bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐FF‐T‐430: Comparison of Dose Volume Histograms From Selected Proton Therapy Treatments Between Geant4.5.0 and Geant4.9.0 Monte Carlo Simulations with and Without Dynamic Densities
Authors: Bednarz B , Hancox C , Paganetti H
Published: April 2010

Introduction: In order to reduce computation time for proton Monte Carlo dose calculations, our group has introduced a method to improve the voxel navigation algorithm in Geant4.5.0 and to dynamically assign material density in a given voxel element during particle transport. In the meantime, we have developed a new fast voxel navigation technique tailored to Geant4.9.0. Furthermore, Geant4.9.0 shows differences in the physics setup and tracking algorithm compared to the Geant4.5.0. Thus, the aim of this study was to assess whether defining all material densities corresponding to a given HU from the CT scan, i.e. without applying dynamic densities, would significantly impact the runtime for the new Geant4 version. In this study we compare dose‐volume histograms as well as runtime from selected proton therapy treatments between Geant4 Monte Carlo calculations using Geant4.5.0 with the dynamic density method and Geant4.9.0 without the dynamic density method. Methods and Materials: The two plans considered in this study were a spinal cord astrocytoma treatment and a prostate treatment. The differences between the Monte Carlo simulations with and without dynamic densities for each treatment were evaluated by plotting the dose‐volume histograms of the PTV and several other organs‐at‐risk considered in the treatment plan. In addition, the dose contours for each treatment and the contour differences were evaluated. Results: There are small discrepancies between dose calculations with and without dynamic densities, particularly in the GTV of both treatments. These discrepancies may suggest problems with the dynamic density method or problems with the CT conversion process used for generating the patient geometry. Conclusion: A comparison of dose calculations using Geant4.5.0 (including improved voxel navigation and dynamic density algorithm) and using Geant4.9.0 (including our new voxel navigation algorithm and no dynamic density algorithm) yields slight but not clinically significant differences with comparable run time.
SU‐FF‐T‐431: 4D Monte Carlo Dose Calculations for Particle Therapy Combined with a Computational Biomechanical Model of Lung Motion
Authors: Ishikawa KL , Takagi S , Matthys K , Wada S
Published: April 2010

Purpose: To evaluate the impact of respiratory motion on particle therapy and to realize 4D planning while keeping CT exposure as low as possible. To accomplish this, we develop a Monte Carlo dose calculation system combined with a computational biomechanical model of lung motion. Method and Materials: The human lung was CT scanned for a single phase of a respiratory motion. The CT images were transformed into tetrahedral elements by automated segmentation. Then, the respiratory motion was simulated using a computational biomechanical model called the spring network model, and the calculated 3D shape of the lung for a given phase was transformed to a voxel data set. For each phase, assuming carbon‐ion beam irradiation, biological dose distribution was calculated using the Monte Carlo particle and heavy ion transport code PHITS coupled with a microdosimetric kinetic model. The dose was mapped onto the reference data set to obtain the accumulated dose. Results: We have developed the first version of the 4D dose calculation system. The lung motion is realistically reproduced. The Monte Carlo module can successfully read the data set for each phase and calculate the accumulated dose. How many phases to use and their weights can be set arbitrarily, without need of additional CT scanning. Our first simulations for a 70 MeV/u carbon ion beam with a diameter of 2 cm indicate that the dose distribution can significantly change with phase and that many data sets may be needed to accurately evaluate the dose to the surrounding normal tissue. Conclusion: The impact of the system we developed is two‐fold: in the short term, it can be used to investigate different issues of 4D treatment planning; our goal is an entirely simulation‐based 4D planning from a single CT scanning. The system is being developed further.
SU‐FF‐T‐434: Neutron and Photon Fluence Distributions and Ambient Dose Equivalents for 250 MeV Proton Interactions in Tissue Using Geant4 Monte Carlo Code
Authors: Chen Y , Ahmad S
Published: April 2010

Purpose: To simulate interaction of 250 MeV protons in tissues using GEANT4 (version 4.8.3) Monte Carlo code that utilizes electromagnetic and hadronic interactions to determine the energy and angular distributions of generated neutron and photon and calculate H*(10) ambient dose equivalent for shielding purposes. Materials and Methods: A cylindrical phantom (length=42 cm, radius=21 cm, ICRU 4‐element soft tissue) was placed in vacuum. A spherical scoring geometry surrounding the phantom with radius = 100 cm was implemented. The energy of generated neutron, and photon crossing this geometry was counted in 9 theta bins (twenty degree each). The physics list consisted of electromagnetic; elastic; inelastic for proton, neutron and heavy ions. Common to all were standard electromagnetic for gamma, electron and positron; low‐energy parameterized electromagnetic for proton and ions; low‐energy parameterized nuclear elastic (G4LElastic) for proton and ions; and low energy parameterized inelastic for ions and binary cascade nuclear inelastic for proton. The elastic and inelastic processes for neutrons with energy higher than 4 eV (G4NeutronHPorLEModel) and lower than 4 eV (G4NeutronHPThermalScattering Data available in library G4NDL3.1) were used for computation. The ambient dose equivalent, H*(10), was calculated as a product of particle fluence, Φ, with the fluence to dose equivalent conversion factor available in the ICRP 74 report (1996). Results: The total number of generated particles per incident proton was 0.208 for neutron and 0.57 for photon. The neutron fluence (energy < 5 MeV) per proton was dominant in forward compared to lateral and backward directions. No substantial directional preferences were observed for photon fluence. H*(10) from neutron are in the forward (59%), backward (6.3%) and lateral directions (34.7%). H*(10) from photon was 7.2% to that from neutron. Conclusions: Monte Carlo simulations thus provided an improved understanding of the directional dependence of neutron and photon spectral fluences and dose equivalents.
SU‐FF‐T‐436: Comparison of Neutron Doses to a Water Target Exposed to a 10 MeV Neutron Beam: Foil Activation Method Vs. Monte Carlo Simulations
Authors: Gunasingha R , Howell C , Crowell A , Fallin B , Yoshizumi T , Song H , Tonchev A , Brady S , Anderson‐Evans C
Published: April 2010

We developed a mouse dosimetry model for neutron beam, and compared the calculated and simulated neutron doses for a water target (mouse) exposed to a 10 MeV neutron beam. We also estimated the longitudinal neutron dose profile for the water target. A water bottle (a simulated mouse, 6 cm × 1.3 cm radius) was exposed to a flux of 10 MeV neutrons produced via the d(d, n)He reaction using the Tandem accelerator at Triangle Universities Nuclear Laboratory at Duke University. An estimation of the neutron flux was obtained by neutron activations of two sets of aluminum and gold activation foils. One foil of each type was placed at the front and back sides of the water target. The flux was then calculated based on gamma spectroscopy of the irradiated foils using HPGe detectors. A Monte Carlo (MC) simulation based on FLUKA2008 code, was also used to estimate the 10 MeV neutron dose for the same geometry. The highest neutron flux measured using the activation technique was (8.538×106 +/− 6.89×104) n.cm−2.s−1 at the front end of the target. Using neutron kerma factors from ICRU data tables, the calculated dose rate to a water target at the location of the foil was (1.890+/− 0.015) Gy.hr−1. Using the data from the MC simulation, the calculated neutron dose to the front end of the water target was (1.870 +/− 0.001) Gy.hr−1. The dose calculated using the foil activation technique was in good agreement with the MC results. The slight discrepancy in the measured flux was likely the result of the closer position of the activation foils to the neutron source than the water bottle target, and also absorption within the activation foils. Assuming these results are in good agreement, we estimated the dose profile for the simulated mouse.
SU‐FF‐T‐439: Dynamic Monte Carlo Dose Calculations for IMRT in Geant4
Authors: Hancox C , Seco J , Sharp G , Peroni M , Paganetti H
Published: April 2010

Purpose: The effectiveness of IMRT to deliver highly conformal doses can be compromised in thoracic patients due to the presence of breathing motion. In order to study motion effects we have implemented a dynamic MLC model in a Geant4 based Monte Carlo system that allows movement of the leaves during the course of a simulation in direct analog to dynamic treatment delivery. We use Geant4 to investigate the effect of breathing motion in three lung patients. Method and Materials: We created a model of the Varian 2100C/D x/y jaws and MLC in Geant4 based on machine drawings. We validated our model by comparing open‐field penumbra and closed‐leaf transmission with measurements taken in‐house and found in the literature. We compared field‐by‐field photon fluence for a seven‐field IMRT treatment plan using dynamic dose delivery in Geant4 with that from an established Monte Carlo package. Step‐and‐shoot dose delivery was used, with each field utilizing between 23 and 39 distinct leaf configurations. Motion effects were investigated for three lung patients. For each patient, 4DCT data were binned into six breathing phases and then registered onto the exhale phase using deformable registration. Dynamic dose delivery was simulated for each breathing phase for comparison. Results: Closed‐leaf transmission of 1.5% using our Geant4 MLC model is in good agreement with values published in the literature and exhibits the characteristic picket‐fence profile expected from the tongue‐and‐groove geometry. Field‐by‐field comparison of photon fluence projected onto the isocenter plane shows 2%/2 mm agreement between Geant4 and the MLC model developed by Siebers et al (Phys. Med. Biol. 47, 3225 (2002)). Conclusion: We have implemented 4D Monte Carlo in Geant4 for IMRT using an in‐house model of the Varian x/y jaws and MLC. We have validated our model and simulated IMRT treatments in three lung patients based on 4DCT.
SU‐FF‐T‐443: Measurement of Lateral Dose Distributions Using GafChromic EBT Films and PTW Starcheck 2‐D Array
Authors: Xu L , McEwen M , Cojocaru C , Faddegon B
Published: April 2010

Purpose: One‐dimensional in‐air scans have been proposed for accurate Monte Carlo commissioning of clinically linac beams. The purpose of this work was to extend the measurement of such electron and photon dose distributions to two dimensions, in order to confirm the circular symmetry assumption of the 1‐D case and investigate differences previously reported between ion chamber scans and EGSnrc calculations. Method and Materials: Two systems were investigated ‐ GafChromic EBT film and the PTW Stacheck device ‐ and dose profiles were obtained for electron and photon beams from a Vickers research accelerator. A range of scattering foils (electron beams) and target materials (photon beams) were investigated for a 20 MeV beam. Prior to the investigation, both systems were accurately commissioned in beams from an Elekta Precise clinical linac. All results were compared with previously published 1‐D ion chamber and Monte Carlo data. Results: The EBT film measurements confirmed the circular symmetry of both electron and photon beams for all scatter foils and targets. Electron relative dose profiles measured using film were consistently narrower than Monte Carlo simulations, while ion chamber scans were broader than simulation. For X‐rays, relative dose profiles measured using film generally agree better with Monte Carlo than ion chamber profiles. X‐ray profiles measured by the Starcheck also show better agreement with Monte Carlo than 1‐D ion chamber scan. In comparing the two 2‐D systems, EBT film shows a lower uncertainty and smoother uniformity response than the Starcheck. Absolute X‐ray dose measurements using film and Starcheck showed significant target‐dependent differences of up to 5%. Conclusion: Both EBT film and Starcheck can be used to obtain relative dose profiles with uncertainties at the 2% level. The systematic difference between absolute dose measurement with the two systems suggests that the Starcheck is more sensitive to changes in X‐ray spectra.
SU‐FF‐T‐444: Validation and Benchmark of a Source Model for a Varian 6 MV Photon Beam Using Monte Carlo Calculations
Authors: Davidson S , Cui J , Kry S , Vicic M , Deasy J , White R , Ibbott G , Followill D
Published: April 2010

Purpose: Validation and benchmarking of a newly‐developed measurement‐driven source model based on Monte Carlo calculations. Method and Materials: A measurement‐driven model using the Dose Planning Method DPM dose calculation algorithm is being developed for use with Varian, Elekta, and Siemens 6 MV and 10 MV photon beams. The present work details the validation and benchmarking for the Varian 6 MV beam. The multi‐source model consists of a primary photon point source, an extra‐focal exponential disk source, and an electron contamination uniform disk source. The model accounts for fluence and off‐axis energy effects due to the flattening filter. Dose calculations for field sizes from 4 cm by 4 cm to 40 cm by 40 cm were performed and tested against the basic beam data measurements. In addition, an IMRT homogeneous plan, a stereotactic lung plan, and an IMRT lung plan were delivered to anthropomorphic phantoms housing TLD and radiographic film dosimeters for benchmark evaluations. Results: Comparisons between calculation and measurement of the PDD and dose profiles for all square field size configurations showed agreement within 2%/2 mm for 90% of the data tested. General agreement at the level of 3%/2mm for 85% of the data tested was found in both of the lung treatment plans. However, calculation of the highly modulated IMRT homogeneous plan showed an underestimation of dose of up to 8% locally in the center of the PTV. Conclusion: This work demonstrates a source model that is robust for the Varian 6 MV photon beam; however, only a simple MLC model that did not include the effects of the rounded leaf ends and interleaf leakage was used. We are currently evaluating a detailed MLC model to improve the agreement with measurement.

Conflict of Interest: Work supported by PHS CA010953, CA081647, and R01 CA85181 awarded by NCI, DHHS
SU‐FF‐T‐446: Deciphering Electron Dose Distributions in Ophthalmologic Radiation Therapy
Authors: Fournier‐Bidoz N , Dendale R , El Barouky J , Desjardins L , Fourquet A , Mazal A
Published: April 2010

Purpose: To decipher dose distributions of electron beams used in ophthalmologic treatments. Method and Materials: Eye region RT associates all the different ingredients that perturb electron fluence: surface irregularities (nose and eyeball), inhomogeneities (sinus air and orbital bone), small beam sizes. Two TPS were used (Eclipse‐Varian & Isogray‐Dosisoft) with 2 different algorithms: Pencil Beam (PB) and Monte Carlo (MC). Gafchromic film dosimetry was performed on an anthropomorphic head phantom. Adult and children size voxelized phantoms modeled the nose and eye contours with an intraorbital target bordered by structures of air on the medial side and bone on the lateral side (Fig.1). Dose distributions for an oblique anterior electron field, normalized at the geometric center of the target, were calculated at all energies, incorporating one or several of the complex ingredients. Their effect was quantified by the relative dose at the medial border (Dmed) and the lateral border (Dlat) of the virtual target, the 90% isodose volume and the target V90. Results: Gafchromic dosimetry showed a better accuracy of the MC model as seen on gamma index maps and profile analysis (Fig.2). The nose and eye external contours caused a peak dose of more than 110% at the eye and nose junction that was found in both PB and MC calculations (Fig.3b). MC model showed more dramatic changes in the dose distributions when air or bone was involved than the PB model: at 12MeV, Dmed decreased by 4% for MC and 1% for PB, whereas Dlat increased by 7% and 2% for MC and PB respectively (Fig.3c). The shape and size of the 90% isodose were affected by all factors. Conclusion: The phantom study quantifies the variations in electron dose distributions due to surface irregularities and inhomogeneities in ophthalmologic targets. Film dosimetry showed a better accuracy of MC dose calculations.
SU‐FF‐T‐452: The Manageable Levels of Induced Radioactivity in Medical Accelerators From High Energy Photon Beams
Authors: Han B , Nath R , Bateman F , Islam M , LaFrance M , Moore M , Thomadsen B , Xu X
Published: April 2010

Purpose: To summarize various relevant aspects of photon activation in medical linear accelerators using high energy x‐rays. Material and methods: For high energy medical accelerators (above 10 MV), One radiation safety concern is neutron production from photonuclear interactions which leading to exposure of personnel. Advanced radiotherapy use much longer beam‐on times for the same delivered dose compared to the conventional treatment. The activation dose to personnel can be substantially higher. The characteristics and levels of radiation from activation can be determined using measurements and Monte Carlo simulations. The activity buildup during weeks and the doses to patients and medical staffs can be estimated under typical clinical conditions. With detailed accelerator model, the location and quantity of activations can be determined using Monte Carlo simulation. Results: Most isotopes produced through photon and neutron activation processes were identified through measurements. The principal photon activation products decay primarily through beta emissions followed by gamma‐rays, with half‐lives from several minutes to several days. Most photon activations occur along the beam‐line components where the photon flux is the highest, while the neutron activations occur everywhere in the treatment room. The induced activities buildup from Mondays through Fridays and decay up through weekends. The additional exposure to the patient due to induced radioactivity is negligible compared to the overall radiation exposure during treatment. The additional exposure to the staff is small at an estimated level of about 1–2 mSv/yr which is below the safety limits. Conclusions: The potential hazard to staff from induced radioactivity in the use of high energy x‐rays is considered to be low and manageable. ALARA principles are followed when deciding steps to reduce this small exposure to an even lower level. The dose reduction strategies suggested should be followed only if these actions are considered reasonable and practical in the individual clinics
SU‐FF‐T‐454: Impact of CT Number and Electron Density in Proton Dose Distribution
Authors: Kuros‐Zolnierczuk J , Das I , Shahnazi K , Tasson A , Allgower C
Published: April 2010

Purpose: The dosimetric impact of different CT number to electron density calibrations used in proton beam treatment planning with emphasis on the dose coverage to targets and organs at risk (OAR) is evaluated. Method: A body CT phantom containing multiple plugs of varying density was scanned to measure CT numbers under different imaging protocols using various tube voltages: 80, 100, 120 and 140kVp on a GE CT simulator. The CT number versus electron density tables were generated for each image at various kVp used clinically. The calibration tables were imported into a CMS proton treatment planning system and used to investigate their impact on real patient dose calculations. Dose volume histograms (DVHs) were calculated using different CT number to electron density calibration tables for various patients (prostate, H&N, lung). Results: The CT number is shown to be a factor of kilovoltage, field of view and reconstruction algorithm. However, its effect on PTV and OAR dose distribution is very small for most clinical situations. The CT values with 80kVp led to the largest deviation with small volume structures like cochlea and optic nerve. The low kVp has higher CT number for most cases compared to higher kVp. The dosimetric differences between the most commonly used cases (140 kVp and 120 kVp) were negligible (less than 1%). Conclusion: Even though CT number differs with tube voltage appreciably, its impact on dosimetry is relatively small (< 2%). The differences are minimal in low density tissue (lung) and largest for high density material like a prosthesis where the accuracy of CT number and dose calculation is uncertain. It is concluded that small changes in CT number due to scanning technique have little dosimetric impact in proton beam planning.
SU‐FF‐T‐455: Methodology to Incorporate the BED and EUD in Patient‐Specific 3‐Dimensional Dosimetry for Non‐Hodgkin's Lymphoma Patients Targeted with 131I Tositumomab Therapy
Authors: Amro H , Wilderman S , Dewaraja Y , Roberson P
Published: April 2010

Purpose: The efficacy of targeted radionuclide therapy depends on the uniformity of radionuclide distribution within the target volume as well as on the radiosensitivity of the tissue. The inclusion of dose non uniformity and biologic effects in the dosimetry of radionuclide may help in correlating dose with patient outcome. Our goal is to develop a methodology incorporating the biologic equivalent dose (BED) and the equivalent uniform dose (EUD) formalism for radionuclide dosimetry. Materials and Methods: A 3D imaging‐based patient‐specific dosimetry methodology was applied to six non‐Hodgkin's lymphoma (NHL) patients treated with I‐131 labeled tositumomab for model evaluation purposes. Six registered SPECT/CT scans were obtained for each patient and used to generate 3D dose rate distributions using a Monte Carlo code. The dose rate distributions were integrated over time to obtain 3D time‐dependent absorbed dose distributions using fitted activity curves. Radial deformation model was used to account for tumor regression during therapy relative to initial volume. 3D time‐dependent biological equivalent dose (BED) distributions were calculated and used to estimate a single equivalent uniform dose (EUD) for each tumor volume. Results: The methodology developed in this work allows for the adjustment of model parameters such as radiosensitivity, proliferation, unlabeled protein effect, and clearance time based on patient data. Model outputs are being validated against tumor regression. The EUD values for the tumors included in this study show a reduction between 11% −23% in the efficiency of dose delivery and appear to correlate with tumor regression better than total tumor dose. Conclusions: The methodology developed in this work allows for the inclusion of various effects that influence the effectiveness of targeted radionuclide therapy of NHL. Model parameters could be adjusted to aid in improving predictions of patient outcome.
SU‐FF‐T‐456: A Comparison of Cysto‐Conray II to Readi‐Cat 2 Contrast Material for Use in Rectal Balloons During Proton Therapy
Authors: Tasson A , Fitzek M , Shahnazi K , Simmons J , Simoneaux V , Speights D , Sullivan‐Dickey M , Thornton A , Wallace D
Published: April 2010

Purpose: In our clinic, a rectal balloon filled with contrast is used to fixate and localize the prostate during proton treatments. We have traditionally used a 70%/30% mixture of water/Cysto‐Conray II, which is iodine‐based. After having a small leak in a rectal balloon, an alternative solution was investigated, namely Readi‐Cat 2 (a barium sulfate suspension), due to iodine related allergies, as well as increasing cost of the contrast, and dilution requirements. Method and Materials: The likelihood of an allergic reaction, as well as cost, was evaluated for the Cysto‐Conray and Readi‐Cat. The electron densities were compared by importing a CT scan of the contrast agents into a treatment planning work station. A depth scan was taken in a water tank after the proton beam passed through the contrast agents allowing the attenuation of the proton beam to be measured. X‐rays were taken of patients where rectal balloons containing both types of contrast were used and evaluated. The amount of preparation required for the Cysto‐Conray and Readi‐Cat was also considered. Results: The Readi‐Cat 2 has a lower risk of an allergic reaction and is six times less expensive than the Cysto‐Conray. The electron densities were found to be 1.18 and 1.28 for the Readi‐Cat and Cysto‐Conray respectively. Both contrast agents have comparable proton range attenuation and visibility on x‐rays. The Cysto‐Conray requires being diluted with water, whereas the Readi‐Cat has no dilution requirements. Conclusions: It has been determined that the Readi‐Cat 2 is a contrast agent that can be used instead of the Cysto‐Conray II solution. The Readi‐Cat is cheaper than the Cysto‐Conray, has a minimal risk of allergy, has a comparable attenuation of the proton beam, can be easily seen with the imaging equipment in the treatment room, and requires no dilution before using.
SU‐FF‐T‐459: The Effect of Proton Therapy Beam Scanning Pattern Size On Secondary Neutron Dose Equivalent
Authors: Hecksel D , Anferov V , Shahnazi K , Fitzek M
Published: April 2010

Purpose: One way to deliver a proton therapy beam is to actively scan a uniform dose across a treatment field using a fast scanning magnet. In this study, we examine how proton therapy beam scanning patterns affect the scattered neutron dose equivalent in an active scanning proton therapy beam delivery nozzle. Method and Materials: The nominal scanning pattern size is a 324 cm2 rectangular pattern which projects a flat proton field of 12 × 12 cm at isocenter for a 12 cm snout size. However, it is possible to reduce the size of this scanning pattern for field sizes smaller than 12 cm and maintain beam flatness while minimizing the scattered neutron dose equivalent. Neutron measurements were taken using a SWENDI‐II (Thermo Electron Corporation™) neutron detector for a treatment field defined by apertures of 10 cm and 5 cm in diameter using protons of approximately 160 MeV. In each case, the field modulation in depth was 10 cm. A Scanditronix Matrixx™ panel was used to determine field flatness. Results: The maximum neutron dose equivalent was measured to be 0.65 mSv/Gy for the 10 cm field and 0.97 mSv/Gy for the 5 cm field 40 cm laterally from isocenter. By minimizing the rectangular scanning pattern, it was possible to reduce the secondary neutron dose equivalent by approximately 20% and 60% for the 10 cm and 5 cm diameter field sizes respectively and maintain acceptable treatment parameters. Conclusion: The efficiency of a proton treatment beam through the final patient collimator has a large influence on the creation of unwanted secondary neutrons. Increasing this efficiency using different scanning patterns minimizes neutron dose equivalent and maintains acceptable treatment parameters for the therapeutic proton beam.
SU‐FF‐T‐462: Treatment of Retinoblastoma Using Different Proton Delivery Methods: Scattering, Rectangular Scanning, and Circular Scanning
Authors: Shahnazi K , Chang A , Anferov V , Hecksel D , Thornton A , Moyers M , Fitzek M
Published: April 2010

Purpose: The high risk of radiation induced malignancy in retinoblastoma with conventional radiotherapy makes treatment with proton beams advantageous since it minimizes exposure of normal tissue in brain and orbit. Until recently, only scattered proton beams were used. In this study we compare contaminating neutron dose from three different beam delivery methods: passive scattering, uniform scanning with a rectangular scan pattern, and uniform scanning with a circular scan pattern adjusted to the target size. In all three scenarios the same brass aperture was used. Methods: CT scans of three patients with retinoblastoma were selected for treatment planning. Patients were treated under anesthesia using an ocular suction cup. Two patients had bilateral, one had unilateral treatment. The plans were reproduced in a phantom using the three delivery methods described above. Dose distributions were measured with MAGIC gel placed inside the phantom with readout performed using MRI. Neutron doses to the phantom were measured using Bubble detectors (Bubble Technology Industries™) and a SWENDI‐II (Thermo Electron Corporation™) detector. Results: In all three patients dose to the ethmoid bone and the frontal lobe was minimized by protons. When the optimized circular beam scanning pattern was used, secondary neutron dose was lower compared to both the rectangular scanning pattern and the passively scattered beam. For a 3 cm circular aperture, the secondary neutron component was 0.23 mSv/Gy for a 12×12 cm rectangular pattern. It was 80% lower for a 4cm optimized circular scan pattern and 15% higher for a 12cm diameter double scattered field. Conclusions: Delivery of proton beams using a scan pattern adjusted to the shape of the treatment field yields comparable dose distributions to conventional proton beam delivery but has the advantage of delivering less contaminating neutron dose to the patient.
SU‐FF‐T‐463: Analytic Technique to Calculate the Out‐Of‐Field Dose From IMRT Therapy
Authors: Kry S , Childress N , Howell R , Stovall M
Published: April 2010

Purpose: IMRT has become a standard technique for the treatment of many tumors. It is often important to know the out‐of‐field dose associated with such treatments, such as for fetal dose evaluation, or estimating organ doses during epidemiologic study of second cancer risk. While evaluating such doses is routine for conventional therapies (e.g., Task Group 36 data), no simple technique is available to estimate doses from IMRT treatments. This work develops and evaluates such a technique. Method and Materials: A simple equation was developed to calculate the out‐of‐field dose (Dimrt) from an IMRT treatment based on treatment parameters and the out‐of‐field dose from conventional therapy (Dconv) with the same jaw setting (which is readily estimated from such sources as TG‐36). The accuracy of this equation was tested by comparing out‐of‐field doses calculated with the developed equation to those calculated for IMRT treatments using Monte Carlo. Results: The following equation was developed to estimate the out‐of‐field dose from IMRT: Dimrt=Dcon[P×CF + (L+C)×MF], where P, L, and C are the fraction of the out‐of‐field dose originating from patient scatter, head leakage, and collimator scatter respectively, CF is the fraction of the open field covered by the CIAO field (continuous irradiated area opening), and MF is the IMRT MU modulation factor. These values are tabulated for typical treatments. Compared to the out‐of‐field dose from IMRT, doses calculated with this equation generally agreed within 25%. Larger variations were sometimes observed, particularly within 5cm of the edge of the treatment field where large variations in the out‐of‐field dose are expected due to its dependence on the particular treatment plan and planning objectives. Conclusion: A simple and suitably accurate equation was derived to calculate the out‐of‐field dose from IMRT treatments. This technique represents a viable approach for estimating the out‐of‐field dose for clinical or epidemiological applications.
SU‐FF‐T‐468: Comparison of Target Dose Inhomogeneity for Four Different Techniques of Breast Cancer Treatment
Authors: Kim Y , Trombetta M , Werts E
Published: April 2010

Purpose: To evaluate target dose inhomogeneity for four different breast cancer treatment techniques. Method and Materials: External beam radiotherapy (EBRT) was performed for 12 patients each using either whole or 3D conformal partial breast irradiation (WBI or PBI), 19 patients with high dose rate (HDR) MammoSite® brachytherapy and 13 patients with Contura® multi‐lumen applicator. The PTV_EVAL volume was defined by following NSABP B‐39/RTOG 0413 for PBI, MammoSite® and Contura® while retrospectively delineated for WBI. The differential dose volume histogram was evaluated using mean dose (Dm) and most probable dose (Dmp) relative to prescribed dose (Dpr) and root mean square deviation (RMSD). The biologically effective dose (BED) accounting for non‐uniform dose distribution was computed. Generalized equivalent uniform dose (gEUD) was calculated together with dose homogeneity index (DHI) and conformal index (COIN). Results: Compared to EBRT, the target received higher dose with HDR (Dm: 143% vs. 101%, Dmp: 111% vs. 101%) which increased BED values (77 Gy vs. 73 Gy for fibrosis, 56 Gy vs.47 Gy for erythema, and 63 Gy vs. 57 Gy for breast carcinoma, respectively) and dose inhomogeneity (RMSD: 12.1 vs. 1.8). Due to steeper dose fall‐off, HDR plans were more conformal than EBRT (COIN: 0.84 vs. 0.45). Compared to MammoSite®, Contura® yielded slightly higher dose (BED difference < 0.5 Gy and 0.3 Gy higher in gEUD) which increased DHI by 5% and COIN by 1%. The PBI had large inter‐patient variability of BED values (2–8 times > others) and the smallest BED and gEUD values. The WBI had large inter‐patient variability of gEUD values (14 times > others) due to cold spots. Conclusion: Despite greater inhomogeneity, HDR plans have higher target dose conformality and are less patient‐specific than EBRT plans. However, based on the biological and dosimetric data, the four different techniques are clinically comparable.
SU‐FF‐T‐474: QA of Dose‐Volume Histogram
Authors: Cheng C , Das I , Srivastava S , Gao Z
Published: April 2010

Purpose: Among the various tools used in evaluating the quality of a treatment plan, dose‐volume histogram (DVH) has become the most important plan evaluation tool. DVH has also been used in TCP and NTCP calculations to aid in plan selection. The accuracy of a dose‐volume relationship of a particular structure depends on the size of the calculation dose grid, but more critically on the contouring of a structure and the dose algorithm used by a treatment planning system (TPS), especially in the presence of heterogeneities. This paper presents a comprehensive review on the calculation of DVH, and attempts to answer the following questions: (1) How do we verify that a DVH calculation is correct? and (2) What is the optimal grid size used in DVH calculation? Materials & Methods: DVHs of rectangular and cylindrical structures of known volumes are calculated for a single 6 MV beam setup. Various grid sizes (1.5mm–10mm) and calculation box sizes are studied. In addition, DVHs of various structures uploaded from VoxelQ software are calculated for 3 disease sites (Prostate, Lung and H&N) with different treatment planning systems (TPS). The volume information from the TPS is then compared with that from VoxelQ. Results: All grid sizes give the same total volume of a structure, even for such small structures as the lens (<0.5 cm3). However, the shape of the DVH is grid size dependent. Grid sizes 2–4 mm yield practically identical DVHs, even for small structures and with the presence of heterogeneity. Largest volume difference (>50%) between TPS with pencil beam algorithm and VoxelQ is observed for small structures. VoxelQ provides a good estimation of the volume of a structure, whereas a TPS may not necessarily provide adequate volume information. Conclusions: DVH QA should be performed with known structures from CT‐simulation as part of TPS commissioning.
SU‐FF‐T‐479: Design of a Flexible, Web Accessible, Clinical Outcomes Database to Support Evidenced Based Radiation Treatment Planning
Authors: Mayo C , Riberdy C , Steadman B , Deegan R
Published: April 2010

Purpose: Lack of patient outcome data for use in retrospective examinations is a notorious problem both for large and small clinics wishing to gain insight on their control rates and morbidity statistics and to correlate these with DVH based endpoints. Often spread sheet based approaches are attempted, but these typically prove inadequate for addressing the department wide problem. Most clinics lack the resources to design databases sufficiently flexible to accommodate evolving determination of clinical endpoints and design of an interface that integrates easily into daily clinical practice. The object of this research was to develop a database and web based interface, to solve these problems and which could be shared as part of an open source effort among multiple institutions. Method and Materials: Objectives for SQL database design were 1) ability to store DVH data and analysis 2) ability to accommodate new or evolving studies without modification of table structure 3) ability to integrate with other department objectives e.g. QA 4) ability to import data from current record and verify system. Web based interface and database were used to conduct internal outcome studies for several anatomic target sites. Results: Meta data tables were used to define, and manage queries from independent endpoint data tables. Database and interface have proven clinical viability and become part of our program to improve documentation. Data reports can be web or spreadsheet based. Largest hurdle for implementation was staff time for data input from charts not yet structured to simplify locating endpoint data. Conclusion: Department databases for monitoring outcome are needed to support evidenced based approach to treatment design. The current application works, is inexpensive, and is promising as the basis of a multi‐institutional open source effort.

Conflict of Interest: Work was supported in part by a grant from Varian Medical Systems
SU‐FF‐T‐481: Computerized Implementation of Radiation Treatment Planning Directives
Authors: McShan D , Kessler M , Keranen W , Fraass B
Published: April 2010

Purpose: This presentation describes the implementation of a system for capturing radiation treatment planning directives. These directives capture site and protocol specific requirements for the various processes required for planning namely imaging studies, registration, contouring, and specification of target goals, and planning objectives. Method and Materials: The computer software used for this work is based on an open‐source electronic healthcare record (EHR) system . The software is based on industry standards and runs on a windows server, is written in Java, a standard database, and provides a web‐based user interface. The system uses a data model based on the HL7 V3 and continuity of care records. Patient related information (documents) trigger a rules‐based decision support engine that is used to maintain lists and initiate messaging to external systems. Documents can also be fed to the system via messages from external system. Customizations of this system have been made to capture and manage template treatment planning directives that are then selected and modified to create patient specific directives. Rules have been created and are triggered by completing various components of the planning directives. Over 50 treatment planning directives have been developed using paper forms and these have served as a guide for the development of the data requirements and user input styles. Extensive processes mapping has been undertaken to determine the best ways to implement this system within our clinical environment. Results: The resulting system has been used to implement most of our current planning directives. Messages from the hospital's HL7 feed provide basic patient identification information and clinical results as needed. Various worklists are maintained along with e‐mail notifications, and communications with our planning system are used to initialize planning parameters. Conclusion: This system for computer‐supported management of treatment planning directives has proven to be flexible and extensible.
SU‐FF‐T‐483: Optical Enhancement of DNA‐Base Radio‐Resistivity
Authors: Abolfath M , Papiez L , Stojadinovic S , Solberg T
Published: April 2010

Purpose: Manipulation of the radio‐sensitivity of the DNA molecules driven by the spin blockade mechanism of diffusive free radicals against ionizing radiation. Materials and methods: We propose a mechanism which uses the simultaneous application of circularly polarized light and an external magnetic field to control the polarization of the free radicals and create S=1 electron‐hole spin excitations (excitons) on DNA molecules. We deploy an ab‐initio molecular dynamics model to calculate the characteristic parameters of the light needed for optical transitions. Results: As a specific example, we present the numerical results calculated for a nucleotide‐base, e.g., Guanine, in the presence of an OH free radical. To increase the radio‐resistivity of this system, an infra‐red and a blue light source for the optical pumping of free radicals and induction of excitons on guanine can be used. Conclusions: The effect of spin‐injection on the formation of a free energy barrier in diffusion controlled chemical reaction pathways leads to the control of radiation‐induced DNA damage. The proposed method allows us to manipulate and partially suppress the damage induced by ionizing radiation.
SU‐FF‐T‐485: Monte Carlo Simulation for DNA Damage in Gold Nanoparticle Solution
Authors: Lee M , Hsiao Y , Chao T , Tu S
Published: April 2010

Purpose: We used EGS4 based BEAMnrc and newly developed fast Monte Carlo damage simulation (MCDS) programs to theoretically evaluate the DNA damage yields, including single‐strand breaks (SSBs) and double strand breaks (DSBs), in the simulated laboratory bench‐top settings of two monolayer cell cultures when irradiated by x‐ray photons. Method and Materials: A layer of water with 10 μm in thickness and 1.0 g cm−3 in density was placed in a container, mimicking to the laboratory cell culture environment. The dish is square‐shaped with 2.6 cm for the length, 2.6 cm for the width at the bottom, and 5 mm for the height. The cell culture dish was then irradiated by a broad parallel simulated photon beam. All these settings were precisely modeled in the EGS4 based BEAMnrc program. Results: Our simulation results suggested that the DSB yield is the largest (9.03) when irradiated by the 30 KeV photons and lowest (8.41) when irradiated by the 1 MeV photons for the gold nanoparticle (GNP) solution. While the SSB yield is the largest (189.21) when irradiated by the 1 MeV photons and nearly the same (186.52 and 186.70) when irradiated by the 30 and 100 KeV photons for the GNP solution. When compared the damage yields between GNP and water solution, the yields were almost identical, with the exception of the irradiation case of 100 KeV photons, DSB yield in GNP solution (8.88) is less than in water (9.17) and SSB yield in GNP solution (186.7) is larger than the yield in water (186.19). Conclusion: Among those nanotechnology applications, gold nanoparticles have been developed and progressed as an excellent x‐ray imaging contrast agent for small animal model study. Our DNA damage simulation results should serve as the prior indication of biological consequences when gold nanoparticles are used in the various molecular imaging techniques.
SU‐FF‐T‐487: Saturation of Repair Model for Cell Survival Applied to X‐Ray and Carbon‐Ion Irradiation
Authors: Luxton G
Published: April 2010

Purpose: To develop and test a model for cell survival after irradiation which ascribes differences in effect of x‐ray and Carbon‐ion beams to dependence on LET of effective available repair units. Methods and Materials: A model by Goodhead of the saturation of the mechanism for cellular repair of radiation damage is shown to behave as a log survival linear‐quadratic (LQ) function of dose at levels which do not saturate the repair and linearly for doses that do. This model is applied to published data for both X‐ray and C+6‐ion beam survival data extending to ∼ 4 × 10−3 survival for stationary phase Chinese hamster lung (V‐79) cells irradiated in the plateau and in the extended Bragg peak of a 400 MeV per amu heavy‐ion beam at LBL by Chapman et al. The same parameters of the model that fit the X‐ray survival data are used to fit the C+6‐ion beam data, except that the parameter defining the available cellular effective repair is allowed to vary according to the location of the irradiation in the extended Bragg peak. The model is also fitted to recently published data, including irradiated cultured cells of human lung cancer origin extending to a single dose 16 Gy and a survival fraction < 2 × 10−7. Results: The saturation of repair model provides an excellent fit to both the x‐ray and C+6‐ion beam data for the V‐79 cells, with a systematic decrease of the parameter of effective available repair with increase of LET. The model also provides excellent representations of recently‐published survival data for NSCLC and other cell lines with parameters that are comparable to those for the CH V‐79 cells. Conclusion: The Saturation of Repair model provides a viable mechanistic modeling of survival for Carbon‐ion and X‐irradiation, and may be tested in further experiments.
SU‐FF‐T‐488: Estimation of Alpha/beta Ratio for Benign Tumor of the Brain From Clinical Data
Authors: Stansook N , Boonkitticharoen V , Dhanachai M
Published: April 2010

Purpose: To estimate a plausible α/β value for benign tumor of the brain from clinical data. Materials and Methods: Forty‐five articles published between 1997 and 2008 were selected for the analysis. These included publications on conventional external beam radiotherapy, fractionated stereotactic radiotherapy and stereotactic radiosurgery. Reports on combined radio‐chemotherapy were excluded. Three methods for α/β estimation were compared. These included two iso‐effect scheme matching, reciprocal iso‐effect dose plot and two‐step graphical matching. A 5‐year tumor control rate (TCR) % was chosen as an end point for the analysis. The α/β values estimated by different methods were tested for their differences by t‐test. Results: The α/β values obtained from reciprocal iso‐effect dose plot, two iso‐effect scheme matching and two‐step graphical matching were 3.53 Gy (95% CI 2.08–4.98 Gy), 2.71 Gy (95% CI 2.67–2.75 Gy) and 2.67 Gy (95% CI 1.87–3.47 Gy), respectively. Statistical analysis showed no significant difference among α/β values obtained from these methods (p⩾ 0.14). Noteworthily, plausible estimate of α/β determined by the two iso‐effect scheme matching and two‐step graphical matching could be obtained only when the size of dose fraction differed by at least a factor of seven folds. Conclusion: The average α/β estimate (2.97 Gy, 95% CI 2.42–3.52) for benign brain tumor obtained in this study was in remarkable agreement with the typical value of 2–3 Gy for the late responding tissue.