bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐FF‐T‐85: Assessing the Reliability of Film and Semiconductor Detector in Measurement of Central Axis Depth Dose of Electron Beams
Authors: Piriyasang D 
Published: July 2007

Purpose: To investigate the possibility of using the Kodak X‐Omat V film for the central axis depth‐dose measurements of electron beams.Method and materials: The X‐Omat V films were exposed in a MED‐TEC film phantom cassette with parallel orientation to produce central axis depth dose curves. These film data were compared with the measured percentage depth dose curves by using a Scanditronix scanning water phantom with both RK ion chamber and electron diode. Measurements were made at a source to surface distance (SSD) of 100 cm for the electron energies between 6 and 20 MeV on a Varian Clinac 2100C linear accelerator for field sizes of 6 × 6 cm2 to 20 × 20 cm2. Results: The comparison of the central axis depth dose parameters, R100, R90, R50, and RP measured by the film and diode with respect to the IC's values showed that the difference did not indicate the dependence either on the energy or cone size. In the buildup region, the film presented higher percent depth dose values for most energies and cone sizes but beyond the depth of maximum dose (R100), the results were opposite. The difference of every parameter for both film and diode was within the acceptable value of ±2 mm. Conclusions: The ionization chamber and diode measurements appear to be more reliable than the film measurements, but film is particularly useful for new electron cutout data where access to accelerator beam time is limited.
SU‐FF‐T‐94: Benchmark Measurements in Heterogeneous Phantoms Under Conditions of Electronic Disequilibrium
Authors: Pillai S , Solberg TD , Medin PM , Chetty IJ 
Published: July 2007

Purpose: To perform systematic measurements of photon beam characteristics under conditions of electronic disequilibrium for the purpose of benchmarking dose algorithms. Method and Materials: Slab phantoms consisted of styrofoam (ρ=0.03g/cm3), lung‐equivalent (ρ=0.21g/cm3), and bone‐equivalent (ρ=1.7g/cm3) materials, embedded within solid water. Ion chambers with active volumes of 0.125cm3 and 0.015cm3 and EDR2 film were used to measure depth dose and off‐axis photon beam characteristics within several phantom geometries. Experiments were conducted for field sizes from 2×2 to 25×25cm, for 6 and 23MV photon beams produced from a Siemens accelerator. Results: In the styrofoam phantom, the average agreement between the two ion chambers was within 2% for both energies with maximum differences of 9% observed in the sharp dose falloff region for small field sizes due to chamber volume effects. The 0.125cm3 chamber over‐estimated dose in the sharp falloff regions within the low density heterogeneities at the smallest field sizes, due to increased volume averaging. Relative dose film measurements demonstrated sharper penumbral gradients than ion chambers. Dose reduction in the lower density phantoms was enhanced with reduced material density and field size, and increased beam energy. Depth dose calculations differed by up to 20% and 10% versus measurements in the lung phantom for the 6 and 23MV beams, respectively. These discrepancies were partly attributed to a poorer fitting beam model for 23MV photons. Calculations were on average within 4% of measurements in the bone phantom for the 6MV beam, but larger differences (∼ 12%) were found for 23MV photons, likely due to increased pair production at this energy. Point dose calculations differed from measurements in a lung/tumor phantom by 6% for 3×3cm, 6MV photons. Conclusion: Measurements under conditions of electronic disequilibrium are confounded by many factors and must be performed with utmost care for algorithmic verification at the ±2% level.Acknowledgement: NIH/NCI‐R01CA106770.
SU‐FF‐T‐101: Characterizing Output for a Static TomoTherapy Field
Authors: Gibbons J , Smith K , Hesston R 
Published: July 2007

Purpose: To determine in‐air and in‐phantom output factors for a static TomoTherapy beam. Method and Materials: Measurements and computer simulations of in‐air output ratios (Sc) and in‐phantom output factors (Scp) have been made for a static TomoTherapy beam. In‐air measurements were made at a depth of 10 cm in a commercial mini‐phantom for field widths ranging from 1.8 cm to 40 cm, for 2.5‐cm and 5.0‐cm jaw selections. Measurements were made at source‐chamber distances (SCDs) of 85 cm and 105 cm. In‐phantom measurements were made at a depth of 10 cm in a full size virtual water phantom for the same field sizes and at an SCD of 85 cm. Data were normalized to the values for the largest available field size (40 × 5 cm2). Both in‐air and in‐phantom measurements were compared with simulations made on the TomoTherapy planning system using simulated CT datasets of the full size and mini‐phantoms. Results: In general, measured and simulated data agreed within 2% for the output factors determined in this work. Measured and simulated Scps varied steeply (∼ 15%) for the field sizes investigated. In contrast, Scs showed little changes with field size or SCD, although the measured data demonstrated a slightly greater variation with field size than the simulated results. Results were consistent between data taken for different jaw selections, with the best agreement observed for the determined phantom scatter factors, Sp. Conclusion: The lack of a flattening filter in the TomoTherapy beam explains the small variation of Sc with field size and SCD. Thus, Scp is due primarily to phantom scatter, which should not vary greatly between TomoTherapy machines. The determination of output factors may be used in the verification of treatment planning doses, both for helical and static deliveries.Supported in part by a research agreement with TomoTherapy, Inc.
SU‐FF‐T‐197: Effect of the Added Buildup On P‐Type Silicon Diodes' Response in Daily in Vivo Dosimetry Measurements
Authors: Alaei P , Higgins P , Gerbi B 
Published: July 2007

The silicon semiconductor diodes used for routine in vivo dosimetry in radiation therapy are commonly constructed with added buildup to place the effective point of measurement (location of the silicon chip) at the depth of maximum dose (dmax) or beyond and to shield against low energy scattered photons. This added buildup, commonly made of high‐density metals, could however introduce increased uncertainty to the accuracy of diode measurements. Previous work in this area has shown that buildup diodes show certain imperfections when applied in small photon fields.1We have studied the effect of this buildup on in vivo dosimetry measurements, especially for small‐field dosimetry associated with IMRT treatments. We compared the response of the buildup diodes to that of no‐buildup ones, commonly referred to as skin diodes. We have used identical commercially available p‐type diodes, with and without the additional buildup, to measure the dose delivered by small static fields. The measurements with the no‐buildup diode were performed by placing tissue‐equivalent bolus on top of the diode to bring the diode measurement point to the depth of Dmax. In addition, we measured the dose to sample IMRT phantom plans as well as patient IMRT plans delivered to phantom, using both types of diodes.Our results indicate that the buildup diodes, in general, produce higher readings than no‐buildup ones for small field dose deliveries, adding to the uncertainty of diode measurements. We have also observed that using the skin (no‐buildup) diodes with added tissue‐equivalent buildup decreases the measured‐to‐expected percentage differences by about 2%.
SU‐FF‐T‐202: EUD‐Based Indication for Re‐Planning During Image‐Guided Adaptive Radiotherapy
Authors: Qi S , Li X 
Published: July 2007

Purpose: A quantitative real‐time indicator for re‐planning due to the inter‐fractional anatomic changes (e.g., volume and shape changes) during the course of radiation treatment is not available for image‐guided adaptive radiotherapy (IG‐ART). In this work, we propose a EUD‐based indicator to address this issue.Methods and Materials: A EUD‐based quantity
urn:x-wiley:00942405:media:mp0863:mp0863-math-0001 is introduced to assess the complicated EUD changes due to the inter‐fractional changes collected with daily CT images. Both target(s) and normal structures are considered. IEUD is calculated using the DVHs based on the original planning CT and the daily CT images. To demonstrate feasibility, we have calculated IEUD for selected representative cases in three tumor types: lung, head‐and‐neck and sarcoma, based on daily CT images acquired with a tomotherapy (HiArt, Tomotherapy) and a CT‐on‐Rail (Primatom, Siemens). The clinical target volumes (CTVs) and various normal structures were contoured on a series of daily CTs. The verification DVHs were generated by applying the original (or previous re‐planning) beam setups to the CT set of the day using either the XiO (CMS) planning system (for the patients treated with the Primatom) or the tomotherapy Planned Adaptive software (for those treated with Tomotherapy). Results: Significant inter‐fractional anatomic changes were observed on all selected cases, and these changes can be quantified by the values of IEUD. For a soft‐tissue sarcoma at chest, for example, the CTV in the middle of the treatment was found approximately doubled from that on the planning day. Such dramatic volume changes resulted in significant decreases in the CTV coverage (95 reduced to 30%), the IEUD value dropped by 15.6% (compared to that of the original plan), indicating the necessity for re‐planning. Conclusions: Dramatic anatomic changes may be observed during the treatment. The presently proposed EUD‐based indicator, capable of quantifying such changes, can be used to trigger re‐planning for IG‐ART.
SU‐FF‐T‐222: Expected Clinical Impact of the Differences Between Planned and Delivered IMRT Dose Distributions
Authors: Mavroidis P , Ferreira B , Papanikolaou N , Svensson R , Lind B , Brahme A 
Published: July 2007

Purpose: Due to the highly conformal distributions that can be obtained with intensity modulated radiation therapy (IMRT), any discrepancy between the intended and delivered distributions would likely affect the clinical outcome. Consequently, there is a need for a measure that would quantify those differences in terms of a change in the expected clinical outcome. Material and Methods: To evaluate such a measure, the case of a cervix cancer was used where the bladder and rectum, are proximal and partially overlapping with the internal target volume. A solid phantom simulating the pelvic anatomy was fabricated and a treatment plan was developed to deliver the prescribed dose to the phantom. The phantom was then irradiated with films positioned in several transverse planes. The racetrack microtron at 50MV was used in the treatment planning and delivery processes. The dose distribution delivered was analyzed based on the film measurements and compared against the treatment plan. The differences in the measurements were evaluated using both physical and biological criteria. Results: For the computerized treatment plan, the maximum value of P+ was 84.1%, for a mean dose to the ITV of D̄ = 93.3Gy, associated relative standard deviation and biologically effective uniform dose, D̿ITV of 89.2 Gy. The delivered dose distribution from all the beams produced a P+ value of 77.0% for and D̿ITV of 83.5 Gy.Discussion and Conclusions: Whereas the physical comparison of dose distributions can assess the geometric accuracy of delivery, it does not reflect the clinical impact of any measured dose discrepancies. With highly conformal IMRT, the accuracy of the patient setup and treatment delivery, are critical for the success of the treatment. A method is proposed to evaluate the precision of the delivered plan based on changes in complication and control rates as they relate to uncertainties in dose delivery.
SU‐FF‐T‐241: High Precision Data Set For Benchmarking of Electron Beam Monte Carlo
Authors: McDonald A , McEwen M , Faddegon B , Ross C 
Published: July 2007

Purpose: In treatment planning, and particularly in beam commissioning, Monte Carlo dose calculation algorithms are finding increasing application. This research aims to create high accuracy reference data, which will be used for benchmarking of Monte Carlo models. Method and Materials: Using the Vickers research linac with beam energy known to 0.5 % and a translational stepping slide with positioning accuracy of 0.2 mm in‐air beam profiles were obtained. The measurements were made using an Exradin #a16 microchamber and PTW Electron Diode type 60012 and these were compared to a BEAMnrc Monte Carlo simulation and also to ICRU report 35 mass scattering powers. Results: An experimental data set has been obtained using a well‐known beam energy, spot size and irradiation geometry. Measurement data was acquired for a range of scattering foils and with different scattering gases between foil and detector. The uncertainty in the detector position is 0.2 mm and the uncertainty in the measured fluence is 0.1 %.i) There was good agreement between the profiles measured by the two detectors.ii) The initial Monte Carlo results indicated that a divergence of the incident beam must be included in the simulation to give agreement with the experimental data.A simple scattering model, using mass scattering powers from ICRU report 35, was used to obtain an estimate of the initial beam divergence. A value of 10 – 15 mrad was obtained, which is in good agreement with the Monte Carlo results. Conclusion: We now have a high accuracy data set for the benchmarking of electron beam Monte Carlo models at better than 1 % /1 mm level. An initial BEAMnrc calculation has indicated that the angular divergence of the beam has a significant affect on the width of the in‐air beam profile.Acknowledgment: Support from NIH grant R01 CA104777‐01A2.
SU‐FF‐T‐261: Independent Point Dose Verification Using TomoTherapy Quality Assurance Phantom
Authors: Cheek D , Hogstrom K , Robertson C , Rosen I , Gibbons J 
Published: July 2007

Purpose: To detect TomoTherapy planning errors by relating a point dose in the patient treatment plan to the dose calculated at the corresponding point in the quality assurance phantom. Methods and Materials: Standard TomoTherapy patient‐specific quality assurance applies the patient treatment plan to a cylindrical QA phantom and then compares measured phantom dose to calculated phantom dose. However, there is no check of dose in the phantom to dose in the patient. We applied a ratio of TMRs to a point dose in the patient treatment plan in order to estimate the dose to the corresponding point in the phantom. Rotational delivery of TomoTherapy was approximated using either a 360° arc, 8 equally‐spaced angles, or 4 equally‐space angles. For each approximation, calculations were done using average physical depth and average radiological depth. The method was tested using data from 87 TomoTherapy patients. TMR ratio method doses were compared to treatment planning system doses. Agreement within ±5% was considered clinically acceptable. Results: Using average radiological depth, the pass rates were 70.6%, 69.4%, and 65.9% for the 360°, 8−, and 4‐;angle approximations, respectively. Using average physical depth, the pass rates were 63.5%, 56.5%, and 58.8% for the 360°, 8‐, and 4‐angle approximations, respectively. The best results were obtained for centrally‐located tumors such as prostate (83.9% pass rate for radiological depth and 360° arc approximation). The pass rates were worst for superficial tumors (50.0% pass rate for radiological depth and 360° arc approximation). Conclusions: The TMR ratio method was used to relate dose in the QA phantom to dose in the patient. For each beam approximation, radiological depths gave better results than physical depths. The site‐specific pass rates could be used to determine action levels for implementing this method in the clinic.Supported in part by a research agreement with TomoTherapy, Inc.
SU‐FF‐T‐264: Influence of Monte Carlo Beamlet Smoothness On Plan Metric Accuracy
Authors: Wattson D , Cui J , Wilkens J , Deasy J 
Published: July 2007

Purpose: Monte Carlo (MC) may be advantageous as a basis for IMRT dose calculations as it provides for reliable heterogeneity corrections even in complex media. However, the upper‐limit of noise in pre‐computed beamlets has not been previously investigated. Method: We investigated convergence in plan metrics for optimized IMRT treatment plans as a function of MC noise in the input pre‐computed beamlet influence matrices. We analyzed seven individual patient cases of head and neck cancer. Each radiotherapy dose calculation involved nine 6 MV beams divided into beamlets of 1cm × 1cm cross‐section. The VMC++ Monte Carlo dose calculation engine was used as a basis for the calculations. A prioritized prescription optimization process was utilized to produce the final plan. As a function of beamlet noise levels, we monitored minimum combined‐PTV dose, D95 (minimum dose to hottest 95% of the combined PTVs), maximum dose to the brain stem, and mean dose to the parotid glands. For all metrics, we took a convergence within 1% of the low‐noise limit as being adequate. Results: For D95, 1% accuracy was typically achieved with an individual beamlet noise level of 2.4% (std. error); minimum target dose was accurate only when very noise levels were reached (< 0.5%); maximum dose to brain stem was accurate when beamlet noise was typically less than approximately 2%; mean dose to the parotid glands was accurate even at relatively noise beamlet levels (5%). Conclusions: Adequate MC beamlet smoothness depends critically on the plan review metrics. Metrics which partially or fully average over voxels (D95 of targets, or mean doses to organs) converge rather quickly compared to metrics which are sensitive to single‐voxel excursions (e.g., maximum organ dose or minimum target volume dose).This research was partially supported by NIH grant R01 CA90445 and a Siteman Cancer Center fellowship.
SU‐FF‐T‐271: Investigation of Convergence and Systematic Dosimetric Errors Resulting From Endorectal Balloon‐Based Heterogeneity in Conformal and IMRT Planning of Prostate Cancer
Authors: Li S , Solberg TD , Rosu M , Foster R , Enke C , Chetty IJ 
Published: July 2007

Purpose: To investigate dosimetric errors caused by endorectal balloon‐based heterogeneity in prostate cancer forward and inverse planning.Method and Materials: Five prostate cancer patients, treated with air‐filled rectal balloons, were retrospectively recalculated assuming air‐equivalent density and were compared to plans in which unit‐density was assigned to the air. Each plan was performed using 3D‐CRT (4‐ and 6 field) and IMRT techniques. For IMRT plans, systematic dose errors were estimated as follows: , where the superscript, “air” assumes the true air density in the rectal balloon and indicates the dataset upon which beam weights were optimized. The subscript represents the final dose calculation dataset based on the optimized beam weights. The convergence dose error may be approximated as follows: , where the final dose calculation dataset is equivalent (assumes air density) while the initial dataset, upon which beam weights are optimized, is changed between the water‐based and air densities. DVHs, and biological dose indices, generalized EUD (gEUD), and NTCP were used to assess the dosimetric consequences of assigning unit‐density to the air in the rectal balloon. Results: Although the posterior aspect of the prostate (prostate/rectum junction) was consistently under‐dosed when air‐densities were assigned to the rectal balloon, these differences did not significantly affect the prostate gEUD. Average differences were approximately 0.5 Gy, with a maximum difference of 1.5 Gy observed in one IMRT plan. Rectal %NTCPs sometimes differed significantly (up to 7%) between the water‐ and air‐density assignment and were more pronounced for the 3D‐CRT plans. IMRT systematic dose errors were generally found to be larger than convergence errors, with the greatest effect observed in the rectum where NTCP differences ranged from 1 to 5%. Conclusion: Tissue heterogeneity effects resulting from use of endorectal balloons may be dosimetrically important and must be considered for accurate 3D‐CRT and IMRT prostate cancer planning.
SU‐FF‐T‐407: The Effect of Weekend‐Off and Day of Treatment Initiation On Tumor Control Probabilities
Authors: Lee T , Rosen I , Hogstrom K 
Published: July 2007

Purpose: Recently developed tumor control probability (TCP) models can incorporate temporal variations in the delivery of treatment fractions. This study investigated the effect on TCP of weekend treatment breaks and of the treatment initiation week day. Methods and Materials: Treatment plans were selected for three patient with tumors of different cell doubling times — squamous cell carcinoma of the head and neck (short doubling time), breast cancer (intermediate doubling time), and prostate adenocarcinoma (long doubline time). TCPs were calculated and compared for each treatment plan using fractionation schedules that included or omitted weekend breaks. We also computed TCPs for fractionation schedules that included weekend breaks but started on different week days — Monday, Wednesday, or Friday. We assumed the same numbers of fractions and total doses for all fractionation schedules. Results: For the primary PTV of the head and neck tumor, the TCP increased by 3.1% when weekend breaks were not given. For the breast cancer, the TCP was independent of weekend break. For the prostate tumor, the TCP increased by 1.4% when weekend breaks were omitted. When comparing different start days for treatment, TCPs were higher for Monday starts than for the other days for all cases. Conclusions: The calculations suggest that TCPs can be increased for the same total dose if treatment is delivered without weekend breaks. In addition, the overall treatment time is reduced, which is known to be an important factor in head and neck treatments. The comparison of TCPs calculated for different treatment start days suggests that Monday is the best day for treatment initiation. This is consistent with current clinical practice. However, we did not examine the effect on normal tissues of fractionation without weekend breaks.Supported in part by a research agreement with TomoTherapy, Inc.