A Jamshidi

TU‐C‐BRB‐10: An Electronic Whiteboard and Associated Databases for Physics Workflow Coordination in a Paperless, Multi‐Site Radiation Oncology Department

Purpose: To enhance medical physics workflow coordination within a multi‐site, paperless radiotherapy department, a virtual physics whiteboard, process controlanalysis and problem reporting tools were developed. In a large department, coordination of planning and verification activities among cross‐site staff can be particularly challenging. Furthermore, Failure Mode and Effects Analysis (FMEA) on department tasks revealed that physics process steps scored particularly high as potential safety risks, making physics process control a high priority. Methods: As part of a department‐ wide, data‐driven quality initiative, a “No Fly” policy was introduced in 2010 that mandates automatic delays to patient treatment starts when delays in the treatment preparation process occur. To address potentially high safety risks in physics tasks, tools were developed to decrease delays in physics‐specific process steps. A virtual whiteboard was created that provides a summary view of the status of all current patients. Key physics tasks are structured with timing guidelines specified in the physics process flow chart. As they are completed, task items are checked and dated. Planning delay events are reported in a new quality reporting database for monthly Quality Management committee review. Significant process or patient safety issues that become evident may lead to formal changes in policies and procedures using a new policiesdatabase, and evolving process control is evaluated using a new quality analysisdatabase that examines task completion slip days. Results: A majority of physics processes have shown a decrease in variability, pointing to increased process control, while others have been flagged as requiring further investigation and mitigation measures. Conclusions: Process and quality control in a multi‐hospital radiation medicine department is critical in maintaining patient safety and smooth workflow. A set of databases has been implemented as tools for monitoring, analyzing, and improving physics processes.

SU-F-T-56: Dosimetric Characterization of the INTRABEAM 50 KV X-Ray System with a Needle Applicator in Heterogeneous Tissues

PURPOSEnWe report the depth dose measurements in air, in solid water, and in bone materials for the Intrabeam 50 kV x-rays with a needle applicator.nnnMETHODSnThe absolute dose was measured using a PTW TN34013W soft x-ray ion chamber. Gammex tissue equivalent materials of solid water, inner bone, and cortical bone slabs (minimum thickness of 2 mm) were used. In addition, the PTW solid water slabs with a minimum thickness of 1 mm were used. The manufactory calibrated depth dose data in water were compared. The x-ray source together with a needle applicator was secured on an Intrabeam stand. The slabs lay on a 6 degrees of freedom treatment couch with a digitally controlled minimum step size of 0.1 mm. The depth of the source to the ion chamber was accurately and reproducibly adjusted by moving the couch up and down.nnnRESULTSnThe depth dose measurements for the Intrabeam 50 kV x-rays with a needle applicator were conducted up to 20 mm in depth. The values for the PTW solid water were close to those for water. The Gammex solid water demonstrated lower values compared to water, consistent with the observation of its positive CT number. At a depth of 10 mm, the dose rates of the system are 29.6, 3.6, 1.2, and 0.24 Gy/min in air, in water, in inner bone, and in cortical bone, respectively. The 10 mm water equivalent depths in inner and cortical bone are about 6.4 and 4.1 mm. A function of power law combining exponential was used to fit and interpolate data well.nnnCONCLUSIONnDirect depth dose measurements in different materials provide a basis for treatment calculation and planning taking into account the heterogeneous effect. The results can be used for verification of analytical and/or Monte Carlo dose calculation methods as well.

TH-CD-304-02: Clinical Uncertainty of in Vivo Dosimetry for Intensity-Modulated Radiation Therapy Using Optically-Stimulated Luminescent Dosimeters

Purpose: nSeveral studies have reported the physical properties of optically-stimulated luminescent dosimeters (OSLDs) and suggest their efficacy for clinical in vivo dosimetry, but few publications have assessed the clinical uncertainties associated with OSLD-based in vivo dosimetry for conformal and intensity-modulated treatment. The purpose of the current work is to identify and characterize clinical uncertainties for OSLD-based in vivo dosimetry. n nMethods: nOSLDs are placed in dosimetrically-appropriate locations on a weekly basis, covered with small 5 mm bolus squares, exposed during patient treatment, read, and compared with doses predicted from the treatment planning system. Six (6) parameters were identified as significant contributors to uncertainty in the process: Inherent physical OSLD uncertainty (σ_ OSLD), OSLD reader uncertainty (σ_reader), dose calculation uncertainty in the build-up region (σ _calc), uncertainty of depth for planned dose (σ_d), dosimetric uncertainty due to daily image-guided shifts (σ_ s), and placement uncertainty (σ_p). σ_d, σ_ s, and σ_p were estimated by analyzing clinical OSLD dosimetry for inverse-planned intensity-modulated treatment plans (prostate, lung, and head-and-neck) and field-in-field intensity-modulated treatment plans (breast). Total uncertainty was estimated by summing the 6 components in quadrature. n nResults: nσ_OSLD was defined by the manufacturer (±3.0%). σ_calc was assumed to be approximately ±5.0% at 5 mm depth from other works in the literature. σ_reader and σ_s were measured to be ±1.0 and ±5.8% at 5 mm depth respectively. σ_p was found to be ±3.6% for breast, ±4.2% for prostate, ±4.4% for lung, and ±10.6% for head-and-neck. Total uncertainty was ±9.0% for breast, ±11.5% for prostate, ±13.2% for lung, and ±16.1% for head-and-neck. n nConclusion: nSite-specific clinical uncertainty for a limited selection of sites ranged from ±9.0% to ±16.1%. The largest components were image-guided shifts and estimated placement uncertainty. A wider selection of anatomical sites, site-specific correction factors, and clinical tolerance/action level guidelines will be presented.

SU‐E‐T‐586: Optimal Determination of Tolerance Level for Radiation Dose Delivery Verification in An in Vivo Dosimetry System

Purpose: To statistically determine the optimal tolerance level in the verification of delivery dose compared to the planned dose in an in vivo dosimetry system in radiotherapy. Methods: The LANDAUER MicroSTARii dosimetry system with screened nanoDots (optically stimulated luminescence dosimeters) was used for in vivo dose measurements. Ideally, the measured dose should match with the planned dose and falls within a normal distribution. Any deviation from the normal distribution may be redeemed as a mismatch, therefore a potential sign of the dose misadministration. Randomly mis-positioned nanoDots can yield a continuum background distribution. A percentage difference of the measured dose to its corresponding planned dose (ΔD) can be used to analyze combined data sets for different patients. A model of a Gaussian plus a flat function was used to fit the ΔD distribution. Results: Total 434 nanoDot measurements for breast cancer patients were collected across a period of three months. The fit yields a Gaussian mean of 2.9% and a standard deviation (SD) of 5.3%. The observed shift of the mean from zero is attributed to the machine output bias and calibration of the dosimetry system. A pass interval of −2SD to +2SD was applied and a mismatch background was estimatedmorexa0» to be 4.8%. With such a tolerance level, one can expect that 99.99% of patients should pass the verification and at most 0.011% might have a potential dose misadministration that may not be detected after 3 times of repeated measurements. After implementation, a number of new start breast cancer patients were monitored and the measured pass rate is consistent with the model prediction. Conclusion: It is feasible to implement an optimal tolerance level in order to maintain a low limit of potential dose misadministration while still to keep a relatively high pass rate in radiotherapy delivery verification.«xa0less

SU-E-T-638: Evaluation and Comparison of Landauer Microstar (OSLD) Readers

PURPOSEnTo evaluate and compare characteristic performance of a new Landauer nanodot Reader with the previous model.nnnMETHODSnIn order to calibrate and test the reader, a set of nanodots were irradiated using a Varian Truebeam Linac. Solid water slabs and bolus were used in the process of irradiation. Calibration sets of nanodots were irradiated for radiation dose ranges: 0 to 10 and 20 to 1000 cGy, using 6MV photons. Additionally, three sets of nanodots were each irradiated using 6MV, 10MV and 15MV beams. For each beam energy, and selected dose in the range of 3 to 1000 cGy, a pair of nanodots was irradiated and three readings were obtained with both readers.nnnRESULTSnThe analysis shows that for 3 photon beam energies and selected ranges of dose, the calculated absorbed dose agrees well with the expected value. The results illustrate that the new Microstar II reader is a highly consistent system and that the repeated readings provide results with a reasonably small standard deviation. For all practical purposes, the response of system is linear for all radiation beam energies.nnnCONCLUSIONnThe Microstar II nanodot reader is consistent, accurate, and reliable. The new hardware design and corresponding software contain several advantages over the previous model. The automatic repeat reading mechanism, that helps improve reproducibility and reduce processing time, and the smaller unit size that renders ease of transport, are two of such features. Present study shows that for high dose ranges a polynomial calibration equation provides more consistent results. A 3rd order polynomial calibration curve was used to analyze the readings of dosimeters exposed to high dose range radiation. It was observed that the results show less error compared to those calculated by using linear calibration curves, as provided by Landauer system software for all dose ranges.

SU‐F‐T‐52: Study of Energy Dependent Effect of Dosimetry Systems Used in Therapeutic Soft X‐Ray Energy Range

PURPOSEnTo investigate energy dependent effects of different dosimetry systems which can be used as in vivo dosimetry monitoring for intraoperative radiotherapy in therapeutic soft x-ray energy range.nnnMETHODSnThree dosimetry systems were evaluated in therapeutic soft x-ray energy range: optically stimulated luminescent dosimeter (OSLD) nanoDots, radiochromic EBT2 and EBT3 films. The x-ray photons were produced by a Zeiss Intrabeam 50 kV x-ray radiotherapy system. Solid water and bolus slabs with different thicknesses were used in the process of irradiation. An aluminum filter set was used to measure HVLs of X-rays. Calibration curves were made at different depth of boluses.nnnRESULTSnHalf Value Layers at depths of 0, 3, 10, and 20 mm of solid water were measured to represent the energy change versus depth, yielding 0.306, 0.482, 0.865 and 0.901 respectively and indicating nearly unchanged HVL beyond 1 cm depth. The responses of each system at different depths were normalized to the response at 2 cm depth. In film dosimetry, the response is calculated as optical density (OD). The results show that there is nearly the same energy dependence for EBT2 and EBT3. At a HVL of 0.482 mm Al, the relative responses of nanoDots and EBT3 are 0.85 ± 0.04 and 0.89 ± 0.03 compared to those at 0.901 mm Al HVL, respectively, indicating no obvious difference between those two systems within the measurement uncertainty.nnnCONCLUSIONnIt was observed that the studied dosimeter response increases about 13% from the x-ray energy of 0.48 mm Al to 0.90 mm Al. Therefore, caution should be exercised in using an appropriate calibration curve, and x-ray beam hardening effect has to be taken into account.

SU-F-T-654: Pacemaker Dose Estimate Using Optically Stimulated Luminescent Dosimeter for Left Breast Intraoperative Radiation Therapy

PURPOSEnTo assess and report the in vivo dose for a patient with a pacemaker being treated in left breast intraoperative radiation therapy (IORT). The ZEISS Intrabeam 50 kVp X-ray beam with a spherical applicator was used.nnnMETHODSnThe optically stimulated luminescent dosimeters (OSLDs) (Landauer nanoDots) were employed and calibrated under the conditions of the Intrabeam 50 kVp X-rays. The nanoDots were placed on the patient at approximately 15 cm away from the lumpectomy cavity both under and above a shield of lead equivalence 0.25 mm (RayShield X-Drape D-110) covering the pacemaker area during IORT with a 5 cm spherical applicator.nnnRESULTSnThe skin surface dose near the pacemaker during the IORT with a prescription of 20 Gy was measured as 4.0±0.8 cGy. The dose behind the shield was 0.06±0.01 Gy, demonstrating more than 98% dose reduction. The in vivo skin surface doses during a typical breast IORT at a 4.5 cm spherical applicator surface were further measured at 5, 10, 15, and 20 cm away to be 159±11 cGy, 15±1 cGy, 6.6±0.5 cGy, and 1.8±0.1 cGy, respectively. A power law fit to the dose versus the distance z from the applicator surface yields the dose fall off at the skin surface following z^-2.5, which can be used to estimate skin doses in future cases. The comparison to an extrapolation of depth dose in water reveals an underestimate of far field dose using the manufactory provided data.nnnCONCLUSIONnThe study suggests the appropriateness of OSLD as an in vivo skin dosimeter in IORT using the Intrabeam system in a wide dose range. The pacemaker dose measured during the left breast IORT was within a safe limit.

SU-F-T-53: Treatment Planning with Inhomogeneity Correction for Intraoperative Radiotherapy Using KV X-Ray Beams

PURPOSEnThe current standard in dose calculation for intraoperative radiotherapy (IORT) using the ZEISS Intrabeam 50 kV x-ray system is based on depth dose measurements in water and no heterogeneous tissue effect has been taken into account. We propose an algorithm for pre-treatment planning including inhomogeneity correction based on data of depth dose measurements in various tissue phantoms for kV x-rays.nnnMETHODSnDirect depth dose measurements were made in air, water, inner bone and cortical bone phantoms for the Intrabeam 50 kV x-rays with a needle applicator. The data were modelled by a function of power law combining exponential with different parameters. Those phantom slabs used in the measurements were scanned to obtain CT numbers. The x-ray beam initiated from the source isocenter is ray-traced through tissues. The corresponding doses will be deposited/assigned at different depths. On the boundary of tissue/organ changes, the x-ray beam will be re-traced in new tissue/organ starting at an equivalent depth with the same dose. In principle, a volumetric dose distribution can be generated if enough directional beams are traced. In practice, a several typical rays traced may be adequate in providing estimates of maximum dose to the organ at risk and minimum dose in the target volume.nnnRESULTSnDepth dose measurements and modeling are shown in Figure 1. The dose versus CT number is shown in Figure 2. A computer program has been written for Kypho-IORT planning using those data. A direct measurement through 2 mm solid water, 2 mm inner bone, and 1 mm solid water yields a dose rate of 7.7 Gy/min. Our calculation shows 8.1±0.4 Gy/min, consistent with the measurement within 5%.nnnCONCLUSIONnThe proposed method can be used to more accurately calculate the dose by taking into account the heterogeneous effect. The further validation includes comparison with Monte Carlo simulation.

SU‐E‐T‐738: Verification of an Automated Weighted Sector‐Integration Algorithm for Determining Output Factors for Electron Cutouts

Purpose: To verify the accuracy of an automated weighted‐sector‐integration electron output factor calculation algorithm for a variety of cone and cutout sizes, beam energies and clinical cutout shapes in a multi‐site radiation medicine department. Methods: A new weighted sector‐integration algorithm for electron output factor estimation has been implemented on a custom database structure. To automate the cutout shape determination, the cutout contour points are imported electronically from the treatment planning system, or digitized on a computer monitor using a digitally reconstructedradiographimage from an Electronic Medical Records system. The contour points are converted to polar coordinates and a sector‐integration summation performed with a weighting scheme corresponding to the angular size of each contour sector. Sector output factors used in the summation process are taken from a database of circular cutout measurements for a range of cone sizes, radii and energies. The algorithm was validated over a range of cutout sizes (2–20 cm), electron cones (10×10 cm2 to 20×20 cm2), cutout shapes (rectangular, circular and irregular including narrow fields and fields with concavities or convexities) and nominal beam energies (6–18 MeV) used in clinical electron beam therapy.Results: Differences between calculated and measured output factors for the patient cutouts studied were less than 2%, except in the case of long and narrow cutout shapes measured at low energies, which remained within 2.5% Conclusions: In a busy multi‐hospital environment, measurement of output factors for electron cutouts places a considerable time burden on physics staff. An estimation method that provides sufficiently accurate output factors for the wide variety of cutouts is a valuable clinical tool. Further work with handling unusually concave and long, narrow shapes at lower energies will be of value to extend the extreme limits of the algorithms accuracy.

SU‐E‐T‐102: Factors That Affect the Accuracy of IMRT Quality Assurance Measurements and Their Clinical Significance

Purpose: The purpose of this work was to perform error analysis on various processes that directly affect the accuracy of quality assurance (QA) measurements for intensity modulated radiation therapy(IMRT)delivery and to gauge their overall clinical impact for various clinical sites. Methods: In this study, we developed a numerical model based on the propagation of errors to quantify the complexity of treatment plans by the level of the intensity of modulation, and correlated the level of the modulation directly to the agreement of the IMRT QA results. We also provide detailed analysis of the uncertainties from IMRT QA results stratified by treatment site specific plans and fidelity in plan delivery. Results: Using a 5%/2mm criterion, it was found that the level of agreement of IMRT QA measurements was better for pelvic and chest plans than for head and neck, breast and brain plans. Errors tended to first increase with an increase in the number of Multi‐leaf Collimator(MLC) segments from 5 to 20 and then decrease with further increase in the number of segments. It was determined that other factors that impact the accuracy of the measurements include measurement device limitations, machine output variations, and phantom setup errors. Similarly, uncertainties in the beam data modeling and the calculation algorithm, as well as the initial beam commissioning data are main contributing factors to the accuracies of the treatment planning systems. Conclusions: The overall agreement of IMRT QA results is affected by both ‐ the accuracy of the measurement and that of the treatment planning system. We will demonstrate that the IMRT QA analysis criteria currently used in many clinics can be modified and improved to reflect the uncertainties of the process using the error propagation model developed in this study.