Phantom-based evaluation of dose exposure of ultrafast combined kV-MV-CBCT towards clinical implementation for IGRT of lung cancer

Purpose: Combined ultrafast 90\ub0+90\ub0 kV-MV-CBCT within single breath-hold of 15s has high clinical potential for accelerating imaging for lung cancer patients treated with deep inspiration breath-hold (DIBH). For clinical feasibility of kV-MV-CBCT, dose exposure has to be small compared to prescribed dose. In this study, kV-MV dose output is evaluated and compared to clinically-established kV-CBCT. Methods: Accurate dose calibration was performed for kV and MV energy; beam quality was determined. For direct comparison of MV and kV dose output, relative biological effectiveness (RBE) was considered. CT dose index (CTDI) was determined and measurements in various representative locations of an inhomogeneous thorax phantom were performed to simulate the patient situation. Results: A measured dose of 20.5mGE (Gray-equivalent) in the target region was comparable to kV-CBCT (31.2mGy for widely-used, and 9.1mGy for latest available preset), whereas kVMV spared healthy tissue and reduced dose to 6.6mGE (30%) due to asymmetric dose distribution. The measured weighted CTDI of 12mGE for kV-MV lay in between both clinical presets. Conclusions: Dosimetric properties were in agreement with established imaging techniques, whereas exposure to healthy tissue was reduced. By reducing the imaging time to a single breathhold of 15s, ultrafast combined kV-MV CBCT shortens patient time at the treatment couch and thus improves patient comfort. It is therefore usable for imaging of hypofractionated lung DIBH patients

Automated ultrafast kilovoltage–megavoltage cone-beam CT for image guided radiotherapy of lung cancer: System description and real-time results

Purpose: To establish a fully automated kV-MV CBCT imaging method on a clinical linear accelerator that allows image acquisition of thoracic targets for patient positioning within one breath-hold (∼15 s) under realistic clinical conditions. Methods and materials: Our previously developed FPGA-based hardware unit which allows synchronized kV-MV CBCT projection acquisition is connected to a clinical linear accelerator system via a multi-pin switch; i.e. either kV-MV imaging or conventional clinical mode can be selected. An application program was developed to control the relevant linac parameters automatically and to manage the MV detector readout as well as the gantry angle capture for each MV projection. The kV projections are acquired with the conventional CBCT system. GPU-accelerated filtered backprojection is performed separately for both data sets. After appropriate grayscale normalization both modalities are combined and the final kV-MV volume is re-imported in the CBCT system to enable image matching. To demonstrate adequate geometrical accuracy of the novel imaging system the Penta-Guide phantom QA procedure is performed. Furthermore, a human plastinate and different tumor shapes in a thorax phantom are scanned. Diameters of the known tumor shapes are measured in the kV-MV reconstruction. Results: An automated kV-MV CBCT workflow was successfully established in a clinical environment. The overall procedure, from starting the data acquisition until the reconstructed volume is available for registration, requires ∼90 s including 17 s acquisition time for 100° rotation. It is very simple and allows target positioning in the same way as for conventional CBCT. Registration accuracy of the QA phantom is within ±1 mm. The average deviation from the known tumor dimensions measured in the thorax phantom was 0.7 mm which corresponds to an improvement of 36% compared to our previous kV-MV imaging system. Conclusions: Due to automation the kV-MV CBCT workflow is speeded up by a factor of >10 compared to the manual approach. Thus, the system allows a simple, fast and reliable imaging procedure and fulfills all requirements to be successfully introduced into the clinical workflow now, enabling single-breath-hold volume imaging

Reliability of transcutaneous measurement of renal function in various strains of conscious mice.

Measuring renal function in laboratory animals using blood and/or urine sampling is not only labor-intensive but puts also a strain on the animal. Several approaches for fluorescence based transcutaneous measurement of the glomerular filtration rate (GFR) in laboratory animals have been developed. They allow the measurement of GFR based on the elimination kinetics of fluorescent exogenous markers. None of the studies dealt with the reproducibility of the measurements in the same animals. Therefore, the reproducibility of a transcutaneous GFR assessment method was investigated using the fluorescent renal marker FITC-Sinistrin in conscious mice in the present study. We performed two transcutaneous GFR measurements within three days in five groups of mice (Balb/c, C57BL/6, SV129, NMRI at 3-4 months of age, and a group of 24 months old C57BL/6). Data were evaluated regarding day-to-day reproducibility as well as intra- and inter-strain variability of GFR and the impact of age on these parameters. No significant differences between the two subsequent GFR measurements were detected. Fastest elimination for FITC-Sinistrin was detected in Balb/c with significant differences to C57BL/6 and SV129 mice. GFR decreased significantly with age in C57BL/6 mice. Evaluation of GFR in cohorts of young and old C57BL/6 mice from the same supplier showed high consistency of GFR values between groups. Our study shows that the investigated technique is a highly reproducible and reliable method for repeated GFR measurements in conscious mice. This gentle method is easily used even in old mice and can be used to monitor the age-related decline in GFR

La Charente

14 octobre 18841884/10/14 (A13,N5584)-1884/10/14.Appartient à l’ensemble documentaire : PoitouCh

HVL measurement setup.

<p>HVL measurement setup.</p

Technical setup of applied imaging presets.

<p>Technical setup of applied imaging presets.</p

Absolute dose correction factors for kV- and MV-energy, based on AAPM TG61 report and IAEA TRS 398, respectively, whereas the values for HVL_BS and Q were calculated from the beam quality measurements.

<p>Absolute dose correction factors for kV- and MV-energy, based on AAPM TG61 report and IAEA TRS 398, respectively, whereas the values for HVL_BS and Q were calculated from the beam quality measurements.</p

Absorbed dose for different presets in inhomogeneous thorax phantom (column 8), ratio between the imaging methods and reference dose output kV-MV (D/D_ref) (column 9), comparison of MV-contribution dose output between measured and calculated (TPS) absolute dose by percentage difference (column 3–5), and separate contributions of kV- and RBE-corrected MV absorbed dose to kV-MV-CBCT in columns 6+7 (GE: Gray-equivalent with RBE = 2 for kV-dose contribution).

<p>Absorbed dose for different presets in inhomogeneous thorax phantom (column 8), ratio between the imaging methods and reference dose output kV-MV (D/D_ref) (column 9), comparison of MV-contribution dose output between measured and calculated (TPS) absolute dose by percentage difference (column 3–5), and separate contributions of kV- and RBE-corrected MV absorbed dose to kV-MV-CBCT in columns 6+7 (GE: Gray-equivalent with RBE = 2 for kV-dose contribution).</p