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Measurement of the radiation doses absorbed by jaw bones during irradiation of nasopharyngeal cancers.

BACKGROUND
Nasopharyngeal carcinoma (NPC) occurs more frequently for Chinese than for other ethnic groups. The most common treatment for NPC is radiotherapy, but there is no report of the doses of radiation absorbed by the mandibular and maxillary bones, although exposure to radiation is one of the most important references for those patients who need to have oral surgical treatments.


METHODS
Thermoluminescent dosimeter (TLD) was used to measure radiation absorbed by a rando phantom and cancer patients.


RESULTS
The results showed that the doses absorbed by the mandible and maxilla depend on the dose applied, field size, and field shape. In the rando phantom, the range of absorption in the mandible was, for the central incisor 1.89-3.36 Gy, canine 1.96-3.78 Gy, bicuspid 2.24-14.14 Gy, second molar 4.34-31.92 Gy, internal pterygoid muscle region 70 Gy. In the maxilla the range was, for the central incisor 2.17-2.94 Gy, canine 2.24-3.36 Gy, bicuspid 3.15-4.41 Gy, second molar 7.00-7.42 Gy. In nasopharyngeal carcinoma patients, the mean radiation absorbed by the bicuspid vestibular region of the mandible was 3.09 Gy, by the bicuspid vestibule of the maxilla 3.35 Gy and by the midline vestibule 2.31 Gy. The radiation doses absorbed by maxilla and mandible from the incisor to the second premolars were less than 20% of the dose to the primary tumor.


CONCLUSIONS
The doses absorbed by the mandible and maxilla are relatively low in NPC patients receiving radiation therapy.