandible irradiated. For Emami35, the TD 5/5 (probability of 5% complication within 5 years from treatment) is 65 Gy for a small section of the mandible (1/3), and 60 Gy for a larger volume; the TD 50/5 (probability of 50% complication within 5 years from treatment) can be projected as approximately 77 Gy for a small volume with 72 Gy for the 2/3 and full volume.

Hypofractionation significantly increases the risk of osteoradionecrosis34'40. A randomised trial of CHART (Continuous Hyperfractionated Accelerated Radiotherapy: 54 Gy in 36 fractions over 12 days) versus conventional radiotherapy (66 Gy in 33 fractions over 6.5 weeks), including 918 patients found similar incidence of osteoradionecrosis in the two arms41. Using hyperfractionated radiotherapy, a short interfraction interval (< 6 hours) is a significant risk factor for osteoradionecrosis42.

The technique employed for irradiation can be a risk factor. The association of external beam therapy and brachytherapy increases the risk of bone complications25'34'43-47. With this technique, total dose is also a risk factor11'44 : doses superior to 80-90 Gy significantly increase the risk of osteoradionecrosis.

The modalities of brachytherapy merit to be studied. A dose rate superior to 0.55 Gy/h is a risk factor for osteoradionecrosis44'48-50 (0.7 Gy/h for Pernot11). The volume irradiated is also one11'48-50; for some authors the risk significantly increases for volumes superior to 25-30 cm3 11'51. It is now clearly established that a leaded protection decreases the dose to the mandible to 50%5 and so decreases the risk of osteoradionecrosis11'44'45.

Several risk factors are related to the tumour. Osteoradionecrosis is more frequent when the tumour is adjacent to bone3'25'31'36'38'39'52. The floor of the mouth is the location for which the risk is greatest4'11'50'53. Dental management has been a topic of debate' and the practices have dramatically changed since twenty years. Before5 all teeth or teeth in radiation port were extracted. This "aggressive" management is a risk factor for osteoradionecrosis; extraction of only unsalvageable teeth with primary closure' restoration of remaining teeth as needed' and daily fluoride application is the most adapted practice ''''''- . A minimum delay between extraction and initiation of radiotherapy of 10-21 days is necessary17'56'57. Daily fluoride application significantly decreases dental caries and periodontal infection10'51'53'56'58-60.

One of the most important risk factor is dental extraction after radiotherapy3'4'11'26'33'53'54'59'61'62. Marx62 in a randomized trial showed that hyperbaric oxygen therapy before and after teeth removal in irradiated patients versus penicillin significantly decreases osteoradionecrosis (increasing angiogenesis and cellular density). Seventy-four patients having received irradiation to doses of 60 Gy or greater were randomised in two groups. One group of 37 patients5 in whom a total of 135 teeth had to be removed' received 1 million units of penicillin G intravenously just before surgery and 500 mg of phenoxymethyl penicillin four times daily for 10 days after surgery. The other group of 37 patients5 in which a total of 156 teeth had to be removed' received no antibiotics but twenty sessions of hyperbaric oxygen before tooth removal and 10 sessions after tooth removal. Sessions of

HBO (2.4 ata, 90' each session) were conducted once daily, 5 or 6 days each week. In the penicillin group eleven patients (29.9%) developed osteoradionecrosis, whereas in the HBO group only two patients (5.4%) developed osteoradionecrosis. This difference is statistically significant, however the incidence of osteoradionecrosis in non-HBO group seems high. Using a similar protocol of hyperbaric oxygen therapy (20 dives before, 10 dives after teeth extraction), Lambert63 in a retrospective study found no osteoradionecrosis in 75 patients.

However, some authors have demonstrated that post-radiation extraction without hyperbaric oxygen is safe with very strict precautions 53,56,64,65.

Horiot56 reported one osteoradionecrosis in 22 patients who required post radiation dental extractions (with peri antibiotic coverage, alveolectomy, primary closure). In Maxymiv's study65 (196 removed teeth included within the treatment volume in 72 patients), no osteoradionecrosis occurred. Clayman66 in a literature review estimates that the incidence of postextraction osteoradionecrosis is relatively low: 5.8% for studies published since 1968, and 2.1% for studies published between 1986 and 1995.

The randomised trial by Marx62 showed the efficacy of HBO in the prevention of osteoradionecrosis following dental extractions in the irradiated territory. Indications should nevertheless be considered for each individual case and could be reserved for patients with the most significant risk.

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Responses

  • daniel petros
    What are the risk factors of oxygen therapy?
    2 years ago
  • amina
    What are the risk factor of oxygen therapy?
    5 months ago

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