bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐F‐T‐230: A Simple Method to Assess Accuracy of Dynamic Wave Arc Irradiation Using An Electronic Portal Imaging Device and Log Files
Authors: Hirashima H , Miyabe Y , Yokota K , Nakamura M , Mukumoto N , Mizowaki T , Hiraoka M
Published: July 2016

Purpose:

The Dynamic Wave Arc (DWA) technique, where the multi‐leaf collimator (MLC) and gantry/ring move simultaneously in a predefined non‐coplanar trajectory, has been developed on the Vero4DRT. The aim of this study is to develop a simple method for quality assurance of DWA delivery using an electronic portal imaging device (EPID) measurements and log files analysis.

Methods:

The Vero4DRT has an EPID on the beam axis, the resolution of which is 0.18 mm/pixel at the isocenter plane. EPID images were acquired automatically. To verify the detection accuracy of the MLC position by EPID images, the MLC position with intentional errors was assessed. Tests were designed considering three factors: (1) accuracy of the MLC position (2) dose output consistency with variable dose rate (160–400 MU/min), gantry speed (2.4–6°/s), ring speed (0.5–2.5°/s), and (3) MLC speed (1.6–4.2 cm/s). All the patterns were delivered to the EPID and compared with those obtained with a stationary radiation beam with a 0° gantry angle. The irradiation log, including the MLC position and gantry/ring angle, were recorded simultaneously. To perform independent checks of the machine accuracy, the MLC position and gantry/ring angle position were assessed using log files.

Results:

0.1 mm intentional error can be detected by the EPID, which is smaller than the EPID pixel size. The dose outputs with different conditions of the dose rate and gantry/ring speed and MLC speed showed good agreement, with a root mean square (RMS) error of 0.76%. The RMS error between the detected and recorded data were 0.1 mm for the MLC position, 0.12° for the gantry angle, and 0.07° for the ring angle.

Conclusion:

The MLC position and dose outputs in variable conditions during DWA irradiation can be easily detected using EPID measurements and log file analysis. The proposed method is useful for routine verification.

This research is (partially) supported by the Practical Research for Innovative Cancer Control (15Ack0106151h0001) from Japan Agency for Medical Research and development, AMED. Authors Takashi Mizowaki and Masahiro Hiraoka have consultancy agreement with Mitsubishi Heavy Industries, Ltd., Japan.
SU‐F‐T‐235: Optical Scan Based Collision Avoidance Using Multiple Stereotactic Cameras During Simulation
Authors: Cardan R , Popple R , Dobelbower M , De Los Santos J , Fiveash J
Published: July 2016

Purpose:

To demonstrate the ability to quickly generate an accurate collision avoidance map using multiple stereotactic cameras during simulation.

Methods:

Three Kinect stereotactic cameras were placed in the CT simulation room and optically calibrated to the DICOM isocenter. Immediately before scanning, the patient was optically imaged to generate a 3D polygon mesh, which was used to calculate the collision avoidance area using our previously developed framework. The mesh was visually compared to the CT scan body contour to ensure accurate coordinate alignment. To test the accuracy of the collision calculation, the patient and machine were physically maneuvered in the treatment room to calculated collision boundaries.

Results:

The optical scan and collision calculation took 38.0 seconds and 2.5 seconds to complete respectively. The collision prediction accuracy was determined using a receiver operating curve (ROC) analysis, where the true positive, true negative, false positive and false negative values were 837, 821, 43, and 79 points respectively. The ROC accuracy was 93.1% over the sampled collision space.

Conclusion:

We have demonstrated a framework which is fast and accurate for predicting collision avoidance for treatment which can be determined during the normal simulation process. Because of the speed, the system could be used to add a layer of safety with a negligible impact on the normal patient simulation experience. This information could be used during treatment planning to explore the feasible geometries when optimizing plans.

Research supported by Varian Medical Systems
SU‐F‐T‐239: Evaluation of Plastic Scintillator Light Output for Various Lead Doping Concentrations: Towards LET Detection
Authors: Nusrat H , Pang G , Sarfehnia A
Published: July 2016

Purpose:

This work seeks to develop a beam quality meter using multiple differently doped plastic scintillators that are thus intrinsically beam‐quality dependent. Plastic scintillators spontaneously emit visible light upon irradiation; the amount of light produced is dependent on stopping power (closely related to LET) according to Birks’ law. Doping plastic scintillators can be used to tune their sensitivity to specific LET ranges.

Methods:

GEANT4.10.1 Monte Carlo (MC) was used to evaluate the response of various scintillator dopant combinations. MC radiation transport and scintillator light response were validated against previously published literature. Current work involves evaluating detector response experimentally; to that end, a detector prototype with interchangeable scintillator housing was constructed. Measurement set‐up guides light emitted by the scintillator to a photomultiplier tube via a glass taper junction coupled to an optical fiber. The resulting signal is measured by an electrometer, and normalized to dose readout from a diode. Measurements have been done using clinical electron and orthovoltage beams. MC response (simulated scintillator light normalized to dose scored inside the scintillating volume) was evaluated for four different LET radiations for an undoped and 1%Pb doped scintillator (σ=0.85%). Simulated incident electrons included: 0.05, 0.1, 0.2, 6, 12, and 18 MeV; these energies correspond to a range of stopping power (related to LET) values ranging from 1.824 to 11.09 MeVcm2g−1 (SCOL from NIST‐ESTAR).

Results:

Initial MC results show a distinct divergence in scintillator response as LET increases. The response for undoped plastic scintillator indicated a 35.0% increase in signal when going from 18 MeV (low LET) to 0.05 MeV (high LET) while 1%‐Pb doped scintillator indicated a 100.9% increase.

Conclusion:

After validating MC against measurement, simulations will be used to test various concentrations (2%, 4%, 6%) of different high‐Z material dopants (W, Mo) to optimize the scintillator types for the beam quality meter.

NSERC Discovery Grant RGPIN‐435608
SU‐F‐T‐241: Reduction in Planning Errors Via a Process Control Developed Using the Eclipse Scripting API
Authors: Barbee D , McCarthy A , Galavis P , Xu A
Published: July 2016

Purpose:

Errors found during initial physics plan checks frequently require replanning and reprinting, resulting decreased departmental efficiency. Additionally, errors may be missed during physics checks, resulting in potential treatment errors or interruption. This work presents a process control created using the Eclipse Scripting API (ESAPI) enabling dosimetrists and physicists to detect potential errors in the Eclipse treatment planning system prior to performing any plan approvals or printing.

Methods:

Potential failure modes for five categories were generated based on available ESAPI (v11) patient object properties: Images, Contours, Plans, Beams, and Dose. An Eclipse script plugin (PlanCheck) was written in C# to check errors most frequently observed clinically in each of the categories. The PlanCheck algorithms were devised to check technical aspects of plans, such as deliverability (e.g. minimum EDW MUs), in addition to ensuring that policy and procedures relating to planning were being followed. The effect on clinical workflow efficiency was measured by tracking the plan document error rate and plan revision/retirement rates in the Aria database over monthly intervals.

Results:

The number of potential failure modes the PlanCheck script is currently capable of checking for in the following categories: Images (6), Contours (7), Plans (8), Beams (17), and Dose (4). Prior to implementation of the PlanCheck plugin, the observed error rates in errored plan documents and revised/retired plans in the Aria database was 20% and 22%, respectively. Error rates were seen to decrease gradually over time as adoption of the script improved.

Conclusion:

A process control created using the Eclipse scripting API enabled plan checks to occur within the planning system, resulting in reduction in error rates and improved efficiency. Future work includes: initiating full FMEA for planning workflow, extending categories to include additional checks outside of ESAPI via Aria database queries, and eventual automated plan checks.
SU‐F‐T‐242: A Method for Collision Avoidance in External Beam Radiation Therapy
Authors: Buzurovic I , Cormack R
Published: July 2016

Purpose:

We proposed a method for collision avoidance (CA) in external beam radiation therapy (EBRT). The method encompasses the analysis of all positions of the moving components of the beam delivery system such as the treatment table and gantry, including patient specific information obtained from the CT images. This method eliminates the need for time‐consuming dry‐runs prior to the actual treatments.

Methods:

The QA procedure for EBRT requires that the collision should be checked prior to treatment. We developed a system capable of a rigorous computer simulation of all moving components including positions of the couch and gantry during the delivery, position of the patients, and imaging equipment. By running this treatment simulation it is possible to quantify and graphically represent all positions and corresponding trajectories of all points of the moving parts during the treatment delivery. The development of the workflow for implementation of the CA includes several steps: a) derivation of combined dynamic equation of motion of the EBRT delivery systems, b) developing the simulation model capable of drawing the motion trajectories of the specific points, c) developing the interface between the model and the treatment plan parameters such as couch and gantry parameters for each field.

Results:

The patient CT images were registered to the treatment couch so the patient dimensions were included into the simulation. The treatment field parameters were structured in the xml‐file which was used as the input into the dynamic equations. The trajectories of the moving components were plotted on the same graph using the dynamic equations. If the trajectories intersect that was the signal that collision exists.

Conclusion:

This CA method was proved to be effective in the simulation of treatment delivery. The proper implementation of this system can potentially improve the QA program and increase the efficacy in the clinical setup.
SU‐F‐T‐244: Radiotherapy Risk Estimation Based On Expert Group Survey
Authors: Koo J , Yoon M , Chung W , Chung M , Kim D
Published: July 2016

Purpose:

To evaluate the reliability of RPN (Risk Priority Number) decided by expert group and to provide preliminary data for adapting FMEA in Korea.

Methods:

1163 Incidents reported in ROSIS for 11 years were used as a real data to be compared with, and were categorized into 146 items. The questionnaire was composed of the 146 items and respondents had to valuate ‘occurrence (O)’, ‘severity (S)’, ‘detectability (D)’ of each item on a scale from 1 to 10 according to the proposed AAPM TG‐100 rating scales. 19 medical physicists from 19 different organizations in Korea had participated in the survey. Because the number of ROSIS items was not evenly spread enough to be classified into 10 grades, 1–5 scale was chosen instead of 1–10 and survey result was also fit to 5 grades to compare.

Results:

The average O,S,D were 1.77, 3.50, 2.13, respectively and the item which had the highest RPN(32) was ‘patient movement during treatment’ in the survey. When comparing items ranked in the top 10 of each survey(O) and ROSIS database, two items were duplicated and ‘Simulation’ and 'Treatment’ were the most frequently ranked RT process in top 10 of survey and ROSIS each. The Chronbach α of each RT process were ranged from 0.74 to 0.99 and p‐value was <0.001. When comparing O*D, the average difference was 1.4.

Conclusion:

This work indicates the deviation between actual risk and expectation. Considering that the respondents were Korean and ROSIS is mainly composed of incidents happened in European countries and some of the top 10 items of ROSIS cannot be applied in radiotherapy procedure in Korea, the deviation could have been came from procedural difference. Moreover, if expert group was consisted of experts from various parts, expectation might have been more accurate. Therefore, further research on radiotherapy risk estimation is needed.
SU‐F‐T‐255: Accuracy and Precision of Dynamic Tracking Irradiation with VERO‐4DRT System
Authors: Hayashi N , Takada Y , Mizuno T , Nakae H , Murai T
Published: July 2016

Purpose:

The VERO‐4DRT system is able to provide dynamic tracking irradiation (DTI) for the target with respiratory motion. This technique requires enough commissioning for clinical implementation. The purpose of this study is to make sure the accuracy and precision of DTI using VERO‐ 4DRT through commissioning from fundamental evaluation to end‐to‐end test.

Method:

We evaluated several contents for DTI commissioning: the accuracy of absorption dose at isocenter in DTI, the field size and penumbra of DTI, the accuracy of 4D modeling in DTI. All evaluations were performed by respiratory motion phantom (Quasar phantom). These contents were compared the results between static irradiation and DTI. The shape of radiation field was set to square from 3 cm × 3 cm to 10 cm × 10 cm. The micro 3D chamber and Gafchromic EBT3 film were used for absorbed dose and relative dose distribution measurement, respectively. The sine and irregular shaped waves were used for demonstrative respiratory motion. The visicoil was implanted into the phantom for guidance of respiratory motion. The respiration patterns of frequency and motion amount were set to 10–15 BPM and 1–2 cm, respectively.

Results:

As the result of absorbed dose of DTI in comparison with static irradiation, the average dose error at isocenter was 0.5% even though various respiratory patterns were set on. As the result of relative dose distribution, the field size (set it on 50% dose line) was not significantly changed in all respiratory patterns. However, the penumbra was larger in greater respiratory motion (up to 4.1 mm). The 4D modeling coincidence between actual and created waves was within 1%.

Conclusion:

The DTI using VERO‐4DRT can provide sufficient accuracy and precision in absorbed dose and distribution. However, the patientspecific quantitative internal margin corresponding respiratory motion should be taken into consideration with image guidance.
SU‐F‐T‐256: 4D IMRT Planning Using An Early Prototype GPU‐Enabled Eclipse Workstation
Authors: Hagan A , Modiri A , Svatos M , Sawant A
Published: July 2016

Purpose:

True 4D IMRT planning, based on simultaneous spatiotemporal optimization has been shown to significantly improve plan quality in lung radiotherapy. However, the high computational complexity associated with such planning represents a significant barrier to widespread clinical deployment. We introduce an early prototype GPU‐enabled Eclipse workstation for inverse planning. To our knowledge, this is the first GPUintegrated Eclipse system demonstrating the potential for clinical translation of GPU computing on a major commercially‐available TPS.

Methods:

The prototype system comprised of four NVIDIA Tesla K80 GPUs, with a maximum processing capability of 8.5 Tflops per K80 card. The system architecture consisted of three key modules: (i) a GPU‐based inverse planning module using a highly‐parallelizable, swarm intelligence‐based global optimization algorithm, (ii) a GPU‐based open‐source b‐spline deformable image registration module, Elastix, and (iii) a CUDA‐based data management module. For evaluation, aperture fluence weights in an IMRT plan were optimized over 9 beams,166 apertures and 10 respiratory phases (14940 variables) for a lung cancer case (GTV = 95 cc, right lower lobe, 15 mm cranio‐caudal motion). Sensitivity of the planning time and memory expense to parameter variations was quantified.

Results:

GPU‐based inverse planning was significantly accelerated compared to its CPU counterpart (36 vs 488 min, for 10 phases, 10 search agents and 10 iterations). The optimized IMRT plan significantly improved OAR sparing compared to the original internal target volume (ITV)‐based clinical plan, while maintaining prescribed tumor coverage. The dose‐sparing improvements were: Esophagus Dmax 50%, Heart Dmax 42% and Spinal cord Dmax 25%.

Conclusion:

Our early prototype system demonstrates that through massive parallelization, computationally intense tasks such as 4D treatment planning can be accomplished in clinically feasible timeframes. With further optimization, such systems are expected to enable the eventual clinical translation of higher‐dimensional and complex treatment planning strategies to significantly improve plan quality.

This work was partially supported through research funding from National Institutes of Health (R01CA169102) and Varian Medical Systems, Palo Alto, CA, USA.
SU‐F‐T‐258: Efficacy of Exit Fluence‐Based Dose Calculation for Prostate Radiation Therapy
Authors: Siebers J , Gardner J , Neal B
Published: July 2016

Purpose:

To investigate the efficacy of exit‐fluence‐based dose computation for prostate radiotherapy by determining if it estimates true dose more accurately than the original planning dose.

Methods:

Virtual exit‐fluencebased dose computation was performed for 19 patients, each with 9–12 repeat CT images. For each patient, a 78 Gy treatment plan was created utilizing 5 mm CTV‐to‐PTV and OAR‐to‐PRV margins. A Monte Carlo framework was used to compute dose and exit‐fluence images for the planning image and for each repeat CT image based on boney‐anatomyaligned and prostate‐centroid‐aligned CTs. Identical source particles were used for the MC dose‐computations on the planning and repeat CTs to maximize correlation. The exit‐fluence‐based dose and image were computed by multiplying source particle weights by FC(x,y)=FP(x,y)/FT(x,y), where (x,y) are the source particle coordinates projected to the exit‐fluence plane and we denote the dose/fluence from the plan by (DP,FP), from the repeat‐CT as (DT,FT), and the exit‐fluence computation by (DFC,FFC). DFC mimics exit‐fluence backprojection through the planning image as FT=FFC. Dose estimates were intercompared to judge the efficacy of exit‐fluence‐based dose computation.

Results:

Boney‐ and prostate‐centroid aligned results are combined as there is no statistical difference between them, yielding 420 dose comparisons per dose‐volume metric. DFC is more accurate than DP for 46%, 33%, and 44% of cases in estimating CTV D98, D50, and D2 respectively. DFC improved rectum D50 and D2 estimates 54% and 49% respectively and bladder D50 and D2 47 and 49% respectively. While averaged over all patients and images DFC and DP were within 3.1% of DT, they differed from DT by as much as 22% for GTV D98, 71% for the Bladder D50, 17% for Bladder D2, 19% for Rectum D2.

Conclusion:

Exit‐fluence based dose computations infrequently improve CTV or OAR dose estimates and should be used with caution.

Research supported in part by Varian Medical Systems.
SU‐F‐T‐262: Commissioning Varian Portal Dosimetry for EPID‐Based Patient Specific QA in a Non‐Aria Environment
Authors: Schmidt M , Knutson N , Herrington J , Price M
Published: July 2016

Purpose:

Development of an in‐house program facilitates a workflow that allows Electronic Portal Imaging Device (EPID) patient specific quality assurance (QA) measurements to be acquired and analyzed in the Portal Dosimetry Application (Varian Medical Systems, Palo Alto, CA) using a non‐Aria Record and Verify (R&V) system (MOSAIQ, Elekta, Crawley, UK) to deliver beams in standard clinical treatment mode.

Methods:

Initial calibration of an in‐house software tool includes characterization of EPID dosimetry parameters by importing DICOM images of varying delivered MUs to determine linear mapping factors in order to convert image pixel values to Varian‐defined Calibrated Units (CU). Using this information, the Portal Dose Image Prediction (PDIP) algorithm was commissioned by converting images of various field sizes to output factors using the Eclipse Scripting Application Programming Interface (ESAPI) and converting a delivered configuration fluence to absolute dose units. To verify the algorithm configuration, an integrated image was acquired, exported directly from the R&V client, automatically converted to a compatible, calibrated dosimetric image, and compared to a PDIP calculated image using Varian's Portal Dosimetry Application.

Results:

For two C‐Series and one TrueBeam Varian linear accelerators, gamma comparisons (global 3% / 3mm) of PDIP algorithm predicted dosimetric images and images converted via the inhouse system demonstrated agreement for ≥99% of all pixels, exceeding vendor‐recommended commissioning guidelines.

Conclusion:

Combinations of a programmatic image conversion tool and ESAPI allow for an efficient and accurate method of patient IMRT QA incorporating a 3rd party R&V system.
SU‐F‐T‐265: Calibration of EBT2 Film Using the Microtek ScanMaker 9800XL Plus Flatbed Scanner with a Modified One Red‐Channel After Three‐Channel Method
Authors: Chang L
Published: July 2016

Purpose:

In this study, we propose a technique to accurately calibrate the film using the Microtek ScanMaker 9800XL plus flatbed scanner following the “one red‐channel after three‐channel method” [Chang et al., Med. Phys. 42, 5838–5847 (2015)], which would be modified for this application.

Methods:

Following the PDD method, 6‐MV photon beams of two different MUs were delivered to eight EBT2 films (four films for each MU), where each film was tightly sandwiched in a 30‐cm cubic polystyrene phantom and parallel to the beam central axis. Before and after irradiation, all films were scanned through the Microtek 9800XL plus scanner, and the pixel values for red, green, and blue channels were extracted along the beam central axis on the film and fitted to the corresponding depth doses. Before performing the “one red‐channel after three‐channel method”, the irradiated film image first needs to be modified with a template matrix, which was generated through the pre‐scanned background images. The calibrated results were compared with the traditional one red‐channel method based on the net optical density.

Results:

Without using the template matrix, the three channel method cannot be correctly performed, since the pixel values did not follow the rational fitting form. Through our proposed method, the differences between the fitted dose and the delivered dose were within 2%, while that of the traditional one red channel method would be higher than 3%.

Conclusion:

We proposed a new technique that the one‐red channel after three‐channel method can be applied to the films scanned on a Microtek 9800XL plus scanner, and in this way, the calibration accuracy was improved. This method could also be used for other brand scanner to improve the calibration accuracy.

MOST No. 104‐2221‐E‐214‐014
SU‐F‐T‐268: A Feasibility Study of Independent Dose Verification for Vero4DRT
Authors: Yamashita M , Takahashi R , Kokubo M , Takayama K , Tanabe H , Sueoka M , Ishii M , Okuuchi N , Iwamoto Y , Tachibana H
Published: July 2016

Purpose:

Vero4DRT (Mitsubishi Heavy Industries Ltd.) has been released for a few years. The treatment planning system (TPS) of Vero4DRT is dedicated, so the measurement is the only method of dose verification. There have been no reports of independent dose verification using Clarksonbased algorithm for Vero4DRT. An independent dose verification software program of the general‐purpose linac using a modified Clarkson‐based algorithm was modified for Vero4DRT. In this study, we evaluated the accuracy of independent dose verification program and the feasibility of the secondary check for Vero4DRT.

Methods:

iPlan (Brainlab AG) was used as the TPS. PencilBeam Convolution was used for dose calculation algorithm of IMRT and X‐ray Voxel Monte Carlo was used for the others. Simple MU Analysis (SMU, Triangle Products, Japan) was used as the independent dose verification software program in which CT‐based dose calculation was performed using a modified Clarkson‐based algorithm. In this study, 120 patients’ treatment plans were collected in our institute. The treatments were performed using the conventional irradiation for lung and prostate, SBRT for lung and Step and shoot IMRT for prostate. Comparison in dose between the TPS and the SMU was done and confidence limits (CLs, Mean ± 2SD %) were compared to those from the general‐purpose linac.

Results:

As the results of the CLs, the conventional irradiation (lung, prostate), SBRT (lung) and IMRT (prostate) show 2.2 ± 3.5% (CL of the general‐purpose linac: 2.4 ± 5.3%), 1.1 ± 1.7% (−0.3 ± 2.0%), 4.8 ± 3.7% (5.4 ± 5.3%) and −0.5 ± 2.5% (−0.1 ± 3.6%), respectively. The CLs for Vero4DRT show similar results to that for the general‐purpose linac.

Conclusion:

The independent dose verification for the new linac is clinically available as a secondary check and we performed the check with the similar tolerance level of the general‐purpose linac.

This research is partially supported by Japan Agency for Medical Research and Development (AMED)
SU‐F‐T‐269: Preliminary Experience of Kuwait Cancer Control Center (KCCC) On IMRT Treatment Planning and Pre‐Treatment Verification
Authors: Sethuraman TKR , Sherif M , Subramanian N , Zoueil O , Mirza K
Published: July 2016

Purpose:

The complexity of IMRT delivery requires pre‐treatment quality assurance and plan verification. KCCC has implemented IMRT clinically in few sites and will extend to all sites. Recently, our Varian linear accelerator and Eclipse planning system were upgraded from Millennium 80 to 120 Multileaf Collimator (MLC) and from v8.6 to 11.0 respectively. Our preliminary experience on the pre‐treatment quality assurance verification is discussed.

Methods:

Eight Breast, Three Prostate and One Hypopharynx cancer patients were planned with step and shoot IMRT. All breast cases were planned before the upgrade with 60% cases treated. The ICRU 83 recommendations were followed for the dose prescription and constraints to OAR for all cases. Point dose measurement was done with CIRS cylindrical phantom and PTW 0.125 cc ionization chamber. Measured dose was compared with calculated dose at the point of measurement. Map CHECK diode array phantom was used for the plan verification. Planned and measured doses were compared by applying gamma index of 3% (dose difference) / 3 mm DTA (average distance to agreement). For all cases, a plan is considered to be successful if more than 95% of the tested diodes pass the gamma test. A prostate case was chosen to compare the plan verification before and after the upgrade.

Results:

Point dose measurement results were in agreement with the calculated doses. The maximum deviation observed was 2.3%. The passing rate of average gamma index was measured higher than 97% for the plan verification of all cases. Similar result was observed for plan verification of the chosen prostate case before and after the upgrade.

Conclusion:

Our preliminary experience from the obtained results validates the accuracy of our QA process and provides confidence to extend IMRT to all sites in Kuwait.
SU‐F‐T‐277: Using Dose Weighted Mean Effective Depth to Improve Accuracy of Secondary MU Calculation for VMAT Plans
Authors: Qu H , Yu N , Qi P , Godley A , Xia P
Published: July 2016

Purpose:

In commercial secondary dose calculation system, an average effective depth is used to calculate the Monitor Units for an arc beam from the volumetric modulated arc (VMAT) plans. Typically, an arithmetic mean of the effective depths (AMED) of a VMAT arc beam is used, which may result in large MU discrepancy from that of the primary treatment planning system. This study is to demonstrate the use of a dose weighted mean effective depth (DWED) can improve accuracy of MU calculation for the secondary MU verification.

Methods:

In‐house scripts were written in the primary treatment planning system (TPS) to first convert a VMAT arc beam to a series of static step & shoot beams (every 4 degree). The computed dose and effective depth of each static beam were then used to obtain the dose weighted mean effective depth (DWED) for the VMAT beam. The DWED was used for the secondary MU calculation for VMAT plans. Six lung SBRT VMAT plans, eight head and neck VMAT plans and ten prostate VMAT plans that had > 5% MU deviations (failed MU verification) using the AMED method were recalculated with the DWED. For comparison, same number VMAT plans that had < 5% MU deviations (passed MU verification) using AMED method were also reevaluated with the dose weighted mean effective depth method.

Results:

For MU verification passed plans, the mean and standard deviation of MU differences between the TPS and the secondary calculation program were 2.2%±1.5% for the AMED and 2.1%±1.7% for the DMED method. For the failed plans, the mean and standard deviation of MU differences of TPS to the secondary calculation program were 9.9%±4.7% and 4.7%±2.6, respectively.

Conclusion:

The dose weighted mean effective depth improved MU calculation accuracy which can be used for the pre‐treatment MU verification of VMAT plans.
SU‐F‐T‐279: Impact of Beam Energy Drifts On IMRT Delivery Accuracy
Authors: Goddu S , Kamal G , Herman A , Edwards S , Yaddanapudi S , Oddiraju S , Cai B , Rangaraj D , Mutic S
Published: July 2016

Purpose:

According to TG‐40 percent‐depth‐dose (PDD) tolerance is ±2% but TG‐142 is ±1%. Now the question is, which one is relevant in IMRT era? The primary objective of this study is to evaluate dosimetric impact of beam‐energy‐drifts on IMRT‐delivery.

Methods:

Beam‐energy drifts were simulated by adjusting Linac's bending‐magnet‐current (BMC) followed by tuning the pulse‐forming network and adjusting gun‐current. PDD change of −0.6% and +1.2% were tested. Planar‐dosimetry measurements were performed using an ionization‐chamber‐array in solid‐water phantoms. Study includes 10‐head‐and‐neck and 3‐breast cancer patients. en‐face beam‐deliveries were also tested at 1.3cm and 5.3cm depths. Composite and single‐field dose‐distributions were compared against the plans to determine %Gamma pass‐rates (%GPRs). For plan dose comparisons, changes in %Gamma pass‐rates (cPGPRs) were computed/reported to exclude the differences between dose‐computation and delivery. Dose distributions of the drifted‐energies were compared against their baseline measurements to determine the% GPRs. A Gamma criteria of 3%/3mm was considered for plan‐dose comparisons while 3%/1mm used for measured dose intercomparisons.

Results:

For composite‐dose delivery, average cPGPRs were 0.41%±2.48% and −2.54%±3.65% for low‐energy (LE) and high‐energy (HE) drifts, respectively. For measured dose inter‐comparisons, the average%GPRs were 98.4%±2.2% (LE‐drift) and 95.8%±4.0 (HE‐drift). The average %GPR of 92.6%±4.3% was noted for the worst‐case scenario comparing LE‐drift to HE‐drift. All en‐face beams at 5.3 cm depth have cPGPRs within ±4% of the baseline‐energy measurements. However, greater variations were noted for 1.3cm depth. Average %GPRs for drifted energies were >99% at 5.3cm and >97% at 1.3cm depths. However, for the worst‐case scenario (LE‐drift to HE‐drift) these numbers dropped to 95.2% at 5.3cm and 93.1% at 1.3cm depths.

Conclusion:

The dosimetric impact of beam‐energy drifts was found to be within clinically acceptable tolerance. However, this study includes a single energy with limited range of PDD change. Further studies are on going and the results will be presented.

Received funding from Varian Medical Systems, Palo Alto, CA
SU‐F‐T‐282: Quality Assurance for IMRT/VMAT QA Devices: Issues Affecting the Timing for ArcCHECK Recalibration
Authors: Steers J , Fraass B
Published: July 2016

Purpose:

To discuss several factors surrounding the decision on when to recalibrate the ArcCHECK device as well as present a simple and efficient monthly check to evaluate ArcCHECK calibrations.

Methods:

ArcCheck (Sun Nuclear) calibrations were evaluated monthly by measuring a 25×25cm2 field with 100 MU. Since ArcCHECK measurements are run on an almost nightly basis, such additional square field measurements are obtained with minimal additional effort. An in‐house MATLAB script compares two radial (y‐direction) profiles from the top/center of the new measurement relative to a baseline measurement acquired at the last device calibration. The program automatically generates PDF profile and percent difference comparisons for inspection. Recalibration is based on inspection of measurement profile shapes and percent differences from the baseline measurement.

Results:

The method presented here shows the utility of a simple monthly check for evaluating ArcCHECK calibrations, and in addition shows the importance of recalibrating after Linac beam steering. Our device required recalibration approximately every 8–10 months. However, for ease of scheduling, we propose a bi‐annual recalibration interval. Clinics with a lighter/heavier IMRT/VMAT QA case load may require different recalibration intervals, which are easily determined using the single‐field method presented. Analysis of additional square fields is also easily incorporated, if desired. We further illustrate the importance of array recalibration given that diode irradiation is not uniform over the entire device, with central diodes receiving more than 900 Gy over the course of 10 months and peripheral diodes receiving as little as 50 Gy (in our experience). Finally, we show that timely device recalibration decreases spread in clinical IMRT/VMAT QA gamma passing rates.

Conclusion:

Quality assurance for ArcCHECK array calibrations is important to ensure quality IMRT/VMAT QA comparisons. For many clinics, calibrations should be performed at least annually, if not more frequently, based on use of the proposed monthly check.
SU‐F‐T‐292: Imaging and Radiation Oncology Core (IROC) Houston QA Center's Anthropomorphic Phantom Program
Authors: Mehrens H , Lewis B , Lujano C , Nguyen T , Hernandez N , Alvarez P , Molineu A , Followill D
Published: July 2016

Purpose:

To describe the results of IROC Houston's international and domestic end‐to‐end QA phantom irradiations.

Methods:

IROC Houston has anthropomorphic lung, liver, head and neck, prostate, SRS and spine phantoms that are used for credentialing and quality assurance purposes. The phantoms include structures that closely mimic targets and organs at risk and are made from tissue equivalent materials: high impact polystyrene, solid water, cork and acrylic. Motion tables are used to mimic breathing motion for some lung and liver phantoms. Dose is measured with TLD and radiochromic film in various planes within the target of the phantoms.

Results:

The most common phantom requested is the head and neck followed by the lung phantom. The head and neck phantom was sent to 800 domestic and 148 international sites between 2011 and 2015, with average pass rates of 89% and 92%, respectively. During the past five years, a general upward trend exists regarding demand for the lung phantom for both international and domestic sites with international sites more than tripling from 5 (2011) to 16 (2015) and domestic sites doubling from 66 (2011) to 152 (2015). The pass rate for lung phantoms has been consistent from year to year despite this large increase in the number of phantoms irradiated with an average pass rate of 85% (domestic) and 95% (international) sites. The percentage of lung phantoms used in combination with motions tables increased from 38% to 79% over the 5 year time span.

Conclusion:

The number of domestic and international sites irradiating the head and neck and lung phantoms continues to increase and the pass rates remained constant. These end‐to‐end QA tests continue to be a crucial part of clinical trial credentialing and institution quality assurance.

This investigation was supported by IROC grant CA180803 awarded by the NCI.
SU‐F‐T‐295: MLCs Performance and Patient‐Specific IMRT QA Using Log File Analysis
Authors: Osman A , Maalej N , Jayesh K , Abdel‐Rahman W
Published: July 2016

Purpose:

To analyze the performance of the multi‐leaf collimators (MLCs) from the log files recorded during the intensity modulated radiotherapy (IMRT) treatment and to construct the relative fluence maps and do the gamma analysis to compare the planned and executed MLCs movement.

Methods:

We developed a program to extract and analyze the data from dynamic log files (dynalog files) generated from sliding window IMRT delivery treatments. The program extracts the planned and executed (actual or delivered) MLCs movement, calculates and compares the relative planned and executed fluences. The fluence maps were used to perform the gamma analysis (with 3% dose difference and 3 mm distance to agreement) for 3 IMR patients. We compared our gamma analysis results with those obtained from portal dose image prediction (PDIP) algorithm performed using the EPID.

Results:

For 3 different IMRT patient treatments, the maximum difference between the planned and the executed MCLs positions was 1.2 mm. The gamma analysis results of the planned and delivered fluences were in good agreement with the gamma analysis from portal dosimetry. The maximum difference for number of pixels passing the gamma criteria (3%/3mm) was 0.19% with respect to portal dosimetry results.

Conclusion:

MLC log files can be used to verify the performance of the MLCs. Patientspecific IMRT QA based on MLC movement log files gives similar results to EPID dosimetry results. This promising method for patient‐specific IMRT QA is fast, does not require dose measurements in a phantom, can be done before the treatment and for every fraction, and significantly reduces the IMRT workload.

The author would like to thank King Fahd University of petroleum and Minerals for the support.
SU‐F‐T‐302: Implementation of the RadCalc Image Analysis Tool for IMRT QA
Authors: Soldner A , Fitzherbert C , Zhou F , Hand C
Published: July 2016

Purpose:

To assess RadCalc as a means for analyzing fluence maps of IMRT QA patient plans. Eclipse generated fluence maps were compared to RadCalc fluence maps generated from both Eclipse parameters and from dynalog trajectory files.

Methods:

Six IMRT plans consisting of fifty individual fields were compared both field‐by‐field and as composite plans. These plans were exported from Eclipse to RadCalc. Each plan was then delivered in QA mode on a Varian Clinac iX, while recording and saving the dynalog trajectory files. These files were then imported into RadCalc, providing three sources of generating fluence maps: Eclipse, RadCalc, and dynalog files. Using the image analysis tool in RadCalc, a gamma analysis was then performed as a point‐by‐point comparison for each IMRT field. The Eclipse fluence map was used as the baseline for each comparison.

Results:

Based on the manufacturer's recommendations, all fields were normalized to the maximum pixel value within each Eclipse field. All data was analyzed using a gamma index of 3mm/3% with passing criteria of 90%. For both dynalog analysis and RadCalc fluence analysis, 48/50 created fluence maps passed at greater than 90% when compared with the Eclipse baseline. In analyzing the composite of each of the six patients’ plans, all plans passed over 90%.

Conclusion:

Using the dynalog trajectory files in combination with RadCalc Version 6.3 image analysis is a promising metric for verifying IMRT QA passing rates. Notably, if a field failed, it did so for both dynalog and RadCalc compared to Eclipse. This suggests RadCalc can accurately simulate fluence maps, with similar results to dynalog comparisons. Limitations within the RadCalc software were discovered in the analytical process such as pixel resolution and the inability to set minimum threshold values. Comparisons could be extended to include dose map and distance to agreement analysis by expanding software capabilities.
SU‐F‐T‐303: Quantification of MLC Positioning Accuracy in VMAT Delivery of Head and Neck Cancer Treatment
Authors: Li X , Yang F
Published: July 2016

Purpose:

Knowing MLC leaf positioning error over the course of treatment would be valuable for treatment planning, QA design, and patient safety. The objective of the current study was to quantify the MLC positioning accuracy for VMAT delivery of head and neck treatment plans.

Methods:

A total of 837 MLC log files were collected from 14 head and neck cancer patients undergoing full arc VMAT treatment on one Varian Trilogy machine. The actual and planned leaf gaps were extracted from the retrieved MLC log files. For a given patient, the leaf gap error percentage (LGEP), defined as the ratio of the actual leaf gap over the planned, was evaluated for each leaf pair at all the gantry angles recorded over the course of the treatment. Statistics describing the distribution of the largest LGEP (LLGEP) of the 60 leaf pairs including the maximum, minimum, mean, Kurtosis, and skewness were evaluated.

Results:

For the 14 studied patients, their PTV located at tonsil, base of tongue, larynx, supraglottis, nasal cavity, and thyroid gland with volume ranging from 72.0 cm3 to 602.0 cm3. The identified LLGEP differed between patients. It ranged from 183.9% to 457.7% with a mean of 368.6%. For the majority of the patients, the LLGEP distributions peaked at non‐zero positions and showed no obvious dependence on gantry rotations. Kurtosis and skewness, with minimum/maximum of 66.6/217.9 and 6.5/12.6, respectively, suggested relatively more peaked while right‐skewed leaf error distribution pattern.

Conclusion:

The results indicate pattern of MLC leaf gap error differs between patients of lesion located at similar anatomic site. Understanding the systemic mechanisms underlying these observed error patterns necessitates examining more patient‐specific plan parameters in a large patient cohort setting.
SU‐F‐T‐306: Validation of Mobius 3D and FX for Elekta Linear Accelerators
Authors: Nelson C , Garcia M , Calderon E , Kirsner S
Published: July 2016

Purpose:

Log file based IMRT and VMAT QA is a system that analyzes treatment log files and uses delivery parameters to compute the dose to the patient/phantom. This system was previously commissioned for Varian machines, the purpose of this work is to describe the process for commissioning Mobius for use with Elekta machines.

Methods:

Twelve IMRT and VMAT plans (6×) were planned and delivered and dose was measured using MapCheck, the results were compared to that computed by Mobius. For 10x and 18x, plans were generated, copied to a phantom and delivered, the dose was measured using a single ion chamber. The difference in measured dose to computed dose (Mobius) was used to adjust the dynamic leaf gap (DLG) in Mobius to achieve optimal agreement between measurements, Mobius and treatment plans.

Results:

For the measured dose comparison, the average 3%/3mm gamma 97.1% of pixels passed criteria using MapCheck where Mobius computed 96.9% of voxels passing. For 10×, a DLG of −5.5 was determined to achieve optimal results for TPS and measured ion chamber data with an average 0.1% difference and −1.7% respectively. For 18×, a DLG of −3 was determined to achieve optimal results from the TPS and measured data with an average of −0.7% and −1.4% difference on average from a set of IMRT and VMAT plans. The 6x data needed no DLG correction to arrive at agreement with the TPS and the MapCheck measured data.

Conclusion:

We have validated with measurements for IMRT and VMAT cases the use of Mobius FX with Elekta treatment machines for IMRT and VMAT QA. For 6×, no adjustments to the DLG were required to obtain good results utilizing Mobius whereas for 10× and 18×, the DLG had to be adjusted to obtain optimum agreement with measured data and our TPS.
SU‐F‐T‐308: Mobius FX Evaluation and Comparison Against a Commercial 4D Detector Array for VMAT Plan QA
Authors: Vazquez Quino L , Huerta Hernandez C , Morrow A , Massingill B , Rangaraj D
Published: July 2016

Purpose:

To evaluate the use of MobiusFX as a pre‐treatment verification IMRT QA tool and compare it with a commercial 4D detector array for VMAT plan QA.

Methods:

15 VMAT plan QA of different treatment sites were delivered and measured by traditional means with the 4D detector array ArcCheck (Sun Nuclear corporation) and at the same time measurement in linac treatment logs (Varian Dynalogs files) were analyzed from the same delivery with MobiusFX software (Mobius Medical Systems). VMAT plan QAs created in Eclipse treatment planning system (Varian) in a TrueBeam linac machine (Varian) were delivered and analyzed with the gamma analysis routine from SNPA software (Sun Nuclear corporation).

Results:

Comparable results in terms of the gamma analysis with 99.06% average gamma passing with 3%,3mm passing rate is observed in the comparison among MobiusFX, ArcCheck measurements, and the Treatment Planning System dose calculated. When going to a stricter criterion (1%,1mm) larger discrepancies are observed in different regions of the measurements with an average gamma of 66.24% between MobiusFX and ArcCheck.

Conclusion:

This work indicates the potential for using MobiusFX as a routine pre‐treatment patient specific IMRT method for quality assurance purposes and its advantages as a phantom‐less method which reduce the time for IMRT QA measurement. MobiusFX is capable of produce similar results of those by traditional methods used for patient specific pre‐treatment verification VMAT QA. Even the gamma results comparing to the TPS are similar the analysis of both methods show that the errors being identified by each method are found in different regions. Traditional methods like ArcCheck are sensitive to setup errors and dose difference errors coming from the linac output. On the other hand linac log files analysis record different errors in the VMAT QA associated with the MLCs and gantry motion that by traditional methods cannot be detected.
SU‐F‐T‐313: Clinical Results of a New Customer Acceptance Test for Elekta VMAT
Authors: Rusk B , Fontenot J
Published: July 2016

Purpose:

To report the results of a customer acceptance test (CAT) for VMAT treatments for two matched Elekta linear accelerators.

Methods:

The CAT tests were performed on two clinically matched Elekta linear accelerators equipped with a 160‐leaf MLC. Functional tests included performance checks of the control system during dynamic movements of the diaphragms, MLC, and gantry. Dosimetric tests included MLC picket fence tests at static and variable dose rates and a diaphragm alignment test, all performed using the on‐board EPID. Additionally, beam symmetry during arc delivery was measured at the four cardinal angles for high and low dose rate modes using a 2D detector array. Results of the dosimetric tests were analyzed using the VMAT CAT analysis tool.

Results:

Linear accelerator 1 (LN1) met all stated CAT tolerances. Linear accelerator 2 (LN2) passed the geometric, beam symmetry, and MLC position error tests but failed the relative dose average test for the diaphragm abutment and all three picket fence fields. Though peak doses in the abutment regions were consistent, the average dose was below the stated tolerance corresponding to a leaf junction that was too narrow. Despite this, no significant differences in patient specific VMAT quality assurance measured were observed between the accelerators and both passed monthly MLC quality assurance performed with the Hancock test.

Conclusion:

Results from the CAT showed LN2 with relative dose averages in the abutment regions of the diaphragm and MLC tests outside the tolerances resulting from differences in leaf gap distances. Tolerances of the dose average tests from the CAT may be small enough to detect MLC errors which do not significantly affect patient QA or the routine MLC tests.