bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐128: Applying Failure Modes and Effects Analysis to a Risk‐Based Quality Management for Stereotactic Radiosurgery in Brazil
Authors: Teixeira F , de Almeida C , Huq M
Published: June 2015

Purpose:

The goal of the present work was to evaluate the process maps for stereotactic radiosurgery (SRS) treatment at three radiotherapy centers in Brazil and apply the FMEA technique to evaluate similarities and differences, if any, of the hazards and risks associated with these processes.

Methods:

A team, consisting of professionals from different disciplines and involved in the SRS treatment, was formed at each center. Each team was responsible for the development of the process map, and performance of FMEA and FTA. A facilitator knowledgeable in these techniques led the work at each center. The TG100 recommended scales were used for the evaluation of hazard and severity for each step for the major process “treatment planning”.

Results:

Hazard index given by the Risk Priority Number (RPN) is found to range from 4–270 for various processes and the severity (S) index is found to range from 1–10. The RPN values > 100 and severity value ≥ 7 were chosen to flag safety improvement interventions. Number of steps with RPN ≥100 were found to be 6, 59 and 45 for the three centers. The corresponding values for S ≥ 7 are 24, 21 and 25 respectively. The range of RPN and S values for each center belong to different process steps and failure modes.

Conclusion:

These results show that interventions to improve safety is different for each center and it is associated with the skill level of the professional team as well as the technology used to provide radiosurgery treatment. The present study will very likely be a model for implementation of risk‐based prospective quality management program for SRS treatment in Brazil where currently there are 28 radiotherapy centers performing SRS. A complete FMEA for SRS for these three radiotherapy centers is currently under development.
SU‐E‐T‐129: Are Knowledge‐Based Planning Dose Estimates Valid for Distensible Organs?
Authors: Lalonde R , Heron D , Readshaw A , Huq M
Published: June 2015

Purpose:

Knowledge‐based planning programs have become available to assist treatment planning in radiation therapy. Such programs can be used to generate estimated DVHs and planning constraints for organs at risk (OARs), based upon a model generated from previous plans. These estimates are based upon the planning CT scan. However, for distensible OARs like the bladder and rectum, daily variations in volume may make the dose estimates invalid. The purpose of this study is to determine whether knowledge‐based DVH dose estimates may be valid for distensible OARs.

Methods:

The Varian RapidPlan™ knowledge‐based planning module was used to generate OAR dose estimates and planning objectives for 10 prostate cases previously planned with VMAT, and final plans were calculated for each. Five weekly setup CBCT scans of each patient were then downloaded and contoured (assuming no change in size and shape of the target volume), and rectum and bladder DVHs were recalculated for each scan. Dose volumes were then compared at 75, 60,and 40 Gy for the bladder and rectum between the planning scan and the CBCTs.

Results:

Plan doses and estimates matched well at all dose points., Volumes of the rectum and bladder varied widely between planning CT and the CBCTs, ranging from 0.46 to 2.42 for the bladder and 0.71 to 2.18 for the rectum, causing relative dose volumes to vary between planning CT and CBCT, but absolute dose volumes were more consistent. The overall ratio of CBCT/plan dose volumes was 1.02 ±0.27 for rectum and 0.98 ±0.20 for bladder in these patients.

Conclusion:

Knowledge‐based planning dose volume estimates for distensible OARs are still valid, in absolute volume terms, between treatment planning scans and CBCT's taken during daily treatment. Further analysis of the data is being undertaken to determine how differences depend upon rectum and bladder filling state.

This work has been supported by Varian Medical Systems.
SU‐E‐T‐130: Are Proton Gantries Needed? An Analysis of 4332 Patient Proton Gantry Treatment Plans From the Past 10 Years
Authors: Yan S , Lu H , Flanz J , Depauw N , Adams J , Gorissen BL , Wang Y , Daartz J , Bortfeld T
Published: June 2015

Purpose:

To ascertain the necessity of a proton gantry, as compared to the feasibility of using a horizontal fixed proton beam‐line for treatment with advanced technology.

Methods:

To calculate the percentage of patients that can be treated with a horizontal fixed beam‐line instead of a gantry, we analyze the distributions of beam orientations of our proton gantry patients treated over the past 10 years. We identify three horizontal fixed beam geometries (FIXED, BEND and MOVE) with the patient in lying and/or sitting positions. The FIXED geometry includes only table/chair rotations and translations. In BEND, the beam can be bent up/down for up to 20 degrees. MOVE allows for patient head/body angle adjustment. Based on the analysis, we select eight patients whose plan involves beams which are still challenging to achieve with a horizontal fixed beam. These beams are removed in the pencil beam scanning (PBS) plan optimized for the fixed beam‐line (PBS‐fix). We generate non‐coplanar PBS‐gantry plans for comparison, and perform a robustness analysis.

Results:

The percentage of patients with head‐and‐neck/brain tumors that can be treated with horizontal fixed beam is 44% in FIXED, 70% in 20‐degrees BEND, and 100% in 90‐degrees MOVE. For torso regions, 99% of the patients can be treated in 20‐degree BEND. The target coverage is more homogeneous with PBS‐fix plans compared to the clinical scattering treatment plans. The PBS‐fix plans reduce the mean dose to organs‐at‐risk by a factor of 1.1–28.5. PBS‐gantry plans are as good as PBS‐fix plans, sometimes marginally better.

Conclusion:

The majority of the beam orientations can be realized with a horizontal fixed beam‐line. Challenging non‐coplanar beams can be eliminated with PBS delivery. Clinical implementation of the proposed fixed beam‐line requires use of robotic patient positioning, further developments in immobilization, and image guidance. However, our results suggest that fixed beam‐lines can be as effective as gantries.
SU‐E‐T‐131: Artificial Neural Networks Applied to Overall Survival Prediction for Patients with Periampullary Carcinoma
Authors: Gong Y , Yu J , Yeung V , Palmer J , Yu Y , Lu B , Babinsky L , Burkhart R , Leiby B , Siow V , Lavu H , Rosato E , Winter J , Lewis N , Sama A , Mitchell E , Anne P , Hurwitz M , Yeo C , Bar‐Ad V , Xiao Y
Published: June 2015

Purpose:

Artificial neural networks (ANN) can be used to discover complex relations within datasets to help with medical decision making. This study aimed to develop an ANN method to predict two‐year overall survival of patients with peri‐ampullary cancer (PAC) following resection.

Methods:

Data were collected from 334 patients with PAC following resection treated in our institutional pancreatic tumor registry between 2006 and 2012. The dataset contains 14 variables including age, gender, T‐stage, tumor differentiation, positive‐lymph‐node ratio, positive resection margins, chemotherapy, radiation therapy, and tumor histology.After censoring for two‐year survival analysis, 309 patients were left, of which 44 patients (∼15%) were randomly selected to form testing set. The remaining 265 cases were randomly divided into training set (211 cases, ∼80% of 265) and validation set (54 cases, ∼20% of 265) for 20 times to build 20 ANN models. Each ANN has one hidden layer with 5 units. The 20 ANN models were ranked according to their concordance index (c‐index) of prediction on validation sets. To further improve prediction, the top 10% of ANN models were selected, and their outputs averaged for prediction on testing set.

Results:

By random division, 44 cases in testing set and the remaining 265 cases have approximately equal two‐year survival rates, 36.4% and 35.5% respectively. The 20 ANN models, which were trained and validated on the 265 cases, yielded mean c‐indexes as 0.59 and 0.63 on validation sets and the testing set, respectively. C‐index was 0.72 when the two best ANN models (top 10%) were used in prediction on testing set. The c‐index of Cox regression analysis was 0.63.

Conclusion:

ANN improved survival prediction for patients with PAC. More patient data and further analysis of additional factors may be needed for a more robust model, which will help guide physicians in providing optimal post‐operative care.

This project was supported by PA CURE Grant.
SU‐E‐T‐133: Assessing IMRT Treatment Delivery Accuracy and Consistency On a Varian TrueBeam Using the SunNuclear PerFraction EPID Dosimetry Software
Authors: Dieterich S , Trestrail E , Holt R , Saini S , Pfeiffer I , Kent M , Hansen K
Published: June 2015

Purpose:

To assess if the TrueBeam HD120 collimator is delivering small IMRT fields accurately and consistently throughout the course of treatment using the SunNuclear PerFraction software.

Methods:

7‐field IMRT plans for 8 canine patients who passed IMRT QA using SunNuclear Mapcheck DQA were selected for this study. The animals were setup using CBCT image guidance. The EPID fluence maps were captured for each treatment field and each treatment fraction, with the first fraction EPID data serving as the baseline for comparison. The Sun Nuclear PerFraction Software was used to compare the EPID data for subsequent fractions using a Gamma (3%/3mm) pass rate of 90%. To simulate requirements for SRS, the data was reanalyzed using a Gamma (3%/1mm) pass rate of 90%. Low‐dose, low‐ and high gradient thresholds were used to focus the analysis on clinically relevant parts of the dose distribution.

Results:

Not all fractions could be analyzed, because during some of the treatment courses the DICOM tags in the EPID images intermittently change from CU to US (unspecified), which would indicate a temporary loss of EPID calibration. This technical issue is still being investigated. For the remaining fractions, the vast majority (7/8 of patients, 95% of fractions, and 96.6% of fields) are passing the less stringent Gamma criteria. The more stringent Gamma criteria caused a drop in pass rate (90 % of fractions, 84% of fields). For the patient with the lowest pass rate, wet towel bolus was used. Another patient with low pass rates experienced masseter muscle wasting.

Conclusion:

EPID dosimetry using the PerFraction software demonstrated that the majority of fields passed a Gamma (3%/3mm) for IMRT treatments delivered with a TrueBeam HD120 MLC. Pass rates dropped for a DTA of 1mm to model SRS tolerances. PerFraction pass rates can flag missing bolus or internal shields.

Sanjeev Saini is an employee of Sun Nuclear Corporation. For this study, a pre‐release version of PerFRACTION 1.1 software from Sun Nuclear Corporation was used.
SU‐E‐T‐136: Assessment of Seasonal Linear Accelerator Output Variations and Associated Impacts
Authors: Bartolac S , Letourneau D
Published: June 2015

Purpose:

Application of process control theory in quality assurance programs promises to allow earlier identification of problems and potentially better quality in delivery than traditional paradigms based primarily on tolerances and action levels. The purpose of this project was to characterize underlying seasonal variations in linear accelerator output that can be used to improve performance or trigger preemptive maintenance.

Methods:

Review of runtime plots of daily (6 MV) output data acquired using in house ion chamber based devices over three years and for fifteen linear accelerators of varying make and model were evaluated. Shifts in output due to known interventions with the machines were subtracted from the data to model an uncorrected scenario for each linear accelerator. Observable linear trends were also removed from the data prior to evaluation of periodic variations.

Results:

Runtime plots of output revealed sinusoidal, seasonal variations that were consistent across all units, irrespective of manufacturer, model or age of machine. The average amplitude of the variation was on the order of 1%. Peak and minimum variations were found to correspond to early April and September, respectively. Approximately 48% of output adjustments made over the period examined were potentially avoidable if baseline levels had corresponded to the mean output, rather than to points near a peak or valley. Linear trends were observed for three of the fifteen units, with annual increases in output ranging from 2–3%.

Conclusion:

Characterization of cyclical seasonal trends allows for better separation of potentially innate accelerator behaviour from other behaviours (e.g. linear trends) that may be better described as true out of control states (i.e. non‐stochastic deviations from otherwise expected behavior) and could indicate service requirements. Results also pointed to an optimal setpoint for accelerators such that output of machines is maintained within set tolerances and interventions are required less frequently.
SU‐E‐T‐140: Automated Daily Patient Treatment Chart Checks Using Data Mining System
Authors: Dhabaan A , Jiang X , Schreibmann E , Elder E
Published: June 2015

Purpose:

The aim of this study is the use of data mining techniques to establish an automated daily chart check. This automated technique increases the likelihood of error capture before subsequent treatment delivery, allowing the delivery of the prescribed treatment course with high confidence level. Furthermore, the scope of inspected parameters expands compared to that able to be performed manually.

Methods:

Considering the significant number of parameters that are checked, performing chart check manually has a number of shortfalls such as human error, comparison of incorrect field and inability to verify MLC shape and leaves positions. Developing a computer‐driven automatic chart checkers eliminates human error, improves the accuracy and the frequency of the process, shortens the time of error discovery and correction, increases the number of parameters that are checked, allows inspection of parameters that are impossible to check manually and reduces the time the physicist need to spend to check a chart. This work will utilizes in house data mining framework (RT Metrix) to establish this QA function. The system utilize ARIA data base to verify the treatment delivery by comparing the plan record in ARIA to record verification which is the delivery parameters. Acceptable tolerances were defined in the software. If the delivery variation from the tolerance is minor then the system will show a warning flag but if the variation is major the system will flag the delivery as failed.

Results:

This system has been developed, tested, compared to ARIA Chart QA and is currently able to check parameters that routinely checked by the clinical physicist.

Conclusion:

The automated chart check system is feasible and offers great potential in the improvement of patient delivery quality assurance. The system can be developed further to include more QA functions.
SU‐E‐T‐142: Automatic Linac Log File: Analysis and Reporting
Authors: Gainey M , Rothe T
Published: June 2015

Purpose:

End to end QA for IMRT/VMAT is time consuming. Automated linac log file analysis and recalculation of daily recorded fluence, and hence dose, distribution bring this closer.

Methods:

Matlab (R2014b, Mathworks) software was written to read in and analyse IMRT/VMAT trajectory log files (TrueBeam 1.5, Varian Medical Systems) overnight, and are archived on a backed‐up network drive (figure). A summary report (PDF) is sent by email to the duty linac physicist. A structured summary report (PDF) for each patient is automatically updated for embedding into the R&V system (Mosaiq 2.5, Elekta AG). The report contains cross‐referenced hyperlinks to ease navigation between treatment fractions. Gamma analysis can be performed on planned (DICOM RTPlan) and treated (trajectory log) fluence distributions. Trajectory log files can be converted into RTPlan files for dose distribution calculation (Eclipse, AAA10.0.28, VMS).

Results:

All leaf positions are within +/−0.10mm: 57% within +/−0.01mm; 89% within 0.05mm. Mean leaf position deviation is 0.02mm. Gantry angle variations lie in the range −0.1 to 0.3 degrees, mean 0.04 degrees. Fluence verification shows excellent agreement between planned and treated fluence. Agreement between planned and treated dose distribution, the derived from log files, is very good.

Conclusion:

Automated log file analysis is a valuable tool for the busy physicist, enabling potential treated fluence distribution errors to be quickly identified. In the near future we will correlate trajectory log analysis with routine IMRT/VMAT QA analysis. This has the potential to reduce, but not eliminate, the QA workload.
SU‐E‐T‐145: Beam Characteristics of Flattening Filter Free Beams Including Low Dose Rate Setting
Authors: Uehara K , Ogata T , Nakayama M , Shinji T , Nishimura H , Masutani T , Ishihara T , Ejima Y , Sasaki R
Published: June 2015

Purpose:

In commissioning of volumetric modulated arc therapy (VMAT), it is necessary to evaluate the beam characteristics of various dose rate settings with potential to use. The aim of this study is to evaluate the beam characteristics of flattened and flattening filter free (FFF) including low dose rate setting.

Methods:

We used a Varian TrueBeam with Millennium 120 MLC. Both 6 and 10 MV beams with or without flattening filter were used for this study. To evaluate low‐dose rate FFF beams, specially‐designed leaf sequence files control out‐of‐field MLC leaf pair at constant dose rate ranging from 80 to 400 MU/min. For dose rate from 80 MU/min to the maximum usable value of all energies, beam output were measured using ionization chamber (CC04, IBA). The ionization chamber was inserted into water equivalent phantom (RT3000‐New, R‐tech), and the phantom was set with SAD of 100cm. The beam profiles were performed using the 2D diode array (Profiler2, Sun Nuclear). The SSD was set to 90cm and a combined 30cmx30cmx9cm phantom which consisted of solid water slabs was put on the device. All measurement were made using 100MU irradiation for 10cmx10cm jaw‐defined field size with a gantry angle of 0°.

Results:

In all energies, the dose rate dependences with beam output and variation coefficient were within 0.2% and 0.07%, respectively. The flatness and symmetry exhibited small variations (flatness ≤0.1 point and symmetry≤0.3 point at absolute difference).

Conclusion:

We had studied the characteristics of flattened and FFF beam over the 80 MU/min. Our results indicated that the beam output and profiles of FFF of TrueBeam linac were highly stable at low dose rate setting.
SU‐E‐T‐148: Benchmarks and Pre‐Treatment Reviews: A Study of Quality Assurance Effectiveness
Authors: Lowenstein J , Nguyen H , Roll J , Walsh A , Tailor A , Followill D
Published: June 2015

Purpose:

To determine the impact benchmarks and pre‐treatment reviews have on improving the quality of submitted clinical trial data.

Methods:

Benchmarks are used to evaluate a site's ability to develop a treatment that meets a specific protocol's treatment guidelines prior to placing their first patient on the protocol. A pre‐treatment review is an actual patient placed on the protocol in which the dosimetry and contour volumes are evaluated to be per protocol guidelines prior to allowing the beginning of the treatment. A key component of these QA mechanisms is that sites are provided timely feedback to educate them on how to plan per the protocol and prevent protocol deviations on patients accrued to a protocol. For both benchmarks and pre‐treatment reviews a dose volume analysis (DVA) was performed using MIM softwareTM. For pre‐treatment reviews a volume contour evaluation was also performed.

Results:

IROC Houston performed a QA effectiveness analysis of a protocol which required both benchmarks and pre‐treatment reviews. In 70 percent of the patient cases submitted, the benchmark played an effective role in assuring that the pre‐treatment review of the cases met protocol requirements. The 35 percent of sites failing the benchmark subsequently modified there planning technique to pass the benchmark before being allowed to submit a patient for pre‐treatment review. However, in 30 percent of the submitted cases the pre‐treatment review failed where the majority (71 percent) failed the DVA. 20 percent of sites submitting patients failed to correct their dose volume discrepancies indicated by the benchmark case.

Conclusion:

Benchmark cases and pre‐treatment reviews can be an effective QA tool to educate sites on protocol guidelines and to minimize deviations. Without the benchmark cases it is possible that 65 percent of the cases undergoing a pre‐treatment review would have failed to meet the protocols requirements.Support: U24‐CA‐180803
SU‐E‐T‐150: Brachytherapy QA Employing a High Resolution Liquid Filled Ionisation Chamber Array: Initial Experience and Limitations
Authors: Gainey M , Kollefrath M , Bruggmoser G
Published: June 2015

Purpose:

Verifying a complex 3D brachytherapy dose distribution by measurement is non‐trivial. Ideally a photon detector array should be independent of energy and angle, have high spatial resolution and be robust for routine clinical use.

Methods:

An iridium‐192 source was used. A PMMA jig was constructed comprising an outer slab and a central insert with eight milled channels for 1.33mm (outer diameter) steel needles, see figure. All calculations were performed using an empty CT study reconstructing eight virtual needles (QA‐CT), using the v2 source model (Elekta AG, Sweden). A high resolution liquid filled ionisation chamber array SRS1000, together with Verisoft software v6.0 (PTW Freiburg, Germany), was used to perform measurements of plans of increasing complexity to evaluate its suitability for device‐ and patient‐specific QA. The dimension of backscatter material was investigated. The patient plan dwell time distribution was entered manually into the QA‐CT and the dose distribution was calculated.

Results:

Our measurements indicate that the array is independent of energy and angle. The resulting measured dose values are linearly interpolated to 2025 values. Shifts of 1mm of the entire needle are readily detectable. Individual dwell position shifts (2.5mm) are also readily measurable. Moreover a dwell time increase of 1 second both in the edge and central region are detectable.

Conclusion:

The high resolution SRS1000 array is a powerful instrument for brachytherapy QA enabling 977 simultaneous measurements to be performed. Our measurements suggest 60mm of RW3 backscatter material upstream and downstream are sufficient. Local percentage difference analysis is useful for device based QA, normalized relative percentage difference is arguably better for patient specific QA. Automated transfer of patient plan dwell time distribution to the QA plan is required to enable a comprehensive patient QA study to be performed. Moreover the described measurement technique can be used for commissioning new brachytherapy applicators.
SU‐E‐T‐151: Breathing Synchronized Delivery (BSD) Planning for RapicArc Treatment
Authors: Lu W , Chen M , Jiang S
Published: June 2015

Purpose:

To propose a workflow for breathing synchronized delivery (BSD) planning for RapicArc treatment.

Methods:

The workflow includes three stages: screening/simulation, planning, and delivery. In the screening/simulation stage, a 4D CT with the corresponding breathing pattern is acquired for each of the selected patients, who are able to follow their own breathing pattern. In the planning stage, one breathing phase is chosen as the reference, and contours are delineated on the reference image. Deformation maps to other phases are performed along with contour propagation. Based on the control points of the initial 3D plan for the reference phase and the respiration trace, the correlation with respiration phases, the leaf sequence and gantry angles is determined. The beamlet matrices are calculated with the corresponding breathing phase and deformed to the reference phase. Using the 4D dose evaluation tool and the original 3D plan DVHs criteria, the leaf sequence is further optimized to meet the planning objectives and the machine constraints. In the delivery stage, the patients are instructed to follow the programmed breathing patterns of their own, and all other parts are the same as the conventional Rapid‐Arc delivery.

Results:

Our plan analysis is based on comparison of the 3D plan with a static target (SD), 3D plan with motion delivery (MD), and the BSD plan. Cyclic motion of range 0 cm to 3 cm was simulated for phantoms and lung CT. The gain of the BSD plan over MD is significant and concordant for both simulation and lung 4DCT, indicating the benefits of 4D planning.

Conclusion:

Our study shows that the BSD plan can approach the SD plan quality. However, such BSD scheme relies on the patient being able to follow the same breathing curve that is used in the planning stage during radiation delivery.

Funded by Varian Medical Systems.
SU‐E‐T‐154: Calculation of Tissue Dose Point Kernels Using GATE Monte Carlo Simulation Toolkit to Compare with Water Dose Point Kernel
Authors: Khazaee M , Asl A Kamali , Geramifar P
Published: June 2015

Purpose:

the objective of this study was to assess utilizing water dose point kernel (DPK)instead of tissue dose point kernels in convolution algorithms.to the best of our knowledge, in providing 3D distribution of absorbed dose from a 3D distribution of the activity, the human body is considered equivalent to water. as a Result tissue variations are not considered in patient specific dosimetry.

Methods:

In this study Gate v7.0 was used to calculate tissue dose point kernel. the beta emitter radionuclides which have taken into consideration in this simulation include Y‐90, Lu‐177 and P‐32 which are commonly used in nuclear medicine. the comparison has been performed for dose point kernels of adipose, bone, breast, heart, intestine, kidney, liver, lung and spleen versus water dose point kernel.

Results:

In order to validate the simulation the Result of 90Y DPK in water were compared with published results of Papadimitroulas et al (Med. Phys., 2012). The results represented that the mean differences between water DPK and other soft tissues DPKs range between 0.6 % and 1.96% for 90Y, except for lung and bone, where the observed discrepancies are 6.3% and 12.19% respectively. The range of DPK difference for 32P is between 1.74% for breast and 18.85% for bone. For 177Lu, the highest difference belongs to bone which is equal to 16.91%. For other soft tissues the least discrepancy is observed in kidney with 1.68%.

Conclusion:

In all tissues except for lung and bone, the results of GATE for dose point kernel were comparable to water dose point kernel which demonstrates the appropriateness of applying water dose point kernel instead of soft tissues in the field of nuclear medicine.
SU‐E‐T‐159: Characteristics of Fiber‐Optic Radiation Sensor for Proton Therapeutic Beam
Authors: Son J , Kim M , Hwang U , Park J , Lim Y , Lee S , Park S , Yoon M , Shin D
Published: June 2015

Purpose:

A fiber‐optic radiation sensor using Cerenkov radiation has been widely studied for use as a dosimeter for proton therapeutic beam. Although the fiber‐optic radiation sensor has already been investigated for proton therapeutic, it has been examined relatively little work for clinical therapeutic proton beams. In this study, we evaluated characteristics of a fiber‐optic radiation sensor for clinical therapeutic proton beams. We experimentally evaluated dose‐rate dependence, dose response and energy dependence for the proton beam.

Methods:

A fiber‐optic radiation sensor was placed in a water phantom. Beams with energies of low, middle and high were used in the passively‐scattered proton therapeutic beam at the National Cancer Center in Korea. The sensor consists of two plastic optical fibers (POF). A reference POF and 2 cm longer POF were used to utilize the subtraction method for having sensitive volume. Each POF is optically coupled to the Multi‐Anode Photo Multiplier Tube (MAPMT) and the MAPMT signals are processed using National Instruments Data Acquisition System (NI‐DAQ). We were investigated dosimetric properties including dose‐rate dependence, dose response and energy dependence.

Results:

We have successfully evaluated characteristics of a fiber optic radiation sensor using Cerenkov radiation. The fiber‐optic radiation sensor showed the dose response linearity and low energy dependence. In addition, as the dose‐rate was increased, Cerenkov radiation increased linearly.

Conclusion:

We evaluated the basic characteristics of the fiber optic radiation sensor, the dosimetry tool, to raise the quality of proton therapy. Based on the research, we developed a real time dosimetry system of the optic fiber to confirm the real time beam position and energy for therapeutic proton pencil beam.
SU‐E‐T‐160: Characterization and Monitoring of Linear Accelerator Gantry Radiation Isocenter Motion
Authors: Letourneau D , Amin N , Wang K , Norrlinger B , Jaffray D , McNiven A
Published: June 2015

Purpose:

To characterize the motion of the radiation isocenter, over time, as a function of gantry rotation for multiple linear accelerators (linacs). Two semi‐automated image‐based quality control (QC) test workflows were designed to achieve this goal.

Methods:

The full QC‐test workflow for motion characterization consisted of acquiring 16 megavoltage images at 8 gantry angles of a ball‐bearing suspended off the end of the couch. Performance constancy was assessed using a shortened QC‐test workflow which consisted of imaging a cube phantom placed on the couch (5 images at 4 gantry angles). Both workflows use an image processing algorithm to determine the field center and phantom position on each image and computed radiation isocenter motion as a function of gantry angle. Motion was characterized for 9 linacs of same model and performance monitored for 2 months on 3 linacs.

Results:

The maximum isocenter motion determined with the full‐workflow for 9 linacs was within 0.38–0.79 mm. The shortened‐workflow usually agreed within 0.1 mm with the full‐workflow and the time required for these methods was about 4 and 15 min, respectively. For all linacs, the isocenter motion perpendicular to the gantry rotation plane followed a consistent pattern with maximum amplitude of 0.36–0.59 mm. In the gantry rotation plane, the variation among linacs was higher and the beam axis described a circle of up to 0.6 mm radius around the gantry axis of rotation (2 linacs). The radiation isocenter motion was stable as a function of time for the monitored linacs and was within ±0.1 mm of the average.

Conclusion:

Radiation isocenter motion parallel and perpendicular to the gantry rotation plane was characterized. In the gantry rotation plane, beam spot positioning adjustment might be used to reduce the observed radiation isocenter motion. A shortened‐workflow was designed and enables performance monitoring over time.
SU‐E‐T‐164: Characterization of Breast Deformation During Accuboost TM Treatment
Authors: Garcia‐Cobian J , Liu F
Published: June 2015

Purpose:

During treatment using AccuboostTM (Advanced Radiation Therapy, Tyngsboro, MA) applicators the breast is compressed between two paddles in order to immobilize it. This causes the breast tissue to expand. The purpose of this study was to analyze the nature of this deformation.

Methods:

CT scans of a breast phantom (Computerized Imaging Reference Systems, Norfolk, VA) were acquired at different compressions in the cranial‐caudal (CC) direction. These were performed by placing the phantom between two plates whose position is controlled by a manual crank. The phantom masses were contoured in order to simulate the clips placed after surgery. For all scans the mean distance between the masses was computed. Additionally, deformable registration was performed between two scans using the Velocity software (Varian Medical Systems, Palo Alto, CA) to assess the shifts of each of these masses.

Results:

As the compression increases so does the average distance between the masses. The relationship between deformation and compression is not linear. Additionally, the largest displacements are in the direction of compression. The mean shift is 1.8mm. The shifts in the RT‐LT direction and ANT‐POST direction are 1.1 mm and 0.7 mm respectively

Conclusion:

When treating patients the clips shift their position as a Result of the plate compression. For CC compressions this is not a problem if they shift their position primarily in the superior‐inferior direction. The problem of not being able to cover all clips (target area) can arise when they shift position on a plane perpendicular to the patient. For clips which are already near the chest wall, care should be exercised not to compress the breast in such a way as to move those clips out of the treatable area.These preliminary results show a larger shift in the RT‐LT direction than the ANT‐POST one. Further research will seek to either confirm or infirm this.
SU‐E‐T‐165: Characterization of Dose Distributions in High‐Dose‐Rate Surface Brachytherapy
Authors: Buzurovic I , Hansen J , Bhagwat M , O'Farrell D , Damato A , Friesen S , Devlin P , Cormack R
Published: June 2015

Purpose:

To characterize dose distributions in high‐dose‐rate(HDR) surface brachytherapy using an Ir‐125 source for different geometries, field sizes and topology of the clinical targets(CT). To investigate the depth doses at the central axis(CAX), edges of the treatment fields(E), and lateral dose distributions(L) present when using flap applicators in skin cancer treatments.

Methods:

When malignancies diagnosed on the skin are treated, various geometries of the CT require proper adaptation of the flap or custom‐made applicators to the treatment site. Consequently, the dose at the depth on CAX and field edges changes with variation of the curvatures and size of the applicators. To assess the dose distributions, we created a total of 10 treatment plans(TP) for 10×10 and 20×20 field sizes(FS) with a step size of 1cm. The geometry of the applicators was: planar(PA), curved to 30(CA30) and 60(CA60) degrees with respect to the CAX, half‐cylinder(HC), and cylindrical shape(CS). One additional TP was created in which the applicators were positioned to form a dome shape(DS) with a diameter of 16cm. This TP was used to emulate treatment of the average sized scalp. All TPs were optimized to deliver a prescription dose at 8mm equidistantly from the planes containing the dwell positions. This optimization is equivalent to the clinical arrangement since the SSD for the flap applicators is 5mm and the prescription depth is 3mm in the majority of clinical cases.

Results:

The depths (in mm) of the isodose lines were: FS(10×10):PA[90%(9.1CAX,8.0E,7.6L),50%(28.3CAX,20E,17.3L), 25%(51.1CAX,40E,27L)],CA30[90%(10.3CAX,8.2E,7.9L),50%(32.1CAX, 16.2E,15.8L),25%(61.3CAX,36.7E,31.8L)],CA60[90%(12.2CAX,6.1E,6.3L ),50%(47CAX,14E,16.6L),25%(70.8CAX,31.9E,35.4L)],HC[90%(11.1CA X,6.3E,7.3L),50%(38.3CAX,14.6E,16.1L),25%(66.2CAX,33.8E,34.2L)];FS (20×20):PA[90%(11.1CAX,9.0E,7.0L),50%(34.4CAX,21.9E,15.3L),25%(7 0.4CAX,50.9E,34.8L)],CA30[90%(10.9CAX,7.5E,7.1L),50%(38.8CAX,16. 7E,15.4L),25%(80.7CAX,39.9E,35.7L)],HC[90%(11.1CAX,10.9E,10.6L),5 0%(34.4CAX,38.8E,47.2L),25%(70.4CAX,80.7E,96.6L);DS[90%(12.1CA X,8.5E,6.8L),50%(60.6CAX,17.7E,15.8L),25%(109.6CAX,40.3E,34.3L)].

Conclusion:

These results can be used for the approximate calculation and quick assessment of the radiation dose to the organs‐at‐risk at depth (heart,brain,thyroid, optical nerve) or at the surface distance from the CT (breast,eyes, gonads), and only the geometry of the CT needs to be measured. Understanding of the dose distributions in HDR surface brachytherapy may improve clinical decision making process.
SU‐E‐T‐172: Characterization of TLD‐100 (LiF:Mg,Ti) Microcube Energy Response in a Cylindrical Chamber Phantom
Authors: Desai V , Hammer C , Kunugi K , Culberson W , DeWerd L
Published: June 2015

Purpose:

To characterize the energy response of TLD‐100 microcubes inside a Virtual Water chamber phantom.

Methods:

Four TLD microcubes were placed inside a water‐proof Virtual Water (VW) chamber phantom and irradiated to a known dose on a Varian linac in a 1D water tank. These chamber phantoms were then replaced by TLD‐100 chips inside a separate VW paddle and irradiated to the same dose. Each energy response reading was calculated as light output per unit dose in nC/cGy and normalized to a calibration set irradiated to the same dose in 60Co. The differences in response between the TLD chips and microcubes were then analyzed.

Results:

Across all energies, the average microcube response was less sensitive to energy than the average chip response with both falling consistently within 2.8% of previously established values in the literature

Conclusion:

TLD microcubes showed a lower average sensitivity to energy than their TLD chip counterparts. The use of TLD‐100 microcubes inside the chamber phantom was validated against TLD‐100 chips inside of VW paddles.
SU‐E‐T‐177: Clinical Experience with Spirometer Guided Breath Hold Lung SBRT
Authors: Liu H , Manning M , Sintay B , Maurer J , Hayes L , Wiant D
Published: June 2015

Purpose:

Tumor motion in lung SBRT is typically managed by creating an internal target volume (ITV) based on 4D‐CT information. Another option, which may reduce lung dose and imaging artifact, is to use a breath hold (BH) during simulation and delivery. Here we evaluate the reproducibility of tumor position at repeated BH using a newly released spirometry system.

Methods:

Three patients underwent multiple BH CT's at simulation. All patients underwent a BH cone beam CT (CBCT) prior to each treatment. All image sets were registered to a patient's first simulation CT based on local bony anatomy. The gross tumor volume (GTV), and the diaphragm or the apex of the lung were contoured on the first image set and expanded in 1 mm increments until the GTVs and diaphragms on all image sets were included inside an expanded structure. The GTV and diaphragm margins necessary to encompass the structures were recorded.

Results:

The first patient underwent 2 BH CT's and fluoroscopy at simulation, the remaining patients underwent 3 BH CT's at simulation. In all cases the GTV's remained within 1 mm expansions and the diaphragms remained within 2 mm expansions on repeat scans. Each patient underwent 3 daily BH CBCT's. In all cases the GTV's remained within a 2 mm expansions, and the diaphragms (or lung apex in one case) remained within 2 mm expansions at daily BH imaging.

Conclusions:

These case studies demonstrate spirometry as an effective tool for limiting tumor motion (and imaging artifact) and facilitating reproducible tumor positioning over multiple set‐ups and BH's.

This work was partially supported by Qfix.
SU‐E‐T‐182: Clinical Implementation of TG71‐Based Electron MU Calculation and Comparison with a Commercial Secondary Calculation
Authors: Xu H , Guerrero M , Yang X , Chen S , Langen K , Prado K , Schinkel C
Published: June 2015

Purpose:

The TG‐71 report was published in 2014 to present standardized methodologies for MU calculations and determination of dosimetric quantities. This work explores the clinical implementation of a TG71‐based electron MU calculation algorithm and compares it with a recently released commercial secondary calculation program–Mobius3D (Mobius Medical System, LP).

Methods:

TG‐71 electron dosimetry data were acquired, and MU calculations were performed based on the recently published TG‐71 report. The formalism in the report for extended SSD using air‐gap corrections was used. The dosimetric quantities, such PDD, output factor, and f‐air factors were incorporated into an organized databook that facilitates data access and subsequent computation. The Mobius3D program utilizes a pencil beam redefinition algorithm. To verify the accuracy of calculations, five customized rectangular cutouts of different sizes–6×12, 4×12, 6×8, 4×8, 3×6 cm2–were made. Calculations were compared to each other and to point dose measurements for electron beams of energy 6, 9, 12, 16, 20 MeV. Each calculation / measurement point was at the depth of maximum dose for each cutout in a 10×10 cm2 or 15×15cm2 applicator with SSDs 100cm and 110cm. Validation measurements were made with a CC04 ion chamber in a solid water phantom for electron beams of energy 9 and 16 MeV.

Results:

Differences between the TG‐71 and the commercial system relative to measurements were within 3% for most combinations of electron energy, cutout size, and SSD. A 5.6% difference between the two calculation methods was found only for the 6MeV electron beam with 3×6 cm2cutout in the 10×102cm applicator at 110cm SSD. Both the TG‐71 and the commercial calculations show good consistency with chamber measurements: for 5 cutouts, <1% difference for 100cm SSD, and 0.5–2.7% for 110cm SSD.

Conclusions:

Based on comparisons with measurements, a TG71‐based computation method and a Mobius3D program produce reasonably accurate MU calculations for electron‐beam therapy.
SU‐E‐T‐185: Clinically‐Relevant Investigation of Flattening Filter Free Skin Dose
Authors: Guy C , Karki K , Sharma M , Kim S
Published: June 2015

Purpose:

Flattening‐filter‐free (FFF) beams are increasingly used for small‐field treatments due to inherent advantages like higher MU efficiency and reduced treatment time and scatter dose. Removal of the flattening‐filter increases the electron contamination and low‐energy x‐rays. As such, surface‐dose characteristics are different from traditional flattened (FF) beams. The goal of this work is to investigate surface dose of 6/10 MV FFF and FF beams under conditions representative of emerging complex techniques like small‐field stereotactic treatments which use small fields formed with multi‐leaf‐collimators (MLCs) at closer SSDs.

Methods:

A parallel‐plate PTW Markus‐chamber (N23343) placed in custom air‐ and water‐equivalent phantoms was used to measure surface‐dose at 2/3/4/6/8/10/20/30 cm2 field sizes, at 80/90/100 cm source‐to‐surface distances, and at fields defined by jaws and MLCs. The effect of dose rate (600 and 1400/2400 MU/min) was also investigated at 100 cm SSD. Measurements were performed on TrueBeam linac (Varian Medical Systems, Palo Alto, CA) for 6X/6XFFF/10X/10XFFF beam energies.

Results:

No dose‐rate dependence was seen for FFF skin‐dose. Air‐phantom measurements were, on average, 5±3% larger than for water‐phantom measurements. With SSD increase from 80 to 100 cm, skin‐dose decreased by an average of 3.9±2.5%. FFF beams were found to be more sensitive to SSD changes in comparison to FF beams. The difference in skin dose between MLC‐ and jaw‐fields was less variable with field size for FFF compared to FF beams. 10 MV beams showed greater difference in FFF‐to‐FF ratio, 50% (jaws) and 22% (MLC), between the largest and smallest field sizes compared to 6 MV beams, 30% (jaws) and 9% (MLC).

Conclusion:

Under clinically‐relevant conditions, surface dose for FFF beams was higher at small field size (<10 cm), lower at largest field size (30 cm), more sensitive to SSD changes, and had less variation with field size compared to dose for FF beams.
SU‐E‐T‐186: Cloud‐Based Quality Assurance Application for Linear Accelerator Commissioning
Authors: Rogers J
Published: June 2015

Purpose:

To identify anomalies and safety issues during data collection and modeling for treatment planning systems

Methods:

A cloud‐based quality assurance system (AQUIRE ‐ Automated QUalIty REassurance) has been developed to allow the uploading and analysis of beam data aquired during the treatment planning system commissioning process. In addition to comparing and aggregating measured data, tools have also been developed to extract dose from the treatment planning system for end‐to‐end testing. A gamma index is perfomed on the data to give a dose difference and distance‐to‐agreement for validation that a beam model is generating plans consistent with the beam data collection.

Results:

Over 20 linear accelerators have been commissioning using this platform, and a variety of errors and potential saftey issues have been caught through the validation process. For example, the gamma index of 2% dose, 2mm DTA is quite sufficient to see curves not corrected for effective point of measurement. Also, data imported into the database is analyzed against an aggregate of similar linear accelerators to show data points that are outliers. The resulting curves in the database exhibit a very small standard deviation and imply that a preconfigured beam model based on aggregated linear accelerators will be sufficient in most cases.

Conclusion:

With the use of this new platform for beam data commissioning, errors in beam data collection and treatment planning system modeling are greatly reduced. With the reduction in errors during acquisition, the resulting beam models are quite similar, suggesting that a common beam model may be possible in the future. Development is ongoing to create routine quality assurance tools to compare back to the beam data acquired during commissioning.

I am a medical physicist for Alzyen Medical Physics, and perform commissioning services
SU‐E‐T‐193: Commissioning of An IntraOp Mobetron
Authors: Grzetic S , Hessler J , Carlson M , James Arthur G.
Published: June 2015

Purpose:

This study will describe the commissioning process of an Intra‐Op Mobetron following the guidance of TG72 and includes a detailed method for measuring gap factors.

Methods:

Beam data was collected for 6, 9, and 12MeV electrons on the Mobetron using a PTW water tank and a Markus chamber. Commissioning data was collected for 3 sets of cones (0°, 15°, and 30° with respect to the water surface) that ranged in size from 3cm to 10cm diameter in half centimeter increments. Profiles were collected at six depths for all integer cones. PDI's were taken for all cones in a path perpendicular to the water surface and then converted to dose using MEPHYSTO's internal algorithm. The depth of maximum dose was determined from the PDD's and used for measurement of output factors. Output factors were normalized to the 10cm flat cone. Gap factors were measured for all flat cones by raising the cone away from the water surface in defined gaps. These gap factors were measured at dmax for gaps of 1cm to 5cm in 1cm increments Gap factors and effective SSD values were calculated.

Results:

Output factors measured for all cones were within 3% of the representative beam data for flat cones. There is no published data on beveled cones, but the angled cone output factors agreed with the flat cones within 5%. Gap factors follow a linear pattern with the output decreasing 3–7% per centimeter gap depending on the size of the cone and energy. Effective SSD values calculated and fit a 3rd order polynomial curve with R2>0.98 for all energies.

Conclusion:

Commissioning of an Intra‐Op Mobetron was completed with general agreement to published data. New data was published for beveled cones and a method for determining gap factors was established.