Major trauma & cervical clearance radiation doses & cancer induction.

AIM

To compare the radiation dose of cervical spine clearance and body CT in a cohort of unconscious, major trauma patients for three different protocols, comparing spiral to multislice CT. To quantify the radiation exposure effect of the protocols on the lifetime cancer risk.

METHOD

The hospital trauma database was used to find the unconscious (GCS<9), severely injured (Injury Severity Score >15) from 1 January 2001 to 31 December 2003, excluding isolated head injuries. The protocols used for imaging the brain and cervical spine were, including the radiographs performed as a mode: The exposure factors and field of view used were put into the Monte Carlo software, to estimate the CT and radiographic X-ray doses to the body as a whole and the dose to the thyroid associated with each region imaged. The associated nominal additional lifetime cancer risk was assessed.

RESULTS

Excluding inter hospital transfers, where data was incomplete, 87 patients survived to be admitted and fulfilled the criteria. In 30 cases, the CT films were missing, the exposure factors were not recorded or no imaging was performed. In a further 21 cases, the X-ray packets were missing. Three patients had brain and cervico-dorsal CT imaging only, leaving 33 cases for evaluation. The effective radiation dose for a spiral CT of the brain using the Toshiba Xpress GX CT scanner was 3.8 mSv. The total effective doses for imaging the brain and cervical spine using the three protocols with the same CT scanner were (S.D. as % of mean): (1) 4.4 mSv (5%), (2) 7.1 mSv (10%) and (3) 8.2 mSv (15%). The corresponding mean thyroid doses were: (1) 8.5 mGy (25%), (2) 48.9 mGy (20%) and (3) 66.5 mSv (20%). The resultant nominal lifetime cancer risks were: (1) 1:4500, (2) 1:2800 and (3) 1:2400. For the Siemens Sensation 16 multislice CT scanner, the total effective doses (S.D. as % of mean) were: (1) 2.3 mSv (10%), (2) 4.3 mSv (25%) and (3) 5.4 mSv (35%). The mean doses to the thyroid were: (1) 5.9 mGy (30%), (2) 36.1 mGy (50%) and (3) 52.4 mGy (40%). The lifetime cancer risks were: (1) 1:8700, (2) 1:4600 and (3) 1:3700. Using the Toshiba spiral CT scanner, the total dose and additional lifetime nominal cancer risk associated with CT of the chest, abdomen and pelvis (CAP) as 16 mSv and 1:1250, respectively. Using the Siemens multislice CT scanner, these were 11.8 mSv and 1:1700. The cancer risk for protocol 1 when combined with a CT scan of the chest, abdomen and pelvis was 1:1000 for the spiral CT scanner and 1:1500 for the multislice CT (MCT) scanner. The cancer risk for protocol 2 with CAP CT using the MCT was 1:1200. The cancer risk for protocol 3 when combined with a CT scan of the chest, abdomen and pelvis was 1:1100 for the multislice CT scanner. Prior to the introduction of the BTS guidelines for cervical clearance, 12% of cases had CT of the body, which increased to 16% post-guidelines.

CONCLUSIONS

CT of the trunk (chest, abdomen and pelvis) is associated with the greatest risk of inducing a fatal cancer in the severely injured patient with a GCS less than 9. In our institution the multislice CT protocols expose the patient to less radiation than single slice CT, which is contrary to much of the published work to date. CT scanning the thyroid (or whole cervical spine) still has a marked effect on the cancer risk in cervical clearance. Many centres will relax cervical spinal precautions in unconscious trauma patients if the cervical spine CT with reconstructions is normal. CT of the whole cervical spine may be justified in the unconscious, severely injured patient. In conscious trauma patients, the additional lifetime risk may not justify CT of the whole cervical spine as a routine practice.