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In hyperthermia induced by electromagnetic applicators, one way to obtain information about the energy absorption is by measurement of electric field strength (E). This paper describes a system which can measure E-distributions, using a two-dimensional array of diodes. It was designed to be used on patient skin, during hyperthermia treatments of superficial tumours, providing additional data for applicator power control. The first prototype consists of a sheet with Schottky diode sensors with a spacing of 2.5cm, connected to high-resistance leads, printed with carbon ink. The rectified diode voltages are passed through a multiplexer unit to an AD-DA card in a PC. The sensitivity of the sensors is linearly proportional to the electric field and to the length of the extended diode connection pins. Relative E-field distributions obtained with 64 sensors are updated within 1s. Phantom measurements, performed with the sensor matrix under a Lucite Cone Applicator (LCA) and under a 2 2 array of Current Sheet Applicators (CSAs) were compared with infrared measurements of the temperature rise after a short power pulse. A fair agreement was found between the square of the diode voltages and the infrared distributions. Movement of a single CSA over the sensor matrix can be visualized clearly by the system. The diode matrix E-field measurement system is sufficiently fast and accurate to give valuable feedback for power steering for an array of LCAs and CSAs. The system has the potential of being a helpful tool in other fields of quality assurance as well. [ABSTRACT FROM AUTHOR]

Purpose: The 27 MHz Multi Electrode Current Source (MECS) interstitial hyperthermia system uses probes consisting of multiple independent electrodes, 10- 20 mm long, to steer the 3-D power deposition. Seven point thermocouples integrated into the probes provide matching 3-D temperature feedback data. To improve spatial steering the number of independent segments was increased; the feasibility and reliability of four independent electrodes integrated into a single probe were evaluated, with special attention to efficiency and to interference between separate electrodes. Methods: The contribution of secondary coupling on the apparent electrode impedance and the dependence of cross coupling on the distance between leads, thermocouple and electrodes are computed using simple analytical models. The effect of this secondary coupling was assessed experimentally by comparing power delivery by dual and quadruple electrodes, and by quadruple electrodes in different electrode configurations (segment length 10 or 20 mm) in a nylon catheter in a muscle equivalent medium. Results: Cross coupling with the thermocouple and other electrodes was computed to be of the same magnitude as the primary coupling for a quadruple electrode. Fortunately, this does not affect operation of the electrode, there was no difference in performance between quadruple and dual electrodes, and the output power was effectively independent of the electrode configuration. Conclusion: Quadruple MECS electrodes for improved 3-D power control are feasible. [ABSTRACT FROM AUTHOR]

Purpose: To describe short-term complications during stent placement for atherosclerotic renal artery ostial stenosis.Methods: Sixty-one arteries in 50 patients were treated with Palmaz stents. Nineteen patients had a single functioning kidney, 23 had a bilateral stenosis, which was stented bilaterally in 11, and 8 had a unilateral stenosis. The complications were grouped as those related to the catheterization procedure, those related to stent placement, and those possibly related to either category. The complications were divided into those with severe clinical significance (SCS), those with minor clinical significance (MCS), and radiological-technical complications (RTC). The stent placement procedures were ordered chronologically according to examination date and the complications were tabulated per group of 10 patients.Results: Five (10%) SCS, 5 (10%) MCS, and 8 (16%) RTC occurred in 50 patients. The catheterization procedure led to 2 SCS, 3 MCS, and 1 RTC. Stent placement gave rise to 7 RTC. Three SCS and 2 MCS could have been related to either catheterization or stent placement. More SCS occurred in the first group of 10 patients than in the following groups.Conclusion: Renal artery stent placement for atherosclerotic ostial stenosis has a considerable complication rate and a learning curve is present. The complications related to the actual stent placement were without clinical consequences. [ABSTRACT FROM AUTHOR]

Background and Purpose: This work reports on the results of a survey performed on the use of computed tomography (CT) imaging for motion management, surface guidance devices, and their quality assurance (QA). Additionally, it details the collected user insights regarding professional needs in CT for radiotherapy. The purpose of the survey is to understand current practice, professional needs and future directions in the field of fan-beam CT in radiation therapy (RT)., Materials and Methods: An online institutional survey was conducted between 1-Sep-2022 and 10-Oct-2022 among medical physics experts at Belgian and Dutch radiotherapy institutions, to assess the current status, challenges, and future directions of motion management and surface image-guided radiotherapy. The survey consisted of a maximum of 143 questions, with the exact number depending on participants' responses., Results: The response rate was 66 % (31/47). Respiratory management was reported as standard practice in all but one institution; surface imaging during CT-simulation was reported in ten institutions. QA procedures are applied with varying frequencies and methodologies, primarily with commercial anatomy-like phantoms. Surface guidance users report employing commercial static and dynamic phantoms. Four main subjects are considered clinically important by the respondents: surface guidance, CT protocol optimisation, implementing gated imaging (4DCT, breath-hold), and a tattoo-less workflow., Conclusions: The survey highlights the scattered pattern of QA procedures for respiratory motion management, indicating the need for well-defined, unambiguous, and practicable guidelines. Surface guidance is considered one of the most important techniques that should be implemented in the clinical radiotherapy simulation workflow., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2023 The Author(s).)

Background and Purpose: To obtain an understanding of current practice, professional needs and future directions in the field of fan-beam CT in RT, a survey was conducted. This work presents the collected information regarding the use of CT imaging for dose calculation and structure delineation., Materials and Methods: An online institutional survey was distributed to medical physics experts employed at Belgian and Dutch radiotherapy institutions to assess the status, challenges, and future directions of QA practices for fan-beam CT. A maximum of 143 questions covered topics such as CT scanner availability, CT scanner specifications, QA protocols, treatment simulation workflow, and radiotherapy dose calculation. Answer forms were collected between 1-Sep-2022 and 10-Oct-2022., Results: A 66 % response rate was achieved, yielding data on a total of 58 CT scanners. For MV photon therapy, all single-energy CT scans are reconstructed in Hounsfield Units for delineation or dose calculation, and a direct- or stoichiometric method was used to convert CT numbers for dose calculation. Limited use of dual-energy CT is reported for photon (N = 3) and proton dose calculations (N = 1). For brachytherapy, most institutions adopt water-based dose calculation, while approximately 26 % of the institutions take tissue heterogeneity into account. Commissioning and regular QA include eleven tasks, which are performed by two or more professions (29/31) with varying frequencies., Conclusions: Dual usage of a planning CT limits protocol optimization for both tissue characterization and delineation. DECT has been implemented only gradually. A variation of QA testing frequencies and tests are reported., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2023 The Author(s).)

Purpose: To determine the accuracy and repeatability of ultrasonography (US) with the ellipsoid formula in calculating the renal volume., Materials and Methods: The renal volumes in 20 volunteers aged 19-51 years were determined by using US with the ellipsoid formula and magnetic resonance (MR) imaging with the voxel-count method by two independent observers for each modality. The observers performed all measurements twice, with an interval between the first and second examinations. The voxel-count method was the reference standard. Repeatability was evaluated by calculating the SD of the difference (method of Bland and Altman)., Results: Renal volume was underestimated with US by 45 mL (25%) on average. A comparable underestimation was found when the ellipsoid formula was applied to MR images. This indicates that the inaccuracy of US renal volume measurements (a) occurred because the kidney does not resemble an ellipsoid and (b) was not primarily related to the imaging modality. Intra- and interobserver variations in US volume measurements were poor; the SD of the difference was 21-32 mL. For comparison, the SD of the difference in reference-standard measurements was 5-10 mL., Conclusion: Use of US with the ellipsoid formula is not appropriate for accurate and reproducible calculation of renal volume.

The multielectrode current source (MECS) interstitial hyperthermia (IHT) system uses thermocouple thermometry. To obtain a homogeneous temperature distribution and to limit the number of traumas due to the implanted catheters, most catheters are used for both heating and thermometry. Implications of temperature measurement inside applicators are discussed. In particular, the impact of self-heating of both the applicator and the afterloading catheter were investigated. A one-dimensional cylindrical model was used to compute the difference between the temperature rise inside the applicators (deltaTin) and in the tissue just outside the afterloading catheter (deltaTout) as a function of power absorption in the afterloading catheter, self-heating of the applicator and the effective thermal conductivity of the surrounding tissue. Furthermore, the relative artefact (ERR), i.e. (deltaTin - deltaTout)/deltaTin, was measured in a muscle equivalent agar phantom at different positions in a dual-electrode applicator and for different catheter materials. A method to estimate the tissue temperature by power-off temperature decay measurement inside the applicator was investigated. Using clinical dual-electrode applicators in standard brachytherapy catheters in a muscle-equivalent phantom, deltaTin is typically twice as high as deltaTout. The main reason for this difference is self-heating of the thin feeder wires in the centre of the applicator. The measurement error caused by energy absorption in the afterloading catheter is small, i.e. even for materials with a high dielectric loss factor it is less than 5%. About 5 s after power has been switched off, Tin in the electrodes represents the maximum tissue temperature just before power-off. This delay time (t(delay)) and ERR are independent of Tin. However, they do depend on the thermal properties of the tissue. Therefore, ERR and t(delay) and their stability in perfused tissues have to be investigated to enable a reliable estimation of the tissue temperatures around electrodes in clinical practice.

Background: Percutaneous transluminal angioplasty (PTA) for ostial atherosclerotic renal-artery stenosis has poor results. Angioplasty with stent placement (PTAS) may be more effective. We undertook a randomised prospective study to compare PTA with PTAS in patients with ostial atherosclerotic renal-artery stenosis., Methods: Patients with ostial atherosclerotic renal-artery stenosis were assigned to receive PTA or PTAS. Secondary PTAS was allowed if PTA failed immediately or during 6 months' follow-up. Analysis was by intention to treat., Findings: 42 patients were assigned PTA and 43 were assigned PTAS, but one patient in the PTAS group was excluded from the study. Primary success rate (<50% residual stenosis) of PTA was 57% (24 patients) compared with 88% (37 patients) for PTAS (difference between groups 31% [95% CI 12-50]). Complications were similar. At 6 months, the primary patency rate was 29% (12 patients) for PTA, and 75% (30 patients) for PTAS (46% [24-68]). Restenosis after a successful primary procedure occurred in 48% of patients for PTA and 14% for PTAS (34% [11-58]). 12 patients underwent secondary stenting for primary or late failure of PTA within the follow-up period: success was similar to that of primary PTAS. Evaluation based on intention to treat showed no difference in clinical results at six months for PTA or PTAS., Interpretation: PTAS is a better technique than PTA to achieve vessel patency in ostial atherosclerotic renal-artery stenosis. Primary PTAS and primary PTA plus PTAS as rescue therapy have similar outcomes. However, the burden of reintervention after PTA outweighs the potential saving in stents, so primary PTAS is a better approach to use.

Purpose: The purpose of this work was to assess the optimal scan delay for spiral CT angiography (SCTA) of the renal arteries in achieving optimal vascular contrast enhancement and to compare the utility of a delay based on these bolus injection versus that of a fixed scan delay., Method: Seventy patients underwent renal artery SCTA with a 140 ml bolus of contrast agent injected a 3 ml/s. In 35 patients (Group A), a fixed scan delay of 27 s was used; in the other 35 (Group B), the scan delay was based on the transit time (TTest) of a test bolus injection. The scan delays in this group were set at TTest + 5 s (n = 5), TTest + 10 s (n = 8), TTest + 15 s (n = 4), or TTest + 20 s (n = 18). For all 70 patients, the time intervals between TRA (time to scanning the renal arteries) and TMax (time to maximum aortic enhancement after 140 ml bolus injection) were calculated, after which it was determined in which group of patients TRA occurred closest to TMax. Linear regression and mean squared error (MSE) were used for statistical analysis., Results: For Group A, mean TRA and TMax were 38 and 50 s, respectively. Mean (TRA - TMax) was -12 s with MSE of 185.76. For Group B, mean TRA and Tmax were 45 and 52 s. Mean (TRA - TMax) values were -15, -12, -11, and -1 s for scan delays of TTEST + 5 s, TTEST + 10 s, TTest + 15 s, and TTEST + 20 s, respectively, with MSEs of 253.80, 158.00, 137.50, and 30.00., Conclusion: SCTA of the renal arteries was best performed with a scan delay of TTEST + 20 s. However, analysis of our data showed that similar results could be expected with a delay of 44 s.

Ischemic nephropathy due to bilateral renovascular disease (RVD) is increasingly recognized as cause of end-stage renal failure in the elderly, but a reliable non-invasive method of detection is nor available. Angiotensin converting enzyme inhibition (ACEi) may impair renal function in such patients, but a prospective study of its diagnostic validity has not been undertaken. We studied the effects of controlled exposure to ACEi on plasma creatinine in 108 patients at risk for severe bilateral atherosclerotic RVD, and compared the findings with subsequent angiography. ACEi was given for two weeks, or, to avoid acute renal failure, for four days if plasma creatinine had increased by 20% or more. If after two weeks of ACEi plasma creatinine had not increased by > or = 20%, while blood pressure was still elevated, plasma creatinine was remeasured after blood pressure control by addition of diuretics. The severity of RVD was scored by the stenosis grade of the best perfused kidney. Fifty-two patients had severe bilateral RVD, defined as > or = 50% stenosis to both kidneys (N = 23) or a solitary functioning kidney (N = 29). Of the others, 21 had less severe bilateral RVD, 20 unilateral RVD, and 15 no apparent RVD. Basal plasma creatinine was higher in severe bilateral RVD (median 170 mumol/liter, range 85 to 654 mumol/liter) than in the others (122 mumol/liter, 62 to 675 mumol/liter; P < 0.01), but not discriminative due to a large variability. The increase during ACEi was correlated with the degree of RVD (r = 0.53, P < 0.001). In 69 patients ACEi caused at least a 20% increase in plasma creatinine, in 26 cases by four days, in 31 after two weeks, and in 12 only after blood pressure control by diuretics. Among these were all 52 patients with severe bilateral RVD, 15 of the 41 patients with lesser forms of RVD, and two with normal renal arteries. Thus, in this selected population the criterion of > or = 20% rise in plasma creatinine upon ACEi was 100% sensitive to detect severe bilateral RVD, while its specificity was 70%. No case of acute renal failure was encountered, and plasma creatinine always recovered after stopping ACEi. In conclusion, controlled exposure to ACEi in these patients is safe, and ACEi-induced increase in plasma creatinine is a very sensitive detector of severe bilateral RVD in a high risk population.