bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐211: Optical Fluorescence Monitoring during External Beam Radiation Therapy Using Cerenkov Emission as Excitation Source
Authors: Axelsson J , Davis S , Gladstone D , Pogue B
Published: November 2011

Purpose: Cerenkov emission is induced when a charged particle travels faster than the speed of light in a given medium. The Cerenkov effect occurs in everyday radiation therapy of tissue, yet this phenomenon has never been quantitatively characterized. In this study, an investigation of high‐energy radiation from a linear accelerator was carried out, to quantify the induced Cerenkov emission in biological media. Furthermore, we demonstrate that the Cerenkov emission can excite a molecularly produced fluorophore, protoporphyrin IX (PpIX), embedded in biological phantoms. Methods: Electrons at 6–18 MeV energies and photons at 6 or 18 MV energies, from a linear accelerator, were used to induce Cerenkov emission in aqueous phantoms. First, a CMOS camera imaged a water tank in order to investigate the dose distribution of external beam radiation. Secondly, the fluorescent photosensitizer PpIX was mixed into the phantom. An optical fiber bundle, positioned at the phantom surface, collected the Cerenkov emission and the Cerenkov‐induced optical fluorescence. Results: Images acquired in a water tank clearly shows the cross section of the electron (or photon) beam at all energies using a dose rate of approximately 4Gy/min. As expected from the Cerenkov theory the intensity increases as the energy of the radiation increases. Spectra acquired, either with photons or electrons, reveal that the Cerenkov emission excites the PpIX molecule, leading to optical fluorescence in the red spectral region. Conclusions: The results here indicate that molecular fluorescence monitoring during external beam radiotherapy is possible. This could potentially be used as a tool for treatment assessment through the evaluation PpIX production from e.g. high‐grade glioma.

This work has been funded by NIH grants RO1CA120368 and PO1CA084203.
SU‐E‐T‐229: Clinical Implementation and Validation of Optically Stimulated Luminescence Dosimeters (OSLDs) for Radiotherapy Dosimetry
Authors: Pokhrel D , David J , Mittal B , Sathiaseelan V
Published: November 2011

Purpose: To experimentally validate and clinically implement a new OSLDs system containing Al2O3: C for measuring skin dose for the patients undergoing radiotherapy treatment. Methods and materials: The calibration measurements of the commercially available OSLDs were performed in a solid water phantom using therapeutic photon and electron beams. All measurements were carried out in a standard clinical set‐up using 100 cm SSD, 10 ×10 cm2 field size, and dmax depth for each photon and electron beam energies. In total, 100 OSLDs were irradiated with the same dose. Inter‐OSLD response variation was calculated by taking the difference between the average value and each OSLD response. A simple optical bleaching system was applied for the OSLDs using a regular fluorescent light. The accuracy of the OSLD measurement was assess by comparing with the expected ion chamber reading and MOSFET measurements carried out under the identical condition in patients. Results: In the phantom study, the overall inter‐OSLD response variations were 2.8% and 6.4% for 10 MV photon and 10MeV e‐beam, respectively. OSLD response variation between the different energies was clinically insignificant. Optical bleaching took less than 2 hours while using fluorescent light with residual signal of less than 0.3%. For the patient study, the OSLDs reading were comparable to MOSFET measurement. Summary and Discussion: Our preliminary results using OSLDs show good agreement with clinically used MOSFET measurement in patients. Screening of general purpose OSLDs is highly recommended before using in patient. The OSLDs are accurate, can be readout/use multiple times, single readout does not anneal the chip, and more importantly it is convenient to put in the patientˈs body. Further validation and clinical implementation of OSLDs for all therapeutic‐beams as well as on‐board‐imaging system will be advantageous for more accurate clinical dosimetry for advanced radiotherapy procedures such as SBRT, IGRT.
SU‐E‐T‐235: Evaluation of Dosimetric Properties of Plastic Detectors in Proton Beam Therapy
Authors: Kim S , Lee S , Yoo S , Cho S , Kim D , Lee S , Kim D , Park S , Shin J , Shin D , Park S
Published: November 2011

Purpose: To evaluate and optimize the dosimetric properties of plastic detectors through the CCD‐based scintillator system in double scattering mode of PBT. Methods: Dosimetric properties like light output and dose distribution, and uniformity considering the thickness of scintillation materials and integration time, CCD camera gain to analyze the CCD image using plastic detectors were used. The proton energy used was between 100 and 150 MeV and dose rate was 200 cGy min‐1Results: Light output and dose distribution of each scintillator depend on integration time and CCD camera gain. According to TG45, flatness and symmetry of a two‐dimensional image were analyzed about uniformityConclusions: : The dosimetric properties of plastic detectors present the main factors that determines whether a CCD‐based scintillator system has with a good sensitivity and high resolution.
SU‐E‐T‐240: In‐Vivo Measurement of Shallow Dose for a Spoiled Mega Voltage Radiotherapy Beam
Authors: Hossain M , Tafo A Guemnie , Lin T , Price R , Ma C
Published: November 2011

Purpose: Calibration factors for electrons and photons are quite different, especially for MOSFETS with inherent buildups. Megavoltage radiotherapy beam in the presence of a beam spoiler has a large low energy electron component near the surface. A method of calibration of the spoiled beam is proposed. This calibration method will be useful for in‐vivo dose measurement for total body irradiation (TBI). Methods: The ionization charge and deposited dose is measured in water at standard and extended source to surface distance (SSD) for a megavoltage beam in the presence of a beam spoiler at various depths. The contribution of low energy electrons generated by the spoiler is separated from the photon contribution. The calibration factors for the electron and photon parts are weighted according to the proportions of their contributions. The net calibration factor is tested for the composite beam. Results: The calibration factor for the electrons is 1.15 while the calibration factor for the photon component is 1.02. At shallow depths the electron contribution is very high. The resultant calibration factor from a preliminary study is found to be about 1.07 at a depth of 1 cm. Conclusions: A method of determining the calibration factor for a mega voltage spoiled beam is proposed. The method yields a calibration factor for in‐vivo dose measurement for the combined photon and low energy electrons generated by the beam spoiler.
SU‐E‐T‐241: Characterization of MOSFET Detectors for in Vivo Dosimetry in Interventional Radiology and for Dose Reconstruction in Case of Accident
Authors: Bassinet C , Huet C , Baumann M , Etard C , Réhel J‐L , Boisserie G , Debroas J , Aubert B , Clairand I
Published: November 2011

Purpose: As MOSFET detectors allow dose measurements in real‐time, the interest for these dosemeters is growing. The aim of this study was to investigate the dosimetric properties of these detectors in order to use them for in vivo dosimetry in interventional radiology and for dose reconstruction in case of accident.Methods: Commercially available TN‐502RD‐H MOSFET detectors (Best medical canada, Ottawa, Canada) were investigated in this study by tests in calibration laboratories. Reproducibility of the measurements, dose response and dose rate dependence of the MOSFET detectors were studied with a Co‐60 source and their energy response with continuous X‐rays beams. In addition, MOSFETs behaviour has been investigated in pulsed X‐rays fields in order to study the influence of the frequency, dose rate and duration of pulses on MOSFET responses. Finally, in order to validate the integrated dose given by MOSFET detectors, MOSFETs and TLD (7LiF:Cu,P) were fixed on an Alderson‐Rando phantom in the conditions of an interventional neuroradiology procedure and their response has been compared.Results: The reproducibility of the dose measurements was found to be very satisfying. The response was linear with the dose and no dependency with the dose rate was found. However, relatively strong energy dependence was observed, i.e. a factor of 1.4 was seen in the response between 57 and 79 keV. In pulsed X‐rays, the response was correct only for duration of pulses equal to or higher than 10 ms. Good agreement was found between TLD and MOSFET measurements Conclusions: The results of this study show the suitability of MOSFET detectors for in vivo dosimetry in interventional radiology and for dose reconstruction in case of accident, provided a well‐corrected energy dependence and a pulse duration equal to or higher than 10 ms and an optimized contact between the detector and the skin of the patient.
SU‐E‐T‐247: A Solution to the Real‐Time Safety Interlock Control of the Linac and the Externally Mounted Multi‐Leaf Collimator
Authors: Tan Youheng , Li Yongjie , Yao Jonathan
Published: November 2011

Purpose: This study aims to provide a solution for a real‐time safety interlock control of the linac and the externally mounted dynamic multi‐leaf collimator (dMLC) from other manufacturers, between which it is difficult to build a bridge because of the internal interfaces unopened to other manufacturers. Methods: An external dMLC is mounted on the linac head. They can not work corporately and safely if no interlock control is built between them. Our solution is to set a VGA splitter between the linac control computer and its monitor, and from this VGA splitter a VGA signal grabber is connected to the MLC control computer. Through this connection, the data sent to the linac console monitor is also captured and sent to the MLC control computer real time in a form of image. By analyzing this captured image using methods of feature extraction and pattern recognition, the current setting of the linac is extracted and used to judge whether the current setting of the linac is consistent with that stored on the MLC control computer. Results: The display format on the monitor is generally fixed for a specified accelerator, which is helpful for the quick and accurate extraction of the parameter setting of the linac from the captured image. When the parameter settings on linac control computer and MLC control computer are not identical, the MLC control computer pops up an error message, and at the same time, a NOT READY signal is sent to the READY/NOT‐READY circuit in the linac, and hence a safety interlock control is realized. Conclusions: Externally mounted dMLC is an economic solution to upgrade the linac that has no built‐in dMLC. Safety interlock control between them can be effectively realized simply using a VGA signal grabber and a control signal sent to the linac.

Funding support: This work was supported by the Program for New Century Excellent Talents in University of China (NCET‐07‐0151) and the Natural Science Foundations of China (61075109, 30730036).
SU‐E‐T‐255: Photoneutron Activation of an IMRT QA Device and the Radiation Safety Implications
Authors: Eagle A , Mann M , Washington J , Sweeney L , Kaurin D , Qi S , Simon W , Newman F
Published: November 2011

Purpose: To characterize the activation of the Sun Nuclear MapCheck2 diode array when exposed to high energy photons. Methods: A Sun Nuclear MapCheck2 diode array was exposed to 6, 15 and 18 MV photons. After activation, radiation levels were measured and analyzed with a calibrated survey meter and with the device moved well away from the linac. Additionally, gamma camera images and energy spectra were obtained. Results: As expected, activation increases with increasing exposure and photon energy. Irradiating the device at 100 cm SSD for 1000 and 3000 MUs yielded survey meter readings at the surface of the device of 30 and 60 mR/hr respectively from 18 MV photons, and 2 and 5 mR/hr from 15 MV photons. 6 MV photons produced no detectable activation. The observed half‐life was approximately 10 minutes. Gamma camera images showed the activated material to be approximately uniformly distributed. The energy spectra showed a strong peak centered on 511 keV, consistent with annihilation photons from positron emission. These data are consistent with the Cu63 (y, n) Cu62 reaction. The decreased activation from 15 MV photons is also consistent with Cu63 activation which has a strongly peaked cross section centered around 16 to 18 MeV. Also observed were strong energy peaks centered near 76 keV and 177 keV, which require further analysis. Conclusions: Although normal operation of this device does not usually require such high doses, the Medical Physicist should be aware of the possibly higher than expected activation of any such QA device and the resultant exposure. Without proper precautions this could have ALARA consequences. For example, Cu63 accounts for nearly 70% of naturally occurring copper and is used extensively in virtually all similar measuring devices. Though the Cu63 (y, n) Cu62 dominates, the other peaks will be discussed as well.
SU‐E‐T‐256: Investigation of Positional Accuracy and Reproducibility of Small Fields Defined by Collimating Jaws and MLC
Authors: Li M , Srivastava S , Cheng C , Das I
Published: November 2011

Purpose: One of the challenges in small field dosimetry is the determination of output factors. The output of small field may be sensitive to the positional accuracy of the collimator jaws and MLC. The positional accuracy and reproducibility of small fields defined by collimating jaws and MLC for different accelerators are investigated. Methods: The reproducibility of field sizes, ranging from 1×1 to 10×10 cm2 was investigated for both 6 and 15 MV on a Varian iX and a Siemens Artiste machines. For the Siemens Artiste, profiles were scanned at 5 cm depth in water with a Steoreotactic Photon Diode (SFD). The water surface was at 95 cm SSD. In addition, profiles at off‐axis distances of 2 and 5 cm respectively were scanned. For the Varian iX machine, an EPID was used for profile measurements at 0.8 cm water equivalent depth. For each field size, both X and Y jaws were opened up to 20×20 cm2 then closed down to the field size to be measured. This was repeated 12 times for each field size. For each measured profile, the field size is estimated by taking the full width of the profile at 50% of maximum value. Results: The measurement shows very good reproducibility of both MLC and Y jaw. The standard deviation of the variations for each field size is between 0.004 to 0.01 cm over the range of field sizes studied. The maximum offset in the x or y dimension is about 0.5 mm, which may affect the output factor. Conclusions: The reproducibility of field size is better than 0.5mm for the range of field sizes studied with possible minimum effect on the output factor. The uncertainty of output factor measurement would be mainly due to the choice of detector and focal size of the accelerator.
SU‐E‐T‐271: A Variable Target Comparison of Whole Breast and Partial Breast Irradiation Fractionation Regimens. Do the Current Margins Make Sense?
Authors: Al Sulaimani E , Arthur D , Todor D
Published: November 2011

Purpose: A novel, variable target approach is used in this study to establish equivalence, in a radiobiological sense, between whole breast and partial breast irradiation schemes. We are questioning the meaning of margins, as they are currently used to create planning target volumes. Ultra‐short fractionation regimens have been recently proposed for APBI, reducing the number of fractions from 10 to as few as two. This work addresses the concept of ˈequivalenceˈ between the currently accepted regimens (both WBI and APBI) and the newly proposed ones. Methods: Four early stage breast cancer patients were included. Two patients were treated with interstitial BT and two patients with balloon BT. Three regimens for WBI were simulated by creating uniform doses for all targets. EUBED and gBEUD were computed and the parameter ‘a’ identified based on equivalence of standard WBI with interstitial APBI. The equivalence of new proposed ultra‐short regimens in balloon BT namely (7Gy × 4fx), (8.25Gy × 3fx) and (10.25Gy × 2 fx) was then compared with the ˈtraditionalˈ APBI. Results: a=‐1 was identified from WBI and APBI equivalence. At GTV+1.0 cm margin, we find gBEUDˈs for ultra‐short regimens to be 20% or higher than current standard fractionation scheme. Conclusions: Somehow unexpected is that despite a larger margin (15mm), the interstitial implants seem to be equivalent, within the validity of the radiobiological model considered, for significantly smaller targets than the one the treatment was planned for. For the balloon BT, the planned margin of 1cm around the balloon, seemed a lot more consistent with the ‘true’ target for which the WBI and APBI would be equivalent. When the new, ultra‐short regimens were compared with the traditional (3.4Gy × 10fx), we find that their equivalent targets are larger than the 1cm planning margin, even when compared with the standard WBI regimen.
SU‐E‐T‐273: Beyond Utilizing Functional Imaging for Contours and Visualization, Towards Physiological Radiotherapy to Improve Patient Outcome
Authors: Zhang H , Mistry N , DˈSouza W
Published: November 2011

Purpose: To reformulate the treatment planning optimization problem by directly incorporating tissue geometry and spatial function heterogeneity derived from anatomical and physiological images, respectively.Methods: Conventional CT has been the gold standard for anatomical definition of treatment targets and OARs for radiotherapy. Functional images derived from imaging modalities have been utilized to date to draw more accurate contours or define “regions of avoidance” or “regions of dose concentration” to aid the treatment planning process. This framework assumes homogeneity among all the voxels of a region of interest, thereby, neglecting functional heterogeneity among voxels. We propose a treatment planning framework that optimizes voxel dose by explicitly incorporating tissue geometry and heterogeneous physiological function. We explore the use of varying penalty functions applied to organs for which functional information is available. Our approach formulates the dose optimization problem as linear program or quadratic program and solves for pencil beam or aperture weights. We illustrate the reformulated treatment planning framework using ventilation function images from ten locally advanced lung cases. Ventilation function images were obtained from 4DCT imaging. Plan quality and lung function preservation were compared with conventional tissue geometry alone‐based plans.Results: When comparing the plans with and without functional information via traditional DVHs, acceptable V5, V15 and V20 of the lung were achieved by both plans. However, when taking the spatial function heterogeneity into account and evaluating via functional DVH (fDVH), a significant 20% reduction of fV20 (p‐value < 0.001) was achieved by our approach Conclusions: Throughout our retrospective study, we notice that without organ function heterogeneity information available at the time of planning process, very frequently high doses were delivered to organ high‐functioning area, which may be the significant reason many of those patients suffered from complications. With our proposed approach, it is very likely such complications could be avoided.
SU‐E‐T‐275: Evaluation of Deformable Contour Propagation
Authors: Morcos M , Sultanem K , Bahoric B , Stroian G , Deblois F
Published: November 2011

Purpose: Deformable contour propagation, when performed accurately, can potentially reduce the workload associated with manual contouring and minimize inter‐observer variability. In this work, we have compared propagated contours to physician‐drawn ones for gynecologic brachytherapy (GYN) and head and neck (HN) external beam radiotherapy cases.Methods: Eleven HN and sixteen GYN cases were randomly and retrospectively chosen for this study. These cases included their respective pre‐treatment (pCT) and follow‐up CT (fCT) scans along with their respective physician‐drawn structures. The pCT volume was registered using a deformable algorithm to the fCT and the resulting deformation field was applied to the pCTˈs structure set to propagate it to the fCT, this was done using Velocity Medical Solutionsˈ VelocityAI software. The propagated contours were compared to the physician drawn‐contours using the Dice similarity coefficient (DSC).Results: Eleven organs at risk (OAR) and the clinical target volume (CTV) were analyzed for the HN cases and two OARs, as well as the Miami applicator and the CTV for the GYN cases. The propagated contours for the brain, brainstem, spinal cord, esophagus, eyes, larynx, mandible, oral cavity, parotids and the CTV yielded mean DSCs ranging between 0.635–0.979 for the HN cases with a poor outcome for the sphincter muscle (mean DSC = 0.576). The mean DSCs ranged between 0.702–0.804 for the Miami applicator, bladder, rectum and CTV for the GYN cases Conclusions: This work has shown that deformable contour propagation is quite accurate and requires minimal modification. The HN cases slightly outperformed the GYN cases primarily due to the fact that the GYN scans are low in contrast and contain high deformation tissues such as the bladder and rectum.
SU‐E‐T‐277: Image‐Guided Radiation Therapy: The Accuracy of CT‐MR Fusion for Prostate Treatment Planning
Authors: Xue J , Liu H , Chen X , Lin M , Dong Z , Wang L , Chen L , Ma C
Published: November 2011

Purpose: CT and MR imaging has been widely accepted as a practical approach for both accurate delineation (using MR data) and dose calculation (using CT data) for image‐guided radiotherapy (IGRT) of prostate cancer. This work investigates the accuracy of CT and MR fusion in target (prostate) delineation for prostate IGRT treatment planning. Methods: Twenty prostate patients were included in this study. Each patient underwent CT‐and MR‐simulation prior to the IMRT or RapidArc treatment. Paired CT‐MR images were obtained on a GE 4D CT scanner and a GE 1.5T MR scanner in our department. MR and CT scans were performed within 30min to minimize organ or structure changes except for patients implanted with Calypso Beacons who received MR scans prior to their Beacon implantation and CT scans 1 week after. External contour variations were quantified from the isocentric slices on both CT and MRI images. Prostate volume was used to evaluate the accuracy of image fusion, which was mainly based on bony structure matching. Results: The maximal differences in lateral dimensions ranged 0.1 to 1.2 cm for patients with lateral dimensions of 33.0–52.4 cm. The vertical dimensions differed by 0.1 – 1.4cm for patients with vertical dimensions of 18.8 –33.1 cm. In general, the contour variations increased with the patient size. There was a residual fusion error for the prostate gland ranging from 0.1 to 0.5cm (average 0.16cm) after bony structure matching. Mismatch occurred when there was a large difference in the bladder/rectal volume between CT and MRI. Conclusions: Large contour variations may occur for large patients due to obesity, which should not change the planning dose distribution significantly. On the whole, the geometrical distortion and target shift between CT and MR images are not obvious and mostly clinically insignificant for treatment planning assuming a fusion uncertainty of 2mm.
SU‐E‐T‐295: Clinical Evaluations of a Novel Metal Artifact Reduction Technique for Helical CT Scans in Radiation Therapy
Authors: Li H , Thorstad W , Ramirez J Garcia , Moore K , Li Horald H. , Noel C , Low D , Mutic S
Published: November 2011

Purpose: To evaluate the performance of a commercial metal artifact reduction algorithm for helical CT scans and to investigate the CT number accuracy improvement on metal‐artifact reduced images and its clinical significance. Methods: 42 helical CT scans of patients with metal implants, 32 cases with small dental or spine filling, 7 with single hip implants, and 3 with bilateral hip prosthesis, were collected and evaluated. The original and corrected images were reviewed side by side from the aspects of overall image quality and visual conspicuity of the prostate (or vagina), bladder, and rectum in consensus for patient cases with hip implants, and visual conspicuity of pharyngeal part of tongue, lymphoma for patient cases with dental filling. The CT number accuracy was evaluated on 10 cases with hip implants by comparing the average CT number and variations within prostate (or vagina) regions on the original and artifact reduced images. Results: While residual artifacts are still presented on the corrected images, the metal artifacts were reduced dramatically on all 42 patient cases, especially for the cases with large hip prosthesis. Evaluation also indicates that, as expected, the geometry of anatomic structures was not affected by the algorithm.Quantitative calibration results using the electron density phantom with tantalum inserts indicates the considerably improvement of electron density distortions. Most importantly, the CT number variations of the prostate/vagina were reduced from 30% to 66.7%. The average CT numbers of those organs were closer to the expected CT number than that on the uncorrected images. Conclusions: The evaluations indicate that the commercial algorithm can dramatically reduce metal artifacts. The corrected images have already been used in our clinic to help with tumor/organ delineation and treatment planning. However, further work is needed to evaluate its full impact in treatment planning and dose computation accuracy.
SU‐E‐T‐301: A Dual TLD System for X‐Ray Energy Discrimination in Personnel Monitoring
Authors: Nelson V , McLean I , Holloway L
Published: November 2011

Purpose: Uncertainly in effective energy of a radiation source is one of the major contributors to uncertainty of dose determination in personnel monitoring. This study was performed to determine the energy dependent response of a number of thermoluminescence (TL) materials and to evaluate the application of this data for x‐ray energy discrimination in personnel monitoring as a method to reduce the uncertainty of radiation dose determination. Methods: Four types of TL dosimeters (TLD100H, TLD200, TLD400 and TLD500) were irradiated to a range of photon energies using a diagnostic x‐ray machine, an orthovoltage radiation therapy machine, a Co‐60 teletherapy machine and a 6 MV Linac. Effective energy of the diagnostic and orthovoltage beams was determined from the measured HVL using standard techniques. TL responses of all types of TLDs were normalized to 1 mGy. Polynomial fits were obtained for the data. Ratios of TL responses were calculated and plotted against the effective energy. The accuracy of the TL response ratio method was investigated through a blind study. The energy determined by the ratio of TL responses was compared with the pre‐determined effective beam energy to assess the accuracy of the method Results: The thermoluminescent response ratios of combinations TLD100H with TLD200 and TLD500 vary sharply with the change in incident photon energy. The blind study results showed that a combination of either of these TL material combinations had an accuracy of approximately ±10% in estimating the photon energy. Conclusions: In this study, using commercially available TL materials, a novel and practical method for estimation of x‐ray energy has been developed for situations where this information is unknown but potentially necessary for radiation dose estimation. The energy discrimination method described in this work can be used to improve the dose estimation in personnel dosimetry and TL dosimetry audits of kilovoltage therapy machines.
SU‐E‐T‐319: Radiochromic Film Characterization of a Small Animal Irradiator
Authors: Lynch B , Samant S , Helmig R , Zhang A , Zhang L , Liu C
Published: November 2011

Purpose: To characterize the output of a Cs‐137‐based Gammacell 40 Exactor Low Dose‐Rate Research Irradiator using radiochromic film measurements.Methods: Gafchromic EBT radiochromic film was used to characterize the the timer error, uniformity, penumbra, and scatter dose for a mouse irradiation device used in conjunction with a Cs‐137 irradiator with a nominal dose rate of 100.04cGy/min. Radiochromic film was chosen because of its good spatial resolution and relative insensitivity to radiation spectral changes. An Epson Expression 10000XL film scanner was used to digitize the films, and generated images were imported into Matlab for analysis. To verify the calibration curve and to calculate timer error, a second set of films from the same batch were irradiated with a 4MV photon beam. Differences between the vendor supplied dose rate and Cs‐137 extrapolated dose rate were compared with Fricke dosimetry results. A uniformity film was placed in the irradiation chamber and exposed for 6 minutes. To measure dose under shielding attributed to scatter, films were cut to fit around the perimeter of the irradiation chamber and irradiated for 100 minutes. To measure the penumbra across the edge of a cerrobend blocking device, films were cut and placed across the block edges. Results: The timer error was estimated to be approximately 2.6sec. Uniformity of better than ±5% was observed both in horizontal and vertical film profiles. A scatter dose of approximately 10% of the irradiation dose was observed. The 20%–80% penumbra distance of 11.9mm was observed, measured from the dose profile in the horizontal dose plane Conclusions: Our study provides independent verification for a number of dosimetric properties of interest when designing mouse irradiation experiments. This was used to improve the dose computation in small animal studies for correlation of dose with biological effects, and improve accuracy of partial body dose estimates.
SU‐E‐T‐334: A Rapid Method for Testing the Accuracy of Heterogeneity Correction Algorithms Using a 2‐D Detector‐Array QA Tool
Authors: Chu A , Feng W , Liu W , Chen Z , Nath R
Published: November 2011

Purpose: To demonstrate an efficient quality assurance (QA) method using a 2‐D diode array to verify the absolute dose distribution generated by heterogeneity corrected treatment plans. Methods: The AAA, ETAR, and modified Batho heterogeneity corrected Eclipse treatment plans were compared against the measured data obtained with 6 and 18MV (Varian 2100CD) photon irradiation with the following two geometric setups: (1) Reference setup: An inhomogeneous phantom was sandwiched by a solid water slab (Gammex) and the 22×22cm2 MapCHECK detector (Sun Nuclear) under the incident photon beam that was perpendicular to the slabs. The sandwiched slab material consisted of low‐density foam occupying half of the detector area (11×22cm2), and another solid‐water slab on the other half. (2) Tested setup: two blocks of solid‐water separated by another slab of low‐density foam were erected vertically on the surface of the 2‐D array. A slightly oblique beam angle (<30o) allows primary photon field to pass through each slab of solid water and foam to project the field onto the array. Results: The measured 2‐D dose profiles from the first configuration (Reference setup) were reasonably predicted by all three algorithms, but only AAA among the three taking into account the electron transport shows the best results for the second setup. Conclusions: The geometric design of the second setup with oblique beam angle can enhance the characteristics of the complicated dose profile projected onto a 2‐D array as the transversal and longitudinal electron transports carry out non‐local dose deposit throughout inhomogeneous slabs by oblique primary photons. The combination of build‐up and build‐down profiles is usually illustrated by film dosimetry with much a more time‐consuming procedure.
SU‐E‐T‐338: Percent Depth Dose Comparison Between Measurements from Three Varian Linear Accelerators and Varian AAA Golden Beam Data
Authors: Wu G , Courlas G , Lewis D , Jackson B
Published: November 2011

Purpose: To validate the use of Varian Golden Beam Data Percentage Depth Dose (PDD) information for the Eclipse AAA algorithm for newly installed Varian Linear Accelerators Methods: Comparison was made between measured data and Varian Golden Beam Data which is often used in AAA beam models in Eclipse treatment planning systems. Open field and wedge field data were compared for 4 × 4 cm, 10×10 cm, 20 × 20 cm, and 30 × 30 cm field sizes for four physical wedges and for two photon energies. Results: Small differences on the order of 1% are observed when comparing measured open field PDD data and PDD data from the AAA Golden Beam Data set. In contrast, larger differences were observed in wedge field percentage depth dose for these data sets with the measured data being greater than AAA data. The difference increases with increasing depth and decreasing field size. For a 4 × 4 cm field with a 15 degree wedge the average difference is 6 % at a 25 cm depth for 6 MV photons. These differences are slightly smaller for 18 MV photon data for most field size and wedge combinations. Conclusions: The Varian Golden Beam wedged field PDD data for photon beams is compiled from older linear accelerators and shows variations from data collected from recently installed machines. This variation could be due to increased beam hardening effect from the wedges compared to previous machines. Therefore, caution should be applied when using the AAA Golden Beam model for wedged field calculations, particularly for field sizes smaller or equal to 20 × 20 cm and depths deeper than 15cm. It is recommended that carefully collected commissioning data be used for physical wedge PDDs in Eclipse.
SU‐E‐T‐356: Intensity Modification of Small Diameter Proton Beam for Proton Radiosurgery
Authors: Ahn S , Choi Y , Lee H , Hur W , Kwak J , Yoon M , Shin D , Lee S , Park S
Published: November 2011

Purpose: The aim of this study is to improve the dose uniformity in the degraded SOBP (Spread‐Out Bragg Peak) of small diameter (less than 1.5 cm) proton beam by modifying beam intensity data in BCM (Beam Current Modulation). Methods: A diode detector with 0.5 mm of effective radius and a 3D‐moving water phantom have been used to measure the small field dosimetric data. The IBA proton therapy facility installed at National Cancer Center in Korea modulates proton beam using the range modulator with 10Hz‐rotating wheels and the Beam Current Modulation in the rotation phases. In a small diameter proton beam, however, the depth‐dose distribution is degraded as inverse proportional because of multiple Coulomb scattering effects. To compensate for it, we modified the proton beam intensity in BCM data of small field. The distal and lateral profiles have been measured for the original fields and the modified. Simple linear correction of BCM was applied.Results: The reduction rate of the degraded SOBP has the quadratic relation with the slope of linear correction. The Strong correlation between the SOBP degradation and beam range was found. Lateral profile was not affected by the BCM correction. Conclusions: By the modification of beam intensity data in BCM files, the dose uniformity in the degraded SOBP of small proton field could be improved. Then, the change of lateral beam shape was negligible. However the strong correlation of beam range was shown. The intensity modification of small diameter proton beam suggests the possibility of proton radiosugery for very small tumor size with more degree of freedom.
SU‐E‐T‐362: Small Field Dosimetry for Double Scattering Proton Beams
Authors: Zhu T , Shen J
Published: November 2011

Purpose: This study examines the accuracy of dose calculation in small square fields for double scattering proton beams using an empirical method based on dose per incident fluence. Methods: Fractional Depth doses (FDD) at SSD = 220 cm for open beam and small square fields (s = 1, 2, 3, 5, 10 and 15cm) are renormalized to surface. The resulting pristine peaks depth dose is normalized to the broad beam FDD to determine a fractional FDD, FDDf for selected proton energies (90 – 200 MeV). The head scatter factor (H), defined as the ratio of proton energy fluence at point of interest to 10×10 cm2 at otherwise the same geometry, is measured using a diode in air without buildup cap as a function of square field sizes for proton energies. The phantom scatter factor, PSF=BF/H, defined as the ratio of blocking factor in water at reference depth and is measured as a function of field size, energy, and SSD. Results: It is found that H is a single function of renormalized equivalent square, sN = s*230/(SSD+d) and is independent of SSD for a given proton energy. Normally, the s dependence of H is a function of SSD. The extrapolated value of PSF from percent depth dose (PDD) renormalized to the surface is remarkably close to the measured PSF data, to within 2%. Conclusions: By normalizing the Fractional depth dose (FDD) to the surface, most characteristics of small field dosimetry can be simplified and adequately described by H, a quantity describing the incident proton energy fluence.
SU‐E‐T‐363: Investigation of PRESAGE® Dosimeters for Proton Therapy
Authors: Grant R , Ibbott G , Zhu X , Carroll M , Adamovics J , Oldham M , Followill D
Published: November 2011

Purpose: To evaluate a formulation of PRESAGE® intended for proton therapy and to use it to compare measurements with calculations for a spot scanning pencil proton beam and a passively scattered proton beam.Methods: Two 7.5 cm high by 9.5 cm diameter cylindrical PRESAGE® dosimeters were used. CT images were used to design two treatment plans with an Eclipse treatment planning system (TPS). The first plan used a single pencil beam of energy 153.2 MeV to provide a range of 16 cm in water. Four regions of the dosimeter were irradiated delivering doses in the peak of approximately 6, 10, 13 and 19 Gy(RBE) by rotating the dosimeter between spot deliveries. The second plan used a single passively scattered field with a spread out Bragg peak (SOBP) of 4 cm. This plan delivered approximately 10 Gy(RBE). The dosimeters were analyzed using an optical CT scanner. The measured optical densities were converted to dose via a calibration curve, exported to the CERR environment and fused to the treatment plan. Dose distributions were scaled to the SOBP plan. Dose profiles were taken along the axis of each spot and the SOBP and perpendicularly across the SOBP.Results: The dose measured in the peak of single spot irradiations increased proportionally to the MU setting. The distal falloff was steeper than predicted by the TPS. The cross profiles for the SOBP plan matched within 2 mm with the TPS. The depth profile was noisy within the modulated area. Noise decreased as dose increased for both dosimeters Conclusions: This formulation of PRESAGE® shows promise as a 3D dosimeter for proton therapy. A dose calibration specific to protons will facilitate further analysis and enable measurement of complex distributions.

Work supported by PHS CA010953 and CA081647, awarded by NCI, DHHS.
SU‐E‐T‐368: Semi‐Independent Plan Verification Method for High‐Dose‐Rate Intracavitary Brachytherapy Using Benchmark Plan
Authors: Takahashi Y , Koizumi M , Sumida I , Ogata T , Akino Y , Yagi M , Isohashi F , Konishi K , Yoshioka Y
Published: November 2011

Purpose: We propose very simple and easy semi‐independent verification method in HDR intracavitary brachytherapy. Methods: We conducted benchmark plans of various sizes of tandem‐ovoid and tandem‐cylinder applications that were constructed with ‘ideal’ form at outside the body by one radiation oncologist. Treatment plans were conducted based on Manchester system with PLATO using semi orthogonal films of these applicator settings. We predicted the dwell time of every treatment from the air kerma strength and total dwell time of the benchmark plans. In addition, we compared the height (dh), width (dw), and thickness (dt) of 100% isodose line of clinical cases with those of benchmark plans. In this study, 49 and 29 datasets were analyzed for tandem‐ovoid and tandem‐cylinder cases, respectively. Results: With regard to tandem‐ovoid cases, differences of total dwell time, dh, dt and dw between benchmark plans and clinical cases were on average 0.3%±3.2%, −0.5mm±2.4 mm, 0.7mm±2.4mm, and − 0.3mm±1.0mm, ranging from −8.3% to 7.5%, −6.2 mm to 5.3mm, −1.0mm to 2.7mm, and −1.7mm to 2.4mm, respectively. With regard to tandem‐cylinder cases, differences of total dwell time, dhfront which is the distance from tandem tip to tandem ring, dt, and dw between benchmark plans and clinical cases tandem‐cylinder settings were on average −1.5%±3.1%, − 1.5mm±4.9mm, 0.1mm±1.0mm, and 0.2mm±0.8mm, ranging from −13.0% to 0.4%, −19.0mm to 4.0mm, −1.3mm to 4.3mm, and −0.4mm to 3.9mm, respectively. Two cases were founded to be planning mistakes in which more than 10% differences of total dwell time and 15mm differences of dhfront were observed between benchmark plans and the clinical cases. Conclusions: This method is very simple and easy but can be used for quick check of treatment planning and can find the planning mistakes.
SU‐E‐T‐374: Use of the Novel RadPos System for In‐Vivo Dose Verification in Gynaecological Brachytherapy Treatment
Authors: Reniers B , Landry G , Eichner R , Abdelbasset H , Verhaegen F
Published: November 2011

Purpose: Due to the increase of treatment complexity related to the improvement of optimization techniques and new model‐based dose calculation algorithms, high dose rate (HDR) brachytherapy with Ir‐192 would benefit from in vivo dosimetry to ensure correct dose delivery. Metal oxide semiconductor field effect transistors (MOSFET) have been proposed as in vivo dosimeters due to their small sensitive volume and direct readout. The prototype RADPOS system (Best Medical Canada) consists of a MOSFET dosimeter physically coupled to a position‐sensing probe, which deduces its 3D position in static magnetic fields generated by an emitter. The purpose of this study was to assess the accuracy of the positioning device and the feasibility of Ir‐192 in vivo dosimetry with the RADPOS system.Methods: Using a PMMA phantom, the positioning accuracy of the RADPOS system was assessed by comparing position readouts with the known position of the detector along the X, Y and Z axes. RADPOS dose measurements were performed at several distances from a Nucletron Ir‐192 source in a PMMA phantom. The photon spectrum at each distance from the Ir‐192 source was calculated using Monte Carlo (MC) simulations to determine the energy response of the micro‐MOSFET used in the RADPOS system. With this knowledge the RADPOS system can be used at arbitrary positions in a PMMA phantom in order to evaluate the delivered dose for realistic plans. Results: Positioning accuracy was found to be within 1mm in the 1–10 cm range from the source, meeting the requirements for in vivo dosimetry. Similar results are obtained for positions along the 3 axes. Calibration factors were determined at different distances from the source to evaluate the energy dependence of the micro‐MOSFET. Conclusions: Combining accurate 3D positioning data and dose measurements, the RADPOS system shows promise as an in vivo dosimetry system for HDR brachytherapy.
SU‐E‐T‐376: Is the Bladder Foley Point Dose Still An Effective Dose Factor for Three‐Dimensional Image‐Based Vaginal Brachytherapy?
Authors: Chen S , Longo J , Wahl A , Enke C , Zhou S
Published: November 2011

Purpose: To evaluate the use of the bladder foley point dose as an effective factor for 3D image‐based vaginal brachytherapy. Methods: Twenty‐one endometrial cancer patients who received postoperative intracavitary vaginal brachytherapy were included in this study (69 fractions). The radiation was delivered through a segmented cylinder applicator with a high dose rate (HDR) afterloader. The prescription dose was either 550 cGy or 700 cGy to a reference line which was 0.5 cm from the applicator surface. The posterior aspect of the foley balloon was identified as the bladder dose point. The bladder was contoured by a radiation oncologist. Two dose‐volume histograms (DVH) were collected for each fraction: 1) absolute bladder volume vs relative dose (% of prescription dose) and 2) relative bladder volume (% of bladder volume) vs relative dose. D2cc (the dose received by 2 cc bladder), D1cc, D0.1cc, and D50% (the dose received by 50% of bladder volume) were collected for each fraction, and the correlation coefficients were calculated between the bladder point dose and these dose factors. The correlation coefficients were also calculated between the bladder point dose and the DVH. The statistical significance of each correlation was determined with statistical significance identified as p‐value < 0.05. Results: : There were significant linear correlations between the bladder point dose and the DVH metrics, between V14% and V68% (p‐value <0.05). Additionally, there were significant linear correlations between bladder point dose and D50%, D2cc, D1cc, and D0.1cc, with p‐ values < 0.001 Conclusions: : In this study, there were a significant linear correlations between the bladder point dose and the bladder DVH, D50%, D2cc, D1cc, and D0.1cc. Subsequently, the bladder point dose remains an effective factor for 3D image‐based vaginal brachytherapy.
SU‐E‐T‐385: Use of a Plastic Scintillation Detector for Calibration of a P32 Dura Plaque
Authors: Mauceri T , Turcotte J , Sliski A
Published: November 2011

Purpose: Radiochromic film has been used to calibrate 32P plaques, which are used to irradiate the dura for patients with sarcomas of the spine. Although this method has been successful, it is time consuming due to the characteristics of the film. A more efficient calibration method utilizing a miniature plastic scintillation detector has been investigated for this work. This new method provides an immediate readout which can be corrected with a factor to determine dose rate. Methods and Materials: The surface dose rate for a 1 cm̂2 flat 2.47 mCi 32P source was measured with radiochromic film. A calibration curve for the radiochromic film was determined using a 90Sr eye plaque of known output. A plastic 2 × 2 × 4 cm mini phantom with a channel through the long dimension to accommodate the plastic scintillation detector, which has a diameter of 5.0 mm and length of 23 mm, was used to measure the count rate at the surface of the 32P source. A multiplicative correction factor for the scintillation detector readout was determined by dividing the dose rate measured by radiochromic film by the count rate measured using the scintillation detector. Results: The radiochromic film measurements yielded a surface dose rate of 2.52 Gy/min. The scintillation detector yielded an average count rate of 2.3 × 106 counts/min. The correction factor from these measurements was determined to be 1.12 × 10̂‐6 Gy/min. Conclusion: The use of a plastic scintillation detector versus radiochromic film for the calibration of 32P plaques will greatly decrease the calibration time by providing an immediate readout of dose rate.