bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐198: Evaluation of Dosimetric Characteristics of MOSFET Dosimeter for the Quality Assurance of Photon and Electron Beams
Authors: Manigandan D , Bharanidharan G , Ganesan S , Aruna P , Sharma S , Subramani V , Rath G
Published: November 2011

Purpose: To study the basic dosimetric characteristics of MOSFET dosimeter for its suitability on constructing the quality assurance phantom. Methods: For all the measurements, the high sensitivity MOSFET with standard bias settings (3mV/cGy) was used. Solid water phantoms were used for both photon and electron beams. Tests were performed for 60Co beams, 6 and 15MV photon beams and 9MeV electrons. The dose‐linearity of MOSFET was studied up to 500 cGy with small increment at lowerdoses. Results were compared with the farmer chamber for photons and PP chamber for electrons. Reproducibility of the MOSFET was studied for the absorbed dose of 100cGy. Beam symmetry was measured at 5‐cm off‐axis position for 15×15cm2 field and comparisons were made with the farmer chamber and EDR‐2 film for photons and PP chamber and Kodak Xomat‐V for electrons. Also, the beam quality index was derived by measuring the dose at 10 and 20cm depth for photon beams. Measurements were done for five different days and compared with ion chamber measurements. Results: The correlation co‐efficient (R2) for MOSFET and ion chamber linearity curve is 0.9999, 0.9999, 0.9998 and 0.9999 for 6MV, 15MV and 60Co beams and 9MeV electrons. High sensitivity MOSFET showed good linearity at lower doses even with standard bias settings. Reproducibility of the MOSFET is 1.680%, 1.815%, 1.7194% and 1.754% for 6MV, 15MV and 60Co beams and 9MeV electrons. Beam Symmetry measured with MOSFET showed maximum variation up to 4.2% where as ion chamber and EDR‐2 was within 2.7% and 3.1%. MOSFET over‐responded consistently at the off‐axis position. Quality index measured with MOSFET was within 0.701% and 1.355% for 6 and 15MV photons, whereas the ion chamber was within 0.450%. Conclusions: The high sensitivity MOSFET may be used as a dosimeter with proper cross‐calibration for the quality assurance phantom, which is under construction.
SU‐E‐T‐200: The Verification of Dose Information for Two‐Dimensional Ion Chamber Array of IMRT Dose Verification Using Mutual Information
Authors: Tateoka K , Nakata A , Saito Y , Yaegashi Y , Nakazawa T , Suzuki J , Shima K , Fujimoto K , Hareyama M
Published: November 2011

Purpose: The Wellhofer® MatriXX is a two‐dimensional ion chamber array designed for IMRT dose verifications. Its dosimetric properties have beencharacterized for megavoltage beams in a number of studies; however, dose verifications for the MatriXX are discrete estimations for the number of ion chambers of the MattiXX. Therefore, there is still a lack of an investigation into its performance in dose verifications for IMRT. In this work, to compare traditional IMRT dose verifications using film dosimetry, we have carried out a systematic study using Mutual Information (MI) on this issue. Methods: Dose distributions from several 6X and 10X IMRT treatment plans for pelvis and head and neck radiotherapy patients were measured using radiographic film, the MatriXX array. In each case the dose distributions predicted by the treatment planning system was compared to the measured dose distribution using Mutual Information(MI). The standard information of MI is dose distributions from treatment plans. MI of dose distributions from treatment plans is normalized itself. Results: The MI comparison with dose distributions from film for plans of pelvis and head and neck were, on the average, within 2%, 3%, respectively. The one of reasons can be given for this lack of high dose information. but, their dose information are almost same. At the same time, the MI comparison with dose distributions from the MattiXX for plans of pelvis and head and neck were, on the average, within 5%, 6%, respectively. The MI was large than MI of film. The reason is that the MattiXX is low the number of dose verification points. There difference is small, therefore, the MattiXX has ability for enough dose verification. Conclusions: Nevertheless, the MatriXX are discrete estimations, this work indicates the MattiXX has ability for IMRT dose verification.
SU‐E‐T‐202: Evaluation and Commissioning of KODAK RT2000 CR System for Its Application in Routine Portal Imaging
Authors: Nookala P , Piskulich F , Wroe A , Patyal B
Published: November 2011

Purpose: Evaluation of KODAK RT2000 CR System for its practical use in replacing portal localization films. Methods: Patient setup verification is critical to accurately deliver a prescribed dose to a patient. We use portal film imaging on some of our old machines. KODAK RT2000 CR System was recently evaluated to replace the conventional portal films with digital imaging. Rando phantom was used to test the functionality and accuracy of the Kodak CR system. A treatment plan was generated using the CT images of the Rando phantom; the plan was then exported to Siemens PRIMUS via ARIA. Portal images were taken using KODAK photostimulable phosphor (PSP) system. The PSP system was read by scanning the phosphor using KODAK CR System. These digitized images were exported to Varian ARIA RT Chart and evaluated in Offline Review for registration of DRRs with the digital portal image. DRRs from the treatment planning system and digital portal images from KODAK CR System were matched and differences between the planned set‐up and the in‐room set‐up of phantom were measured with tools in Offline Review. Shifts in lateral, longitudinal and vertical directions along with tilt angle were obtained to finally register the DRRs with the digital portal images. Results: We converted our old film‐based portal imaging system into a digital portal imaging system. These digital images can be shared across a network. A digital imaging system provides easy access through ARIA network for physicianˈs approval of portal images. Conclusions: We successfully integrated four different multi‐vendor modalities (Odyssey TPS from Optivus, Siemenˈs Primus, Varian ARIA and KODAK CR System) to develop a portal digital imaging system. The system increases accuracy of treatment, offers flexibility of offline review by a physician, and thus makes the whole process more efficient.
SU‐E‐T‐207: Local and Limited Projection Tomography Reconstructions for Contrast‐Enhanced Synchrotron Stereotactic Radiotherapy in Vivo Dosimetry
Authors: Le Bourhis J , Vautrin M , Elleaume H , Esteve F , Desbat L , Nemoz C , Adam J
Published: November 2011

Purpose: Contrast‐enhanced stereotactic synchrotron radiation therapy (SSRT) is an innovative technique based on localized dose‐enhancement effects obtained by reinforced photoelectric absorption in the target. Medium energy monochromatic x‐rays (50 –100 keV) are used for irradiating tumors previously loaded with high‐Z elements. SSRT clinical trials are being prepared at the ESRF. The first patients (scheduled in summer‐autumn 2011) should be treated at 80 keV, with 10 conformational beams. The treatment plan will use CT images acquired prior and after systemic iodine injection. However the exact dose delivered to the patient relies on the exact 3D iodine biodistribution in the tumor during the treatment itself. An in vivo dosimetry methodology based on portal imaging was developed to retrieve the absolute 3D iodine concentrations reached during the treatment. Methods: The proposed algorithm uses the images acquired with a high‐purity germanium detector located behind the patient. The proposed methodology has to solve a tomography reconstruction problem with a restricted field of view (local tomography) and a limited number of projections (10 at maximum). None of the currently available algorithms can solve both local and limited projection tomography problems at once while being quantitative. However, in SSRT, a large amount of a priori information is available (three CT‐scans acquired prior the treatment, with and without iodine). Thus the proposed algorithm proposed in this paper is based on filtered backprojection and uses extensively the a priori information related to patient morphology, with a few geometrical hypothesis. Results: The results obtained from numerical simulation on a human head phantom show that the proposed algorithm is able to retrieve the iodine concentrations with a relative error lower than 2%. Conclusions: The in vivo dosimetry methodology for SSRT has been validated with numerical simulations. It has now to be tested on real patient data before the first patient is treated.
SU‐E‐T‐208: Optimizing Parameters in Imaging for Accurate EPID Exit Dosimetry Application
Authors: Li K , Beardmore A , Able A
Published: November 2011

Purpose: Besides being used for patient treatment alignment, EPIDs treatment quality control is advancing to application of exit dosimetry analysis. The absolute dosimetry is determined by the accuracy of the calibration between portal image pixel value and dose. In this study, a generic IMRT field was selected as an evaluation reference, the dosimetric effect of pixel value and dose calibration was investigated by varying energy, dose rate and total delivered dose. Method and Materials:Varian EPID and Imaging acquisition system (IAS3‐aS1000) were used to create images from dose delivered from a Varian Trilogy Linac machine. The doses were delivered with a 60 degree enhance dynamic wedges (EDW) field varied with different energies, total doses and dose rates. And the images were exported to the RIT system (RIT113V5.3) for analysis. The dosimetric calibration curves were used to analyze the effect of each parameter. The slopes between the calibration curves were also calculated. then a prostate IMRT field was employed for absolute dosimetry verification. Results: At dose rate of 400MU per minute, the magnitudes of slope range from 10 pixel value per cGy to 27 pixel value per cGy for calibration from 50MU to 5000MU. When dose rates vary from 100 to 600 MU per minute, the slopes change from 29 pixel value per cGy to 1 pixel value per cGy. A selected point dose from an IMRT field was compared with EPID measurement and was within 5% using calibrations at 200MU delivered at 600 MU per minute, or 100MU delivered at 400MU per minute. Conclusions: Accurate dosimetric application for EPID requires meticulous selection of imaging parameters. For high precision exit dosimetry based on EPID imaging, further investigation is needed for total Monitor Unit and delivery temporal effect from IMRT Fields.
SU‐E‐T‐212: Measurement Comparison and Monte Carlo Analysis for Rapid Arc Delivery Verification Using ArcCheck Dosimetry System
Authors: Koren S , Lin M , Veltchev I , Ma C
Published: November 2011

Purpose: The RapidArc technique requires sophisticated treatment plan optimization and beam delivery technology. This work investigates the capabilities of the ArcCheck dosimetry system for RapidArc treatment planning verification and Linac dose delivery validation. Methods: A total of 10 (6 prostate, H&N, pelvis, liver and breast) clinical RapidArc treatment cases were investigated using a delivery QA procedure with the use of the ArcCheck dosimetry system. A custom acrylic plug with the ability to host an ion chamber was used for CAX phantom dose measurements. In addition to the Eclipse TPS, the treatment dose distributions were simulated using a Monte Carlo code in order to compare and evaluate the dose delivery based on the treatment plan. In both ways the distributions were evaluated in terms of the absolute dose and distance to agreement on a cylindrical plane dose distribution that overlaps with the ArcCheck detector plane. The system sensitivity to setup misalignment errors, and field size dependency, were also investigated. Results: Excluding the H&N case, the difference between calculated to measure absolute CAX dose was less than 3%. The H&N CAX fell on a dose distribution gradient, and hence showed a 6.6% and 7.1% dose difference, respectively, between the measurement dose and that calculated by the TPS and Monte Carlo. Gamma analysis passing rate varied from 92.8% for the pelvis case, and 98.8% for a prostate case, when using the 3% dose difference and 3mm distance to agreement criteria for the TPS dose distributions. A field‐size dependence was found for large field sizes (above 21 × 21 cm2). Conclusions: The ArcCheck dosimetry system showed good capabilities for RapidArc plan verification and dose delivery validation, with respect to the CAX dose and the overall dose distribution. The system sensitivity to setup misalignment and dose variation is demonstrated for the clinical cases investigated.
SU‐E‐T‐215: Tissue Optical Properties Determination in PDT Treated Head & Neck Patients Using a Balloon Diffusing Light Source
Authors: Dimofte A , Zhu T , Finlay J , Sandell J
Published: November 2011

Purpose: The main objective of this study was to determine the optical properties (scattering and absorption coefficients) in vivo by interstitial measurements using a light detection device made for this purpose. Methods: Patients were enrolled in a phase I dose escalation study of photodynamic therapy for the treatment of pre‐malignant tumors and superficial microinvasive disease of the head and neck. Patients were given the photosensitizer Levulan orally followed by the administration of red light (629–635 nm) to the tumor from a laser to a dose of 50–200 J/cm2. Because of technical challenges, some of the patients were not able to be treated using the classic microlens fiber and instead used a translucent diffusing balloon catheter to deliver the light. Measurements were performed using a light detection device before and after light treatment delivery. The detector is scanned along the length of the light source containing catheter. Scans are done with the device placed on the treatment area and on the normal oral cavity tissue. Optical properties of both the normal and diseased tissue before and after the light treatment were obtained and compared to those measured with a fiber‐optic probe. The fiber‐optic based probe was placed on the tissue surface, and white light was delivered to the tumor surface by one of its source fibers. The diffusely reflected white light was collected by a spectrograph and analyzed to determine the absorption and scattering spectra of the tissue. Results: A theory based on light source on semi‐infinite medium has been developed to interpret the measured data. Results from both methods were compared for accuracy. This model was also validated by measurements performed in tissue‐simulating. Conclusions: We developed a model for quick and accurate determination of tissue optical properties in semi‐infinite medium, which is theoretically suitable for determination of optical properties head and neck PDT. Conclusions:
SU‐E‐T‐228: Correlation of 3D Surface Matching with AlignRT and MV Imaging for Whole‐Breast Radiotherapy (WBRT)
Authors: Li J , Kang H , Wu T , Farrey K , Chmura S , Al‐Hallaq H
Published: November 2011

Purpose: Surface matching provides quantitative shifts for patient positioning of superficial treatment sites such as breast. We investigated the reliability of 3D surface matching using AlignRT compared to positioning using skin marks followed by MV portal imaging for WBRT. Methods: Five patients receiving two‐field WBRT without respiratory gating were positioned daily on a breastboard (n=2) or custom alphacradle (n=3). For each treatment fraction guided by MV (n=23), the 3D surface captured using AlignRT (v4.5) was compared to the surface generated from CT simulation data. The AlignRT registration algorithm outputs 3D rotations plus translations to optimize matching between surfaces in user‐defined ROIs. The correlation of AlignRT and MV shifts in 4 degree‐of‐freedom (3D translations and table rotation) was studied for two ROIs: the entire surface (‘all’) and the treated breast (‘Breast’). Two surfaces were re‐captured in the treatment position to compare residual registration errors. Parametric statistical tests were considered significant at p<0.05. Results: The 3D distance of the table shifts was 3.8±5.1mm following MV imaging, 5.9±4.1mm for ‘all’, and 5.7±3.3mm for ‘Breast’ registration. while AlignRT distances were significantly different from MV, only ˈallˈ registration correlated with MV shifts (r=0.76). The 3D difference in initial and final positions correlated with table shifts for both ROIs (r>0.9) although residual 3D distances according to AlignRT remained high for ‘all’ (5.0±4.7mm) and ‘Breast’ (4.7±4.2mm). Furthermore, absolute table rotations calculated by AlignRT for consecutively acquired surfaces exhibited fluctuations that were significantly larger for registrations of ‘Breast’ (0.62±0.58 degrees) than ‘all’ (0.27±0.18 degrees). Conclusion: Breast surface matching using AlignRT depends upon the registered ROI. A large ROI showed higher correlation with MV shifts and increased stability when calculating table rotations. Registrations exhibited a large baseline offset for all ROIs, indicating that quantitative table shifts from AlignRT overestimate those determined from MV imaging by expert physicians for WBRT.
SU‐E‐T‐230: Intracavitary in Vivo Dosimetry Based on Multichannel Real‐Time Fiber‐Coupled Radioluminescence (RL) and Optically Stimulated Luminescence (OSL) of Al2O3:C
Authors: Spasic E , Magne S , de Carlan L , Aubineau‐Lanièce I , Malet C , Ginestet C , Ferdinand P
Published: November 2011

Purpose: This work is aimed at developing a new probe to improve the accuracy of the dose delivery follow up in some Radiotherapy (RT) treatments that involve small fields like Irradiation Modulated RT (IMRT) and/or high dose gradients like Brachytherapy (BT) where the In Vivo Dosimetry (IVD) still remains challenging. Material and Methods: The OSL/FO (Optically Stimulated Luminescence/Fibre Optics) system designed by CEA LIST is composed of a multichannel reader and OSL OFS (Optical Fibre Sensors) incorporating dosimetric‐grade alumina crystals (Al2O3:C, grown in reducing atmosphere in the presence of carbon). Al2O3 :C crystals exhibit good sensitivity and small fading at room temperature. They are small (0.09 mm3), optically transparent, non‐hygroscopic, chemically inert. The OSL OFS are made of low‐Z materials (polymer, PMMA, alumina). They are electromagnetic‐immune, radiation‐resistant and transparent. The reader unit may deal with up to 15 channels with the use of an optical switch thus leading to an optimised cost‐per‐sensor ratio. During irradiation, part of free electrons promptly recombine and generate a RL (that provides realtime dose estimation) while another portion is kept stored. After irradiation, the crystal is remotely reset by laser light and the OSL is recorded to get the absorbed dose. Results and Conclusion: Within the French INTRADOSE project, the CEA‐LIST is currently developing small dosimetric catheters with the aim of measuring the intracavitary dose distribution, close to organs at risk. This yields the maximal dose and the source‐sensor distance. This device would allow checking that the source of 192Ir moves along the tubes, according to the treatment planning system. Metrological validations will be performed for both BT (prostatic cancer) and IMRT (head and neck cancer) treatments.
SU‐E‐T‐231: Exit Fluence Analysis in RapidArc Using EPID
Authors: Prabakar S. , Sriram P. , Dhanabalan R. , Muniyappan K. , Vivekanandan N.
Published: November 2011

Purpose: In measuring the exit fluences, there are several sources of deviations which include the changes in the entrance fluence, changes in the detector response and patient orientation or geometry. The purpose of this work is to quantify these sources of the errors. Methods: The quantification of the errors caused by the machine delivery is done by comparing arc picket fence test for a period of 30 days. To quantify the sources of error due leaf and gantry positions and positioning of the patient a RapidArc plan created for the pelvis site was delivered with and without rando phantom and the exit portal images were measured. The day to day exit fluence variation in the patient anatomy were analysed by comparing the daily exit dose images during the course of treatment. For comparison, the first fraction image is used as the reference image. Standard deviation and the gamma analysis were used to quantify the errors between fractions. The gamma criterion used for analysis is 3% Dose Difference and 3 mm Distance to Agreement. Results: The maximum gamma value and Standard deviation for the picket fence test fields was 3.3 and 1.35 respectively. The area failing the gamma criteria was less than 0.1%. The delivery of the RapidArc plans without phantom shows a maximum standard deviation of 1.85 and the maximum gamma value of 0.59. The maximum gamma value for the RapidArc plan delivered with the phantom was found to be 1.2. The largest observed fluence deviation during the delivery for patient was 5.7% and the maximum standard deviation was 4.1%. Conclusions: From this study, it is found that the variation in exit fluence due to patient interfraction organ motion found to be significant than the deviations caused by the machine and detectors.
SU‐E‐T‐232: Using EPID Images for MLC QA: A Northwestern Memorial Hospital Experience
Authors: Pokhrel D , Gopalakrishnan M , Luo G , David J , Sathiaseelan V
Published: November 2011

Purpose: To verify experimentally MLC leaf gaps position using EPID images for an advanced radiotherapy treatment delivery such as IMRT, SBRT. Methods and materials: EPID images were acquired with 6 MV x‐rays of Elekta linear accelerators utilizing garden fence image technique, with 8 and 11‐strips of MLC preset values at 0o, 90o, 180o, and 270o gantry angles. The dark strips were created by eleven exposures of 0.5×20.0cm2 strip fields, which were separated by 20mm gaps. The eight exposures were of 2.0×20.0cm2 strip fields separated by 5mm gaps. These images were exported for analysis in dicom format. The EPID images were filtered to reduce background distortion and enhanced MLC leaf edge. In‐house software was used to estimate inter‐MLC leakage and absolute MLC leaf gaps position. The accuracy of EPID‐based MLC leaf gaps position detection was estimated by comparing with the known preset‐MLC leaf gaps. Results: In all measurements, the inter‐MLC leakage was less than 1.5%. Using simple strip‐test patterns, the MLC leaf gaps position determined from EPID images agreed to within ±0.5mm of the corresponding preset values. Difference images show significant effect of gravity in MLC leaf motion along lateral gantry angles. Summary and Discussion: Our preliminary results show EPID images can be used as an alternative to radiographic films for routine‐QA of MLCs. Since, the EPID is rigidly‐mounted with linear‐accelerator and digital‐intrinsically, it could be more accurate and convenient MLC QA tool than that of the conventional film. In addition, the EPID images can be acquired easily, analyzed automatically, and stored more rapidly and conveniently than that of radiographic films. Availability of EPID on all new linear‐accelerators makes it a promising tool for quantitative MLC QA. Routine clinical application of EPID‐based MLC QA will be helpful for more accurate delivery of highly modulated IMRT and SBRT plans, including VMAT.
SU‐E‐T‐233: Commissioning of An Implantable Dosimeter for External Beam Radiation Therapy
Authors: Buzurovic I , Showalter T , Dicker A , Cao J , Xiao Y , Yu Y , Harrison A
Published: November 2011

Purpose: To commission a Dose Verification System (DVS) with permanently implanted in vivo dosimeters. To acquire and evaluate sufficient data for establishing standard of quality in a clinical setting.Methods: DVS is permanent implantable wireless radiation sensor based on MOSFET for absolute dose measurements. To evaluate characteristics of dosimeter, following tests were performed: temperature dependence, reproducibility, field size dependence, post‐irradiation signal drift, dependence on average dose‐rate, linearity test, angular dependence, dose‐rate dependence, irradiation depth dependence and a multiple reading effect. Dosimeter is not currently calibrated for use in kV range. Nonetheless, effects of conebeam CT(CBCT) imaging to dosimeter were investigated. Phantom studies were performed in both air and water using an Elekta Synergy‐S Beam‐Modulator linear accelerator. Results: DVS dosimeters have been calibrated to be used at 37C. Reproducibility tests were performed at room temperature. Readings were −3.2% low (SD=2.5%, or 5.06cGy for 200cGy delivered). Same tests in water at human body temperature showed 1.5% absolute difference, with a similar deviation (SD=2.85%). It was observed that measurement signal decayed significantly with time post‐irradiation, from +3% after 0.5min to −3.5% after 10min. Dose linearity was within 2% for absorbed total dose of 75Gy. Signal rapidly decayed after total dose of 82Gy. Angular dependence was −0.3% (SD=2.31%). Readings decreased with increase in depth, about 0.3%/cm. No filed size and dose‐rate difference were observed. Average dose reading due to CBCT imaging using the pelvis protocol was 7.89cGy (SD=1.46cGy) Conclusions: Extensive acceptance and commissioning measurements have shown considerable post‐radiation signal drift, temperature dependence, reproducibility variation, and rotational isotropy. This process confirmed manufacturerˈs stated performance and provided baseline QA necessary to implement DVS clinically. System is currently implemented with ±7% tolerance. Dosimeter can be used to quantify dose at depth, as well as to evaluate adherence between dose from treatment plan and daily delivery.
SU‐E‐T‐237: Patient‐Specific Quality Assurance of Dose Delivery for Intracranial Linac‐Based Stereotactic Radiosurgery Using High‐Definition Multileaf Collimators
Authors: Morales‐Paliza M , Krauss R , Coffey C , Ding G
Published: November 2011

Purpose: Patient‐specific Quality Assurance (QA) of dose delivery for intracranial linac‐based Stereotactic Radiosurgery (SRS) is not a common practice. This study describes an efficient patient‐specific measurement using an ion chamber array system to validate the dose at the isocenter plane when High‐Definition Multileaf Collimators (HDMLC) are used for planning dynamic arcs in small fields.Methods: Measurement of dose in typical SRS treatments is a challenge due to the small sizes of the fields. This study focuses in the measurement of dose at one isocenter plane by using the ion chamber array system MatriXX® embedded into the MultiCube® phantom (IBA Dosimetry Inc.) for patients treated with SRS delivered by HDMLC (2.5‐mm leaf thickness) using the Novalis‐TX linear accelerator. The patient plan is mapped into the phantom placing the isocenter of the lesion in the center of the array, and converting the non‐coplanar arcs into coplanar ones. The total dose distribution in the ion‐chamber array plane is calculated using the same Treatment Planning Algorithm (TPA) used for the patient plan. The phantom‐mapped plan is fully delivered on the phantom such that the combined dose distribution at the isocenter plane of the array is measured directly. A statistical analysis using both the gamma‐factor criteria (3% dose difference and 3 mm distance‐to‐agreement) and the absolute dose difference is then performed between the measured and the calculated dose distributions.Results: This patient‐specific QA was applied to 14 lesions (greater than 1.8 cm in the longest extension) in 7 patients. The percent of pixels with gamma factor greater than one were below 3%, and the percent of pixels with absolute dose difference greater than 5% were less than 5% in all cases Conclusions: This patient‐specific QA for HDMLC is feasible and effective to ensure the accuracy of calculations by the TPA.
SU‐E‐T‐238: OnedosePlus MOSFET Dosimeter Performance in Tangential Field in Vivo Dosimtery
Authors: Chen T , Levinson L , Zhang M , Goyal S , Haffty B , Yue N
Published: November 2011

Purpose: To investigate the incident angle dependence of the OnedosePlus MOSFET dosimeter and to evaluate the dosimeterˈs performance in vivo dosimetry for tangential fields treatments. Methods: Two types of external beam radiation plan were generated based on a solid water phantom: one with a group of oblique beams directed toward the anterior surface of the phantom and other with two opposing half blocked beams directed parallel to the anterior surface. The second plan represented an extreme case of tangential field treatments. In the deliveries of the plans, OnedosePlus dosimeters were placed at various locations on the phantom anterior surface. Calibrated Radiochromic EBT2 film dosimeters were placed at the same locations of the phantom anterior surface and at the corresponding locations 1cm away from the anterior surface. The measured doses from the OnedosePlus dosimeters were compared against the corresponding doses in the plans and the film measurements. Results: As the incident beam angle increased from 0 to 90 degree to the CAX, the OnedosePlus reading increased 15%. The doses measured using the OnedosePlus dosimeters in the extreme tangential field plan did not have a clear correspondence to either the surface dose or the doses at 1 cm depth. The film readings were in close agreement with the TPS calculated doses with an average dose difference less than 5%. The OnedosePlus measured doses were higher than the TPS calculated doses at the 1cm depth by a constant (average: 31.45+/− 2.71cGy), and much higher than the surface film measurements by an average of 246%. Conclusions: OnedosePlus dosimeter readings have a strong dependence on the incident beam angle, especially when the beam angle is larger than 45 degree. The point of measurement for OnedosePlus dosimeter is unclear for the treatments involving tangential beams and it overestimates doses for the assumed point of measurement (1cm depth).
SU‐E‐T‐239: Evaluation of Daily Patient Setup for Various Treatment Sites Using MVCT Image Guidance
Authors: Sandhu R , Lack D , Burmeister J
Published: November 2011

Purpose: The accuracy and reproducibility of daily patient setup is crucial, especially for highly conformal delivery techniques like Tomotherapy. We retrospectively analyzed daily setup uncertainties for six treatment sites using Tomotherapy MVCT. Methods and Material: Translational shift data based on daily Tomotherapy MVCT registration has been analyzed for 103 patients and six sites: head/neck(n=32), brain(n=16), lung(n=16), abdomen(n=13), prostate(n=18), and pelvis(n=8). Statistical analysis included calculation of group mean shifts, and population systematic and random errors. Van Herkˈs margin formula was used to calculate rigid setup error margins based on population statistics for each site. To evaluate our clinical data with respect to the community, our setup results were compared with published studies. Results: Group mean for head/neck and brain are 0.1–0.3mm (lateral), 0.5–1.1 mm(longitudinal) and 4.0–4.9mm(vertical). Amongst the different treatment sites, population systematic and random errors are smallest for head/neck and brain patients with a range of 1.4 mm to 3.0 mm, corresponding to rigid margins between 4.5 – 9.2mm. These large vertical shifts are due to couch sag and use of shims to account for thermoplastic mask shrinkage between simulation and treatment. The group mean for all other sites ranged from 0.2–1.3 mm(lateral), 0.5–3.7mm (longitudinal) and 1.9&–4.1mm(vertical). Population systematic and random errors for other treatment sites ranged from 2.1–3.9mm(lateral), 2.2–5.6mm(longitudinal) and 2.6–6.5mm(vertical). This corresponds to rigid margins between 7.4–18.9mm. Comparatively, our data is similar to published data which ranges between 0.7 – 3.3mm for head/neck and brain, and 1.7 – 7.2mm for other sites. Conclusion: Our patient setup error on helical Tomotherapy is consistent with the published literature. ACR‐ASTRO guidelines recommend setting clinical tolerances for IGRT patient shifts. Currently, our institution has a 10 mm shift policy. Further analysis is needed to determine if this tolerance is appropriate for our clinic.
SU‐E‐T‐243: The Utilization of a Head‐And‐Neck IMRT QA Benchmark to Identify the Cause of Individual Imrt Qa Failure
Authors: Gao Z , Cheng C , Wu G , Li M
Published: November 2011

Purpose: In this work, a H&N IMRT QA plan was created and then utilized as the benchmark to monitor all subsequent IMRT processes. This benchmark plan is delivered as a consistency check on the same day when a Patient Specific QA (PSQA) fails the passing criteria. The establishment of such an QA benchmark allows to determine whether the failure of a PSQA is due to the TPS or MLC performance. Methods: A changeling QA plan was generated as benchmark for a 7‐beam IMRT for H&N cancer in Pinnacle TPS. Prior to benchmarking of this QA case, the accelerator is serviced to ensure MLC positioning accuracy and output calibration. The composite dose distribution of the benchmark plan was measured with IMRTrix® and then compared with the fluence map generated from TPS. This plan is delivered to check the consistency of imrt process whenever a PSQA fails the passing criteria. Results: For the baseline measurement, the point dose discrepancy was found to be 2.5% and Gamma passing rate was 97.3% and is then setup as our benchmark for IMRT process consistency check. 74 PSQA have been analyzed since the establishment of the benchmark. Seven cases failed the passing criteria. the benchmark plan was delivered to check the system consistency. Of the two cases, the benchmark case passed, thus required replanning. For the other five cases, the benchmark was substantially lower than the initial passing rate, thus the MLC performance may cause the failure and required MLC recalibration. Conclusions: We have established a benchmark QA plan for consistency check of IMRT process. The IMRT consistency check can be performed as a periodic QA check (monthly QA), after mlc recalibration or whenever a PSQA failure occurs. This will help to maintain the best performance of IMRT process.
SU‐E‐T‐245: Continuous Quality Improvement for Patient‐Specific IMRT/SBRT QA
Authors: Boddu S , Perks J
Published: November 2011

Purpose: A continuous quality improvement (CQI) process for patient‐specific Quality Assurance (PSQA) was implemented to track those that did not meet the pass criteria. We investigated the reasons for the failures and derived corrective actions. Methods: At our clinic SBRT, Tomotherapy, and linac IMRT treatments are checked prior to treatment by a formal PSQA procedure. Plans are delivered using the record and verify system in QA mode, measured data are compared with calculated plan data and PSQA is assigned a pass or fail. We use MapCheck for point/planar dosimetry for IMRT and ion chamber/film in cheese phantom for Tomotherapy and SBRT with pass criteria of ≥ 90% (using 3%/3mm criteria). Plans that fail initial QA are re‐measured and sometimes re‐planned, costing departmental resources and causing patient treatment delays. Data for 2010 were analyzed and categorized. Results: A total of 321 PSQA measurements were analyzed ‐ 52% Tomotherapy, 7 % SBRT and 41% linac IMRT patients. Overall failure rate was 15% of which majority was Tomotherapy (11.2%). Failure due to incorrect QA plan generation was major reason followed by issues related to treatment planning such as small segment sizes, machine related failures, and Tomotherapy output being out of tolerance (+3%). Conclusions: In one case, the failures lead to discovery of a machine problem. Tomotherapy failures in June and July lead to an investigation which led to a better understanding of the limitations of our current QA methodology, particularly the film measurement (artifacts). The point dose measurement pass criteria were re‐evaluated and changes made. Patient treatment can continue if point dose >3% but <5% if approved by physicist. These type failures are tracked and if upward trending noted, a thorough investigation is triggered. Recognition of PSQA failure categories and implementing proactive measures has led to decrease in failure rate.
SU‐E‐T‐248: Development of Checklist Enabling Comprehensive Review of Plan Quality and R&V Parameter Fidelity in a Paperless Environment
Authors: Malhotra H , Kumaraswamy L , Podgorsak M
Published: November 2011

Introduction: Many believe that a paperless environment leads to enhanced efficiency within medical environment. Unfortunately, Record and verify (R&V) systems may not be flexible enough to provide openness which was available in a paper environment and additional steps are needed to ensure equivalent quality of patient care. Presently Mosaiq, a popular R&V system, supports only Microsoft word document as the standard document type which doesnˈt support conditional formatting, various formulas etc. However, word does support an embedded Excel object which is powerful enough to handle these requirements. Methods: A number of quality checklist templates specific to nature of the check viz. initial physics (photon/electron) chart/plan check, total body irradiation check, therapist pretreatment check, final physics check etc. have been developed in Excel utilizing simple check box items, numerical and logical formulas and the automatic status change [red=unchecked/out of specification item, green=checked/in specification item, orange=caution etc.], helping to easily identify the problem. Results: The initial physics (photon/electron) chart/plan check template provides a recipe for checking of all parameters which affect the patientˈs treatment in terms of verification of MDs script, treatment plan and R&V system parameters. Also included are the necessary parameters to ensure beam direction & evaluation of treatment plan based on standard dosimetric indices. The TBI quality check‐list provides an independent verification of all the physics related parameters [e.g. MUs, dose to various OARs, computation of the lead‐sheets to increase the patientˈs mid‐plane dose uniformity, given dose and appropriate correction due to lung transmission etc.]. Color coded check list items are available to verify the necessary R&V parameters. Computed parameters were within ±0.5% of that of the primary computation. Conclusion: Integration of these templates in our R&V system provides a framework for consistent verification of patientˈs treatment parameters including treatment plan evaluation prior to initiation of treatment.
SU‐E‐T‐252: Safety Systems and Failure Modes and Effects Analysis for a Linear Accelerator — Magnetic Resonance Imager — Brachytherapy System
Authors: Lamey M , Carlone M , Alasti H , Bissonnette J , Borg J , Breen S , Coolens C , Heaton R , Islam M , Sharpe M , Stanescu T , van Prooijen M , Jaffray D
Published: November 2011

Purpose: To evaluate and identify safety system concerns and possible failure modes for a multimodality, linear accelerator (linac) — magnetic resonance imager (MRI) ‐ brachytherapy, radiotherapy system. Methods: A Delphi process is applied to investigate the safety system concerns and possible failure modes in a linac‐MRI‐brachytherapy system. Well established, for instance in the automotive or airline industries, system, design and process failure modes effect analysis can be applied to the design of a multimodality radiation therapy system. Results: Safety design, systems, processes and culture in radiation therapy is of great importance. When implementing new technologies a review of the necessary staff and patient safety may be necessary. To address patient and staff safety concerns a thoughtful design process must be implemented when an MRI is present or near a linac or a brachytherapy system. Each input into a patient specific process map, such as consent, screening, immobilization, planning, image guidance and machine movement coordination must be analyzed for safety and failure modes concerns. Numerous items have been identified as potential failure modes, these items have been classified into the following nine categories: screening, motion, interlocks, imaging, treatment delivery, dosimetry, plan adaptation, mechanical and miscellaneous. A broad range of failure modes have been identified some of these include and range from non‐compatible in‐room finishing to linac performance degradation under repeated small magnetic field influences to improper patient screening and the possibility of machine collisions. Conclusions: An abridged list of suggestions resulting from our safety systems analysis includes a rigorous staff educational and training program, the evaluation of current quality assurance devices used for mechanical and dosimetric tests, an interlocked computerized system for machine translations and rotations, machine servicing protocols and both fire and patient emergency protocols.
SU‐E‐T‐254: Comprehensive Quality Assurance Program for Accelerated Partial Breast Irradiation Using the SAVI HDR Applicator
Authors: Cui J , Mayadev J , Stern R
Published: November 2011

Purpose: To present a comprehensive prescriptive quality assurance (QA) program for Accelerated Partial Breast Irradiation (APBI) using the Cianna Medical SAVI (Strut Adjusted Volume Implant) multi‐catheter applicator. Methods: We established a robust QA program for the SAVI technique based on our previous experience with various HDR procedures and documentation provided by the manufacturer. During the simulation, the location of the SAVI in relation to the patientˈs anatomy is recorded by measuring the distance from the patientˈs skin to the SAVIˈs hub, by marking the skin and denoting which catheter aligned with the mark, and by taking AP and lateral scout views. A “SAVI Simulation Worksheet” was developed to denote the key measurements during the simulation QA. Our QA process continues with treatment planning. After the plan is reviewed by the physician, the physicist checks the delineation of each catheter and the dose distributions using a developed “Pre‐Plan Check Sheet” as a guide. The third set of the major checks is performed prior to each delivery. The SAVI location is verified via repeating the measurements taken during the simulation including the daily images. A therapist and physician sign‐off are required. “HDR Treatment Check” is the last key component of the QA flow, which required 3 independent checks of the catheter connections, dwell positions and time, and post‐treatment checks. Results: 10 SAVI patients have been treated using the QA protocol. There was 1 catheter each for 2 patients that were misconnected. This error was detected by the third independent checker. Conclusions: We established a robust QA program for the SAVI technique and successfully implemented it for 10 SAVI patients, 100 treatments. We are initiating Failure Modes and Effects Analysis (FMEA) for the SAVI process to better distribute the limited resources and enhance the efficiency and safety of our SAVI program.
SU‐E‐T‐257: Examination of Medical Events on High‐Dose‐Rate Brachytherapy Repored to the NRC
Authors: Saw C , Juliano J , Wagner H
Published: November 2011

Purpose: A series of reports on medical errors recently published in New York Times highlights the need to be aware of patient safety in radiation medicine. Various groups are using the risk assessment technique to reduce medical errors. This work examined medical events associated with high‐dose‐rate (HDR) brachytherapy as reported and posted on the NRC website to understand the causes of these medical events. Methods: A task was undertaken to systematically assess the notification of events as reported to the NRC from January 2010 to March 2011. These notifications include all events under the jurisdiction of the NRC from nuclear power to the medical use of byproduct materials. Eleven notification events associated with HDR brachytherapy were identified for this time period. These notifications were read and discussed to identify the possible causes of these medical events. Results: Among these medical events, two were related to equipment failure: the failure to withdraw source and the punching through a catheter by the source. One of the event was due to a software bug. The rest of the events were associated with human errors. The first event was associated with inadvertent pressing of the auto‐radiography button instead of the treatment button. The rest of the events were due to incorrect determination of the length of the catheter, the dwell spacing, or the data entry in the treatment planning system. These occurrences point directly at the need for a checklist to remind the medical physicist to review these parameters prior to dose delivery. Conclusions: A systematic checklist that incorporates the reevaluation of the (a) length of catheter, (b) dwell spacing, and (c) data entered into the treatment planning system would eliminate over 60% of the error seen last year and early part of this year.
SU‐E‐T‐260: Daily Quality Assurance of Volumetric Modulated Arc Therapy and Intensity Modulated Radiotherapy Using Dynamic Log Files: Retrospective Study
Authors: Tachibana H , Luxton G , Xing L
Published: November 2011

Purpose: We designed and developed a daily QA software for patientsˈ treatment using dynamic MLC log files for IMRT and RapidArc. The log files of patientsˈ clinical treatments were also assessed retrospectively. Methods: The log files were sent to the server using our in‐house client software in a treatment console PC via a network, and then the errors of leaf position, leaf gap, and dose were analyzed using our in‐house server software in a PC. Dose errors in 2D plane were computed. In the retrospective data analysis, the log files of a total of 5871 treatment fields from 2010/11/02 to 2011/02/04 were collected from 2 Linac console PCs at the Cancer Center. The errors of leaf gap and dose between treatment methods were compared. Results: All of the log files were sent and analyzed normally. The results of analyzing the 5871 treatment fields were that the average values of the leaf gap errors [mm] were 0.42±0.26, 0.53±0.24, 0.42±0.26, and 0.47±0.84, and the average values of the dose errors [%] were −0.11±1.14, 0.32±1.28, −0.22±1.86, and −0.19±3.70, for non‐gated IMRT, gated IMRT, IMRT and RapidArc, respectively. Consecutive daily errors of the gaps and doses for RapidArc showed similar trends to those of IMRT. Since actual leaf gaps for RapidArc (21.29±11.72mm) were larger than those of IMRT (11.18±6.35mm), dose errors for RapidArc were decreased compared to IMRT. RapidArc had similar accuracy for dose distribution in terms of MLC movements. For gating, dose errors can arise from MLC gating signal hold‐on and hold‐off. Conclusions: The results of retrospective study could contribute to patient‐specific QA by providing a reference of the accuracy of MLC movement. Furthermore, the use of our system based on the retrospective analysis could document the accuracy of machine performance with regard to patient treatment.