Purpose: To compare organ doses from the standard abdominopelvic CT and the protocol with reduced scan range, and to investigate the correlation of size-specific dose estimate (SSDE) with absorbed organ doses.
Methods: CT scans were performed using clinical protocols implementing dose modulation on Somatom Sensation 64 and Somatom Definition Flash 128 (Siemens Healthineers, Germany). The standard protocol imaged patients from the top of the diaphragm to ischial tuberosities. The reduced scan range CT protocol included anatomy from the upper L2 vertebral body to the superior border of the symphysis pubis. Other technical settings were kept constant for both protocols on each scanner. Absorbed organ doses were measured with optically stimulated luminescent dosimeters (OSLDs) placed within a female adult anthropomorphic phantom (ATOM 702-G, CIRS). The phantom consists of 38 adjoining 25-mm-thick sections, each containing several 14-mm-diameter holes specific to radiosensitive internal organs. Overall, 42 OSLDs were inserted in 17 organs of the phantom for each scan. Organ dose was calculated as the mean of readings from all dosimeters placed in an organ. The bone marrow dose was evaluated using the fraction of active bone marrow in each bone. A paired two-tailed t-test was used to determine the statistical significance between organ doses from each scan. Absorbed doses were divided by phantom SSDE to determine the correlation between organ dose and SSDE.
Results: The mean absorbed organ doses from the two protocols were significantly different with p=0.001 for both scanners. The highest dose savings of 58%– 86% were determined in organs receiving scattered radiation and located mostly outside of the primary beam. Correlation for those organs was determined to be poor (0.1–0.5). For organs fully covered by the beam, the correlation was near unity (0.7–1.3).
Conclusion: The reduced range CT protocol resulted in a significantly lower patient dose not affecting clinical outcome.