The effect of optimum, indication-specific imaging fields on the radiation exposure from CBCT examinations of impacted maxillary canines and mandibular third molars

Figures & data

Table 1. Reference location center points of the PCXMC simulations for different sizes of field-of-view (FOV) on maxillary canines and mandibular third molars.

Target	FOV (mm) (diameter x height)	Xref (cm)	Yref (cm)	Zref (cm)
Canine (left)	Ø 40 × 35	3	−6.5	60.0
	Ø 50 × 50	3	−6.5	60.0
	Ø 70 × 80	1	−6.0	58.5
Canines (both)	Ø 80 × 50	0	−6.0	58.5
	Ø 100 × 100	0	−6.0	58.5
Third molar (left)	Ø 35 × 35	5	−3.0	82.0
	Ø 50 × 50	4	−3.0	82.0
	Ø 70 × 80	4	−3.0	82.0
Third molars (both)	Ø 80 × 50	0	−3.0	83.0
	Ø 140 × 100	0	−3.0	82.0
Whole skull	Ø 260 × 300	0	−1.0	87.0

Table 2. Simulated effective and absorbed organ doses from CBCT examinations of impacted maxillary canines and mandibular third molars.

	Scanning parameters					Radiation doses				Organ doses (µGy)
Target	FOV (mm) (diameter x height)	Voxel size(µm)	Voltage(kV)	Current(mA)	Exposuretime(s)	DAP(mGy cm^2)	ESAK* (mGy)	Effective dose** E(µSv)	Ratio E/DAP(µSv/mGycm^2)	Thyroid	Brain	Salivary glands	Esophagus	Oral mucosa
Canine (left)	Ø 40 × 35	150	100	12.5	5.04	151	10.8	58	0.384	110	104	1043	7	1709
	Ø 40 × 35	75	100	12.5	8.00	237	16.9	91	0.384	172	163	1637	11	2683
	Ø 50 × 50	150	100	12.5	5.04	245	9.8	87	0.355	181	180	1605	12	2458
	Ø 70 × 80	150	100	12.5	5.04	506	9.0	183	0.362	718	284	3816	41	3928
Canines (both)	Ø 80 × 50	150	100	12.5	5.04	371	9.3	147	0.396	463	180	3399	30	3933
	Ø 100 × 100	150	100	12.5	5.04	847	8.5	284	0.335	1671	566	5326	65	4902
Third molar (left)	Ø 35 × 35	150	100	12.5	5.04	135	11.0	38	0.281	48	48	1441	3	1110
	Ø 50 × 50	150	100	12.5	5.04	245	9.8	69	0.282	103	98	2461	5	1900
	Ø 70 × 80	150	100	12.5	5.04	506	9.0	122	0.241	224	225	4150	10	2819
Third molars (both)	Ø 80 × 50	150	100	12.5	5.04	371	9.3	96	0.259	116	218	2741	6	2917
	Ø 140 × 100	450	100	12.5	2.56	398	2.8	75	0.188	164	209	2175	8	1585
Whole skull	Ø 260 × 300	450	100	10.0	3.20	1370	1.7	115	0.084	703	1486	1628	19	1147

FOV: Field-of-view, DAP: Dose-area product; ESAK: Entrance surface air-kerma at scan isocenter (without scatter).

* ESAK is calculated according to displayed DAP and FOV area (in cm²) at isocenter.

** Effective dose is simulated.

Figure 1. Monte Carlo (ImpactMC) simulation of the 3D radiation dose distribution for CBCT scans of impacted maxillary canines and mandibular third molars with 40Ø × 35 mm FOV as applied to ATOM anthropomorphic female adult head and neck phantom model. (a) Imaging field positioning according to the location of a left maxillary canine tooth. (b) Simulated radiation dose distribution in axial view and (c) sagittal view for impacted maxillary canine, presented as a relative color heatmap. (d) Imaging field positioning according to the location of a left mandibular third molar tooth. (e) Simulated radiation dose distribution in axial view and (f) sagittal view for impacted mandibular third molar, presented as a relative color heatmap.

Table 3. Results of sensitivity analysis simulation with variable positioning of minimum FOV.

a. Position translations of 40Ø x 35 mm FOV for left impacted maxillary canine (DAP 151 mGy cm^2, voxel size 150 µm)
Effective dose (E)	58 µSv
FOV position translation on x-axis	x −1 cm (right/in)	x +1 cm (left/out)
E	60 µSv	54 µSv
Ratio	1.03	0.93
FOV position translation on y-axis	y −1 cm (front/out)	y +1 cm (back/in)
E	53 µSv	60 µSv
Ratio	0.91	1.03
FOV position translation on z-axis	z −1 cm (down)	z +1 cm (up)
E	59 µSv	51 µSv
Ratio	1.02	0.88
b. Position translations of 35Ø x 35 mm FOV for left impacted mandibular third molar (DAP 135 mGy cm^2, voxel size 150 µm)
Effective dose (E)	38 µSv
FOV position translation on x-axis	x −1 cm (right/in)	x +1 cm (left/out)
E	38 µSv	38 µSv
Ratio	1.00	1.00
FOV position translation on y-axis	y −1 cm (front/out)	y +1 cm (back/in)
E	36 µSv	39 µSv
Ratio	0.95	1.03
FOV position translation on z-axis	z −1 cm (down)	z +1 cm (up)
E	35 µSv	41 µSv
Ratio	0.92	1.08