A combined system comprising the TrueBeam linear accelerator and a new real‐time, tumor‐tracking radiotherapy system, SyncTraX, was installed in our institution. The goals of this study were to assess the capability of SyncTraX in measuring the position of a fiducial marker using color fluoroscopic images, and to evaluate the dosimetric and geometric accuracy of respiratory‐gated radiotherapy using this combined system for the simple geometry. For the fundamental evaluation of respiratory‐gated radiotherapy using SyncTraX, the following were performed: 1) determination of dosimetric and positional characteristics of sinusoidal patterns using a motor‐driven base for several gating windows; 2) measurement of time delay using an oscilloscope; 3) positional verification of sinusoidal patterns and the pattern in the case of a lung cancer patient; 4) measurement of the half‐value layer (HVL in mm AL), effective kVp, and air kerma, using a solid‐state detector for each fluoroscopic condition, to determine the patient dose. The dose profile in a moving phantom with gated radiotherapy having a gating window ≤4 mm was in good agreement with that under static conditions for each photon beam. The total time delay between TrueBeam and SyncTraX was <227 ms for each photon beam. The mean of the positional tracking error was <0.4 mm for sinusoidal patterns and for the pattern in the case of a lung cancer patient. The air‐kerma rates from one fluoroscopy direction were 1.93±0.01, 2.86±0.01, 3.92±0.04, 5.28±0.03, and 6.60±0.05 mGy/min for 70, 80, 90, 100, and 110 kV X‐ray beams at 80 mA, respectively. The combined system comprising TrueBeam and SyncTraX could track the motion of the fiducial marker and control radiation delivery with reasonable accuracy; therefore, this system provides significant dosimetric improvement. However, patient exposure dose from fluoroscopy was not clinically negligible.PACS number(s): 87.53.Bn, 87.55.km, 87.55.Qr

Ischemic preconditioning is a phenomenon in which one or several cycle(s) of brief ischemia-reperfusion protects the myocardium against the cell injury caused by subsequent prolonged ischemia. Protein kinase C (PKC) inhibitors blunt the cardioprotection arising from ischemic preconditioning. To investigate which PKC isoform is involved in ischemic preconditioning, we identified the PKC isoform that translocates to the membrane fraction by means of immunoblotting with specific antibodies. PKC-alpha, delta, epsilon isoforms all increased in the membrane fraction after three cycles of 3 min ischemia and 5 min reperfusion (ischemic preconditioning) in the perfused rat heart. The ischemic preconditioning significantly improved the recovery of left ventricular developed pressure (LVDP) during reperfusion following 20 min of ischemia. A PKC specific inhibitor, chelerythrine (1.0 microM) blocked the effect of ischemic preconditioning on LVDP recovery and the translocation of PKC-alpha, delta, epsilon isoforms. These data suggest that one or more of these three isoforms of PKC is involved in ischemic preconditioning by phosphorylating membrane proteins.

The ion chamber measurement of absorbed dose-to-water with a sandwich method for the (192)Ir source provides a more accurate, direct, and reference dose compared to the dose-to-water determination based on air-kerma strength in the TG-43 protocol. Due to the simple but accurate assembly, the sandwich measurement method is useful for daily dose management of (192)Ir sources.

PurposeThe aim of this study is to describe a phantom designed for independent examination of a source position in brachytherapy that is suitable for inclusion in an external auditing program.Material and methodsWe developed a phantom that has a special design and a simple mechanism, capable of firmly fixing a radiochromic film and tandem-ovoid applicators to assess discrepancies in source positions between the measurements and treatment planning system (TPS). Three tests were conducted: 1) reproducibility of the source positions (n = 5); 2) source movements inside the applicator tube; 3) changing source position by changing curvature of the transfer tubes. In addition, as a trial study, the phantom was mailed to 12 institutions, and 23 trial data sets were examined. The source displacement ΔX and ΔY (reference = TPS) were expressed according to the coordinates, in which the positive direction on the X-axis corresponds to the external side of the applicator perpendicular to source transfer direction Y-axis.ResultsTest 1: The 1σ fell within 1 mm irrespective of the dwell positions. Test 2: ΔX were greater around the tip of the applicator owing to the source cable. Test 3: All of the source position changes fell within 1 mm. For postal audit, the mean and 1.96σ in ΔX were 0.8 and 0.8 mm, respectively. Almost all data were located within a positive region along the X-axis due to the source cable. The mean and 1.96σ in ΔY were 0.3 and 1.6 mm, respectively. The variance in ΔY was greater than that in ΔX, and large uncertainties exist in the determination of the first dwell position. The 95% confidence limit was 2.1 mm.ConclusionsIn HDR brachytherapy, an effectiveness of independent source position assessment could be demonstrated. The 95% confidence limit was 2.1 mm for a tandem-ovoids applicator.

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