ORGAN EQUIVALENT DOSE AND LIFETIME ATTRIBUTABLE RISK OF CANCER INCIDENCE AND MORTALITY ASSOCIATED WITH CARDIAC CT ANGIOGRAPHY

Clinical Question Influence on Radiation Dose of Cardiac CT Scan in Children

Background: To assess the impact of different clinical questions on radiation doses acquired during cardiac computed tomography in children. Methods: A total of 116 children who underwent cardiac CT on a third-generation dual-source CT scanner were included. The clinical questions were divided into three main categories: the extent of scanning in the z-axis, coronary artery assessment and cardiac function assessment. Radiation dose values represented as a dose-length product (DLP) in mGy*cm were recorded from the CT scanner protocols. Results: There were significantly higher doses in cases with cardiac function assessment (median DLP 348 versus 59 mGy*cm, p < 0.01) and in cases with coronary artery assessment (median DLP 133 versus 71 mGy*cm, p < 0.01). Conclusion: The most important factor was the assessment of cardiac function, where the median radiation dose was 4.3× higher in patients with a request for cardiac function assessment. We strongly recommend that clinical requests for cardiac CT should be carefully considered in the paediatric population.

OPTIMIZATION OF LUNG CT PROTOCOL FOR THE DIAGNOSTIC EVALUATION OF COVID-19 LUNG DISEASE

This study intends to evaluate the different lung CT scan protocols used for the diagnostic evaluation of COVID-19-induced lung disease in Iranian imaging centers in terms of radiation dose and image quality. After data collecting, subjective image quality, radiation dose and objective image quality such as noise, SNR and CNR were assessed. Statistically significant differences in effective dose and image quality were evident among different lung CT protocols. Lowest and highest effective dose was1.31 ± 0.53 mSv related to a protocol with activated AEC (reference mAs = 20) and 6.15 ± 0.57 mSv related to a protocol with Fixed mAs (mAs = 100), respectively. A protocol with enabled tube current modulation with 70 mAs as a reference mAs, and protocol with 20 mAs and enabled AEC had the best and lowest image quality, respectively. To optimize the scan parameters, AEC must be used, and a range of tube currents (between 20 and 50 mAs) can produce acceptable images in terms of diagnostic quality and radiation dose for the diagnosis of COVID-19-induced lung disease.

Lifetime attributable cancer risk related to prevalent CT scan procedures in pediatric medical imaging centers

PURPOSE

Evaluation of the organ dose in pediatric patients up to 15 years old and Estimation of lifetime attributable risk (LAR) of cancer incidence in pediatric computed tomography procedures.

MATERIALS AND METHODS

Data from 532 patients below 15 years old was collected and they were categorized into four age groups of <1, 1-5, 5-10, and 10-15 years old. NCICT software was used to calculate the organ dose, and LAR of cancer incidence has been estimated according to the BEIR VII report.

RESULTS

The highest median dose in all age groups was related to eye lens (head scan), thyroid (chest scan), and colon (abdomen-pelvic scan). The highest average LAR of cancer incidence was observed for breast cancer and colon cancer following a chest CT scan of the youngest group (<1-year-olds) [68.23 per 100,000] and abdomen-pelvic scans of the oldest group (10- to 15-year-olds) [57.30 per 100,000].

CONCLUSION

This study shows that the average LAR is higher in females and it decreases with age in both genders. Although CT scan has an indispensable application in diagnosis, the patient dose should be taken into account before any examination specifically in pediatric patients.

Low dose radiation therapy for COVID-19: Effective dose and estimation of cancer risk

BACKGROUND AND PURPOSE

The objective of this work is to evaluate the risk of carcinogenesis of low dose ionizing radiation therapy (LDRT), for treatment of immune-related pneumonia following COVID-19 infection, through the estimation of effective dose and the lifetime attributable risk of cancer (LAR).

MATERIAL AND METHODS

LDRT treatment was planned in male and female computational phantoms. Equivalent doses in organs were estimated using both treatment planning system calculations and a peripheral dose model (based on ionization chamber measurements). Skin dose was estimated using radiochromic films. Later, effective dose and LAR were calculated following radiation protection procedures.

RESULTS

Equivalent doses to organs per unit of prescription dose range from 10 mSv/cGy to 0.0051 mSv/cGy. Effective doses range from 204 mSv to 426 mSv, for prescription doses ranging from 50 cGy to 100 cGy. Total LAR for a prescription dose of 50 cGy ranges from 1.7 to 0.29% for male and from 4.9 to 0.54% for female, for ages ranging from 20 to 80 years old.

CONCLUSIONS

The organs that mainly contribute to risk are lung and breast. Risk for out-of-field organs is low, less than 0.06 cases per 10000. Female LAR is on average 2.2 times that of a male of the same age. Effective doses are of the same order of magnitude as the higher-dose interventional radiology techniques. For a 60 year-old male, LAR is 8 times that from a cardiac CT, when prescription dose is 50 cGy.