bluuebunny/crossref_metadata_2025 huggingface dataset:
Absorption Heat Pump/Refrigeration System Utilizing Ionic Liquid and Hydrofluorocarbon Refrigerants
Authors: Kim Sarah , Kim Yoon Jo , Joshi Yogendra K. , Fedorov Andrei G. , Kohl Paul A.
Published: July 2012

The ionic liquid butylmethylimidazolium hexafluorophosphate (bmim)(PF6) and five different hydrofluorocarbon refrigerants were investigated as the working fluid pairs for a waste-heat driven absorption heat pump system for possible applications in electronics thermal management. A significant amount of the energy consumed in large electronic systems is used for cooling, resulting in low grade waste heat, which can be used to drive an absorption refrigeration system if a suitable working fluids can be identified. The Redlich–Kwong-type equation of state was used to model the thermodynamic conditions and the binary mixture properties at the corresponding states. The effects of desorber and absorber temperatures, waste-heat quality, and system design on the heat pump performance were investigated. Supporting experiments using R134a/(bmim)(PF6) as the working fluid pair were performed. Desorber and absorber outlet temperatures were varied by adjusting the desorber supply power and the coolant temperature at the evaporator inlet, respectively. For an evaporator temperature of 41 °C, which is relevant to electronics cooling applications, the maximum cooling-to-total-energy input was 0.35 with the evaporator cooling capability of 36 W and the desorber outlet temperature in the range of 50 to 110 °C.
Poster — Thur Eve — 18: Characterization of a camera and LED lightbox imaging system for radiochromic film dosimetry
Authors: Alexander K , Percy E , Olding T , Schreiner LJ , Salomons G
Published: July 2012

Radiation therapy treatment modalities continue to develop and have become increasingly complex. With this, dose verification and quality assurance (QA) is of great importance to ensure that a prescribed dose is accurately and precisely delivered to a patient. Radiochromic film dosimetry has been adopted as a convenient option for QA, because it is relatively energy independent, is near tissue equivalent, and has high spatial resolution. Unfortunately, it is not always easy to use. In this study, preliminary work towards developing a novel method of imaging radiochromic film is presented. The setup consists of a camera mounted vertically above a lightbox containing red LEDs, interfaced with computer image acquisition software. Imaging results from this system will be compared with imaging performed using an Epson Expression 10000XL scanner (a device in common clinical use). The lightbox imaging technique with camera readout is much faster relative to a flatbed scanner. The film measurements made using the camera are independent of film orientation, and show reduced artifacts, so that there are fewer corrections required compared to the use of flatbed scanners. Optical scatter also appears to be less of an issue with this design than with the flat bed scanner. While further work needs to be done to optimize the lightbox imaging system, the lightbox system shows great promise for a rapid, simple, and orientation independent setup, improving on existing film scanning systems.
Poster — Thur Eve — 19: Risk assessment of clinical radiation processes using failure modes and effect analysis
Authors: Angers C , Studinski R , La Russa D , Bahm J , Renaud J , Clark BG
Published: July 2012

The aim of this work was to apply failure modes and effect analysis (FMEA) to assess risk in two radiation planning and treatment processes; our on‐call (out‐of‐clinical hours) process and our tomotherapy process. The motivation was provided by analysis of 2506 adverse incidents reported over a 5 year period, the on‐call process for giving rise to a higher than expected number of incidents and our tomotherapy process for the reverse. For the on‐call scenario, three separate processes were analysed: our current process, our current process incorporating a software upgrade eliminating several planning steps and a fully integrated process in which the patient is imaged, planned and treated on a single platform (TomoTherapy Hi Art, Accuray Incorporated, Sunnyvale, CA). After construction of a detailed process map for each case, a multidisciplinary group identified potential failure modes for each process step, the effects of each failure and existing controls. Risk probability numbers were determined from severity, frequency of occurrence and detectability scores assigned to each failure mode according to a standard scale. The results were analysed to identify and prioritise feasible and effective process improvements. For the on‐call process, our current workflow was identified as incurring the highest risk of the three processes analysed, demonstrating quantitatively the value of the software upgrade and providing a clear rationale for the associated expense. In summary, we have found FMEA to be a feasible tool for assessing relative risk in a clinical process. However, operational and resource issues must be considered separately.
Poster — Thur Eve — 20: Serial FDG 4DPET imaging during radiotherapy in advanced lung cancer patients
Authors: Becker N , Clarke K , Pekar V , St‐Hilaire J , Leavens C , Higgins J , Bezjak A , Sun A , Bissonnette J‐P
Published: July 2012

The availability of respiratory synchronized PET (4DPET) imaging has enabled more accurate analysis of metabolic response since motion blur is minimized. We present our preliminary analysis of serial FDG 4DPET images acquired at weeks 0, 2, 4, and 7 during radiotherapy of seven stage II–III NSCLC patients. The tumor and nodal PTV of the week 0 images restrained a 4DPET image thresholding algorithm to automatically contour SUV levels ranging from 20 to 80% of the maximum SUV, creating an intensity volume histogram (IVH) for each week. These contours allowed analysis of PET volumes and standard PET metrics such as SUVmax and SUVmean. We found a trend for decreasing SUVmax and SUVmean over a treatment course in both the tumor and nodal regions. On average, the SUVmax within the tumor decreased by 17±13% (1 SD) after 2 weeks, 30±13% after 4 weeks, and 39±19% after 7 weeks of radiotherapy. Decreasing volume trends were also observed in the 20 to 80% max SUV autocontours, ranging from 26±29% to 50±40% respectively, over 7 weeks of treatment. Only one patient demonstrated an increase in FDG uptake within the tumor volume between week 0 and week 2 of treatment, and was also the only patient to recur locally at 3 months following treatment. Changes in tumor metabolism over the course of advanced NSCLC radiotherapy are quantifiable with serial FDG 4DPET imaging. Preliminary analysis suggests that variations in these trends could be useful in identifying non‐responding patients that may require an alternative radiotherapeutic approach.
Poster — Thur Eve — 24: Clinical application of the new dosimetry formalism for composite nonstandard beams
Authors: Chung E , Conneely E , Ruo R , Foley M , Seuntjens J
Published: July 2012

The IAEA‐AAPM new dosimetry formalism [Med. Phys. 35, 5179 (2008)] was applied to clinical IMRT quality assurance (QA). Twenty different IMRT QA fields were created on the CT images of a 30×30×17 cm3 Solid Water™ phantom. Two Farmer‐type chambers, Exradin A12 and NE2571, and a smaller Exradin A1SL ionization chamber were cross‐calibrated against a reference detector, the PTW micro liquid ion chamber (microLion), in the lowest dose gradient region in each IMRT QA field delivery. Based on the new dosimetry formalism, the clinical correction factor was measured in a fully‐rotated delivery and a delivery at a single gantry angle, a collapsed delivery. For the calibrated Exradin A12, the measured dose with the clinical correction factor was compared with a calculated dose using Monte Carlo (MC) methods. The clinical correction factor deviated from unity by up to 2.4% and 3.7% in the fully‐rotated and collapsed deliveries, respectively, depending on the dose distribution in the chamber collecting volume. For the Exradin A1SL, the correction factor was generally closer to unity due to the reduced dose gradient on the smaller collecting volume. In the fully‐rotated delivery, the measured dose with the clinical correction factor is different from the MC‐calculated dose to within 4%; while the discrepancy was greater, up to 8%, in the collapsed delivery due to the much heterogeneous dose distribution in the chamber collecting volume. This work proves that the suggested dosimetry technique is effective to improve the dosimetric consistency of clinical IMRT QA.
Poster — Thur Eve — 25: In vivo dosimetric verification of intensity‐modulated radiation therapy
Authors: Chytyk‐Praznik K , Van Uytven E , Van Beek T , McCurdy BMC
Published: July 2012

Dosimetric verification of patient treatment plans has become increasingly important due to the widespread use of complicated delivery techniques. IMRT and VMAT treatments are typically verified prior to start of the patient's course of treatment, using a point dose and/or a film measurement. Pre‐treatment verification will not detect patient or machine‐related errors; therefore, in vivo dosimetric verification is the only way to determine if the patient's treatment was delivered correctly. Portal images were acquired throughout the course of five prostate and six head‐and‐neck patient IMRT treatments. The corresponding predicted images were calculated using a previously developed portal dose image prediction algorithm, which combines a versatile fluence model with a patient scatter and EPID dose prediction model. The prostate patient image agreement was found to vary day‐to‐day due to rectal gas pockets and the effect of adjustable support rails on the patient couch. The head‐and‐neck patient images were observed to be more consistent daily, but an increased measured dose was evident at the periphery of the patient, likely due to patient weight loss. The majority of the fields agreed within 3% and 3 mm for greater than 90% of the pixels, as established by the χ‐comparison. This work demonstrates the changes in patient anatomy that are detectable with the portal dose image prediction model. Prior to clinical implementation, the effect of the couch must be incorporated into the model, the image acquisition must be automatically scheduled and routine EPID QA must be undertaken to ensure the collection of high‐quality EPID images.
Poster — Thur Eve — 27: Scattering foil redesign for modulated electron radiotherapy
Authors: Connell T , Seuntjens J
Published: July 2012

This work serves to build on existing work that discussed the advantages of removing the scattering foil from the beamline for modulated electron radiotherapy (MERT) much like flattening filter‐free beams in photon IMRT. Due to concerns about the ability of the accelerators transmission ionization chamber to function normally with narrow, minimally‐scattered beams as well as a limited maximum field size, this study focused on the design of a new custom scattering foil that was optimized for MERT applications. Different foil parameters such as material, thickness and shape were investigated to produce a minimally scattered beam, as opposed to a flat beam in the case of the clinical foil, while preserving the dosimetric benefits of a reduced thickness foil such as dramatically higher dose rate and reduced photon contamination in the bremsstrahlung tail. Using a Monte Carlo model that was verified against measured data, fluence profiles at the level of the transmission ionization chamber were produced and analyzed for all foil configurations, as well as PDDs and profiles in a water phantom. It was found that a simple foil of slab geometry made of low to medium Z material with the thickness determined by the maximum desirable field size and chosen electron energy produced a sufficiently scattered beam that maintained the dosimetric advantages of a scattering‐foil‐free beamline. These new foils, when applied to MERT, have the advantage of reducing treatment time due to higher dose rates and reducing dose to healthy tissue due to reduced dose in the bremsstrahlung tail.
Poster — Thur Eve — 28: Optimization of a prostate cancer IGRT protocol
Authors: Dona O , Diamond K , Ostapiak O , Wierzbicki M
Published: July 2012

Our image‐guided radiation therapy (IGRT) protocol for post‐prostatectomy patients involves acquiring a kV cone beam computed tomography (CBCT) dataset at each fraction and shifting the treatment couch to align the surgical clips. This IGRT strategy requires significant resources, and delivers non‐negligible dose to normal tissues. The objective of this work is to evaluate this IGRT protocol against two alternative strategies in terms of the dose‐volume statistics for target and organ at risk regions. Our method involves deforming the planning CT to the CBCT dataset acquired at each fraction, computing dose on the deformed dataset, and inversely transforming the dose back onto the original planning CT dataset. The treatments of six patients were evaluated assuming three IGRT scenarios: no IGRT, daily IGRT using the clinically employed couch shifts, and alternating day IGRT. The doses delivered to the clinical target volumes are within approximately 3.2, 1.3, and 2.1% of the plan for the non‐IGRT, daily, and alternating day IGRT protocols, respectively. Doses to relevant portions of the organs at risk deviate from the plan by up to 10.5, 13.1 and 10.7% for non‐IGRT, daily IGRT, and alternating day IGRT protocols, respectively. Some cases do not differ significantly between IGRT and non‐IGRT protocols in terms of cumulative DVHs, highlighting the difficult task of correcting prostate bed deformations via the treatment couch translations. In general, the alternating day IGRT protocol was found to result in a clinically insignificant deviation in delivered dose while providing a significant reduction in resource use and patient imaging dose.
Poster — Thur Eve — 29: Detecting changes in IMRT QA using statistical process control
Authors: Drever L , Salomons G
Published: July 2012

Statistical process control (SPC) methods were used to analyze 239 measurement based individual IMRT QA events. The selected IMRT QA events were all head and neck (H&N) cases with 70Gy in 35 fractions, and all prostate cases with 76Gy in 38 fractions planned between March 2009 and 2012. The results were used to determine if the tolerance limits currently being used for IMRT QA were able to indicate if the process was under control. The SPC calculations were repeated for IMRT QA of the same type of cases that were planned after the treatment planning system was upgraded from Eclipse version 8.1.18 to version 10.0.39. The initial tolerance limits were found to be acceptable for two of the three metrics tested prior to the upgrade. After the upgrade to the treatment planning system the SPC analysis found that the a priori limits were no longer capable of indicating control for 2 of the 3 metrics analyzed. The changes in the IMRT QA results were clearly identified using SPC, indicating that it is a useful tool for finding changes in the IMRT QA process. Routine application of SPC to IMRT QA results would help to distinguish unintentional trends and changes from the random variation in the IMRT QA results for individual plans.
Poster — Thur Eve — 31: RapidArc total body photon irradiation: A feasibility study
Authors: Evans MDC , Ruo R , Seuntjens J , Freeman CR , Parker W
Published: July 2012

Total body photon irradiation (TBI) may be delivered with a number of standard techniques, typically using extended SSD geometries to obtain large field sizes. Since 1982 we have treated over 620 patients (adult and pediatric) mostly in the floor‐located prone/supine treatment position with AP/PA beams using a column mounted 4 MV linac, and more recently with a fixed field, extended SSD, Cobalt teletherapy unit. This treatment position has many advantages for TBI including ease of delivery (especially for pediatric or compromised patients), improved dose uniformity, simplicity for partial or complete organ shielding, and imaging capabilities to name a few. In an effort to transfer this technique to a conventional isocentric linac, we have undertaken a feasibility study for RapidArc based extended SSD total body irradiation. Proof of principle was first explored using the DBD (Dynamic Beam Delivery) toolbox to configure a 6 MV beam with an 80 degree arc, centered on the 12 o'clock gantry angle with a sliding‐window beam. This was followed by the development of an ECLIPSE generated 80 degree RapidArc plan. Initial measurements were conducted with a Varian 21EX using the 6 MV DBD beam to explore characteristics such as PDD, surface dose, off‐axis ratios, output, dose per MU, and linearity. Subsequently ECLIPSE generated RapidArc TBI plans using similar partial arcs were also evaluated. Encouraged by our results, we believe this technique shows potential for making floor‐located AP/PA total body photon irradiation possible for any standard RapidArc enabled isocentric linac.
Poster — Thur Eve — 34: Evaluation of 4DCT on the GE lightspeed RT16 using a respiratory motion phantom
Authors: Garcia L , Joshi C , Kerr A
Published: July 2012

Purpose: This study encompasses several quality assurance tests performed during the commissioning of the 4DCT technique on the GE Lightspeed RT16 CT scanner for SBRT at the Cancer Centre of Southeastern Ontario. The main purpose is to assess geometric position and volumetric delineation accuracy. A limited assessment of the image quality and dose was performed. Methods: The Quasar Respiratory Motion with a modified cylindrical moving insert was used. Clinically relevant breathing motion patterns analyzed were: sinusoidal with amplitudes of 5 and 15 mm, and periods of 3 s and 6 s; and a typical respiratory breathing motion of amplitude of 10 mm and period of 4 s. Results: Couch position errors were ≤ 1mm for maximum inspiration (Ph 0%) and expiration (Ph 50%) phases. errors were greater for mid‐phases, the largest being 8.1 mm (Ph 20%) for the typical respiratory pattern. MIP volume deviations ranged from −0.3 to −3.2 cm3; the greater deviations corresponding to larger amplitudes and shorter periods, where image distortion is also more severe. SUP and INF position error of MIP on coronal views for the lung window and level used in our centre ranged from −0.07 to 1.4 mm and from −0.04 to 1 mm on the SUP and INF direction respectively. The dose from a 4DCT acquisition was 2.8 times higher than in a free breading scan, while the noise was comparable. Conclusions: Although higher doses are obtained, 4DCT is a sufficiently accurate approach that could be used safely to account for breathing motion.
Poster — Thur Eve — 35: Characterization of performance of two deformable registration software
Authors: Gauthier J‐F , Varfalvy N , Cyr MF , Archambault L
Published: July 2012

Purpose: To evaluate the performance of two deformable registration softwares (a commercial and an open source software) using cone‐beam computed tomography (CBCT) images. Methods: We used a set of 34 lung patients with generally large tumors each having between 1 and 20 CBCT scans. A radiation oncologist resident contoured GTVs on each CBCTs using planning CT contours as reference. Deformable registrations were performed on CT scans to adapt it to the first CBCT of each patient independently with both software. Then each CBCT was registered to the next CBCT. Contour structures have been deformed in the process for the commercial software and for the open source software contours have been drawn manually on deformed images. Results: Mean remaining volume (±SD) for manual GTV contours was 59 ± 32 %. GTVs obtained with the open source software were closer to the manual GTV in size than the commercial software. Mean relative errors on volume were 45 ± 60 % for the commercial system (33 patients) and 9 ± 2 % for the open source software (6 patients). Relative errors for the commercial software increased exponentially with the volume reduction but were constant over all CBCT for the open source software. Mean Jaccard and Dice's index were 0.57 and 0.71 for the commercial software (24 patients) and 0.80 and 0.88 for the open source software (6 patients). Conclusion: Open source software shown tendency to give better results than commercial software but was slower than the commercial software.
Poster — Thur Eve — 36: Out‐of‐Field dose in craniospinal irradiation
Authors: Jalbout W , Howell R , Newhauser W , Geara F , Khater N , Taddei P
Published: July 2012

The risk of radiotherapy induced secondary cancer depends on the integral dose delivered to the patient where the dose delivered within the radiation field is accounted for, as well as dose to out‐of‐field organs from scattered and leakage radiation. While commercial treatment planning systems allow accurate determination of in‐field dose, they are generally not capable of accurate out‐of‐field dose prediction. Secondary cancer risk is especially an issue in craniospinal treatments where involved patients are often children or young adults. In this work we therefore propose a mathematical model that accurately predicts out‐of‐field dose for patients treated by craniospinal irradiation at the American University of Beirut Medical Center. An anthropomorphic phantom was imaged, planned and treated, with thermoluminescent dosimeters inserted in the phantom at in‐field and out‐of‐field locations. The measurements showed that our treatment planning system calculated accurately (within 2%) dose inside the field, but did not perform well at points just outside the field edge and consistently underestimated the dose at points further away from the field edge. From the out‐of‐field measured data, a model was developed that predicts out‐of‐field dose at a point in the patient based on the distance of that point to the treatment field edge. The developed model is of the double‐gaussian type; it contains parameters that can be tuned to make it applicable in other centers where linac geometry and treatment techniques may differ.
Poster — Thur Eve — 38: Review of couch parameters using an FMEA
Authors: Larouche R , Doucet R , Rémy E , Filion A , Poirier L
Published: July 2012

To improve patient safety during positioning, we undertook a systematic review of the processes used by our center to obtain couch positions. We used a Failure Mode and Effects Analysis (FMEA) framework and fifteen different possible failures were identified and rated. The three major failures were 1) Loss of planned couch position and bias from the previous day's couch position, 2) DICOM origin or isocenter is different between two plans (imaging or treatment), and 3) Patient shift in opposite direction than intended. The main effect of these failures was to cause an override of couch parameters. Based on these results, we modified our processes, introduced new QA and software checks and developed new tolerance tables so as to improve system robustness and increase our success rate at catching failures before they can affect the patient. It has been a year since we made these modifications. Based on our results, we have reduced the number of overrides at our center from a maximum of 20.5% to a maximum of 6.3%, with an average at 4% of daily treatments. Our results suggest that FMEA is an effective tool in improving treatment quality that could be used in other centers.
Poster — Thur Eve — 39: SBRT imaging analysis — patient results and QA of imaging systems
Authors: Mason D , Neath C
Published: July 2012

Our centre began offering stereotactic body radiation therapy (SBRT) treatments for peripheral lung lesions in 2011. As a high‐precision technique, SBRT requires precise positioning of the target, and precise quality assurance (QA) of the imaging systems; these may be dependent on local equipment and procedures. We aimed to maintain target position within 3 mm throughout each treatment, and imaging and mechanical systems to at least 2 mm accuracy. A retrospective analysis was done of patient cone‐beam (CB) data, and of our imaging system QA, to assess our spatial objectives and look for opportunities for improvement. The data indicated that, using our immobilization and imaging procedures, target position was maintained within 3 mm 96% of the time, and 75% within 2 mm, similar to results from other centres. Imaging system QA using the standard ball‐bearing test showed system accuracy was maintained well within 1 mm. These results were compared with a simpler daily QA procedure using a Pentaguide phantom. The mean and standard deviation of the radial difference in the kV‐MV isocenter coincidence for the two techniques was 0.62mm +/− 0.23mm. With appropriate choice of tolerance and action level, the morning QA was sufficient for identifying outliers requiring further investigation. This analysis gives us confidence in understanding the performance of our SBRT lung treatments, and gives baselines for analyzing changes to patient immobilization or imaging procedures.
Poster — Thur Eve — 43: Is faster always better? An evaluation of frame rate effects on continuous acquisition mode EPID imaging for dose verification
Authors: Peca S , Granville D , Brown D
Published: July 2012

INTRODUCTION: As radiotherapy moves towards intensity modulated arc therapy (arc‐IMRT), there is a need for electronic portal imaging (EPID) to move towards continuous acquisition (cine) mode for dosimetric verification purposes. However, as the EPID resolution and frame rate (fps) increase, so does the computational burden of image processing. We investigated the reliability of cine mode EPID imaging in IMRT as a function of frame rate. METHODS: We acquired EPID images continuously while running an IMRT plan (6MV photons, 150MU, dose rate = 300MU/min) with frame rates ranging from 1–12 fps, as well as a single integrated mode image. Each cine dataset was then averaged to form a single image, which was compared with the integrated mode image by means of a pixel‐by‐pixel absolute value subtraction. RESULTS: Although a greater frame rate gave better agreement with the integrated mode image in all cases, the relative benefit diminished with increasing frame rate. In particular, for the IMRT plan delivered, there was little benefit of imaging faster than 6 fps, and virtually no benefit in increasing from 9 to 12 fps. In contrast, 12 fps produces twice the number of images as 6 fps which significantly increases the image processing and data storage burdens. CONCLUSION: Increasing frame rate in cine mode EPID imaging may be beneficial in some cases, but there is likely a threshold level above which no relevant additional information is obtained. Further research to determine the ideal frame rate for any particular IMRT or arc‐IMRT plan is warranted.
Poster — Thur Eve — 45: Commissioning of the Varian ECLIPSE eMC algorithm for clinical electron treatment planning
Authors: Serban M , Ruo R , Sarfehnia A , Parker W , Evans M
Published: July 2012

Fast electron Monte Carlo systems have been developed commercially, and implemented for clinical practice in radiation therapy clinics. In this work the Varian eMC (electron Monte Carlo) algorithm was commissioned for clinical electron beams of energies between 6 MeV and 20 MeV. Beam outputs, PDDs and profiles were measured for 29 regular and irregular cutouts using the IC‐10 (Wellhöfer) ionization chamber. Detailed percentage depth dose comparisons showed that the agreement between measurement and eMC for different characteristic points on the PDD are generally less than 1 mm and always less than 2 mm, with the eMC calculated values being lower than the measured values. Of the 145 measured output factors, 19 cases fail a ±2% agreement but only 8 cases fail a ±3% agreement between calculation and measurement. Comparison of central axis dose distributions for two electron energies (9, and 20 MeV) for a 10 × 10 cm2 field, centrally shielded with Pb of width 0 cm (open), 1, 2 and 3 cm, shows agreement to within 3% except near the surface. Comparison of central axis dose distributions for 9 MeV in heterogeneous phantoms including bone and lung inserts showed agreement of 1 mm and 3 mm respectively with measured TLD data. The overall agreement between measurement and eMC calculation has enabled us to begin implementing this calculation model for clinical use.
Poster — Thur Eve — 46: The upcoming international code of practice for small static photon field dosimetry
Authors: Palmans H , Alfonso R , Andreo P , Capote R , Huq MS , Izewska J , Johansson J , Kilby W , Mackie TR , Meghzifene A , Rosser K , Seuntjens J , Ullrich W
Published: July 2012

The increased use of small photon fields in stereotactic and intensity‐modulated radiotherapy has raised the need for standardizing the dosimetry of such fields using procedures consistent with those for conventional radiotherapy. An international working group, established by the IAEA in collaboration with AAPM and IPEM, is finalising a Code of Practice for the dosimetry of small static photon fields. Procedures for reference dosimetry in nonstandard machine specific reference (msr) fields are provided following the formalism of Alfonso et al. (Med. Phys. 35: 5179; 2008). Reference dosimetry using ionization chambers in machines that cannot establish a conventional 10 cm × 10 cm reference field is based on either a direct calibration in the msr field traceable to primary standards, a calibration in a reference field and a generic correction factor or the product of a correction factor for a virtual reference field and a correction factor for the difference between the msr and virtual fields. For the latter method, procedures are provided for determining the beam quality in non‐reference conditions. For the measurement of field output factors in small fields, procedures for connecting large field measurements using ionization chambers to small field measurements using high‐resolution detectors such as diodes, diamond, liquid ion chambers, organic scintillators and radiochromic film are given. The Code of Practice also presents consensus data on correction factors for use in conjunction with measured, detector‐specific output factors. Further research to determine missing data according to the proposed framework will be strongly encouraged by publication of this document.
Poster — Thur Eve — 47: Evaluation of the ArcCHECK device for commissioning and patient‐specific QA
Authors: Shahine B , Badragan I , Ramaseshan R
Published: July 2012

The most promising method of accurately verifying VMAT treatments is by direct dose measurement over the three dimensions of irradiated volume. ArcCHECK device (Sun Nuclear, Melbourne, FL) have the potential to detect delivery errors on the treatment machine due to mechanical problems resulting from gantry and MLC motion. The estimation of the dosimetric leaf gap (DLG) parameter for Varian MLC (Varian Medical Systems, Palo Alto, CA) was attempted using ArcCHECK. Finding the optimal DLG value for use in TPS requires a measuring device like ArcCHECK to be employed especially in highly intensity modulated fields. In addition, ArcCHECK was used to assess the effect of positional error of MLC leaf in a given VMAT plan. Patient‐specific QA tests were performed using the ArcCHECK device. QA results of patient plans that failed considering portal dosimetry technique were reassessed with ArcCHECK measurements for IMRT plans. The preliminary test results and performance of the ArcCHECK device were very encouraging. VMAT plans for head and neck cases were generated and their delivery was evaluated using ArcCHECK. Results have shown a success rate greater than 90% in the quality assurance of individual plans. Optimal DLG value was detected using ArcCHECK. Also, the device showed enough sensitivity to identify failed QA plans. Moreover, MLC central leaf pair position offset in a VMAT plan of the order of 1mm was fairly distinguished by ArcCHECK measurements.
Poster — Thur Eve — 49: Application of plastic scintillating detectors to orthovoltage x‐ray measurements
Authors: Nasonkin S , Syme A
Published: July 2012

Plastic scintillating detectors (PSDs) have found numerous dosimetric applications in radiotherapy due to their approximate water equivalence at high energies and their small physical size. At low photon energies, however, the ratio of mass attenuation coefficients (PSD : water) deviates from unity, which potentially limits their utility in this range. In this work, measurements of orthovoltage cutout factors were made with PSDs and and ion chamber. Results were compared to Monte Carlo simulations of the same geometry. Results indicated that the PSDs performed better than the IC in almost all field sizes. Further work is required to more thoroughly characterize the Monte Carlo model of the x‐ray unit and to investigate any discrepancies that might have resulted from slight differences in the effective point of measurement of the two detector systems.
Poster — Thur Eve — 52: Clinical use of nanoDots: In‐vivo dosimetry and treatment validation for stereotactic targets with VMAT techniques
Authors: Wierzbicki W , Nicol S , Furstoss C , Brunet‐Benkhoucha M , Leduc V
Published: July 2012

A newly acquired nanoDot In‐Light system was compared with TLD‐100 dosimeters to confirm the treatment dose in the multiple cases: an electron eye treatment, H&N IMRT and VMAT validation for small targets. Eye tumour treatment with 9 MeV electrons A dose of 1.8 Gy per fraction was prescribed to the 85% isodose. The average dose measured by three TLDs and three Dots was 1.90 and 1.97 Gy. Both detectors overestimated dose, by 2.9% and 6.7% respectively. H&N IMRT treatment of skin cancer with 6 MV photons Dose per fraction is 2.5 Gy. The average doses measured by two TLDs and two Dots were 2.48 and 2.56 Gy, which represent errors of −0.8% and 2.2%, respectively. VMAT validation for small targets using an Agarose phantom, dose 15 Gy A single‐tumour brain treatment was delivered using two coplanar arcs to an Agarise phantom containing a large plastic insert holding 3 nanoDots and 4 TLDs. The difference between the average Pinnacle dose and the average dose of the corresponding detectors was −0.6% for Dots and −1.7% for TLDs. A two‐tumour brain treatment was delivered using three non‐coplanar arcs. Small and large plastic inserts separated by 5 cm were used to validate the dose. The difference between the average Pinnacle dose and the average dose of the corresponding detectors was the following; small phantom 0.7% for Dots and 0.3% for TLDs, large phantom‐1.9% for Dots and −0.6% for TLDs. In conclusion, nanoDot detectors are suitable for in‐vivo dosimetry with photon and electron beams.
Poster — Thur Eve — 53: Analysis of the distribution of dose delivery during respiratory‐gated step‐and‐shoot IMRT for lung cancer radiotherapy
Authors: Xhaferllari I , El‐Sherif O , Gaede S
Published: July 2012

Respiratory motion is a large source of dosimetric error when treating lung cancer with Intensity Modulated Radiation Therapy (IMRT). The asynchronicity of the tumour motion and the multileaf collimator (MLC) used to modulate the radiation beam intensity, leads to the interplay effect. One method to account for this effect is respiratory gating. Treatment planning optimization for gated IMRT is performed on a subset average 4D‐CT which includes the phases surrounding end exhalation. However, this assumes that the beam delivery will be evenly distributed amongst those phases. This study investigates the distribution of beam delivery during gated step‐and‐shoot IMRT (SS‐IMRT) for both early and late stage non‐small cell lung cancer (NSCLC). Four Stage I NSCLC patients, prescribed a dose of 54 Gy in 3 fractions, and five Stage III NSCLC patients, prescribed a dose of 60 Gy in 30 fractions, were retrospectively planned with high and low modulation beams‐IMRT, and delivered using the QUASAR™ Programmable Respiratory Motion Platform with 15 mm and 20 mm peak‐to‐peak sinusoidal motion and real patient breathing motion. The percent monitor units delivered at each phase were compared. For Stage I patients, the monitor units delivered were evenly distributed over the gating window due to a high number of monitor units delivered per control point. For Stage III patients, as the complexity of SS‐IMRT increases, there were more monitor units delivered in the initial gating phase. This dose discrepancy could potentially lead to geographic miss of the tumour and should be taken into account during treatment planning.
Poster — Thur Eve — 54: A software solution for ongoing DVH quality assurance in radiation therapy
Authors: Annis S‐L , Zeng G , Wu X , Macpherson M
Published: July 2012

Purpose: A program has been developed in MATLAB for use in quality assurance of treatment planning of radiation therapy. It analyzes patient DVH files and compiles dose volume data for review, trending, comparison and analysis. Material and methods: Patient DVH files are exported from the Eclipse treatment planning system and saved according to treatment sites and date. Currently analysis is available for 4 treatment sites; Prostate, Prostate Bed, Lung, and Upper GI, with two functions for data report and analysis: patient‐specific and organ‐specific. The patient‐specific function loads one patient DVH file and reports the user‐specified dose volume data of organs and targets. These data can be compiled to an external file for a third party analysis. The organ‐specific function extracts a requested dose volume of an organ from the DVH files of a patient group and reports the statistics over this population. A graphical user interface is utilized to select clinical sites, function and structures, and input user's requests. Results: We have implemented this program in planning quality assurance at our center. The program has tracked the dosimetric improvement in GU sites after VMAT was implemented clinically. It has generated dose volume statistics for different groups of patients associated with technique or time range. Conclusion: This program allows reporting and statistical analysis of DVH files. It is an efficient tool for the planning quality control in radiation therapy.
Poster — Thur Eve — 55: Monte Carlo simulations of variations in planned dose distributions in a prostate patient population
Authors: Balderson MJ , Brown DW , Quirk S , Ghasroddashti E , Kirkby C
Published: July 2012

Clinical outcome studies with clear and objective endpoints are necessary to make informed radiotherapy treatment decisions. Commonly, clinical outcomes are established after lengthy and costly clinical trials are performed and the data are analyzed and published. One the challenges with obtaining meaningful data from clinical trials is that by the time the information gets to the medical profession the results may be less clinically relevant than when the trial began, An alternative approach is to estimate clinical outcomes through patient population modeling. We are developing a mathematical tool that uses Monte Carlo techniques to simulate variations in planned and delivered dose distributions of prostate patients receiving radiotherapy. Ultimately, our simulation will calculate a distribution of Tumor Control Probabilities (TCPs) for a population of patients treated under a given protocol. Such distributions can serve as a metric for comparing different treatment modalities, planning and setup approaches, and machine parameter settings or tolerances with respect to outcomes on broad patient populations. It may also help researchers understand differences one might expect to find before actually doing the clinical trial. As a first step and for the focus of this abstract we wanted to see if we could answer the question: “Can a population of dose distributions of prostate patients be accurately modeled by a set of randomly generated Gaussian functions?” Our results have demonstrated that using a set of randomly generated Gaussian functions can simulate a distribution of prostate patients.
Poster — Thur Eve — 56: Verification of buildup region dose calculation of a treatment planning system
Authors: Bassey B , Sidhu N
Published: July 2012

Buildup region dose calculation of Pinnacle3 (version 9.0), a treatment planning system (TPS) commissioned using cylindrical ionization chamber measurements, have been verified experimentally. Dose values measured using Attix parallel plate ionization chamber were compared with those calculated by Pinnacle3 for a variety of clinical setups involving: 6 MV and 15 MV photon beams, open fields, enhanced dynamic wedges, physical wedges, block tray, 85, 100 and 120 cm source‐to‐surface distances, and square field sizes ranging from 3 × 3 to 30 × 30 cm2. The dose difference (DD) and distance‐to‐agreement (DTA) techniques were used to evaluate the discrepancy between measured and calculated dose values. Based on the criteria of DD less than 2% or DTA less than 2mm, 93.7% of 1,710 dose points for the 6 MV and 96.1% of 2,244 dose points for 15 MV passed. Dose points that failed were mostly for open fields, block tray fields, and physical wedges (15 and 30 degrees) fields; this is attributed to high electron contamination (EC) associated with these fields. The levels of discrepancies between measured and calculated dose values were greatly reduced after remodeling the EC in Pinnacle3 using Attix chamber measurements, an indication that the EC equation in Pinnacle3 may be adequate for modeling EC in the dose buildup region, and the commissioning of a TPS using cylindrical ionization chamber measurements may not provide accurate buildup region dose calculation. Attix chamber measurements were validated using GafChromic EBT2 film; the disagreement was less than 3% for 89.9% of dose values compared.
Poster — Thur Eve — 57: Craniospinal irradiation with jagged‐junction IMRT approach without beam edge matching for field junctions
Authors: Cao F , Ramaseshan R , Corns R , Harrop S , Nuraney N , Steiner P , Aldridge S , Liu M , Carolan H , Agranovich A , Karva A
Published: July 2012

Purpose: Craniospinal irradiation were traditionally treated the central nervous system using two or three adjacent field sets. A intensity‐modulated radiotherapy (IMRT) plan (Jagged‐Junction IMRT) which overcomes problems associated with field junctions and beam edge matching, improves planning and treatment setup efficiencies with homogenous target dose distribution was developed. Methods and Materials: Jagged‐Junction IMRT was retrospectively planned on three patients with prescription of 36 Gy in 20 fractions and compared to conventional treatment plans. Planning target volume (PTV) included the whole brain and spinal canal to the S3 vertebral level. The plan employed three field sets, each with a unique isocentre. One field set with seven fields treated the cranium. Two field sets treated the spine, each set using three fields. Fields from adjacent sets were overlapped and the optimization process smoothly integrated the dose inside the overlapped junction. Results: For the Jagged‐Junction IMRT plans vs conventional technique, average homogeneity index equaled 0.08±0.01 vs 0.12±0.02, and conformity number equaled 0.79±0.01 vs 0.47±0.12. The 95% isodose surface covered (99.5±0.3)% of the PTV vs (98.1±2.0)%. Both Jagged‐Junction IMRT plans and the conventional plans had good sparing of the organs at risk. Conclusions: Jagged‐Junction IMRT planning provided good dose homogeneity and conformity to the target while maintaining a low dose to the organs at risk. Jagged‐Junction IMRT optimization smoothly distributed dose in the junction between field sets. Since there was no beam matching, this treatment technique is less likely to produce hot or cold spots at the junction in contrast to conventional techniques.
Poster — Thur Eve — 58: The clinical significance of couch top modeling in VMAT and IMRT treatment planning
Authors: Chan GH , Chin L
Published: July 2012

In recent years, carbon fibre couch tops have become popular in radiation therapy with marketed attributes such as high tensile strength, light weight, and relative radiotranslucence. We have performed a detailed analysis of the iBEAM evo couch top using two models created in the Pinnacle v9.0 treatment planning system. The first model is a single ROI, and its thickness and shape was determined based on attenuation factor measurements in cylindrical phantoms. The second model is a thin shell made of two ROIs with exact outer dimensions as the real couch top. The couch top attenuation was found to range from 2% to 6.5% for a 6 MV beam energy. The two models were found to match the attenuation factor measurements to within 4.2% and 1.7%, respectively. The clinical impact of the couch top models was examined in 4 VMAT and 4 IMRT prostate plans by comparing mean and maximum point doses, DVHs, and measurements (VMAT plans only) using Gamma analysis. A very small, but clinically insignificant difference was observed between the two couch top models for both VMAT and IMRT plans. The lack of a couch top model in treatment planning was also examined and found to result in ∼ 1% average underdose to the PTV. This study suggests that the iBEAM evo couch top is relatively radiotranslucent for typical VMAT and IMRT delivery as long as the number of control points with extremely oblique beam angles is relatively small.
Poster — Thur Eve — 59: Dosimetric evaluation on the variation of PTV coverage due to patient size reduction using the prostate dose‐volume factor in prostate radiotherapy
Authors: Chow J , Jiang R , Markel D
Published: July 2012

We proposed to use the prostate dose‐volume factor (PDVF), derived from the dose‐volume dataset of planning target volume (PTV) in prostate radiotherapy to evaluate treatment plans of prostate volumetric modulated arc therapy (VMAT) and intensity modulated radiotherapy (IMRT). To demonstrate plan evaluation using PDVF, VMAT and 7‐beam IMRT plans were created in three patients with prostate volumes equal to 32, 48.4 and 86.5 cm3. Dose variation of PTV was made by reducing the body contour of the patients with reduced depth equal to 0.5 – 2 cm, mimicking a patient size reduction in the treatment. The Gaussian error function was used to model the cumulative dose‐volume histogram of the PTV, and PDVF was calculated as per the parameters of the error function. PDVF = 1 reflects an ideal PTV coverage (i.e. 100% prescribed dose in 100% target volume). We found that for PDVF ranged 0.98 – 1 in prostate VMAT and IMRT without patient size change, reduced depth led to PDVF decreasing 0.03 ± 4.7 × 10−4 (VMAT) and 0.04 ± 9.7 × 10−3 (IMRT) per cm for the patients. The variation of PTV coverage on the prostate volume due to the reduced depth was less significant in VMAT plans than IMRT. It is concluded that PDVF was successfully used to evaluate the variation of PTV coverage due to the weight loss of patient in prostate VMAT and IMRT. Degradation of PTV coverage in prostate VMAT regarding patient size reduction is less significant than that in IMRT.