A strategy to optimize radiation exposure for non-contrast head CT: comparison with the Japanese diagnostic reference levels.
OBJECTIVE
To describe how we performed a protocol review, analyzed data, identified opportunities to reduce radiation exposure, and then implemented a new imaging protocol for non-contrast adult head CT at our institution with reduced radiation exposure, using the Japanese diagnostic reference levels (DRLs) as the reference.


METHODS
After analyzing the CT dose index (CTDIvol) and dose length product (DLP) in all non-contrast adult head CT examinations performed during a 3-month period (September to November 2015) in order to identify a specific protocol that contributed to the above-DRL-level radiation exposure observed for non-contrast adult head CT at our institution, phantom studies with objective and subjective image quality analyses were performed to develop a new imaging protocol. After implementing the new protocol, its feasibility was evaluated in terms of radiation exposure, prevalence of significant disease detection, and subjective image quality.


RESULTS
The review of 2040 examinations revealed that a helical protocol (CTDIvol = 93.4 mGy) with one of four CT scanners mainly contributed to the above-DRL-level radiation exposure (mean DLP at this scanner = 1401.2 mGy cm) in non-contrast adult head CT at our institution. To replace this protocol, the phantom study identified a wide-volume scan using 120 kVp, 350 mAs, a 4-cm detector, a slice thickness of 5 mm, and a CTDIvol of 69.8 mGy as a new protocol that yielded comparable image quality to the existing protocol. After the implementation of the new protocol, the overall mean DLP reduced to 1365 mGy cm without any apparent degradation of image quality. No significant decrease in the prevalence of significant findings after protocol revision was noted.


CONCLUSIONS
We report the successful implementation of a new protocol with reduced radiation exposure for non-contrast head CT examinations.
Department of Radiology, Juntendo University, 2-1-1 Hongo, Bunkyo-ku, Tokyo, 113-8421, Japan. k-kumamaru@juntendo.ac.jp.
Kanako K
KK
Kumamaru
Department of Radiology, Juntendo University, 2-1-1 Hongo, Bunkyo-ku, Tokyo, 113-8421, Japan.
Yosuke
Y
Kogure
Department of Radiology, Juntendo University, 2-1-1 Hongo, Bunkyo-ku, Tokyo, 113-8421, Japan.
Michimasa
M
Suzuki
Department of Radiology, Juntendo University, 2-1-1 Hongo, Bunkyo-ku, Tokyo, 113-8421, Japan.
Masaaki
M
Hori
Department of Radiology, Juntendo University, 2-1-1 Hongo, Bunkyo-ku, Tokyo, 113-8421, Japan.
Atsushi
A
Nakanishi
Department of Radiology, Juntendo University, 2-1-1 Hongo, Bunkyo-ku, Tokyo, 113-8421, Japan.
Koji
K
Kamagata
Department of Radiology, Juntendo University, 2-1-1 Hongo, Bunkyo-ku, Tokyo, 113-8421, Japan.
Akifumi
A
Hagiwara
Department of Radiology, Juntendo University, 2-1-1 Hongo, Bunkyo-ku, Tokyo, 113-8421, Japan.
Christina
C
Andica
School of Medicine, Juntendo University, 2-1-1 Hongo, Bunkyo-ku, Tokyo, 113-8421, Japan.
Keiken
K
Ri
Department of Radiology, Juntendo University, 2-1-1 Hongo, Bunkyo-ku, Tokyo, 113-8421, Japan.
Naoyoshi
N
Houshido
Department of Radiology, Juntendo University, 2-1-1 Hongo, Bunkyo-ku, Tokyo, 113-8421, Japan.
Shigeki
S
Aoki
D000368:Aged; D005260:Female; D006257:Head / Q000000981:diagnostic imaging*; D006801:Humans; D007564:Japan; D008297:Male; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D000069079:Radiation Exposure / Q000706:statistics & numerical data*; D012015:Reference Standards; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed / Q000379:methods*
Computed tomography; Diagnostic reference level; Radiation exposure