Study of displayed radiation dose and size-specific dose estimate from computed tomography brain examinations in accordance to head sizes

Table 1 Computed tomography scan parameters (mean ± SD)

Protocol parameter	CT head
Tube voltage (kVp)	120
Reference noise (mAs)	299.27 ± 3.58
Pitch	0.43 ± 0.09
Slice thickness (mm)	5
Scanning mode	Helical
Orientation	Caudocranial
CTDI vol (mGy)	46.83 ± 1.43
DLP (mGy.cm)	869.44 ± 98.47
Scanning range (mm)	16.77 ± 0.76
SSDE calculated (mGy)	46.95 ± 2.07
SSDE displayed (mGy)	41.64 ± 2.07
E (mSv)	1.83 ± 0.21

CT: Computed tomography; CTDI: Computed tomography dose index; DLP: Dose-length product; SSDE: Size specific dose effect.

Table 2 Gender-wise distribution of study participants (n = 195)

Gender	Frequency	Percentage, %
F	71	36.4
M	124	63.6
Total	195	100.0

F: Female; M: Male.

Table 3 Distribution of examination types performed among the study population

Exam	Frequency	Percentage, %
CECT head	3	1.5
NCCT head	192	98.5
Total	195	100.0

CECT: Contrast-enhanced computed tomography; NCCT: Non-contrast computed tomography.

Table 4 Department-wise referral pattern for computed tomography head examinations

Department	Frequency	Percentage, %
EMG	121	62.1
IPD	19	9.7
OPD	55	28.2
Total	195	100.0

EMG: Emergency department; IPD: Inpatient department; OPD: Outpatient department.

Table 5 Patient characteristics and radiation dose parameters

Descriptive statistics	n	Minimum	Maximum	Mean	SD
AGE	195	18.0	60.0	36.99	12.92
AP (mm)	195	162.5	205.8	186.54	8.84
LAT (mm)	195	125.2	160.1	142.67	7.46
AP (cm)	195	16.25	20.58	18.65	0.88
LAT (cm)	195	12.52	16.01	14.26	0.74
Effective diameter (mm)	195	145.12	178.77	163.08	6.88
Effective diameter (cm)	195	14.52	17.87	16.31	0.68
Kvp	195	120.0	120.0	120.00	0.00
mAs	195	298.0	349.0	299.27	3.58
SSDE displayed	195	35.75	46.15	41.64	2.07
SSDE calculated	195	40.77	55.56	46.95	2.07
Pitch	195	0.40	0.70	0.43	0.09
CTDI vol	195	42.03	55.01	46.83	1.43
CTDI w	195	16.82	33.02	20.19	3.76
DLP displayed (mGy.cm)	195	687.8	1230.06	869.44	98.47
SCAN length (cm)	195	14.10	18.69	16.77	0.76
Effective dose (mSv)	195	0.14	2.58	1.83	0.21

AP: Anterio-posterior; PA: Posterio-anterior; LAT: Lateral; SSDE: Size specific dose estimated; CTDI: Computed tomography dose index; DLP: Dose length product.

Table 6 Paired sample statistics and correlation analysis between effective diameter and dose indices

Paired samples statistics	Mean	n	SD	Correlation	t test statistics
Effective diameter (mm)	163.08	195	6.88	1.00	331.01
Effective diameter (cm)	16.31	195	0.68	P = 0.0001	P = 0.001
SSDE displayed	41.64	195	2.07	-0.43	144.24
SSDE displayed	41.64	195	2.07	P = 0.0001	P = 0.001
SSDE calculated	46.95	195	2.07	0.571	38.620

SSDE: Size specific dose estimated.

Table 7 Stochastic cancer risk calculation (incidence) for size specific dose estimated displayed and calculated using BEIR VII report, mean ± SD

Parameter	SSDE displayed	SSDE calculated
Dose	41.63 ± 2.07	46.94 ± 2.07
Calculated mean risk (LAR)	9.57 × 10-5	1.08 × 10-4
Risk probability	1 in 10450	1 in 9260
Risk range (± 1 SD)	9.10 × 10-5-1.00 × 10-4	1.03 × 10-4-1.13 × 10-4

SSDE: Size specific dose estimated; LAR: Lifetime attributable risk.

Table 8 Calculated stochastic risk (brain cancer incidence) for males

Parameter	SSDE displayed	SSDE calculated
Mean dose (mGy)	41.63	46.94
Mean risk (average)	2.08 × 10-4	2.34 × 10-4
Risk probability	1 in 4800	1 in 4270
Risk range (age 18-60)	0.8 × 10-4-4.6 × 10-4	0.9 × 10-4-5.1 × 10-4

SSDE: Size specific dose estimated.

Table 9 Calculated stochastic risk (brain cancer incidence) for females

Parameter	SSDE displayed	SSDE calculated
Mean dose (mGy)	41.63	46.94
Mean risk (average)	0.66 × 10-4	0.74 × 10-4
Risk probability	1 in 15150	1 in 13500
Risk range (age 18-60)	0.3 × 10-4-1.4 × 10-4	0.3 × 10-4-1.6 × 10-4

SSDE: Size specific dose estimated.