Modulated Arc Therapy for hippocampal-avoidance whole brain radiation therapy: planning comparison with intensity modulated Radiation Therapy.

This study aimed to evaluate the modulated arc therapy (mARC) technique as a planning and treatment option for hippocampal sparing whole brain radiotherapy (HS-WBRT) following the Radiation Therapy Oncology Group (RTOG) 0933 dosimetric criteria. Computed tomography (CT) and magnetic resonance imaging (MRI) were selected retrospectively for 15 patients. Two types of plans were created for each patient, namely an intensity-modulated radiation therapy (IMRT) and a mARC plan. IMRT and mARC plans were compared in terms of plan quality indices, absorbed dose to organs at risk (OARs), number of monitor units (MUs), and treatment time. All plans in both techniques were considered clinically acceptable for treatment. However, IMRT plans presented a higher conformity (p = 0.01) as well as a higher homogeneity as compared to mARC plans, but this difference was not statistically significant (p > 0.05). In terms of the preservation of the hippocampus, it was observed that the IMRT plans achieved significantly lower doses for both 100% of its volume and for its maximum dose (p < 0.001). The evaluation of the remaining OARs showed that the IMRT technique resulted in lower doses, and significant differences were observed for the following organs: left cochlea (p < 0.001), left eye (p < 0.001), right eye (p = 0.03), both lenses of the eye (p < 0.001), and right optic nerve (p = 0.02). Despite these differences, the absolute differences in all dosimetric parameters were low enough to bear any clinical relevance. A drastic (close to 65%) and significant (p < 0.001) decrease was observed in the number of MUs for the mARC plans. This resulted in a substantial decrease in treatment time (60.45%, p < 0.001). It is concluded that the mARC technique is a feasible planning and treatment solution for HS-WBRT that meets the RTOG 0933 criteria. The main advantage of using mARC over IMRT for HS-WBRT is the considerable reduction in MUs and treatment time.

Dosimetric study of a hybrid plan technique for external beam radiotherapy in patients with cervical cancer.

The aim of this study was to investigate the effect of a hybrid technique which results from combining intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) for the treatment of cervical cancer patients. Plans made with the hybrid technique and pure IMRT and VMAT were retrospectively compared in 20 patients with cervical cancer at different stages. All plans were made using the same contours based on the original computed tomography (CT) scans. Conformity (CI) and homogeneity (HI) indices of the planning target volumes (PTVs) were calculated for each technique in order to evaluate plan quality. All techniques were compared in terms of dose to organs at risk (OARs), number of monitor units (MUs) and treatment time. It turned out that plans made with the hybrid technique had improved dose conformity and homogeneity compared to plans made only with IMRT and VMAT (p < 0.001). Regarding the OARs, the maximum dose (Dmax) delivered to the bladder, rectum and femoral heads was lower for the hybrid plans compared to the IMRT and VMAT plans (p < 0.001). The volumes irradiated to doses of 50 Gy (V50Gy) for rectum, bladder and bowel were lower for the hybrid plans (p < 0.001, p = 0.002). Furthermore, the treatment time and MU values for the hybrid plans were found to be between of the values for the IMRT and VMAT plans. It is concluded that, as compared to IMRT and VMAT plans, the hybrid plan technique allowed a better conformity and homogeneity for the dose distribution in the PTV and a dose reduction to the OARs.

Clinical validation of a pressure-standardized compression mammography system.

OBJECTIVES: Validation of a pressure-standardized compression mammography (PSCM) system, which aims to reduce discomfort and pain by applying the same pressure to every breast, independent of breast size. METHODS: We retrospectively studied mammograms of 39 patients acquired with a conventional force-standardized compression mammography (FSCM) technique and intra-individually compared them to mammograms acquired on a checkup visit with PSCM technique. Patients received one craniocaudal (CC) and one mediolateral oblique (MLO) compression for both breasts. All images were processed to obtain the contact area between the breast and the compression paddle. The pressure was calculated by dividing the compression force by the contact area. RESULTS: A total of 150 FSCM and 150 PSCM images were analyzed. The mean pressure decreased significantly from 17.1 to 12.8 kPa (p < 0.001), when using PSCM instead of FSCM. The applied pressure hardly depended on the breast contact area with the paddle (-0.014 kPa/cm2), while a clear dependency was observed using FSCM. Furthermore, the relative number of over-compressions reduced from 26% to 2%, benefitting patients with smaller breasts. CONCLUSIONS: Our study suggests that using PSCM can reduce patient discomfort and pain during mammographic compression compared to conventional FSCM as a result of lower average pressure. Moreover, standardized pressure may provide a more constant image quality, which could improve diagnostic performance.

Clinical value of dacryoscintigraphy using a simplified analysis.

PURPOSE: To study the discriminatory ability of dacryoscintigraphy in differentiating between patients with epiphora and volunteers using a simple method. METHODS: Twenty eyes in ten volunteers and 66 eyes in 55 patients with severe epiphora were studied. Dacryoscintigraphy (15 frames of 1 min) was performed after administration of 4 MBq (99m)Tc-pertechnetate (10 mul) in both eyes. By mapping a single region of interest (ROI) over the conjunctival sac we determined T1 (%dose in first minute) and linear clearance rate (LCR, defined as [see text] from the tracer disappearance curve. Reproducibility was determined in volunteers. Conjunctival resorption was determined from completely obstructed systems. Sensitivity and specificity were calculated and receiver operating characteristics (ROC) analysis was conducted. RESULTS: In volunteers mean T1 was 52.8+/-11.9% (95% CI 47.1-58.4%), and LCR was 74.2+/-11.1% (95% CI 69.0-79.4%). Reproducibility was good (mean difference 4.1+/-13.3% for T1 and 0.7+/-17% for LCR). Epiphora patients had clearly higher T1 (82.1+/-15.2%, P<0.0001) and lower LCR (38.9+/-22.5%, P<0.0001) values. Tracer resorption was 24%. Based on ROC analysis 70% for T1 and 50% for LCR were considered optimal cut-off levels to separate patients from volunteers. Sensitivity/specificity were 77/95% for T1 and 71/100% for LCR. T1 and LCR values did not correlate with symptom scores or Anel test results. CONCLUSION: Dacryoscintigraphy, using LCR and T1 as parameters, is a reliable and objective method to detect tear-flow abnormalities.

Sentinel node detection in patients with breast cancer: low-energy all-purpose collimator or medium-energy collimator?

Sentinel node detection in patients with breast cancer is routinely performed in our department. Images frequently show star-shaped activity at the site of injection caused by septum penetration. These star-shaped artifacts could possibly impair visualization of nearby sentinel nodes. The aim of this study was to determine whether sentinel node detection in patients with breast cancer can be improved using a medium-energy all-purpose (ME) collimator instead of a low-energy all-purpose (LEAP) collimator. For this purpose, 15 patients were studied and a phantom study was performed. The LEAP collimator was used for a dynamic study immediately after injection, and both the LEAP and the ME collimators were used for static studies. A total of 20 sentinel nodes were found with both collimators. All sentinel nodes were found in the axilla. To separate sentinel nodes from the injection site, the ME collimator gave the best results in 4 of 15 patients, but only within the first hour after injection. To separate 2 nearby sentinel nodes from each other, the LEAP collimator gave the best results in 3 of 15 patients. Our conclusion is that the LEAP collimator gave better results than the ME collimator as a result of the better resolution and the higher sensitivity. Use of the ME collimator did not improve sentinel node detection.

Gated blood-pool SPECT automated versus manual left ventricular function calculations.

Planar gated blood-pool imaging (GBPI) is a standard method for non-invasive assessment of left ventricular (LV) function. Gated blood-pool single photon emission computed tomographic (GBPS) data acquisition can be accomplished in the same time as GBPI, with the benefit of enabling visualization of all cardiac chambers simultaneously. The purpose of this investigation was to evaluate the degree to which automated and manual LVEF calculations agree with one another and with conventional GBPI LVEF measurements. GBPI studies were performed in 22 consecutive, unselected patients, followed by GBPS data acquisition. GBPS left ventricular ejection fraction (LVEF) calculations were performed by available software (NuSMUGA, Northwestern University, Chicago, IL) automatically and manually, using all LV gated short axis slices. Automatic LVEF assessed by GBPS correlated well with conventional planar GBPI (r = 0.88, P < 0.001). Mean planar GBPI LVEF was 50% +/- 12%, and mean GBPS automatic LVEF was significantly lower at 45% + 14% (P = 0.001), with a mean difference of 6% +/- 5%. Manual GBPS LVEF also correlated well with conventional planar GBPI (r = 0.90, P < 0.0001). Mean LVEF measurement by manual GBPS versus GBPI was significantly higher at 59% +/- 13%, with a mean difference of 10% +/- 6% (P < 0.001). Manual GBPS LVEF values were also significantly higher than automatically determined GBPS LVEF values (P < 0.001). It is concluded that LVEF values assessed by NuSMUGA GBPS software were reproducible, and automatic and manual values correlated well with conventional GBPI values. However, both automatic and manual GBPS calculations were significantly different from one another and from GBPI values, so that GBPI and NuSMUGA calculations cannot be considered to be equivalent.

Asymmetric dynamics of adaptation after onset and offset of flicker.

We measured human psychophysical detection thresholds for test pulses which are superimposed on spatially homogeneous backgrounds that have abrupt onsets and offsets of high-contrast 25 Hz flicker. After the onset of the background flicker, test thresholds reach their steady-state levels within 20-60 ms. After the offset of the background flicker, test thresholds remain elevated above their steady-state level for much longer durations. Adaptation after onsets and offsets of background flicker is modeled with a divisive gain control that is activated by temporal contrast. We show that a feedback structure for the gain control can explain the asymmetric dynamics observed after onsets and offsets of the background contrast. Finally, we measure detection thresholds for tests presented on steadily flickering backgrounds as a function of the contrast of the background flicker. We show that the divisive feedback model for contrast gain control can describe these results as well.

Evaluation of right ventricular function by NuSMUGA software: gated blood-pool SPECT vs. first-pass radionuclide angiography.

BACKGROUND: In comparison with planar imaging gated blood-pool single photon emission computed tomography (GBPS) has the advantage of separating left and right ventricle. The purpose of this investigation was to evaluate the right ventricular ejection fraction (RVEF) calculations by GBPS software ('NuSMUGA', Northwestern University, Chicago, IL) in comparison to first-pass radionuclide angiography (FPRNA). METHODS: In 22 consecutive patients FPRNA and GBPS acquisition was performed. GBPS RVEF calculations were manually and automatically performed, using all gated short-axis-slices of the right ventricle. RESULTS: Automatic RVEF assessed by GBPS did not correlate with conventional FPRNA (r = 0.40, p = 0.065). Mean FPRNA RVEF was 55 +/- 10% and mean GBPS automatic RVEF was 32 +/- 8%. Also manual GBPS RVEF did not correlate with conventional FPRNA (r = 0.41, p = 0.055). Mean RVEF measurement by manual GBPS was 33 +/- 8%. Manual GBPS RVEF values correlated well with automatically determined GBPS RVEF values (r = 0.96, p < 0.0001). CONCLUSION: Automatic and manual values RVEF values assessed by GBPS did not correlate with conventional FPRNA values. FPRNA and GBPS calculations cannot be considered to be equivalent. Therefore the NuSMUGA program cannot be used to calculate RVEF.

Clinical value of gallium-67 scintigraphy in assessment of disease activity in Wegener's granulomatosis.

BACKGROUND: Diagnosis of active pulmonary and paranasal involvement in patients with Wegener's granulomatosis (WG) can be difficult. The diagnostic value of gallium-67 scintigraphy in WG is unclear. OBJECTIVE: To evaluate the added diagnostic value of gallium-67 scintigraphy in patients with WG with suspected granulomatous inflammation in the paranasal and chest regions. METHODS: Retrospectively, the diagnostic contribution of chest and head planar gallium scans in 40 episodes of suspected vasculitis disease activity in 28 patients with WG was evaluated. Scans were grouped into normal or increased uptake for each region. Histological proof or response to treatment was the "gold standard" for the presence of WG activity. RESULTS: WG activity was confirmed in 8 (20%) episodes, with pulmonary locations in three, paranasal in four, and both in one (n=7 patients); all these gallium scans showed increased gallium uptake (sensitivity 100%). Gallium scans were negative for the pulmonary area in 23/36 scans (specificity 64%), and negative for paranasal activity in 13/16 scans (specificity 81%) in episodes without WG activity. Positive predictive value of WG activity for lungs and paranasal region was 24% and 63%, respectively, negative predictive value was 100% for both regions. False positive findings were caused by bacterial or viral infections. CONCLUSION: Gallium scans are clinically helpful as a negative scan virtually excludes active WG. Gallium scintigraphy of chest and nasal region has a high sensitivity for the detection of disease activity in WG. However, because of positive scans in cases of bacterial or viral infections, specificity was lower.

A temporal model for early vision that explains detection thresholds for light pulses on flickering backgrounds.

A model is presented for the early (retinal) stages of temporal processing of light inputs in the visual system. The model consists of a sequence of three adaptation processes, with two instantaneous nonlinearities in between. The three adaptation processes are, in order of processing of the light input: a divisive light adaptation, a subtractive light adaptation, and a contrast gain control. Divisive light adaptation is modeled by two gain controls. The first of these is a fast feedback loop with square-root behavior, the second a slow feedback loop with logarithm-like behavior. This can explain several aspects of the temporal behavior of photoreceptor outputs. Subtractive light adaptation is modeled by a high-pass filter equivalent to a fractional differentiation, and it can explain the attenuation of low frequencies observed in ganglion cell responses. Contrast gain control in the model is fast (Victor, 1987), and can explain the decreased detectability of test signals that are superimposed on dynamic backgrounds. We determine psychophysical detection thresholds for brief test pulses that are presented on flickering backgrounds, for a wide range of temporal modulation frequencies of these backgrounds. The model can explain the psychophysical data for the full range of modulation frequencies tested, as well as detection thresholds obtained for test pulses on backgrounds with increment and decrement steps in intensity.

Dynamics of adaptation at high luminances: adaptation is faster after luminance decrements than after luminance increments.

As is well known, dark adaptation in the human visual system is much slower than is recovery from darkness. We show that at high photopic luminances the situation is exactly opposite. First, we study detection thresholds for a small light flash, at various delays from decrement and increment steps in background luminance. Light adaptation is nearly complete within 100 ms after luminance decrements but takes much longer after luminance increments. Second, we compare sensitivity after equally visible pulses or steps in the adaptation luminance and find that detectability is initially the same but recovers much faster for pulses than for increment steps. This suggests that, whereas any residual threshold elevation after a step shows the incomplete luminance adaptation, the initial threshold elevation is caused by the temporal contrast of the background steps and pulses. This hypothesis is further substantiated in a third experiment, whereby we show that manipulating the contrast of a transition between luminances affects only the initial part of the threshold curve, and not later stages.