A new respiratory monitoring and processing system based on Wii remote: proof of principle.

PURPOSE: To create a patient respiratory management system and patient self-practice tool using the Wii remote, a widely available consumer hardware product. METHODS: The Wii remote (Wiimote) (Nintendo, Redmond, WA) contains an infrared (IR) camera that can track up to four spots whose coordinates are reported to a host computer via Bluetooth. The Wiimote is capable of tracking a fiducial box currently used by a commercial monitoring system [Real-time Position Management(TM) (RPM) system, Varian Associates, Palo Alto, CA], if the correct IR source is used. The authors validated the Wiimote tracking by comparing the amplitude and frequency of signals among those reported by Wiimote with known movements from an inhouse servo-driven respiratory simulator, as well as with those measured using the RPM. The simulator comparison was done using standard sinusoid signals with amplitude of 2.0 cm as well as recorded patient respiratory traces. The RPM comparisons were done by simultaneously recording the RPM reflective box position with the Wiimote and the RPM. Timing was compared between these two systems by using the digital beam-on signal from the CT scanner, for the 4DCT to synchronize these acquisitions. RESULTS: The data acquisition rate from the Wiimote was 100.0 ± 0.4 Hz with a version 2.1 Bluetooth adaptor. The standard deviation of the height of the motion extrema was 0.06 and 1.1 mm when comparing those measured by the Wiimote and the servomotor encoder for standard sinusoid signal and prerecorded patient respiratory signal, respectively. The standard deviation of the amplitude of motion extrema between the Wiimote and RPM was 0.9 mm and the timing difference was 253 ms. CONCLUSION: The performance of Wiimote shows promise for respiratory monitoring for its faster sampling rate as well as the potential optical and GPU abilities. If used with care it can deliver reasonable spatial and temporal accuracy.

WE-F-BRCD-01: Transitioning from 3D IMRT to 4D IMRT and Role of Image Guidance.

Tumors often change shape and position over the course of Radiation Therapy. The adaptation of the treatment to these changes, or its initial design to be robust in light of these changes, can be referred to as 4D radiation therapy. The 4th dimension is time and includes short term (intrafraction) and longer term (inter-fraction) changes. IMRT is an important modality for designing plans that can be optimized for or can adapt to these changes. The combination of management of the tumor changes and the optimization of the radiotherapy plans to deal with these changes is 4DIMRT and will be the focus of this 2 part talk. Part 1 : Head and Neck and Prostate treatments, focusing on adaptive therapy and image guidance. Part 2: Thoracic treatments focusing on 4DCT, IGRT, IMRT in the lung and motion management strategies Learning Objectives: 1. Understand currently available IGRT and 4DCT technologies 2. Explain how these technologies can be used to improve dose delivery precision and accuracy, in particular with dynamically changing tumor volumes 3. Understand the challenges and strategies in clinical implementation of IMRT in head and neck, prostate, and thorax.

SU-E-T-285: Flatness as a Measure of Changes in Photon Energy for Megavoltage X- Ray Radiotherapy.

PURPOSE: To compare the sensitivity of flatness based energy metrics versus an attenuation based metric (percent depth dose) as a function of energy changes from the linac's nominal clinical energy. METHODS: Energy changes were accomplished by adjusting the bending magnet current (BMI) ±15% away from the value used clinically. Two metrics for flatness, relative flatness in the central 80% of the field (flatness) and average maximum dose along the diagonals normalized by central axis (CAX) dose (diagonal normalized flatness, DNF), were measured using a commercially available ion chamber array (IC profiler, Sun Nuclear, Melbourne FL). Percent depth dose was measured in water for depths of 5 and 10 cm in 3×3 and 10×10 cm̂2 field sizes. RESULTS: The sensitivity of percent depth dose (PDD) and flatness to energy changes were smaller than changes in DNF. For 6X the changes in PDD were from -1+ to +3% and the changes in flatness were from -5% to +2% for energy changes of ±15% from the nominal energy, for 18X the PDD changed from -0.5% to +2.5% and the flatness from -5% to +2% over this energy range. DNF changed from +12% to -8% for 6X and from +8% to -6% for 18X over a ±15% change from the nominal energy and showed a near linear correlation with energy. In addition DNF was the only metric that was found to be sensitive to both increases and reductions of energy for both the 6 and 18 MV beams. CONCLUSIONS: Diagonal normalizedflatness was found to be the most sensitive metric to energy changes for photon beams of 6 and 18 MV. The IC profiler allows this metric to be conveniently measured as part of routine linac quality assurance. Sun Nuclear Corporation provided the IC profiler.

SU-E-J-29: Evaluation of Effectiveness of Immobilization Devices for Radiation Therapy with Repeated CBCT Studies.

PURPOSE: To evaluate the effectiveness of three different immobilization devices for lung radiation therapy with daily and/or weekly cone-beam CTs (CBCT). METHODS: Three different immobilization devices, short (IM1) and long (Im2 ) Vac-lok cushion with wing boards (Civco), BodyFix (Im3 , Elekta), were investigated. Repeated CBCT images for 3 SBRT patients immobilized with Im3 , and 6 IMRT patients immobilized with IM1 and Im2 (3 each) were acquired. Each SBRT patient received 70 Gy in 10 fractions and setup daily with CBCT, while IM1 and Im2 patients were setup daily with orthogonal kV, and weekly CBCT (week 0-6). The day 1, 6 and 10 CBCT for Im3 were considered week 0-2 CBCT. Patient setup was first based on skins markers then shifts were made based on bony landmarks in kV and GTV with CBCT. Skin contours, which are further away from the isocenter and thus more sensitive to rotation and skin folding, were extracted in each CBCT data set and the difference on skin contours were investigated for both before and after shifts. RESULTS: Over 2 weeks of treatment, Im3 has the smallest standard deviation for setup shifts (0.09, 0.16, 0.20 cm on LR, UD and IO directions) compared to IM1 (0.29, 0.35, 0.34 cm) and Im2 (0.11, 0.19, 0.40 cm), which indicates setup based on skin markers were the most reproducible for Im3 . Over 6 weeks of treatment, Im2 (0.16, 0.18, 0.42 cm) is more reproducible than IM1 (0.44, 0.45, 0.35 cm). All 3 patients with IM1 and 2 patients with Im2 were found to have >1 cm difference in skin contour even after shifts were made. 1 patient with IM1 was found to have non-reproducing skin folding of >3 cm difference. CONCLUSIONS: Information derived from repeated CT images could be used to evaluate the effectiveness of the immobilization devices.

SU-E-J-52: Validation of 3D Structure Projection Onto 2D DRR in Commercial Treatment Planning Systems.

PURPOSE: The use of structure overlay on setup DRRs can aid the image alignment procedure for daily image-guided setup procedures. However, the accuracy of a 3D region-of-interest (ROI) projected on a 2D digitally reconstructed radiograph (DRR) has rarely been evaluated quantitatively. The goal of this study is to test the accuracy of two commercial treatment planning systems (TPS) in producing overlay structures on setup DRRs. METHOD AND MATERIALS: We designed a novel method to identify landmarks which were on the boundary of the projected ROI on a DRR. The 3D ROIvolume is composed of a stack of 2D curves. We first mathematically project each 2D curve onto a beams-eye-view (BEV) plane. Next, we detectthe boundary points of the projected curves. Those boundary points serve aslandmarks. Finally, we project the binary mask of the 3D ROI volume using ray tracing method onto the BEV plane. This projected binary mask is used to exclude the false landmarks. Once those landmarks are detected, wecompute the distance between the landmarks and ROI outlines from the TPS. RESULTS: We applied our validation method to 13 ROIs from a lung patient and 4 simulated ROIs on 2 BEV DRRs for two different TPS (Eclipse and Pinnacle). Average distance between the landmarks and ROIoutlines was 0.5mm for both Eclipse and Pinnacle approaches, which is close to the pixel resolution of the DRR. The maximum distance andaverage maximum distance was 2mm and 1 mm, respectively, for both TPS.The maximum distance occurred at points where the ROI curve has a sharpchange between slices. CONCLUSION: The accuracy of Eclipse and Pinnacle ROI projection method seems to be acceptable to within 1mm althoughprojection error can be as large as 2mm when structure shape has a sharp variation from one slice to the next.

SU-E-T-184: LINAC Commissioning Measurements Utilizing the Cylindrical Arc Check Phantom.

PURPOSE: New devices for IMRT and VMAT QA are continually becoming available. Despite the availability of these devices they are underutilized for routine mechanical QA. In this work we take advantage of the cylindrical geometry of the Arc Check phantom to perform tests that are an integral part of commissioning and routine QA. METHODS: The Arc Check is a cylindrical phantom with a diameter of 26.59cm and a 1386 diode array arranged on a cylindrical plane. Owing to its cylindrical design it is capable of measuring entry and exit radiation. For this experiment the Arc Check was set up using the mechanical pointer at 86.7cm SSD. The device was leveled using its inclinometer and was properly rotated to align with the lasers and cross-hair. With the phantom set up at the expected isocenter of the LINAC, 100MUs with a 10×10 field were delivered at different gantry angles, couch and collimator rotations. Each delivery was recorded individually and for each one the radiation center at the entry and exit levels of the detector were estimated. That provided the path of the radiation center through the device. The radiation path was reconstructed for each rotation individually and the coincidence of the mechanical and radiation isocenter was evaluated. RESULTS: A procedure and MATLAB routine were developed that accepted as input the text files that are the output of the Arc Check measurement and geometrically reconstructed in 3-dimensions the isocenter and radiation central axis for each rotation. The coincidence of the radiation and mechanical isocenter was verified. CONCLUSIONS: This work demonstrates that by utilizing the geometry of a commercially available device multiple mechanical LINAC tests that are part of routine QA can be evaluated in one single setup.

Comparison between TG-51 and TG-21: Calibration of photon and electron beams in water using cylindrical chambers.

A new calibration protocol, developed by the AAPM Task Group 51 (TG-51) to replace the TG-21 protocol, is based on an absorbed-dose to water standard and calibration factor (N(D,w)), while the TG-21 protocol is based on an exposure (or air-kerma) standard and calibration factor (N(x)). Because of differences between these standards and the two protocols, the results of clinical reference dosimetry based on TG-51 may be somewhat different from those based on TG-21. The Radiological Physics Center has conducted a systematic comparison between the two protocols, in which photon and electron beam outputs following both protocols were compared under identical conditions. Cylindrical chambers used in this study were selected from the list given in the TG-51 report, covering the majority of current manufacturers. Measured ratios between absorbed-dose and air-kerma calibration factors, derived from the standards traceable to the NIST, were compared with calculated values using the TG-21 protocol. The comparison suggests that there is roughly a 1% discrepancy between measured and calculated ratios. This discrepancy may provide a reasonable measure of possible changes between the absorbed-dose to water determined by TG-51 and that determined by TG-21 for photon beam calibrations. The typical change in a 6 MV photon beam calibration following the implementation of the TG-51 protocol was about 1%, regardless of the chamber used, and the change was somewhat smaller for an 18 MV photon beam. On the other hand, the results for 9 and 16 MeV electron beams show larger changes up to 2%, perhaps because of the updated electron stopping power data used for the TG-51 protocol, in addition to the inherent 1% discrepancy presented in the calibration factors. The results also indicate that the changes may be dependent on the electron energy.

Screening for extreme postdialysis urea rebound using the Smye method: patients with access recirculation identified when a slow flow method is not used to draw the postdialysis blood.

To look for patients with extreme urea rebound, we drew intradialytic samples one third of the way into dialysis during routine modeling for 3 months. The samples taken postdialysis were obtained after stopping the blood pump, without any slow flow period. Using the Smye equations, the intradialytic urea level was used to predict urea rebound, expressed as Kt/V-equilibrated minus Kt/V-single pool (deltaKt/V). Results were averaged for the 3-month period in 369 patients. Mean estimated deltaKt/V was -0.20 +/- 0.13, which was similar to but slightly higher than the predicted value (-0.6 x K/V + 0.03) of -0.19 +/- 0.04. In 27 patients, extreme rebound (mean deltaKt/V < -0.40) was found. Sixteen of these patients consented to further study, but only after access revision in four patients. In these patients, additional slow flow samples after 15 seconds and 2 minutes of slow flow, respectively, were drawn one third of the way into dialysis and postdialysis, and a sample was drawn 30 minutes after dialysis. On restudy, postdialysis rebound was still high with full flow samples deltaKt/V = -0.40 +/- 25, but was much lower (-0.18 +/- 0.07) and similar to predicted rebound (-0.19 +/- 0.05; P = NS) when based on 15-second slow flow samples. Eight of the 16 had marked (>15%) access recirculation by urea sampling, and deltaKt/V based on full flow post samples correlated with access recirculation (r = -0.91). The results suggest that the Smye method is valuable for identifying patients with aberrantly large postdialysis rebound values. When the postdialysis samples are drawn without an antecedent slow flow period, most patients with extreme rebound values turn out to have marked access recirculation.

Optimizing radiologic costs in the DRG environment.

Previously developed consensus algorithms expressing a suggested radiologic workup for the diagnostic related groups (DRGs) specified by the prospective reimbursement policy have proven to be useful tools for investigating radiologic decision making and the resulting economic implications. The mathematical equations for determining diagnostic and therapeutic costs for two alternative algorithms for suspected acute cholecystitis are formulated. Illustrative examples and graphic displays are given regarding how such algorithms and equations are useful in finding answers to questions about the appropriate diagnostic workup, time, and cost. Exploration of the effect of different parameter values on the choice of the appropriate algorithm is illustrated.

Chronic toxic nephropathies--diagnosis and management.

As a result of industrial and medical progress, man is exposed to an ever changing array of chemicals, drugs and biological products. The kidneys are extremely vulnerable to chronic toxic effects of these substances. Although acute renal failure, nephrotic syndrome and renal tubular disorders result from acute nephrotoxicity, chronic renal failure with renal failure and hypertension result from chronic nephrotoxicity. Heavy metals, analgesic agents and antimicrobials are the common nephrotoxic substance producing chronic renal disease. Medical management consists of preventive exposure measures and early detection of nephrotoxicity by modern industrial medicine. In addition, early clinical diagnosis with appropriate management may prevent the need for chronic hemodialysis and renal transplantation.