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MO‐E‐17A‐06: Organ Dose in Abdomen‐Pelvis CT: Does TG 111 Equilibrium Dose Concept Better Accounts for KVp Dependence Than Conventional CTDI?
Author(s) -
Li X,
Morgan A,
Dong F,
Primak A,
Davros W,
Segars W
Publication year - 2014
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4889158
Subject(s) - nuclear medicine , imaging phantom , monte carlo method , automatic exposure control , dosimetry , effective dose (radiation) , scanner , collimator , medicine , mathematics , physics , statistics , optics
Purpose: In CT imaging, a desirable quality assurance (QA) dose quantity should account for the dose variability across scan parameters and scanner models. Recently, AAPM TG 111 proposed to use equilibrium dose‐pitch product, in place of CT dose index (CTDI100), for scan modes involving table translation. The purpose of this work is to investigate whether this new concept better accounts for the kVp dependence of organ dose than the conventional CTDI concept. Methods: The adult reference female extended cardiac‐torso (XCAT) phantom was used for this study. A Monte Carlo program developed and validated for a 128‐slice CT system (Definition Flash, Siemens Healthcare) was used to simulate organ dose for abdomenpelvis scans at five tube voltages (70, 80, 100, 120, 140 kVp) with a pitch of 0.8 and a detector configuration of 2×64×0.6 mm. The same Monte Carlo program was used to simulate CTDI100 and equilibrium dose‐pitch product. For both metrics, the central and peripheral values were used together with helical pitch to calculate a volume‐weighted average, i.e., CTDIvol and (Deq)vol, respectively. Results: While other scan parameters were kept constant, organ dose depended strongly on kVp; the coefficient of variation (COV) across the five kVp values ranged between 70–75% for liver, spleen, stomach, pancreas, kidneys, colon, small intestine, bladder, and ovaries, all of which were inside the primary radiation beam. One‐way analysis of variance (ANOVA) for the effect of kVp was highly significant (p=3e−30). When organ dose was normalized by CTDIvol, the COV across the five kVp values reduced to 7–16%. The effect of kVp was still highly significant (p=4e−4). When organ dose was normalized by (Deq)vol, the COV further reduced to 4−12%. The effect of kVp was borderline significant (p=0.04). Conclusion: In abdomen‐pelvis CT, TG 111 equilibrium dose concept better accounts for kVp dependence than the conventional CTDI. This work is supported by a faculty startup fund from the Cleveland State University.