bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐J‐211: Design and Study of In‐House Software Based Respiratory Motion Monitoring, Controlling and Breath‐Hold Device for Gated Radiotherapy
Authors: Shanmugam Senthilkumar
Published: July 2014

Purpose:

The purpose of this present work was to fabricate an in‐house software based respiratory monitoring, controlling and breath‐hold device using computer software programme which guides the patient to have uniform breath hold in response to request during the gated radiotherapy.

Methods:

The respiratory controlling device consists of a computer, inhouse software, video goggles, a highly sensitive sensor for measurement of distance, mounting systems, a camera, a respiratory signal device, a speaker and a visual indicator. The computer is used to display the respiratory movements of the patient with digital as well as analogue respiration indicators during the respiration cycle, to control, breath‐hold and analyze the respiratory movement using indigenously developed software.

Results:

Studies were conducted with anthropomophic phantoms by simulating the respiratory motion on phantoms and recording the respective movements using the respiratory monitoring device. The results show good agreement between the simulated and measured movements. Further studies were conducted for 60 cancer patients with several types of cancers in the thoracic region. The respiratory movement cycles for each fraction of radiotherapy treatment were recorded and compared. Alarm indications are provided in the system to indicate when the patient breathing movement exceeds the threshold level. This will help the patient to maintain uniform breath hold during the radiotherapy treatment. Our preliminary clinical test results indicate that our device is highly reliable and able to maintain the uniform respiratory motion and breathe hold during the entire course of gated radiotherapy treatment.

Conclusion:

An indigenous respiratory monitoring device to guide the patient to have uniform breath hold device was fabricated. The alarm feature and the visual waveform indicator in the system guide the patient to have normal respiration. The signal from the device can be connected to the radiation unit in near future to carry out the gated radiotherapy treatment.
SU‐E‐J‐213: Imaging and Treatment Isocenter Verification of a Gantry Mounted Proton Therapy System
Authors: Price S , Goddu S , Rankine L , Klein E
Published: July 2014

Purpose:

The Mevion proton therapy machine is the first to feature a gantry mounted sychro‐cyclotron. In addition, the system utilizes a 6D motion couch and kV imaging for precise proton therapy. To quantify coincidence between these systems, isocentricity tests were performed based on kV imaging alignment using radiochromic film.

Methods:

The 100 ton gantry and 6D robotic couch can rotate 190° around isocenter to provide necessary beam angles for treatment. The kV sources and detector panels are deployed as needed to acquire orthogonal portals. Gantry and couch mechanical isocenter were tested using star‐shots and radiochromic‐film (RCF). Using kV imaging, the star‐shot phantom was aligned to an embedded fiducial and the isocenter was marked on RCF with a pinprick. The couch and gantry stars were performed by irradiating films at every 45° and 30°, respectively. A proton beam with a range and modulation‐width of 18 cm was used. A Winston‐Lutz test was also performed at the same gantry and couch rotations using a custom jig holding RCF and a tungsten ball placed at isocenter. A 2 cm diameter circular aperture was used for the irradiation.

Results:

The couch star‐shot indicated a minimum tangent circle of 0.6 mm, with a 0.9 mm offset from the manually marked isocenter. The gantry star‐shot showed a 0.6 mm minimum tangent circle with a 0.5 mm offset from the pinprick. The Winston Lutz test performed for gantry rotation showed a maximum deviation from center of 0.5 mm.

Conclusion:

Based on star‐shots and Winston‐Lutz tests, the proton gantry and 6D couch isocentricity are within 1 mm. In this study, we have shown that the methods commonly utilized for Linac characterization can be applied to proton therapy. This revolutionary proton therapy system possesses excellent agreement between the mechanical and radiation isocenter, providing highly precise treatment.
SU‐E‐T‐03: 3D GPU‐Accelerated Secondary Checks of Radiation Therapy Treatment Plans
Authors: Clemente F , Perez C
Published: July 2014

Purpose:

Redundant treatment verifications in conformal and intensity‐modulated radiation therapy techniques are traditionally performed with single point calculations. New solutions can replace these checks with 3D treatment plan verifications. This work describes a software tool (Mobius3D, Mobius Medical Systems) that uses a GPU‐accelerated collapsed cone algorithm to perform 3D independent verifications of TPS calculations.

Methods:

Mobius3D comes with reference beam models for common linear accelerators. The system uses an independently developed collapsed cone algorithm updated with recent enhancements. 144 isotropically‐spaced cones are used for each voxel for calculations. These complex calculations can be sped up by using GPUs. Mobius3D calculate dose using DICOM information coming from TPS (CT, RT Struct, RT Plan RT Dose). DVH‐metrics and 3D gamma tests can be used to compare both TPS and secondary calculations. 170 patients treated with all common techniques as 3DCFRT (including wedged), static and dynamic IMRT and VMAT have been successfully verified with this solution.

Results:

Calculation times are between 3–5 minutes for 3DCFRT treatments and 15–20 for most complex dMLC and VMAT plans. For all PTVs mean dose and 90% coverage differences are (1.12±0.97)% and (0.68±1.19)%, respectively. Mean dose discrepancies for all OARs is (0.64±1.00)%. 3D gamma (global, 3%/3 mm) analysis shows a mean passing rate of (97.8 ± 3.0)% for PTVs and (99.0±3.0)% for OARs. 3D gamma pasing rate for all voxels in CT has a mean value of (98.5±1.6)%.

Conclusion:

Mobius3D is a powerful tool to verify all modalities of radiation therapy treatments. Dose discrepancies calculated by this system are in good agreement with TPS. The use of reference beam data results in time savings and can be used to avoid the propagation of errors in original beam data into our QA system. GPU calculations permit enhanced collapsed cone calculations with reasonable calculation times.
SU‐E‐T‐10: A Dosimetric Comparison of Copper to Lead‐Alloy Apertures for Electron Beam Therapy
Authors: Rusk B , Hogstrom K , Gibbons J , Carver R
Published: July 2014

Purpose:

To evaluate dosimetric differences of copper compared to conventional lead‐alloy apertures for electron beam therapy.

Methods:

Copper apertures were manufactured by .decimal, Inc. and matching lead‐alloy, Cerrobend, apertures were constructed for 32 square field sizes (2×2 – 20×20 cm2) for five applicator sizes (6×6–25×25 cm2). Percent depth‐dose and off‐axis‐dose profiles were measured using an electron diode in water with copper and Cerrobend apertures for a subset of aperture sizes (6×6, 10×10, 25×25 cm2) and energies (6, 12, 20 MeV). Dose outputs were measured for all field size‐aperture combinations and available energies (6–20 MeV). Measurements were taken at 100 and 110 cm SSDs. Using this data, 2D planar absolute dose distributions were constructed and compared. Passing criteria were ±2% of maximum dose or 1‐mm distance‐to‐agreement for 99% of points.

Results:

A gamma analysis of the beam dosimetry showed 93 of 96 aperture size, applicator, energy, and SSD combinations passed the 2%/1mm criteria. Failures were found for small field size‐large applicator combinations at 20 MeV and 100‐cm SSD. Copper apertures showed a decrease in bremsstrahlung production due to copper's lower atomic number compared to Cerrobend (greatest difference was 2.5% at 20 MeV). This effect was most prominent at the highest energies with large amounts of shielding material present (small field size‐large applicator). Also, an increase in electrons scattered from the collimator edge of copper compared to Cerrobend resulted in an increased dose at the field edge for copper at shallow depths (greatest increase was 1% at 20 MeV).

Conclusion:

Apertures for field sizes ≥6×6 cm2 at any energy, or for small fields (≤4×4 cm2) at energies <20 MeV, showed dosimetric differences less than 2%/1mm for more than 99% of points. All field size‐applicator size‐energy combinations passed 3%/1mm criteria for 100% of points.

Work partially funded by .decimal, Inc. (Sanford, FL).
SU‐E‐T‐11: A Dosimetric Comparison of Robotic Prostatic Radiosugery Using Multi‐ Leaf Collimation Vs Circular Collimators
Authors: Feng J , Yang J , Lamond J , Lavere N , Laciano R , Ding W , Arrigo S , Brady L
Published: July 2014

Purpose:

The study compared the dosimetry plans of Stereotatic Body Radiotherapy (SBRT) prostate cancer patients using the M6 Cyberknife with Multi‐leaf Collimation (MLC) compared with the plans using G4 Cyberknife with circular collimators.

Methods:

Eight previously treated prostate cancer patients' SBRT plans using circular collimators, designed with Multiplan v3.5.3, were used as a benchmark. The CT, contours and the optimization scripts were imported into Multiplan v5.0 system and replanned with MLC. The same planning objectives were used: more than 95% of PTV received 36.25Gy, 90% of prostate received 40Gy and maximum dose <45Gy, in five fractions. For organs at risk, less than 1cc of rectum received 36Gy and less than 10cc of bladder received 37Gy. Plans were evaluated on parameters derived from dose volume. The beam number, MU and delivery time were recorded to compare the treatment efficiency.

Results:

The mean CTV volume was 41.3cc (27.5∼57.6cc) and mean PTV volume was 76.77cc (59.1∼99.7cc). The mean PTV coverage was comparable between MLC (98.87%) and cone (98.74%). MLC plans had a slightly more favorable homogeneity index (1.22) and conformity index (1.17), than the cone (1.24 and 1.15). The mean rectum volume of 36 Gy (0.52cc) of MLC plans was slightly larger than cone (0.38cc) and the mean bladder volume of 37 Gy was smaller in MLC (1.82cc) than in cone plans (3.09cc). The mean number of nodes and beams were 65.9 and 80.5 in MLC vs 65.9 and 203.6 in cone. The mean MUs were significantly less for MLC plans (24,228MUs) than cone (32,347MUs). The total delivery time (which included 5 minutes for setup) was less, 29.6min (26∼32min) for MLC vs 45min (35∼55min) for cone.

Conclusion:

While the differences in the dosimetry between the MLC and circular collimator plans were rather minor, the MLC plans were much more efficient and required significantly less treatment time.
SU‐E‐T‐13: A Feasibility Study of the Use of Hybrid Computational Phantoms for Improved Historical Dose Reconstruction in the Study of Late Radiation Effects for Hodgkin's Lymphoma
Authors: Petroccia H , O' Reilly S , Mendenhall N , Li Z , Slopsema R , Bolch W
Published: July 2014

Purpose:

Radiation‐induced cancer effects are well‐documented following radiotherapy. Further investigation is needed to more accurately determine a dose‐response relationship for late radiation effects. Recent dosimetry studies tend to use representative patients (Taylor 2009) or anthropomorphic phantoms (Wirth 2008) for estimating organ mean doses. In this study, we compare hybrid computational phantoms to patient‐specific voxel phantoms to test the accuracy of University of Florida Hybrid Phantom Library (UFHP Library) for historical dose reconstructions.

Methods:

A cohort of 10 patients with CT images was used to reproduce the data that was collected historically for Hodgkin's lymphoma patients (i.e. caliper measurements and photographs). Four types of phantoms were generated to show a range of refinement from reference hybrid‐computational phantom to patient‐specific phantoms. Each patient is matched to a reference phantom from the UFHP Library based on height and weight. The reference phantom is refined in the anterior/posterior direction to create a ‘caliper‐scaled phantom’. A photograph is simulated using a surface rendering from segmented CT images. Further refinement in the lateral direction is performed using ratios from a simulated‐photograph to create a ‘photograph and caliper‐scaled phantom’; breast size and position is visually adjusted. Patient‐specific hybrid phantoms, with matched organ volumes, are generated and show the capabilities of the UF Hybrid Phantom Library. Reference, caliper‐scaled, photograph and caliper‐scaled, and patient‐specific hybrid phantoms are compared with patient‐specific voxel phantoms to determine the accuracy of the study.

Results:

Progression from reference phantom to patient specific hybrid shows good agreement with the patient specific voxel phantoms. Each stage of refinement shows an overall trend of improvement in dose accuracy within the study, which suggests that computational phantoms can show improved accuracy in historical dose estimates.

Conclusion:

Computational hybrid phantoms show promise for improved accuracy within retrospective studies when CTs and other x‐ray images are not available.
SU‐E‐T‐20: A Novel Hybrid CBCT, Bioluminescence and Fluorescence Tomography System for Preclinical Radiation Research
Authors: Zhang B , Yang Y , Eslami S , Iordachita I , Patterson M , Wong J , Wang K
Published: July 2014

Purpose:

A novel standalone bioluminescence and fluorescence tomography (BLT and FT) system equipped with high resolution CBCT has been built in our group. In this work, we present the system calibration method and validate our system in both phantom and in vivo environment.

Methods:

The CBCT is acquired by rotating the animal stage while keeping the x‐ray source and detector panel static. The optical signal is reflected by the 3‐mirror system to a multispectral filter set and then delivered to the CCD camera with f/1.4 lens mounted. Nine fibers passing through the stage and in contact with the mouse skin serve as the light sources for diffuse optical tomography (DOT) and FT. The anatomical information and optical properties acquired from the CBCT and DOT, respectively, are used as the priori information to improve the BLT/FT reconstruction accuracy. Flat field correction for the optical system was acquired at multiple wavelengths. A home‐built phantom is used to register the optical and CBCT coordinates. An absolute calibration relating the CCD photon counts rate to the light fluence rate emitted at animal surface was developed to quantify the bioluminescence power or fluorophore concentration.

Results:

An optical inhomogeneous phantom with 2 light sources (3mm separation) imbedded is used to test the system. The optical signal is mapped onto the mesh generated from CBCT for optical reconstruction. Our preliminary results show that the center of mass can be reconstructed within 2.8mm accuracy. A live mouse with the light source imbedded is also used to validate our system. Liver or lung metastatic luminescence tumor model will be used for further testing.

Conclusion:

This hybrid system transforms preclinical research to a level that even sub‐palpable volume of cells can be imaged rapidly and non‐invasively, which largely extends the scope of radiobiological research.

The research is supported by the NCI grant R01CA158100‐01
SU‐E‐T‐22: A Novel Sub‐Pixel MTF Calculation Algorithm for Arbitrarily Shaped QA Phantoms
Authors: Sibley A , Wiersma R
Published: July 2014

Purpose:

Measurement of MV, kV, and CBCT imager resolution is recommended by AAPM Task Group 142 for commissioning and quality assurance. A sub‐pixel modulation transfer function (MTF) calculation algorithm was formulated for use with arbitrary shaped phantoms such as circular, ring, or rectangular shapes. This allows resolution to be measured on many commonly available phantoms such as the MV Las Vegas (square), kV Leeds (ring), and CBCT Catphan (circular).

Methods:

The algorithm was implemented in Python and takes the Laplacian of a phantom edge profile. The zero crossing of the Laplacian corresponds to the location of the edge. A 6th degree polynomial spline fitted to the Laplacian was used to interpolate the sub‐pixel position corresponding to the zero crossing of the Laplacian. Testing of the algorithm was performed on a square Las Vegas EPID phantom image with a pixel resolution of .784 mm. A linear fit was performed to the sub‐pixel localizations for each of the 4 edges of the Las Vegas phantom. This linear fit was taken to be the true location of the edges. This sub‐pixel localization allowed construction of a sub‐pixel ESF, which is then differentiated to obtain an LSF. The fast Fourier transform of the LSF is taken to obtain the MTF. A Hann window is also applied to the LSF. The MTF was normalized to its zero frequency.

Results:

The standard deviation from the linear fit for all sub‐pixel localizations was 0.12 pixels or .09 mm. An average MTF was produced corresponding to crossings of the 4 edges of our Las Vegas phantom.

Conclusion:

Our sub‐pixel edge localization allows computation of the MTF for an arbitrarily rotated Las Vegas phantom. Simple modifications to this algorithm would allow subpixel MTF calculation for arbitrarily rotated circular phantoms, ring phantoms, or any other potential phantom shape.

Research was partially funded by NIH Grant T32 EB002103‐21 from NIBIB. Contents are solely the responsibility of the authors and do not necessarily represent the official views of the NIBIB or NIH.
SU‐E‐T‐23: A Novel Two‐Step Optimization Scheme for Tandem and Ovoid (T&O) HDR Brachytherapy Treatment for Locally Advanced Cervical Cancer
Authors: Sharma M , Fields E , Todor D
Published: July 2014

Purpose:

To present a novel method allowing fast, true volumetric optimization of T&O HDR treatments and to quantify its benefits.

Materials and Methods:

27 CT planning datasets and treatment plans from six consecutive cervical cancer patients treated with 4–5 intracavitary T&O insertions were used. Initial treatment plans were created with a goal of covering high risk (HR)‐CTV with D90 > 90% and minimizing D2cc to rectum, bladder and sigmoid with manual optimization, approved and delivered. For the second step, each case was re‐planned adding a new structure, created from the 100% prescription isodose line of the manually optimized plan to the existent physician delineated HR‐CTV, rectum, bladder and sigmoid. New, more rigorous DVH constraints for the critical OARs were used for the optimization. D90 for the HR‐CTV and D2cc for OARs were evaluated in both plans.

Results:

Two‐step optimized plans had consistently smaller D2cc's for all three OARs while preserving good D90s for HR‐CTV. On plans with “excellent” CTV coverage, average D90 of 96% (range 91–102), sigmoid D2cc was reduced on average by 37% (range 16–73), bladder by 28% (range 20–47) and rectum by 27% (range 15–45). Similar reductions were obtained on plans with “good” coverage, with an average D90 of 93% (range 90–99). For plans with inferior coverage, average D90 of 81%, an increase in coverage to 87% was achieved concurrently with D2cc reductions of 31%, 18% and 11% for sigmoid, bladder and rectum.

Conclusions:

A two‐step DVH‐based optimization can be added with minimal planning time increase, but with the potential of dramatic and systematic reductions of D2cc for OARs and in some cases with concurrent increases in target dose coverage. These single‐fraction modifications would be magnified over the course of 4–5 intracavitary insertions and may have real clinical implications in terms of decreasing both acute and late toxicity.
SU‐E‐T‐26: A Study On the Influence of Photonuclear Reactions On the Biological Effectiveness of Therapeutic High Energy X‐Ray Beam
Authors: Wakita A , Matsufuji N , Kohno T , Kodaira S , Yokoyama K , Suzuki Y , Itami J
Published: July 2014

Purpose:

Photons from a modern high‐energy therapeutic linear accelerator used in X‐ray radiotherapy causes photonuclear reactions in an accelerator or patient's body. The aim of this study is to evaluate the biological effectiveness including these particles by Microdosimetric Kinetic Model (MKM) based on microdosimetry.

Methods:

A linear accelerator operating at 15 MV was used. CR‐39 was used to obtain LET spectra of secondary ions selectively, as CR‐39 is regarded insensitive to photons. CR‐39 was put on the central axis of the X‐ray beam at depths of 0, 5 and 10 cm in plastic phantom at a source to detector distance of 100 cm. Pits formed by the traversal of ions were etched then analyzed to obtain restricted LET distribution. Frequency‐mean and dose‐mean lineal energy was evaluated from the relationship between the restricted LET and the lineal energy required to evaluate the biological effectiveness by MKM. The relationship was calculated by Monte Carlo simulations with GEANT4.

Results:

Restricted LET distributions of secondary particles showed broad distributions that decreases exponentially with increasing LET. Frequency‐mean and dose‐mean lineal energy were determined uniquely within the scope of the energies of secondary particles generated from photons of 15 MeV. The frequency‐mean lineal energies at the depth of 0, 5 and 10 cm were 15.1, 16.0 and 19.7 keV/μm respectively, and the dose‐mean lineal energies were 18.6, 20.5 and 19.6 keV/μm, respectively. RBE of secondary particles for HSG cell evaluated by MKM was about 2.0 at all depths, and RBE of all particles including photons was evaluated 1.0.

Conclusion:

We investigated the biological effectiveness of secondary particles by photonuclear reactions. The method to evaluate RBE by MKM was established with measurements and simulations. However, the influence of these secondary ions on RBE was found negligible in the entire biological effectiveness of the high‐energy X‐ray.

This study has been supported by JSPS KAKENHI Grant Number 25861144.
SU‐E‐T‐28: A Treatment Planning Comparison of Volumetric Modulated Arc Therapy Vs. Proton Therapy for Post‐Mastectomy Radiotherapy
Authors: Hernandez M , Zhang R , Sanders M , Newhauser W
Published: July 2014

Purpose:

The delivery of post‐mastectomy radiotherapy (PMRT) can be challenging for patients with left‐sided breast cancer due to the PTV size and proximity to critical organs. This study investigates the use of protons for PMRT in a clinically‐representative cohort of patients, and quantitatively compares volumetric modulated arc therapy (VMAT) to proton therapy to have an evidence‐based rationale for selecting a treatment modality for these patients.

Methods:

Eight left‐sided PMRT patients previously treated at our clinic with VMAT were identified for the study. PTVs included the chest wall and regional lymph nodes. Passively scattered (PS) and intensity modulated proton therapy (IMPT) plans were constructed using the Eclipse proton planning system. The resulting plans were compared to the original VMAT plan on the basis of PTV coverage; dose homogeneity index (DHI) and conformity index (CI); dose to organs at risk (OAR); tumor control probability (TCP), normal tissue complication probability (NTCP) and secondary cancer complication probability (SCCP). Differences were tested for significance using the paired Student's t‐test (p<0.01).

Results:

All modalities produced clinically acceptable PMRT plans. The comparison demonstrated proton treatment plans provide significantly lower NTCP values for the heart and the lung while maintaining significantly better CI and DHI. At a prescribed dose of 50.4 Gy (RBE) in the PTV, the calculated mean NTCP value for the patients decreased from 1.3% to 0.05% for the whole heart (cardiac mortality) and from 3.8% to 1.1% for the lungs (radiation pneumonitis) for both proton therapy plans from VMAT plans. Both proton modalities showed a significantly lower SCCP for the contralateral breast compared to VMAT.

Conclusion:

All three plans (VMAT, PS, and IMPT) provide acceptable treatment plans for PMRT. However, proton therapy shows a significant advantage over VMAT with regards to sparing OARs and may be more advantageous for patients with unfavorable anatomy.
SU‐E‐T‐31: Alternative VMAT Technique Reduces Total Monitor Units for Lung SBRT
Authors: Happersett L , Mechalakos J , Kuo L , Zhang P , Rimner A
Published: July 2014

Purpose:

To investigate an alternative approach to VMAT optimization for hypofractionation lung treatment which increases average aperture opening and results in lower total Monitor Units (MU) without significantly sacrificing plan quality.

Methods:

Benchmark Volumetric Modulated Arc Therapy (bVMAT) plans were generated for 10 lung Stereotactic Body radiotherapy (SBRT) cases using Eclipse Version 11.0.42 (Varian Medical Systems) without a maximum MU constraint. Prescriptions ranged from 40 to 54Gy in 3 to 5 fractions. AAA dose calculation and PRO fluence based optimization was utilized. Two comparison VMAT plans were generated for each case, one that forced an initial “open” mlc aperture conformal to the tumor as a starting condition (oVMAT) with similar optimization parameters and arc geometries, and one that repeated the bVMAT optimization but added a maximum MU constraint (muVMAT). All plans used two arcs with lengths between 168 to 230 degrees. PTV D 95% and Dmean, lung V20 Gy, chest wall V30 Gy, average aperture opening and MU's were compared. Statistical significance was evaluated using Wilcoxon signed rank test.

Results:

Average PTV D(95), PTV mean and lung V20Gy over all plans was 99.2 ± 1.7%, 103.3 ± 0.6% and 7.8 ± 2.4% respectively. The average chest wall V30Gy was 61 ± 61 cc and ranged between 0 to 166 cc. There were no significant differences between the three techniques for the dosimetric quantities. MUs were reduced by 11 ±11% (p<0.01) and 25 ± 5% (p<0.01) and the average aperture size was increased by 13.7 ± 14% (p=0.02) and 35.8 ± 10% (p<0.01) with muVMAT and oVMAT, respectively, compared to bVMAT.

Conclusion:

oVMAT and muVMAT techniques were both able to increase average aperture size and reduce total MU compared to the benchmark VMAT plan, but the magnitude of the changes observed for oVMAT was larger.
SU‐E‐T‐32: An Application of GafChromic RTQA2 Film to the Patient Specified Quality Assurance
Authors: Peng J , Hu W
Published: July 2014

Purpose:

GafChromic RTQA2 film is known as a quality assurance (QA) tool for light field and radiation field verification. This study is attempted to apply the RTQA2 film to the patient specified quality assurance.

Methods:

Pre‐irradiated and post‐irradiated RTQA2 films were scanned in a reflection mode using a flatbed scanner. A plan‐based dose calibration method utilized the mapping information of calculated dose image and measured film image to create a dose vs. pixel value calibration model. This model was used to calibrate the measured film image from the pixel value (gray value) image to the dose image. The dose agreement between calculated and measured dose images were analyzed using the gamma analysis. To evaluate the feasibility of this method, three clinical approved RapidArc cases (one abdomen cancer and two head‐and‐neck cancer patients) were tested. The tolerance of 3% dose difference and 3 mm distance to agreement (DTA) and gamma index ≤ 1 were set for the analysis.

Results:

The calibrated film dose image from measurement was successfully compared to the predicted dose image from the commercial treatment planning. The gamma analysis results showed good consistency. Gamma passing rates were 99.02%, 94.84%, and 98.33% for the three patients, respectively.

Conclusion:

The plan based calibration method has the feasibility for dose verification without shortages of film batch and development time variation.
SU‐E‐T‐37: An Optical Investigation Into the Polarization and Scattering Effects Underlying the Artifacts of Radiochromic Film Dosimetry with Commercial Flatbed Scanners
Authors: Schoenfeld A , Poppinga D , Harder D , Doerner K , Poppe B
Published: July 2014

Purpose:

This study aims to investigate the optical properties of radiochromic EBT3 films on exposure to polarized incident light.

Methods:

An optical table setup was used to investigate the properties of exposed and unexposed EBT3 films. The films were placed with their long side horizontally and illuminated with polarized incident white light. The polarization of light with the electrical vector pointing vertically is referred to as 0°, accordingly horizontal orientation corresponds to 90°. The light transmission was measured depending on the polarization angle of the incident light and the polarization of a polarizer in front of the detector. Secondly, the scattering properties of exposed and unexposed films were measured by placing a plane convex lens behind the films and a screen in its focal plane. Thereby, the distribution of the scattering angles appears as an intensity map on the screen. The distributions of scattering angles caused by EBT3 films and by neutral density filters were compared.

Results:

EBT3 films show a strong dependence of the light transmission on the polarization of the incident light. With both polarizers parallel, a peak transmission was found at 90° orientation of the polarizers. With the rear polarizer at right angles with the front polarizer, peak transmissions were found at front polarizer orientations 45° and 135°. The scattering appears to be anisotropic with a preference direction parallel to the long side of the film. The portion of scattered light and the half value scattering angle both increase with the dose on the film.

Conclusion:

EBT3 films show dose dependent changes in polarized light transmission and anisotropic light scattering. These effects impair the light absorption measurements on exposed films performed with commercial flatbed scanners and are causing the well‐known artifacts of radiochromic film dosimetry with flatbed scanners, the “orientation effect” and the “parabola effect”.
SU‐E‐T‐44: Angular Dependence of Surface Dose Enhancement Measured On Several Inhomogeneities Using Radiochromic EBT3 Films
Authors: Jansen A , Schoenfeld A , Poppinga D , Chofor N , Poppe B
Published: July 2014

Purpose:

The quantification of the relative surface dose enhancement in dependence on the angle of incidence and the atomic number Z of the surface material.

Methods:

Experiments were performed with slabs made of aluminum, titanium, copper, silver, dental gold and lead. The metal slabs with equal sizes of 1.0×8.0×8.8mm3 were embedded in an Octavius 4D phantom (PTW Freiburg, Germany). Radiochromic EBT3 films were used to measure the surface dose for angles of incidence ranging from 0° to 90°. The setup with the metals slabs at the isocenter was irradiated with acceleration voltages of 6MV and 10MV. Water reference measurements were taken under equal conditions.

Results:

The surface dose enhancement is highest for angles of incidence below 30° and drops significantly for higher. The surface dose enhancement produced by lead and dental gold at 6MV showed a peak of 65%. At 90°, the surface dose enhancement dropped to 15% for both materials. The surface dose enhancements for silver, copper, titanium and aluminum were 45%, 32%, 22% and 12% at 0°, respectively. At an angle of incidence of 80°, the values dropped to 22%, 18%, 12% und 6%. The values for 10MV were very similar. Lead and dental gold showed peaks of 65% und 60%. Their values dropped to 18% at an angle of 90°. The surface dose enhancements for silver, copper, titanium and aluminum were 45%, 30%, 20% and 8% at 0°. At 80° the values dropped to 30%, 20%, 12% and 5%. A dependence of the magnitude of the surface dose enhancement on the atomic number of the surface material can be seen, which is in consistence with literature.

Conclusion:

The results show that the surface dose enhancements near implant materials with high Z‐values should be taken into consideration in radio therapy, even when the angle of incidence is flat.
SU‐E‐T‐49: Automatic Beam Angle Determination for Lung IMRT Planning Using a Beam Configuration Atlas
Authors: Yuan L , Ge Y , Yin F , Li Y , Sheng Y , Wu Q J.
Published: July 2014

Purpose:

To present a technique to automatically determine beam angle configurations for lung IMRT planning based on the patient‐specific anatomy and tumor geometry.

Methods:

The relationship between individual patient anatomy and proper beam configurations was learned from high quality clinical plans in three steps. First, a beam configuration atlas was obtained by classifying 60 lung IMRT plans into 6 beam configuration clusters based on a dissimilarity measure defined between different beam configurations. A beam configuration template was extracted from each cluster to form an atlas. Second, a beam efficiency index map (EI map) was constructed to characterize the geometry of the tumor relative to the lungs, the body and other OARs along each candidate beam direction. Finally, the EI maps of the clinical cases and the cluster assignments of their beam configurations were paired to train a Bayesian classification model. This technique was validated by leave‐one‐out cross validation with 16 cases randomly selected from the original dataset. An IMRT plan (autobeam plan) for each test case was generated using the beam configuration template according to the cluster assignment given by the model and was compared with the corresponding clinical plan.

Results:

The dosimetric parameters (mean±S.D. in percentage of prescription dose) in the auto‐beam plans and in the clinical plans, respectively, and the p‐values by a paired ttest (in parenthesis) are: lung Dmean: 16.3±9.3, 18.6±7.4 (0.48), esophagus Dmean: 28.4±18, 30.7±19.3 (0.02), Heart Dmean: 21.5±17.5,21.1±17.2 (0.76), Spinal Cord D2%: 48±23, 51.2±21.8 (0.01), PTV dose homogeneity (D2%–D99%): 22±27.4, 20.4±12.8 (0.10). The dose reductions by the autobeam plans in esophagus Dmean and cord D02 are statistically significant but the differences (<4%) may not be clinically significant. The other dosimetric parameters are not statistically different.

Conclusion:

Plans generated by the automatic beam angle determination method can achieve dosimetric quality equivalent to that of clinical plans.

Partially supported by NIH/NCI under grant #R21CA161389 and a master research grant by Varian Medical System.
SU‐E‐T‐235: Monte Carlo Analysis of the Dose Enhancement in the Scalp of Patients Due to Titanium Plate Backscatter During Post‐Operative Radiotherapy
Authors: Hardin M , Wolf E , Elson H , Warnick R , Lamba M
Published: July 2014

Purpose:

To quantify the clinically observed dose enhancement adjacent to cranial titanium fixation plates during post‐operative radiotherapy.

Methods:

Irradiation of a titanium burr hole cover was simulated using Monte Carlo code MCNPX for a 6 MV photon spectrum to investigate backscatter dose enhancement due to increased production of secondary electrons within the titanium plate. The simulated plate was placed 3 mm deep in a water phantom, and dose deposition was tallied for 0.2 mm thick cells adjacent to the entrance and exit sides of the plate. These results were compared to a simulation excluding the presence of the titanium to calculate relative dose enhancement on the entrance and exit sides of the plate. To verify simulated results, two titanium burr hole covers (Synthes, Inc. and Biomet, Inc.) were irradiated with 6 MV photons in a solid water phantom containing GafChromic MD‐55 film. The phantom was irradiated on a Varian 21EX linear accelerator at multiple gantry angles (0–180 degrees) to analyze the angular dependence of the backscattered radiation. Relative dose enhancement was quantified using computer software.

Results:

Monte Carlo simulations indicate a relative difference of 26.4% and 7.1% on the entrance and exit sides of the plate respectively. Film dosimetry results using a similar geometry indicate a relative difference of 13% and ‐10% on the entrance and exit sides of the plate respectively. Relative dose enhancement on the entrance side of the plate decreased with increasing gantry angle from 0 to 180 degrees.

Conclusion:

Film and simulation results demonstrate an increase in dose to structures immediately adjacent to cranial titanium fixation plates. Increased beam obliquity has shown to alleviate dose enhancement to some extent. These results are consistent with clinically observed effects.
SU‐E‐T‐237: Monte Carlo Dosimetric Characterization of the Mobetron Mobile Linac
Authors: Garcia F , Granero D , Vijande J , Perez‐Calatayud J , Ballester F
Published: July 2014

Purpose:

The aim of this work is to characterize dosimetrically a clinical intraoperative electron beam accelerator, Mobetron (IntraOp Medical, Inc.) in clinical use in our Hospital. Once this first step is completed our purpose is to evaluate shielding requirements for such a device by preparing adequate phase space files.

Methods:

It is known that electron beam simulation parameters required for state‐of‐the‐art Monte Carlo codes to obtain a good match with measured data, like the mean energy or the FWHM, may not be code‐independent due to the different set of process simulated and formalisms involved. Then, to cross‐check our results against any issue in the simulation we have compared experimental data (PDD and profiles for electrons in the range 4 to 12 MeV) with simulations performed independently using both Penelope2011 and Geant4 codes. To do so, the geometry and materials of the head of the accelerator have been fully characterized following information provided by the manufacturer.

Results:

Both simulations agree with experimental data within experimental uncertainties (±1 mm displacement), although small variations (less than 10%) in the mean energy and FWHM are required to match measured values depending on the code used.

Conclusion:

Independent Monte Carlo simulations were used to obtain an excellent match to measured electron dose distributions. This opens the road to use such data for evaluating shielding requirements which is the main objective of this project.
SU‐E‐T‐238: Monte Carlo Estimation of Cerenkov Dose for Photo‐Dynamic Radiotherapy
Authors: Chibani O , Eldib A , Price R , Mora G , Ma C
Published: July 2014

Purpose:

Estimation of Cerenkov dose from high‐energy megavoltage photon and electron beams in tissue and its impact on the radiosensitization using Protoporphyrine IX (PpIX) for tumor targeting enhancement in radiotherapy.

Methods:

The GEPTS Monte Carlo code is used to generate dose distributions from 18MV Varian photon beam and generic high‐energy (45‐MV) photon and (45‐MeV) electron beams in a voxel‐based tissueequivalent phantom. In addition to calculating the ionization dose, the code scores Cerenkov energy released in the wavelength range 375–425 nm corresponding to the pick of the PpIX absorption spectrum (Fig. 1) using the Frank‐Tamm formula.

Results:

The simulations shows that the produced Cerenkov dose suitable for activating PpIX is 4000 to 5500 times lower than the overall radiation dose for all considered beams (18MV, 45 MV and 45 MeV). These results were contradictory to the recent experimental studies by Axelsson et al. (Med. Phys. 38 (2011) p 4127), where Cerenkov dose was reported to be only two orders of magnitude lower than the radiation dose. Note that our simulation results can be corroborated by a simple model where the Frank and Tamm formula is applied for electrons with 2 MeV/cm stopping power generating Cerenkov photons in the 375–425 nm range and assuming these photons have less than 1mm penetration in tissue.

Conclusion:

The Cerenkov dose generated by high‐energy photon and electron beams may produce minimal clinical effect in comparison with the photon fluence (or dose) commonly used for photo‐dynamic therapy. At the present time, it is unclear whether Cerenkov radiation is a significant contributor to the recently observed tumor regression for patients receiving radiotherapy and PpIX versus patients receiving radiotherapy only. The ongoing study will include animal experimentation and investigation of dose rate effects on PpIX response.
SU‐E‐T‐239: Monte Carlo Modelling of SMC Proton Nozzles Using TOPAS
Authors: Chung K , Kim J , Shin J , Han Y , Ju S , Hong C , Kim D , Kim H , Shin E , Ahn S , Chung S , Choi D
Published: July 2014

Purpose:

To expedite and cross‐check the commissioning of the proton therapy nozzles at Samsung Medical Center using TOPAS.

Methods:

We have two different types of nozzles at Samsung Medical Center (SMC), a multi‐purpose nozzle and a pencil beam scanning dedicated nozzle. Both nozzles have been modelled in Monte Carlo simulation by using TOPAS based on the vendor‐provided geometry. The multi‐purpose nozzle is mainly composed of wobbling magnets, scatterers, ridge filters and multi‐leaf collimators (MLC). Including patient specific apertures and compensators, all the parts of the nozzle have been implemented in TOPAS following the geometry information from the vendor. The dedicated scanning nozzle has a simpler structure than the multi‐purpose nozzle with a vacuum pipe at the down stream of the nozzle.A simple water tank volume has been implemented to measure the dosimetric characteristics of proton beams from the nozzles.

Results:

We have simulated the two proton beam nozzles at SMC. Two different ridge filters have been tested for the spread‐out Bragg peak (SOBP) generation of wobbling mode in the multi‐purpose nozzle. The spot sizes and lateral penumbra in two nozzles have been simulated and analyzed using a double Gaussian model. Using parallel geometry, both the depth dose curve and dose profile have been measured simultaneously.

Conclusion:

The proton therapy nozzles at SMC have been successfully modelled in Monte Carlo simulation using TOPAS. We will perform a validation with measured base data and then use the MC simulation to interpolate/extrapolate the measured data. We believe it will expedite the commissioning process of the proton therapy nozzles at SMC.
SU‐E‐T‐240: Monte Carlo Modelling of SMC Proton Nozzles Using TOPAS
Authors: Mora G , Chibani O , Li J , Eldib A , Ma C
Published: July 2014

Purpose:

To simulate the 60Co beam from a novel Gamma—Tomo SBRT system and to calculate the output factors and dose rates for different source configurations and collimator sizes.

Methods:

The BEAM‐Monte Carlo code is used to realistically model the system geometry, including 32 source capsules, source housing, primary collimator and 4 different changeable collimators. The sources (6.22 mm of diameter) are located in 2 rows with different angles and distances to the longitudinal axis and the beams can be collimated to obtain four different circular field sizes at the isocenter (35 mm, 16 mm, 7mm, and 3.5mm). Since the dose distributions will be determined in a spherical polystyrene phantom of 8cm radius centered at the isocenter, a new geometry module is designed for the dose calculation.

Results:

: The caracteristics of the particle spectra emerging from each source are determined and the influence of the source position on the spectra reaching the isocenter is found to be minimal (<2%). We found that the scattered photons represent about 15% of the total number of photons reaching the scoring plane immediately (1 mm) below the source and primary collimator. The radial photon fluence does not vary significantly inside the collimator opening and decreases quickly beyond the 3cm radius (projected at the isocenter plane).

Conclusion:

Our preliminary results indicate that the position of the source and primary collimator assembly does not affect the energy spectra and fluence distributions reaching the isocenter significantly. This allows the use of a well‐represented source model for all the sources to perform the dose calculations for all the changeable collimators for this novel Gamma‐Tomo SBRT system.
SU‐E‐T‐242: Monte Carlo Simulations Used to Test the Perturbation of a Reference Ion Chamber Prototype Used for Small Fields
Authors: Vazquez Quino L , Calvo O , Huerta C , DeWeese M
Published: July 2014

Purpose:

To study the perturbation due to the use of a novel Reference Ion Chamber designed to measure small field dosimetry (KermaX Plus C by IBA).

Methods:

Using the Phase‐space files for TrueBeam photon beams available by Varian in IAEA‐compliant format for 6 and 15 MV. Monte Carlo simulations were performed using BEAMnrc and DOSXYZnrc to investigate the perturbation introduced by a reference chamber into the PDDs and profiles measured in water tank. Field sizes ranging from 1×1, 2×2,3×3, 5×5 cm2 were simulated for both energies with and without a 0.5 mm foil of Aluminum which is equivalent to the attenuation equivalent of the reference chamber specifications in a water phantom of 30×30×30 cm3 and a pixel resolution of 2 mm. The PDDs, profiles, and gamma analysis of the simulations were performed as well as a energy spectrum analysis of the phase‐space files generated during the simulation.

Results:

Examination of the energy spectrum analysis performed shown a very small increment of the energy spectrum at the build‐up region but no difference is appreciated after dmax. The PDD, profiles and gamma analysis had shown a very good agreement among the simulations with and without the Al foil, with a gamma analysis with a criterion of 2% and 2mm resulting in 99.9% of the points passing this criterion.

Conclusion:

This work indicates the potential benefits of using the KermaX Plus C as reference chamber in the measurement of PDD and Profiles for small fields since the perturbation due to in the presence of the chamber the perturbation is minimal and the chamber can be considered transparent to the photon beam.
SU‐E‐T‐247: Multi‐Leaf Collimator Model Adjustments Improve Small Field Dosimetry in VMAT Plans
Authors: Young L , Yang F
Published: July 2014

Purpose:

The Elekta beam modulator linac employs a 4‐mm micro multileaf collimator (MLC) backed by a fixed jaw. Out‐of‐field dose discrepancies between treatment planning system (TPS) calculations and output water phantom measurements are caused by the 1‐mm leaf gap required for all moving MLCs in a VMAT arc. In this study, MLC parameters are optimized to improve TPS out‐of‐field dose approximations.

Methods:

Static 2.4 cm square fields were created with a 1‐mm leaf gap for MLCs that would normally park behind the jaw. Doses in the open field and leaf gap were measured with an A16 micro ion chamber and EDR2 film for comparison with corresponding point doses in the Pinnacle TPS. The MLC offset table and tip radius were adjusted until TPS point doses agreed with photon measurements. Improvements to the beam models were tested using static arcs consisting of square fields ranging from 1.6 to 14.0 cm, with 45° collimator rotation, and 1‐mm leaf gap to replicate VMAT conditions. Gamma values for the 3‐mm distance, 3% dose difference criteria were evaluated using standard QA procedures with a cylindrical detector array.

Results:

The best agreement in point doses within the leaf gap and open field was achieved by offsetting the default rounded leaf end table by 0.1 cm and adjusting the leaf tip radius to 13 cm. Improvements in TPS models for 6 and 10 MV photon beams were more significant for smaller field sizes 3.6 cm or less where the initial gamma factors progressively increased as field size decreased, i.e. for a 1.6cm field size, the Gamma increased from 56.1% to 98.8%.

Conclusion:

The MLC optimization techniques developed will achieve greater dosimetric accuracy in small field VMAT treatment plans for fixed jaw linear accelerators. Accurate predictions of dose to organs at risk may reduce adverse effects of radiotherapy.