bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐T‐519: Investigation of the CyberKnife MultiPlan Monte Carlo Dose Calculation Using EBT3 Film Absolute Dosimetry for Delivery in a Heterogeneous Thorax Phantom
Authors: Lamberto M , Chen H , Huang K , Mourtada F 
Published: June 2015

PurposeTo characterize the Cyberknife (CK) robotic system's dosimetric accuracy of the delivery of MultiPlan's Monte Carlo dose calculations using EBT3 radiochromic film inserted in a thorax phantom.MethodsThe CIRS XSight Lung Tracking (XLT) Phantom (model 10823) was used in this study with custom cut EBT3 film inserted in the horizontal (coronal) plane inside the lung tissue equivalent phantom. CK MultiPlan v3.5.3 with Monte Carlo dose calculation algorithm (1.5 mm grid size, 2% statistical uncertainty) was used to calculate a clinical plan for a 25‐mm lung tumor lesion, as contoured by the physician, and then imported onto the XLT phantom CT. Using the same film batch, the net OD to dose calibration curve was obtained using CK with the 60 mm fixed cone by delivering 0– 800 cGy. The test films (n=3) were irradiated using 325 cGy to the prescription point. Films were scanned 48 hours after irradiation using an Epson v700 scanner (48 bits color scan, extracted red channel only, 96 dpi). Percent absolute dose and relative isodose distribution difference relative to the planned dose were quantified using an in‐house QA software program. Multiplan Monte Carlo dose calculation was validated using RCF dosimetry (EBT3) and gamma index criteria of 3%/3mm and 2%/2mm for absolute dose and relative isodose distribution measurement comparisons.ResultsEBT3 film measurements of the patient plans calculated with Monte Carlo in MultiPlan resulted in an absolute dose passing rate of 99.6±0.4% for the Gamma Index of 3%/3mm, 10% dose threshold, and 95.6±4.4% for 2%/2mm, 10% threshold criteria. The measured central axis absolute dose was within 1.2% (329.0±2.5 cGy) of the Monte Carlo planned dose (325.0±6.5 cGy) for that same point.ConclusionMultiPlan's Monte Carlo dose calculation was validated using the EBT3 film absolute dosimetry for delivery in a heterogeneous thorax phantom.
SU‐E‐T‐523: Investigation of Various MR‐Compatible Shielding Materials for Direction Modulated Brachytherapy (DMBT) Tandem Applicator for Cervical Cancer Treatment
Authors: Safigholi H , Han D , Soliman A , Meigooni A Soleimani , Scanderbeg D , Song W 
Published: June 2015

Purpose:To evaluate various shielding materials such as Gold (Au), Osmium (Os), Tantalum (Ta), and Tungsten (W) based alloys for use with a novel intensity modulation capable direction modulated brachytherapy (DMBT) tandem applicator for image guided cervical cancer HDR brachytherapy.Methods:The novel MRI‐compatible DMBT tandem, made from nonmagnetic tungsten‐alloy rod with diameter of 5.4 mm, has 6 symmetric peripheral holes of 1.3 mm diameter with 2.05 mm distance from the center for a high degree intensity modulation capacity. The 0.3 mm thickness of bio‐compatible plastic tubing wraps the tandem. MCNPX was used for Monte Carlo simulations of the shields and the mHDR Ir‐192 V2 source. MC‐generated 3D dose matrices of different shielding materials of Au, Os, Ta, and W with 1 mm3 resolution were imported into an in‐house‐coded inverse optimization planning system to evaluate 19 clinical patient plans. Prescription dose was 15Gy. All plans were normalized to receive the same HRCTV D90.Results:In general, the plan qualities for various shielding materials were similar. The OAR D2cc for bladder was very similar for Au, Os, and Ta with 11.64±2.30Gy. For W, it was very close 11.65±2.30Gy. The sigmoid D2cc was 9.82±2.46Gy for Au and Os while it was 9.84±2.48Gy for Ta and W. The rectum D2cc was 7.44±3.06Gy for Au, 7.43±3.07Gy for Os, 7.48±3.05Gy for Ta, and 7.47±3.05Gy for W. The HRCTV D98 and V100 were very close with 16.37±1.87 Gy and 97.37±1.93 Gy, on average, respectively.Conclusion:Various MRI‐compatible shielding alloys were investigated for the DMBT tandem applicator. The clinical plan qualities were not significantly different among these various alloys, however. Therefore, the candidate metals (or in combination) can be used to select best alloys for MRI image guided cervical cancer brachytherapy using the novel DMBT applicator that is capable of unprecedented level of intensity modulation.
SU‐E‐T‐525: Ionization Chamber Perturbation in Flattening Filter Free Beams
Authors: Czarnecki D , Voigts‐Rhetz P von , Zink K 
Published: June 2015

Purpose:Changing the characteristic of a photon beam by mechanically removing the flattening filter may impact the dose response of ionization chambers. Thus, perturbation factors of cylindrical ionization chambers in conventional and flattening filter free photon beams were calculated by Monte Carlo simulations.Methods:The EGSnrc/BEAMnrc code system was used for all Monte Carlo calculations. BEAMnrc models of nine different linear accelerators with and without flattening filter were used to create realistic photon sources. Monte Carlo based calculations to determine the fluence perturbations due to the presens of the chambers components, the different material of the sensitive volume (air instead of water) as well as the volume effect were performed by the user code egs_chamber.Results:Stem, central electrode, wall, density and volume perturbation factors for linear accelerators with and without flattening filter were calculated as a function of the beam quality specifier TPR20/10. A bias between the perturbation factors as a function of TPR20/10 for flattening filter free beams and conventional linear accelerators could not be observed for the perturbations caused by the components of the ionization chamber and the sensitive volume.Conclusion:The results indicate that the well‐known small bias between the beam quality correction factor as a function of TPR20/10 for the flattening filter free and conventional linear accelerators is not caused by the geometry of the detector but rather by the material of the sensitive volume. This suggest that the bias for flattening filter free photon fields is only caused by the different material of the sensitive volume (air instead of water).
SU‐E‐T‐528: Is It Essential to QA HDR Applicators Annually in Clinic?
Authors: Xu H , Yang X , Yi B 
Published: June 2015

Purpose:There is no rigid prescription recommended for the periodic QA of HDR applicators in terms of what must be done and in what frequency. This study investigates the necessity of an annual QA program for HDR applicators, which was performed at an HDR clinic.Methods:In this clinic, all HDR applicators and dummy sources used for HDR treatment are tested on an annual basis. 10 different types of gyn applicators were involved including CT‐compatible and non‐CT compatible tandem & ovoid set, interstitial tandem &ring set, cylinder set Miami set, vaginal applicator set, ring set, Fletcher Williamson set. The annually QA tests for these applicators included (1) visual inspection, (2) mechanical integrity, (3) source positioning accuracy tests using kV imaging, or a combination of (1)– (3). The source positioning accuracy tolerance was 2mm. Over 100 tests were performed on 48 and 61 pieces of applicator components in 2013 and 2014, respectively.Results:Due to the annual QA, the degraded of applicators or dummy source were ascertained. The degradation either affected the feasibility of source delivery or introduced significant source position errors. The failure rate of the HDR applicator annual QA was 1.6% in 2013 and 2.4% in 2014. Each year, different problems on difference components were detected. The unacceptable applicator components were discarded and replaced by the new orders before affecting any patient treatment. This annual QA takes physicist half to one day to finish depending on his or her experience and expertise.Conclusion:The annual QA tests are determined as essential in clinic and should include visual inspection, mechanical integrity and source positioning accuracy tests. It is strongly suggested to perform annual HDR applicator QA in clinic to increase the confidence to deliver a safe, accurate and appropriate HDR treatment.
SU‐E‐T‐529: Is MFO‐IMPT Robust Enough for the Treatment of Head and Neck Tumors? A 2‐Year Outcome Analysis Following Proton Therapy On the First 50 Oropharynx Patients at the MD Anderson Cancer Center
Authors: Frank S , Garden A , Anderson M , Rosenthal D , Morrison W , Gunn B , Fuller C , Phan J , Zhang X , Poenisch F , Wu R , Li H , Gautam A , Sahoo N , Gillin M , Zhu X 
Published: June 2015

Purpose:Multi‐field optimization intensity modulated proton therapy (MFO‐IMPT) for oropharyngeal tumors has been established using robust planning, robust analysis, and robust optimization techniques. While there are inherent uncertainties in proton therapy treatment planning and delivery, outcome reporting are important to validate the proton treatment process. The purpose of this study is to report the first 50 oropharyngeal tumor patients treated de‐novo at a single institution with MFO‐IMPT.Methods:The data from the first 50 patients with squamous cell carcinoma of the oropharynx treated at MD Anderson Cancer Center from January 2011 to December 2014 on a prospective IRB approved protocol were analyzed. Outcomes were analyzed to include local, regional, and distant treatment failures. Acute and late toxicities were analyzed by CTCAE v4.0.Results:All patients were treated with definitive intent. The median follow‐up time of the 50 patients was 25 months. Patients by gender were male (84%) and female (16%). The average age was 61 years. 50% of patients were never smokers and 4% were current smokers. Presentation by stage; I–1, II–0, III– 9, IVA–37 (74%), IVB–3. 88% of patients were HPV/p16+. Patients were treated to 66–70 CGE. One local failure was reported at 13 months following treatment. One neck failure was reported at 12 months. 94% of patients were alive with no evidence of disease. One patient died without evidence of disease. There were no Grade 4 or Grade 5 toxicities.Conclusion:MFO‐IMPT for oropharyngeal tumors is robust and provides excellent outcomes 2 years after treatment. A randomized trial is underway to determine if proton therapy will reduce chronic late toxicities of IMRT.
SU‐E‐T‐542: Measurement of Internal Neutrons for Uniform Scanning Proton Beams
Authors: Islam M , Zheng Y , Collums T , Monsoon J , Rana S , Ahmad S , Benton E 
Published: June 2015

Purpose:In proton radiotherapy, the production of neutrons is a wellknown problem since neutron exposure can lead to increased risk of secondary cancers later in the patient's lifetime. The assessment of neutron exposure is, therefore, important for the overall quality of proton radiotherapy. This study investigates the secondary neutrons created inside the patient from uniform scanning proton beams.Methods:Dose equivalent due to secondary neutrons was measured outside the primary field as a function of distance from beam isocenter at three different angles, 45, 90 and 135 degree, relative to beam axis. Plastic track nuclear detector (CR‐39 PNTD) was used for the measurement of neutron dose. Two experimental configurations, in‐air and cylindrical‐phantom, were designed. In a cylindrical‐phantom configuration, a cylindrical phantom of 5.5 cm diameter and 35 cm long was placed along the beam direction and in an in‐air configuration, no phantom was used. All the detectors were placed at nearly identical locations in both configurations. Three proton beams of range 5 cm, 18 cm, and 32 cm with 4 cm modulation width and a 5 cm diameter aperture were used. The contribution from internal neutrons was estimated from the differences in measured dose equivalent between in‐air and cylindrical‐phantom configurations at respective locations.Results:The measured ratio of neutron dose equivalent to the primary proton dose (H/D) dropped off with distance and ranged from 27 to 0.3 mSv/Gy. The contribution of internal neutrons near the treatment field edge was found to be up to 64 % of the total neutron exposure. As the distance from the field edge became larger, the external neutrons from the nozzle appear to dominate and the internal neutrons became less prominent.Conclusion:This study suggests that the contribution of internal neutrons could be significant to the total neutron dose equivalent.
SU‐E‐T‐556: Monte Carlo Generated Dose Distributions for Orbital Irradiation Using a Single Anterior‐Posterior Electron Beam and a Hanging Lens Shield
Authors: Duwel D , Lamba M , Elson H , Kumar N 
Published: June 2015

Purpose:Various cancers of the eye are successfully treated with radiotherapy utilizing one anterior‐posterior (A/P) beam that encompasses the entire content of the orbit. In such cases, a hanging lens shield can be used to spare dose to the radiosensitive lens of the eye to prevent cataracts.Methods:This research focused on Monte Carlo characterization of dose distributions resulting from a single A‐P field to the orbit with a hanging shield in place. Monte Carlo codes were developed which calculated dose distributions for various electron radiation energies, hanging lens shield radii, shield heights above the eye, and beam spoiler configurations. Film dosimetry was used to benchmark the coding to ensure it was calculating relative dose accurately.Results:The Monte Carlo dose calculations indicated that lateral and depth dose profiles are insensitive to changes in shield height and electron beam energy. Dose deposition was sensitive to shield radius and beam spoiler composition and height above the eye.Conclusion:The use of a single A/P electron beam to treat cancers of the eye while maintaining adequate lens sparing is feasible. Shield radius should be customized to have the same radius as the patient's lens. A beam spoiler should be used if it is desired to substantially dose the eye tissues lying posterior to the lens in the shadow of the lens shield. The compromise between lens sparing and dose to diseased tissues surrounding the lens can be modulated by varying the beam spoiler thickness, spoiler material composition, and spoiler height above the eye. The sparing ratio is a metric that can be used to evaluate the compromise between lens sparing and dose to surrounding tissues. The higher the ratio, the more dose received by the tissues immediately posterior to the lens relative to the dose received by the lens.
SU‐E‐T‐557: Monte Carlo Modeling of Philips RT‐250 Orthovoltage Unit for Beam Spectrum Modulation
Authors: Reynoso F , Cho S 
Published: June 2015

Purpose:To develop and validate a Monte Carlo (MC) model of a Phillips RT‐250 orthovoltage unit to test various beam spectrum modulation strategies for in vitro/vivo studies. A model of this type would enable the production of unconventional beams from a typical orthovoltage unit for novel therapeutic applications such as gold nanoparticle‐aided radiotherapy.Methods:The MCNP5 code system was used to create a MC model of the head of RT‐250 and a 30 × 30 × 30 cm3 water phantom. For the x‐ray machine head, the current model includes the vacuum region, beryllium window, collimators, inherent filters and exterior steel housing. For increased computational efficiency, the primary x‐ray spectrum from the target was calculated from a well‐validated analytical software package. Calculated percentage‐depth‐dose (PDD) values and photon spectra were validated against experimental data from film and Compton‐scatter spectrum measurements.Results:The model was validated for three common settings of the machine namely, 250 kVp (0.25 mm Cu), 125 kVp (2 mm Al), and 75 kVp (2 mm Al). The MC results for the PDD curves were compared with film measurements and showed good agreement for all depths with a maximum difference of 4 % around dmax and under 2.5 % for all other depths. The primary photon spectra were also measured and compared with the MC results showing reasonable agreement between the two, validating the input spectra and the final spectra as predicted by the current MC model.Conclusion:The current MC model accurately predicted the dosimetric and spectral characteristics of each beam from the RT‐250 orthovoltage unit, demonstrating its applicability and reliability for beam spectrum modulation tasks. It accomplished this without the need to model the bremsstrahlung xray production from the target, while significantly improved on computational efficiency by at least two orders of magnitude.Supported by DOD/PCRP grant W81XWH‐12‐1‐0198
SU‐E‐T‐559: Monte Carlo Simulation of Cobalt‐60 Teletherapy Unit Modeling In‐Field and Out‐Of‐Field Doses for Applications in Computational Radiation Dosimetry
Authors: Petroccia H , Li Z , Mendenhall N , Bolch W 
Published: June 2015

Purpose:Mean organ doses from structures located in field and outside of field boundaries during radiotherapy treatment must be considered when looking at secondary effects. Treatment planning in patients with 40 years of follow‐up does not include 3‐D treatment planning images and did not estimate dose to structures out of the direct field. Therefore, it is of interest to correlate actual clinical events with doses received.Methods:Accurate models of radiotherapy machines combined with whole body computational phantoms using Monte Carlo methods allow for dose reconstructions intended for studies on late radiation effects. The Theratron‐780 radiotherapy unit and anatomically realistic hybrid computational phantoms are modeled in the Monte Carlo radiation transport code MCNPX. The major components of the machine including the source capsule, lead in the unit‐head, collimators (fixed/adjustable), and trimmer bars are simulated. The MCNPX transport code is used to compare calculated values in a water phantom with published data from BJR suppl. 25 for in‐field doses and experimental data from AAPM Task Group No. 36 for out‐of‐field doses. Next, the validated cobalt‐60 teletherapy model is combined with the UF/NCI Family of Reference Hybrid Computational Phantoms as a methodology for estimating organ doses.Results:The model of Theratron‐780 has shown to be agree with percentage depth dose data within approximately 1% and for out of field doses the machine is shown to agree within 8.8%. Organ doses are reported for reference hybrid phantoms.Conclusion:Combining the UF/NCI Family of Reference Hybrid Computational Phantoms along with a validated model of the Theratron‐780 allows for organ dose estimates of both in‐field and out‐of‐field organs. By changing field size, position, and adding patient‐specific blocking more complicated treatment set‐ups can be recreated for patients treated historically, particularly those who lack both 2D/3D image sets.
SU‐E‐T‐566: Neutron Dose Cloud Map for Compact ProteusONE Proton Therapy
Authors: Syh J , Patel B , Syh J , Rosen L , Wu H 
Published: June 2015

Purpose:To establish the base line of neutron cloud during patient treatment in our new compact Proteus One proton pencil beam scanning (PBS) system with various beam delivery gantry angles, with or without range shifter (RS) at different body sites. Pencil beam scanning is an emerging treatment technique, for the concerns of neutron exposure, this study is to evaluate the neutron dose equivalent per given delivered dose under various treatment conditions at our proton therapy center.Methods:A wide energy neutron dose equivalent detector (SWENDI‐II, Thermo Scientific, MA) was used for neutron dose measurements. It was conducted in the proton therapy vault during beam was on. The measurement location was specifically marked in order to obtain the equivalent dose of neutron activities (H). The distances of 100, 150 and 200 cm at various locations are from the patient isocenter. The neutron dose was measured of proton energy layers, # of spots, maximal energy range, modulation width, field radius, gantry angle, snout position and delivered dose in CGE. The neutron dose cloud is reproducible and is useful for the future reference.Results:When distance increased the neutron equivalent dose (H) reading did not decrease rapidly with changes of proton energy range, modulation width or spot layers. For cranial cases, the average mSv/CGE was about 0.02 versus 0.032 for pelvis cases. RS will induce higher H to be 0.10 mSv/CGE in average.Conclusion:From this study, neutron per dose ratio (mSv/CGE) slightly depends upon various treatment parameters for pencil beams. For similar treatment conditions, our measurement demonstrates this value for pencil beam scanning beam has lowest than uniform scanning or passive scattering beam with a factor of 5. This factor will be monitored continuously for other upcoming treatment parameters in our facility.
SU‐E‐T‐572: Normal Lung Tissue Sparing in Radiation Therapy for Locally Advanced Non‐Small Cell Lung Cancer
Authors: Hong C , Ju S , Ahn Y 
Published: June 2015

Purpose:To compare normal lung‐sparing capabilities of three advanced radiation therapy techniques for locally advanced non‐small cell lung cancer (LA‐NSCLC).Methods:Four‐dimensional computed tomography (4DCT) was performed in 10 patients with stage IIIb LA‐NSCLC. The internal target volume (ITV); planning target volume (PTV); and organs at risks (OARs) such as spinal cord, total normal lung, heart, and esophagus were delineated for each CT data set. Intensity‐modulated radiation therapy (IMRT), Tomohelical‐IMRT (TH‐IMRT), and TomoDirect‐IMRT (TD‐IMRT) plans were generated (total prescribed dose, 66 Gy in 33 fractions to the PTV) for each patient. To reduce the normal lung dose, complete and directional block function was applied outside the normal lung far from the target for both TH‐IMRT and TD‐IMRT, while pseudo‐ OAR was set in the same region for IMRT. Dosimetric characteristics of the three plans were compared in terms of target coverage, the sparing capability for the OAR, and the normal tissue complication probability (NTCP). Beam delivery efficiency was also compared.Results:TH‐IMRT and TD‐IMRT provided better target coverage than IMRT plans. Lung volume receiving ≥–30 Gy, mean dose, and NTCP were significant with TH‐IMRT than with IMRT (p=0.006), and volume receiving ≥20–30 Gy was lower in TD‐IMRT than in IMRT (p<0.05). Compared with IMRT, TH‐IMRT had better sparing effect on the spinal cord (Dmax, NTCP) and heart (V45) (p<0.05). NTCP for the spinal cord, V45 and V60 for the heart, and Dmax for the esophagus were significantly lower in TD‐IMRT than in IMRT. The monitor units per fraction were clearly smaller for IMRT than for TH‐IMRT and TD‐IMRT (p=0.006).Conclusion:In LA‐NSCLC, TH‐IMRT gave superior PTV coverage and OAR sparing compared to IMRT. TH‐IMRT provided better control of the lung volume receiving ≥5–30 Gy. The delivery time and monitor units were lower in TD‐IMRT than in TH‐IMRT.