bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐321: Whole Brain Irradiation Technique for Radiation‐Induced Cognitive Impairment
Authors: Bourland J , Robbins M , Deadwyler S
Published: November 2011

Purpose: Development of an easily reproduced, fractionated whole brain irradiation technique for the study of radiation‐induced cognitive impairment in nonhuman primates. Methods: A nonhuman primate (NHP) irradiation technique has been developed that replicates the fractionated whole brain irradiation technique for humans. Right and left lateral 6MV x‐ray beams are used, with opposed central axes matched at the level of the outer canthi. An eye block shields both eyes for each lateral beam. Monitor unit calculations to mid‐brain are based on anatomical measurements with a mid‐field slant distance incorporated. Total dose is 40 Gy, delivered at 5 Gy/fraction × 8 fractions, two fractions/week for four weeks. A clinical linear accelerator is used, with personnel procedures, room preparation, and clean‐up per research animal and human care requirements. Results: NHP positioning and beam parameter choices (eg, gantry and collimator rotation) allow for flexibility at the time of irradiation, based on anesthesia requirements and individual animal anatomy. Computed monitor units scale with NHP cranial measurements, which scale with NHP weight. A record/verify system facilitates set‐up and dose recording for each animal. Each right and left lateral radiation field is delivered via image‐guidance by the use of pre‐irradiation electronic portal imaging to verify positioning immediately before irradiation. Portal imaging dose, also performed at 6 MV, is recorded as irradiation dose. The portal image record enables post‐irradiation assessment of each fraction as well as cumulative dose. Room readiness techniques include preparations to minimize potential contamination of clinical equipment, and clean‐up procedures for return of equipment to human use. Conclusions: A simple, reproducible approach has been devised to replicate human fractionated whole brain irradiation of NHP cohorts to enable research studies of radiation‐induced cognitive impairment. Our irradiation techniques and experience are reviewed for the safe and efficient irradiation of this unique animal species.

Supported in part by the Brain Tumor Center of Excellence, the Kulynych Interdisciplinary Cancer Research Fund, and the Sticht Family Foundation at Wake Forest University Health Sciences.
SU‐E‐T‐322: The Effects of Microsphere and Surrounding Material Composition on Y‐90 Dose Kernels
Authors: Paxton A , Davis S , DeWerd L
Published: November 2011

Purpose: To investigate the effects of microsphere and surrounding material composition on Y‐90 dose kernels. Methods: Dose kernels can be convolved with activity concentrations to calculate non‐uniform dose distributions for patient‐specific dosimetry of Y‐90 microsphere treatments. Monte Carlo simulations were completed with EGSnrc user code EDKnrc to calculate the dose rate at multiple radial distances around various Y‐90 microsphere sources. Glass and resin microsphere simulations were completed with average diameter and density values as well as maximum values based on those given in literature. Both water and liver (as defined in ICRU44, density of 1.06g/cm̂3) were used as the surrounding/scoring material. Point source simulations in water were compared to ICRU72 reference data to validate the simulations. Point source simulations were also completed in water with a density of 1.06g/cm̂3 to evaluate the effects of the density of the surrounding material. All simulations had statistical uncertainties less than 1%.Results: Point source simulations agree to within 2% of the ICRU72 reference data over the range investigated. Glass and resin microsphere simulations in water show a slight decrease in dose rate relative to ICRU72 near the maximum range of Y‐90. The maximum differences were −3.1% and −1.9%, respectively. Simulations in liver show large differences relative to ICRU72, approaching 60% near the maximum range of Y‐90. However, this deviation can be mostly attributed to the difference in density between water and liver Conclusions: The presence of microsphere material causes slight differences in the dose kernel near the maximum range of Y‐90. Large differences were seen in simulations in liver relative to those in water. This is mostly attributed to differences in density of the materials. For accurate patient‐specific dosimetry, it would be necessary to take these differences into account in the calculation of delivered dose.
SU‐E‐T‐324: A Nephron‐Based Dosimetry Model for Alpha‐Particle Radiopharmaceutical Therapy
Authors: Hobbs R , Song H , Huso D , Sgouros G
Published: November 2011

Purpose: We describe a nephron‐based dosimetry model for renal toxicity for alpha‐particle radipharmaceutical therapy suited to the short range and high linear energy transfer of alpha‐particle emitters. This model is applied to Ac‐225‐7.16.4 radioimmunotherapy of murine metastatic breast cancer, where renal toxicity is observed for whole‐kidney and renal cortex absorbed dose values below toxicity thresholds established by external beam and targeted radiopeptide therapy. Methods: Using GEANT4 Monte Carlo software an idealized nephron model is created using geometrical and anatomical parameters taken from the literature and from murine samples. These samples also provide the data for volume of occupancy of the different compartments of the nephron in the kidney: glomerulus vs. proximal tubule vs. distal tubule. Radiopharmaceutical uptake in the different components of potential toxicity from (a) bound Ac‐225 and (b) free Bi‐213 are taken from experimental data and the literature and supplemented by tissue imaging with a beta‐Imager. Monte Carlo simulations were run, the absorbed doses to the model components were calculated and the results compared to experimental observations of renal toxicity. The renal cortex and medulla absorbed doses were also calculated and the results compared to traditional absorbed fraction results. Results: Preliminary results show an absorbed dose to the proximal tubule and glomerular cells approximately 3 times greater than that to the nephron as a whole. This difference in conjunction with the relative biological effect of alpha particles (a factor of about 5) would be consistent with the toxicity observed in the murine experiments. The renal cortex and renal medulla absorbed doses are consistent with the absorbed fraction methodology. Conclusions: Alpha‐particle radipharmaceutical therapy is a promising treatment modality for cancer. The nephron model enables optimal implementation of treatment and is a critical step in understanding toxicity for human translation of alpha‐particle radiopharmaceutical therapy.
SU‐E‐T‐327: Guidelines of Measurements Required for Extended SSD Electron Beam Therapy
Authors: Wilson D
Published: November 2011

Purpose: To present a system of dosimetric beam measurements which are used to accurately calculate multiple low energy electron fields to be used for palliative therapy of skin malignancies in patients where total skin irradiation is not feasible.Methods: Abutting 4 MeV and 6 MeV electron fields are used without the electron applicator in place to form a broad beam at SSDs ranging from 140 cm to 200 cm. Beam profiles were measured at three different SSDs in phantom at dmax to evaluated the fields. Data for the field edges was differentiated and a resulting beam kernel was fitted to a Gaussian. Virtual source position around the treatment SSD is determined from the change in beam widths at the three distances. Output factors are calculated from the measurements made at the beam axis, and a fit to the inverse square law is used to calculate the effective SSD.Results: Final beam profies and output factors for multiple abutting electron fields of flat and sloping surfaces were verified with TLD. Beams set at extended couch distances as well as floor setups were accurately predicted Conclusions: Large multiple extended SSD low energy electron fields can be accurately be described and set up for therapy by employing the limited set of beam measurements outlined in this work. TLD is then used for verification.
SU‐E‐T‐329: Degrading Electron Beam Energy in Rotational Total Skin Electron Therapy
Authors: Xu M
Published: November 2011

Purpose: In rotational total skin electron therapy (RTSET), degraded electron beam energy may be required for patient treatment. A method is developed by inserting an acrylic plate in TBIe‐tray to deliver a lower energy beam. The change in percentage depth dose (PDD) verses thickness of plate is studied. Methods: A Rando phantom is used on a rotational platform at an extended SSD (=332 cm) with a linac gantry angled at 90°. A special mode with a TBIe‐insert delivers a 6 MeV electron beam on a Varian 21EX. An acrylic plate is inserted in the TBIe‐tray to degrade 6 MeV electron beam energy. Three different thickness of acrylic plates are 4, 6, and 10 mm. For PDD measurements, Kodak EDR films are sandwiched in the Rando phantom slides. The film surface is oriented parallel to the incident electron beam. The films are analyzed using the RIT113 dosimetry software with a Vidar‐VXR 16 Pro Scanner. Results: Several physical parameters dmax, R50, and Rp are determined in the PDD curves. These parameters vary with the inserted plate thickness. The dmax is around 0.4 cm without acrylic plate (t = 0) and decreases as the plate thickness increases. For 10 mm plate thickness, dmax shifts to the surface of the phantom. The mean energy E0 at the phantom surface can be obtained from R50 for each degraded electron beam using the relationship between Eo and R50. The E0 decreases as the plate thickness increases, indicating 6 MeV electron beam degraded to a lower energy beam. Conclusions: The method to degrade electron beam energy in RTSET offers advantages of easy setup and manageable beam energy than spoiler technique. Most of the treatment parameters can be readily obtained from the PDD data for each degraded electron beam.
SU‐E‐T‐330: Comparison of Measured, Calculated and Verified Electron Dose Distribution in Varian Trilogy
Authors: Gao M , Yin Y , Liu T
Published: November 2011

Purpose: To compare the similarity of measured, calculated and verified electron dose distribution in Varian Trilogy. Methods: Percentage depth doses (PDDs) and transverse dose profiles (TDPs) were measured and calculated by electron beams with different energies (6, 9, 12, 16 and 20 MeV respectively), which were produced by the accelerator. The PDDs and TDPs were also experimentally determined. And according to the electron energies, both measurements and calculations were done in the central axis of the beam for the PDDs and at different depths in water for TDPs. The electron beams obtained with have been modeled by pencil bean convolution (PBC). Then the PDDs and TDPs were verified by phantom. Finally, the measured, calculated and verified electron dose distribution of PDDs and TDPs were compared. Results: The deviations of measurements, calculations and verifications were generally less than ±2% with applicator, which shows that the values used in this work for the energy and spatial distribution of the initial electron beam as well as the modeling and verification parameters are realistic. Conclusions: The accelerator modeling proposed in this work gives accurate phase‐space data files which can be used for fully characteristic determination for all clinical beams produced by the accelerator.
SU‐E‐T‐332: Determination of Skin Dose during Smart Arc Delivery
Authors: Regan M , Stathakis S , Papanikolaou N
Published: November 2011

Purpose: Treatment Planning systems (TPSˈs) inaccurately quantify the dose delivered to the skin during radiation therapy, due to their inability to account for all surface dose contributing factors. The purpose of this work was to use near tissue equivalent ultra‐thin Thermo Luminescent Dosimeters to determine and compare the average skin dose for Prostate patients using the Volumetric Arc Therapy (VMAT) Delivery System with measurements taken on other delivery systems. Method and Materials: Reference beam measurements were taken at energy of 6MV for both a 10×10 open field and for an open, unmodulated arc with a 10×10 field from multiple angles. Five (n=5)_prostate patients using the VMAT delivery system were evaluated. The dose per fraction was set to 2 Gy for all patients. Two TLDs were placed at discrete locations, every 25 degrees, on the periphery of the “cheese” phantom. Results: The average skin dose for all locations of interest for the five prostate patients varied from 5.25cGy to 7.47cGy. Compared to previous work done with skin dose measurements, the VMAT delivery system delivers an overall lower skin dose than IMRT step and shoot, Helical Tomotherapy, and Serial Tomotherapy. Conclusions: The VMAT delivery method delivers lower dose to the surface than other IMRT delivery methods. The lower doses probably due to lower monitor units required for VMAT compared to static field IMRT.
SU‐E‐T‐339: Target Change Effect on Surface Dose of Treatment and Imaging Helical Tomotherapy Beams
Authors: Ehler E , Gerbi B
Published: November 2011

Purpose: The target of the TomoTherapy unit is replaced at regular intervals. This work studies surface dose both before and after a target change for the treatment and imaging beams.Methods: Attix parallel plate chamber, as well as LiF powder thermoluminescent dosimeter (TLD) monolayer measurements were performed on the surface and at depths up to 1.5 cm in solid water before and after the target change. Due to the 1.0 cm diameter collecting volume of the Attix chamber, broad imaging beam measurements were performed with a 5 cm jaw width at isocenter; TLD measurements were performed using the narrow jaw width used for clinical MVCT imaging. Measurements at depths of 10 and 20 cm in solid water were also performed using A1SL cylindrical ionization chambers with a 5 cm field width.Results: Attix chamber measurements in the broad imaging beam showed surface dose versus dose at 5 mm to be constant before (31.3 ± 0.6%) and after (31.4 ± 0.3%) the target change. TLD monolayer measurements showed no change in the narrow imaging beam surface dose (25.0 ± 0.8% before and 24.6 ± 0.5% after). The treatment beam showed a small decrease in surface dose after the target change (18.2 ± 0.7% before and 17.0 ± 0.3% after). The ratio of dose at depths of 10 and 20 cm for the imaging beam was 2% greater after the target change whereas the the treatment beam ratio was 0.6% greater after the target change as compared to the ratio measured before the target change Conclusions: Even though degradation of the thin tungsten target occurs with use, little to no change is observed in the surface dose for either the imaging or the treatment beam. This is likely due to a thick, low atomic number metal block located immediately after the target.
SU‐E‐T‐340: Dose Enhancement Due to Backscattered Electrons of Gold Nanoparticle: Size and Shape Dependency Study by Thermoluminescent Dosimetry
Authors: Marques T , Barbi G , Baffa O , Nicolucci P
Published: November 2011

Purpose: Quantify dose enhancement fractions (DEF) caused by backscattered electrons of gold nanoparticles with different size and shape using thermoluminescent dosimeters (TLD). Methods: Gold nanorods (AuNP‐rod) of 45nm and spherical gold nanoparticles (AuNP) of 5nm average diameter were used in this study. Fourteen Lithium Fluoride TLDs (LiF‐100) groups were pre‐calibrated in the 200kV x‐ray beam studied. Different mass‐fractions of gold (0%, 0.1%, 0.2%, 0.3%, 0.5%, 0.7% and 0.8%) were casted only in one surface of each tablet. An acrylic plate with a small recess properly designed to fit tablets of a same group each time; 10cm of acrylic were also positioned down the TLDs to guarantee backscattering conditions. 2Gy were delivered to all groups. The AuNPs films were down positioned related to the beam incidence during the experiments aiming to measure backscattered electrons of AuNPs. TLDs were positioned in two depths: surface and build‐up. DEF was calculated as the ratio between dose measured with TLD tablets with and without AuNP. Results: Experimental DEF varies between 1 and 1.26 to both AuNP‐rods and AuNPs when positioned on the surface. At the build‐up depth the experimental DEFs found were 1, 1.02, 1.04, 1.09, 1.12, 1.16 and 1.17 respectively to concentrations 0%, 0.1%, 0.2%, 0.3%, 0.5%, 0.7% and 0.8% of AuNP‐rods; To the same gold concentrations of spherical nanoparticles the DEFs found were 1, 1.02, 1.02, 1.03, 1.04, 1.08 and 1.11. A linear behavior between gold concentration casted and DEFs measured was observed to both depths of irradiation. Conclusions: Differences of 6% in fractions of dose enhancements can be found when 45nm AuNP‐rods and 5nm spherical AuNPs are considered. The angular distribution of scattered electrons in AuNP combined to nanoparticle size and shape implies in its self attenuation inside the nanoparticles and thereof the fractions of dose enhancements around the particles.
SU‐E‐T‐342: Dosimetric Verification of Treatment Planning Systems in a Clinical Setting Using IAEA Test Package
Authors: Lahroodi K Asnaashari , Khosravi H R , Golrokh M , Gholami S
Published: November 2011

Purpose: To evaluate and verify current situation of radiation therapy treatment planning process for external high‐energy photon beams in radiotherapy centers in Iran. This is apart of an ongoing audit that will cover all the radiotherapy departments in different hospitals.Methods: To simulate typical conventional and conformal radiotherapy techniques, an anthropomorphic phantom (CIRS phantom Model 002LFC) representing the human thorax was used. The phantom was scanned using computed tomography and eight test cases of IAEA test package based on TRS 430 were planned on TPS which represent different irradiation geometries in routine conformal radiotherapy. The doses were measured with ion chamber, and the deviation between measured and TPS calculated doses, were normalized to the dose measured at the reference point and Error [%] reported. So far this methodology, which employs the same phantom and the same set of test cases, was tested in 6 different hospitals /accelerators which were using 2 different algorithms/ in homogeneity correction methods implemented in different TPS. Results: The total number of 32 clinical test case data sets for different energies and calculation algorithms were produced. Dose differences up to 15% were discovered for some of the simple algorithms and high energy X‐ray beams. The origin of systematic errors was analyzed and the source of the problems resolved after 3 to 4 times repetitions. Conclusions: This work is an ongoing project to evaluate accuracy of treatment planning chain in radiotherapy centers to deliver treatments with less uncertainty and possibility of accidental exposure. Sources of large disagreement between Error [%] and agreement criteria were determined. In some centers large deviations exist in some simple dose calculation algorithms, therefore implementation of comprehensive commissioning and using more progressive TPSs is strongly recommended in clinical practice.
SU‐E‐T‐345: Evaluation of Dose Distribution in Total Body Photon Irradiation
Authors: Piriyasang D , Sakulsingharoj S , Khachonkham S , Tangboonduangjit P
Published: November 2011

Purpose: To improve dose homogeneity in the body using the compensator and to reduce the dose in some critical organs using the shielding blocks. Methods: The bilateral opposing beams of the fully opened collimator produced by a 6MV Clinac iX with Perspex beam spoiler of 1 cm thick were used to irradiate the Randophantom at 415 cm treatment distance. The measurements of the radiation doses at the surface and inside the phantom were performed using thermoluminescent dosimeters. The midpoint of the level at the umbilicus represents the point of the reference dose. The experiments are divided into two parts. The first involved irradiation without any bolus and shielding block and the second was with bolus and shielding block. Results: The first study without bolus and shielding showed higher doses at the surface of the head, neck and chest than the dose at the reference point. The dose inside the phantom for the brain, larynx, cervical cord, heart and both lungs were more than 10% higher than the reference dose. In the second study, the bolus was added to the region of the neck and brain for improving uniformity of dose distribution and one half‐value thickness of shielding block for both lungs. The dose variations are within ±10% obtained at the surface and inside the phantom.Conclusions: The bilateral fields TBI with the patient in supine position can undergo irradiation. The surface and inside organ doses excluding the shielding organs achieved uniformity within ±10%. The dose at the larynx with bolus was higher than the reference dose because of the thickness of the bolus was not enough to compensate for the missing tissue. The appropriate bolus thickness should be placed carefully at the neck, and the size of the lung block should be patient‐specific.
SU‐E‐T‐346: Evaluation of Inverse‐Compton Scattering Gamma‐Ray Sources for Clinical Use in Radiotherapy
Authors: Tonner B. P.
Published: November 2011

Purpose: To evaluate the potential clinical uses of gamma‐ray beams generated by the process of laser‐Compton backscattering from relativistic electron beams. Methods: Inverse‐Compton backscattering has been demonstrated to produce short pulse‐length, high brightness, gamma‐ray beams with energy in the neighborhood of 1 MV (F. Albert et al., Phys. Rev. ST 13, 070704 (2010)). The reported experimental parameters for inverse‐ Compton beams in the high orthovoltage energy range are used to estimate potential future performance of >1 MV sources, with realistically achievable parameters for spectral bandwidth and beam emittance. A model source based on these parameters is implemented in a commercial treatment planning system (Pinnacle 8.0) and used to deliver small‐field treatments to phantoms, and to compare to retrospective stereotactic radiosurgery plans. Results: The emittance of current and future laser‐gamma sources are compared to the requirements of SRS and SBRT. These features have a measurable effect on the beam penumbra that can be beneficially exploited in radiotherapy. Not unexpectedly, the principle limitation of such sources would appear to be the peak flux that can be obtained, since these sources are high brightness, but not necessarily high flux producers, leading to long treatment times that would not be clinically useful. Relaxation of some beam parameters, such as larger source size, would not significantly affect the use of such a source in SRS. Conclusions: The generation of highly collimated gamma‐rays of energy 1 MV and above is possible using the Thompson‐Compton scattering of laser photons from linac accelerated electron beams. The flux produced by these beams has been increasing steadily with each new construction project, and theoretical estimates of the achievable flux indicate that they may reach clinically relevant levels of output in the future. Certain characteristics of these beams, specifically the angular divergence and small source size, can be beneficially employed in radiotherapy.
SU‐E‐T‐347: A Cost‐Effective Technique for Treating Penis Cancer with Delivery Accuracy Verified with In‐Vivo Measurement
Authors: Liang L , Arterbery V
Published: November 2011

Purpose: To report an in‐house cost‐effective, easily made and set up, yet accurate technique for treating penis cancer at a community freestanding cancer. Methods: Recently, a patient with penis cancer was under radiotherapy at our institution. The treated site was his penis only. The patient was simulated in supine position with his penis inserted in a custom supporting tool. This supporting tool is made of a regular candle that can be bought at any retail store. It measures about 10 cm in diameter and has a HU about −100. A hole slightly larger than the patientˈs penis was drilled in the middle with enough buildup wall left for a 6 MV beam used for the treatment plan. For the remaining space not occupied by the patientˈs penis, regular flour was filled in tightly, which has a HU about −200. The plan was done with an opposing lateral conformal field setup to get a uniform dose distribution across the treatment site. It makes essential no difference whether the heterogeneity is turned on or not in the dose calculation with Varianˈs Eclipse TPS. Four MOSFET dosimeters were placed on the surface of the penis for in‐vivo measurement for two consecutive fractions. The prescription was 180 cGy/fx. The mean dose for the skin (3 mm deep region from the surface contoured in Eclipse) was 182.9 cGy with a minimum of 179.3 cGy and a maximum of 185.8 cGy. Results: The in‐vivo measurement was 183.2 cGy +/− 1.4 cGy, including a port film with 2 MU. The measurement was in good agreement with the calculation. Conclusions: In‐vivo measurement proved the in‐house developed supporting tool to be cost‐effective, easily made, and easy to set up on a daily basis for accurately treating penis cancer.
SU‐E‐T‐349: Evaluating a Stochastic Reconstruction Algorithm for Compton Camera Based Prompt Gamma Imaging during Proton Therapy
Authors: Mackin D , Polf J , Peterson S , Gillin M , Beddar S
Published: November 2011

Purpose: Prompt gamma photons emitted during proton radiotherapy may provide a method to measure dose delivery and range. The utility of this method depends on how well the gammas can be detected and reconstructed. The purpose of this study is to demonstrate the feasibility of the stochastic origin ensemble (SOE) algorithm for reconstructing images of the origins of prompt gammas emitted during proton therapy and to introduce a metric for quantifying the accuracy of this image. Methods: Using Geant4 we simulated a Compton camera detecting prompt gamma emission from proton irradiated tissue phantoms. The information recorded by the simulated detector is used as the input to the SOE reconstruction algorithm, which iteratively determines the likely gamma emission origin. We introduce a metric to quantify the accuracy of the reconstruction and use the metric to provide a quantitative analysis of the SOE reconstructions. Results: We show both qualitatively and quantitatively that the SOE algorithm can reconstruct images which accurately predict the origins of prompt gammas emitted during proton therapy. We also show that the distal falloff of gamma production based on the reconstructed image agrees with the distal falloff in Monte Carlo calculated gamma origin distribution to within 1 mm for both the 50% and 20% regions. Conclusions: The SOE algorithm was able to reconstruct usable images of prompt gamma emission during proton irradiation. We believe these results justify further investigation of this technique for in‐vivo prompt gamma imaging.

This work was supported by Award Number R21CA137362 from the National Cancer Institute.
SU‐E‐T‐350: Calibration of a Prototype Proton CT Scanner
Authors: Hurley F , Schulte R , Bashkirov V , Wroe A , Ghebremedhin A , Patyal B , Penfold S , Rykalin V , Sadrozinsk H
Published: November 2011

Purpose: To calibrate a novel proton CT scanner using polystyrene degraders of accurately known thickness and relative stopping power.Methods: A prototype proton CT scanner was constructed and installed on a horizontal proton research beam line for further study of this novel, potentially low‐dose tomographic imaging modality. The proton CT scanner registers individual protons up to a maximum rate of about 10̂5 protons/sec, recording their entry and exit coordinates and directions with high‐resolution silicon strip detectors, as well as their residual energy by stopping them in an augmented 18‐crystal CsI calorimeter. To avoid uncertainties in the mean excitation energy (I) of water when converting energy loss to water equivalent path length (WEPL) via the Bethe‐Bloch equation, the response of the calorimeter was calibrated using polystyrene plates of known water‐equivalent thickness (WET). Stacks of polystyrene plates of variable thickness were placed between the proton CT detectors and about 3 × 10̂5 protons were recorded for each thickness. For each proton event, the calorimeter response was derived from the weighted sum of the response of the 18 crystals, taking into account variations in the sensitivity of each crystal. A Gaussian distribution function was fitted to the response data at each WET, and the mean of each distribution was used to establish the WEPL calibration curve. Results: For protons of 100 MeV and 200 MeV, the mean response of the calorimeter was obtained for 7–8 different WET values (including zero) and the WEPL vs. response calibration curve was fitted with a quadratic polynomial with an excellent goodness of fit. A WEPL measurement accuracy of 1 mm or better can be achieved by measuring the calorimeter response of about 150 protons Conclusions: This work is an important step towards a thorough investigation of proton computed tomography for therapeutic and imaging applications.

Funded in part by DOD Contract W81XWH‐08‐1‐0205 and the Department of Radiation Medicine, Loma Linda University Medical Center
SU‐E‐T‐353: Verification of Water Equivalent Thickness (WET) and Water Equivalent Spreadness (WES) of Proton Beam
Authors: Demez N , Lee T , Keppel C
Published: November 2011

Purpose: To verify calculated water equivalent thickness (WET) and water equivalent spreadness (WES) in various tissue equivalent media for proton therapy Methods: Water equivalent thicknesses (WET) of tissue equivalent materials have been calculated using the Bragg‐Kleeman rule. Lateral spreadness and fluence reduction of proton beams both in those media were calculated using proton loss model (PLM) algorithm. In addition, we calculated lateral spreadness ratios with respect to that in water at the same WET depth and so the WES was defined. The WETs of those media for different proton beam energies were measured using MLIC (Multi‐Layered Ionization Chamber). Also, fluence and field sizes in those materials of various thicknesses were measured with ionization chambers and films Results: Calculated WETs are in agreement with measured WETs within 0.5%. We found that water equivalent spreadness (WES) is constant and the fluence and field size measurements verify that fluence can be estimated using the concept of WES. Conclusions: Calculation of WET based on the Bragg‐Kleeman rule as well as the constant WES of proton beams for tissue equivalent phantoms can be used to predict fluence and field sizes at the depths of interest both in tissue equivalent media accurately for clinically available proton energies.
SU‐E‐T‐355: Dose and Range Perturbation by LiF TLD‐100 in Proton Beam Therapy
Authors: Jin H , Su Z , Slopsema R , Li Z
Published: November 2011

Purpose: To investigate dose and range perturbation by LiF TLD‐100 chips in proton beam therapy. Methods: Three passively scattered proton beams (range: 10.6 (R1), 15.1 (R2), and 20.6 g/cm2 (R3); modulation: 5.2, 10.4, and 9.2 g/cm2, respectively) were selected and delivered to a solid water phantom with 9 TLD chips on the surface. Isocenters of the beams were aligned with centers of spread‐out Bragg peak. An aperture opening was 10×10 cm2 with an air gap of 10 cm. Films were placed at depths of isocenters, 0.5 (R2), 8.5 (R2), 10.3 (R1), 15.4 (R2) and 20.3 cm (R3). Profiles from the film measurements were examined and compared with those of simulations using the Eclipse treatment planning system. Results: Dose in the regions shadowed by the chips was lower than that without the TLD. The TLD reduced the dose by 1.6% (R1 isocenter), 3.7% (R1: 10.3 cm), 1.0% (R2: 8.5 cm), 3.1% (R2 isocenter), 11.1% (R2: 15.4 cm), and 3.8% (R3: 20.3 cm). There was no distinct dose perturbation at 0.5 cm depth of R2 and at the isocenter of R3. Since the dose gradient of distal fall‐off was ∼12%/mm, the TLD reduced the proton range by ∼1 mm based on ∼11% dose reduction by the chips in the distal fall‐off region. The Eclipse simulation study using R1, R2, and R3 demonstrated the similar dose and range perturbation. Conclusions: Since considerably high dose perturbation and about 1 mm range shortening were observed in the TLD dosimetry of proton beam therapy, the number of TLD measurements should be limited not to cause significant dose perturbation in a complete treatment course. In particular, it is of great importance to properly implement hypofractionated proton beam therapy by considering the proton dose and range perturbation, when the TLD dosimetry is used.
SU‐E‐T‐357: Development of An Anthropomorphic Head Phantom for the Assessment of Proton Therapy Treatment Procedures
Authors: Summers P , Followill D , Sahoo N , Poenisch F , Tucker S , Gillin M , Riley B , Ibbott G
Published: November 2011

Purpose: Develop an anthropomorphic head phantom for the evaluation of proton therapy treatment procedures from simulation to treatment planning and treatment delivery. Methods: A head phantom was designed and constructed from materials tested specifically with proton beams to match stopping powers and Hounsfield Units of corresponding human anatomy. Separate MR (water‐filled)‐ and CT (polyethylene)‐compatible inserts were designed for imaging (including target delineation) and dosimetry verification. The dosimetry insert contained radiochromic film and TLD dosimeters. The phantom was imaged with MR to outline the target and fused with a CT image for the dose distribution calculation. Passive scattering and spot scanning treatment plans were designed using the Eclipse proton planning system per M.D. Anderson Proton Centerˈs standard brain protocol. The phantom was irradiated according to each treatment plan three separate times. The dose distributions and absolute point doses determined with film and TLD were compared to calculated points, dose profiles and dose distributions, using a gamma analysis with pass criteria of 5%/3mm and 5%/5mm, to determine agreement and reproducibility. Results: The average passive scatter plan pixel pass rates were 91.9% and 97.4% for 5%/3mm and 5%/5mm criteria, respectively. The average lateral shift ‐ mean(standard deviation) ‐ was 2.5mm(1.8mm); the average longitudinal shift was −2mm(1.9mm); the average transverse shift was 1.7mm(2.8mm). The average spot scan plan pass rates were 90.4% and 98.4% for 5%/3mm and 5%/5mm criteria, respectively. The average lateral shift was 2.2mm (1.4mm); the average longitudinal shift was −1.6mm(1.1mm) on the inferior side and 3.1mm(4.3mm) on the superior side; the average transverse shift was −0.9mm(0.4mm). Conclusions: A proton head phantom made of proton suitable plastics was developed that can verify the agreement between treatment plans and measurement that can be used to credential proton therapy facilities for participation in NCI‐funded clinical trials.

Work supported by PHS CA010953 and CA081647, awarded by NCI, DHHS and Massachusetts General Hospital Federal Share Funds.
SU‐E‐T‐358: Dosimetric Effects of Beam Angle Arrangements in Lung Proton Therapy
Authors: Kang Y , Zeidan O , Schenkenfelder P , Hsi W , Zheng Y , Mascia A , Ding X , Larson G , Prabhu K , Keole S
Published: November 2011

Purpose: The Inclined Beam Line (IBL) is an innovative partial gantry design which provides two beam angles at 30 and 90 degrees with full flexibility of the patient positioning system of the gantry design. Compared to the full gantry design in proton therapy, the IBL is a simplified design allowing for less equipment maintenance, physics quality assurance, and costs. The purpose of this study was to demonstrate that IBL provides sufficient choice of beam angles and efficient beam delivery to treat most proton lung patients.Methods: Eight lung patients who had proton treatment at our center were selected for this study. We designed three treatment plans for each of the eight patients in supine position, using beam arrangements with (1) full gantry, (2) IBL, and (3) hybrid, i.e., a combination of a gantry plan and an IBL plan with the patients being treated with each plan in alternative days. Xio TPS (CMS, St. Louis, MO) was used to design treatment plans. Results: We have compared the dosimetric differences of the three planning strategies. The PTV D95 was within 1% for all three plans for each patient. On average, the lung V20, V10, and V5 were 3.6%/3.7%, 5.1%/3.7%, and 5.1%/1.6% higher for the IBL plans than that for the gantry/hybrid plans, respectively. Cord max dose, esophagus dose, and heart dose showed similar trends. Among all eight patients, IBL plan was not able to meet cord dose limit for only one patient who was treated for right posterior chest wall. Conclusions: Our results showed that seven out of the eight patients (88%) could be treated with full gantry, IBL, or hybrid plans with sufficient target coverage and reasonable critical structure sparing. Therefore, IBL was a sufficient proton treatment delivery method for most of the lung patients in this study.
SU‐E‐T‐361: Three Dimensional Dose Verification in Proton Therapy Using EBT2 Film Array
Authors: Yoon M , Kim S , Choi S , Han J , Hwang D , Jeon Y , Kim H , Kim M
Published: November 2011

Purpose: The purpose of this study was to determine whether a three dimensional (3D) film based quality assurance verifies patient‐specific characteristics such as dose distribution, beam range and compensator all together for the passively scattered and uniform scanning proton beams. Methods: Three passively scattered and one uniform scanning proton beams were irradiated to a 3D phantom based on 5 mm thick acrylic slabs with Gafchromic EBT films. The measured 3D dose distributions with proton beam range data were compared with data provided by a proton treatment planning system (TPS). Results: For passively scattered and uniform scanning proton beams, the gamma index for the dose‐distribution comparison for treatment fields was less than 1.0 for 97.2% and 98.1% of total pixels for a 3% dose tolerance and 3 mm distance‐to‐dose agreement, respectively. The experimental proton beam ranges based on 3D film measurement also shows good agreement with the calculated beam ranges from TPS. Conclusions: Our results show that both the dose distribution and the proton range based on 3D EBT film measurement are well matched with planned data. These results indirectly show that 3D film data can be also used for the quality assurance method for physically manufactured proton range compensators.
SU‐E‐T‐364: Measurements of Field Size Factor for Proton Therapy
Authors: Zhao Z , Toramatsu C , Slopsema R , Li Z
Published: November 2011

Purpose: To measure the field size factor and establish reference values for clinical use Methods and Materials: The field size factors (FSF), which is the ratio of output factor of a certain field size to the output of a reference field size, were measured for five clinical proton beams. The proton ranges of the selected beams are from 5.35 cm to 13.0 cm and modulations are from 3.3 cm and 8.9 cm. for each beam, the output was measured using a 0.01 cc compact chamber for field sizes of 11.6 cm diameter (open field), 5.6×5.6 cm2, 4.5×4.5 cm2, 3.0×3.0 cm2, 2.0×2.0 cm2 and 1.1 cm diameter. A 1D‐translational water phantom was used. The point of the measurement is on the central axis in the center of the Spread Out Bragg Peak (SOBP), aligned with the isocenter. Results: For field size larger than 3.0 cm diameter, the FSF is close to 100%. The FSF started to drop when field size became smaller than 3.0 cm diameter for the five beams. It decreased to about 90% for field size of 2.0 cm diameter and further decreased to about 45% for field size of 1.1 cm diameter. Conclusions: The FSFs were measured for five beams with either square or circular apertures. It was observed the FSF changes significantly with field size. The values of FSF measured with square or circular apertures may not be directly used for irregular shaped patient fields, they however provide reference values for these fields.
SU‐E‐T‐367: Cervix Brachytherapy Dosimetry: Inconsistencies in Defining Bladder and Rectal Points
Authors: Lowenstein J , Roll J , Harris I , Hall F , Hollan A , Followill D
Published: November 2011

Purpose: The Radiological Physics Center (RPC) reviews patient records on brachytherapy cervix trials for completeness, consistency with the protocol and dosimetric accuracy to minimize patient dose delivery and reporting uncertainty for NCI funded clinical trials. Within cervical protocols, bladder and rectum doses are specified to limit toxicity to these normal tissues. However, bladder and rectal doses reported by institutions often disagree with the RPCˈs calculated doses. The RPC has investigated the sources of these disagreements. Methods: The RPC reviewed 182 HDR brachytherapy (tandem and ovoids (T&O)/tandem and ring (T&R)) implants and compared the institutionˈs bladder and rectum point locations and doses to those determined by the RPC strictly adhering to protocol specifications (ICRU 38) for point location and using its independent dose calculation algorithm. The RPC also analyzed its own uncertainty in defining these two points. A dose agreement criterion of ±15% was used as agreed upon by the study group and RPC. Results: The RPC disagreed with the bladder and rectal doses in 25% and 45%, respectively, of the 182 implants. The RPCˈs own uncertainty in defining the bladder and rectal points was 1mm±0. 1(STDEV), respectively which in a worst case scenario might account for 7% of the dose disagreement. The majority of the dose disagreements were due to the institutionˈs incorrect localization of the bladder and rectal points, by greater than 5mm and 4mm, respectively, away from the ICRU 38 defined location. There were no differences noted whether the applicator used was a T&O or T&R. Conclusions: Most errors resulted from institutions incorrectly defining the bladder and rectum dose calculation points per ICRU 38. Additional education, timely reviews of implant data and communication with institutions are needed to reduce the number of discrepancies.

Work supported by PHS grant CA 10953 awarded by NCI, DHHS
SU‐E‐T‐371: Measurement of Transit Dose of An Ir‐192 HDR Brachytherapy Stepping Source Using a 2D‐Array of Ion Chambers
Authors: Yewondwossen M
Published: November 2011

Purpose: The MatriXX Evolution 2D ionization chamber array is one of the 2D ionization chamber arrays developed by IBA dosimetry (IBA Dosimetry, Germany) for megavoltage real‐time absolute 2D dosimetry, verification of intensity‐modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT). We have recently shown that this 2D ionization chamber array can be used for HDR brachytherapy Ir‐192 beam dose verification. The aim of this work is to investigate the use of the movie mode of the MatriXX Evolution for measurement of transit dose of the Ir‐192 source of a Nucletron Micro‐Selectron HDR brachytherapy unit. Methods: The MatriXX Evolution measurement can be performed in different measurement modes depending on the measurement situation. For megavoltage dynamic field measurement the 2D ionization chamber array is equipped with movie mode to perform measurements continuously. During this measurement each single shot is saved and can be viewed, played as a movie, or analyzed afterwards. The integration time for each sample or movie image can be varied by the user with the shortest sampling time being 20 ms. This dynamic mode measurement of the MatriXX Evolution was used to measure the entrance, exit and the inter‐dwell transit dose of the HDR source. Results: At a fixed point of measurement, the transit dose depends on the radioactive source strength and velocity along the trajectory. The transit dose measured with MatriXX Evolution move mode has been found to be consistent with that already presented by other dosimeters. Conclusions: The feasibility of using a 2D ionization chamber move mode in determining the transit dose of HDR stepping source is explored in the present work. Results of this investigation show that 2D ionization chamber move mode can be used to measure transit dose.
SU‐E‐T‐373: Treatment Plan Validation of the XPS (Interstitial) Applicator for Use with the Xoft Axxent 50kVp X‐Ray Source
Authors: Kelley L , Rusch T
Published: November 2011

Purpose: To determine the dosimetric properties of a new interstitial applicator designed for the Xoft 50 kVp X‐ray Electronic Brachytherapy (eBx) system. Methods: A 0.64 cm diameter polymer sheath applicator interfaces with the Xoft 50kVp x‐ray source to provide radiation treatment to interstitial and other small target areas using eBx. Measurements of the dose profiles in a plane parallel to the applicator axis were determined. The absolute dose delivered to a prescription point at 90° off the central axis 1 cm from the source center, was determined using GafChromic EBT‐2 radiochromic film. The dose distribution measured in this parallel plane is compared to the distribution determined by the treatment planning software (Varian Brachyvision V8). Three x‐ray sources were paired with three interstitial applicators for the tests. Results: Using a single position treatment plan, the absolute dose at the defined prescription point was determined from calibrated film images. The measured dose agreed with the dose predicted by the treatment plan to within ±5%, with the actual range from −4.6% to +3.1% for the three samples. The measured isodose contours, including the 1 cm prescription point contour, agreed with the contours predicted by the treatment plan to within 5% (1 sigma) and the applicator does not perturb the water‐based dose distribution. The absolute dose determined from each of these contours agreed with the predicted dose to within +1/−6%. Conclusions: The XPS applicator can be used to treat small cavities using eBx with the Xoft X‐ray source. The applicator delivers dose profiles in good agreement with those predicted from the treatment planning software. It can be used for treatment in lightly shielded rooms due to the low energies employed. There are also intriguing possibilities for this applicator to be used intra‐operatively.

Research supported by Xoft, Inc. — an iCAD Company