bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐F‐T‐143: Implementation of a Correction‐Based Output Model for a Compact Passively Scattered Proton Therapy System
Authors: Ferguson S , Ahmad S , Chen Y , Ferreira C , Islam M , Keeling V , Lau A , Jin H
Published: July 2016

Purpose:

To commission and investigate the accuracy of an output (cGy/MU) prediction model for a compact passively scattered proton therapy system.

Methods:

A previously published output prediction model (Sahoo et al, Med Phys, 35, 5088–5097, 2008) was commissioned for our Mevion S250 proton therapy system. This model is a correction‐based model that multiplies correction factors (d/MUwnc=ROFxSOBPF xRSFxSOBPOCFxOCRxFSFxISF). These factors accounted for changes in output due to options (12 large, 5 deep, and 7 small), modulation width M, range R, off‐center, off‐axis, field‐size, and off‐isocenter. In this study, the model was modified to ROFxSOBPFxRSFxOCRxFSFxISF_OCFxGACF by merging SOBPOCF and ISF for simplicity and introducing a gantry angle correction factor (GACF). To commission the model, outputs over 1,000 data points were taken at the time of the system commissioning. The output was predicted by interpolation (1D for SOBPF, FSF, and GACF; 2D for RSF and OCR) with inverse‐square calculation (ISF_OCR). The outputs of 273 combinations of R and M covering total 24 options were measured to test the model. To minimize fluence perturbation, scattered dose from range compensator and patient was not considered. The percent differences between the predicted (P) and measured (M) outputs were calculated to test the prediction accuracy ([P‐M]/Mx100%).

Results:

GACF was required because of up to 3.5% output variation dependence on the gantry angle. A 2D interpolation was required for OCR because the dose distribution was not radially symmetric especially for the deep options. The average percent differences were −0.03±0.98% (mean±SD) and the differences of all the measurements fell within ±3%.

Conclusion:

It is concluded that the model can be clinically used for the compact passively scattered proton therapy system. However, great care should be taken when the field‐size is less than 5×5 cm2 where a direct output measurement is required due to substantial output change by irregular block shape.
SU‐F‐T‐146: Comparing Monte Carlo Simulations with Commissioning Beam Data for Mevion S250 Proton Therapy System
Authors: Prusator M , Jin H , Ahmad S , Chen Y
Published: July 2016

Purpose:

To evaluate the Monte Carlo simulated beam data with the measured commissioning data for the Mevion S250 proton therapy system.

Method:

The Mevion S250 proton therapy system utilizes a passive double scattering technique with a unique gantry mounted superconducting accelerator and offers effective proton therapy in a compact design concept. The field shaping system (FSS) includes first scattering foil, range modulator wheel (RMW), second scattering foil and post absorber and offers two field sizes and a total of 24 treatment options from proton range of 5 cm to 32 cm. The treatment nozzle was modeled in detail using TOPAS (TOolkit for PArticle Simulation) Monte Carlo code. The timing feathers of the moving modulator wheels were also implemented to generate the Spread Out Bragg Peak (SOBP). The simulation results including pristine Bragg Peak, SOBP and dose profiles were compared with the data measured during beam commissioning.

Results:

The comparison between the measured data and the simulation data show excellent agreement. For pristine proton Bragg Peaks, the simulated proton range (depth of distal 90%) values agreed well with the measured range values within 1 mm accuracy. The differences of the distal falloffs (depth from distal 80% to 20%) were also found to be less than 1 mm between the simulations and measurements. For the SOBP, the widths of modulation (depth of proximal 95% to distal 90%) were also found to agree with the measurement within 1 mm. The flatness of the simulated and measured lateral profiles was found to be 0.6 % and 1.1 %, respectively.

Conclusion:

The agreement between simulations and measurements demonstrate that TOPAS could be used as a viable platform to proton therapy applications. The matched simulation results offer a great tool and open opportunity for variety of applications.
SU‐F‐T‐160: Commissioning of a Single‐Room Double‐Scattering Proton Therapy System
Authors: Jin H , Ahmad S , Chen Y , Keeling V , Lau A , Islam M , Ferreira C , Ferguson S
Published: July 2016

Purpose:

To report the detailed commissioning experience for a compact double‐scattering Mevion S250 proton therapy system at a University Cancer Center site.

Methods:

The commissioning of the proton therapy system mainly consisted of ensuring integrity of mechanical and imaging system, beam data collection, and commissioning of a treatment planning system (TPS). First, mechanical alignment and imaging were tested including safety, interlocks, positional accuracy of couch and gantry, image quality, mechanical and imaging isocenter and so on. Second, extensive beam data (outputs, PDDs, and profiles) were collected and analyzed through effective sampling of range (R) and modulation width (M) from 24 beam options. Three different output (cGy/MU) prediction models were also commissioned as primary and secondary MU calculation tool. Third, the Varian Eclipse TPS was commissioned through five sets of data collections (in‐water Bragg peak scans, in‐air longitudinal fluence scans, in‐air lateral profiles, in‐air half‐beam profiles, and an HU‐to‐stopping‐power conversion curve) and accuracy of TPS calculation was tested using in‐water scans and dose measurements with a 2D array detector with block and range compensator. Finally, an anthropomorphic phantom was scanned and heterogeneity effects were tested by inserting radiochromic films in the phantom and PET activation scans for range verification in conjunction with end‐to‐end test.

Results:

Beam characteristics agreed well with the vendor specifications; however, minor mismatches in R and M were found in some measurements during the beam data collection. These were reflected into the TPS commissioning such that the TPS could accurately predict the R and M within tolerance levels. The output models had a good agreement with measured outputs (<3% error). The end‐to‐end test using the film and PET showed reasonably the TPS predicted dose, R and M in heterogeneous medium.

Conclusion:

The proton therapy system was successfully commissioned and was released for clinical use.
SU‐F‐T‐163: Improve Proton Therapy Efficiency: Report of a Workshop
Authors: Zheng Y , Flanz J , Mah D , Pankuch M , Beltran C , Robison B , Kreydick B , Schreuder A
Published: July 2016

Purpose:

The technology of proton therapy, especially the pencil beam scanning technique, is evolving very quickly. However, the efficiency of proton therapy seems to lag behind conventional photon therapy. The purpose of the abstract is to report on the findings of a workshop on improvement of QA, planning and treatment efficiency in proton therapy.

Methods:

A panel of physicists, clinicians, and vendor representatives from over 18 institutions in the United States and internationally were convened in Knoxville, Tennessee in November, 2015. The panel discussed several topics on how to improve proton therapy efficiency, including 1) lean principle and failure mode and effects analysis, 2) commissioning and machine QA, 3) treatment planning, optimization and evaluation, 4) patient positioning and IGRT, 5) vendor liaison and machine availability, and 6) staffing, education and training.

Results:

The relative time needed for machine QA, treatment planning & check in proton therapy was found to range from 1 to 2.5 times of that in photon therapy. Current status in proton QA, planning and treatment was assessed. Key areas for efficiency improvement, such as elimination of unnecessary QA items or steps and development of efficient software or hardware tools, were identified. A white paper to summarize our findings is being written.

Conclusion:

It is critical to improve efficiency by developing reliable proton beam lines, efficient software tools on treatment planning, optimization and evaluation, and dedicated proton QA device. Conscious efforts and collaborations from both industry leaders and proton therapy centers are needed to achieve this goal and further advance the technology of proton therapy.
SU‐F‐T‐176: Therapeutic Proton Beam Range Measurement Method with EBT3 Film
Authors: Lee N
Published: July 2016

Purpose:

Ocular proton therapy has the following advantages: i) sparing optic nerve, ii) the minimal dose is delivered to surrounding normal tissues. Since the proton therapy center was opened in 2007, 30 patients with ocular tumor have been treated at National Cancer Center using single scattering technique. To develop a solid eye phantom which can verify the output and the beam range with EBT3 film for independent patient QA in ocular proton therapy.

Methods:

The proton therapy is very effective to treat ocular tumor, because of the Bragg peak feature. In general, the beam shape of eye treatment is about 3 cm in diameter and the beam range is under 5 cm. However, proton therapy has uncertainty of beam range problem due to various stopping power of normal tissue, bone, air and so on, so that we should verify the beam range before treatment. For this purpose, a new PMMA phantom with wedge has been developed to use the film dosimetry and the ionization chamber. It is able to place a film on the slope of the phantom, which the spread out Bragg Peak by the water equivalent thickness value of PMMA can be made on the film. We considered to relation with quenching effect of proton energy and range for simple second check. In addition, the ionization chamber (Pin‐point chamber, PTW 31014) can be inserted into a hole in the phantom to measure the absolute dose.

Results:

The output difference and beam range difference were less than 2% and 1.0 mm, respectively, between the measurement and the plan.

Conclusion:

An eye phantom was developed and its performance was evaluated successfully and it was useful to verify the output. Also with EBT3 film with the quenching effect for measurement depth‐dose profile, range to patient QA
SU‐F‐T‐186: A Treatment Planning Study of Normal Tissue Sparing with Robustness Optimized IMPT, 4Pi IMRT, and VMAT for Head and Neck Cases
Authors: Zhang J , Nguyen D , Woods K , Tran A , Li X , Ding X , Kabolizadeh P , Guerrero T , Sheng K
Published: July 2016

Purpose:

We performed a retrospective dosimetric comparison study between the robustness optimized Intensity Modulated Proton Therapy (RO‐IMPT), volumetric‐modulated arc therapy (VMAT), and the non‐coplanar 4? intensity modulated radiation therapy (IMRT). These methods represent the most advanced radiation treatment methods clinically available. We compare their dosimetric performance for head and neck cancer treatments with special focus on the OAR sparing near the tumor volumes.

Methods:

A total of 11 head and neck cases, which include 10 recurrent cases and one bilateral case, were selected for the study. Different dose levels were prescribed to tumor target depending on disease and location. Three treatment plans were created on commercial TPS systems for a novel noncoplanar 4π method (20 beams), VMAT, and RO‐IMPT technique (maximum 4 fields). The maximum patient positioning error was set to 3 mm and the maximum proton range uncertainty was set to 3% for the robustness optimization. Line dose profiles were investigated for OARs close to tumor volumes.

Results:

All three techniques achieved 98% coverage of the CTV target and most photon plans had less than 110% of the hot spots. The RO‐IMPT plans show superior tumor dose homogeneity than 4? and VMAT plans. Although RO‐IMPT has greater R50 dose spillage to the surrounding normal tissue than 4π and VMAT, the RO‐IMPT plans demonstrate better or comparable OAR (parotid, mandible, carotid, oral cavity, pharynx, and etc.) sparing for structures closely abutting tumor targets.

Conclusion:

The RO‐IMPT's ability of OAR sparing is benchmarked against the C‐arm linac based non‐coplanar 4π technique and the standard VMAT method. RO‐IMPT consistently shows better or comparable OAR sparing even for tissue structures closely abutting treatment target volume. RO‐IMPT further reduces treatment uncertainty associated with proton therapy and delivers robust treatment plans to both unilateral and bilateral head and neck cancer patients with desirable treatment time.
SU‐F‐T‐191: 4D Dose Reconstruction of Intensity Modulated Proton Therapy (IMPT) Based On Breathing Probability Density Function (PDF) From 4D Cone Beam Projection Images: A Study for Lung Treatment
Authors: Zhou J , Ding X , Liang J , Zhang J , Wang Y , Yan D
Published: July 2016

Purpose:

With energy repainting in lung IMPT, the dose delivered is approximate to the convolution of dose in each phase with corresponding breathing PDF. This study is to compute breathing PDF weighted 4D dose in lung IMPT treatment and compare to its initial robust plan.

Methods:

Six lung patients were evaluated in this study. Amsterdam shroud image were generated from pre‐treatment 4D cone‐beam projections. Diaphragm motion curve was extract from the shroud image and the breathing PDF was generated. Each patient was planned to 60 Gy (12GyX5). In initial plans, ITV density on average CT was overridden with its maximum value for planning, using two IMPT beams with robust optimization (5mm uncertainty in patient position and 3.5% range uncertainty). The plan was applied to all 4D CT phases. The dose in each phase was deformed to a reference phase. 4D dose is reconstructed by summing all these doses based on corresponding weighting from the PDF. Plan parameters, including maximum dose (Dmax), ITV V100, homogeneity index (HI=D2/D98), R50 (50%IDL/ITV), and the lung‐GTV's V12.5 and V5 were compared between the reconstructed 4D dose to initial plans.

Results:

The Dmax is significantly less dose in the reconstructed 4D dose, 68.12±3.5Gy, vs. 70.1±4.3Gy in the initial plans (p=0.015). No significant difference is found for the ITV V100, HI, and R50, 92.2%±15.4% vs. 96.3%±2.5% (p=0.565), 1.033±0.016 vs. 1.038±0.017 (p=0.548), 19.2±12.1 vs. 18.1±11.6 (p=0.265), for the 4D dose and initial plans, respectively. The lung‐GTV V12.5 and V5 are significantly high in the 4D dose, 13.9%±4.8% vs. 13.0%±4.6% (p=0.021) and 17.6%±5.4% vs. 16.9%±5.2% (p=0.011), respectively.

Conclusion:

4D dose reconstruction based on phase PDF can be used to evaluate the dose received by the patient. A robust optimization based on the phase PDF may even further improve patient care.
SU‐F‐T‐218: Validation of An In‐Vivo Proton Range Verification Method for Reducing the Risk of Permanent Alopecia in the Treatment of Pediatric Medulloblastoma
Authors: Lucconi G , Bentefour E , Deepak S , Janssens G , Weaver K , Moteabbed M , Lu H‐M
Published: July 2016

Purpose:

The clinical commissioning of a workflow for pre‐treatment range verification/adjustment for the head treatment of pediatric medulloblastoma patients, including dose monitoring during treatment.

Methods:

An array of Si‐diodes (DIODES Incorporated) is placed on the patient skin on the opposite side to the beam entrance. A “scout” SOBP beam, with a longer beam range to cover the diodes in its plateau, is delivered; the measured signal is analyzed and the extracted water equivalent path lengths (WEPL) are compared to the expected values, revealing if a range correction is needed. Diodes stay in place during treatment to measure dose. The workflow was tested in solid water and head phantoms and validated against independent WEPL measurements. Both measured WEPL and skin doses were compared to computed values from the TPS (XiO); a Markus chamber was used for reference dose measurements.

Results:

The WEPL accuracy of the method was verified by comparing it with the dose extinction method. It resulted, for both solid water and head phantom, in the sub‐millimeter range, with a deviation less than 1% to the value extracted from the TPS. The accuracy of dose measurements in the fall‐off part of the dose profile was validated against the Markus chamber. The entire range verification workflow was successfully tested for the mock‐treatment of head phantom with the standard delivery of 90 cGy per field per fraction. The WEPL measurement revealed no need for range correction. The dose measurements agreed to better than 4% with the prescription dose. The robustness of the method and workflow, including detector array, hardware set and software functions, was successfully stress‐tested with multiple repetitions.

Conclusion:

The performance of the in‐vivo range verification system and related workflow meet the clinical requirements in terms of the needed WEPL accuracy for pretreatment range verification with acceptable dose to the patient.
SU‐F‐T‐223: Radiotherapy Incident Reporting and Analysis System (RIRAS):Early Experience
Authors: Kapoor R , Burkett D , Leidholdt E , Palta J , Hagan M
Published: July 2016

Background & Purpose:

RIRAS is a web‐based information system deployed on the Veterans Health Administration intranet in early 2014 to collect adverse events and good catch data; analyze the causes and contributing factors; and find ways to prevent future occurrences. Material and

Methods:

Incident learning consists of a feedback loop which starts with reporting an event, followed by analysis of contributing factors, and culminates in the development of a patient safety work product (PSWP) to prevent recurrence. RIRAS permits both anonymous and non‐anonymous reporting. Each report is analyzed by a team of medical physicists who are independent of the reporting facility. The analysts usually contact the reporting facilities for additional information. We analyzed all reports and held telephonic interviews (when necessary) with the reporters. We then generated PSWPs with corrective/preventive and learning actions. Anonymous reporting is handled in the same manner, except without the ability to further interview the reporter.

Results:

In a significant number of reports, the causes and recommended preventive actions were considerably altered by the independent analysis and additional information from the facility. 130 reports have been entered in RIRAS; 9 misadministrations, 83 good catches, 3 anonymous good catches, and 35 earlier reported incidents from FY2005‐14. 45% of the reported incidents occurred in the treatment delivery stages, 19% in on‐treatment management, and 16% in pre‐treatment verification. 80% of the good catches were found in the treatment delivery workflow. Majority of these incidents were due to inconsistent patient setup instructions or documentation, nonadherence to policies and procedures, lax time‐out policy, distracted RTTs, and inadequate RTT staffing.

Conclusion:

RIRAS has identified many areas for improvement and elevated the quality and safety of radiation treatments in the VHA. We found that the ability to learn is significantly diminished when the analysts do not have the ability to request additional information.
SU‐F‐T‐224: Importance of Timely Review of Daily Cone‐Beam CTs: Dosimetric Evaluation of Rejected CBCTs for Head and Neck Patients
Authors: Andrews M , Lin S , Yu N , Joshi N , Koyfman S , Xia P
Published: July 2016

Purpose:

To dosimetrically evaluate the importance of timely reviewing daily CBCTs for patients with head and neck cancer.

Methods:

After each fraction daily cone‐beam CT (CBCT) for head and neck patients are reviewed by physicians prior to next treatment. Physician rejected image registrations of CBCT were identified and analyzed for 17 patients. These CBCT images were rigidly fused with planning CT images and the contours from the planning CT were transferred to CBCTs. Because of limited extension in the superior‐inferior dimension contours with partial volumes in CBCTs were discarded. The treatment isocenter was placed by applying the clinically recorded shifts to the volume isocenter of the CBCT. Dose was recalculated at the shifted isocenter using a homogeneous dose calculation algorithm. Dosimetrically relevant changes defined as greater than 5% deviation from the clinically accepted plans but with homogeneous dose calculation were evaluated for the high dose (HD), intermediate dose (ID), and low dose (LD) CTVs, spinal cord, larynx, oropharynx, parotids, and submandibular glands.

Results:

Among seventeen rejected CBCTS, HD‐CTVs, ID‐CTVs, and LD‐CTVs were completely included in the CBCTs for 17, 1, and 15 patients, respectively. The prescription doses to the HD‐CTV, ID‐CTV, and LD‐CTV were received by < 95% of the CTV volumes in 5/17, 1/1, and 5/15 patients respectively. For the spinal cord, the maximum doses (D0.03cc) were increased > 5% in 13 of 17 patients. For the oropharynx, larynx, parotid, and submandibular glands, the mean dose of these organs at risk was increased > 5% in 7/17, 8/12, 11/16 and 6/16 patients, respectively.

Conclusion:

Timely review daily CBCTs for head and neck patients under daily CBCT guidance is important, and uncorrected setup errors can translate to dosimetrically relevant dose increases in organsat‐ risk and dose decreases in the clinical target volumes.
SU‐F‐T‐233: Evaluation of Treatment Delivery Parameters Using High Resolution ELEKTA Log Files
Authors: Kabat C , Defoor D , Alexandrian A , Papanikolaou N , Stathakis S
Published: July 2016

Purpose:

As modern linacs have become more technologically advanced with the implementation of IGRT and IMRT with HDMLCs, a requirement for more elaborate tracking techniques to monitor components’ integrity is paramount. ElektaLog files are generated every 40 milliseconds, which can be analyzed to track subtle changes and provide another aspect of quality assurance. This allows for constant monitoring of fraction consistency in addition to machine reliability. With this in mind, it was the aim of the study to evaluate if ElektaLog files can be utilized for linac consistency QA.

Methods:

ElektaLogs were reviewed for 16 IMRT patient plans with >16 fractions. Logs were analyzed by creating fluence maps from recorded values of MLC locations, jaw locations, and dose per unit time. Fluence maps were then utilized to calculate a 2D gamma index with a 2%–2mm criteria for each fraction. ElektaLogs were also used to analyze positional errors for MLC leaves and jaws, which were used to compute an overall error for the MLC banks, Y‐jaws, and X‐jaws by taking the root‐meansquare value of the individual recorded errors during treatment. Additionally, beam on time was calculated using the number of ElektaLog file entries within the file.

Results:

The average 2D gamma for all 16 patient plans was found to be 98.0±2.0%. Recorded gamma index values showed an acceptable correlation between fractions. Average RMS values for MLC leaves and the jaws resulted in a leaf variation of roughly 0.3±0.08 mm and jaw variation of about 0.15±0.04 mm, both of which fall within clinical tolerances.

Conclusion:

The use of ElektaLog files for day‐to‐day evaluation of linac integrity and patient QA can be utilized to allow for reliable analysis of system accuracy and performance.
SU‐F‐T‐234: Quality Improvements in the Electronic Medical Record of Patients Treated with High Dose‐Rate Brachytherapy
Authors: Diener T , Wilkinson D
Published: July 2016

Purpose:

To improve workflow efficiency and patient safety by assessing the quality control documentation for HDR brachytherapy within our Electronic Medical Record System (Mosaiq).

Methods:

A list of parameters based on NRC regulations, our quality management program (QMP), recommendations of the ACR and the American Brachytherapy Society, and HDR treatment planning risks identified in our previous FMEA study was made. Next, the parameter entries were classified according to the type of data input—manual, electronic, or both. Manual entry included the electronic Brachytherapy Treatment Record (BTR) and pre‐treatment Mosaiq Assessments list. Oncentra Treatment Reports (OTR) from the Oncentra Treatment Control System constituted the electronic data. The OTR includes a Pre‐treatment Report for each fraction, and a Treatment Summary Report at the completion of treatment. Each entry was then examined for appropriateness and completeness of data; adjustments and additions as necessary were then made.

Results:

Ten out of twenty‐one recorded treatment parameters were identified to be documented within both the BTR and OTR. Of these ten redundancies, eight were changed from recorded values to a simple checklist in the BTR to avoid recording errors. The other redundancies were kept in both documents due to their value to ensuring patient safety. An edit was made to the current BTR quality assessment; this change revises the definition of a medical event in accordance with ODH Regulation 3701:1‐58‐101. One addition was made to the current QMP documents regarding HDR. This addition requires a physician to be present through the duration of HDR treatment in accordance with ODH Regulation 3701:1‐58‐59; Paragraph (F); Section (2); Subsection (a).

Conclusion:

Careful examination of HDR documentation that originates from different sources can help to improve the accuracy and reliability of the documents. In addition, there may be a small improvement in efficiency due to elimination of unnecessary redundancies.
SU‐F‐T‐245: The Investigation of Failure Mode and Effects Analysis and PDCA for the Radiotherapy Risk Reduction
Authors: Xie J , Wang J , P J , Chen J , Hu W
Published: July 2016

Purpose:

To optimize the clinical processes of radiotherapy and to reduce the radiotherapy risks by implementing the powerful risk management tools of failure mode and effects analysis(FMEA) and PDCA(plan‐do‐check‐act).

Methods:

A multidiciplinary QA(Quality Assurance) team from our department consisting of oncologists, physicists, dosimetrists, therapists and administrator was established and an entire workflow QA process management using FMEA and PDCA tools was implemented for the whole treatment process. After the primary process tree was created, the failure modes and Risk priority numbers(RPNs) were determined by each member, and then the RPNs were averaged after team discussion.

Results:

3 of 9 failure modes with RPN above 100 in the practice were identified in the first PDCA cycle, which were further analyzed to investigate the RPNs: including of patient registration error, prescription error and treating wrong patient. New process controls reduced the occurrence, or detectability scores from the top 3 failure modes. Two important corrective actions reduced the highest RPNs from 300 to 50, and the error rate of radiotherapy decreased remarkably.

Conclusion:

FMEA and PDCA are helpful in identifying potential problems in the radiotherapy process, which was proven to improve the safety, quality and efficiency of radiation therapy in our department. The implementation of the FMEA approach may improve the understanding of the overall process of radiotherapy while may identify potential flaws in the whole process. Further more, repeating the PDCA cycle can bring us closer to the goal: higher safety and accuracy radiotherapy.
SU‐F‐T‐246: Evaluation of Healthcare Failure Mode And Effect Analysis For Risk Assessment
Authors: Harry T , Manger R , Cervino L , Pawlicki T
Published: July 2016

Purpose:

To evaluate the differences between the Veteran Affairs Healthcare Failure Modes and Effect Analysis (HFMEA) and the AAPM Task Group 100 Failure and Effect Analysis (FMEA) risk assessment techniques in the setting of a stereotactic radiosurgery (SRS) procedure were compared respectively. Understanding the differences in the techniques methodologies and outcomes will provide further insight into the applicability and utility of risk assessments exercises in radiation therapy.

Methods:

HFMEA risk assessment analysis was performed on a stereotactic radiosurgery procedure. A previous study from our institution completed a FMEA of our SRS procedure and the process map generated from this work was used for the HFMEA. The process of performing the HFMEA scoring was analyzed, and the results from both analyses were compared.

Results:

The key differences between the two risk assessments are the scoring criteria for failure modes and identifying critical failure modes for potential hazards. The general consensus among the team performing the analyses was that scoring for the HFMEA was simpler and more intuitive then the FMEA. The FMEA identified 25 critical failure modes while the HFMEA identified 39. Seven of the FMEA critical failure modes were not identified by the HFMEA and 21 of the HFMEA critical failure modes were not identified by the FMEA. HFMEA as described by the Veteran Affairs provides guidelines on which failure modes to address first.

Conclusion:

HFMEA is a more efficient model for identifying gross risks in a process than FMEA. Clinics with minimal staff, time and resources can benefit from this type of risk assessment to eliminate or mitigate high risk hazards with nominal effort. FMEA can provide more in depth details but at the cost of elevated effort.
SU‐F‐T‐252: An Investigation of Gamma Knife Frame Definition Error When Using a Pre‐Planning Workflow
Authors: Johnson P
Published: July 2016

Purpose:

To determine causal factors related to high frame definition error when treating GK patients using a pre‐planning workflow.

Methods:

160 cases were retrospectively reviewed. All patients received treatment using a pre‐planning workflow whereby stereotactic coordinates are determined from a CT scan acquired after framing using a fiducial box. The planning software automatically detects the fiducials and compares their location to expected values based on the rigid design of the fiducial system. Any difference is reported as mean and maximum frame definition error. The manufacturer recommends these values be less than 1.0 mm and 1.5 mm. In this study, frame definition error was analyzed in comparison with a variety of factors including which neurosurgeon/oncologist/physicist was involved with the procedure, number of post used during framing (3 or 4), type of lesion, and which CT scanner was utilized for acquisition. An analysis of variance (ANOVA) approach was used to statistically evaluate the data and determine causal factors related to instances of high frame definition error.

Results:

Two factors were identified as significant: number of post (p=0.0003) and CT scanner (p=0.0001). Further analysis showed that one of the four scanners was significantly different than the others. This diagnostic scanner was identified as an older model with localization lasers not tightly calibrated. The average value for maximum frame definition error using this scanner was 1.48 mm (4 posts) and 1.75 mm (3 posts). For the other scanners this value was 1.13 mm (4 posts) and 1.40 mm (3 posts).

Conclusion:

In utilizing a pre‐planning workflow the choice of CT scanner matters. Any scanner utilized for GK should undergo routine QA at a level appropriate for radiation oncology. In terms of 3 vs 4 post, it is hypothesized that three posts provide less stability during CT acquisition. This will be tested in future work.
SU‐F‐T‐259: GPR Tables for the Estimation of Mid‐Plane Dose Using EPID
Authors: Annamalai Gopiraj , Watanabe Yoichi
Published: July 2016

Purpose:

To develop a simple method for estimating the mid‐plane dose (MPD) of a patient using Electronic Portal imaging Device (EPID).

Methods:

A Varian TrueBeam with aSi100 EPID was used in this study. The EPID images were acquired for a 30 cm × 30 cm homogeneous slab phantom and a 30 cm diameter 20 cm thick cylindrical phantom in the continuous dosimetry mode. The acquired EPID images in XIM format were imported into in‐house MATLAB program for the data analysis. First, the dosimetric characteristics of EPID were studied for dose‐response linearity, dose‐rate dependence, and field size dependence. Next, the average pixels values of the EPID images were correlated with the MPD measured by an ionisation chamber for various thicknesses of the slab phantom (8 cm – 30 cm) and for various square field sizes (3×3 cm2 – 25×25 cm2 at the isocenter). Look‐up tables called as GPR tables were then generated for both SSD and SAD setup by taking the ratio of MPD measured by the ionisation chamber and the corresponding EPID pixel values. The accuracy of the GPR tables was evaluated by varying the field size, phantom thickness, and wedge angles with the slab and cylindrical phantoms.

Results:

The dose response of EPID was linear from 20 MU to 300 MU. The EPID response for different dose rates from 40 MU/min to 600 MU/min was within ±1%. The difference in the doses from the GPR tables and the doses measured by the ionization chambers were within 2% for slab phantoms, and 3% for the cylindrical phantom for various field sizes, phantom thickness, and wedge angles.

Conclusion:

GPR tables are a ready reckoner for in‐vivo dosimetry and it can be used to quickly estimate the MPD value from the EPID images with an accuracy of ±3% for common clinical treatment. project work funded by Union for International cancer control(UICC) under ICRETT fellowship
SU‐F‐T‐260: Using Portal Image Device for Pre‐Treatment QA in Volumetric Modulated Arc Plans with Flattening Filter Free (FFF) Beams
Authors: Qu H , Qi P , Yu N , Xia P
Published: July 2016

Purpose:

To implement and validate a method of using electronic portal image device (EPID) for pre‐treatment quality assurance (QA) of volumetric modulated arc therapy (VMAT) plans using flattering filter free (FFF) beams for stereotactic body radiotherapy (SBRT).

Methods:

On Varian Edge with 6MV FFF beam, open field (from 2×2 cm to 20×20 cm) EPID images were acquired with 200 monitor unit (MU) at the image device to radiation source distance of 150cm. With 10×10 open field and calibration unit (CU) provided by vendor to EPID image pixel, a dose conversion factor was determined by dividing the center dose calculated from the treatment planning system (TPS) to the corresponding CU readout on the image. Water phantom measured beam profile and the output factors for various field sizes were further correlated to those of EPID images. The dose conversion factor and correction factors were then used for converting the portal images to the planner dose distributions of clinical fields. A total of 28 VMAT fields of 14 SBRT plans (8 lung, 2 prostate, 2 liver and 2 spine) were measured. With 10% low threshold cutoff, the delivered dose distributions were compared to the reference doses calculated in water phantom from the TPS. A gamma index analysis was performed for the comparison in percentage dose difference/distance‐to‐agreement specifications.

Results:

The EPID device has a linear response to the open fields with increasing MU. For the clinical fields, the gamma indices between the converted EPID dose distributions and the TPS calculated 2D dose distributions were 98.7%±1.1%, 94.0%±3.4% and 70.3%±7.7% for the criteria of 3%/3mm, 2%/2mm and 1%/1mm, respectively.

Conclusion:

Using a portal image device, a high resolution and high accuracy portal dosimerty was achieved for pre‐treatment QA verification for SBRT VMAT plans with FFF beams.
SU‐F‐T‐280: An Assessment of Deviations in Gamma Index Between PTW Octavius4D Phantom Measurements and Various Treatment Planning Systems
Authors: Roring JE , Alexandrian A , Papanikolaou N , Stathakis S
Published: July 2016

Purpose:

There is a variety of treatment planning systems (TPS) available for clinical use all with highly variable settings to calculate patient dose. Patient specific IMRT QA is often a daily procedure at most clinics and each clinic devises their own policy on the TPS settings for testing the quality of the patient plan against a measured dose on IMRT QA phantoms. With this in mind, it is the aim of this study to evaluate the effect of dose calculation parameters on IMRT QA.

Methods:

Six patient plans were optimized and calculated using Pinnacle3 (v9.10). Patient QAs were calculated using the PTW Octavius4D phantom with a dose grid resolution of 3mm and a phantom density of 1.045g/cc. Using PTW's VeriSoft, the calculated dose distribution of Pinnacle3, Monaco, and Eclipse were compared to the delivered plan (the control) on the Octavius4D. For each TPS, the dose grid was varied from 2–4mm, and the phantom density varied ±10% in increments of 2%. Additionally, statistical uncertainties ranging from 0.7%–3% were calculated for Monaco. Using the evaluation metric of 3% and 3mm with a threshold of 10% of the max dose, the average and standard deviation of the 3D γ‐index were calculated for each plan. The γ‐index from axial, sagittal, and coronal slices at isocenter and the overall 3D γ‐index were used for the comparisons.

Results:

The disparity in γ‐index was small between most plan modifications. An extreme example is one case in which a 3D slice yielded a γ‐index that differed up to 12.9% whereas the maximum variation in total volume for any case was merely 2.3%. The average standard deviation of all slices was ±1.49% and the average standard deviation for total volume was only ±0.55%.

Conclusion:

Dose calculation resolution and algorithm does not significantly affect the patient QA measurements.
SU‐F‐T‐287: A Preliminary Study On Patient Specific VMAT Verification Using a Phosphor‐Screen Based Geometric QA System (Raven QA)
Authors: Lee M , Wong J , Ding K , Yi B
Published: July 2016

Purpose:

The RavenQA system (LAP Laser, Germany) is a QA device with a phosphor screen detector for performing the QA tasks of TG‐142. This study tested if it is feasible to use the system for the patient specific QA of the Volumetric Modulated Arc Therapy (VMAT).

Methods:

Water equivalent material (5cm) is attached to the front of the detector plate of the RavenQA for dosimetry purpose. Then the plate is attached to the gantry to synchronize the movement between the detector and the gantry. Since the detector moves together with gantry, The 'Reset gantry to 0’ function of the Eclipse planning system (Varian, CA) is used to simulate the measurement situation when calculating dose of the detector plate. The same gantry setup is used when delivering the treatment beam for feasibility test purposes. Cumulative dose is acquired for each arc. The optical scatter component of each captured image from the CCD camera is corrected by deconvolving the 2D spatial invariant optical scatter kernel (OSK). We assume that the OSK is a 2D isotropic point spread function with inverse‐squared decrease as a function of radius from the center.

Results:

Three cases of VMAT plans including head & neck, whole pelvis and abdomen‐pelvis are tested. Setup time for measurements was less than 5 minutes. Passing rates of absolute gamma were 99.3, 98.2, 95.9 respectively for 3%/3mm criteria and 96.2, 97.1, 86.4 for 2%/2mm criteria. The abdomen‐pelvis field has long treatment fields, 37cm, which are longer than the detector plate (25cm). This plan showed relatively lower passing rate than other plans.

Conclusion:

An algorithm for IMRT/VMAT verification using the RavenQA has been developed and tested. The model of spatially invariant OSK works well for deconvolution purpose. It is proved that the RavenQA can be used for the patient specific verification of VMAT.

This work is funded in part by a Maryland Industrial Partnership Program grant to University of Maryland and to JPLC who owns the Raven technology. John Wong is a co‐founder of JPLC.
SU‐F‐T‐63: Dosimetric Relevance of the Valencia and Leipzig HDR Applicators Plastic Cap
Authors: Granero D , Candela‐Juan C , Vijande J , Ballester F , Perez‐Calatayud J , Jacob D , Mourtada F
Published: July 2016

Purpose:

Utilization of HDR brachytherapy treatment of skin lesions using collimated applicators, such as the Valencia or Leipzig is increasing. These applicators are made of cup‐shaped tungsten material in order to focalize the radiation into the lesion and to protect nearby tissues. These applicators have an attachable plastic cap that removes secondary electrons generated in the applicator and flattens the treatment surface. The purpose of this study is to examine the dosimetric impact of this cap, and the effect if the cap is not placed during the HDR fraction delivery.

Methods:

Monte Carlo simulations have been done using the code Geant4 for the Valencia and Leipzig applicators. Dose rate distributions have been obtained for the applicators with and without the plastic cap. An experimental study using EBT3 radiochromic film has been realized in order to verify the Monte Carlo results.

Results:

The Monte Carlo simulations show that absorbed dose in the first millimeter of skin can increase up to 180% for the Valencia applicator if the plastic cap is absent and up to 1500% for the Leipzig applicators. At deeper distances the increase of dose is smaller being about 10–15%.

Conclusion:

Important differences have been found if the plastic cap of the applicators is absent in the treatment producing an overdosage in the skin. The user should have a checklist to remind him check always before HDR fraction delivery to insure the plastic cap is placed on the applicator.

This work was supported in part by Generalitat Valenciana under Project PROMETEOII/2013/010, by the Spanish Government under Project No. FIS2013‐42156, and by a research agreement with Elekta Brachytherapy, Veenendaal, The Netherlands.
SU‐F‐T‐297: Quality Assurance of Multiple Brain Metastases with Single Isocenter Using Measurement Guided Dose Reconstruction
Authors: Leung R , Wong M , Lee V , Cheung S , Lee K , Law G , Chan M
Published: July 2016

Purpose:

To evaluate the use of measurement guided dose reconstruction (MGDR) in quality assurance (QA) of stereotactic radiosurgery (SRS) of multiple brain metastases (MBM) planned with single isocenter (SI).

Methods:

Seven clinically approved multi‐isocenter MBM (MI‐MBM) plans were re‐optimized using SI (SI‐MBM) by coplanar volumetric arc therapy (VMAT) in Monaco v5.0 (Elekta CMS, Maryland Heights, MO, USA). These plans were delivered on an Elekta Agiltiy Linac and measured by OCTAVIUS 4D system with OCTAVIUS 1500 2D array (PTW, Freiburg, Germany). Measurements were repeated with a shift of the phantom by 5mm to double the detector resolution. 3D γ analysis in Verisoft 6.1 with 1.5mm/1.5%, 1.5mm/2% and 2mm/2% at local‐dose passing criteria and 20% dose suppression were made.

Results:

3D γ passing rates are 94.3±2.7%, 85.2±5.4% and 84±5.7% at 1.5mm/1.5%, 1.5mm/2% and 2mm/2% criteria.

Conclusion:

MGDR of OCTAVIUS 4D system provides adequate and efficient VMAT QA solution for SI‐MBM SRS. However, the results showed significant spatial dependence due to rapid dose fall‐off in radiosurgery. Further improvement in detector spatial resolution is desired. PTV margins should be carefully adopted for those MBM treated with single isocenter.
SU‐F‐T‐298: The Impact of Modeling the Treatment Couch On Patient Specific VMAT QA
Authors: Gelover E , Dalhart A , Hyer D
Published: July 2016

Purpose:

The aim of this work is to quantify the impact of modeling the treatment couch on the passing rate of ion chamber measurements during VMAT quality assurance.

Methods:

For the initial characterization, attenuation and surface dose measurements were performed following the guidelines of TG‐176 for the Civco Universal couch top using an Elekta VersaHD accelerator at an energy of 6 MV. A simulation CT was performed to aid in the creation of contours for representing the shape and size of the couch top in the treatment planning system (TPS). A uniform value of density for the couch wall was determined by comparing the ratios of ion chamber measurements made in a 30×30×11 cm3 water phantom with the TPS dose values of a plan with the same geometry. At our institution, patient specific quality assurance is performed using a Sun Nuclear ArcCheck with a multi‐plug for chamber measurements, a 0.125cc PTW TN31010 chamber, and a Sun Nuclear 1010 electrometer. Ten VMAT plans were transferred into the phantom geometry created in the TPS with two settings: with and without the couch. The chamber measurements were compared to both treatment plans.

Results:

A maximum attenuation of 3.6% was observed when the gantry angle was set to 120 and 240 degrees, passing obliquely through the couch. A uniform density of 0.6 g/cm3 for the couch wall was determined in the TPS by comparison with measured data. The VMAT ion chamber measurement/plan ratios systematically improved by 1.79% ±0.53% for all patients when the couch was included in the calculation.

Conclusion:

The attenuation and surface dose changes produced by the Civco couch can generate observable dose difference in VMAT plans. Including a couch model in the phantom plan used for patient specific VMAT QA can improve the ionization chamber agreement by up to ∼2%.
SU‐F‐T‐299: An Experimental 2D Computed Radiography (CR) Dosimeter for IMRT. Are In‐Field Measurements Affected by the Low Energy Photon Overresponse?
Authors: Crijns W , Vandenbroucke D , Leblans P , Depuydt T
Published: July 2016

Purpose:

Computed Radiography (CR) dosimetry could offer film dosimetry resolution and flexibility but with reusability and instantaneous processing. For an experimental CR‐plate, designed for radiotherapy (Zeff=18), CR's typical out‐of‐field over‐response to low energy photons was previously reduced to 8%. The present work assesses the impact of the residual over‐response when open‐fields are combined or when intensity modulated fields are used.

Methods:

Agfa Healthcare's experimental CRplate was scanned and erased 4min after each irradiation using a flying‐spot CR‐15‐X‐engine based reader, which was adapted for radiotherapy dosimetry. A CR‐plate specific calibration and uniformity correction was used.For open‐fields two abutting half beams (5×10cm2) captured out‐offield and in‐field doses in a single image. Additionally, both half beams were measured individually as well as a 3×18Gy open‐field SBRT‐lung treatment. For intensity modulated fields standard test patterns (Chair and Pyramid) and a clinical 5×5Gy rectal VMAT plan were captured. All measurements were compared to the corresponding dose calculations.

Results:

For open‐fields the out‐of‐field overdose was clearly larger than the in‐field overdose (10% vs. 4%). The sum of the individual measurements corresponded well with the combined measurement (dose difference, ΔD<−2.2%). The SBRT case had no overdose in the high dose region; ΔD=−5.6%±3.3%, the deviation was attributed to CR‐fading effects (−0.3%/min) which were not corrected for.Compared to open‐fields, intensity modulated deliveries had a further increased over‐response out‐offield (ΔD=+58% to +125% [Chair] +43% [Pyramid]), due to the increased amount of low energy photons for IMRT. However, this effect was not measured in‐field where even decreased dose signals were observed (ΔD=−0.3% to +2.25% [Chair], −4.5% to −0.1% [Pyramid]). The rectal VMAT treatment had a dose difference +2.4%±6.0%. The in‐field deviations were attributed to a residual non‐uniformity.

Conclusion:

The experimental CRplate's out‐of‐field over‐response does not propagate in in‐field overresponse errors when static or dynamic (IMRT/VMAT) abutting fields are used.