bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐GG‐T‐311: Implementing Patient Specific Plan QA for CyberKnife: Comparison between Two Independent Systems
Authors: Mardirossian G , Koltermann P , Mirzasadeghi M , Muniruzzaman M
Published: August 2010

Purpose: Patient specific plan QA (PSPQA) is not in current practice for CyberKnife (CK) application mainly due to lack of facilitated procedures. We present the importance of implementing PSPQA for CK, compare, discuss procedures involved and analyze results obtained from two independent systems. Method and Materials: Since CyberKnife was designed to deliver SRS/SRT treatments plans to critical structures no PSPQA has been introduced for the system yet. In this work, we evaluate two independent systems in performing PSPQA; First PTW 2D array with Octavius; a planar chamber array with 1cm center‐to‐center distance and 5mm spacing (Seven29) and the other is film‐chamber‐based analysis with FilmQA. Eight plans were evaluated with target volume ranging from 37cc to 225cc. Results: The PTW system exhibited standard gamma criteria characteristic (3% dose difference, 3mm DTA) for most CK plans larger than 3 cm. Eight plans exhibited an absolute % dose difference of 0.0(1.8) and an overall average %dose difference, %DTA and %gamma equivalent to 75.4(7.0), 89.6(4.1) and 95.2(2.3). The % dose differences improved following the correction from an average of %75 to over %85. With 3% and 2 mm criteria, Gafchromic FilmQA presented excellent fusion and dose overlay with DD, DTA and gamma index agreements of 90.5(6.6), 95.8(7.0) and 98.6(2.0) respectively (n=74). The percent chamber absolute dose difference equivalent to %1.1(2.2). Evaluations showed surprising variation based on the filtering option selected. Conclusion: PSPQA is absolutely essential for CK plans. Tools such as film‐stereotactic chamber or 2D ion chamber array can be used to achieve it. Further investigation needed to evaluate PTW 2D array for target lesions that are either < 3 cm or with high dose. The optimal choice of performing the QA analyses may depends on the policy and passing criteria set by the user.
SU‐GG‐T‐315: Single Event Effects in Radiotherapy
Authors: Guo F.Q. , Zhai Y , Chen Z , Nath R
Published: August 2010

Introduction A single event effect (SEE) is a change of state of a microelectronic device caused by a single energetic particle. Single event upsets (SEUs) is one kind of SEEs. A SEU on a Siemens Linac has been reported in a SRAM of PLC. With more and more integrated circuits in modern Linacs and treatment head, such as MLC, the probability of SEEs becomes larger. The consequences of the SEEs in radiotherapy, especially of safety functions and considerations, need further investigation. Method and materials A Linac with high energy (15MV) mode (Varian, Palo Alto, CA) was investigated. Integrated circuits used inside treatment room were identified. Of interest wert those CMOS and FPGA. The SEE rates were estimated based on published papers. Further estimation was made with Monte Carlo code and data from NASA's SEE test reports. SEEs in beam delivery and MLC control were also scrutinized. Results SEU rate of 0.047 events⋅MiB−1⋅MU−1 for Varian 15 MV photons has been derived. If the response of the ICs is linear, a radiotherapy room with 32 patients/day, 1/8 patients treated with high energy, and 200 MU/patient, the SEUs will be 38 SEUs⋅MiB−1⋅day−1. If somewhat arbitrary one megabyte is taken for memory size in use, the SERs will be 38 events per day. Thus, there is a significant potential for quite a few SEEs in radiotherapy. Conclusion The SEE is well known phenomena of increased importance. SEE is a critical to electronic reliability in certain environment like radiotherapy. The SEE characteristics of electronics should be tested further and evaluated for clinical application. Further knowledge on their impact to radiotherapy, especially to under‐dose or over‐dose delivery, and control of parts like MLC, should be investigated. Care should be taken by the manufacturer to use ICs which are immune of SEEs.
SU‐GG‐T‐318: External Beam Dose Perturbation from Non‐Radioactive I‐125 Seeds: Film and Monte‐Carlo Measurements
Authors: Steinman J , Malhotra H
Published: August 2010

Purpose: Large numbers of radioactive seeds are often used in prostate brachytherapy procedures. External beam radiotherapy is often used to salvage failed brachytherapy treatments ignoring their presence. Present study attempts to quantify the dose perturbation due to these seeds as a function of energy, depth, field size, number of seeds, etc. during external beam treatments. Method and Materials: A number of non‐radioactive I‐125 seeds were procured. Film measurements were primarily carried out using Kodak XV2 layered above and below an I‐125 seed placed in a groove on a Lucite plate with 5‐cm buildup and 10‐cm backscatter at 95‐cm SSD. The phantom was irradiated with and without seed with 6 MV photons with a 1×1cm2 field‐size. Monte‐Carlo simulations were done using DOSXYZnrc and compared with Gafchromic‐EBT2 film. Effect of energy, depth, and field size including metals of various Z of the seed's dimensions was also studied. Study also looked into effect of 3 seeds spaced 0.5‐cm vertically with single and with two opposing fields. Results: XV film measurements for a single and three I‐125 seeds show a localized dose enhancement of 6.3% upstream but reduction of 10.9% downstream. With two opposing fields, a cold spot around the seed of ∼3 percent was observed. Increasing beam energy and field size decreased the effect. Use of higher Z of materials greatly increased perturbation. At higher depths, a slight increase was noticed. DOSXYZnrc and EBT2 film verified maximum dose enhancement of 15% upstream and −20% downstream of the I‐125 seed surface. In general, the range of the dose perturbation was noticed up to ∼2‐mm upstream and ∼5‐mm downstream. Conclusion: Presence of I‐125 seeds causes dose perturbation which depends on energy, field size, depth, and material. With multiple seeds spaced apart and multi‐fields external beam radiotherapy, the net perturbation may not be clinically significant.
SU‐GG‐T‐319: Effects of Esophageal Stents on Radiotherapy Dose Perturbation Examined in an Experimental Model
Authors: Atwood T , Ogara M , Luba D , Tamler B , DiSario J , Maxim P
Published: August 2010

Purpose: To investigate the radiotherapy dose perturbations caused by esophageal stents in patients undergoing x‐ray beam therapy for esophageal cancer. Method and Materials: Four experimental esophageal stents from Boston Scientific were examined (three metallic stents: Wallflex, Ultraflex and Alimaxx, and one polymeric stent with limited radiopaque markers for visualization: Polyflex). All experiments were performed in a water phantom with a custom acrylic stent holder in order to closely model the scatter and absorption characteristics of human soft tissue. Gafchromic film was used to measure the dose distributions at locations above and below the stents, which were placed in an air‐filled cavity to simulate the esophagus. Treatment plans were created and delivered for clinically relevant photon energies of 6 and 15 MV, and data analysis was performed on uniform regions of interest to quantify the dose perturbations. Results: The three metallic stents produced the largest dose fluctuations with distinct patterns of ‘hot’ spots (increased dose) measured above the stents (up to +15.4%) and both ‘cold’ (decreased dose) and ‘hot’ spots measured below the stents (range: −6.2 to +5.4%). The polymeric Polyflex stent produced similar dose alterations when the radiopaque markers were examined (range: −6.4 to +15.4%). However, when the markers were excluded from the analysis, the Polyflex stent produced significantly smaller dose fluctuations, with maximum ‘hot’ spots of +6.8% and cold spots of −2.5%. Minimal energy dependence was observed. Conclusion: The non‐metallic Polyflex stent appears to be the most suitable for patients undergoing radiotherapy. The radiopaque markers would facilitate precise localization in the esophagus, while the polymeric composition would have the least affect on the dose distribution within the treatment volume. More work needs to be performed to determine the clinical significance of the observed ‘hot’ and ‘cold’ spots but is beyond the scope of this study.
SU‐GG‐T‐321: Effect of Uneven Surface of Incidence on Dose Distribution for Electron Beams during Radiotherapy
Authors: Shah N , Sinha U , Jani S
Published: August 2010

Purpose: To measure and quantify the effects of an uneven surface of incidence on depth dose parameters (Dmax, D90 and D50), as well as dose output, and its clinical implications during electron beam radiotherapy. Method and Materials: Five phantoms with uneven surfaces were fabricated out of thermoplastic material to shape the surface of water in a three‐dimensional motor driven water phantom. Beam scanning was performed with five energies (6, 9, 12, 16 and 20 MeV) along with two field sizes (10cm2 and 15cm2) for each uneven surface of incidence. Central axis depth doses and profiles were measured, as well as outputs at Dmax, for the case of an uneven surface of incidence vs. a flat surface of incidence. These values were then compared to computed values using a Philips ADAC TP system. Results: Depth dose parameters became shallower for an uneven surface of incidence by as much as 9mm. The effect of an uneven surface was small for low energy electron beams. For a concave surface of incidence, the TPS calculated depth doses were off by as much as 6mm as compared to measured values. The beam output (cGy/MU) at Dmax was altered by as much as 17% according to measured values. The outputs computed on ADAC Pinnacle were off by as much as 15% compared to measured values. Conclusion: Manual MU calculations assume flat surface of incidence which leads to significant differences between dose desired and dose delivered. Computerized planning also did not predict correct output values. It is critical to pay close attention to an uneven surface of incidence when performing planning and dosimetry of electron beam radiotherapy.
SU‐GG‐T‐330: Experimental Comparison of Six Commercial Dosimetry Diodes for Measurement of Stereotactic Radiosurgery Cone Factors
Authors: Sherouse G , Dieterich S
Published: August 2010

Purpose: The purpose of this work is to measure SRS cone factors with commercially available diodes to determine the “best” instrumentation for beam data acquisition in small field dosimetry. Method and Materials: Measurements were made in 6 MV photon beams with fixed SRS cones for two accelerator‐based SRS systems: a Varian Clinac 2300iX (Varian/ZMed cones) at 600 MU/min‐and a CyberKnife G4 at 800 MU/min. Measurements were made at 1.5 cm depth in water using the IBA Dosimetry “blue phantom” 3D scanning system, controlled by OmniPro‐Accept software. The same author performed set‐ups on both machines for consistency. Source‐to‐detector distance was 100 cm for the Clinac, 80 cm for the CyberKnife. Two curves were calculated for the Clinac, one directly from 10×10 diode measurements and the other indirectly by “daisy‐chaining” diode measurements to a 10×10 reference ion chamber measurement through an intermediate 4×4 square field. CyberKnife factors were calculated directly from measurements in the 60 mm reference field. Six commercial diodes were evaluated: PTW TN60008, TN60012, TN60016, TN60017; IBA SFD; Sun Nuclear EDGE; Exradin SD1. Results: With one exception, all the evaluated devices yielded surprisingly consistent results. Standard deviations of Clinac factors for all diodes excluding the outlier ranged from approximately 0.50% at 30 mm to 1.9% at 5 mm cones size when referenced directly to the 10×10 measurement. The daisy‐chaining strategy reduced the standard deviation to approximately 0.14% at 30 mm and 1.7% at 5 mm. Standard deviations in the CyberKnife beam ranged from 0.40% at 60 mm to 1.2% at 5 mm. Conclusion: The inter‐detector variation is small and appears to be systematic with detector packaging, more inherent filtration producing flatter curves for both the relatively hard Clinac beam and the softer CyberKnife beam. The daisy‐chain strategy reduces the variance between diodes by about half in the Clinac beam.
SU‐GG‐T‐331: Performance Evaluation of a New‐Model P‐Type Si Diode for Small Field Dosimetry
Authors: Dugas J , Speiser M , Medin P , Solberg T
Published: August 2010

Purpose: Accurate small field characterization affects patient safety and success in stereotactic radiosurgery (SRS). This study provides critical characterization data for clinical implementation of a new p‐type Si scanning diode, the Exradin SD1, for SRS dosimetry. Method and Materials: SD1 performance was compared against the Scanditronix‐Wellhöfer SFD stereotactic diode and PTW PinPoint® ionization chamber for a 6 MV beam. Percent depth dose (PDD) curves for square, jaw‐shaped fields (12, 24, 40, 80, and 98 mm) and diagonal profiles at 5, 14, 25, 50, 100, 200, and 350‐mm depths (98×98‐mm2 field) were attained in a large water phantom. Scatter factors were calculated from output measurements in a 30×30×30‐cm3 water tank at 100‐cm SSD, 5‐cm depth for MLC‐shaped square field sizes of 6, 12, 18, 24, 36, 42, 60, and 80 mm (98×98‐mm2 reference field). Results: SD1 PDD data agrees well with SFD diode and pinpoint chamber data at depths ≥dmix for all measured fields. The SD1 overestimates dose in the buildup region, likely because its design includes a 3.5 mm dome of buildup material over the active detector. Displacement of the effective measurement point from the SFD diode surface is 0.7 mm. Both SD1 and SFD diodes over‐estimate PDD for fields ≥40 mm, likely from silicon's increased sensitivity to low‐energy scatter. All three dosimeters produced similar beam profiles at all depths, excepting minor disagreement in the tail regions. The SD1 diode exhibited no drift (change in response over time), possibly due to higher outputs yielding smaller percentage drift. SD1‐measured scatter factors trend higher than their ion chamber‐measured counterparts with poor agreement for the smallest (6mm) field size evidenced by large absolute differences in measured values between all three dosimeters. Conclusion: Exradin SD1 performance for small field measurements has been evaluated, providing critical characterization data for its clinical implementation for SRS dosimetry.
SU‐GG‐T‐332: Dose to Contralateral Breast: A Comparison of Traditional Linac and Tomotherapy Techniques
Authors: Fountain T , Lamba M , Lavigne R , Skidmore T
Published: August 2010

Purpose: To characterize the dose and its distribution to the contralateral breast in patients undergoing whole‐breast radiotherapy using helical tomotherapy, and traditional linac with enhanced dynamic wedges or field‐in‐field techniques. Method and Materials: At the start of this IRB approved study, patients were selected and offered consent and enrollment. Dosimetry was performed using thermoluminescent dosimeters (TLDs) which were individually calibrated and tracked to generate a linear dose response curve for each. Positions for measurement were marked on the patient for reproducibility. The measurement positions were 5 cm superior, inferior, medial, and lateral to the breast center of the contralateral breast and 2 cm from center of sternum toward the contralateral breast. TLDs were placed in buildup caps to ensure buildup to electronic equilibrium. TLDs were placed daily for five consecutive treatments and then read 10 days after the last treatment. Calibration curves were applied to the TLD readings. Results: To date, three patients have been treated on Tomotherapy and five patients with traditional tangents. The contralateral breast doses, presented as a percentage of the prescription dose ± 1 standard deviation, are as follows: Tomotherapy; two cm from sternum 36 ± 8%, five cm medial 17 ± 6%, five cm superior 6 ± 1%, five cm lateral 6 ± 1%, five cm inferior 6 ± 1%. Traditional tangents; two cm from sternum 12 ± 5%, five cm medial 5 ± 2%, five cm superior 2 ± 1%, five cm lateral 2 ± 1%, five cm inferior 2 ± 1%. The average breast dose, calculated as the arithmetic mean of the doses five cm from the breast center, were 9 ± 6% for Tomotherapy and 3 ± 2% for traditional tangents. Conclusion: At our institution, helical tomotherapy produces doses in the contralateral breast that are approximately three times that of traditional tangents.
SU‐GG‐T‐333: Validation of Experimental Results in Small Field Dosimetry
Authors: Sabino T , Rodrigues L
Published: August 2010

Purpose: During the implementation of Radiosurgery in clinical routine it is important to use as many detectors as possible since small field dosimetry is not a very easy task due to the lack of lateral equilibrium. In order to validate the experimental results obtained during the implementation of stereoteactic Radiosurgery fields, a comparison was performed with the theoretical data published in the literature. Method and Materials: The first theoretical approximation proposed by Sauer et al which calculates the beam quality parameter (Q) and the tissue‐phantom ratios (TPR), for any field size. The TPR20,10 used in this investigation was derived from measurements taken from a linear accelerator of 6 MV photons (Varian 6EX) by using different detectors: a pin point ion chamber (CC01); a small ion chamber (CC13); a stereotactic diode from Scanditronix/Wellhöfer. Results: The comparison of experimental results obtained in this investigation by comparing with Sauer et al values show −1,8%, 4,0% and 4,9% for the pin point chamber, the CC13 ion chamber and stereotactic diode respectively. Regarding the BJR‐25 published data one can consider the results provided by a Farmer type chamber which were more common at that time. On the other hand, the zero‐field approximation (Cheng et al) gives a small difference of 0,7% since only the stereotactic diode has been considered in both investigations. By comparing the experimental results with those provided by Cho et al, a much better agreement is found except for the pin point chamber. Further investigations will me made with this late detector in order to clarify all possible deviations. Conclusion: The comparison of experimental results with pin point chamber, small ion chamber and stereotactic diode shows good agreement with literature data, thus providing an appropriate method for validation of experimental results for small field dosimetry.
SU‐GG‐T‐334: Comparison of Measurements and Eclipse Electron Monte Carlo Calculations for Small Electron Fields with Central Block
Authors: Ivanova T , Kassaee A
Published: August 2010

Purpose: Dosimetric comparison between measurements and Eclipse electron Monte Carlo calculations for small electron fields with central block, used in ocular lymphoma treatment. Method and Materials: Cutout factors for Cerrobend electron blocks with circular apertures of 3, 4 and 5 cm diameters were measured in solid water at dmax for 6 and 9 MeV on Varian iX Linac using electron diode and Markus chamber. The dose at dmax for the same cutouts with an additional central block (1.2 cm in diameter) was measured in the center of the open area adjacent to central block using the same instruments. The experimental setup was modeled in the Eclipse treatment planning system and the calculated doses were compared with the measured values. Kodak X‐OmatV films were used for measurements of relative dose distribution in planes along (axial) and perpendicular (coronal) to central axis at 1 and 2 cm depth. Results: Cutout factors measured by diode and Markus chamber agreed well within 1.9% for both energies with and without central block. Eclipse prediction for open cutouts for 9 MeV agrees better than 1% with diode measurements, while for 6 MeV discrepancy is about 3.1 % for 3 cm cutout. However, Eclipse overestimates the dose at dmax in case of central block setup by 4.9% and 1.4% for 5 cm cutout for 6 and 9 MeV and by 13.7% and 10.2% for 3 cm cutout, respectively. There is a general disagreement between the film measured and calculated profiles with largest differences observed in the shielded region under the central block and at the deeper depths. Conclusion: For small electron cutouts with central blocking, measurements of beam characteristics including output factors and dose distributions are warranted for verification of treatment plans.
SU‐GG‐T‐335: Analytical Formalism for the Output Factors of Small MLC‐Shaped Beams
Authors: Arida L Abu , Wadi‐Ramahi S , Dababneh S
Published: August 2010

Purpose: The output factor, Scp, of small MLC‐shaped beams suffer from two competing effects: The loss of lateral CPE which tends to reduce the dose, and the extra leakage which tends to increase it. Scp measurement is further complicated by the size of the chamber used. We show that for small MLC‐beams, CPE is regained. Subsequently, we find measurement‐based analytical formula to calculate the output factors of small MLC‐shaped beams that is independent of chamber size. Method and Materials: A series of Scp measurements, with three photon energies, were taken using various chambers and various MLC‐shaped and jaw‐shaped fields ranging from 1×1 to 10×10 cm2. Results: The measured Scp of small MLC‐shaped beams was found to closely follow the linear trend of the larger fields. The linear curve joining the Scp of large fields was called the CPE‐line and it was extrapolated towards the small fields. For each energy/chamber combination, the CPE linear fitting parameters were calculated and chamber‐size effect was found to be minimal. The parameters were averaged over all chambers to present formula that is dependent only on energy and field size. Conclusion: Establishing CPE conditions for small MLC‐shaped beams allows the use of measurement‐based formula to calculate Scp. The formula is a function of field size and energy but not of chamber size. The removal of chamber dependence reduces the potential of underestimating Scp and consequently overdosing the patient. We propose that our formalism can be used in treatment planning systems for modeling of Scp for small MLC‐shaped beams for IMRT or SRS treatment or used by physicists to estimate the expected Scp value for the MLC‐shaped beams and compare them to their measured data.
SU‐GG‐T‐336: Effect of Treatment and Beam Parameters on Surface Dose in Proton Beam Therapy
Authors: Das I , Fanelli L , Gautam A , Zhao L , Wolanski M , Nichiporov D , Cheng C
Published: August 2010

Purpose: The advantage of lower skin dose in proton beam therapy may result in less radiation‐related side effects which are typically seen in hypo‐fractionated conventional external beam therapies. In this study, we evaluate the surface dose (SD) in proton therapy as a function of various beam parameters. Materials & Methods: SD is defined as the ratio of absorbed dose on CAX at surface to that at the middle of the Spread‐Out Bragg Peak (SOBP). SD in proton therapy is affected by several parameters: energy (E), SOBP, source‐to‐surface distance (SSD), air gap (g), field radius (r), material thickness upstream of surface besides air (t), atomic number of medium (Z), beam angle relative to surface (q), and nozzle type (N). The parameters, t, Z and q are not included in this study.. Results: Giving a proton range in water of 27 cm, SD rises from 30 to 90% with SOBP increasing from 0 to17cm. At high energy, SD is 5% higher in the uniform scanning (US) nozzle than in double scattering (DS) nozzle. This can be explained by the large difference in source‐to‐axis distances in US and DS nozzles (250 cm vs 320 cm). SSD and g have minimal impact on SD for r > 2.5cm. For small fields (r < 2.5cm), SD increases significantly with field size decreases. Within 15mm of the surface there is a small but pronounced 2% buildup in proton beam at high energies, which may be partially due to secondary electrons, secondary protons and heavy charged particles. Conclusions: In a clinical setting, SD is most significantly affected by SOBP extent, followed by field size, SAD, and beam energy. In general, SD ranges from 50 to 95%. It is important to clearly understand and minimize SD in Proton therapy, especially in hypo‐fractioned treatments.
SU‐GG‐T‐339: New Small Volume Scanner for Radiosurgery Beam Data Collection
Authors: Hevezi J , Monterroso I , Nikesch W , Navarro D
Published: August 2010

Purpose: To determine the minimum dimensions of a water tank for small field Radiosurgery (SRS) and Stereotactic Body Radiation Therapy (SBRT) beam data collection. In addition, to describe the use of the small‐volume tank in its movement to measure direct SAD data, such as TMR/TPR. Methods and Materials: After several iterations in tank design, a cylindrical water tank with dimensions 20 cm diameter and 40 cm high was felt to have enough scatter volume to yield results to full size water tank for SRS and SBRT beam data collection. The entire tank movement is directed by the usual 3D drives (X,Y,Z). A separate vertical drive in the tank can move the detector probe independently of the external drive such that it can be synchronized with the external Z‐drive to keep the detector at a fixed SAD to obtain direct TPR/TMR profiles. For radial, transverse and diagonal profiles, the whole tank is moved across the beam to accumulate cross profiles at various depths determined by the vertical drive in the tank. PDD measurements can also be obtained. Results: Complete sets of beam data for a CyberKnife® SRS treatment unit were obtained with the new scanner (Output factors, Off‐Center Ratios and TPR data) and compared to data taken with a large water tank scanner. All data compared favorably, with the greatest deviation appearing for the 60 mm collimator and 300 mm depth, where the small tank showed values past the penumbra region of about 0.5% less. Total scanning time for a single collimator to obtain TPR data and 10 cross profiles at 5 depths was under 10 minutes. Conclusion: A small volume scanning system was found to yield beam scanning results virtually identical to those obtained with a large water tank for small fields, with less acquisition time.
SU‐GG‐T‐341: Initial Results of Real‐Time External Surface Motion and Dose Monitoring Study for Lung Patients
Authors: Cherpak A , Cygler J , Andrusyk S , Pantarotto J , MacRae R , Perry G
Published: August 2010

Purpose: To describe results from an ongoing clinical trial that aims to evaluate the potential of the RADPOS system, which combines a MOSFET dosimeter and electromagnetic positioning sensor, for applications in external beam treatments for lung cancer patients. Method and Materials: Measurements were done at the time of each patient's 4DCT and throughout the course of treatment. Each day, three RADPOS sensors were positioned at marked points on the patient's chest and abdomen while a fourth detector was placed on the CT or treatment couch for reference. Position coordinates of the sensors and dose information can be read in real‐time, but for these trials the total dose was read after each treatment fraction. Results: Measurements have been completed on ten patients during 7–14 fractions each. The standard deviation of the average dose measured at each point ranged from 3.0–13.7 cGy at CT zero and 2.5–11.1 cGy at the site of the tumour. Large differences were sometimes seen between data collected during the 4DCT and treatment fractions. Most patients settled into a more consistent breathing pattern as treatment progressed, with maximum interfraction variations in average amplitude and period between 0.9–3.5 mm and 0.2–1.8 s during treatment. A cross‐correlation analysis comparing the displacements measured simultaneously at the three locations found that correlation varied between patients, as no two detectors were consistently the most correlated. The magnitude of the correlation coefficients also varied greatly, ranging from ρ=0.13–0.24 for Patient G and from ρ=0.74–0.81 for Patient E. Conclusion: RADPOS system can provide real‐time feedback regarding motion due to breathing, coughing or other patient movement. Variations in breathing patterns are patient‐specific and should be monitored to ensure accurate positioning and treatment delivery. Acknowledgements: This project is supported by grants from HTX and ORCC Foundation. Financial and technical support from Best Medical Canada is also acknowledged.
SU‐GG‐T‐344: Comparison of Characteristics of Two Liquid‐Filled Ionization Chambers
Authors: Chung E , Seuntjens J
Published: August 2010

Purpose: To characterize two liquid‐filled ionization chambers for reference dosimetry of nonstandard fields. Methods and Materials: Two chambers used in this work, an in‐house developed guarded liquid‐filled ionization chamber (GLIC‐03) and a commercial PTW microLion chamber 31018, were filled with anhydrous 2,2,4‐Trimethylpentane liquid. The stability and reproducibility of each chamber was evaluated by delivering a series of certain dose to each chamber and repeating the same process with polarizing voltages of +500 V (GLIC‐03) and +800 V (microLion). The polarity effect was measured for each chamber. The directional dependence of each chamber's response was measured by irradiating the chamber at different radial directions by either chamber rotation or gantry rotation. The relative ion recombination effect in the liquid was determined theoretically and experimentally for each chamber. Results: During a single measurement set both chambers' responses were stable within 0.13 % after pre‐irradiation to 130 Gy and 65 Gy for the GLIC‐03 and the microLion, respectively. The reproducibility of the chamber's response was 1 % (GLIC‐03) and 0.20 % (microLion). The measured polarity correction factor Ppol was 1.005–1.006 and 1.001–1.002 for the GLIC‐03 and the microLion, respectively. When rotating each chamber, its response was not different more than 0.18 %. When irradiating it from different directions, the GLIC‐03 showed anisotropic response due to the filling tubes, while the microLion's response was the same to within 0.18 %. The theoretical and experimental relative ion recombination effect for the GLIC‐03 agreed to within 0.7 %, which is due to incomplete charge collection in the time period between pulses. The microLion showed a better agreement, within 0.25 %, between the calculated and measured relative ion recombination effect. Conclusions: We have evaluated two liquid‐filled ionization chambers' characteristics in various aspects. These characterized chambers can be used to accurately measure reference dose in nonstandard fields.
SU‐GG‐T‐345: Dose Response and Energy Dependency of Gafchromic EBT2 Film over a Wide Range of Beam Energies and Modalities
Authors: Anand A , Arjomandy B , Tailor R , Sahoo N , Gillin M
Published: August 2010

Purpose: The Gafchromic films have been used generally in absolute and relative dosimetry in radiation therapy. The ISP Corporation® has recently replaced a widely used Gafchromic EBT film by a newer version, namely, “EBT2” film. The purpose of this study is to evaluate the EBT2 film for its energy dependencies and dose responses for a broad range of energies and modalities used in clinical radiation therapies. Method and Materials: The beams used for this study consisted of kilo‐voltage x‐rays (75,125, and 250 kVp), 137Cs gamma (662 KeV), 60Co gamma (1.17–1.33 MeV), Mega‐voltage x‐rays (6 and 18 MV), electron beams (6 and 20 MeV), and proton beams (100 and 250 MeV). The film's response was measured over the range of 0.4–10 Gy, which corresponds to optical density ranging from 0.05 to 0.74, for each of the beam energies. An X‐Rite pocket densitometer and an Epson flatbed scanner were used to read the films. Results: The measured dose response for EBT2 film over the energy ranges investigated was ±4.5% (1σ). The two extremes among the dose response data for various beams were 100‐MeV proton beams and 60Co (or 137Cs) beams. Uncertainty in beam calibrations was estimated to be 0.82% after compounding the margins of error from contribution of uncertainties in NIST calibration, ADCL calibration, and setup error and beam outputs. The film uniformity and film‐to‐film variation was found to be within 0.9% (1σ) for a single batch. Conclusion: Our results indicate that for measurement of relative and absolute dosimetry, EBT2 film is a robust dosimeter with weak energy dependency over a broad range of energies and modalities used in radiation therapy.
SU‐GG‐T‐347: Determination of Proton Beam Range by Using Scintillating Fiber Optic Dosimetry
Authors: Hwang U , Rah J , Jeong H , Ahn S , Kim D , Lee S , Shin D , Lee S , Yoon M , Park S , Jang K , Lee B
Published: August 2010

Purpose: Scintillating fiber type dosimeter was investigated to determine the proton beam range in a short time for the purpose of quality assurance of the patient in the proton therapy. Degradation of output signal in scintillator has to be overcome for applying the scintillating fiber dosimeter on clinical use. One dimensional dosimeter array was tried to measure the range at a time and required characteristics for this application were evaluated. Methods: The dosimetry system was composed of commercial scintillating fiber optically coupled with organic based optical fiber. Scintillating light was amplified by photo multiplier tube before being gathered by commercial data acquisition system. Bragg peak and SOBP was measured with scintillating fiber dosimetry. One dimensional scintillating fiber array dosimeter was prepared and Bragg peak and SOBP of proton beam were measured and analyzed. Results: The Bragg peak measured by scintillating fiber dosimetry showed degradation of the output signal in high dose region when comparing with the results of the ionization chamber, which is known as quenching effect of scintillator. Quenching effect could corrected by fitting the measured data to quenching equation. However, it didn't show significant degradation of the signal enough to miss the range within sub‐millimeter for the scintillator smaller than the diameter of 0.5 mm. The SOBP curve also showed good agreement with the ionization chamber results after being modified by considering the quenching effect. It can be applied to construct the scintillator array to measure the depth dose distribution at a time. Conclusions: Scintillating fiber optic dosimetry was suitable for measuring depth dose distribution of proton therapy beam and determining its range. Quenching effect of scintillator was dealt with well within our tolerable range by fitting method. One dimensional scintillating fiber array provided more applicable and faster way for applying it to clinical field.
SU‐GG‐T‐350: Beam Quality Correction of Radiophotoluminescence Glass Dosimeter in Accordance with Burlin Cavity Theory
Authors: Hashimoto S , Fujita Y , Kawachi T , Tohyama N , Kojima T , Hayashi N , Kitou S , Kurooka M , Okamoto H , Kumazaki Y , Suzuki Y , Hatano K , Saitoh H
Published: August 2010

Purpose: The radiophotoluminescence (RPL) glass dosimeter is suitable detector for postal dose audit program because it doesn't have fading effect and luminescence can be read repeatedly. However energy dependence cause of high‐Z is significant. Burlin cavity theory can be applied to dosimetry with RPL glass (r=2.4 g cm‐3) because it extended the Bragg‐Gray and Spencer‐Attix cavity theories to cavities of intermediate dimensions. Therefore, by using Burlin cavity theory, the methods to correct beam quality dependence is proposed and it was evaluated for several beam quality and field size in this report. Materials and methods: The energy spectrum of photons and electrons in water were simulated for several photon energy, depth and field size using the EGSnrc MonteCarlo code. The (μen/r)w,glass and (L/r)w,glass were determined with the spectrum. The physical quantity d is a weighting factor which gives the contribution to the total dose from electrons generated by photonin ter a (1 d) is the contribution to the total dose from electrons generated by photon interaction in the RPL glass. The d was determined using original user code of the EGSnrc. In addition, measurement using the RPL glass was performed in the same condition as simulation. Results: Beam quality correction factor by Burlin's, when RPL glass dosimeter was calibrated in 6 MV X‐ray, 10 cm depth in water and 10 cm by 10 cm field, was 0.994 for 4 MV and 1.010 for 10 MV. This correction factors were in good agreement with that of measurement within 0.5%. Conclusion: In this study, the correction methods of beam quality dependence of RPL glass dosimeter were investigated. As a result, good agreement between Burlin's and measurement was obtained, and it was shown that beam quality dependence of RPL glass dosimeter can be corrected by suggested method.
SU‐GG‐T‐356: Investigation on Fading of MAGIC Gel Dosimeter
Authors: Dextraze K , Siddiqi A , Cho S
Published: August 2010

Purpose: To characterize the fading of MAGIC gel dosimeters by simple measurements using a He‐Ne laser and photodiode detector. Method and Materials: A normoxic polymer gel known as MAGIC gel was prepared, using hydroquinone as a free radical scavenger. The MAGIC gel‐containing phantoms were irradiated by 110 kVp x‐rays from six different directions (rotation of 60°) and 4 different dose levels of 10 Gy increments. Gel fading was monitored by measuring the voltage drop (as a measure of optical density) due to the presence of irradiated gel between a He‐Ne laser source and photodiode detector at three different time points (i.e., 24, 48, and 72 hours) post‐irradiation. Laser light was directed along the transverse axis of the cylindrical gel phantoms. The gel phantoms were immersed in a water bath to provide a better optical impedance matching during the laser measurements. Also, they were randomly rotated to several angular positions to check the uniformity in optical density along the radial direction. Two independent trials of reading session were conducted. Results: Measured voltage drop remained inversely linear with delivered dose up to 48 hours, with decreasing linearity at 72 hours and beyond. Detectable non‐uniformity in optical density was noted along the radial direction of the phantom. This non‐uniformity was more pronounced for the phantoms irradiated with larger doses, which contributed more fluctuation in the measured data. Conclusion: Statistically significant gel fading up to 10% was noted between 24 and 48 hour post‐irradiation. However, no significant gel fading was observed between 48 and 72 hours post‐irradiation.
SU‐GG‐T‐361: Feasibility of Making In‐Vivo Peripheral Dose Measurements Using a Portable Dosimeter System ‐ Beta Testing of a Novel Device
Authors: Jani S , Shah N
Published: August 2010

Purpose: Peripheral Dose (PD) to structures such as testes, thyroid, or contra‐lateral breast has important clinical implications regarding the health of a patient. The purpose of this study was to determine utility of a new Portable Dosimeter System for PD measurements to critical structures outside of radiation fields. Method and Materials: Measurements were made using a pair of Portable Dosimeters, Model TN‐RD‐90 (Best Medical Canada Ltd.) At the time of the study, the device was going through the FDA approval process and this study was part of beta testing in a community hospital environment. The dosimeters were calibrated at high sensitivity of 3 mV/cGy as opposed to standard sensitivity of about 1 mV/cGy. Reproducibility and linearity of dose response were tested from a low dose range of 1–50 cGy. Peripheral dose measurements were made using solid water phantoms (100cm SSD; 10cm × 10cm field) on a 6MV (Novalis) and a 6/18 MV linac (Clinac‐2100EX) and compared them to ion chamber values. Results: Calibration of dosimeters showed both to have 3mV/cGy response. These MOSFETs were able to read a dose of 50 cGy or less with over 95% accuracy. Their dose linearity was excellent; R‐sq value was near 1 for both. Accuracy of dose readout decreased with lower dose values. At 1 cGy, the error was about 10% when averaged over 2 dosimeters. At a dose level of 0.25 cGy, the dosimeters' reproducibility and accuracy suffered. However, even with a 50% uncertainty in measured dose, the absolute dose derived was still clinically useful. Conclusion: The new mosfet dosimeters were easy to use, linear in response and reproducible. They will be clinically useful for in‐vivo dosimetry.
SU‐GG‐T‐362: Is Distance‐Dependent Energy Correction Needed for Dosimetric Measurements Surrounding Brachytherapy Sources?
Authors: Song H , Oldham M , Yin F
Published: August 2010

Purpose: The answer depends on both the dosimeter's energy response and energy spectrum at distance (point of measurement) from the source. The latter is object of this study. Method and Materials: The spectra in water were calculated with Monte Carlo code MCNP5. The source point was centered within a spherical water medium, divided into concentric spherical shells of various thickness. The f4 fluence tally of MCNP, with fine energy bins, was used to register photon energy spectrum in thin shells (0.01 cm thick) centered at radii 0.2, 0.5, 1, 2, 3, …9 and 10 cm. One million particles were used for each MCNP run, to achieve good statistical uncertainty. Seven commonly used brachytherapy sources were studied: 60Co (Eavg;=1.25 MeV), 137Cs (.615 MeV), 198Au (.406 MeV), 192Ir (.372 MeV), 131Cs (.0304 MeV), 125I (.0274 MeV), and 103Pd (.0207 MeV). Results: For high energy sources: 60Co, 137Cs, 198Au, and 192Ir, the average energy has all decreased by about 50% at radius 10 cm. For low energy sources: 31Cs, 125I, and 103Pd, the average energy does not decrease with radius. For 103Pd, the average energy increases from 21 keV at radius 0.2 cm to 30 keV at 10 cm. The beam hardening effect with 21Pd is due to its two high energy photons: 39.8 keV and 42.5 keV, whose intensity increases substantially at 10 cm relative to that of the dominant 20.1 and 22.7 keV photons. Due to space limit, other spectral details will not be discussed in this abstract. Conclusions: Within10 cm range, the three low energy sources have demonstrated hardening of energy spectrum. For the four high energy sources, the energy spectrum all softens but the average energy is still higher than 100 keV, which may often justify a distance‐independent energy dependence correction for the whole measurement range.
SU‐GG‐T‐368: Automated Measurement of Water Equivalent Path Length of a Patient Based on a Computed Radiography in Total Body Irradiation
Authors: Yoshidome S , Arimura H , Tachibana M , Shioyama Y , Nomoto S , Fukunaga J , Hirano N , Noguchi Y , Toyofuku F , Honda H , Hirata H
Published: August 2010

Purpose: In total body irradiation (TBI), it is necessary to archive a uniform dose over the midline of a patient's whole body by using a compensator such as a water compensator. However, it would be tedious and time consuming to measure the water equivalent path lengths (WELs) of a patient in each x‐ray trajectory for producing a water compensator. Therefore, the purpose of this study was to develop an automated method for measurement of the WELs of a patient based on computed radiography (CR) in the TBI. Method and Materials: The basic principle of our proposed method was to estimate the WELs of patients based on two relationships; i.e., the first one between the phantom thickness and the absorbed dose; and the second one between the pixel value in a CR image and the absorbed dose in a water‐equivalent phantom. First, the relationship between the CR pixel value and the phantom thickness was obtained by taking CR images with changing the phantom thicknesses from 1 cm to 40 cm at a souse‐to‐target distance of 500 cm. Next, the relationship between the phantom thickness and the absorbed dose was measured by using a chamber in the same geometry as taking CR images. Finally, the relationship between the CR pixel value and the absorbed dose was determined. For validation of the proposed method, the WELs of an anthropomorphic torso phantom in x‐ray trajectories were estimated by the proposed method, and were compared with gold standards calculated from a computed tomography image of the phantom. Results: The mean error in the WELs between the gold standard and the proposed method was 12.0±9.7 mm. Conclusion: The preliminary results suggest that the proposed method would be useful for measuring the WELs of a patient in producing a water compensator.
SU‐GG‐T‐370: Optical Fiber Based Ionizing Radiation Microdetector
Authors: Vulcan T , Marchena‐Vega S , Manciu M
Published: August 2010

Purpose: Develop an optical fiber based isotropic detector for ionizing radiation dose in water‐equivalent materials that could be used for a variety of measurements in situations where isotropy and spatial resolution are of major concern (e.g. for IMRT, IGRT, and brachytherapy QA in complex non‐idealized geometry settings, where currently available diode‐type detectors display relatively large un‐isotropy). Method and Materials: Commercially available plastic scintillators, optical fibers, a QE65000 Ocean Optics spectrometer, and a laptop computer were used to measure the response of “in house” built milimetric detectors for several setups and known calibrated ionizing radiation beams (from a Varian 21EX linear accelerator). Results: A proportional response was observed for the known dose at different depths in a water‐equivalent phantom for 6 MV and 18 MV photon beams and electron beams between 6 MeV and 20 MeV in a relatively wide window of the measured spectra, after background and stray light corrections were applied. Conclusion: A relatively simple, robust, and inexpensive isotropic detector based device can be developed by replacing the spectrometer with a set of inexpensive light detectors with an efficient response at the desired wavelength window.
SU‐GG‐T‐374: Use of a Rad‐Hard Si Diode in Clinical Electron Beam Dosimetry
Authors: Santos T , Neves‐Junior W , Gonçalves J , Haddad C , Harkonen J , Bueno C
Published: August 2010

Purpose:The preliminary results obtained with a MCz silicon diode as online clinical electron beam dosimeter are presented in this work. Method and Materials: The diode was manufactured by Okmetic Oyj (Finland) and processed by the Microelectronics Center of Helsinki University of Technology in the framework of the CERN RD50 Collaboration. The n+‐p‐p+ junction device used (area of 25 mm2) was housed in a PMMA probe designed to operate without bias voltage in the direct current mode. During all measurements, the diode was held in a PMMA plate, placed at Zref and centered in a radiation field of 10 cm × 10 cm, with the SSD kept in 100 cm. The device's dosimetric response was evaluated for the 6, 9, 12, 15, 18 e 21 MeV electron beams from a Siemens KD2 Accelerator. The radiation induced current in the diode, for ach electron beam energy, was registered as a function of the exposure time during 60 s for a fixed 300 MU. To study the instantaneous repeatability of the MCZ diode, 5 consecutive current signals were registered for a same radiation dose around of 300 cGy. Measurements were performed with an average dose rate of 5.0 cGy/s for the electron beam energies of 6,9,12,15,18 and 21 MeV. Results: The results indicated a linear dose response for doses up to 93,28 Gy for electron beams energies of 6, 9, 12, 15, 18 e 21 MeV with very good instantaneous repeatability (CV better than 2,76 %). Conclusion: It worth noting that these results are preliminar and still remains to be investigated this energy dependence, the central axis depth dose response, the long term stability and the radiation hardness of this diode for absorbed doses higher than investigated in this work. All these studies are under way.