Room: Exhibit Hall | Forum 9
Purpose: To investigate impact of applying size-specific dose estimate (SSDE) factors derived for full rotation scans (360Â°) and partial rotation scans (200Â°) under different conditions.
Methods: Monte Carlo simulations were employed to model a kV on-board imaging (OBI) system, and to derive SSDE factors for narrow (2 and 4 cm) and wide (8, 16, and 24 cm) beams for full and partial scan modes. The factors were derived using water phantoms with diameters ranging from 10 â€“ 40 cm with increments 2 cm, to represent water-equivalent diameter (Dw), linked to patient size. Four tube potentials of 80 â€“ 140 kV were used with two scan protocols head and body.
Results: For the head and body scan protocols, variations between SSDE factors of the full scans and those for the partial scans were comparable for all narrow and wide beams. The variations between the SSDE factors were in the range (0.91 â€“ 1.01) for the head and (0.96 â€“ 1.08) for the body for all kVs studied. SSDE factors for full scans were smaller than those for partial scans over almost all Dw for the head, and the variations increased with the magnitude of Dw. For the body, however, SSDE factors of the full scans were higher than those for partial scans for diameters up to ~34 cm, after which they became smaller. For both head and body protocols, the tube potential was found to affect the variations between the scan modes by up to 3%.
Conclusion: The use of SSDE factors derived for the full scan mode to assess the patient dose undergoing a partial scan mode may lead to over/underestimation by up to 9% and 8% for the head and body protocols, respectively. Moreover, SSDE factors are slightly affected by the starting and ending points of the partial scan.
Not Applicable / None Entered.