A Harrison

SU-F-T-466: An Enhanced Daily Quality Assurance Process for a Six Degrees of Freedom Robotic Table

PURPOSE A Varian PerfectPitch six degrees of freedom robotic table necessitates daily quality assurance (QA). Therapists were credentialed for this QA procedure which was easily incorporated into the existing daily warmup process. This procedure adds depth to TG-142 requirements without additional morning time costs. METHODS This PerfectPitch table QA introduces a consistent rotation of the QUASAR™ Penta-Guide phantom and requires automatic table corrections through image fusions. Rotational offsets are generated by inserting a platform tool under a specified corner of the phantom; then a conebeamCT is performed. This conebeamCT image is fused with a planned reference CT image set and the table is auto-adjusted to correct for induced translational and rotational offsets. After executing table shifts, a second conebeamCT verifies the table movement and the phantoms return to isocenter. RESULTS Pre-shift and post-shift table corrections were recorded daily. It was discovered that due to slight variations in the setup, it took three performances of the QA for each therapist to have consistent induced rotations. Four therapists performed this QA and after the initial training period, the inter-user variability was minimal. Consistency of the induced rotation was evaluated by the variation of the pre-shift table corrections. Excluding the first three attempts of each therapist, the pre-shift table correction standard deviations were ≤ 0.67mm for the translational axes and ≤ 0.49° for the rotational axes. Accuracy of the automatic table movement was confirmed by the post-shift table corrections. The average post-shift table corrections for the translational axes were ≤ 0.15mm and for the rotational axes were ≤ 0.42°. Using our clinics existing table corrections tolerance of <1mm and <0.5°, these results were deemed acceptable. CONCLUSION Therapists successfully and rapidly adopted daily QA procedures using the PerfectPitch table; automated rotational robotic table motions were confirmed through image fusions. This procedure enhances existing TG-142 recommendations.

SU‐E‐T‐222: How to Define and Manage Quality Metrics in Radiation Oncology

PURPOSE Since the 2001 IOM Report Crossing the Quality Chasm: A New Health System for the 21st Century, the need to provide quality metrics in health care has increased. Quality metrics have yet to be defined for the field of radiation oncology. This study represents one institutes initial efforts defining and measuring quality metrics using our electronic medical record and verify system(EMR) as a primary data collection tool. This effort began by selecting meaningful quality metrics rooted in the IOM definition of quality (safe, timely, efficient, effective, equitable and patient-centered care) that were also measurable targets based on current data input and workflow. METHODS Elekta MOSAIQ 2.30.04D1 was used to generate reports on the number of Special Physics Consults(SPC) charged as a surrogate for treatment complexity, daily patient time in department(DTP) as a measure of efficiency and timeliness, and time from CT-simulation to first LINAC appointment(STL). The number of IMRT QAs delivered in the department was also analyzed to assess complexity. RESULTS Although initial MOSAIQ reports were easily generated, the data needed to be assessed and adjusted for outliers. Patients with delays outside of radiation oncology such as chemotherapy or surgery were excluded from STL data. We found an average STL of six days for all CT-simulated patients and an average DTP of 52 minutes total time, with 23 minutes in the LINAC vault. Annually, 7.3% of all patient require additional physics support indicated by SPC. CONCLUSIONS Utilizing our EMR, an entire years worth of useful data characterizing our clinical experience was analyzed in less than one day. Having baseline quality metrics is necessary to improve patient care. Future plans include dissecting this data into more specific categories such as IMRT DTP, workflow timing following CT-simulation, beam-on hours, chart review outcomes, and dosimetric quality indicators.

SU‐GG‐J‐92: Motion Control Consistency with Abdominal Compression Device from Daily 4D CBCT

Purpose: To investigate the effectiveness of abdominal compression in tumor motion control for lungcancerradiotherapy. To study the motion control consistency during radiation treatment course through 4D reconstruction of daily cone beam computed tomography(CBCT) images.Method and Materials: Patients with lungtumor were scanned with 4D helical CT and the tumor motion was evaluated in left‐right(LR), superior‐inferior(SI), and anterior‐posterior(AP) directions. Patients with tumor motion greater than 1cm in any of the three directions and who could not tolerate the active breathing control(ABC) were treated with abdominal compression. Kilovoltage(kV) CBCTimage was acquired for each treatment fraction to correct patient setup. The CBCTimaging data were then reconstructed using a respiratory‐correlated technique to derive 4D CBCTimages with 10 different phases of breathing cycle. Daily tumor motion with abdominal compression was evaluated from the 4D CBCT by recording the tumor center position relative to the treatment isocenter in each phase. Three patient data (1 upper lobe tumor and 2 middle lobe tumors) were included in this study and 4 consecutive treatment fractions for each patient were studied. The extent of tumor motion was compared between different treatment fractions to assess the daily variation of motion control with abdominal compression. Results: Mean value and standard deviation(SD) of tumor motions from all patients and treatment fractions studied were 3.1mm±0.9mm (mean±SD), 6.8mm±1.7mm, and 5.3mm±1.8mm in LR, SI, and AP directions respectively. The variation of tumor motion extent of same patient between different fractions was 1.1mm±0.7mm, 2.0mm±1.9mm, and 2.3mm±2.0mm, in LR, SI, and AP directions respectively. Conclusion:Tumor motions which were greater than lcm with free‐breathing were reduced to less than 1cm with abdominal compression. Variation of motion control during treatment course was significant relative to the tumor motion in the patients and treatment fractions studied.

SU‐GG‐T‐600: IMRT for Craniospinal Irradiation: A Comparison with Traditional Techniques

Purpose: This work tests the possibility of using IMRT to promote organ sparing for the treatment of CSI. The traditional CSI technique uses opposed lateral fields to treat the brain and posterior fields to treat the spine. Published manuscripts focusing on the possibility of IMRT for CSI have only looked at pediatric cases. Here, we will plan IMRT for CSI on adult patients to quantify the dosimetric gains when compared to traditional techniques. Method and Materials: Four patients treated at our institution were chosen and a traditional 3D plan along with an IMRT plan was computed for each patient. The planned dose was 10 Gy and only the spine fields were optimized. The traditional plan used a cervical and thoracic spine field at 100 SSD while the IMRT plan split these two fields into five isocentric fields. OAR and target volumes receiving certain doses were calculated for each plan. Results:IMRT resulted in greater target coverage, lower overall dose, and reduced OAR although the low dose was more spread out. The best target coverage was obtained on the single patient treated supine. For almost every OAR at each point, IMRT reduced the dose. Conclusion:IMRT for CSI has a dosimetric advantage in both target coverage and OAR sparing over traditional beam arrangements. To further this study, we plan on repeating this process for six more patients and we also want to examine if there is a benefit to optimize the cranial fields in the IMRT plan along with the spine fields. Although it results in a more time consuming process, we have shown that there is evidence to pursue IMRT for adult CSI.

SU-GG-T-302: Measuring Pacemaker Dose: A Clinical Perspective

Purpose: The number of patients presenting with pacemakers in our clinic has increased recently. Following AAPM recommendations, a treatment plan is developed that minimizes the dose to the pacemaker. The most efficient way to measure in vivo dose during treatment is to use MOSFETs or diodes which offer a simple but inaccurate (up to 25% error) method of recording. In this abstract, we analyze the dose measured by these different devices in an attempt to assess pacemaker dose. Method and Materials: Five patients with different disease sites and pacemakers were chosen. To simulate the treatment delivery, a Rando phantom was placed on the table in the patient treatment position. An ion chamber was taped to the phantom under 1 cm bolus. Two MOSFETs and a diode were placed on top of the bolus and the treatment was delivered. One cone beam CT was obtained where the pacemaker was in the field‐of‐view to quantify the MOSFET and diode reading in this situation. Results: The measurement from the ion chamber agreed well with the predicted dose from the planning system. Some errors resulted from misalignment of the phantom and ion chamber. Both the MOSFET and diode measurements agreed with the ion chamber and TPS with greater distances. Dose from CBCT was overestimated for both MOSFETs and diodes. Conclusion: The simplest and most efficient in vivo measurement is to use a MOSFET or diode. When the pacemaker is more than 20 cm from the field edge these dosimeters are appropriate. When the field is less than 20 cm away, the most accurate although inefficient method is to use an ion chamber since there is little angular or energy dependence unlike diodes or MOSFETs. Another solution would be to use TLDs or OSL dosimeters although these are not simplistic dosimeters either.

SU‐GG‐T‐313: A Procedure for Standardizing MLC Quality Assurance for Elekta Linacs

Purpose: As specified in TG142, MLC position accuracy needs to be tested on weekly/monthly basis, with 1mm tolerance. This study focuses on developing techniques, hardware and software tools for implementation of MLC QA tests for Elekta Linacs.Material and Methods: This process was tested with an Elekta Synergy S, Beam Modulator™, which has 40 leaf pairs of 4mm width (maximum 16cm×21cm field size). Based on the machine characteristics, two picket‐fence IMRT plans were designed: one has 5 2cm×16cm strips separated by 2cm gap; the other has the same setup with individual leafs intentionally displaced by ±1mm, ±1.2mm, etc. Both plans used 6MV x‐rays and 50MU on each strip. We overcame the limitation of Xio planning system in generating picket‐fence IMRT plan by modifying leaf positions from a DICOM RT plan file. In‐house software was executed to validate the files before imported into Record and Verify system (Mosaiq) for delivery. Radiographic images were acquired using Kodak XV films. The borders of a 16cm×21cm light field were first traced on the film. These reference lines helped reduce the orientation errors during image registration. Two sets of films were exposed with full buildup. After development, each film was digitized with 0.06mm resolution using a high‐resolution scanner. The images were then imported into Matlab. In‐house code was used to detect leafs exceeding the 1mm threshold. Results: The plans were delivered smoothly. Leaf positions in the first image were used as baselines, instead of using reference leaf positions from the same exposure. This reduced systematic errors. After image registration, leafs displacing from the baseline by 16 pixels (1mm) or more were detected. Conclusion: This efficient procedure provides a sufficiently accurate test for MLC positioning reproducibility. It is a simple and straightforward procedure that can be used for routine MLC position checks.

WE-C-BRC-07: Image Quality QA for Three Radiotherapy Cone-Beam CT Systems

Purpose: With the increased presence of volumetric radiotherapy cone beam CT (RT‐CBCT) systems, the importance of high grade image quality is crucial to achieve daily image‐guided adaptive radiotherapy (IGART) capabilities. We subjected three commercially available RT‐CBCT systems to a battery of standard diagnostic image quality tests acquired under clinical conditions. This study reports on the evaluation of image qualities for RT‐CBCTs and a diagnostic CT.Methods and Materials: RT‐CBCT scans were performed on Elekta XVI, Nucletron Simulix, and Varian OBI Advanced Imaging using clinical pelvis scan settings on a CATPHAN Model 600. They were then compared to results from a GE Lightspeed CT scanner. The phantom contained modules allowing measurement of low contrast resolution, slice thickness, Hounsfield Unit (HU) sensitivity, spatial resolution, and image uniformity. Results: No CBCT system was able to detect any targets in the low contrast module. Six targets could be seen on diagnostic CTs. All RT‐CBCT systems had greater than 33% variations in slice thickness reconstruction. The HU sensitometry test showed absolute differences between accepted HU values and measured values for XVI and Simulix systems to be on average 6 times and 3 times the error seen in a diagnostic CT respectively. HU sensitivity for OBI is within 15% of a diagnostic CT. Both OBI and Simulix had spatial resolution twice that of XVI but were 3 lp/cm worse than a diagnostic CT. Measurements of image uniformity showed that all three RT‐CBCT systems have a standard deviation of HU values on the order of 10 times that of a diagnostic CT.Conclusions: The image qualities of three evaluated RT‐CBCT systems are relatively comparable, yet still inferior to those from helical CT. It is important to note that dosimetric settings can have a clear impact on image quality, and dose measurements were not done for this work.

SU-FF-T-42: A Novel Approach to Scar Boost in Mesothelioma Treatment

Purpose: To evaluate the potential advantages of high dose rate(HDR) brachytherapy for boosting mesothelioma incisions extending beyond the hemithoracic target volume. HDR treatment was compared with abutted, enface electron fields. Methods and Materials: One case describes catheter placement, dosimetric advantages, setup uncertainties, and treatment delivery. The right lateral decubitus position, in alpha cradle, was selected to permit consideration of HDR versus electrons. Comparative analyses of treatment plans were performed, and HDR setup and dosimetry were preferred. The HDR treatment utilized 3 catheters atop 5mm of bolus. The HDR setup required physician to confirm catheter placement. Tape, 5mm bolus, and wet towels secured the catheters and provided shielding. The prescription was 3.0Gy to 1.2cm from catheter including bolus (7mm depth in tissue). Dwell positions every 5mm were used to cover the entire length of the scars (22cm and 34cm). The corresponding electron plan required 5 thin strip cutouts and a physician present to approve field setup and feathering of the junctions. A phantom was used to simulate treatment of lesion with electrons and entire process was timed. Results: The total setup and treatment time for 6 HDR treatments was approximately 270minutes (time varies with activity, prescription dose, and volume) compared with 450minutes for 15 electron fractions (2Gy/fraction). Planning time for either modality is comparable. Electron treatments involve additional time for cutting blocks, measuring cutout factors, and physician approved junction changes. One additional concern is dose homogeneity caused by feathering electrons versus brachytherapy which provides a reliable dose distribution. Conclusions: HDR brachytherapy provided an optimal solution over the complicated and time‐consuming electron treatment and should be considered as a viable option for mesothelioma patients with a considerable scar length beyond hemithoracic target volume. Clinical data to support the use of brachytherapy over electrons for coverage of incisional scars is still needed.

SU‐FF‐T‐593: The Feasibility of Volumetric Comparison Between Respiratory Gating and ABC

Purpose: To evaluate the feasibility of respiratory gating with respect to Active Breathing Control (ABC) for motion reduction through quantitative comparison. Methods and Materials: 4D scans from a GE(Light speed)scanner with RPM were used for the feasibility study. Ten phase reconstructions were generated from the 4D projections and target volumes on all 10 phases were created by radiation oncologists. For free breathing treatments, target volumes from all 10 phases were added to generate the ITV used for clinical target. In order to simulate the gated treatment, the three phases of exhalation which best matched the gated delivery time period were combined. The target thus obtained was then compared with those obtained from the standard scan with the ABC device in place. Targets were contoured for the ABC scan as well. A volumetric comparison of the targets was performed for the above three methods. Results: We tested the feasibility of the method on one of our patient cases for whom we utilized the ABC device for breathing motion control. The target volume for the 10 phase target was 25.49cc. The target volume from the simulated gated phases was 12.09cc and the target volume with the ABC was 11.19cc. Both the gated technique and the ABC control are able to reduce the target volume significantly, with about the same amount of reduction (52.57% and 56.1%). Conclusions: This study established quantitatively that gated delivery technique can mimic the volumetric outcome of ABC delivery for motion control. Both are able to reduce the target volume significantly. We plan to further this study with more data collection.

SU‐FF‐T‐125: Commissioning of Monaco Monte Carlo IMRT Treatment Planning System

Purpose: To commission CMS Monaco IMRTtreatment planning system for clinical applications using a standard test suite. Methods and Materials: A system test including IMRT planning and plan delivery was performed for CMS Monaco IMRTtreatment planning system, version 1.0.2. Four cases from TG‐119 were studied: one head and neck case, one prostate case, and two C shape cases. IMRT plans were generated with the dose goals set by TG‐119 and were compared with the plans generated using CMS XiO treatment planning system. Analysis metrics were for dose coverage, number of segments, total MU, MU efficiency, number of segments per beam, and delivery time. The IMRT plans were delivered on an Elekta Synergy linear accelerator with step‐and‐shoot technique. This linac has 4‐mm MLC.IMRT QA was performed with field by field review using a diode array device Mapcheck. Results: Monaco plans showed similar target dose coverage as XiO plans and improved organ sparing in some cases. The ratios (Monaco/XiO) of number of total segments, total MU, number of segments per beam, and MU efficiency (Dose/MU) were 0.21–0.76, 0.56–0.77, 0.21–0.50, and 1.31–1.86, respectively. The delivery time of a Monaco plan was shorter than the XiO plan having the same number of beams by approximately 33%. IMRT QA pass rates of the Monaco plans were 93.8%–97.6% for the criteria of 3‐mm, 3%, and 10% threshold, which in three cases were higher than the XiO plans (93.1%–96.6%). Conclusion: The IMRT plans from the Monaco treatment planning system showed advantages over XiO plans. These advantages include smaller number of segments, smaller MU, smaller number of segments per beam, and higher MU efficiency. Additionally, the delivery time was shorter. The QA pass rates were similar to or higher than the XiO plans.