bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐FF‐T‐324: Modifications of Megavoltage Photon Beams for Gold Nanoparticle‐Aided Radiation Therapy (GNRT): A Monte Carlo Study
Authors: Cho S , Vassiliev O , Jang S , Krishnan S
Published: July 2006

Purpose: To produce megavoltage photon beams capable of achieving clinically significant (> 10%) macroscopic tumor dose enhancement during gold nanoparticle‐aided radiation therapy (GNRT). Method and Materials: GNRT is an emerging treatment modality currently under development, based on the following observations: a) high tumor specificity of gold nanoparticles due to passive extravasation; b) significant tumor dose enhancement during x‐ray irradiation as a result of increased photoelectric absorption due to high atomic number (Z) of gold. A previous Monte Carlo study found that no meaningful tumor dose enhancement would occur during GNRT with typical megavoltage photon beams, even after the removal of the flattening filter from linear accelerators. Therefore, the current Monte Carlo study investigated a number of ways to further increase the amount of low energy photons in the beam and consequently to achieve clinically significant tumor dose enhancement with photon beams in megavoltage range. Specifically, the macroscopic tumor dose enhancement under the identical geometry was calculated using the BEAMnrc/DOSXYZnrc code as the following conditions changed: the energy of electron pencil beam incident on the target, the target thickness, and the target material. Results: The current results showed that the macroscopic dose enhancement up to 40 and 18% across the tumor volume could be achievable with unflattened 2 and 4 MV photon beams, respectively, at a reasonable gold concentration of 3% within the tumor, after the proposed changes in target thickness and material. These beams were found capable of producing clinically acceptable treatment plans for GNRT, in spite of their softer photon energy spectra and larger buildup doses, compared to conventional megavoltage beams at the same nominal photon energies. Conclusion: Clinically significant tumor dose enhancement could be achievable during GNRT with megavoltage photon beams, provided that the proposed modifications to linear accelerators are made.
SU‐FF‐T‐325: Modifying the BEAMnrc Phase‐Space to Match Monte Carlo and Measured Dose Distributions
Authors: Zavgorodni S , Locke C , Bush K , Beckham W
Published: July 2006

Purpose: To present a method for improving agreement between clinically measured and Monte Carlo (MC) calculated dose distributions (profiles and PDDs) in water for the full range of field sizes. Method and Materials: Linac beam characteristics are modeled using BEAMnrc code that produces particle phase space above the secondary collimators as a new “source” in MC calculations. We assume that the photon energy spectra, represented in the phase space as achieved by the BEAMnrc model and electron beam characteristics, are reasonably accurate. The 3D dose distributions generated from MC and measured data are then used to modify the weights of each particle in the phase‐space. The weight modification occurs through a few (typically 3) iterations and new weights are proportional to the ratio of the measures to MC calculated dose at a point where primary photon crosses the dose matrix plane. One‐dimensional (assuming radial symmetry), 2D and 3D correction techniques were investigated. Denoising of the modified phase space has also been performed to reduce the “latent” dose uncertainty. Results: The method has been applied to our 6 MV and 18 MV beam models and allowed to reduce MC/measured beam profile differences from ∼3% to less than 1% for 6 MV beam, and from ∼5% to ∼1% for 18 MV in the central region of the beam. It also reduced the difference between measured and calculated dose from over 15% to less than 3% in the penumbra of the diagonal profile of the 40 × 40 cm2 field. Conclusion: The developed technique provides a relatively simple alternative to a very time‐consuming process of fine‐tuning BEAMnrc parameters. Initial BEAM model has to be “reasonably accurate” (producing results within ∼5% agreement to measured data) prior to correction. 2D correction technique showed optimal performance providing required dose agreement and performing fasted than 3D correction.
SU‐FF‐T‐326: Monte Carlo Based Simulation and Analysis of SRS X‐Ray 6 MV Beam Tenth‐Value‐Layer Data for Common Shielding Materials
Authors: Rodgers J
Published: July 2006

Treatment room shielding design depends on barrier attenuation data. It is common practice to use tenth‐value‐layers (TVLs) or related quantities measured for a given beam quality and shielding material. This investigation has applied Monte Carlo simulation to accurately determine the first, second and third TVLs for the three most common building materials: ordinary concrete, lead, and steel (iron). The radiation beam is 6 MV x‐rays coming from a robotically mounted stereotactic radiosurgery (SRS) accelerator which has a maximum field diameter of 6 cm at 80 cm from the target. The first three TVLs are presented for a range of field sizes up to the broad beam equivalent of a 40 cm by 40 cm field at 1 m. The x‐ray spectrum used to perform these simulations was generated for the CyberKnife™ accelerator with the BEAMnrc Monte Carlo code. This spectrum was used as input to the MCNP5 Monte Carlo code, to predicted tissue‐maximum‐ratio (TMR) values for a 6 cm diameter field (at 80 cm from the target) and benchmarked against measured TMR data. The MCNP5 code was used to simulate all barrier transmission factors, keeping the standard error of each data point below 1% of the mean. The results show that SRS TVLs change rapidly with the diameter of the radiation field incident on the barrier (with a slower rate of increase above about 15 cm diameter). Also analyzed were the characteristics of TVLs (specifically, the ordering TVL1, TVL2, and TVL3) as a function of field diameter at the barrier for all materials, with special attention given to the TVL properties in iron. The TVL results compare very well with previously measured concrete TVLs for the SRS machine and, also, with published broad‐beam 6 MV TVL data for all three barrier materials.
SU‐FF‐T‐329: Monte Carlo Dosimetric Study of the Flexisource Ir‐192 HDR Source
Authors: Casal E , Perez‐Calatayud J , Granero D , Ballester F , Cases R , Venselaar J
Published: July 2006

Purpose: Brachytherapy with high dose rate (HDR) sources of is a usual practice in clinical brachytherapy today. The TG43 U1 update report recommends that accurate dose distribution data of the brachytherapy source in use should be obtained experimentally or by Monte Carlo (MC), to be used as input in the HDR Treatment Planning System (TPS). The purpose of this study is to obtain the dose rate distribution in liquid water media for the Flexisource HDR source (Isodose Control GmbH, Germany) using the Monte Carlo method to obtain the TG43 U1 parameters and the 2‐D rectangular dose rate table. Material and methods: The MC code GEANT4 (7.1 version) was used to estimate dose rate in water and air‐kerma strength around the Flexisource Ir‐192 source following the TG43 U1 recommendations. All the details about the design an material of the Flexisource have been included in the simulation. Results: A complete dosimetric dataset for the Flexisource is presented. TG43 dosimetric functions and parameters have been obtained as well as a 2‐D rectangular dose rate table, consistent with the TG43 dose calculation formalism. Conclusions: The dosimetric parameters and functions obtained for the Flexisource have been compared with that obtained in the literature for others HDR sources, showing that the use of specific datasets for this new source is justified. This dataset can be used as input in the TPS and to validate its calculations. As policy of BRAPHYQS‐ESTRO task group, this dataset will be incorporated to the website: http://www.uv.es/braphyqs available to users in excel format.
SU‐FF‐T‐330: Monte Carlo Investigation of Dose Perturbation by Hip Replacements in Intensity Modulated Radiotherapy of Prostate Cancer
Authors: Chen Z , Ma C , Li J , Paskalev K , Price R , Luo W , Fan J , Chen Y , Lin T , Chen L
Published: July 2006

Purpose: To quantify the effects of hip replacements (prostheses) on IMRT dose distributions for prostate cancer and to determine their dose perturbations in IMRT treatment caused by the daily setup uncertainty and the inter‐fractional motion of prostate. Method and Materials: Different IMRT plans were generated with different beam arrangements for each selected prostate cancer patient with a hip prosthesis, and both uniform geometry and a bulk‐density assignment to the prosthesis were used in the planning dose calculation. Those plans were then recomputed on the EGS4 based Monte Carlo planning system with the shifts of the position of the prostates and isocenter, which were used to simulate the uncertainties in the daily routine treatment. Results were compared with and without the shifts for the same plans or between plans with uniform geometry and bulk‐density assignment to the prosthesis. Isodose distributions and DVHs were used to quantify the perturbations of dose caused by the hip replacements. Results: For the IMRT plans with one lateral beam passing through or close by the prosthesis, our results showed that the dose perturbations caused by the internal movement of the prostate and the uncertainty in patient positioning could be clinically significant. Since the intensity for the beam passing through the prosthesis is highly modulated in the optimization due to the high density of the prosthesis, the changes on the uniformity of the dose to the target and the effects to the critical structures were more significant compared with the plan without the presence of a hip prosthesis. Conclusions: This work indicates that the potential significant dose perturbations could happen due to setup uncertainties and inter‐fractional motion of the prostate in the presence of a hip prosthesis for the treatment of prostate cancer.
SU‐FF‐T‐332: Monte Carlo Simulation of Tomotherapy: Derivation of a Dual Source Model for Treatment Planning
Authors: Hsiao Y , Stewart R , Olivera G , Ruchala K , Li X
Published: July 2006

Purpose: To simulate a commercial Tomotherapy unit using Monte Carlo methods and to derive a dual‐sources model for the treatment planning. Method and Materials: The EGSnrc/BEAMnrc codes were used to simulate the linac head geometry of a Tomotherapy unit (HiArt, Tomotherapy Inc.). Various component modules were used to consider the head design including the target, primary collimator and multi‐leaf collimators (MLC). The percentage depth dose (PDD) and beam profile in a water phantom were generated using the phase‐space data below MLC and then compared to measurements. Using tools from the BEAMnrc package, the phase‐space data above MLC were used to extract a dual source model, consisting of a ring photon source located at the target and another ring source located at the primary collimator. The source model was verified in the following steps: (1) the source model was used to reconstruct the phase‐space data below MLC, which, in turn, was used to calculate PDD and beam profiles, (2) the PDD and beam profiles generated by (1) were compared to those generated by the original phase‐space data. Results: It was found that the PDD and beam profiles using Monte Carlo methods (the phase‐space data) agreed well (within 2%) with the measurements. The dose distributions using the source model were found to agree with (within 2%) the Monte Carlo and measurement data, indicating the source model is suitable to replace the Monte Carlo simulation for dose calculations in routine treatment planning. Conclusion: Monte Carlo simulation of a Tomotherapy unit has been carried out and a source model suitable for dose calculations in treatment planning has been derived. This model is useful for better understanding linac head design and for improving the accuracy and efficiency in dose calculations for Tomotherapy. Conflict of Interest: Research sponsored in part by TomoTherapy Inc.
SU‐FF‐T‐333: Monte Carlo Simulations Using Whole‐Body Pediatric and Adult Phantoms as Virtual Patients to Assess Secondary Organ Doses in Proton Radiation Therapy
Authors: Zacharatou‐Jarlskog C , Lee C , Jiang H , Bolch W , Xu X , Paganetti H
Published: July 2006

Introduction: Early cancer detection combined with new treatment technologies has resulted in higher numbers of long‐term cancer survivors. The risk of radiation‐induced secondary cancers to tissues away from the PTV is a growing concern in particular for pediatric patients. The focus of this project is to use whole‐body pediatric phantoms in Monte Carlo dose calculations in order to determine the effective dose from secondary radiation in patients undergoing proton treatment. Methods: Age and gender specific pediatric phantoms have been implemented into the Geant4 Monte Carlo package for organ dose calculations. A proton therapy treatment plan for a pediatric head and neck tumor case was chosen to address the significance of age dependent phantoms for radiation protection calculations. To mimic radiation therapy treatment, the setup of the phantom position was based on field parameters (based on a full treatment head model), including gantry angle, couch angle, and iso‐center position. We distinguish between secondary radiation from the treatment head and secondary radiation generated within the patient. Results: Results using an adult phantom as well as phantoms of a 4‐year old female and an 11‐year old male were analyzed. Organ doses and radiation and tissue weighting factors were used to calculate the effective dose. For proton treatments with double‐scattering system, range modulator and aperture, a significant number of secondary neutrons are generated in the treatment head. More important, differences between phantoms (age dependent) were found with respect to dose to specific organs and relative importance of neutrons generated in the patient versus neutrons from the treatment head. Conclusion: We present results of doses to various anatomic sites in the human body for whole‐body phantoms. The magnitude of secondary dose in organs/tissues depends on the distance from the PTV. For the first time, the significance of age‐dependent phantoms for secondary dose calculations was studied.
SU‐FF‐T‐339: Neutron Fluence Measurements Around the Siemens Oncor Medical Linear Accelerator Utilizing Gold Foil Activation
Authors: Hill T , Parsai E
Published: July 2006

Introduction: Neutron production in photon beams from high energy Linacs is a concern in radiation therapy centers. Neutrons are produced in the accelerator's head when high energy photons strike high Z materials of the target. Through a (γ, n) reaction, energy from the photon gets transferred to the atomic nucleus which then decays via the ejection of a neutron. In this paper, we measured the neutron fluence produced from the new Siemens Oncor using the Moderated Gold Foil Activation Method. In the process, neutron head leakage, in‐beam neutron contamination, the Q factor used for shielding purposes, and an estimate of the dose a patient may receive from a typical course of treatment were also measured and will be reported. Methods: Two gold foils were calibrated to provide a fluence per activity per gram conversion factor. The gold foils were then placed between two 3″×6″ polyethylene cylinders which were covered in 0.025″ cadmium metal. The gold foils were placed at distances of 112cm and 140cm from the target in the patient plane and exposed to doses that ranged from 5–10 photon Gy. After a 24 hour wait period, the activated gold foils (Au‐198) were read on a Capintec 3000 MCA with a ROI set at a value of 400 to 424 KeV with the center at 412 KeV. The calculated activity at the time of irradiation was used to determine the fast neutron fluence. Results: The average neutron fluence measured from a 20cm × 20cm field was 1.6 ×106 +/− 7.7 ×104 n/cm2/Gy. The Q value was calculated to be 0.27 ×1012 +/− 0.3 ×1011 n/Gy. Conclusion: The measured neutron fluence and calculated Q value from the Siemens Oncor is slightly higher than the published values for other Siemens accelerators, but is within the range for other accelerators.
SU‐FF‐T‐340: Neutron Spectra Measurements For Fast Neuron Brachytherapy Effective Dose Evaluation
Authors: Forman L , Vanier P , Dioszegi I , Welsh K , Meek A , Reinstein L
Published: July 2006

Purpose: We are developing a miniature neutron generator capable of brachytherapy, contact therapy and perioperative therapy applications. The neutrons are produced at 14MeV in a thermonuclear reactant target located at the end of a needle. The fast neutron effective dose depends on the lineal spectrum of charged particles produced by neutron interactions in tissue. Neutron interaction probabilities, cross sections, vary with neutron energy and the neutron spectra change with transmission through tissue. The change in spectra of initially 14MeV neutrons with tissue depth in brachytherapy is in itself not dramatic because the neutron mean free path is 10cm. But more seriously, the LET of neutron scattered protons increases with the inverse of proton energy and higher LET protons (bellow 120keV/micron) have increased relative biological effectiveness. The measurement of neutron spectra below 2 MeV is therefore important for understanding the mechanism of effective dose. In this paper, we will describe our development of a double scatter neutron spectrometer (DSNS) that has proven effective in low energy neutron spectral measurements. Method and Materials: The DSNS consists of detector planes of two liquid organic scintillators separated by 18cm. A neutron that scatters in the first plane starts a timer which is stopped by a coincident neutron detection signal for the same neutron in the second detector plane. Energy of the scattered neutron is determined by time‐of‐flight over the distance between detectors, which is the incident energy when the source is aligned with the detector axis. Results: The useful energy range of the DSNS is 0.3MeV to 5MeV and is dependent on the separation distance of the detector planes. Conclusion: The DSNS should be useful for measuring the low energy neutron component of our brachytherapy accelerator based source.
SU‐FF‐T‐341: New BEAMnrc Tools for Photon and Electron Beam Model Analysis
Authors: Schreiber E , Lehmann J , Chen J , Faddegon B
Published: July 2006

Purpose: Accurate radiotherapy planning requires precise and adaptable beam models. A beam model must be able to reproduce the full range of output on a clinical accelerator if a 2%/2mm or better accuracy goal is to be met. Most beam models have not been able to consistently meet this goal. While beam models can be based largely on measurements, Monte Carlo calculations can also be useful for determining the needed parameters and the breadth of flexibility required. In particular, Monte Carlo calculations are critical for exploring the impact of asymmetries in the accelerator geometry. As part of an effort to develop flexible beam models meeting a 2%/2mm accuracy goal, we have developed new tools for use with BEAMnrc. Method and Materials: A version of beamnrc.mortran incorporating a lateral shift for each component module has been designed, allowing the impact of laterally offsetting electron beam and accelerator elements to be evaluated. The point source model has also been modified to permit a non‐normal beam angle to allow a sensitivity analysis to include an angular distribution at the focal spot with a tilted beam. In addition, we have developed a new component module RECT which includes a simple rectilinear phantom as part of BEAMnrc, removing the necessity of using DOSXYZnrc for simple geometries. Results: By bypassing the need for a phase space file, RECT can facilitate high‐statistic runs for large field configurations by eliminating restrictions on disk space. RECT can also take advantage of the homogeneity in a water phantom by allowing photon step sizes beyond individual voxel boundaries, speeding up the simulation. Conclusion: The inclusion of lateral offsets in Monte Carlo beam models has been demonstrated to reproduce asymmetries of several percent in large electron fields, and is being used to study the 1–2% asymmetries found in clinical photon fields.
SU‐FF‐T‐343: Normalized Data for the Estimation of Fetal Radiation Dose From Radiotherapy of the Breast
Authors: Osei E , Bradley B , Fleck A , Darko J
Published: July 2006

There can be several reasons why a pregnant patient may receive a radiological examination. It could have been a planned exposure or the exposure may have resulted from an emergency when a thorough evaluation of pregnancy was impractical. Sometimes the pregnancy was unsuspected at the time of the examination and with younger women being diagnosed with breast cancer, the likelihood of this will increase in the radiotherapy departments. Whatever the reason, when presented with a pregnant patient who has received a radiological examination involving ionizing radiation, the dose to the fetus should be assessed. However, a major source of uncertainty in the estimation of fetal absorbed dose is the influence of fetal size and position as these changes with gestational age. We have investigated doses to the fetus from radiation therapy of the breast of a pregnant patient using an anthropomorphic phantom. Data for estimating fetal dose that takes into account the size and depth within the maternal abdomen for different treatment techniques have been provided. The data indicate that fetal dose is dependent on both depth within the maternal abdomen and gestational age and hence these factors should always be considered when estimating dose. The data shows that fetal dose can be underestimated up to about 10% or overestimated up to about 30% if the dose to the uterus is assumed instead of the actual fetal dose. It can also be underestimated up to about 23% or overestimated up to about 12% if a mean depth of 9cm is assumed, instead of using the actual depth of the fetus within the maternal abdomen.
SU‐FF‐T‐345: On the Suitability of Radiographic Film for Low Density Material Dosimetry and Photon Algorithm Verification
Authors: Wiesmeyer M , Cui J , Zakaryan K , Alaly J , Klein E , Mutic S , Low D , Deasy J
Published: July 2006

Purpose: To assess potential errors in radiographic film dosimetry in low density materials and to compare film measurements to dose estimates of a commercial convolution/superposition photon (CSP) dose calculation algorithm. Method and Materials: A standard film phantom was modified by replacing water‐equivalent slabs (30 HU) in its central portion with very low‐density material (−960 HU) to produce a lung slab phantom. Experiments were performed irradiating this phantom with 6 and 18 MV photons and field sizes of 2×2, 5×5, and 10×10 cm with 13 films placed between slabs. With unprocessed film in place, the phantom was then imaged in a computed tomography scanner and Monte Carlo (MC) and CSP calculations were done for each field size and energy combination. The phantom was then rescanned without film and dose was recalculated using MC to estimate the effect of the film in the prior MC calculations. Results: Measurements and MC calculations demonstrated field size and energy‐dependent dose perturbations at film planes in the low density material (up to 20% of maximum dose). In the phantom with film, central axis measurements and MC calculations matched within about 3%. The CSP algorithm was not perturbed by the film and overestimated dose in the low density region. Relying on film measurements alone would indicate a maximum overestimate of about 17% for 6 MV beams and 30% for 18 MV beams for the 2×2 cm fields. The filmless MC calculations show the true error to be about 6–9% higher. Conclusion: The error in CSP calculations will be underestimated if film is used as a dosimeter in very low‐density materials. The use of somewhat denser lung‐equivalent materials (e.g., −700 HU) would likely result in reduced, but still significant, error estimates. Supported by NIH grant RO1 CA85181 and a grant from Sun Nuclear, Corp.
SU‐FF‐T‐353: Parameters Study for the Severity Acute Radiation Induced Skin Reaction for the Breast Cancer Patients
Authors: Su M , Torres C , Grant D , Kim T , Papadopoulos D
Published: July 2006

Purpose: Radiation induced skin reaction is a common side effect for the breast cancer patient undergoing radiotherapy (RT). Severe acute radiation skin reaction (ARSR) not only brings distress to the patient, it may also cause an unexpected treatment delay and consequently reduce the treatment efficacy. It is important to understand the factors that cause ARSR and eventually to prevent or minimize it. Method and Materials: A retrospective study was conducted to 154 breast cancer patients who received a whole breast external photon beam treatment at source‐to‐axis distance (SAD) setup with 6MV or 6MV combined with 18MV photon energy at our hospital between 2003 and 2005. The relation between ARSR, the source‐to‐surface distance (SSD) and treatment technique was evaluated in this study. The treatment techniques included conformal three‐dimensional (3D) treatment and intensity‐modulated radiation therapy (IMRT). These techniques were further classified into: (1) 3D open field, (2) 3D with cerrobend block, (3) 3D with MLC, (4) IMRT sliding window, and (5) IMRT step‐and‐shoot. Receiver operating characteristic (ROC) curve and p‐value were applied for the statistic analysis. Results: Out of total 154 patients, 21 (13.6 %) patients developed ARSR. The results showed that ARSR was sensitive to SSD variation when the patient was treated with 3D MLC and IMRT sliding window treatment techniques (Az=0.9±0.12 with p‐value=0.014, and Az=0.8±0.08 with p‐value=0.017, respectively). And ARSR was non‐sensitive to the SSD variation when patient treated 3D open field and 3D block field treatment techniques (Az=0.37±0.16 with p‐value=0.67 and Az=0.66±0.13 with p‐value=0.19, respectively). There was not distinction in the development of ARSR observed between each of the treatment techniques (p‐value>0.08). Conclusions: SSD was found to be a sensitivity factor to predict ARSR for the patient undergoing RT with 3D MLC and IMRT sliding window treatment. A larger SSD should decrease the risk of ARSR.
SU‐FF‐T‐356: Permanent Prostate Implants: Dose to Critical Structures Inferior to the Prostate
Authors: Narayana V , Spirou G , Berri S , McLaughlin P
Published: July 2006

The basic goal of any radiation therapy is to maximize the dose to the tumor while minimizing dose to normal structure. With permanent prostate implants, treatment plans are developed to spare the urethra and the rectum. Post‐implant evaluation shows that the actual implant does not mimic the plan primarily due to prostate swelling and source position shift either at the time of deposition or post implant. Dose indices have been developed to evaluate dose coverage to the implant. 90% prescription to the 100% of the prostate (V100) is considered an excellent implant. A good execution of the implant plan will still maintain a cooler urethra and low dose to the rectum. It is common to see under‐dose in the base region of the prostate and seeds below the apex of the prostate. Sources below the apex of the prostate result in dose to the external sphincter, corpus cavernosum and internal pudendal artery. At our institution, we routinely obtain an MR for anatomic delineation and a CT for source localization 2 weeks after the implant. The datasets are registered based on mutual information techniques and dose to the normal tissue are reported. Fifteen patient entered in this study received a permanent implant to 145 Gy using I125 sources. The average volume of the MR prostate was 50.7cc. The average V100 was 90.5%. The average max dose to the right and left corpus cavernosum was 26.1(10.6) Gy and 28.1(12.4) Gy, respectively. The average max dose to the right and left pudendal arteries was 39.7(25.2) and 40.9(18.5) Gy, respectively. The average dose to 90% of the external sphincter was 132.1(44.9) Gy. With sufficient follow‐up it is possible to correlate the dose to the vascular structures and their effect on erectile function, and dose to the external sphincter and the effect on urinary function.
SU‐FF‐T‐357: Physical and Biological Characteristics of Megavoltage Grid Radiation Therapy
Authors: Dou K , Soleimani‐Meigooni N , Gnaster M , Awan S , Dini S , Johnson E , Meigooni A
Published: July 2006

Purpose: Dosimetric characteristics of a newly designed GRID block for megavoltage radiotherapy were investigated using TLD, film, and ionization chamber. Therapeutic advantage of this treatment modality was determined using a linear quadratic model in terms of treatment dose, GRID hole size, center‐to‐center spacing between the holes, and sensitivity of tissues to radiation. Method and Materials: Recently a newly redesigned GRID block has been introduced by Radiation Product Design, Inc. for different linear accelerators. Dosimetric characteristics (i.e. GRID output, dose profiles, and %DD) of three GRID blocks with different hole size and spacing were experimentally investigated. These GRID blocks were designed for a Varian 21EX linear accelerator. The measurements were performed using radiographic films and thermoluminescent dosimeters (TLDs) in Solid Water™ phantom materials and an ionization chamber in water. The measured dose profiles were then utilized to evaluate the therapeutic advantage of the GRID therapy as a function of dose, grid hole size and spacing, and also radiosensitivity of tissues with a linear‐quadratic (LQ) model. Therapeutic advantage of these GRID blocks was determined for a single fraction dose of up to 30 Gy. Results: Dosimetric characteristics of the GRID field were determined as a function of field size, beam energy, and Grid geometry. The results had shown that the therapeutic advantage of GRID increases by increasing the hole size, decreasing the spacing between the holes, and increasing the treatment dose. Moreover, the advantage of the GRID therapy was more pronounced for the radioresistant cells than radiosensitive cells. Conclusion: GRID radiotherapy exhibited a significant therapeutic advantage over the open field radiotherapy when the tumor cells were more radioresistant than normal cells. In addition, the therapeutic advantage of the GRID therapy is dependent on the treatment dose, GRID hole size and spacing between the holes.
SU‐FF‐T‐362: PLanUNC as An Open‐Source Radiotherapy Planning System for Research and Education
Authors: Schreiber E , Xu Z , Lorenzen A , Foskey M , Cullip T , Tracton G , Chaney E
Published: July 2006

Purpose: PLanUNC is a radiotherapy planning software package that has been under development and clinical use at the University of North Carolina for approximately 20 years. Under a joint grant from the NCRR and NCI (R01 RR 018615), PLanUNC has been documented, commented, and prepared for distribution as a freely available open‐source treatment planning tool for use as an adaptable and common platform for radiotherapy research. Method and Materials: The software and source code have been made available to qualifying users through a web portal located at http://planunc.radonc.unc.edu. Licenses for PLanUNC are available without fee to institutions, departments, and other facilities engaged in research and education involving radiation therapy. Results: Recent research milestones demonstrating the extensibility and increasing utility of PLanUNC include tools for 4D planning, interfaces with ITK segmentation and registration tools, daily correction of patient positioning, and interfaces with a variety of Monte Carlo dose engines. PLanUNC is currently supported for Linux and Windows operating systems, but has been successfully compiled on Alpha, Macintosh, Solaris, and other platforms. Conclusion: Licensed users will have access to PLanUNC source code, user and development documentation, annual training workshops, and limited support from UNC and the PLanUNC research community. PLanUNC is distributed as source code, making it customizable and extensible to meet the needs of a diverse range of research applications.
SU‐FF‐T‐363: Plastic Scintillator Preparation and Coupling in Scintillation Dosimetry
Authors: Archambault L , Ayotte G , Gingras L , Beddar A , Beaulieu L
Published: July 2006

Introduction: One way to improve the performance of scintillation dosimeters is to increase the light collection efficiency at the coupling interfaces of the detector. The present work present a detailed study of scintillating fiber preparation and their coupling to clear optical fibers in order to minimize light losses and to increase the light signal collected. Methods and Materials: Surface polishing with aluminum oxide sheets, reflector coating with MgO and use of eight different coupling agents (air, three optical gels, optical curing, ultraviolet curing, cyanoacrylate glue and acetone) were considered. For each coupling technique, ten samples were prepared. The procedure followed was: first, both the scintillating fiber and the optical fiber were cut. Then, each extremity was cleaned and polished. Finally the coupling between the scintillating fiber and the optical fiber was made either in a polyethylene cylinder or in a V‐grooved support depending on the kind of coupling agent used. To produce a large quantity of light, a UV lamp was used to stimulate scintillation. Results: A typical series of similar couplings showed a standard deviation equal to 10 %. This can be explained by the difference in the surface quality and the alignment of the scintillating fiber over the optical fiber. Surface polishing improves the light collection by approximately 65 % and a reflective coating on the distal end of the scintillator by approximately 40 %. For the coupling agents, the best results were obtained using an optical gel. Conclusion: In plastic scintillation dosimetry, there is usually a compromise to be made between the spatial resolution of the probe (i.e. its size) and the total signal collected by the photodetector. Since a large amount of the light produced inside the scintillator is usually lost, a better collection efficiency will result in improved spatial resolution for a given signal intensity.
SU‐FF‐T‐364: Positioning in Cranial Stereotactic Radiotherapy: Anatomical Points Vs. Full 3D Transformation
Authors: Paskalev K , Feigenberg S , Wang L , Ma C
Published: July 2006

Purpose: Some commercial IGRT systems do not have yet proper software tools for stereotactic localization. We evaluated two different isocenter realignment techniques for fractionated cranial treatments (previously presented). The goal of this report is to compare these two techniques and quantify the importance of using isocenter shifts derived from full 3D alignments. Method and Materials: A comparison study was carried out based on a total of 26 treatments (7 patients localized with the GTC relocatable frame; total of 41 isocenters,). Prior to each treatment a scan was acquired with Primatom CT‐on‐rails system (Siemens, Concord, CA), and the scan was registered by the treatment planning system (Radionics, Boston, MA). Three anatomical control points (ACP) were used for realignment. First, the control points were identified by a physician, their coordinates were recorded and a daily shift was calculated as an average value of the control point shifts (ACP method). Then using 3D transformation, we separately calculated the shifts of the control points and the shifts of the isocenters (3D alignment method). Statistical analysis was performed separately for (1) control points shifts and (2) isocenter shifts. Results: As expected, the differences between the two methods in control point shifts (0.6 to 0.9 mm, one SD) correlated with the root‐mean‐square of the individual uncertainties of each method. When comparing isocenter shifts, we found greater random (0.9 to 1.1 mm) and systematic differences between the methods. The increased errors observed in isocenter shift comparison were due to several peripheral isocenters, for which the ACP method failed. The maximum discrepancies observed were from 3 to 5 mm. Conclusion: The results from this study show that when using the GTC relocatable frame a physician can use the ACP method for patient alignment, provided that the treated isocenter is close to at least one point or between points.
SU‐FF‐T‐371: Properties of Unflattened Photon Beams Shaped by a Multi Leaf Collimator
Authors: Poenisch F , Titt U , Vassiliev O , Kry S , Mohan R
Published: July 2006

Purpose: Several studies have shown that removal of the flattening filter from the treatment head of a clinical accelerator increases the dose rate and changes the lateral profile in radiation therapy with photons. However, the multi‐leaf collimator (MLC) used to shape the field was not taken into consideration in these studies. We therefore investigated the effect of the MLC on flattened and unflattened beams. Method and Materials: To do this, we performed measurements on a Varian Clinac 21EX and MCNPX Monte Carlo simulations to analyze the physical properties of the photon beam. We compared lateral profiles, depth dose curves, MLC leakages, and total scatter factors for two energies (6 MV and 18 MV) of MLC‐shaped fields and jaw‐shaped fields. Results: Our study showed that flattening filter‐free beams shaped by an MLC differ from the jaw‐shaped beams. Similar differences were also observed for flattened beams. Although both collimating methods produced identical depth dose curves, the penumbra size and the MLC leakage were reduced in the softer, unflattened beam and the total scatter factors showed less field size dependence. Conclusion: Our findings suggest that, when commissioning a treatment‐planning system, one should use the profiles of the MLC‐shaped fields in addition to profiles of the jaw‐shaped fields.
SU‐FF‐T‐376: Radiation Leakage From Acrylic Electron Cones for An Intraoperative Therapy Linear Accelerator
Authors: Changmanee S , Tannanonta C
Published: July 2006

Purpose: To determine the radiation leakage at the outer wall of intraoperative radiation treatment (IORT) cones. Method and Materials: The leakage radiation dose for the acrylic IORT cone system attached with a Clinac 2100C of Varian was studied. Radiographic films were wrapped around the cone wall to locate the area of the high radiation leakage according to the optical density of the films. Then the leakage doses at the cone wall with high optical density starting from the distance of 0 – 8 cm upward from the cone end and also the dose at the depth of maximum dose were measured by using TLD‐700 rods type in solid water phantoms. The measurement were made for 4.5, 6.4, 8.3, and 9.5 cm diameter cones (both flat and bevel ends) with 6, 12 and 20 MeV electron beams. Results: The leakage dose as the percentage of the maximum dose at the central axis of the beam tended to increase with the energy and cone size except the 8.2 cm cone at 20 MeV which showed more leakage dose than the value of 9.5 cm diameter for both flat and bevel ends at the distance 8 cm from the cone end. Both flat and bevel cones presented the minimum and maximum leakage radiation with the same cone size (4.5 cm for minimum and 8.2 cm for the maximum) and the distance from the cone end (at the cone end for minimum and 8 cm for maximum). Their values were very close with the minimum of 4.37% and 4.92% and the maximum of 22.94% and 23.10% for flat and bevel end cones respectively. Conclusions: The tolerance dose of the normal tissue involved in each treatment should be considered together with the maximum leakage dose for the cone size and energy used in the treatment.
SU‐FF‐T‐382: Reduction of Total Body Exposure in Breast Radiotherapy Using Breast IMRT Or Virtual Wedge ‐ Importance in the Prevention of the Leukemia in Combined Chemo‐Radiation Regimens for Breast Cancer
Authors: Pignol JP , Woo T , Rakovitch E , O'Brien P
Published: July 2006

Purpose: The reported risk of leukemia following adjuvant radiotherapy for breast cancer has been reported to be low. However, two recent publications demonstrated that patients receiving combined high‐dose anthracycline chemotherapy and breast radiation as part of their adjuvant treatment have a significant increased rate of secondary leukemia above 1.3%. Radiation was found to be an independent factor for the development of leukemia by a factor 2.38. This study aimed at evaluating the total body radiation exposure during breast radiotherapy and to characterize the factors associated with an increased exposure and more particularly the method of compensation technique. Patients and Methods: In a prospective cohort of 120 women, radiation measurements were taken at the time of adjuvant breast radiotherapy using TLD's placed on the contralateral breast, on the anterior abdomen, on the back, and on the contralateral ankle. Multiple regression analysis was performed to analyze patient and treatment factors associated with the amount of scatter radiation exposure. Results: For standard 50Gy breast radiotherapy, the minimal dose received by abdominal organs is on average 0.45Gy, ranging from 0.06 to 1.55Gy. The use of physical wedges as a compensation technique was the most significant factor associated with increased scattered dose (p<0.001), resulting in approximately three times more exposure compared to breast IMRT and dynamic wedge. Conclusions: The amount of radiation that is scattered to a patient's body is of a magnitude that has been observed to be associated with excess of leukemia in previous studies. In accordance with the As Low As Reasonably Achievable (ALARA) principle we recommend using only breast IMRT or virtual wedging instead of physical wedging for the radiotherapy of breast cancer patients receiving also high‐dose anthracycline chemotherapy.
SU‐FF‐T‐383: Regularization and the L‐Curve for Inverse Planning Based On Equivalent Uniform Dose
Authors: Chvetsov A
Published: July 2006

Purpose: In the dose optimization based on equivalent uniform dose (EUD), a single dose value is assigned to PTV or organ at risk. Obviously, this optimization problem is poorly defined ‐ there is an unlimited number of nonuniform dose distributions (and, correspondingly, beam intensity functions) which will satisfy the EUD‐based objective function. Together with the ill‐posedness of the underlying integral equation, this may present a challenging mathematical problem. We propose an objective function for the EUD‐based inverse planning which can solve this problem and produce stable and accurate numerical solutions. Method and Materials: We apply to EUD‐based inverse treatment planning a variational regularization technique which was previously studied for the least squares dose optimization. The regularization parameter is found using the L‐curve method which is based on minimization of the residual norm and the smoothing norm of beam intensity functions. The optimization technique is applied to the prostate cancer treatment. Results: We have compared inverse treatment planning with the standard least squares objective function and an EUD‐based objective function. The dose distributions obtained from EUD‐based optimization are extremely nonuniform with significant hot spots in the PTV. We have applied to the EUD‐based optimization the variational regularization technique with the L‐curve method for determining an optimal value of the regularization parameter. We demonstrate that the regularization method decreases dose variance and mean dose in the PTV while keeping EUD of the same value. The regularized dose distribution is stable and uniform in the PTV. Conclusion: Inclusion of a variational regularization technique into the EUD‐based dose optimization produces robust dose distributions and beam intensity functions without deterioration of optimization accuracy.
SU‐FF‐T‐384: Reliable Radiation Dosimetry for Acquiring Beam Data for a 6 MV Linac Based Stereotactic Radiosurgery
Authors: Tannanonta C , Rutchantuek S , Yongvithisatid P
Published: July 2006

Purpose: To evaluate the reliability of the dosimetry systems available at our institution in the measurement of beam data for 6 MV linac based stereotactic radiosurgery. Method and Materials: The measurements of total scatter factor (St), tissue maximum ratio (TMR) were made by using X‐Omat V films, IC03, IC10, and a PTW Markus chambers. Only the films, IC03 and IC10 were employed in off axis ratio (OAR) measurements. Eight collimators with 10 to 50 mm diameters were involved in all measurements. Results: The TMR values measured by IC10 and Markus were agreeable within 2% for the collimators of 20 to 50 mm. The TMR values determined by all detectors for the collimators smaller than 20 mm may not be accurate enough for clinical use. The St values determined by all detectors with field sizes equal to or greater than 30 mm agreed within 2%. Markus and IC10 showed very closed values of St within 0.2%. For all collimators, the values of IC03 and film were about 1% less than the ones of Markus, and IC10. With the collimators of less than 25 mm, film presented the highest St values but Markus gave the highest values for the larger collimators. Film showed higher values of off axis ratios inside the beam area than IC10 and IC03 for all collimators. Comparisons of St Conclusions: From our study, it is concluded that the TMR values for 10 mm collimator should be measured by IC03 but the for larger collimators, IC10 is preferred. Among our detectors, film is the best one for the measurements of OAR for all collimators and St for the two small collimators (10 to 20 mm), with the larger collimators, Markus chamber should be used.
SU‐FF‐T‐387: Rotational Total Skin Electron Irradiation Using a Commercially Available Linear Accelerator with a High Dose Rate Total Body Electron Mode
Authors: Evans M , Olivares M , Seuntjens J , Parker W , Devic S , Poli E , Freeman C , Podgorsak E
Published: July 2006

Purpose: During the past 25 years, 185 patients have been treated with a rotational total skin electron irradiation (RTSEI) technique in our center. To modernize the technique we recently transferred it from a linac (Varian Clinac‐18) with a custom modified beam line to a linac (Varian 21EX) with a commercially available electron mode intended for total skin electron irradiation. Methods and Materials: The new technique uses a “high dose rate” mode and a “high dose per Monitor Unit” mode in conjunction with a custom‐made flattening filter to produce a uniform beam at an extended SSD of 378 cm. The accessory tray holds the custom‐made flattening filter and automatically selects the beam energy (6 MeV) and high dose rate (888 MU/min) while moving the collimators to the maximum 40 × 40 cm2 field size. Beam parameters are monitored using the record‐and‐verify (VARIS) system. Results: Reference dosimetry for the stationary and rotational electron fields was performed to allow delivery of the prescription dose using the linac's transmission ionization chamber. Patients are treated on a rotating platform with a high dose rate rotational electron beam having a zmax at the skin surface, an R50 at 15 mm and a bremsstrahlung contamination of the order of 3%. The nominal dose rate to water at zmax (surface) for the rotational technique was determined to be 24.1 cGy/1000 MU, and beam delivery is monitored with a secondary Farmer‐type ionization chamber located near the patient in the treatment field. Conclusions: Treatment times with the rotational total skin electron irradiation technique at an SSD of 378 cm for a daily dose of 2.0 Gy are of the order of 9.5 minutes and to date we have treated 15 patients with this technique.