An IAEA survey of radiotherapy practice including quality assurance extent and depth.

Background: The IAEA recommends a quality assurance program in radiotherapy to ensure safe and effective treatments. In this study, radiotherapy departments were surveyed on their current practice including the extent and depth of quality assurance activities.Methods: Radiotherapy departments were voluntarily surveyed in three stages, firstly, in basic facility information, secondly, in quality assurance activities and treatment techniques, and thirdly, in a snapshot of quality assurance, departmental and treatment activities.Results: The IAEA received completed surveys from 381 radiotherapy departments throughout the world with 100 radiotherapy departments completing all three surveys. Dominant patterns were found in linac-based radiotherapy with access to treatment planning systems for 3D-CRT and 3D imaging. Staffing levels for major staff groups were on average in the range recommended by the IAEA. The modal patient workload per EBRT unit was as expected in the range of 21-30 patients per day, however significant instances of high workload (more than 50 patients per day per treatment unit) were reported. Staffing levels were found to correlate with amount of treatment equipment and patient workload. In a self-assessment of quality assurance performance, most radiotherapy departments reported that they would perform at least 60% of the quality assurance activities itemized in the second survey, with particular strength in equipment quality control. In a snapshot survey of quality assurance performance, again equipment quality control practice was well developed, particularly for the treatment equipment.Conclusions: The IAEA surveys provide a snapshot of current radiotherapy practice including quality assurance activities.

Electrical and thermal transport properties of the electron-doped cuprate Sm2-x Ce x CuO4-y system.

Electrical and thermal transport measurements were performed on thin films of the electron-doped superconductor Sm2-x Ce x CuO4-y (x = 0.13 - 0.19) in order to study the evolving nature of the charge carriers from the under-doped to over-doped regime. A temperature versus cerium content (T - x) phase diagram has been constructed from the electrical transport measurements, yielding a superconducting region similar to that found for other electron-doped superconductors. Thermopower measurements show a dramatic change from the underdoped region (x < 0.15) to the overdoped region (x > 0.15). Application of the Fisher-Fisher-Huse (FFH) vortex glass scaling model to the magnetoresistance data was found to be insufficient to describe the data in the region of the vortex-solid to vortex-liquid transition. It was found instead that the modified vortex glass scaling model of Rydh, Rapp, and Anderson provided a good description of the data, indicating the importance of the applied field on the pinning landscape. A magnetic field versus temperature (H - T) phase diagram has also been constructed for the films with [Formula: see text], displaying the evolution of the vortex glass melting lines H g (T) across the superconducting regime.

SU-E-T-321: Dynamic Modulated Brachytherapy.

PURPOSE: We introduced the concept of Dynamic Modulated Brachytherapy (DMBT) for rectal cancer, last year. To continue our work, we studied different shield designs and investigated the system's tolerance against systematic setup errors. METHODS: As previously presented, our system uses a cylindrical tungsten shield to create a directional radiation profile, which is modulated through translation and rotation using a specialized robotic arm. We used Monte Carlo simulations and an in-house gradient projection optimization algorithm to look at key design parameters. First, we used ideal phantoms to study treatment quality from shield radii ranging 0.5-1.5 cm in 0.25 cm increments. Second, using 36 patient plans, the dependence on radial source position within the shield was studied. We also analyzed the tolerance of the system to systematic setup errors by simulating dose distributions from possible inaccuracies. These included translational and rotational errors as well as possible Ir-192 source misplacements by the afterloading system. RESULTS: Changes in shield radius followed steady patterns. Increasing the radius showed a consistent increase in dose conformality to the tumor volume and better sparing to surrounding tissues. However, there was also a linear increase in total dwell time. There was a trade off to changing the radial position of the source. As the source is brought away from the center, there is a decrease in conformality to the tumor volume, but sparing to healthy tissues was increased and there is a decrease in total dwell time. We found that any potential setup errors for our system, within anticipated margins, had negligible effects on the dose distributions (< 3% deviation). CONCLUSION: Various parameters for shield designs must be balanced for an effective DMBT application. It was found that the system is highly robust against systematic setup uncertainties.

SU-D-213AB-04: Evaluation of the Dose Calculation in a Commercial Planning System for a Breast Cancer Brachytherapy Technology Using Monte Carlo Simulation.

PURPOSE: To evaluate the dose calculation in a commercial treatment planning system (TPS) for a breast cancer brachytherapy technology using Monte Carlo simulation for 21 patients. METHODS: Plans for 21 patients who received SAVI treatments were modeled using data from the TPS including CT images, structures and source information. The MC code PENELOPE was used, inputting images in voxel format, where density and material (tissue, air, bone and Nitinol) for each voxel were assigned based on its calibrated Hounsfield units and contoured structure sets, respectively. For the source model only gamma-rays and fluorescence X-rays of the NuDat database 192Ir spectrum were used, leaving out photons with emission intensity less than 0.1% and X-rays with energies below 10 keV. Source positions were entered into the plan and run individually. Dose was totaledby individually weighting the dose for each source position using the original TPS plan dwell times and then summing the weighted dose for all positions. RESULTS: Dose from the Monte Carlo plan was compared with dose from the original plan using isodose lines at 50, 100, 150 and 200% of the prescription dose of 34Gy. Dosimetric coverage of the target was compared by evaluating the V100, V150 and V200 (volume of the target covered by 100%, 150 and 200% of the dose respectively). The V200 and V150 had an average increase (and standard deviation) of 9.1% (3.2%) and 3.8% (1.4%) respectively, while the average change in V100 was 1.2% (1.0%). Where variance for the entire simulation was 0.9%. CONCLUSION: We have compared dose distributions of a commercial TPS using Monte Carlo simulation for SAVI breast cancer brachytherapy and found that a dose increase near the air-tissue interface.

SU-E-T-546: Cumulative Dose Evaluation for Head and Neck Cancers.

PURPOSE: In this study, we retrospectively analyzed patient treatments utilizing a prototype of the Varian Eclipse™ treatment planning system integrated with their new DART™ technology. Structure volume changes, structure displacements, and dose deviations were analyzed to assess the need for more adaptive treatment planning. METHODS: Ten patients with head and neck cancer who received daily cone-beam imaging CTs, as part of their radiation therapy, were chosen from the University of California San Diego Moores Cancer Center database. With the aid of DART™, we were able to retrospectively calculate the accumulated dose to both the tumor and healthy tissue over the entire course of treatment. This process was accomplished through rigid and deformable registrations of their daily cone-beam CT scans and cumulative dose measurements. Volumetric changes were compared to their original planning CT image. RESULTS: Our results showed notable changes to the parotid glands in all patients, in both structure shrinkage and dose escalation, which were often correlated with a medial displacement of the glands towards the high-dose region. Our study estimated that the mean rate of parotid volume reduction was 0.18 cm3 /treatment day with a range of 0.08 - 0.31 cm3 /treatment day. GTV, CTV, and PTV regions also showed significant volume reductions which was shown to be more pronounced during the first half of treatment. In 6 out of 9 patients with contoured parotids, the absorbed dose increase to these glands was >3%. The GTV, CTV, and PTV showed smaller variations, and in only 1 out of the 10 patients studied did the dose accumulation increase >3%. CONCLUSIONS: While the program used was just a prototype, it is our hope for the future that this project could be integrated clinically to develop more adaptive treatment plans allowing for better treatment accuracy and patient care.