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At least 829 records · Page 46
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

SU-E-T-226: Correction of a Standard Model-Based Dose Calculator Using Measurement Data

Purpose: To propose a hybrid method that combines advantages of the model-based and measurement-based method for independent dose calculation. Modeled-based dose calculation, such as collapsed-cone-convolution/superposition (CCCS) or the Monte-Carlo method, models dose deposition in the patient body accurately; however, due to lack of detail knowledge about the linear accelerator (LINAC) head, commissioning for an arbitrary machine is tedious and challenging in case of hardware changes. On the contrary, the measurement-based method characterizes the beam property accurately but lacks the capability of dose disposition modeling in heterogeneous media. Methods: We used a standard CCCS calculator, which is commissioned by published data, as the standard model calculator. For a given machine, water phantom measurements were acquired. A set of dose distributions were also calculated using the CCCS for the same setup. The difference between the measurements and the CCCS results were tabulated and used as the commissioning data for a measurement based calculator. Here we used a direct-ray-tracing calculator (ΔDRT). The proposed independent dose calculation consists of the following steps: 1. calculate D-model using CCCS. 2. calculate D-ΔDRT using ΔDRT. 3. combine Results: D=D-model+D-ΔDRT. Results: The hybrid dose calculation was tested on digital phantoms and patient CT data for standard fields and IMRT plan. The results were compared to dose calculated by the treatment planning system (TPS). The agreement of the hybrid and the TPS was within 3%, 3 mm for over 98% of the volume for phantom studies and lung patients. Conclusion: The proposed hybrid method uses the same commissioning data as those for the measurement-based method and can be easily extended to any non-standard LINAC. The results met the accuracy, independence, and simple commissioning criteria for an independent dose calculator.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

SU-E-T-263: Development of Dose Monitor Unit Calculation Using Clarkson Integration for Proton Beam Therapy Using Beam-Wobbling System

Purpose: The purpose of the present study is to develop a calculation method of dose-calibration-factor using Clarkson integration for proton therapy employing the wobbling system and to evaluate accuracy of the calculation by comparison between calculations and measurements. Methods: CF and CALF stand for a dose-calibration-factor and a dose per monitor unit (MU), respectively. A measured dose-calibration-factor CFmeas is defined as a ratio of the measured dose per monitor unit in a patient-specific condition CALFpat to the measured dose per MU in a reference beam condition CALFref. The CFcalc is a product of three factors: CF1, CF2 and CF3. The CF1 and CF2 are a factor reflecting the effect of common beam delivery devices and that of patient specific devices and parameter (an aperture collimator, a range compensator and an air gap), respectively. The CF1 was obtained by interpolation using measured data. The CF2 was calculated using the Simplified Monte Carlo (SMC) method. The SMC method calculates a dose distribution by tracing individual protons and by using a measured Bragg curve in water. The CF3 representing the correction factor of field size effect was obtained by using the Clarkson integration. We compared the calculated and measured CF values for 20 prostate cases. Results: Field size correction was found to be important. The calculations reproduce the measurement results within an error of ±2.0%, except for a few cases. The error was about –3.1% for the small field area of less than19 square centimeters. Conclusion: We have developed a calculation method of dose-calibration-factor. Calculations agreed with measurements within ±2.0% for 90% of 20 prostate cases. Except for a small field size cases, the calculation method can be applied to determine the dose-calibration–factor for majority cases of prostate cancer.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

SU-E-T-273: Do Task Group External Beam QA Recommendations Guarantee Accurate Treatment Plan Dose Delivery?

Purpose: AAPM task groups 40/142 have provided an invaluable set of goals for physicists designing QA programs, attempting to standardize what would otherwise likely be a highly variable phenomenon across institutions. However, with the complexity of modalities such as VMAT, we hypothesize that following these guidelines to the letter might still allow unacceptable dose discrepancies. To explore this hypothesis we simulated machines bordering on QA acceptability, and calculated the effect on patient plans. Methods: Two errant machines were simulated in Aria/Eclipse, each just within task group criteria for output, percent depth dose, beam profile, gantry and collimator rotations, and jaw and MLC positions. One machine minimized dose to the PTV (machine A) and the other maximized dose to the OARs (machine B). Clinical treatment plans (3-phase prostate, n=3; hypofractionated lung, n=1) were calculated on these machines and the dose distributions compared. A prostate case was examined for contribution of error sources and evaluated using delivery QA data. Results: The prostate plans showed mean decreases in target D95 of 9.9% of prescription dose on machine A. On machine B, The rectal and bladder V70Gy each increased by 7.1 percentage points, while their V45Gy increased by 16.2% and 15.0% respectively. In the lung plan, the target D95 decreased by 12.8% and the bronchial tree Dmax increased by 21% of prescription dose, on machines A and B. One prostate plan showed target dose errors of 3.8% from MLC changes, 2% from output, ∼3% from energy and ∼0.5% from other factors. This plan achieved an 88.4% gamma passing rate using 3%/3mm using ArcCHECK. Conclusion: In the unlikely event that a machine exhibits all maximum errors allowed by TG 40/142, unacceptably large changes in dose delivered are possible especially in highly modulated VMAT plans, despite the machine passing routine QA.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

SU-E-T-388: Evaluation of Electronic Brachytherapy Dose Distributions in Tissue Equivalent Materials

Purpose: To study the measured and calculated dose distributions for electronic brachytherapy (EBT) in various tissue equivalent homogenous materials. Methods: Calculated dose distributions in water were generated using published TG-43 parameters in Varian BrachyVision software for a 50 kVp, 50 cm Xoft source. Dose distributions were measured within a 3D-scanning tank using dosimeters including: PTW 0.125 cc, pin-point, and parallel-plate ion chambers, Sun Nuclear “Edge” diode and Gafchromic EBT3 film. Multi-channel film dosimetry was used in film analysis. EBT3 film curves were calibrated via radial dose comparison to both independently measured and published data. The resulting film calibration was utilized to measure dose distributions created by titanium filtered source utilized in clinical brachytherapy applications. Data was collected within homogenous PMMA, vinyl, polystyrene, paraffin, and water-equivalent plastic phantoms. Results: Ion-chamber data was corrected to effective points of measurement and normalized prior to comparison between calculated and measured dose distributions. Measurements made in water and water equivalent materials compared well with results from treatment planning software. The maximum percent differences (relative to water) observed between 1 cm and 3.5 cm depth from source for each of the phantom materials are as follows: PMMA 35%, polystyrene 41%, plastic-water 23%, vinyl 115%, and paraffin 46%. Conclusion: The increased probability of photoelectric interactions occurring within the patient during electronic brachytherapy will emphasize the radiological differences between varying human tissues in dose deposition. These differences can Result in clinically significant dose perturbations and it is therefore recommended to move to a model based dose calculation, as outlined in TG-186, to improve the dosimetric accuracy of low energy EBT.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

SU-E-T-463: Impact to Total Scatter Factors On the Calculated Dose Distribution in Radiosurgery

Purpose: To assess the impact of relative measurements: off axis ratios (OAR), tissue phantom ratios (TPR) and especially total scatter factor (TSF) on the calculated dose distribution in stereotactic radiosurgery with circular cones. Methods: Six detectors were employed to characterize circular collimated photon beams of 6 MV: three diodes (SFD, E, SRS), one ionization chamber (CC01) and two radiochromic films (EBT, EBT2). The relative measurements were incorporated in the treatment planning system (TPS) in order to compare and analyze the calculated dose distributions (DD). Each dose distribution was re-scaled by the TSF to observe its effect in the final dose distribution. The comparison was performed by using the gamma index. A Monte Carlo generated dosimetry was used as reference. Results: The results showed that in terms of relative dosimetry all the detectors have a good agreement within 2%, with the exception of the CC01 and EBT2 film. However, the analysis performed with the dose distributions re-scaled relative to the TSF for each detector showed that the impact it was not only to the isocenter dose. The dose to the PTV and normal tissue showed differences up to 13% depending of the dosimeter used for TSF measurements. Conclusion: With the exception of the CC01 ionization chamber and EBT2 radiochromic film, all the studied dosimeters were adequate for the measurement of OAR and TPR. However, attention must be put in the measurement of TSF. The use of the wrong detector does not only affect the isocenter dose, it may have an impact in the PTV and normal tissue dose.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

WE-D-BRA-03: Four-Dimensional Dose Reconstruction Through Retrospective Phase Determination Using Cine Images of Electronic Portal Imaging Device

Purpose: To test a method to reconstruct a four-dimensional (4D) dose distribution using the correlation of pre-calculated 4D electronic portal imaging device (EPID) images and measured cine-EPID images. Methods: 1. A phantom designed to simulate a tumor in lung (a polystyrene block with 3.0 cm diameter embedded in cork) was placed on a sinusoidally moving platform with 2 cm amplitude and 4 sec/cycle. Ten-phase 4D CT images were acquired for treatment planning and dose reconstruction. A 6MV photon beam was irradiated on the phantom with static (field size=5×8.5 cm{sup 2}) and dynamic fields (sliding windows, 10×10 cm{sup 2}, X1 MLC closing in parallel with the tumor movement). 2. 4D and 3D doses were calculated forwardly on PTV (1 cm margin). 3. Dose images on EPID under the fields were calculated for 10 phases. 4. Cine EPID images were acquired during irradiation. 5. Their acquisition times were correlated to the phases of the phantom at which irradiation occurred by inter-comparing calculated “reference” EPID images with measured images (2D gamma comparison). For the dynamic beam, the tumor was hidden under MLCs during a portion of irradiation time; the correlation performed when the tumor was visible was extrapolated. 6. Dose for each phase was reconstructed on the 4D CT images and summed over all phases. The summation was compared with forwardly calculated 4D and 3D dose distributions. Monte Carlo methods were used for all calculations. Results: For the open and dynamic beams, the 4D reconstructed doses showed the pass rates of 92.7 % and 100 %, respectively, at the isocenter plane given 3% / 3 mm criteria. The better agreement of the dynamic beam was from its dose gradient which blurred the otherwise sharp difference between forward and reconstructed doses. This also contributed slightly better agreement in DVH of PTV. Conclusion: The feasibility of 4D reconstruction was demonstrated.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

Calibration of GafChromic EBT3 for absorbed dose measurements in 5 MeV proton beam and {sup 60}Co γ-rays

Purpose: To study EBT3 GafChromic film in low-energy protons, and for comparison purposes, in a reference {sup 60}Co beam in order to use it as a calibrated dosimetry system in the proton irradiation facility under construction within the framework of the Oncological Therapy with Protons (TOP)-Intensity Modulated Proton Linear Accelerator for RadioTherapy (IMPLART) Project at ENEA-Frascati, Italy. Methods: EBT3 film samples were irradiated at the Istituto Nazionale di Fisica Nucleare—Laboratori Nazionali di Legnaro, Italy, with a 5 MeV proton beam generated by a 7 MV Van de Graaff CN accelerator. The nominal dose rates used were 2.1 Gy/min and 40 Gy/min. The delivered dose was determined by measuring the particle fluence and the energy spectrum in air with silicon surface barrier detector monitors. A preliminary study of the EBT3 film beam quality dependence in low-energy protons was conducted by passively degrading the beam energy. EBT3 films were also irradiated at ENEA-National Institute of Ionizing Radiation Metrology with gamma radiation produced by a {sup 60}Co source characterized by an absorbed dose to water rate of 0.26 Gy/min as measured by a calibrated Farmer type ionization chamber. EBT3 film calibration curves were determined by means of a set of 40 film pieces irradiated to various doses ranging from 0.5 Gy to 30 Gy absorbed dose to water. An EPSON Expression 11000XL color scanner in transmission mode was used for film analysis. Scanner response stability, intrafilm uniformity, and interfilm reproducibility were verified. Optical absorption spectra measurements were performed on unirradiated and irradiated EBT3 films to choose the most sensitive color channel to the dose range used. Results: EBT3 GafChromic films show an under response up to about 33% for low-energy protons with respect to {sup 60}Co gamma radiation, which is consistent with the linear energy transfer dependence already observed with higher energy protons, and a negligible dose-rate dependence in the 2–40 Gy/min range. Short- and long-term scanner stabilities were 0.5% and 1.5%, respectively; film uniformity and reproducibility were better than 0.5%. Conclusions: The main purpose of this study was to implement EBT3 dosimetry in the proton low-energy radiobiology line of the TOP-IMPLART accelerator, having a maximum energy of 7 MeV. Low-energy proton and {sup 60}Co calibrated sources were used to investigate the behavior of film response vs to be written in italicum dose. The calibration in 5 MeV protons is currently used for dose assessment in the radiobiological experiments at the TOP-IMPLART accelerator carried out at that energy value.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

A 1.5 T transverse magnetic field in radiotherapy of rectal cancer: Impact on the dose distribution

Purpose: MRI guidance during radiotherapy has the potential to enable more accurate dose delivery, optimizing the balance between local control and treatment related toxicity. However, the presence of a permanent magnetic field influences the dose delivery, especially around air cavities. Here, electrons are able to return to the surface through which they entered the air cavity (electron return effect, ERE) locally resulting in dose hot- and cold-spots. Where RT of rectal cancer patients might benefit from MRI guidance for margin reduction, air cavities in and around the target volume are frequently present. The purpose of this research is to evaluate the impact of the presence of a 1.5 T transverse magnetic field on dose delivery in patients with rectal cancer. Methods: Ten patients treated with 5 × 5 Gy RT having large changes in pelvic air content were selected out of a cohort of 33 patients. On the planning CT, a 1.5 T, 6 MV, 7-field intensity modulated radiotherapy (IMRT) plan was created. This plan was subsequently recalculated on daily CT scans. For each daily CT, the CTV V{sub 95%} and V{sub 107%} and bowel area V{sub 5Gy}, V{sub 10Gy}, V{sub 15Gy}, V{sub 20Gy}, and V{sub 25Gy} were calculated to evaluate the changes in dose distribution from fraction to fraction. For comparison, the authors repeated this procedure for the 0 T situation. To study the effect of changing air cavities separate from other anatomical changes, the authors also generated artificial air cavities in the CTV of one patient (2 and 5 cm diameter), in the high dose gradient region (2 cm), and in the low dose area (2 cm). Treatment plans were optimized without and with each simulated air cavity. For appearing and disappearing air cavities, the CTV V{sub 95%} and V{sub 107%} were evaluated. The authors also evaluated the ERE separate from attenuation changes locally around appearing gas pockets. Results: For the ten patients, at 1.5 T, the V{sub 95%} was influenced by both appearing and disappearing air, and dropped to <98% in 2 out of 50 fractions due a disappearing air cavity of 150 cm{sup 3}. V{sub 95%} differences between 0 and 1.5 T were all within 2%. The V{sub 107%} was below 1% in 46 out of 50 fractions, and increased to 3% in the remaining fractions due to appearing air of around 120 cm{sup 3}. For comparison, V{sub 107%} was <1% at 0 T for all fractions. In the bowel area, the V{sub 15Gy} varied strongest from fraction to fraction, but differences between 1.5 and 0 T were minimal with an average difference of 2.3 cm{sup 3} (SD = 18.7 cm{sup 3}, p = 0.38). For the simulated air cavities, the ERE resulted in cold-spots maximally 5% lower than prescribed and hot-spots maximally 6% higher than prescribed. Conclusions: The presence of a 1.5 T magnetic field has an impact on the dose distribution when the air content changes of within a few percent in these selected rectal cancer patients. The authors consider this influence of the transverse magnetic field on the dose distribution in IMRT for rectal cancer patients clinically acceptable.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

Influence of nuclear interactions in body tissues on tumor dose in carbon-ion radiotherapy

Purpose: In carbon-ion radiotherapy treatment planning, the planar integrated dose (PID) measured in water is applied to the patient dose calculation with density scaling using the stopping power ratio. Since body tissues are chemically different from water, this dose calculation can be subject to errors, particularly due to differences in inelastic nuclear interactions. In recent studies, the authors proposed and validated a PID correction method for these errors. In the present study, the authors used this correction method to assess the influence of these nuclear interactions in body tissues on tumor dose in various clinical cases. Methods: Using 10–20 cases each of prostate, head and neck (HN), bone and soft tissue (BS), lung, liver, pancreas, and uterine neoplasms, the authors first used treatment plans for carbon-ion radiotherapy without nuclear interaction correction to derive uncorrected dose distributions. The authors then compared these distributions with recalculated distributions using the nuclear interaction correction (corrected dose distributions). Results: Median (25%/75% quartiles) differences between the target mean uncorrected doses and corrected doses were 0.2% (0.1%/0.2%), 0.0% (0.0%/0.0%), −0.3% (−0.4%/−0.2%), −0.1% (−0.2%/−0.1%), −0.1% (−0.2%/0.0%), −0.4% (−0.5%/−0.1%), and −0.3% (−0.4%/0.0%) for the prostate, HN, BS, lung, liver, pancreas, and uterine cases, respectively. The largest difference of −1.6% in target mean and −2.5% at maximum were observed in a uterine case. Conclusions: For most clinical cases, dose calculation errors due to the water nonequivalence of the tissues in nuclear interactions would be marginal compared to intrinsic uncertainties in treatment planning, patient setup, beam delivery, and clinical response. In some extreme cases, however, these errors can be substantial. Accordingly, this correction method should be routinely applied to treatment planning in clinical practice.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

Dose enhancement in radiotherapy of small lung tumors using inline magnetic fields: A Monte Carlo based planning study

Purpose: To report on significant dose enhancement effects caused by magnetic fields aligned parallel to 6 MV photon beam radiotherapy of small lung tumors. Findings are applicable to future inline MRI-guided radiotherapy systems. Methods: A total of eight clinical lung tumor cases were recalculated using Monte Carlo methods, and external magnetic fields of 0.5, 1.0, and 3 T were included to observe the impact on dose to the planning target volume (PTV) and gross tumor volume (GTV). Three plans were 6 MV 3D-CRT plans while 6 were 6 MV IMRT. The GTV’s ranged from 0.8 to 16 cm{sup 3}, while the PTV’s ranged from 1 to 59 cm{sup 3}. In addition, the dose changes in a 30 cm diameter cylindrical water phantom were investigated for small beams. The central 20 cm of this phantom contained either water or lung density insert. Results: For single beams, an inline magnetic field of 1 T has a small impact in lung dose distributions by reducing the lateral scatter of secondary electrons, resulting in a small dose increase along the beam. Superposition of multiple small beams leads to significant dose enhancements. Clinically, this process occurs in the lung tissue typically surrounding the GTV, resulting in increases to the D{sub 98%} (PTV). Two isolated tumors with very small PTVs (3 and 6 cm{sup 3}) showed increases in D{sub 98%} of 23% and 22%. Larger PTVs of 13, 26, and 59 cm{sup 3} had increases of 9%, 6%, and 4%, describing a natural fall-off in enhancement with increasing PTV size. However, three PTVs bounded to the lung wall showed no significant increase, due to lack of dose enhancement in the denser PTV volume. In general, at 0.5 T, the GTV mean dose enhancement is around 60% lower than that at 1 T, while at 3 T, it is 5%–60% higher than 1 T. Conclusions: Monte Carlo methods have described significant and predictable dose enhancement effects in small lung tumor plans for 6 MV radiotherapy when an external inline magnetic field is included. Results of this study indicate that future clinical inline MRI-guided radiotherapy systems will be able to deliver a dosimetrically superior treatment to small (PTV < 15 cm{sup 3}), isolated lung tumors over non-MRI-Linac systems. This increased efficacy coincides with the reimbursement in the United States of lung CT screening and the likely rapid growth in the number of patients with small lung tumors to be treated with radiotherapy.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2016

SU-D-BRB-02: Combining a Commercial Autoplanning Engine with Database Dose Predictions to Further Improve Plan Quality

Purpose: Database dose predictions and a commercial autoplanning engine both improve treatment plan quality in different but complimentary ways. The combination of these planning techniques is hypothesized to further improve plan quality. Methods: Four treatment plans were generated for each of 10 head and neck (HN) and 10 prostate cancer patients, including Plan-A: traditional IMRT optimization using clinically relevant default objectives; Plan-B: traditional IMRT optimization using database dose predictions; Plan-C: autoplanning using default objectives; and Plan-D: autoplanning using database dose predictions. One optimization was used for each planning method. Dose distributions were normalized to 95% of the planning target volume (prostate: 8000 cGy; HN: 7000 cGy). Objectives used in plan optimization and analysis were the larynx (25%, 50%, 90%), left and right parotid glands (50%, 85%), spinal cord (0%, 50%), rectum and bladder (0%, 20%, 50%, 80%), and left and right femoral heads (0%, 70%). Results: All objectives except larynx 25% and 50% resulted in statistically significant differences between plans (Friedman’s χ{sup 2} ≥ 11.2; p ≤ 0.011). Maximum dose to the rectum (Plans A-D: 8328, 8395, 8489, 8537 cGy) and bladder (Plans A-D: 8403, 8448, 8527, 8569 cGy) were significantly increased. All other significant differences reflected a decrease in dose. Plans B-D were significantly different from Plan-A for 3, 17, and 19 objectives, respectively. Plans C-D were also significantly different from Plan-B for 8 and 13 objectives, respectively. In one case (cord 50%), Plan-D provided significantly lower dose than plan C (p = 0.003). Conclusion: Combining database dose predictions with a commercial autoplanning engine resulted in significant plan quality differences for the greatest number of objectives. This translated to plan quality improvements in most cases, although special care may be needed for maximum dose constraints. Further evaluation is warranted in a larger cohort across HN, prostate, and other treatment sites. This work is supported by Philips Radiation Oncology Systems.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

SU-F-P-44: A Direct Estimate of Peak Skin Dose for Interventional Fluoroscopy Procedures

Purpose: There is an increasing demand for medical physicist to calculate peak skin dose (PSD) for interventional fluoroscopy procedures. The dose information (Dose-Area-Product and Air Kerma) displayed in the console cannot directly be used for this purpose. Our clinical experience shows that the use of the existing methods may overestimate or underestimate PSD. This study attempts to develop a direct estimate of PSD from the displayed dose metrics. Methods: An anthropomorphic torso phantom was used for dose measurements for a common fluoroscopic procedure. Entrance skin doses were measured with a Piranha solid state point detector placed on the table surface below the torso phantom. An initial “reference dose rate” (RE) measurement was conducted by comparing the displayed dose rate (mGy/min) to the dose rate measured. The distance from table top to focal spot was taken as the reference distance (RD at the RE. Table height was then adjusted. The displayed air kerma and DAP were recorded and sent to three physicists to estimate PSD. An inverse square correction was applied to correct displayed air kerma at various table heights. The PSD estimated by physicists and the PSD by the proposed method were then compared with the measurements. The estimated DAPs were compared to displayed DAP readings (mGycm2). Results: The difference between estimated PSD by the proposed method and direct measurements was less than 5%. For the same set of data, the estimated PSD by each of three physicists is different from measurements by ±52%. The DAP calculated by the proposed method and displayed DAP readings in the console is less than 20% at various table heights. Conclusion: PSD may be simply estimated from displayed air kerma or DAP if the distance between table top and tube focal spot or if x-ray beam area on table top is available.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

SU-F-I-53: Coded Aperture Coherent Scatter Spectral Imaging of the Breast: A Monte Carlo Evaluation of Absorbed Dose

Purpose: Coherent scatter based imaging has shown improved contrast and molecular specificity over conventional digital mammography however the biological risks have not been quantified due to a lack of accurate information on absorbed dose. This study intends to characterize the dose distribution and average glandular dose from coded aperture coherent scatter spectral imaging of the breast. The dose deposited in the breast from this new diagnostic imaging modality has not yet been quantitatively evaluated. Here, various digitized anthropomorphic phantoms are tested in a Monte Carlo simulation to evaluate the absorbed dose distribution and average glandular dose using clinically feasible scan protocols. Methods: Geant4 Monte Carlo radiation transport simulation software is used to replicate the coded aperture coherent scatter spectral imaging system. Energy sensitive, photon counting detectors are used to characterize the x-ray beam spectra for various imaging protocols. This input spectra is cross-validated with the results from XSPECT, a commercially available application that yields x-ray tube specific spectra for the operating parameters employed. XSPECT is also used to determine the appropriate number of photons emitted per mAs of tube current at a given kVp tube potential. With the implementation of the XCAT digital anthropomorphic breast phantom library, a variety of breast sizes with differing anatomical structure are evaluated. Simulations were performed with and without compression of the breast for dose comparison. Results: Through the Monte Carlo evaluation of a diverse population of breast types imaged under real-world scan conditions, a clinically relevant average glandular dose for this new imaging modality is extrapolated. Conclusion: With access to the physical coherent scatter imaging system used in the simulation, the results of this Monte Carlo study may be used to directly influence the future development of the modality to keep breast dose to a minimum while still maintaining clinically viable image quality.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

SU-F-J-99: Dose Accumulation and Evaluation in Lung SBRT Among All Phases of Respiration

Purpose: To calculate the total planning dose on lung tumors (GTV) by accumulating the dose received in all respiration phases. Methods: A patient 4D planning CT (phase-binned, from a Siemens Somatom CT) was used to locate the GTV of a lung tumor in all respiratory phases with Pinnacle (v9.10). GTV contours defined in all phases were projected to the reference phase, where the ITV was defined. Centroids were calculated for all the GTV projections. No deformation or rotation was taken into account. The only GTV contour as defined in the reference phase was voxelized to track each voxel individually. We accumulated the absorbed dose in different phases on each voxel. A 3DCRT and a VMAT plan were designed on the reference phase fulfilling the ITV dosimetric requirements, using the 10MV FFF photon model from an Elekta Versa linac. ITV-to-PTV margins were set to 5mm. In-house developed MATLAB code was used for tumor voxeling and dose accumulation, assuming that the dose distribution planned in the reference phase behaved as a “dose-cloud” during patient breathing. Results: We tested the method on a patient 4DCT set of images exhibiting limited tumor motion (<5mm). For the 3DCRT plan, D95 was calculated for the GTV with motion and for the ITV, showing an agreement of 0.04%. For the VMAT plan, we calculated the D95 for every phase as if the GTV in that phase had received the whole treatment. Differences in D95 for all phases are within 1%, and estimate the potential interplay effect during delivery. Conclusion: A method for dose accumulation and assessment was developed that can compare GTV motion with ITV dosage, and estimate the potential interplay effect for VMAT plans. Work in progress includes the incorporation of deformable image registration and 4D CBCT dose calculation for dose reconstruction and assessment during treatment.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

SU-F-T-46: The Effect of Inter-Seed Attenuation and Tissue Composition in Prostate 125I Brachytherapy Dose Calculations

Purpose: To investigate the difference of dose distributions with/without the effect of inter-seed attenuation and tissue compositions in prostate {sup 125}I brachytherapy dose calculations, using Monte Carlo simulations of Particle and Heavy Ion Transport code System (PHITS). Methods: The dose distributions in {sup 125}I prostate brachytherapy were calculated using PHITS for non-simultaneous and simultaneous alignments of STM1251 sources in water or prostate phantom for six patients. The PHITS input file was created from DICOM-RT file which includes source coordinates and structures for clinical target volume (CTV) and organs at risk (OARs) of urethra and rectum, using in-house Matlab software. Photon and electron cutoff energies were set to 1 keV and 100 MeV, respectively. The dose distributions were calculated with the kerma approximation and the voxel size of 1 × 1 × 1 mm{sup 3}. The number of incident photon was set to be the statistical uncertainty (1σ) of less than 1%. The effect of inter-seed attenuation and prostate tissue compositions was evaluated from dose volume histograms (DVHs) for each structure, by comparing to results of the AAPM TG-43 dose calculation (without the effect of inter-seed attenuation and prostate tissue compositions). Results: The dose reduction due to the inter-seed attenuation by source capsules was approximately 2% for CTV and OARs compared to those of TG-43. In additions, by considering prostate tissue composition, the D{sub 90} and V{sub 100} of CTV reduced by 6% and 1%, respectively. Conclusion: It needs to consider the dose reduction due to the inter-seed attenuation and tissue composition in prostate {sup 125}I brachytherapy dose calculations.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2019

Maxine Onsite: Estimating Dose from Chronic Atmospheric Radioactive Releases

Maxine Onsite: Developed to estimate dose to individuals who are working onsite but are not site employees. Follows the methodologies discussed in US NRC Regulatory Guides 1.109 and 1.111 to determine dose from a chronic atmospheric release. Determines the dose given relative air concentrations and deposition concentrations as input. We look at four locations onsite that may be accessed by members of the public. To show compliance with the EPA and DOE public dose limit of 10 mrem/yr, determining who is a member of the public or a worker onsite is necessary. SRS has defined a member of the public for NESHAPS and DOE O 458.1. Maxine Onsite runs on Microsoft Windows Operating System through a Microsoft Excel spreadsheet. Input from the user includes parameters that are variable such as air concentrations, and fixed, such as distance to the receptor and elemental iodine fraction. Maxine Onsite was developed from Maxine which is a program meant to calculate dose to the MEI via three pathways, external, inhalation, and ingestion. Maxine Onsite is meant for looking at the exposure through the external and inhalation pathways only, no local food production onsite. The ways that Maxine Onsite is used to calculate the dose to the MEI includes the following: - Determining the respective air concentration values at each location using distances from the release stack; - Breathing rates for the MEI; - Determining the amount of time the MEI is outside; - Determining the plume travel time. The following relative air and ground deposition values for proper execution of the spreadsheet come from MAXDOSE-SR and are needed to accurately determine the dose to the MEI: relative air concentration, relative air concentration decayed by 2.26 days, relative air concentration decayed and depleted for 8 days, and relative deposition. Test cases were designed, developed, and executed to determine the accuracy of Maxine Onsite, which were verified additionally through hand calculations. Several changes were made for testing, including varying air concentrations, distances, breathing rates, and shielding factors. Each test case was then verified through hand calculations to assure the accuracy of the calculated doses. The results from the test cases, as well as the default parameters, can be used for benchmarking Maxine Onsite in the future. Maxine Onsite performs as expected and produces correct and accurate results at each of the different locations onsite (TRL, B-Area Barracks, SRELCC, and Gunsite 51) for varying test cases. The input required by the user is minimal and includes the results of the dose to the MEI on the first page for ease of access. Future plans for Maxine Onsite include adding in the ingestion pathway and adding in atmospheric dispersion estimates to the spreadsheet.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2015

The Effect of Realtime Monitoring on Dose Exposure to Staff Within an Interventional Radiology Setting

PurposeThe purpose of this study is to evaluate a new device providing real-time monitoring on radiation exposure during fluoroscopy procedures intending to reduce radiation in an interventional radiology setting.Materials and MethodsIn one interventional suite, a new system providing a real-time radiation dose display and five individual wireless dosimeters were installed. The five dosimeters were worn by the attending, fellow, nurse, technician, and anesthesiologist for every procedure taking place in that suite. During the first 6-week interval the dose display was off (closed phase) and activated thereafter, for a 6-week learning phase (learning phase) and a 10-week open phase (open phase). During these phases, the staff dose and the individual dose for each procedure were recorded from the wireless dosimeter and correlated with the fluoroscopy time. Further subanalysis for dose exposure included diagnostic versus interventional as well as short (<10 min) versus long (>10 min) procedures.ResultsA total of 252 procedures were performed (n = 88 closed phase, n = 50 learning phase, n = 114 open phase). The overall mean staff dose per fluoroscopic minute was 42.79 versus 19.81 µSv/min (p < 0.05) comparing the closed and open phase. Thereby, anesthesiologists were the only individuals attaining a significant dose reduction during open phase 16.9 versus 8.86 µSv/min (p < 0.05). Furthermore, a significant reduction of total staff dose was observed for short 51 % and interventional procedures 45 % (p < 0.05, for both).ConclusionA real-time qualitative display of radiation exposure may reduce team radiation dose. The process may take a few weeks during the learning phase but appears sustained, thereafter.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Comparing Effective Doses During Image-Guided Core Needle Biopsies with Computed Tomography Versus C-Arm Cone Beam CT Using Adult and Pediatric Phantoms

PurposeTo compare the effective doses of needle biopsies based on dose measurements and simulations using adult and pediatric phantoms, between cone beam c-arm CT (CBCT) and CT.MethodEffective doses were calculated and compared based on measurements and Monte Carlo simulations of CT- and CBCT-guided biopsy procedures of the lungs, liver, and kidney using pediatric and adult phantoms.ResultsThe effective doses for pediatric and adult phantoms, using our standard protocols for upper, middle and lower lungs, liver, and kidney biopsies, were significantly lower under CBCT guidance than CT. The average effective dose for a 5-year old for these five biopsies was 0.36 ± 0.05 mSv with the standard CBCT exposure protocols and 2.13 ± 0.26 mSv with CT. The adult average effective dose for the five biopsies was 1.63 ± 0.22 mSv with the standard CBCT protocols and 8.22 ± 1.02 mSv using CT. The CT effective dose was higher than CBCT protocols for child and adult phantoms by 803 and 590 % for upper lung, 639 and 525 % for mid-lung, and 461 and 251 % for lower lung, respectively. Similarly, the effective dose was higher by 691 and 762 % for liver and 513 and 608 % for kidney biopsies.ConclusionsBased on measurements and simulations with pediatric and adult phantoms, radiation effective doses during image-guided needle biopsies of the lung, liver, and kidney are significantly lower with CBCT than with CT.

62 RADIOLOGY AND NUCLEAR MEDICINE↗