Dose comparison of different scan projections of Implagraphy cone beam computed tomography for dental maxillofacial use

Abstract

Objective To evaluate the subject's absorbed dose,equivalent dose and effective dose.Methods The CBCT unit was Implagraphy and three scan projections were selected such as mandible,maxilla and temporamandibular joint (TMJ).Thermoluminescent dosimeter tubes were used to record the absorbed dose at special positions in the head and neck region of an adult skull and tissue-equivalent phantom.16 interested organs included pituitary,lens,parotid glands,submandibular glands,sublingual glands、diploe,spongy bone of the chin and cervical vertebra,skins of cheeks and nuchal region,thyroid and esophagus.The absorbed dose was measured in these organs,and then the effective dose(E1990,E2007)were calculated according to different ICRP tissue weighting factors.Results The absorbed dose of mandible,maxilla and TMJ scan varied from (0.99 ±0.09) to (12.85 ±0.09)mGy,(0.93 ±0.01) to (13.07 ±0.02) mGy and (0.68 ±0.01) to (10.18 ± 0.04)mGy.There was significant difference among the three scan projections (F =19.61-30992.27,p ＜ 0.05).The equivalent doses of lens and skin were (1.11± 0.07)-(5.76 ± 0.06) mSv and (6.96 ± 0.06)-(10.64 ± 0.07) mSv.There was significant difference among the three scan projections(F =4473.02,9385.50,P ＜0.05).The effective dose(E1990,E2oo7) was [(191.35±1.53),(325.17 ±2.58) μSv] for mandible scan,[(106.62 ±2.17),(226.28 ±2.81)μSv] for maxilla scan,[(104.21 ± 1.02),(142.36 ± 1.90) μSv]for TMJ scan,respectively.Conclusions The valid measurement should be taken to reduce the subject' s dose such as a careful history and clinical examination before the performance of CBCT,the latest risk/benefit assessment,precise scan position,the shielding of thyroid as well as brain and the smaller volume size as well. Key words: Cone beam computed tomography; Absorbed dosage; Equivalent dosage; Effective dosage