Spatial distribution of the imaging dose and characterization of the scatter radiation contribution in CyberKnife radiosurgery.

PURPOSE: The imaging dose for intra- and extra-cranial CyberKnife radiosurgery applications was calculated and the scattered radiation reaching the digital detectors was quantified and analyzed with regard to its origin. METHODS: The image guidance subsystem of the CyberKnife was modeled based on vendor-provided information. The emitted X-ray energy spectrum for 120 kV was estimated using the SpekPy software tool. Monte Carlo (MC) image acquisition simulations were performed to calculate the total, primary and scattered photon fluences reaching each detector as a function of the imaged object dimensions. MC calculations of the imaging dose were performed for intra- and extra-cranial applications assuming 120 kV and 10 mAs acquisition settings. RESULTS: The amount of scattered radiation reaching each detector was found to depend on the dimensions of the imaged anatomical region, contributing more than 40 % to the total photon fluence for regions more than 20 cm thick. More than 20 % of this scattered radiation originates from the contralateral imaging field. A maximum organ dose of 1.5 mGy at the nasal bones and an average dose of 0.37 mGy to the eye lenses per image pair acquisition was calculated for head applications. An entrance imaging dose of 0.4 mGy was calculated for extracranial applications. CONCLUSIONS: Scattered radiation reaching each detector in the skull and spine tracking applications can be reduced by acquiring the pair of radiographs sequentially instead of simultaneously. A dose of 3.7 cGy to the eye lenses is estimated assuming 100 image pair exposures required for treatment completion.

Comparison between the Parks Medical Doppler and the Mano Médical Vet BP Doppler for recording indirect systemic blood pressure in conscious dogs.

Background: The acquisition of systemic blood pressure (SBP) provides valuable information regarding cardiovascular function and tissue perfusion in human and veterinary species. Aim: To evaluate the agreement between Parks Medical Doppler (PMD) and Mano Médical Vet BP (MMVBP) Doppler for assessing SBP in conscious dogs. Methods: 40 client-owned dogs were prospectively enrolled; SBP measurements were acquired by a single operator using the PMD and then the MMVBP. The mean of five consecutive measurements for each device was classified according to target organ damage (TOD) risk scores (1: <140 mmHg; 2: 140-160 mmHg; 3: 160-180 mmHg; 4: ≥ 180 mmHg). Results: Total mean SBP for the devices was not statistically different (p = 0.77). However, the Bland-Altman analysis revealed wide limits of agreement (LoA), with MMVBP slightly underestimating SBP compared to PMD (bias = -0.6 mmHg, 95% LoA: -26.3 to 25.09). Both devices correlated well ( r = 0.8269; p < 0.0001) and had identically acceptable intra-observer repeatability (coefficients of variation = 4.09% for MMVBP and 3.86% for PMD). Four dogs (10%) had a TOD score of 3 by one device but scored <3 with the other. Conclusion: A good agreement and correlation was observed between the PMD and the MMVBP, suggesting that both devices can be used interchangeably for assessment of SBP in conscious dogs. The wide LoA observed between both devices was most likely associated with intraindividual variability in SBP over time.