bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐122: Dose Response Analysis of Radiochromic Films in Regions of Low Dose Using Separation Color Components
Authors: Marini G , Nicolucci P
Published: June 2012

Purpose: To evaluate the dose response of EBT2 films in regions of low dose using the decomposition of the image's color channels (RGB, Red, Green and Blue). Methods: Doses ranging from 1 Gy to 60 Gy were used to calibrate the dose response of Gafchromic ® EBT2 films irradiated in 6MV photons beams. Segments of film with dimensions of 8.5 cm × 8.5 cm were used. Another segment of film with dimensions 8.5 cm × 20.25 cm was also irradiated with a maximum dose of 4Gy to determine the percentage depth dose (PDD). The films were digitized by a LaserJet M1132 MFP ‐ HP ® scanner in standard resolution of 150dpi and analyzed by a routine created in MatLab to convert the image to gray levels as well as assess the desired color components from the image. Results: The green component presented the higher sensitivity (17.8 a.u./Gy) when the separated color channels and the shades of gray analysis are compared. The red component presented the highest signal to noise ratio in the low dose range (63% at 1Gy). The blue component presented low sensitivity (0.66 a.u./Gy) in the entire dose range. A linear fitting (r=0.998) was used to the green and gray components until a dose of 4 Gy. The red component presented a non‐linear behavior in the entire dose range. The useful dose range found was from 1 Gy to 15 Gy. The maximum differences between the reference PDD, measured with ionization chamber in a water phantom, and the PDDs determined with film were 6%, 9% and 14% for the green, gray and red components, respectively. Conclusions: This work results show that the use of radiochromic films on planning verification procedures in low dose ranges can be benefit from the analysis of the image's separated color components.
SU‐E‐T‐125: High‐Resolution Linear Diode Array for Use in Stereotactic Beam Commissioning
Authors: Gersh JA , Lovell S , DeWeese M
Published: June 2012

Purpose: Task Group 106 discusses detector arrays and their usefulness in “soft‐wedge” profile measurements. This study verifies an extension of their use; where a high‐resolution linear diode array is used to measure profile scans for use in commissioning stereotactic beam. Small‐field data is acquired with the LDA‐99sc (IBA Dosimetry America, Memphis, TN), an array of 99 two‐mm‐diameter Hi‐pSi diodes. These data are compared to data collected during serial scanning with an IBA SFD stereotactic diode. Methods: Field measurements were taken at varying depths using an LDA‐99sc in 1×1 cm2, 2×2cm2, and 3×3cm2 fields of a Trilogy accelerator (Varian Medical Systems, Palo Alto, CA). These scans were duplicated in resolution and sample rate with an SFD scanning diode. Both techniques acquired point data in 1.0mm increments. Results: In identical conditions, the LDA‐99sc provided readings with significantly less signal fluctuation than with traditional diode scanning; which is attributed to the reduction of water motion associated with detector travel during traditional scanning. This smoother data precluded the use of smoothing and filtration algorithms; allowing the beam to be modeled using raw data. The LDA‐99sc measured an average penumbra of 0.1 mm wider than that which was measured with the diode. The LDA‐99sc also measured an average field size of 0.3mm wider than that which was measured with the diode. With respect to time, a single profile scan (30cm‐depth, 3×3cm2 field) using the LDA‐99sc took 31 seconds, while a diode scan took 229 seconds. Conclusions: The LDA99 provided accurate commissioning‐grade small‐field beam profile data, as verified by comparison with diode scans, with a reduction of uncertainty in readings and a substantial reduction in time. Variation in penumbra and beam widths were deemed acceptable and can be attributed to the LDA‐99sc data being raw, while the diode data was processed. Research supported in‐part by IBA Dosimetry America.
SU‐E‐T‐126: Non‐Reference Condition Correction Factor KNR of Typical Radiation Detectors for the Dosimetry of High‐Energy Photons
Authors: Chofor N , Poppe B , Harder D
Published: June 2012

Purpose: To correct for the deviations of the detector response when typical radiation detectors are used under non‐reference conditions, factor kNR was calculated from the known energy dependence of the detector response at photon energies from 10 keV upwards and from clinical photon spectra within a large water phantom beneath a Siemens Primus 6/15 MV linac. A Farmer type ion chamber (NE2571), two TLD detector types and two diodes were investigated. Methods: Factor kNR was obtained as the ratio of the weighted responses Yt of a given detector t under reference conditions xref (axial distance r = 0 cm, depth d = 10 cm, field size 10 × 10 cm2 and SSD = 100 cm) and that under non‐reference conditions × (off‐axis points and depths for various field sizes); kNR = Yt(xref)/Yt(x). For small field (SF) dosimetry, we evaluated correction factor kNRSF, which refers to small field reference conditions (4 × 4 cm2 field). Results: For all detectors investigated, the deviations of kNR from unity were highest outside the field, due to prevailing low‐energy scatter contributions. For the Farmer chamber and EDP‐10 diode, the kNR deviations did not exceed 2%, but were up to 60% for the EDD‐5 diode, while kNR values for LiF:Mg,Cu,P and LiF:Mg,Ti deviated at most 15% and 5% respectively. kNR values appear as unique functions of the mean photon energy at the point of interest. Conclusions: Air‐filled ion chambers show only small kNR variations, while for non‐water equivalent detectors, kNR variations depend on the detector response at low photon energy. kNR can be presented as a unique function of the mean photon energy at the point of interest. A 4 × 4 cm2 reference field is recommended for small fields, with correction factor kNRSF varying almost negligibly from kNR except for unshielded Si diodes.
SU‐E‐T‐129: Rescaling of IMRT Verification Deviations from Detector Arrays into the Patient
Authors: Poppe B , Looe H , Heilemann G , Harder D
Published: June 2012

Purpose: To discuss a method of “rescaling” failures detected in a Gamma‐Index analysis with detector arrays into the patient as a re‐evaluation method in IMRT verifications. Methods: In a homogeneous phantom, plane signals measured with ionisation chamber arrays during IMRT field‐by‐field verifications can be understood as resulting from the convolution of the incident photon fluence with two spatially invariant kernels (dose deposition in the measurement plane and spatial detector response). In principle, Gamma‐Index deviations between planned and the measured plane signal profiles can therefore be “back‐projected” into a deviation of the photon fluence profile from the planned one which can be “forward‐projected” as a dose deviation at test points in the patient. Assuming this model for each field under investigation, all Gamma‐Index failures in a certain array region can thus be “rescaled” as deviations of the patient dose and evaluated by with patient related tolerances. The method is evaluated in the prostate and H&N region by use of the 2D‐ARRAY729 and VeriSoft5.0. The software offers the possibility to project the position of the ionization chambers onto the patient's CT. Thereby, the field specific analysis of deviations between measurements and plan is supported by suitable imaging procedures. Simulated Gamma‐Index failures (3mm/3%) have been evaluated according to the method described above and compared with direct dose calculations. Results: The degree of consistency between relative dose deviations predicted from 2D‐ARRAY evaluations and corresponding relative dose deviations calculated within the patient is found to be in an acceptable range. The applicability in regions of inhomogeneity boundaries (air‐tissue) and out of field regions was not included in this study and will be analyzed in the future. Conclusions: In combination with the described visualization tools, the method offers the possibility to re‐evaluate the dose deviations inside the patient when Gamma‐Index failures have been detected with 2D‐arrays.
SU‐E‐T‐133: Isocenter Measurements with the Winston‐Lutz Test: Impact on Treatment Planning
Authors: Templeton A , Chu J , Turian J
Published: June 2012

Purpose: To assure high accuracy in radiation delivery during linear accelerator based stereotactic radiosurgery procedures, a Winston‐Lutz test is typically performed to measure the effective isocenter wander over the wide range of gantry and couch angles employed. Ideally, this deviation is lower than 1–1.5 mm depending on institutional tolerances. Automation of this test with portal imaging allows a large amount of data to be taken and processed. This study explores the effect of various collimation techniques on beam‐center stability, and addresses one technique of repositioning in response. Methods: Winston‐Lutz shots were obtained using a Trilogy linear accelerator, BrainLab Winston‐Lutz pointer, and electronic portal imaging from a full range of gantry and couch angles. The test was repeated using MLCs, a 10mm stereotactic cone from BrainLab, and jaws for beam collimation. All images were processed using an in‐house MATLAB‐based program which calculates the distance between the tungsten ball and aperture center with accuracy within ∼0.1mm. Ideal shifts were calculated by minimizing this variation from gantry rotation alone, and performed manually. Results: The in‐plane gantry sag was found to be on the order of ∼0.8mm, independent of collimation technique or setup. The MLC carriage had a ∼0.3mm cross‐plane displacement to the inferior from the cone center, negated by a 90 degree collimator rotation. The total gantry misalignment was greatest near gantry 180 (∼1.5mm), varying by collimation method. Optimizing to minimize gantry error reduced errors to less than 0.7mm but increased the effect of couch rotation. Conclusions: Isocenter evaluation is dependent on collimation method used, and should be conducted with the same technique as delivery. It may be useful to consider the varying delivery accuracy from different couch/gantry angles during treatment planning. Repositioning methods after couch rotation may affect ideal laser positions.
SU‐E‐T‐134: Patient Specific Quality Assurance of RapidArc Pre Treatment Plans Using Semiflex 0.125 Cc Ionization Chamber
Authors: Kumar SA Syam , Prabakar S , Sriram P , Vivekanandan N
Published: June 2012

Purpose: To evaluate the Patient specific pre‐treatment quality assurance for hundred RapidArc plans using semiflex (0.125cc) ionization chambers. Methods: Absolute point dose were measured for head and neck, thorax and abdomen cases using semiflex (0.125 cc) ionization chamber. Verification plan was created for each treatment plan in eclipse 8.6 treatment planning system with the semiflex ionization chamber and the octavius phantom. Measurements were performed on a Varian Clinac2100C/D linear accelerator equipped with a millennium 120 leaf collimator. All the results were compared with the fluence measurements using 2D Seven29 ion chamber array combined with octavius phantom. Results: Positive absolute mean dose variation of 0.56 % was observed with thorax cases with a standard deviation (SD) of ± 1.13 between the plans with a range of −1.78% to 2.70%. Negative percentage dose errors were found with head and neck and abdomen cases, with a mean variation of −0.43 % (SD ± 1.50), (range ‐3.25 % to 2.85 %) and −0.35 % (SD ± 1.48), (range −3.10 % to 2.65 %) for head and neck and abdomen cases respectively. Relative dose measurements with 2D array agreed well with the TPS calculate for all the cases. The maximum percentage value failed in gamma analysis was found to be 4.95, 4.75, and 4.88 for head and neck, thorax, and abdomen cases respectively. In all the cases analysed the percentage dose points failed the gamma criteria was less than 5%. Conclusions: On the basis of the studies performed it can be concluded that the semiflex ionization chamber having a volume of 0.125cc can be used efficiently for measuring the pre‐treatment quality assurance of RapidArc plans for all the sites. The results provide an overall accuracy when compared to fluence measurement done using 2D array seven29.
SU‐E‐T‐139: Feasibility Study of Glass Dosimeter for in Vivo Measurement: Dosimetric Characterization and Clinical Application in Proton Beams
Authors: Lah J , Kim D , Park S
Published: June 2012

Purpose: To evaluate the suitability of the GD‐301 glass dosimeter for use in in vivo dose verification in proton therapy. Methods: The glass dosimeter was analyzed for its dosimetric characteristic in proton beam. Dosimeters were calibrated in a water phantom using a stair‐like holder specially designed for this study. To determine the accuracy of the glass dosimeter in proton dose measurements, we compared the glass dosimeter and TLD dose measurements of plan delivery using a cylindrical phantom. We investigated the feasibility of the glass dosimeter for the measurement of dose distributions near the superficial region for proton therapy plans with a varying separation between the target volume and the surface of 6 patients. Results: Uniformity was within 1.5%. The dose‐response has a good linear. Dose‐rate, fading, and energy dependence were found to be within 3%. The beam profile measured using the glass dosimeter was in good agreement with the profile obtained from the ionization chamber. Depth‐dose distributions in non‐modulated and modulated proton beams obtained with the glass dosimeter were estimated to be within 3%, which was lower than those with the ionization chamber. In the phantom study, the difference of isocenter dose between the delivery dose calculated by the Eclipse and that of the measured by the glass dosimeter was within 5%. In vivo dosimetry of patients, given the results of the glass dosimeter and TLD measurements, calculated doses on the surface of the patient are typically overestimated between 4% and 16%. Conclusions: As such, it is recommended that bolus be added for these clinical cases. We also believe that the glass dosimeter has considerable potential to be used for in vivo patient proton dosimetry.
SU‐E‐T‐140: A Study of Gafchromic EBT‐3 Film for the Dosimetry of X‐Ray Beams
Authors: Alnemi I , Hill R
Published: June 2012

Purpose: To evaluate the dosimetric characteristics of the newly released Gafchromic EBT3 film and determine its suitability for surface dose measurements of 6MV x‐ray beams. Methods: Sheets of Gafchromic EBT3 film (Ashland Specialty Ingredients, NJ, USA) were cut into rectangular samples according to the providing user guide. All irradiations were performed using the 6MV x‐ray beam on a Novalis linear accelerator (Varian Medical Systems). Optical density (OD) ‐ dose calibration curves were determined by irradiating different film samples with doses in the range from 0 to 3 Gy and were read out using an X‐rite densitometer using multiple readings over the samples surface. The OD was measured at different times after irradiation in order to determine stability of the film development. Surface doses were determined by placing film samples on the surface of a Virtual Water phantom for a range of field sizes from 3×3 to 20×20 cm2. Results: Sheets of Gafchromic EBT3 film (Ashland Specialty Ingredients, NJ, USA) were cut into rectangular samples according to the providing user guide. All irradiations were performed using the 6MV x‐ray beam on a Novalis linear accelerator (Varian Medical Systems). Optical density (OD) ‐ dose calibration curves were determined by irradiating different film samples with doses in the range from 0 to 3 Gy and were read out using an X‐rite densitometer using multiple readings over the samples surface. The OD was measured at different times after irradiation in order to determine stability of the film development. Surface doses were determined by placing film samples on the surface of a Virtual Water phantom for a range of field sizes from 3×3 to 20×20 cm2. Conclusions: The Gafchromic EBT‐3 film has shown to be a stable and useful dosimeter for megavoltage x‐ray beams including the determination of surface dose.
SU‐E‐T‐146: Reference Dosimetry for Protons and Light‐Ion Beams Based on Graphite Calorimetry
Authors: Rossomme S , Palmans H , Thomas R , Lee N , Bailey M , Shipley D , Al‐Sulaiti L , Cirrone P , Romano F , Kacperek A , Bertrand D , Vynckier S
Published: June 2012

Purpose: The IAEA TRS‐398 code of practice can be applied for the measurement of absorbed dose to water under reference conditions with an ionization chamber. For protons, the combined relative standard uncertainty on those measurements is less than 2% while for light‐ion beams, it is considerably larger, i.e. 3.2%, mainly due to the higher uncertainty contributions for the water to air stopping power ration and the W air‐value on the beam quality correction factors kQ,Q0. To decrease this uncertainty, a quantification of kQ,Q0 is proposed using a primary standard level graphite calorimeter. This work includes numerical and experimental determinations of dose conversion factors to derive dose to water from graphite calorimetry. It also reports on the first experimental data obtained with the graphite calorimeter in proton, alpha and carbon ion beams. Methods: Firstly, the dose conversion has been calculated with by Geant4 Monte‐Carlo simulations through the determination of the water to graphite stopping power ratio and the fluence correction factor. The latter factor was also derived by comparison of measured ionization curves in graphite and water. Secondly, kQ,Q0 was obtained by comparison of the dose response of ionization chambers with that of the calorimeter. Results: Stopping power ratios are found to vary by no more than 0.35% up to the Bragg peak, while fluence correction factors are shown to increase slightly above unity close to the Bragg peak. The comparison of the calorimeter with ionization chambers is currently under analysis. For the modulated proton beam, preliminary results on W air confirm the value recommended in TRS‐398. Data in both the non‐modulated proton and light‐ion beams indicate higher values but further investigation of heat loss corrections is needed. Conclusions: The application of graphite calorimetry to proton, alpha and carbon ion beams has been demonstrated successfully. Other experimental campaigns will be held in 2012. This work is supported by the BioWin program of the Wallon Government.
SU‐E‐T‐148: An Optimizing Study of a New Multi Channel Virginal Cylinder Applicator in Brachytherapy
Authors: Patel B , Syh J , Wu H , Rosen L
Published: June 2012

Purpose: A new CT/MRI vaginal multichannel applicator was introduced by Elekta/Nucletron® recently. The multi‐lumen cylindrical device intends to improve and optimize treatment of local advanced vaginal cancer. The design of this applicator includes several inner peripheral channels in equal spacing isotropically 5 mm from the surface of cylinder. The central tube provides the unique function as it was in traditional single channel treatment. Methods: Ninteen CT image sets of six patients were taken with multichannel applicator inserted. The single channel plan was planned before multichannel plan to justify the dose coverage to the prescribed volume and the doses received by bladder and rectum. The Oncentra® Brachytherapy planning system was employed to generate forward plan in single channel and inverse plan in multichannel where doses to bladder and rectum were evaluated and weighted by using Inverse Planning Simulated Annealing (IPSA) algorithm. Results: Figure.1 shows plan Result from single channel and Figure.2 shows multichannel Result with IPSA. The comparison confirms multichannel provides better coverage of V90, V95 and V100 to the prescribed 5 mm vaginal cuff rind. The maximal doses delivered to bladder and rectum were reduced and the mean dose was lowered in average by 5‐9% and 7‐11% respectively. Conclusions: The nature of Brachytherapy is to take advantages of short fall off of radiation dose outside the intended treated tumor and minimize dose to surrounding tissues and critical organs. However treatment technique and plan optimization could be improved and be enhanced to benefit cancer treatment from advanced design of the applicators. This study demonstrates a new multichannel applicator affords promising conformal treatment to the tumor and liberates the doses to the critical structures by using optimization to meet our objectives.
SU‐E‐T‐151: Effect of Surface Dose and Depth of Maximum Dose with Physical Wedge Filters for 6MV Flattened and 7MV Unflattened Photon Beams
Authors: Ashokkumar S , Sinha SN , Yadav Girigesh , Raman Kothanda , Thiyagarajan Rajesh , Nambiraj N Arunai
Published: June 2012

Purpose: To evaluate impact on surface dose, Depth of dose maximum (dmax) and depth dose distribution due to physical wedge filters for different wedge angle were studied for 6MV flattened (6MV FB) and 7MV unflattened (7MV UFB) photon beams. Methods: The flattening filter and primary collimator are the major sources of producing the scattered radiation and these parameters affect the surface dose, dmax and dose distribution. In this study, open fields surface dose, dmax and depth dose distribution values were compared with physical wedge filter for 6MV FB and 7MV UFB .The measurement carried out in Siemens ‐ ARTISTE linear accelerator with diode detector along the central axis of the beam at 100 cm source to surface distance using IBA blue water phantom for 6MV FB and 7MV UFB x‐ray beams. Results: The surface dose increased as the field size increased for open and physical wedge fields for 6MV FB and 7MV UFB beams. For open fields, Surface doses relative to the dose at dmax ranged from 0.443 to 0.569 and 0.463 to 0.668 for field sizes of 5 × 5 to 20×20 cm2 for the 7MV UFB and 6MV FB beam respectively. The measured surface dose for 150, 300,450 and 600 wedge field values are 0.396 to 0.504, 0.366 to 0.484, 0.342 to 0.464 and 0.347 to 0.47 respectively for 7MV UFB and 0.424 to 0.566, 0.398 to 0.555, 0.3860 to 0.5430 and 0.389 to 0.55 respectively for 6MV FB. Conclusions: We found that dmax of wedged beams were higher than those open beams for field size up to 10 × 10 cm2, Surface doses of wedged beams were lower than those of open beams for 7MV UFB and 6MV FB. Surface dose of the 7MV UFB were lower than the 6MV FB for open and wedged beams.
SU‐E‐T‐159: Sensitivity of in Line Real Time Scintillating Fiber Detectors for External Beam Treatment Verification and Patient Safety
Authors: Izaguirre EW , Price SG , Smajlovic S , Yaddanapudi S , Wooten H , Mutic S
Published: June 2012

Purpose: We studied the sensitivity of a novel transmission fiber scintillator array designed and built for in line treatment verification. The purpose of this project is to assess the capability of the fiber detector array technology to detect treatment errors in real time without false positives to enhance patient safety. Methods: We developed a linear scintillator array detector using radiation hard scintillating fibers and high speed parallel signal conditioning and data acquisition to monitor external beam treatment fluence in real time. The detector captures and resolves the time and amplitude of each linac pulse at each MLC segment. The detector has 60 fibers aligned to each MLC leaf and two output channels per fiber. The data is captured by a high speed parallel digitizer to determine the IMRT beam output delivered to a patient in real time. We evaluated the detector peak pulse linearity according to dose rate, MLC positioning, and beam energy. We analyzed the detector sensitivity, signal to noise ratio, and pulse distribution statistics to determine beam output and fluence in real time. Results: We analyzed the response of the detector to 6 MV and 10 MV photon beams. The statistical analysis of the detected linac pulses indicates that a minimum of 20 pulses are required to evaluate MLC positioning and fluence with 3 mm and 3% resolution, respectively. During testing, no false positives were detected. Linearity with respect to output rate, MLC or jaw opening, and fluence is within 2%. Conclusions: Measured sensitivity and signal to noise ratio of a real time linear fiber array detector show that delivered beam fluence can be monitored every 55 msec, with no observed false positives during treatment to provide in vivo real time patient safety and beam monitoring.
SU‐E‐T‐165: Protocol for Simplified Radiochromic Film Dosimetry
Authors: Lewis D , Chan M , Micke A , Yu X
Published: June 2012

Purpose: Radiochromic film provides dose measurement at high spatial resolution, but often is not selected for routine evaluation of patient‐specific IMRT plans owing to ease‐of‐use factors. We have developed a simplified protocol that avoids complications encountered in commonly used methods. Methods: We evaluated the simplified protocol by collecting dose‐response data from six production lots of EBT3 film at doses up to 480 cGy. In this work, we used eight different scanners of two different models ‐ Epson 10000XL and V700; post‐exposure times before scanning from 30 minutes to 9 days; ambient temperatures for scanning spanning 23°F and two film orientations. Scanning was in 48‐bit rgb format at 72 dpi resolution. Dose evaluation was conducted using a triple‐channel dosimetry method. To validate the simplified protocol, patient specific IMRT QA was performed using a Varian Trilogy Linac to expose EBT3 films. Scanning and film analysis was done following the protocol. Results: The results indicated that the dose‐response data could be fit by a set of related rational functions leading to the description of a universal calibration curve. A simplified protocol was established where dose‐response data for a specific film lot, scanner, and scanning conditions could be derived from no more than two films exposed to known doses. In most cases only one calibrated exposure was required. Using the Gamma test criterion of 2%/2mm to evaluate the measurements, passing rates ranged between 95% and 99%. Conclusions: We have demonstrated a simplified protocol to measure doses delivered by an IMRT treatment plan using only the patient film, one calibration film, one unexposed film, and applying a single scan to acquire a digital image for calculation and analysis. The simplification and time‐savings provide a practical solution for using radiochromic film for routine IMRT QA without sacrificing spatial resolution for convenience. David Lewis, Andre Micke and Xiang Yu are all employed by Ashland Specialty Ingredients the manufacturer of GAFCHROMIC EBT3 radiochromic film that is the subject of the work presented in the Abstract
SU‐E‐T‐168: Development of a Liquid Scintillation Detector for External Beam Dosimetry
Authors: Sinn D , Mackenzie M
Published: June 2012

Purpose: The goal of this research was to design a liquid scintillation dosimeter that could be used forrelative dosimetry of linear accelerator fields. The project emphasized minimization of cost and ease of use. Methods: The scintillator that was used in this research was BETAMAX‐ ES scintillation cocktail from MPBiomedical. This particular scintillator was selected due to its relatively high scintillation yield and lowcost. The entirety of the scintillator used the measurements was supplied free of cost. The housing for the liquid was constructed from PVC and is cylindrical with one tapered end. One fiber of the dual optical fibers transmits the generated photons to the CCD while the other fiber is used for Cerenkovsubtraction.The detector used comes from a Philips SPC880NC webcam. The plastic casing of the webcamwas removed so that only the printed circuit board, USB cable and lens eyepiece holder remained. Thesensor employed is the Sony ICX098QB CCD, which is 3.2mm by 2.4mm and each pixel is 5.6mm by 5.6mm. A small cylindrical insert was manufactured that was inserted into the lens eyepiece holder to get adequate mechanical coupling of the fibers to the CCD face. Images were acquired with a freeware image acquisition tool, SharpCap, and analyzed with theMatlab commercial math package from Mathworks. Results: Measurements have been performed that show that the detector is able to accurately measuretissue maximum ratio and the relative dose factor. The detector was able to accurately measurephysical wedge factors and made good predictions of the modulation factor for a patient's 7‐field IMRT plan. Conclusions: This work has shown that relative dosimetry can be performed using an inexpensive liquidscintillation detector. This could be expanded to include an array of liquid scintillator cells formeasurement of beam profiles and other more complex problems.
SU‐E‐T‐174: Synopsis of the Experimental and Monte Carlo Calculated Values of the Radial EPOM Shift of Cylindrical Ionization Chambers for Photon‐Beam Dosimetry
Authors: Harder D , Looe H , Poppe B
Published: June 2012

Purpose: According to the concept of the effective point of measurement (EPOM), the values of depth z serving as the variable of photon‐beam depth dose distributions in water measured with cylindrical ionization chambers are commonly corrected according to the formula zeff=zR+▵z, were zeff is the depth of the EPOM, zR the depth of the reference point of the chamber, i.e. of its symmetry axis, and Az the EPOM shift. Agreed‐upon values of the EPOM shift are for instance ▵z=−0.6r (IAEA TRS 398, 2000) and ▵z=−0.5r (DIN6800‐2,2008) with r=radius of the air‐filled volume. The EPOM concept holds in the falling as well as in the rising curve branch. The Az versus r relationship is currently reviewed. Methods: Measurements of the EPOM shift of cylindrical ionization chambers for 6/15 MV photons had been based upon a comparison with depth dependent dose distributions in water measured with the Roos chamber (PTW Freiburg). Its EPOM position (1.5 mm below the front face) had been determined by comparison with radiochrome films. (Looe et al, Phys.Med.Biol. 2011;56:4267–4290). Available are also the experimental EPOM shift values by Huang et al, Physica Medica 2010;26:126–131 and the classical value of Johansson et al, IAEA ‐SM‐222/35,243–270(1978). Accurate Monte Carlo values had been supplied by Tessier and Kawrakow, Med.Phys. 2010;37:96‐107. Results: As shown by the graphical display of Az versus r, the relationship is nonlinear, shaped as a hockey stick, with values around −0.2 mm for the “pinpoint” chambers and with values near −1.4 mm for the often‐used chambers with radii near 3 mm. For r ranging from 1 to 4 mm, the relationship can be approximated by ▵z = −(2.25 mm)×[1‐exp(−0.0122 r̂4)] with r in mm. Conclusions: Time has come for a nonlinear updating of the EPOM shift versus radius relationship of cylindrical ionization chambers applied in photon‐beam dosimetry.
SU‐E‐T‐175: A Study on Design and Fabrication of 25 * 25 cm2 Beam Monitor for Scanning Carbon Beam
Authors: Lee H , Yang T , Kim C , Jang H , Hong S , Kim H , Kim J , Park D , Kim C
Published: June 2012

Purpose: The KHIMA is developing a superconducting cyclotron of 430 MeV/u for carbon therapy. In order to verify the irradiated beam dose and position, detectors have been developed. The detector has a considered in the active area of 25*25cm2 to cover the entire beam scanning area. To minimize the loss of data during beam irradiation, a fast data acquisition system was required. Methods: A PPIC type was adopted. To measure the beam position and profile, the electrode of PPIC was designed to have a strip pattern. The PCB technique was applied to large area with thin FR‐4 plate of electrodes. The chamber has a strip interval of 1.7mm. He was used as the filling gas in order to reduce the ion collection time. Output signal from the detector connected to the two charge integrators was transferred every 10us. The signal can be stored temporarily in memory of FPGA through one of 2 integrators. Results: The fabricated large electrode plates did not show any deformation on their shape. Depending on the beam position, the amount of dose from the ion chamber will be measured. For fast data acquisition, the DAQ board was fabricated by using 2 charge integrators and the FPGA. The obtained data from the ion chamber was displaced on the PC screen every 10us. The fluence map of a single layer will be shown on the PC screen at the end of beam irradiation on the layer. The output data from the profile monitor will be compared with Gafchromic Film results. Conclusions: PCB method for active area of thin electrodes was used in the strip pattern. To reduce the loss of data during irradiation, 2 charge integrators are used alternately. The response of the readout data was set 1 0us. The beam tests will be performed with the MC‐50 Cyclotron.
SU‐E‐T‐177: Deconvolution of Line Dose Profiles with Ionization Chambers ‐ Experiences with the First Software Implementation in Mephisto 3.0
Authors: Poppe B , Looe H , Stelljes T , Harder D
Published: June 2012

Purpose: To evaluate the first implementation of a deconvolution algorithm in a commercial water phantom scanning software. Methods: Line dose profile measurements in a water phantom are an essential part of a quality assurance system and in base data measurements in radiotherapy. Usually these measurements are performed with waterproof ionization chambers of various sizes. These dose profile measurements are broadened by the Gaussian response functions of the detectors. In recent studies we showed that the undisturbed line dose profiles can be reconstruced by iterative deconvolution of the measured signal profiles with the Gaussian detector response functions. Recently, the proposed method was implemented in Mephisto 3.0. In this work we analyze the applicability and the limits of the deconvolution algorithm for several chambers by comparing the result with diode measurements. Results: As long as the dose gradient becomes not too steep the deconvolution algorithm is able to reconstruct the undisturbed dose profiles with sufficient accuracy. Deviations occur for smallest field sizes in which the width of the detector's lateral response functions reaches the dimensions of the field. A simple chart for those limits is derived. Conclusion: The implemented deconvolution algorithm allows a fast and simple correction of measured dose profiles broadened by the volume effect of the ionization chambers. It offers therefore for the first time a clinical deconvolution of the profiles on a regular base and by this the implementation of undisturbed base data in the treatment planning systems as well as in the quality assurance process in modern radiotherapy.
SU‐E‐T‐178: Optically Stimulated Luminescence (OSL) Dosimetry: A Study of A‐Al2O3:C Assessed by PENELOPE Monte Carlo Simulation
Authors: Nicolucci P , Schuch F
Published: June 2012

Purpose: To use the Monte Carlo code PENELOPE to study attenuation and tissue equivalence properties of a‐Al2O3:C for OSL dosimetry. Methods: Mass attenuation coefficients of α‐Al2O3 and α‐Al2O3:C with carbon percent weight concentrations from 1% to 150% were simulated with PENELOPE Monte Carlo code and compared to mass attenuation coefficients from soft tissue for photon beams ranging from 50kV to 10MV. Also, the attenuation of primary photon beams of 6MV and 10MV and the generation of secondary electrons by α‐Al2O3 :C dosimeters positioned on the entrance surface of a water phantom were studied. Results: A difference of up to 90% was found in the mass attenuation coefficient between the pure \agr;‐A12O3 and the material with 150% weight concentration of dopant at 1.5 keV, corresponding to the K‐edge photoelectric absorption of aluminum. However for energies above 80 keV the concentration of carbon does not affect the mass attenuation coefficient and the material presents tissue equivalence for the beams studied. The ratio between the mass attenuation coefficients for \agr‐A12O3:C and for soft tissue are less than unit due to the higher density of the \agr‐A12O3 (2.12 g/cms) and its tissue equivalence diminishes to lower concentrations of carbon and for lower energies due to the relation of the radiation interaction effects with atomic number. The larger attenuation of the primary photon beams by the dosimeter was 16% at 250 keV and the maximum increase in secondary electrons fluence to the entrance surface of the phantom was found as 91% at 2MeV. Conclusions: The use of the OSL dosimeters in radiation therapy can be optimized by use of PENELOPE Monte Carlo simulation to provide a study of the attenuation and response characteristics of the material.
SU‐E‐T‐179: MVCB Pelvic Surface Dosimetry
Authors: Mallah J , Mihailidis D
Published: June 2012

Purpose: To compare commonly clinically available methods of estimating skin dose for a Megavoltage Conebeam CT of the pelvis. Methods: The clinical 6 MV conebeam uses 15 MU on a Siemens Oncor linac. Film tests using XV‐2 film were done on a solid water phantom, as were tests using a parallel plate ion chamber at 2 mm depth. A Rando pelvic phantom was set up for a MVCB CT, and a cylindrically symmetric Isorad 6‐12 MV PDM diode was placed at various angles around the phantom and irradiated using a 150 MU 6 MV arc beam with the same geometry as the clinical conebeam, giving higher and more accurate readings than would be obtained with the 15 MU conebeam. A comparison was made with the Pinnacle 8.0m treatment planning system. A strip of Optically Stimulated Luminescence dosimeters provides an accurate check of the surface dose distribution. Results: All methods revealed an expected lateral asymmetry in the dose due to the starting and stopping angles of 270 (−90) and 110 for the conebeam. On the sides of the phantom, the diode dose was comparable to the Pinnacle‐calculated dose at a depth of 3–5 mm. Near the anterior portion the diode dose was about 5% higher than the maximum Pinnacle‐calculated dose at that angle. This difference is partly due to the increased diode response at shorter SSDs and higher dose rates, and to the geometry with the arc beam radiation being mainly anterior to posterior. The skin dose, corresponding to a depth of about 2 mm, is expected to be somewhat lower. Conclusions: To estimate pelvic skin dose in the MV CB geometry, corrections for measurement depth and geometry can be used to improve the dosimetry for these common clinically available dosimeters.
SU‐E‐T‐186: An Automated Quality Assurance Tool for HDR Treatment Planning
Authors: Nelson C , Gifford K , Kisling K , Bloom E , Kirsner S
Published: June 2012

Purpose: Treatment planning for high dose rate (HDR) brachytherapy requires many user inputs, all of which are potential sources of error. The goal of quality assurance (QA) is to ensure that errors are not made. In this study, we developed a software program to analyze the treatment printout from the HDR treatment planning computer and flag any suspected errors. Methods: The treatment printout from the HDR planning computer is imported by the software. The software then performs the following checks: (1) verifies that the correct source was chosen (we have multiple in our database), (2) performs an independent decay of the Ir‐192 source, (3) verifies source step size, (4) verifies the offsets and indexer lengths in the catheter definitions based upon expected values for the applicator used, (4) performs an independent 2nd check of dose to a cloud of dose points surrounding the treatment region, (5) verifies that the dose per fraction and the number of fractions were entered correctly in the planning computer, and (6) verifies that the dose volume histogram (DVH) metrics were within acceptable tolerances. The software then prints this information to a PDF file, which is appended to the original treatment printout and placed in the patient's medical record. Results: This QA tool has now been implemented for six months in our clinic, and is a critical QA tool in our HDR program. Although each plan is checked by an independent 2nd physicist, this tool provides an additional independent check on the treatment plan. Conclusions: A simple series of automatic 2nd checks helps reduce the risk of errors occurring in the treatment planning portion of HDR brachytherapy and can easily be implemented.
SU‐E‐T‐188: Evaluation of a 3D Patient Relevant Dose QA Tool: Multiple Institutional Studies
Authors: Shiu A , Chan M , Chung H , Wang H , Yan D , Yang K , Li X , Chang Y , Bai S , Qi Z , Deng X
Published: June 2012

Purpose: To evaluate 3DVHTM as a patient dose‐verification and analysis tool through multiple institutional studies. Virtual patient doses were measured and compared among different vendors' treatment planning systems (TPS) and delivered by different vendors' LINACS so that we better understand the uncertainty of entire process within a patient undergone radiotherapy. Methods: One head‐and‐neck (H&N) and one lung patient were selected in this study. The DICOM images/RT structures along with clinical protocols including prescription doses (59.4Gy for H&N and 70.2Gy for lung) and normal‐tissues tolerances were distributed to six institutions. Based on the same criteria, each institution generated their IMRT plans for the patients. Four different TPS and six different LINACS were used. The conventional per‐beam IMRT QA using MapCHECK was performed by all participants. All the measured and calculated data were sent back to one institution for 3DVH analysis. Through the use of planned‐dose‐perturbation (PDP)TM algorithm (Sun Nuclear Corp.), the ‘actual‐DVHs' were generated and then compared to the ‘reference‐DVHs' from plans. Their differences represented errors induced from the combination of TPS dose‐calculation algorithm and beam‐delivery systems. Results: All plans in the study have met the clinical criteria. The 3D matching rates for 3%global/3mm (DD/DTA) ranged from 95.8–99.9% for H&N and 93.5–100% for lung. The dose‐difference‐histogram for PTV had a mean of 0.67% [0–2%] for H&N cases and 1% [0.6–2.8%] for lung cases. The QA tool was able to spot the doses outside 3%/3mm criteria for critical structures much easier than conventional planar QA methods. In addition, the hot/cold spots at the boundaries of collimators are attributed to the uncertainty of collimator‐positioning greater than 1‐mm. Conclusions: The analysis of IMRT plans in this study has shown that 3DVH is a vital QA tool for assessing clinically relevant doses as well as diagnosing potential systematic errors from both TPS and delivery systems.
SU‐E‐T‐189: Arc Splitting for VMAT Patient QA
Authors: Sweet J , Nicolaou N
Published: June 2012

Purpose: To determine the need for arc splitting for VMAT prostate patient quality assurance. Methods: Prior to Eclipse version 10.0, a verification plan for VMAT treatment could only be created which mirrored the clinical plan; if the plan called for a full arc, then the verification plan also contained a full arc. In this case, for a center that uses the Sun Nuclear MapCheck device with its Isocentric Mounting Fixture, the full fluence of an arc is delivered en face to the device. The question arose as to whether partial arcs, if they could be created, would fail a center's criteria, while the full arc passed them, in effect, whether there are cancellations occurring and not being observed. With Eclipse version 10.0, it is now possible to split a clinical arc into many subdivisions for verification, the software recommends no more than 40 partial arcs, for computing speed limitations. Twelve VMAT plans for prostate patients were investigated, in order to search for the aforementioned cancellations. Two full arcs were used clinically in all cases. Verification plans were created consisting of (1) the two full arcs; (2) 8 partial arcs of 90 degrees each; and (3) 16 partial arcs of 45 degrees each. These were all analyzed against our criteria of 3%/3mm with a threshold of 10%, and 95% of points passing. Results: Of 288 partial arcs and 49,670 points analyzed, there were a total of 100 points (0.2%) that failed the 3%/3mm criteria. No arcs, however, failed the 95% passing criteria. Moreover, there was no evidence of cancellation; if a point failed low, there was no corresponding high failure in another partial arc. Conclusions: In this study, splitting a full arc into partial arcs revealed no unseen failures.
SU‐E‐T‐196: Commissioning for Volumetric Modulated Radiation Therapy on Varian Clinac 21EX
Authors: Yada R , Hayashi N , Matsunaga T , Nozue M , Sai H , Yamada K , Yamanaka R , Kato Y , Muraki Y
Published: June 2012

Purpose: Recently the volumetric arc therapy (VMAT) technology such as RapidArc is widely distributed in Japan. These technologies are normally provided by the high spec linear accelerator such as Trilogy, Novalis Tx, Synergy, et al. The specific DICOM‐file is generally used for commissioning of these technologies. On the other hand, we had to apply RapidArc into historic linear accelerator. This title expresses an experience how we performed the commissioning of RapidArc with the old linear accelerator. Methods: Two Varian's linear accelerators “Clinac 21EX” equipped with Millenium multi‐leaf collimator and a Varian's treatment planning system “Eclipse ver.8.9” were used for this study. The commissioning for RapidArc was performed in energy 4,6,10,15 MV (Max‐DR: 250, 600, 400, 600 MU/min). Commissioning procedure composed two categories: the general machine QA for DMLC‐IMRT procedure and the specific RapidArc QA procedure. In RapidArc QA procedure, we modified DICOM‐file to apply into the potential spec of Clinac 21EX optimally. The specific MLC‐motion sequence and the gantry rotation speed were created by the dedicated programs (Shaper and DicomEdit, Varian) for RapidArc QA procedure. Each tolerance value was defied by the data from daily/monthly QA and the paper by Ling et al. Results: As the results of the general machine QA procedure, the variance of radiation output during static/dynamic gantry rotation was less than 1%. The deference of fence tests during static/dynamic gantry rotation and RapidArc were less than 1 mm in each. However, the results of the RapidArc QA were worse than the latest machine (especially variable gantry speed) and it was careful to define tolerance level. Conclusion: The procedure of commissioning for RapidArc on historic linear accelerator was proposed. Several minor revisions for DICOM‐file should be required for suitable commissioning and it may ensure the tolerance limit for gantry/MLC‐leaf motion speeds.