BEAM MATCHING EVALUATION OF TWO SIMILAR LINEAR ACCELERATORS.

To evaluate the beam-matching of two Siemens Primus medical linear accelerators (Linacs), the output factor (Sc,p), wedge factor, quality index (TPR20/10), percentage depth dose (PDD) and beam profiles were compared for 6 and 15 MV photon beams. The output factor, the PDD and the beam profile for electron beam compared for 5, 7, 8, 10 and 12 MeV electron beams. The gamma (γ) analysis of 2 mm/2% and 3 mm/3% was performed. According to the measurements, it can be said that 6 MV photon beams in all field sizes (except 4 × 4 cm2) are beam matched. For 15 MV, although the PDDs were matched in all field sizes (except 4 × 4 cm2) for both 2 mm/2% and 3 mm/3% γ criteria, beam profiles in field sizes larger than 10 × 10 cm2 for 3 mm/3% and in field sizes larger than 8 × 8 cm2 for 2 mm/2% were not matched. The electron beams in all applicator sizes (except 5 × 5 cm2 applicator) pass the acceptance γ criteria of 3 mm/3% (γ < 1). Electron beams do not fulfill beam matched in case of the acceptance γ criteria of 2 mm/2%.

Assessment and comparison of radiation dose and image quality in multi-detector CT scanners in non-contrast head and neck examinations.

PURPOSE: To assess and compare radiation dose and image quality from non-contrast head and neck computed tomography (CT) examinations from four different multi-detector CT (MDCT) scanners. MATERIAL AND METHODS: Four CT scanners with different numbers of detector rows including one 4-MDCT, a 6-MDCT, a 16-MDCT, and a 64-MDCT were investigated. Common CT dose descriptors including volumetric CT dose index (CTDIv), dose length product (DLP), and the effective dose (ED), and image quality parameters include image noise, uniformity, and spatial resolution (SR) were estimated for each CT scanner with standard tools and methods. To have a precise comparison between CT scanners and related doses and image quality parameters, the ImPACT Q-factor was used. RESULTS: Minimum and maximum CTDIv, DLP, and ED in the head scan were 18 ± 3 and 49 ± 4 mGy, 242 ± 28 and 692 ± 173 mGy × cm, 0.46 ± 0.4 and 1.31 ± 0.33 mSv for 16-MDCT and 64-MDCT, respectively. And 16 ± 2 to 27 ± 3, 286 ± 127 to 645 ± 79 and 1.46 ± 0.65 to 3.29 ± 0.40 for neck scan, respectively. The Q-factor in head scan was 2.4, 3.3, 4.4 and 5.6 for 4-MDCT, 6-MDCT, 16-MDCT and 64-MDCT, respectively. The Q-factor in neck scan was 3.4, 4.6, 4.7 and 6.0 for 4-MDCT, 6-MDCT, 16-MDCT and 64-MDCT, respectively. CONCLUSIONS: The results clearly indicate an increasing trend in the Q-factor from 4-MDCT to 64-MDCT units in both head and neck examinations. This increasing trend is due to a better SR and less noise of images taken and/or fewer doses in 64-MDCT.

Estimation and comparison of the radiation effective dose during coronary computed tomography angiography examinations on single-source 64-MDCT and dual-source 128-MDCT.

GOAL: To estimate and compare the radiation dose associated with coronary computed tomography angiography (CCTA) examinations on two multi-detector CT scanners (MDCT), 64-MDCT and 128-MDCT, in daily practice. METHODS: Scan parameters of 90 patients undergoing retrospective electrocardiographic gating spiral CCTA exam were recorded during a period on a single-source 64-MDCT and a dual-source 128-MDCT, and average scan parameters were derived that were used for dosimetry. The computed tomography dose index (CTDI) with a pencil ionisation chamber and polymethyl methacrylate body phantom with diameter of 32 cm was measured on both scanners. The dose-length product (DLP) was calculated and the DLP to effective dose conversion factor (for chest scan at 120 kV of 0.014 mSv mGy-1 cm-1) was used to estimate effective dose (ED). RESULTS: Patients' heart rate, scan length, pitch factor, CTDIv, DLP and ED for 128-MDCT were 64 (5) (beats min-1), 161 (10) (mm), 0.26, 47 (12) (mGy), 769 (212) (mGy cm) and 10.3 (3.1) (mSv), respectively [mean (one standard deviation)]. Patients' heart rate, scan length, pitch factor, CTDIv, DLP and ED for 64-MDCT were 60 (7) (beats min-1), 172 (14) (mm), 0.2, 60 (6) (mGy), 1068 (98) (mGy cm) and 14.9 (1.4) (mSv), respectively. CONCLUSION: Our results indicated that the CTDIv, DLP and the effective dose with 128-MDCT is significantly lower than with 64-MDCT (p < 0.05). As differences between the exposure parameter mAs on two CT scanners was not significant (p > 0.05) and the kV was constant for both scanners (120 kV), the differences resulted from a shorter scan length on the 128-MDCT and use of a higher pitch factor (0.26 and 0.2 in the 128-MDCT and 64-MDCT, respectively). Comparison with other published studies confirms the findings and indicates methods for reducing patient dose.