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DOE OSTI2015

Quality of Intensity Modulated Radiation Therapy Treatment Plans Using a {sup 60}Co Magnetic Resonance Image Guidance Radiation Therapy System

Purpose: This work describes a commercial treatment planning system, its technical features, and its capabilities for creating {sup 60}Co intensity modulated radiation therapy (IMRT) treatment plans for a magnetic resonance image guidance radiation therapy (MR-IGRT) system. Methods and Materials: The ViewRay treatment planning system (Oakwood Village, OH) was used to create {sup 60}Co IMRT treatment plans for 33 cancer patients with disease in the abdominal, pelvic, thorax, and head and neck regions using physician-specified patient-specific target coverage and organ at risk (OAR) objectives. Backup plans using a third-party linear accelerator (linac)-based planning system were also created. Plans were evaluated by attending physicians and approved for treatment. The {sup 60}Co and linac plans were compared by evaluating conformity numbers (CN) with 100% and 95% of prescription reference doses and heterogeneity indices (HI) for planning target volumes (PTVs) and maximum, mean, and dose-volume histogram (DVH) values for OARs. Results: All {sup 60}Co IMRT plans achieved PTV coverage and OAR sparing that were similar to linac plans. PTV conformity for {sup 60}Co was within <1% and 3% of linac plans for 100% and 95% prescription reference isodoses, respectively, and heterogeneity was on average 4% greater. Comparisons of OAR mean dose showed generally better sparing with linac plans in the low-dose range <20 Gy, but comparable sparing for organs with mean doses >20 Gy. The mean doses for all {sup 60}Co plan OARs were within clinical tolerances. Conclusions: A commercial {sup 60}Co MR-IGRT device can produce highly conformal IMRT treatment plans similar in quality to linac IMRT for a variety of disease sites. Additional work is in progress to evaluate the clinical benefit of other novel features of this MR-IGRT system.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2014

SU-E-J-47: Development of a High-Precision, Image-Guided Radiotherapy, Multi- Purpose Radiation Isocenter Quality-Assurance Calibration and Checking System

Purpose: To develop a system that can define the radiation isocenter and correlate this information with couch coordinates, laser alignment, optical distance indicator (ODI) settings, optical tracking system (OTS) calibrations, and mechanical isocenter walkout. Methods: Our team developed a multi-adapter, multi-purpose quality assurance (QA) and calibration device that uses an electronic portal imaging device (EPID) and in-house image-processing software to define the radiation isocenter, thereby allowing linear accelerator (Linac) components to be verified and calibrated. Motivated by the concept that each Linac component related to patient setup for image-guided radiotherapy based on cone-beam CT should be calibrated with respect to the radiation isocenter, we designed multiple concentric adapters of various materials and shapes to meet the needs of MV and KV radiation isocenter definition, laser alignment, and OTS calibration. The phantom's ability to accurately define the radiation isocenter was validated on 4 Elekta Linacs using a commercial ball bearing (BB) phantom as a reference. Radiation isocenter walkout and the accuracy of couch coordinates, ODI, and OTS were then quantified with the device. Results: The device was able to define the radiation isocenter within 0.3 mm. Radiation isocenter walkout was within ±1 mm at 4 cardinal angles. By switching adapters, we identified that the accuracy of the couch position digital readout, ODI, OTS, and mechanical isocenter walkout was within sub-mm. Conclusion: This multi-adapter, multi-purpose isocenter phantom can be used to accurately define the radiation isocenter and represents a potential paradigm shift in Linac QA. Moreover, multiple concentric adapters allowed for sub-mm accuracy for the other relevant components. This intuitive and user-friendly design is currently patent pending.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2015

SU-E-T-464: Implementation and Validation of 4D Acuros XB Dose Calculations

Purpose: In this abstract we implement and validate a 4D VMAT Acuros XB dose calculation using Gafchromic film. Special attention is paid to the physical material assignment in the CT dataset and to reported dose to water and dose to medium. Methods: A QUASAR phantom with a 3 cm sinusoidal tumor motion and 5 second period was scanned using 4D computed tomography. A CT was also obtained of the static QUASAR phantom with the tumor at the central position. A VMAT plan was created on the average CT dataset and was delivered on a Varian TrueBeam linear accelerator. The trajectory log file from this treatment was acquired and used to create 10 VMAT subplans (one for each portion of the breathing cycle). Motion for each subplan was simulated by moving the beam isocentre in the superior/inferior direction in the Treatment Planning System on the static CT scan. The 10 plans were calculated (both dose to medium and dose to water) and summed for 1) the original HU values from the static CT scan and 2) the correct physical material assignment in the CT dataset. To acquire a breathing phase synchronized film measurements the trajectory log was used to create a VMAT delivery plan which includes dynamic couch motion using the Developer Mode. Three different treatment start phases were investigated (mid inhalation, full inhalation and full exhalation). Results: For each scenario the coronal dose distributions were measured using Gafchromic film and compared to the corresponding calculation with Film QA Pro Software using a Gamma test with a 3%/3mm distance to agreement criteria. Good agreement was found between calculation and measurement. No statistically significant difference in agreement was found between calculations to original HU values vs calculations to over-written (material-assigned) HU values. Conclusion: The investigated 4D dose calculation method agrees well with measurement.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

Measurement of time delays in gated radiotherapy for realistic respiratory motions

Purpose: Gated radiotherapy is used to reduce internal motion margins, escalate target dose, and limit normal tissue dose; however, its temporal accuracy is limited. Beam-on and beam-off time delays can lead to treatment inefficiencies and/or geographic misses; therefore, AAPM Task Group 142 recommends verifying the temporal accuracy of gating systems. Many groups use sinusoidal phantom motion for this, under the tacit assumption that use of sinusoidal motion for determining time delays produces negligible error. The authors test this assumption by measuring gating time delays for several realistic motion shapes with increasing degrees of irregularity. Methods: Time delays were measured on a linear accelerator with a real-time position management system (Varian TrueBeam with RPM system version 1.7.5) for seven motion shapes: regular sinusoidal; regular realistic-shape; large (40%) and small (10%) variations in amplitude; large (40%) variations in period; small (10%) variations in both amplitude and period; and baseline drift (30%). Film streaks of radiation exposure were generated for each motion shape using a programmable motion phantom. Beam-on and beam-off time delays were determined from the difference between the expected and observed streak length. Results: For the system investigated, all sine, regular realistic-shape, and slightly irregular amplitude variation motions had beam-off and beam-on time delays within the AAPM recommended limit of less than 100 ms. In phase-based gating, even small variations in period resulted in some time delays greater than 100 ms. Considerable time delays over 1 s were observed with highly irregular motion. Conclusions: Sinusoidal motion shapes can be considered a reasonable approximation to the more complex and slightly irregular shapes of realistic motion. When using phase-based gating with predictive filters even small variations in period can result in time delays over 100 ms. Clinical use of these systems for patients with highly irregular patterns of motion is not advised due to large beam-on and beam-off time delays.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

SU-F-T-264: VMAT QA with 2D Radiation Measuring Equipment Attached to Gantry

Purpose: To introduce a method of VMAT QA by 2D measuring device. The 2D device is attached to the gantry throughout measurement duration. This eliminates error caused by the angular dependence of the radiation detectors. Methods: A 2D radiation measuring device was attached to the gantry of linear accelerator. The center of the detector plane was at the isocenter. For each patient plan, two verification plans were created for QA purpose. One was like an ordinary VMAT plan, to be used for radiation delivery. The other is a plan with gantry angle fixed at zero, so the dose distribution as seen by the rotating 2D device. Points above 10% dose threshold were analyzed. Data is in tolerance if it fits within the 3 mm or 3% dose gamma criteria. For each patient, the plan was passed when 95% of all the points in the 2D matrix fit the gamma criteria. The following statistics were calculated: number of patient plans passed, percentage of all points passed, average percentage difference of all points. Results: VMAT QA was performed for patients during one year in our department, and the results were analyzed. All irradiation was with 6 MV photon beam. Each plan has calculated and measured doses compared. After collecting one year’s result, with 81 patient plans analyzed, all (100%) of the plans passed the gamma criteria. Of the points analyzed from all plans, 98.8% of all points passed. Conclusion: This method of attaching a 2D measuring device on the linac gantry proves to be an accurate way for VMAT QA. It is simple to use and low cost, and it eliminates the problem of directional dependence.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

Control Point Analysis comparison for 3 different treatment planning and delivery complexity levels using a commercial 3-dimensional diode array

To investigate the use of “Control Point Analysis” (Sun Nuclear Corporation, Melbourne, FL) to analyze and compare delivered volumetric-modulated arc therapy (VMAT) plans for 3 different treatment planning complexity levels. A total of 30 patients were chosen and fully anonymized for the purpose of this study. Overall, 10 lung stereotactic body radiotherapy (SBRT), 10 head-and-neck (H and N), and 10 prostate VMAT plans were generated on Pinnacle{sup 3} and delivered on a Varian linear accelerator (LINAC). The delivered dose was measured using ArcCHECK (Sun Nuclear Corporation, Melbourne, FL). Each plan was analyzed using “Sun Nuclear Corporation (SNC) Patient 6” and “Control Point Analysis.” Gamma passing percentage was used to assess the differences between the measured and planned dose distributions and to assess the role of various control point binning combinations. Of the different sites considered, the prostate cases reported the highest gamma passing percentages calculated with “SNC Patient 6” (97.5% to 99.2% for the 3%, 3 mm) and “Control Point Analysis” (95.4% to 98.3% for the 3%, 3 mm). The mean percentage of passing control point sectors for the prostate cases increased from 51.8 ± 7.8% for individual control points to 70.6 ± 10.5% for 5 control points binned together to 87.8 ± 11.0% for 10 control points binned together (2%, 2-mm passing criteria). Overall, there was an increasing trend in the percentage of sectors passing gamma analysis with an increase in the number of control points binned together in a sector for both the gamma passing criteria (2%, 2 mm and 3%, 3 mm). Although many plans passed the clinical quality assurance criteria, plans involving the delivery of high Monitor Unit (MU)/control point (SBRT) and plans involving high degree of modulation (H and N) showed less delivery accuracy per control point compared with plans with low MU/control point and low degree of modulation (prostate)

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2012

Definition of parameters for quality assurance of flattening filter free (FFF) photon beams in radiation therapy

Purpose: Flattening filter free (FFF) beams generated by medical linear accelerators have recently started to be used in radiotherapy clinical practice. Such beams present fundamental differences with respect to the standard filter flattened (FF) beams, making the generally used dosimetric parameters and definitions not always viable. The present study will propose possible definitions and suggestions for some dosimetric parameters for use in quality assurance of FFF beams generated by medical linacs in radiotherapy. Methods: The main characteristics of the photon beams have been analyzed using specific data generated by a Varian TrueBeam linac having both FFF and FF beams of 6 and 10 MV energy, respectively. Results: Definitions for dose profile parameters are suggested starting from the renormalization of the FFF with respect to the corresponding FF beam. From this point the flatness concept has been translated into one of 'unflatness' and other definitions have been proposed, maintaining a strict parallelism between FFF and FF parameter concepts. Conclusions: Ideas for quality controls used in establishing a quality assurance program when introducing FFF beams into the clinical environment are given here, keeping them similar to those used for standard FF beams. By following the suggestions in this report, the authors foresee that the introduction of FFF beams into a clinical radiotherapy environment will be as safe and well controlled as standard beam modalities using the existing guidelines.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2014

WE-E-BRE-02: BEST IN PHYSICS (THERAPY) - Stereotactic Radiotherapy for Renal Sympathetic Ablation for the Treatment of Refractory Hypertension

Purpose: To determine the safety and efficacy of stereotactic radiotherapy as a novel treatment for patients with refractory hypertension in a swine model. Uncontrolled hypertension is a significant contributor to morbidity and mortality, substantially increasing the risk of ischemic stroke, ischemic heart disease, and kidney failure. Methods: High-resolution computed tomography (CT) images of anesthetized pigs were acquired and treatment plans for each renal artery and nerve were developed using our clinically implemented treatment planning system. Stereotactic radiotherapy, 40Gy in single fraction was delivered bilaterally to the renal nerves using a state-of-the-art medical linear accelerator under image guidance utilizing dynamic conformal arcs. Dose to nearby critical organs was evaluated by dosevolume histogram analysis and correlated to toxicity data obtained through follow up pathology analysis. The animals were observed for six months with serial measurements of blood pressure, urine analysis, serum laboratories, and overall clinical and behavioral status. Results: All animals survived to the follow-up point without evidence of renal dysfunction (stable serum creatinine), skin changes, or behavioral changes that might suggest animal discomfort. Plasma norepinephrine levels (ng/ml) were followed monthly for 6 months. The average reduction observed was 63%, with the median reduction at 73.5%. Microscopic evaluation 4–6 weeks after treatment showed evidence of damage to the nerves around treated renal arteries. Considerable attenuation in pan neurofilament expression by immunohistochemistry was observed with some vacuolar changes indicative of injury. There was no histological or immunohistochemical evidence of damage to nearby spinal cord or spinal nerve root structures. Conclusion: Our preclinical studies have shown stereotactic radiotherapy to the renal sympathetic plexus to be safe and effective in reducing blood pressure, thus this approach holds great promise as a novel treatment modality for patients with refractory hypertension. This study was funded by the Stanford University Cardiovascular Institute. B. Loo and P. Maxim have received funding from RaySearch Laboratories.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

SU-F-J-45: Sparing Normal Tissue with Ultra-High Dose Rate in Radiation Therapy

Purpose: To spare normal tissue by reducing the location uncertainty of a moving target, we proposed an ultra-high dose rate system and evaluated. Methods: High energy electrons generated with a linear accelerator were injected into a storage ring to be accumulated. The number of the electrons in the ring was determined based on the prescribed radiation dose. The dose was delivered within a millisecond, when an online imaging system found that the target was in the position that was consistent with that in a treatment plan. In such a short time period, the displacement of the target was negligible. The margin added to the clinical target volume (CTV) could be reduced that was evaluated by comparing of volumes between CTV and ITV in 14 cases of lung stereotactic body radiation therapy (SBRT) treatments. A design of the ultra-high dose rate system was evaluated based clinical needs and the recent developments of low energy (a few MeV) electron storage ring. Results: This design of ultra-high dose rate system was feasible based on the techniques currently available. The reduction of a target volume was significant by reducing the margin that accounted the motion of the target. ∼50% volume reduction of the internal target volume (ITV) could be achieved in lung SBRT treatments. Conclusion: With this innovation of ultra-high dose rate system, the margin of target is able to be significantly reduced. It will reduce treatment time of gating and allow precisely specified gating window to improve the accuracy of dose delivering.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

SU-E-T-105: Development of 3D Dose Verification System for Volumetric Modulated Arc Therapy Using Improved Polyacrylamide-Based Gel Dosimeter

Purpose: The aim of this dosimetric study was to develop 3D dose verification system for volumetric modulated arc therapy (VMAT) using polyacrylamide-based gel (PAGAT) dosimeter improved the sensitivity by magnesium chloride (MgCl{sub 2}). Methods: PAGAT gel containing MgCl{sub 2} as a sensitizer was prepared in this study. Methacrylic-acid-based gel (MAGAT) was also prepared to compare the dosimetric characteristics with PAGAT gel. The cylindrical glass vials (4 cm diameter, 12 cm length) filled with each polymer gel were irradiated with 6 MV photon beam using Novalis Tx linear accelerator (Varian/BrainLAB). The irradiated polymer gel dosimeters were scanned with Signa 1.5 T MRI system (GE), and dose calibration curves were obtained using T{sub 2} relaxation rate (R{sub 2} = 1/T{sub 2}). Dose rate (100-600 MU min{sup −1}) and fractionation (1-8 fractions) were varied. In addition, a cubic acrylic phantom (10 × 10 × 10 cm{sup 3}) filled with improved PAGAT gel inserted into the IMRT phantom (IBA) was irradiated with VMAT (RapidArc). C-shape structure was used for the VMAT planning by the Varian Eclipse treatment planning system (TPS). The dose comparison of TPS and measurements with the polymer gel dosimeter was accomplished by the gamma index analysis, overlaying the dose profiles for a set of data on selected planes using in-house developed software. Results: Dose rate and fractionation dependence of improved PAGAT gel were smaller than MAGAT gel. A high similarity was found by overlaying the dose profiles measured with improved PAGAT gel dosimeter and the TPS dose, and the mean pass rate of the gamma index analysis using 3%/3 mm criteria was achieved 90% on orthogonal planes for VMAT using improved PAGAT gel dosimeter. Conclusion: In-house developed 3D dose verification system using improved polyacrylamide-based gel dosimeter had a potential as an effective tool for VMAT QA.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

SU-E-T-137: Attenuation of Carbon Fiber IGRT Couch Top for SBRT By Using a MapCheck 2 and Ion Chamber

Purpose: It is common to use posterior oblique beams in intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT) for regular and stereotactic body radiotherapy (SBRT). Beam attenuation by the treatment couch is not negligible when the couch is in the beam portal. In this study, we have correlated relative dose versus beam angle through a MapCheck 2TM diode array and an ionization chamber measurement. Methods: A Varian TrueBeam linear accelerator equipped with the image-guided radiation therapy (IGRT) carbon fiber couch was used for delivery of radiation with different photon energies of 6MV, 15MV and 6MV FFF. A MapCHECK 2TM diode array with a MapPhan was employed for the measurement at three field sizes (3 by 3, 5 by 5, and 10 by 10 cm). The independent measurement was performed with an ionization chamber placed at the center of an acrylic cylindrical phantom at the isocenter. The measured data with the MapCHECK 2TM diode array were averaged over the central 2×2 cm diodes for each measurement. The couch attenuation was deduced from the angular dependence with and without the couch involvement. Results: For the MapCHECK 2TM with MapPhan used only the obvious attenuation was observed at the beam angle between 5 and 10 degree from the angular dependence using a 6MV photon beam. The similar Result was obtained for the MapCHECK 2TM /MapPhan with the couch involvement. The couch attenuation was then deduced from the difference of these two sets of data measurements. Maximum couch attenuation was found up to 4.2% which was verified with the ion chamber measurement. Conclusion: A maximum attenuation of 4.2% was found for the carbon fiber couch top using the MapCHECK 2TM/MapPhan, which is consistent with the ion chamber measurement.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

SU-E-T-305: Study of the Eclipse Electron Monte Carlo Algorithm for Patient Specific MU Calculations

Purpose: To evaluate the Eclipse electron Monte Carlo (eMC) algorithm based on patient specific monitor unit (MU) calculations, and to propose a new factor which quantitatively predicts the discrepancy of MUs between the eMC algorithm and hand calculations. Methods: Electron treatments were planned for 61 patients on Eclipse (Version 10.0) using the eMC algorithm for Varian TrueBeam linear accelerators. For each patient, the same treatment beam angle was kept for a point dose calculation at dmax performed with the reference condition, which used an open beam with a 15×15 cm2 size cone and 100 SSD. A patient specific correction factor (PCF) was obtained by getting the ratio between this point dose and the calibration dose, which is 1 cGy per MU delivered at dmax. The hand calculation results were corrected by the PCFs and compared with MUs from the treatment plans. Results: The MU from the treatment plans were in average (7.1±6.1)% higher than the hand calculations. The average MU difference between the corrected hand calculations and the eMC treatment plans was (0.07±3.48)%. A correlation coefficient of 0.8 was found between (1-PCF) and the percentage difference between the treatment plan and hand calculations. Most outliers were treatment plans with small beam opening (< 4 cm) and low energy beams (6 and 9 MeV). Conclusion: For CT-based patient treatment plans, the eMC algorithm tends to generate a larger MU than hand calculations. Caution should be taken for eMC patient plans with small field sizes and low energy beams. We hypothesize that the PCF ratio reflects the influence of patient surface curvature and tissue inhomogeneity to patient specific percent depth dose (PDD) curve and MU calculations in eMC algorithm.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

SU-F-T-360: Dosimetric Impacts On the Mucosa and Bone in Radiotherapy with Unflattened Photon Beams

Purpose: This study investigated the dosimetric impacts on the mucosa and bone when using the unflattened photon beams in radiotherapy. Dose calculations were carried out by Monte Carlo simulation. Methods: Heterogeneous phantoms containing water (soft tissue and mucosa), air and bone, with mucosa thicknesses varying from 0.5 – 3 mm were irradiated by the 6 MV unflattened and flattened photon beams (field size = 10 × 10 cm{sup 2}), produced by a Varian TrueBEAM linear accelerator. The photon energy spectra of the beams, mean bone and mucosal doses with different mucosa thicknesses were calculated using the EGSnrc Monte Carlo code. Results: It is found that the flattened photon beams had higher mean bone doses (1.3% and 2% for upper and lower bone regarding the phantom geometry, respectively) than the unflattened beams, and the mean bone doses of both beams did not vary significantly with the mucosa thickness. Similarly, flattened photon beams had higher mucosal dose (0.9% and 1.6% for upper and lower mucosa, respectively) than the unflattened beams. This is due to the larger slope of the depth dose for the unflattened photon beams compared to the flattened. The mucosal doses of both beams were found increased with the mucosa thickness. Moreover, the mucosal dose differences between the unflattened and flattened beams increased with the mucosa thickness. For photon energy spectra on the mucosal layers, it is found that the unflattened photon beams contained a larger portion of lowenergy photons than the flattened beams. The photon energy spectra did not change significantly with the mucosa thickness. Conclusion: It is concluded that the mucosal and bone dose for the unflattened photon beams were not more than 2% lower than the flattened beams, though the flattening filter free beams contained larger portion of low-energy photons than the flattened beams.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2012

Beam properties and stability of a flattening-filter free 7 MV beam--An overview

Purpose: Several works have recently focused on flattening-filter-free (FFF) beams of linear accelerators of various companies (in particular, Varian and Elekta), but no overview as yet exists for the flattening-filter free 7XU beam (Siemens Artiste). Methods: Dosimetric properties of the 7XU beam were measured in May and September 2011. We present depth dose curves and beam profiles, output factors, and MLC transmission and assess the stability of the measurements. The 7XU beam was commissioned in the Pinnacle Superscript-Three treatment planning system (TPS), and modeling results including the spectrum are presented. Results: The percent depth dose curve of the 7XU beam is similar to the flat 6X beam line, with a slightly smaller surface dose. The beam profiles show the characteristic shape of flattening-filter free beams, with deviations between measurements of generally less than 1%. The output factors of the 7XU beam decrease more slowly than for the 6X beam. The MLC transmission is comparable but slightly less for the 7XU beam. The 7XU beam can be adequately modeled by the Pinnacle Superscript-Three TPS, with successful dosimetric verification. The spectrum of the 7XU beam has lower photon fluence up to approximately 2.5 MeV and higher fluence beyond, with a slightly higher mean energy. Conclusions: The 7XU beam has been commissioned for clinical use after successful modeling, stability checks, and dosimetric verification.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

SU-E-T-62: A Preliminary Experience of Using EPID Transit Dosimetry for Monitoring Daily Dose Variations in Radiation Treatment Delivery

Purpose: To investigate the use of EPID transit dosimetry for monitoring daily dose variations in radiation treatment delivery. Methods: A patient with head and neck cancer treated using nine field IMRT beams was used in this study. The prescription was 45 Gy in 25 fractions. A KV CBCT was acquired before each treatment on a Varian NTX linear accelerator. Integrated images using MV EPID were acquired for each treatment beam. Planning CT images, treatment plan, and daily integrated images were imported into a commercial QA software Dosimetry Check (v4r4 Math Resolutions, LLC, Columbia, MD) to calculate 3D dose of the day assuming 25 fractions treatment. Planning CT images were deformed and registered to each daily CBCT using Varian SmartAdapt (v11.MR2). ROIs were then propagated from planning CT to daily CBCT. The correlation between maximum, average dose of ROIs and ROI volume, center of mass shift, Dice Similarity Coefficient (DSC) were investigated. Results: Not all parameters investigated showed strong correlations. For PTV and CTV, the average dose has inverse correlation with their volume change (correlation coefficient −0.52, −0.50, respectively) and DSC (−0.59, −0.59, respectively). The average dose of right parotid has correlation with its volume change (0.56). The maximum dose of spinal cord has correlation with the center of mass superior-inferior shift (0.52) and inverse correlation with the center of mass anterior-posterior shift (−0.73). Conclusion: Transit dosimetry using EPID images collected during treatment delivery offers great potential to monitor daily dose variations due to patient anatomy change, motion, and setup errors in radiation treatment delivery. It can provide a patient-specific QA tool valuable for adaptive radiation therapy. Further work is needed to validate the technique.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

SU-E-T-255: Development of a Michigan Quality Assurance (MQA) Database for Clinical Machine Operations

Purpose: A unified database system was developed to allow accumulation, review and analysis of quality assurance (QA) data for measurement, treatment, imaging and simulation equipment in our department. Recording these data in a database allows a unified and structured approach to review and analysis of data gathered using commercial database tools. Methods: A clinical database was developed to track records of quality assurance operations on linear accelerators, a computed tomography (CT) scanner, high dose rate (HDR) afterloader and imaging systems such as on-board imaging (OBI) and Calypso in our department. The database was developed using Microsoft Access database and visual basic for applications (VBA) programming interface. Separate modules were written for accumulation, review and analysis of daily, monthly and annual QA data. All modules were designed to use structured query language (SQL) as the basis of data accumulation and review. The SQL strings are dynamically re-written at run time. The database also features embedded documentation, storage of documents produced during QA activities and the ability to annotate all data within the database. Tests are defined in a set of tables that define test type, specific value, and schedule. Results: Daily, Monthly and Annual QA data has been taken in parallel with established procedures to test MQA. The database has been used to aggregate data across machines to examine the consistency of machine parameters and operations within the clinic for several months. Conclusion: The MQA application has been developed as an interface to a commercially available SQL engine (JET 5.0) and a standard database back-end. The MQA system has been used for several months for routine data collection.. The system is robust, relatively simple to extend and can be migrated to a commercial SQL server.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2012

Comparison Between Infrared Optical and Stereoscopic X-Ray Technologies for Patient Setup in Image Guided Stereotactic Radiotherapy

Purpose: To compare infrared (IR) optical vs. stereoscopic X-ray technologies for patient setup in image-guided stereotactic radiotherapy. Methods and Materials: Retrospective data analysis of 233 fractions in 127 patients treated with hypofractionated stereotactic radiotherapy was performed. Patient setup at the linear accelerator was carried out by means of combined IR optical localization and stereoscopic X-ray image fusion in 6 degrees of freedom (6D). Data were analyzed to evaluate the geometric and dosimetric discrepancy between the two patient setup strategies. Results: Differences between IR optical localization and 6D X-ray image fusion parameters were on average within the expected localization accuracy, as limited by CT image resolution (3 mm). A disagreement between the two systems below 1 mm in all directions was measured in patients treated for cranial tumors. In extracranial sites, larger discrepancies and higher variability were observed as a function of the initial patient alignment. The compensation of IR-detected rotational errors resulted in a significantly improved agreement with 6D X-ray image fusion. On the basis of the bony anatomy registrations, the measured differences were found not to be sensitive to patient breathing. The related dosimetric analysis showed that IR-based patient setup caused limited variations in three cases, with 7% maximum dose reduction in the clinical target volume and no dose increase in organs at risk. Conclusions: In conclusion, patient setup driven by IR external surrogates localization in 6D featured comparable accuracy with respect to procedures based on stereoscopic X-ray imaging.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2015

SU-E-T-93: Activation of Psoralen at Depth Using Kilovoltage X-Rays: Physics Considerations in Implementing a New Teletherapy Paradigm

Purpose: Psoralen is a UV-light activated anti-cancer biotherapeutic used for treating skin lesions (PUVA) and advanced cutaneous T-cell lymphoma (ECP). To date psoralen has not been used to treat deep seated tumors due to difficulty in generating UV-light at depth. We recently demonstrated psoralen activation at depth by introducing energy converting particles that absorb kV x-ray radiation and re-emit UV-light. Our in-vitro work found that 0.2–1Gy using 40–100kVp x-rays combined with psoralen and particles can induce a substantial apoptotic response beyond that expected from the sum of individual components. In preparation for a phase I clinical trial of canine companion animals, we address the physics and dosimetry considerations for applying this new teletherapy paradigm to an in-vivo setting. Methods: The kV on-board imaging (OBI) system mounted on a medical linear accelerator (Varian) was commissioned to deliver the prescribed dose (0.6Gy) using 80 and 100kVp. Dosimetric measurements included kVp, HVL, depth dose, backscatter factors, collimator and phantom scatter factors, field size factors, and blade leakage. Absolute dosimetry was performed following AAPM TG61 recommendations and verified with an independent kV dose meter. We also investigated collimated rotational delivery to minimize skin dose using simple dose calculations on homogeneous cylindrical phantoms. Results: Single beam delivery is feasible for shallow targets (<5cm) without exceeding skin tolerance, while a rotational delivery may be utilized for deeper targets; skin dose is ∼75% of target dose for 80kVp collimated rotational delivery to a 3cm target within a 20cm phantom. Heat loading was tolerable; 0.6Gy to 5cm can be delivered before the anode reaches 75% capacity. Conclusion: KV teletherapy for Psoralen activation in deep seated tissue was successfully commissioned for a Varian OBI machine for use in a phase I clinical trial in canines. Future work will use Monte Carlo dosimetry to investigate dose in presence of bone. Research funded by Immunolight LLC. H. Walder, Z. Fathi, & W. Beyer are employees of Immunolight LLC which holds a patent on the technology. Drs. Adamson and Oldham are consultants to Immunolight LLC.

60 APPLIED LIFE SCIENCES↗