bluuebunny/crossref_metadata_2025 huggingface dataset:
TU‐C‐ValB‐08: Modeling Dose Delivery Accuracy of IMRT Head‐And‐Neck Cancer Treatment
Authors: O'Daniel J , Garden A , Wang H , Asper J , Ang K , Ahamad A , Schwartz D , Rosenthal D , Morisson W , Zhang L , Tung S , Mohan R , Dong L
Published: July 2006

Purpose: To evaluate the impact of internal organ variations on IMRT treatments of head‐and‐neck cancers using different daily alignment techniques. Method and Materials: Eleven head‐and‐neck cancer patients were imaged twice weekly during their course of treatment (141 CT scans total) using an integrated CT‐linear accelerator (EXaCT, Varian Oncology Systems). The clinical IMRT plans were copied onto the daily CT images. The plans were aligned with (1) the daily marked isocenter using three radio‐opaque markers (BBs) and (2) bone alignment, using in‐house software to align the cervical vertebrae. Daily dose distributions were mapped from the daily CT images onto the planning CT image with an in‐house deformable image registration algorithm. Cumulative dose‐volume histograms from the planning CT image were analyzed. Results: The differences in the clinical target volumes (CTV) gEUD between the planned and delivered doses (with BB or bone alignment) were typically ⩽1Gy; therefore the differences in target coverage were most likely clinically insignificant. However, the alignment method did have a statistically significant impact on the percentage‐volume of the CTV at the prescription dose. Neither BB alignment nor bone alignment maintained the planned coverage (average=98.2%), which was reduced to 95.6% with bone alignment (p=0.000) and 94.3% with BB alignment (p=0.000).

BB alignment significantly increased the average percentage‐volume receiving ⩾25Gy above the original plan for the ipsilateral (59.6% vs. 51.4%, p=0.003) and contralateral (42.0% vs. 36.4%, p=0.016) parotid glands. The parotid gland gEUD increased by more than 5Gy in 35% of BB alignments and 15% of bone alignments. However, there was no statistically significant difference between BB and bone alignments in parotid dose received. Conclusions: The differences in CTV coverage between bone and BB alignment were statistically significant but small. Bone alignment more closely reproduced the planned parotid dose than BB alignment, although both gave higher dose than the original plan.
TU‐C‐ValB‐09: Setup Error Analysis of HN‐IMRT Patients Using Electronic Portal Images and Cone‐Beam CTs
Authors: Wu Q , Wloch J , Fayad J , Yan D
Published: July 2006

Purpose: It is important to monitor and correct patient setup during treatment course for head and neck IMRT because highly conformal dose distribution is sensitive to setup uncertainties. Setup for HN region is unstable because patient is usually uncomfortable under the mask and the flexible bony structures in the neck region. The purpose of this study is to analyze the setup errors during entire treatment course. These findings will help make appropriate corrective decisions. Method and Materials: Patients enrolled in our IMRT protocol are immobilized with a large thermoplastic mask attached to the MedTec IPPS. 2D analysis is accomplished by comparing electronic portal images to DRRs using in‐house software. Systematic setup error exceeding 3mm is corrected. 3D analysis is performed by registering cone‐beam CT to planning CT. Data from 21 patients with total 185 sessions were used. Correlation between 2D and 3D were analyzed. Time trend was analyzed for patients with daily CBCTs (4 patients with 131 scans total). Results: Good correlations were observed between 2D and 3D analyses with mean difference less than 1mm. Both methods showed that the mean of setup errors is under 1mm in all directions. The systematic and random errors were about 2mm. Margin of 5mm used in the planning seemed to be adequate based on empirical recipes. Time trend analysis shows that changes occurring during treatment course are significant for 3 (out of 4) patients. Conclusion: 2D and 3D analyses agree with each other, but 3D should be used whenever possible because it has the advantage of better image quality, lower imaging dose, and better software to interpret information. The difference is caused mainly from image quality and non‐rigid bony motion. It may be necessary to redo the mask in the middle of treatment course to reduce overall setup error.
TU‐C‐ValB‐10: Rectal Dose Variation in Image Guided Radiation Therapy of Prostate Cancer
Authors: Chen L , Paskalev K , Xu X , Zhu J , Wang L , Price R , Horwitz E , Feigenberg S , Pollack A , Ma C
Published: July 2006

Purpose/Objective: To investigate the change in rectal dose during the treatment course for prostate IMRT with image‐guidance. Materials & Methods: Ten prostate cancer patients treated with IMRT were included in this study. Each patient was administered an enema prior to CT‐ and MRI simulations. MR and CT were fused for target delineation. IMRT treatment planning was performed on the CT image. Prostate motion during the treatment course was corrected using a CT‐on‐Rails system. Rectal contours were generated on both simulation CT images and subsequent treatment CT images. IMRT plans were generated based on our clinical acceptance criterion. The subsequent treatment CT images for each patient from the CT‐on‐Rails system were used to recompute the patient dose distributions with the same leaf sequences used for treatment. The isocenter was shifted relative to the simulation CT, as required by the protocol, to ensure appropriate target coverage. The rectal doses based on the subsequent treatment CT were compared with the original doses planned on the simulation CT scans using our clinical acceptance criteria. Results: Based on ten patients with 84 treatment CT sets, 14% of the subsequent treatment dose distributions did not meet our criterion of V40 < 35% (V40=36%∼50%), and 7% did not meet our criterion of V65<17% (V65=18%∼36%). The inter‐fractional rectal volume variation is significant for some patients. The minimum changes in rectum volume are between 31 and 39.8cc while the maximum changes are between 50.2 and 161.7 cc. In general, IMRT planning with an empty rectum results in better subsequent treatment dose distributions to the rectum. Conclusions: Due to the large inter‐fractional variation of the rectal volume it is more favorable to plan prostate IMRT based on an empty rectum.
TU‐C‐224A‐03: 4D‐Image‐Guided Treatment Planning Optimization for Management of Organ Motion in Radiotherapy Planning
Authors: Lee E , Cha K , Bortfeld T , Deasy J
Published: July 2006

The management of breathing‐registered IMRT treatment planning is explored by direct incorporation of 4D images within the planning process. The movement of the voxels from one CT timeframe to another is “tracked” and modeled. A timestamp for each voxel is used to specify its position throughout the breathing cycle. A single treatment model incorporates planning constraints throughout multiple time periods. Robustness of the algorithm, plan quality, and potential clinical significance are evaluated.

4D‐CT scans of lung/liver cancer patients were acquired with different breathing phases(phases 0–9, 0:full‐inhale, 5:full‐exhale), Three treatment planning strategies are performed and compared. 1)Standard planning with a static PTV based on a single selected phase (control). 2)The Internal Target Volume (ITV) approach, where ITV is defined as the union of CTVs in all breathing phases. 3)Single‐stage‐4D‐image‐guided planning, where within a single treatment optimization model, planning constraints are incorporated on each voxel for each phase throughout the multiple‐phase period. Sophisticated computational optimization techniques are used to solve these models.

For both lung/liver cases, the static‐PTV‐plan results in unacceptable PTV‐underdose. Compared to ITV‐pamns, 4D‐image‐guided‐plans offer good coverage and comparable min‐PTV‐dose; while in lung, it reduces normal‐lung‐mean‐dose by 20%, heart‐mean‐dose by 20%, and esophagus‐max‐dose by 15%; and in liver, it reduces normal‐liver mean‐dose by 15% and other normal‐tissue mean‐dose by 20%, with improved PTV‐conformity of 10%.

4D‐Image‐Guided treatment planning optimization can provide good PTV‐coverage plans, improve PTV‐underdose, and significantly reduce dose to organs‐at‐risk, especially those organs in the proximity of the tumor. Evidence of morbidity reduction to organs‐at‐risk is observed. The challenge involves the ability to solve a large‐scale treatment planning problem. With sophisticated mathematical optimization modeling and computational strategies, such planning is possible and can be made available for clinical use. Clinical studies are needed to validate the importance of our approach to treatment outcome.
TU‐C‐224A‐04: Simplifying Parameter Adjustment for Prostate IMRT Planning Using Sensitivity Analysis
Authors: Lu R , Radke R , Happersett L , Chui C , Yorke E , Jackson A
Published: July 2006

Purpose: To simplify the trial‐and‐error process of adjusting objective function parameters (e.g. weights, dose limits) in prostate IMRT planning, we present a feasibility study showing that an outer loop optimization over 6 automatically‐identified sensitive parameters can quickly and automatically determine parameters that lead to a plan meeting the clinical requirements. Method and Materials: We apply statistical sensitivity analysis to quantify the effect of each hand‐tunable parameter of the IMRT cost function on each clinical objective, automatically identifying those parameters with the strongest impact. Second, we globally optimize a plan quality score over the six most sensitive parameters in an outer loop to determine acceptable parameters, using a search algorithm based on multiscale random sampling. Results: Experiments on a 36‐patient dataset showed that a clinically acceptable five‐field 8640cGy prostate IMRT plan could be automatically determined in 35 minutes on the average in 87% of the cases. Compared to the plans from the planner's protocol default settings, the mean value of the minimum dose in PTV increased from 67.5% to 79.7%, and the mean value of PTV V95 coverage increased from 82.2% to 94.1%. The mean values of rectal wall V54%, rectal wall V87% and bladder wall V54% are 50.4%, 12.6% and 36.1%, respectively. The outer‐loop‐optimized plans met DVH constraints defining clinical acceptability and were comparable to manually‐determined plans. Confining the parameter search to the sensitive parameter set greatly improves the quality and speed of the outer‐loop optimization. Conclusion: The reduced‐order outer‐loop optimization can facilitate parameter selection for dose‐volume‐based IMRT objectives. It may also be applicable to other types of objective functions, and has the potential to ease the manual burden of IMRT planning in more complex sites (e.g. head and neck).

Supported by National Cancer Institute grant 5P01CA59017‐13 and the NSF Center for Subsurface Sensing and Imaging Systems, grant EEC‐9986821.
TU‐C‐224A‐06: Exploiting the Full Potential of MLC Based Aperture Optimization Through Collimator Rotation
Authors: Milette M , Rolles M , Otto K
Published: July 2006

Purpose: To investigate the benefits of MLC rotation in Direct Aperture Optimization (DAO) inverse treatment planning. Method and Materials: An alternative to fluence based inverse planning is to optimize directly the leaf positions and field weights of MLC apertures. Here we introduce a new technique called Rotating Aperture Optimization (RAO) which is based on an extension of DAO. Our technique differs from existing aperture based IMRT techniques in that the MLC is rotated in between each aperture. Treatment plans are generated for 10 nasopharynx recurrence patients with and without MLC rotation for 5 mm and 1cm leaf width MLCs. A comparison study is performed between RAO and DAO in order to assess the benefits of RAO over and above those available with fixed collimator angle DAO. Film verification is also performed to evaluate the accuracy of fixed and rotated collimator aperture delivery. Results: An analysis of the final cost values and DVHs indicate that plans generated with RAO are as good as or better than DAO while maintaining a smaller number of apertures and MU than conventional IMRT. In particular, RAO with the 1cm leaf width MLC is able to produce better plans than DAO with the 1 cm leaf width MLC and plans that are equivalent to DAO with the higher resolution 5mm leaf width MLC. Film verification results show that RAO is less sensitive to tongue and groove effects than DAO. Although delivery time is increased due to the collimator rotation speed this is a mechanical limit that could be easily overcome. Conclusion: Our results indicate that RAO is able to provide superior dose distributions, particularly with larger (1 cm) leaf width MLCs, while maintaining the lower MU and number of apertures afforded by the direct aperture approach.

Conflict of Interest: Supported in part by Varian Medical Systems.
TU‐C‐224A‐08: A Scientific Comparison of Inverse Treatment Plan Quality Using a Convex Non‐Linear Programming Model as a Function of Beam Quality and Beam Number
Authors: Fox C , Lynch B , Aleman D , Li H , Romeijn H , Dempsey J
Published: July 2006

Purpose: Recent advances in large scale fluence map optimizations for IMRT allow the use of large beam numbers that conform to the target to generate the desired target coverage while at the same time maintaining dose to critical organs below tolerance limits. Additionally, IMRT has effectively removed the need for high energy accelerator beams due to the excellent plan quality achievable with low beam quality. We investigate the diminishing returns in plan quality with increasing beam numbers and compare IMRT treatment planning of 6MV and 60Co therapy dose models. Method and Materials: A convex non‐linear model was used to compare the plan quality, from dose volume histograms and fluence maps, for three treatment sites (H & N, CNS and prostate) for a 6MV and 60Co dose model. Plans were calculated for 5, 7, 9, 11, 17, 35 and 71 equidistant beam angles and quality assessed on target coverage (R95% > RRx) and organ sparing for each case. Results: Similar target coverage was achieved for 60Co as with 6MV and equivalent organ sparing was also observed for all three sites. Increasing the number of beams provided some improvement in organ sparing while maintaining target coverage conditions. Dose calculation times increased linearly with beam number and FMO calculations increased by up to 900% between 5 and 71 beams. Conclusion: We have demonstrated that IMRT plan quality using a 60Co dose model produces similar dose distributions to 6MV. We also show that plan quality does not show considerable improvement above 11 beams for IMRT and significant increases in the treatment planning times are observed extending the number of treatment beams to 71 beams.

This work supported in part by NSF grant DMI‐0457394 and the State of Florida DOH Grant 04‐NIR03.
TU‐C‐224A‐09: Implementation and Comparison of Several Proton IMRT Algorithms
Authors: Li H , Fox C , Romeijn H , Dempsey J
Published: July 2006

Purpose: To computationally compare the plan quality provided by 3 different intensity modulation proton therapy (IMPT) techniques: 3D modulation; 2.5D modulation; and distal edge tracking (DET) with optimization. Plan quality, problem size, and efficiency were assessed. Method and Materials: The dose calculation was based a finite sized beamlet model, which was 1×1 cm2 at isocenter. The dose from each beamlet was the superposition/convolution of infinitesimal pencil beams falling within the beamlet. Ray tracing to each voxel was performed for each beamlet to find out the radiological depth to each voxel. In the 3D modulation algorithm, a stack of Bragg peaks were placed between the maximal and minimal radiological depths of targets passed by a beamlet with 2.5 mm spacing. The fluence of each Bragg peak was modulated independently by the optimizer. The placement of the Bragg peaks in the 2.5D algorithm was similar to the 3D algorithm, but the Bragg peaks belong to a beamlet were pre‐optimized to make a spread out Bragg (SOBP) whose dose level was equal to the prescription dose of the target it passed. The weights of SOBPs were optimization variables. In the DET algorithm, the Bragg peaks were set at the distal edge of the targets. Results: The 3D algorithm could produce the best plan with least beams, but the data size was large. The DET was most efficient in dose calculation and fluence map optimization, its plan quality was fair. The advantage of the 2.5D algorithm was in its small data size and efficiency in fluency map optimization. Conclusion: An appropriate algorithm should be selected to meet the trade‐off of plan quality versus computational and delivery efficiency.

This work was supported in part by Florida DOH Grant 04‐NIR03.
TU‐C‐224A‐10: A Novel Neighborhood for Local Search and Simulated Annealing Methods in Beam Orientation Optimization in IMRT
Authors: Aleman D , Romeijn H , Dempsey J
Published: July 2006

Purpose: To select quality coplanar solutions to the beam orientation optimization (BOO) problem in intensity‐modulated radiation therapy (IMRT) treatment planning, and to demonstrate that high‐quality treatment plans can be obtained using fewer beams than typically used in equi‐spaced plans. Method and Materials: We consider the problem of obtaining quality 3‐ and 4‐beam coplanar radiation treatment plans. Two methods to obtaining these solutions are tested: the simulated annealing (SA) algorithm, which provides a global approach to the problem, and the Add/Drop heuristic, which provides a locally optimal solution. In the algorithms, a novel neighborhood is considered wherein a beam's neighborhood consists of a number of beams adjacent to the current beam plus a number of beams adjacent to the parallel‐opposed beam, which we call the “flip neighborhood”. For the SA algorithm, several methods of obtaining neighboring solutions and different cooling schedules are considered. The algorithms were tested on six head‐and‐neck cases using coplanar beams on a 5° grid. The resulting treatment plans were compared to the 5‐ and 7‐beam equi‐spaced plans typically used in practice. Results: While the 3‐beam treatment plans were poor in quality, the 4‐beam treatment plans obtained using both the SA method and the Add/Drop heuristic had comparable or improved quality to the 5‐ and 7‐beam equi‐spaced plans typically used in head‐and‐neck treatment. Conclusion: For head‐and‐neck cases, quality plans with fewer beams than standard 5–7 beam treatment plans can be obtained if BOO is applied. We also show that although the flip neighborhood increases run time for the Add/Drop heuristic (the run‐time of the simulated annealing algorithm is unchanged), it improves the FMO value for both the simulated annealing algorithm and the Add/Drop heuristic.

This work supported in part by NSF DMI‐0457394 and the NSF Alliances for Graduation Education and the Professoriate and Graduate Research Fellowship programs.
TU‐C‐224C‐01: Investigation of Properties of a New Liquid Ionization Chamber
Authors: Elliott A , Stewart K , Seuntjens J
Published: July 2006

Purpose: Liquid ionization chambers (LICs) have characteristics that can remedy some of the drawbacks of air‐filled ionization chamber dosimetry: large sensitive volumes (i.e. low spatial resolution), fluence perturbations, and energy dependence over the clinical range of beam qualities. However, there are significant problems in liquid chambers. High ionization density and low ion mobility lead to high ion recombination rates. In this work, extensive experimental work has been performed to investigate properties of a new liquid chamber. This includes chamber stability over time, chamber reproducibility, and establishing recombination corrections. Methods and Materials: The new chamber is called the GLIC‐03 (Guarded Liquid Ionization Chamber). The diameter of the collecting electrode is 1.5 mm and the plate separation is 0.4 mm, giving a sensitive volume of 0.7 mm3. The dielectric liquid used is isooctane. We used the 18 MV beam of a Varian Clinac 21EX linear accelerator. The lowest pulse rate setting, 100 MU/min, was used in order to avoid incomplete collection of charge from one pulse before the arrival of the next. Measurements were taken in solid water at 15 cm depth, with various field sizes and SSDs. Boag's theory for general collection efficiency for parallel‐plate gas ionization chambers, applied to isooctane in pulsed radiation, was used for recombination corrections. Results: The GLIC‐03 response varied by less than 1% over 10 hours, and was reproducible within 1.5% of the mean over different liquid fills. The collection efficiency decreased with increasing dose per pulse due to general recombination of ions from a larger number of ionizing particle tracks. Recombination corrections were within 1% for low dose rates and high electric field strengths. Conclusion: The establishment of these characteristics in the present work allows us to perform accurate relative measurements in high gradient non‐equilibrium fields as well as energy dependence investigations.
TU‐C‐224C‐05: Energy Response of LiF:Mg,Ti Thermoluminescent Dosimeters to Moderately Filtered X‐Ray Spectra in the Range of 20 to 250 KV Relative to 60Co
Authors: Nunn A , Davis S , DeWerd L , Micka J
Published: July 2006

Purpose: To use experimental methods to determine the response of LiF:Mg,Ti thermoluminescent dosimeters (TLDs) irradiated using moderately filtered (M‐series) x‐ray spectra in the energy range of 20 to 250 kV relative to the response to 60Co photons. Also, to determine if LiF:Mg,Ti TLDs are intrinsically linear detectors (i.e. the response is proportional to energy imparted). Method and Materials: TLDs were irradiated to a known air kerma using the NIST traceable M‐series x‐ray beams, which were located at an Accredited Dosimetry Calibration Laboratory (ADCL), in the range of 20 to 250 kV. Using each x‐ray beam, several sets of TLDs were irradiated to different air kerma levels to take into account any dose non‐linearity. TLD response was then compared to that from several sets of TLDs irradiated at corresponding air kerma levels using 60Co. The Monte Carlo code MCNP5 was used to correct for scatter from the holder and to determine the predicted/expected TLD response to the experimentally used x‐ray beams. Results: The measured TLD energy response compared to the response to 60Co shows a rapid decrease toward very low photon energies. This response dropped to approximately 0.90 at the lowest effective energy of 11.5 keV. The highest response was found to be 1.37 at an effective energy of 28.5 keV. The results showed poor agreement between measured energy response and calculations using the mass‐energy absorption coefficients of pure LiF. A significant increase in measured response compared to calculated response was seen at effective energies higher then 25 keV. Conclusion: These results demonstrate that the measured energy response differs by up to 14% from Monte Carlo calculations and is highly dependent on the energy of the source. The results also suggest that LiF:Mg,Ti TLDs are not intrinsically linear with energy imparted.
TU‐C‐224C‐06: Determination of TG‐43U1 Recommended Parameters for Elongated RadioCoil™ Brachytherapy Sources 1.0 to 6.0 Cm in Length Using Experimental and Monte Carlo Simulation Techniques
Authors: Dini S , Awan S , Dou K , Mokhberiosgouei R , Meigooni A
Published: July 2006

Purpose: In this project TG‐43U1 recommended dosimetric characteristics of newly designed elongated RadioCoil™ brachytherapy sources(1 to 6)cm in length have been determined following experimental and Monte Carlo simulation techniques. Monte Carlo simulated dose profiles have also been calculated for sources 1 to 6cm in length. Materials and Methods: TG‐43U1 recommended dosimetric characteristics (Λ, g(r), F(r,θ), φan) of RadioCoil™ sources have been determined using experimental(TLD) and Monte Carlo(MCNP5) simulation techniques. MCNP5 simulations were performed in spherical Solid Water™ and water phantoms 20cm in diameter for 108 histories. F(r,θ) of RadioCoil™ were determined for angles 0° to 90° for r⩾L/2(where L=active length), and angles 5°⩽θ⩽90° for r⩾L/2, with 5° increment. TLD measurements were performed in solid Water™ using same geometric arrangement as that of Monte Carlo simulations. Measured and calculated dose profiles along the longitudinal axis of these sources were utilized to validate the dose calculation with commercially available treatment planning systems. Results: Results of these investigations indicate good agreement between MCNP5 simulated and TLD determined values for RadioCoil™ sources. Upon the good agreement between these two methodologies, confirming the accuracy of our simulation geometry, dosimetric parameters of these sources have been determined in liquid water for their clinical applications. It has been found that in order to achieve a good agreement between the treatment planning dose distribution, the F(r,θ) of these sources have to be determined at radial distances ranging from 0.5 to 5.0cm with 0.5cm increment and L/2 ±0.2cm. Conclusion: Dosimetric characteristics of newly designed RadioCoil™ have been determined following TG‐43U1 recommendations using experimental and Monte Carlo simulation technique. In these determinations it has been found that the dose profile can be closely reproduced if the 2D anisotropy function is determined at 0.5 cm increments for radial distance ranging from 0.5 cm to 5cm, and L/2 ± 0.2cm.
TU‐C‐224C‐07: A Comprehensive Dosimetric Protocol for the Cyberknife Radiosurgery System
Authors: Francescon P , Cavedon C , Scalchi P , Cora S , Satariano N , Polloniato P , Berna E
Published: July 2006

Purpose: To propose dosimetric guidelines specifically designed for the Cyberknife radiosurgery system. Non‐availability of 10×10cm2 field and use of small circular collimators (5mm to 60mm) pose serious problems, that have been faced in this study by means of 8 different detectors and Monte Carlo simulation. This work is oriented to measurement of total scatter factors (Sc,p) and to reference dosimetry, though indications will also be given in view of a comprehensive guideline. Method and Materials: PTW PinPoint 31014, Exradin A16 and T14P microchambers, TN 502RDM micromosfet, PTW 30008 diode and TM60003 diamond, MD55 and EBT radiochromic films were used to measure Sc,p. Monte Carlo simulations (BEAMnrc) were used to produce phase space descriptions at the exit plane of each collimator, to calculate: 1) theoretical Sc,p values in water, and 2) correction factors to be applied to Sc,p as measured by 5 detectors (PinPoint, A16, T14P, diode, diamond), obtained by simulating shape and chemical composition of each detector. BEAMnrc was also used to calculate stopping power ratios and chamber correction factors for the Cyberknife linac, to decide whether values of kQ from the IAEA398 protocol could be applied without using a 10×10cm2 field. Results: Sc,p of the 5mm collimator as measured by simulated detectors averaged 0.653 − 9%+14%. Variation for larger collimators was smaller. After Monte Carlo correction, Sc,p of the 5mm collimator became 0.686 −2%+1%. Pure Monte Carlo calculation gave Sc,p=0.715 +/−1%. Calculation of correction factors showed that kQ values for the investigated chambers could be chosen when using IAEA398, introducing +/−0.2% uncertainty. Conclusion: Pure Monte Carlo calculation gave higher values of Sc,p compared to Monte Carlo‐corrected measurement. The latter is to be preferred because correction factors are less sensitive to beam parameters than pure calculation of Sc,p. For determination of Sc,p use of microchambers and Monte Carlo correction is recommended.
TU‐C‐224C‐08: Design of a Small Radiation Facility for Radiobiology Studies
Authors: Rodriguez M , Jeraj R
Published: July 2006

Purpose: To design a small radiation facility for the partial‐ and fully ‐ body irradiation of zebrafish embryos, cell cultures or any other small specimen used for radiobiology studies. Method and Materials: Zebrafish embryos larger than 1mm are the main animal to be irradiated in this micro‐irradiator. Radiation is provided by a 50 kV photon beam from a miniature x‐ray source, Xoft Inc., CA. Radiation field is delimited by a pinhole collimator. Diameter of the pinhole ranges from 0.5mm. A movable table and a video camera connected to a computer are used to position the specimen under the beam. Radiochromic film has been irradiated to test positional accuracy and dose distribution. Results: Coordinates of the position of the zebrafish with respect to the collimator are calculated from the image provided by the video camera and sent to the computer‐controlled movable table to position the specimen under the beam. The micro‐irradiator is totally portable and it can fit on the desktop. Positioning can be acquired with uncertainties of 50 μm in X and Y axis. Collimator design and portable shielding reduce both primary beam and scattering at safe radiation levels. Dose distribution is good enough for zebrafish irradiation and penumbra is in the order of 150μm ± 50μm. Conclusion: The designed micro‐irradiator has attractive characteristics to facilitate zebrafish irradiation. Its portability and shielding simplicity make it adequate for any radiobiology laboratory. Its uncertainty in positioning is significantly smaller than zebrafish embryo size and radiation penumbra is acceptable for specimen larger than 1mm. This novel micro‐irradiator design is appropriate for irradiation of partial‐and fully‐ body zebrafish, cell cultures and any other small specimen used in radiobiology.
TU‐C‐224C‐09: Radiation Characteristics of a Gated Fiber‐Optic‐Coupled Detector
Authors: Reft C
Published: July 2006

Purpose: To study the dosimetric characteristics of a gated fiber‐optic‐coupled detector for measuring absorbed dose from a linear accelerator. The favorable properties of these dosimeters are their superior spatial resolution, real‐time readout and potential as in‐vivo dosimeters. In an application that takes advantage of its spatial resolution, small field tissue‐phantom‐ratio (TPRs) measurements from 0.6×0.6 to 2.0×2.0 cm2 are obtained and compared to those measured with a diamond and diode detector. Method and Materials: The detector is a short length of Cu1+ fused doped quartz fiber coupled to a fiber‐optic cable. It has an atomic number of about 10.8 with a density of 2.2 g/cm3 and is 1 mm long with a diameter of 0.4 mm. The background signal generated by Cerenkov radiation and native fluorescence within the optical fiber during irradiation is separated from the detector luminescence via gating the signal with the radiation pulses from the accelerator. A linear accelerator provides mega‐voltage photon and electron beams to investigate its energy response, dose rate dependence, dose linearity and reproducibility. Results: There is no measurable difference in the detector response between 6 and 18 MV photons. However, for electrons the dose response increases gradually by 7% from 6 to 20 MeV. Its dose rate response relative to a Farmer chamber exhibits a behavior similar to a diamond detector decreasing by about 4.5% from 0.8 to 10.7 Gy/min for both 6 and 18 MV photons. The measured response is linear from 0.2 to 10 Gy and its reproducibility is better than 2%. The small field TPR measurements are in good agreement with the diamond and diode detector. Conclusion: The dosimetric properties of this detector compare favorably with other radiation detectors, and its small size and optical interface make it potentially very useful for small field and in‐vivo radiation dosimetry.
TU‐E‐330D‐02: Monte Carlo Simulation to Assess Fetal Dose From MDCT Imaging Using Patient Based Voxelized Models
Authors: Angel E , Wellnitz C , Goodsitt M , DeMarco J , Cagnon C , Cody D , Stevens D , McCollough C , Primak A , McNitt‐Gray M
Published: July 2006

Purpose: To use detailed Monte Carlo simulations to investigate fetal dose from a multidetector CT (MDCT) using voxelized models created from actual patient images including early and late term pregnancies. Method and Materials: Detailed voxelized models of anatomy were created based on image data from a cohort of pregnant patients who had previously undergone abdomen/pelvis CT scans. The gestational ages ranged from less than 5 weeks to 33.7 weeks. Three regions, corresponding to fetus, gestational sac, and uterus, were contoured on each image series by a radiologist.

A MDCT model was created using details about the source spectra, filtration, collimation, and geometry. To simulate an actual scan, a helical source path was defined and particles were transported through the anatomy of the voxelized patient models; radiation dose was tallied in voxels belonging to the three regions of interest. The simulated abdomen/pelvis scan used a helical scan of 120kVp, pitch 1, and 4 × 5 mm total nominal beam collimation.

Dose on a per mAs basis was separately calculated for the fetus when the fetus was distinguishable from the gestational sac and uterus in the original image. These doses were then compared to two generally accepted fetus dose estimations: the Felmlee et al method and the ImPact estimation of dose to a uterus (for fetuses < 8 weeks). Results: The radiation dose to the fetus in the models with gestational ages of <5 weeks, 6.6 weeks, 7.1 weeks, and 28.3 weeks, were 8.31 mGy/100mAs, 9.67 mGy/100mAs, 14.22 mGy/100mAs, and 11.70 mGy/100mAs, respectively. The fetus dose estimate using the Felmlee technique was 11.30 mGy/100mAs. The ImPact dose estimate to a fetus was 13.0mGy/100mAs. Conclusion: Radiation dose to the fetus was successfully estimated at different gestational ages using detailed models of actual patient and fetus morphology, scanner geometry, and acquisition protocols.
TU‐E‐330D‐05: Potential Radiation Guidance Levels for Invasive Cardiology
Authors: Balter S , Bernardi G , Cotelo E , Faulkner K , Miller DL , Nowotny R , Ortiz Lopez P , Padovani R , Ramirez A , Vano E
Published: July 2006

Purpose: An International Atomic Energy Coordinated Research Program investigated the feasibility of providing guidance levels for fluoroscopically guided invasive cardiology procedures. Method and Materials: A sample of 6,000 cases of coronary angiography (CA), coronary angioplasty (PTCA) or combined CA and PTCA from ten laboratories in four different countries were used for the analysis. Dosimetric and patient demographic data were collected. Intercalibration of kerma area product (KAP) meters and quality control tests were periodically performed. Image quality and skin dose distributions were evaluated in a small sample of procedures. Procedure complexity was evaluated in a subset of 1,000 PTCA cases. Results: Classification into three clean categories proved difficult due to the rapid evolution of interventional cardiology and considerable variability in routine clinical practice among the centers. It may be better to categorize cases as either coronary angiography only (DX) or interventional, with a variable CA component (RX).

Median values of KAP (for similar procedures) varied by a factor of three between centers. Complexity has a factor of two influence on KAP. The data suggest that a laboratory can normalize its data by complexity scaling.

Dose inefficient laboratories were identified by noting that the median value of procedures exceeded the third‐quartile value for the entire pool. One laboratory exceeded the guidance level because of the use of 25 fps imaging in place of the more common 12.5 fps. Another laboratory, not under routine QA testing, had high fluoroscopic and cinefluorographic dose rates. Conclusion: Guidance levels for invasive cardiology appear to be feasible. Suggested KAP guidance levels for a facility performing procedures of moderate complexity are 50 Gycm2 for DX and 120 Gycm2 for RX. These values should identify dose inefficient laboratories. Guidance for fluoro time and cine frame count is being developed. Further research is needed as clinical procedures and technologies evolve.
TU‐E‐330D‐06: Assessing Patient Radiation Exposure From Fluoro‐Guided Procedures Based On Direct Dose and Dose‐Area Products
Authors: Kuan H , Lawson W , Ferretti J , Pohlman J , Oatman G
Published: July 2006

Purpose: To assess patient radiation exposure from fluoro‐guided procedures based on direct dose and dose‐area product. Method and Materials: Various procedures performed by members of Cardiology and Radiology Departments at SUNY Stony Brook were monitored for radiation exposure to patients' skin. Dose, dose‐area product, fluoro‐time, and beam parameters were recorded for each fluoro‐cine run. Along with clinical data, dosimetry print‐out was reviewed after each procedure to identify possible high doses to any given site of the exposed area and to have appropriate medical care provided timely. Accrued data were analyzed and evaluated in detail. Results: Data from a total of 3040 consecutive cases, 1883 diagnostic and 1157 interventional, performed by 16 and 10 physicians respectively were analyzed. Based on dosimetry print‐out, the total skin dose averaged 87 rads for diagnostic procedures, with maximum skin dose below 100 rads to any given site found in over 90% of cases, that for interventional procedures respectively were 223 rads, with maximum skin dose over 300 rads to any given site found in over 15% of cases. Conclusions: Our experience demonstrated the value of careful monitoring and thorough assessment of radiation dose and dose distribution in keeping medical staff informed timely of their patients' exposures.
TU‐E‐330D‐07: The Effect of Subcutaneous Fat On Patient Effective Dose in Diagnostic Radiology
Authors: Yanch J , Behrman R , Hendricks M , McCall J
Published: July 2006

Purpose: To quantify the dependence of effective dose on subcutaneous fat thickness in x‐ray radiography and develop a set of relative radiation risk factors for comparing overweight to “lean” patients. Materials and Methods: Using the MCNP Monte Carlo code and geometric phantoms patterned after Christy et al, effective dose calculations were performed for abdominal and chest radiographs of a “normal weight” adult male phantom. The effective dose, Eo, was normalized to the number of x‐rays exiting the patient to model a constant exposure to the image receptor. Varying thicknesses of adipose tissue were then added to the anterior, lateral, and /or posterior regions of the torso of the phantom and the normalized effective dose, E, calculated at the same kVp and source to image receptor distance. The ratio E/Eo provides an index of the increased stochastic risk. Anterior:lateral:posterior fat ratios used ranged from 6:5:1 to 1:3:6 with total anterior plus posterior additional fat thicknesses extending from 1 to 30 cm. Results: For AP and PA projections, both the lateral fat and the fat layer proximal to the x‐ray beam had negligible effect on E/Eo. E/Eo was shown to depend only on the distal fat layer thickness with an exponential dependence of the form exp(kx), where k is an exam/kVp specific constant, and x the distal fat layer thickness. For the AP abdominal projection, k values were 0.127, 0.119, 0.106, and 0.094 cm−1 at 80, 100, 120, and 140 kVp, respectively. R2 for all fits were better than 0.96. E/Eo ranged as high as 12.4 for an extremely obese patient with 20 cm of posterior fat at 80 kVp. Conclusions: Overweight and obese patients incur significantly elevated stochastic risks from radiographic procedures as compared to their lean counterparts, depending upon the kVp and fat layer thickness closest to the image receptor.
TU‐E‐ValA‐01: IMRT of the Central Nervous System
Authors: Munley M , Stieber V
Published: July 2006

Intensity modulated radiation therapy (IMRT) for the central nervous system (CNS) is being used more frequently in radiation oncology clinics. There are two general situations that the treatment of CNS disease may benefit from the use of IMRT compared to conventional, three‐dimensional conformal radiation therapy: 1) when multiple critical structures confined within the intracranial vault are to be avoided, one may desire an optimal dose distribution that allows for the dose to these structures to be minimized, and 2) since high‐grade gliomas tend to recur locally, IMRT should allow for dose escalation proportional to the corresponding heterogeneous cell populations. Based on the anatomic location of the treatment volumes, one can visualize examples where IMRT could be of benefit. Patients with a concave or irregularly‐shaped target in a frontal lobe may require IMRT in order to spare the adjacent globe and any uninvolved optic apparatus. In patients with well‐lateralized tumors involving the brain parenchyma, complete sparing of the contralateral hemisphere is desirable. Patients with infiltrative gliomas traditionally have large margins placed around the treatment volumes, and these may often encompass uninvolved critical normal structures. For such cases, IMRT may allow for non‐uniform reduction of the treatment volume around these normal structures. The primary goal of this presentation is to provide a practical overview of IMRT for the CNS.

Though much attention has been given to the inverse planning and quality assurance aspects of IMRT, one should have an adequate understanding of the entire process; from proper patient selection to positioning/immobilization and continuing through treatment. A discussion of the steps of the CNS IMRT process will include: patient selection, immobilization, recommended imaging acquisitions, structure delineation, planning strategies/parameters, dose objectives, plan evaluation, QA, and potential delivery issues. Guidelines and practical examples for each component of this process will be presented.

To gain further familiarization of CNS IMRT, one should review the corresponding technological and clinical outcome literature. Comparisons to conventional radiotherapy methods will be examined in terms of technique, dosimetry and clinical outcome. Finally, current research and future directions of CNS IMRT will be introduced such as the novel use of sophisticated imaging techniques for improved structure definition, patient positioning and dose modulation.

Educational Objectives:

1. To understand the general practice of CNS IMRT from patient selection through actual treatment.

2. To become familiar with specific details pertaining to the CNS IMRT process through several illustrative examples.

3. To be introduced to some of the research and future directions of CNS IMRT.

Research supported, in part, by Varian Medical Systems.
TU‐E‐224A‐01: Evaluation of Heterogeneity Corrections Algorithms Through the Irradiation of a Lung Phantom
Authors: Alvarez P , Molineu A , Hernandez N , Followill D , Ibbott G
Published: July 2006

Purpose: To evaluate the impact of applying heterogeneity corrections to the calculation of prescribed doses to a target located within the lung. Method and Materials: The Radiological Physics Center's (RPC) anthropomorphic lung phantom was sent to institutions nationwide. This phantom simulates a patient not only in dimensions but also in densities for imaging and treatment purposes. This design includes two lungs with density of 0.33 g/cm3 and a target centrally located in the left lung with density near 1 g/cm3. TLD and radiochromic films were used as dosimeters within and near the target region. Institutions that received the phantom were requested to image, plan and treat the phantom as if a patient. The prescription dose, based on a stereotactic plan, was 20 Gy to the target, calculated without applying heterogeneity corrections. The institutions were asked to submit both the homogeneous and heterogeneity corrected treatment plans using the same number of monitor units. Results: Twenty‐one irradiations, mostly with 6 MV x‐rays, were analyzed from 7 different Treatment Planning Systems (TPS). The ratio of dose to the target from the plan with to the plan without heterogeneity corrections was calculated and analyzed based on the algorithms used for the heterogeneity correction. A comparison of corrected dose given by the TPS and dose given by TLD was performed. The average ratio between dose with to dose without the heterogeneity correction was 1.18 with values ranging from 1.12 to 1.21. The superposition convolution algorithms agreed better with measurements than the other algorithms studied. The average TLD/Inst dose ratio in the target was 0.97 ranging from 0.92 to 0.99. Conclusions: There continues to be a differences in the heterogeneity corrected tumor doses within the lung from different planning systems.

Work supported by PHS grant CA10953 and CA081647 from the NCI, DHHS.
TU‐E‐224A‐02: Dosimetry of Very Small (1.5 and 3 Mm Diameter) Photon Beams: Diode and Film Measurements Versus Monte Carlo Calculations
Authors: Sham E , Devic S , Seuntjens J , Podgorsak E
Published: July 2006

Purpose: To measure the dosimetric parameters of 10 MV photon beams in 1.5 and 3 mm diameter fields with a small‐field diode, radiographic XV film, and radiochromic HS film, and to compare measured data with the same parameters calculated by Monte Carlo (MC) simulations. Methods and Materials: A 10‐MV Clinac‐18 linac was used as the radiation source and the very small diameter fields were set up with radiosurgical collimators. PDDs, profiles, and output factors of the very small photon beams were measured with diode/water tank and film/scanner techniques. The measured parameters were compared against those calculated by MC simulations using an experimentally determined circular source diameter of 1.5 mm in beam modeling. For improved accuracy, the PDDs were measured with the diode and the water tank using beam profile scans. A document scanner was used as film densitometer to offer high spatial resolution (254 lpi) required in very small photon field dosimetry. Results: PDDs measured by the diode agree well with the MC‐calculated results, within ± 2% and ± 3% in 3 and 1.5 mm fields, respectively. Lateral profiles measured by the diode and film generally agree with MC calculations, but significant discrepancies are observed in the tail portion of the 1.5‐mm beam profile. Relative dose factors obtained by averaging the diode, HS film, and MC results are 0.22 ± 0.01 and 0.43 ± 0.01 for the 1.5 and 3 mm fields, respectively. Conclusion: Based on the good agreement between the measured and MC‐calculated dosimetric parameters for the 1.5 and 3 mm diameter, 10 MV beams, we conclude that MC calculations can be used in general for dosimetry of very small photon fields, provided that the physical source size of the linac is correctly measured and used in the MC simulations.