bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐748: Theoretical Investigation On Using High Energy Proton Beam for Total‐Body‐Irradiation
Authors: Zhang M , Zou J , Chen T , Yue N
Published: June 2015

Purpose:

The broad‐slow‐rising entrance dose region proximal to the Bragg peak made by a mono‐energetic proton beam could potentially be used for total body irradiation (TBI). Due to the quasi‐uniform dose deposition, customized thickness compensation may not be required to deliver a uniform dose to patients with varied thickness. We investigated the possibility, efficacy, and hardware requirement to use such proton beam for TBI.

Methods:

A wedge shaped water phantom with thickness varying from 2 cm to 40 cm was designed to mimic a patient. Geant4 based Monte Carlo code was used to simulate broad mono‐energetic proton beams with energy ranging from 250 MeV to 300 MeV radiating the phantom. A 6 MV photon with 1 cm water equivalent build‐up used for conventional TBI was also calculated. A paired‐opposing beam arrangement with no thickness compensation was used to generate TBI plans for all beam energies. Dose from all particles were scored on a grid size of 2 mm3. Dose uniformity across the phantom was calculated to evaluate the plan. The field size limit and the dose uniformity of Mevion S250 proton system was examined by using radiochromic films placed at extended treatment distance with the open large applicator and 90° gantry angle.

Results:

To achieve a maximum ± 7.5% dose variation, the largest patient thickness variation allowed for 250 MeV, 275 MeV, and 300 MeV proton beams were 27.0 cm, 34.9 cm and 36.7 cm. The value for 6 MV photon beam was only 8.0 cm to achieve the same dose variation. With open gantry, Mevion S250 system allows 5 m source‐to‐surface distance producing an expected 70 cm2 field size.

Conclusion:

Energetic proton beam can potentially be used to deliver TBI. Treatment planning and delivery would be much simple since no thickness compensation is required to achieve a uniform dose distribution.
SU‐E‐T‐749: Thorough Calibration of MOSFET Dosimeters
Authors: Plenkovich D , Thomas J
Published: June 2015

Purpose:

To improve the accuracy of the MOSFET calibration procedure by performing the measurement several times and calculating the average value of the calibration factor for various photon and electron energies.

Methods:

The output of three photon and six electron beams of Varian Trilogy linear accelerator SN 5878 was calibrated. Five reinforced standard sensitivity MOSFET dosimeters were placed in the calibration jig and connected to the Reader Module. As the backscatter material was used 7 cm of Virtual Water. The MOSFET dosimeters were covered with 1.5 cm thick bolus for the regular and SRS 6 MV beams, 3 cm bolus for 15 MV beam, 1.5 cm bolus for 6 MeV electron beam, and 2 cm bolus for the electron energies of 9, 12, 15, 18, and 22 MeV. The dosimeters were exposed to 100 MU, and the calibration factor was determined using the mobileMOSFET software. To improve the accuracy of calibration, this procedure was repeated ten times and the calibration factors were averaged.

Results:

As the number of calibrations was increasing the variability of calibration factors of different dosimeters was decreasing. After ten calibrations, the calibration factors for all five dosimeters were within 1% of one another for all energies, except 6 MV SRS photons and 6 MeV electrons, for which the variability was 2%.

Conclusions:

The described process results in calibration factors which are almost independent of modality or energy. Once calibrated, the dosimeters may be used for in‐vivo dosimetry or for daily verification of the beam output. Measurement of the radiation dose under bolus and scatter to the eye are examples of frequent use of calibrated MOSFET dosimeters. The calibration factor determined for full build‐up is used under these circumstances. To the best of our knowledge, such thorough procedure for calibrating MOSFET dosimeters has not been reported previously.

Best Medical Canada provided MOSFET dosimeters for this project.
SU‐E‐T‐750: Three Dimensional in Silico Study of Brachytherapy Application with In‐Situ Dose‐Painting Administered Via Gold‐Nanoparticle Eluters
Authors: Sinha N , Cifter G , Ngwa W
Published: June 2015

Purpose:

Brachytherapy Application with in‐situ Dose‐painting Administered via Gold‐Nanoparticle Eluters (BANDAGE) has been proposed as a new therapeutic strategy for radiation boosting of high‐risk prostate tumor subvolume while minimizing dose to neighboring organs‐at‐risk. In a previous study the one‐dimensional dose‐painting with gold nanoparticles (GNP) released from GNP‐loaded brachytherapy spacers was investigated. The current study investigates BANDAGE in three‐dimensions.

Methods:

To simulate GNPs transport in prostrate tumors, a three dimensional, cylindrically symmetric transport model was generated using a finite element method (FEM). A mathematical model of Gold nanoparticle (GNPs) transport provides a useful strategy to optimize potential treatment planning for BANDAGE. Here, treatment of tumors with a radius of 2.5 cm was simulated in 3‐D. This simulation phase considered one gold based cylindrical spacer (GBS of size 5mm × 0.8 mm) introduced at the center of the spherical tumor with initial concentration of 100 mg/g or 508 mol/m3 of GNP. Finite element mesh is used to stimulate the GNP transport. Gold concentrations within the tumor were obtained using a 3‐D FEM solution implemented by COMSOL.

Results:

The analysis shows the spread of the GNPs through‐out the tumor with the increase of concentration towards the periphery with time. The analysis also shows the concentration profiles and corresponding dose enhancement factors (dose boost factor) as a function of GNP size.

Conclusion:

This study demonstrates the use of computational modeling and optimal parameter estimation to predict local GNPs from central implant as a function of x, y and z axis . Such a study provides a useful reference for ongoing translational studies for the BANDAGE approach
SU‐E‐T‐751: Three‐Component Kinetic Model of Tumor Growth and Radiation Response for Stereotactic Radiosurgery
Authors: Watanabe Y , Dahlman E , Leder K , Hui S
Published: June 2015

Purpose:

To develop and study a kinetic model of tumor growth and its response to stereotactic radiosurgery (SRS) by assuming that the cells in irradiated tumor volume were made of three types.

Methods:

A set of ordinary differential equations (ODEs) were derived for three types of cells and a tumor growth rate. It is assumed that the cells were composed of actively proliferating cells, lethally damaged‐dividing cells, and non‐dividing cells. We modeled the tumor volume growth with a time‐dependent growth rate to simulate the saturation of growth. After SRS, the proliferating cells were permanently damaged and converted to the lethally damaged cells. The amount of damaged cells were estimated by the LQ‐model. The damaged cells gradually stopped dividing/proliferating and died with a constant rate. The dead cells were cleared from their original location with a constant rate. The total tumor volume was the sum of the three components. The ODEs were numerically solved with appropriate initial conditions for a given dosage. The proposed model was used to model an animal experiment, for which the temporal change of a rhabdomyosarcoma tumor volume grown in a rat was measured with time resolution sufficient to test the model.

Results:

To fit the model to the experimental data, the following characteristics were needed with the model parameters. The α‐value in the LQ‐model was smaller than the commonly used value; furthermore, it decreased with increasing dose. At the same time, the tumor growth rate after SRS had to increase.

Conclusions:

The new 3‐component model of tumor could simulate the experimental data very well. The current study suggested that the radiation sensitivity and the growth rate of the proliferating tumor cells may change after irradiation and it depended on the dosage used for SRS. These preliminary observations must be confirmed by future animal experiments.
SU‐E‐T‐754: Three‐Dimensional Patient Modeling Using Photogrammetry for Collision Avoidance
Authors: Popple R , Cardan R
Published: June 2015

Purpose:

To evaluate photogrammetry for creating a three‐dimensional patient model.

Methods:

A mannequin was configured on the couch of a CT scanner to simulate a patient setup using an indexed positioning device. A CT fiducial was placed on the indexed CT table‐overlay at the reference index position. Two dimensional photogrammetry targets were placed on the table in known positions. A digital SLR camera was used to obtain 27 images from different positions around the CT table. The images were imported into a commercial photogrammetry package and a 3D model constructed. Each photogrammetry target was identified on 2 to 5 images. The CT DICOM metadata and the position of the CT fiducial were used to calculate the coordinates of the photogrammetry targets in the CT image frame of reference. The coordinates were transferred to the photogrammetry software to orient the 3D model. The mannequin setup was transferred to the treatment couch of a linear accelerator and positioned at isocenter using in‐room lasers. The treatment couch coordinates were noted and compared with prediction. The collision free regions were measured over the full range of gantry and table motion and were compared with predictions obtained using a general purpose polygon interference algorithm.

Results:

The reconstructed 3D model consisted of 180000 triangles. The difference between the predicted and measured couch positions were 5 mm, 1 mm, and 1 mm for longitudinal, lateral, and vertical, respectively. The collision prediction tested 64620 gantry table combinations in 11.1 seconds. The accuracy was 96.5%, with false positive and negative results occurring at the boundaries of the collision space.

Conclusion:

Photogrammetry can be used as a tool for collision avoidance during treatment planning. The results indicate that a buffer zone is necessary to avoid false negatives at the boundary of the collision‐free zone. Testing with human patients is underway.

Research partially supported by a grant from Varian Medical Systems
SU‐E‐T‐755: Timing Characteristics of Proton and Carbon Ion Treatments Using a Synchrotron and Modulated Scanning
Authors: Zhao J , Li Y , Sun L , Huang Z , Deng Y , Moyers M , Hsi W , Wu X
Published: June 2015

Purpose:

The time required to deliver a treatment impacts not only the number of patients that can be treated each day but also the accuracy of delivery due to potential movements of patient tissues. Both macroscopic and microscopic timing characteristics of a beam delivery system were studied to examine their impacts on patient treatments.

Methods:

35 patients were treated during a clinical trial to demonstrate safety and efficacy of a Siemens Iontris system prior to receiving approval from the Chinese Food and Drug Administration. The system has a variable cycle time and can provide proton beams from 48 to 221 MeV/n and carbon ions from 86 to 430 MeV/n. A modulated scanning beam delivery technique is used where the beam remains stationary at each spot aiming location and is not turned off while the spot quickly moves from one aiming location to the next. The treatment log files for 28 of the trial patients were analyzed to determine several timing characteristics.

Results:

The average portal time per target dose was 172.5 s/Gy for protons and 150.7 s/Gy for carbon ions. The maximum delivery time for any portal was less than 300 s. The average dwell time per spot was 12 ms for protons and 3.0 ms for carbon ions. The number of aiming positions per energy layer varied from 1 to 258 for protons and 1 to 621 for carbon ions. The average spill time and cycle time per energy layer were 1.20 and 2.68 s for protons and 0.95 and 4.73 s for carbon ions respectively. For 3 of the patients, the beam was gated on and off to reduce the effects of respiration.

Conclusion:

For a typical target volume of 153 cc as used in this clinical trial, the portal delivery times were acceptable.
SU‐E‐T‐764: Track Repeating Algorithm for Proton Therapy Applied to Intensity Modulated Proton Therapy for Head‐And‐Neck Patients
Authors: Yepes P , Mirkovic D , Mohan R
Published: June 2015

Purpose:

To determine the suitability of fast Monte Carlo techniques for dose calculation in particle therapy based on track‐repeating algorithm for Intensity Modulated Proton Therapy, IMPT. The application of this technique will make possible detailed retrospective studies of large cohort of patients, which may lead to a better determination of Relative Biological Effects from the analysis of patient data.

Methods:

A cohort of six head‐and‐neck patients treated at the University of Texas MD Anderson Cancer Center with IMPT were utilized. The dose distributions were calculated with the standard Treatment Plan System, TPS, MCNPX, GEANT4 and FDC, a fast track‐repeating algorithm for proton therapy for the verification and the patient plans. FDC is based on a GEANT4 database of trajectories of protons in a water. The obtained dose distributions were compared to each other utilizing the g‐index criteria for 3mm‐3% and 2mm‐2%, for the maximum spatial and dose differences. The γ‐index was calculated for voxels with a dose at least 10% of the maximum delivered dose. Dose Volume Histograms are also calculated for the various dose distributions.

Results:

Good agreement between GEANT4 and FDC is found with less than 1% of the voxels with a γ‐index larger than 1 for 2 mm‐2%. The agreement between MCNPX with FDC is within the requirements of clinical standards, even though it is slightly worse than the comparison with GEANT4.The comparison with TPS yielded larger differences, what is also to be expected because pencil beam algorithm do not always performed well in highly inhomogeneous areas like head‐and‐neck.

Conclusion:

The good agreement between a track‐repeating algorithm and a full Monte Carlo for a large cohort of patients and a challenging, site like head‐and‐neck, opens the path to systematic and detailed studies of large cohorts, which may yield better understanding of biological effects.
SU‐E‐T‐768: Treatment Time Nomogram for Strut‐Based Accelerated Partial Breast Applicators
Authors: Yock A , Reiff J , Morcovescu S , Scanderbeg D
Published: June 2015

Purpose:

The purpose of this work was to generate a tabular nomogram of treatment times for strut‐based APBI applicators. The nomogram is intended to provide guidance and a quality assurance check for clinics establishing new treatment techniques or transitioning from balloon‐based applicators.

Methods:

A retrospective analysis was conducted of 486 patients receiving APBI using strut‐based applicators at three separate institutions. Strut‐based applicators are composed of a central channel surrounded by 6 close‐range (“mini”), 6 mid‐range, 8, or 10 peripheral channels. Patient data was organized based on applicator size (a surrogate of treatment volume) and number of organs at risk. Three organs at risk categories were determined based on the proximity of the device to the patient's skin and/or chest wall (0, 1, or 2 OARs). The proximity criterion was defined as being < 5 mm from the cavity wall/peripheral struts. A tabular nomogram of treatment time (based on nominal 10 Ci source strength) was generated from descriptive statistics of each combination of applicator size and organs at risk category.

Results:

The average treatment time was observed to be directly related to applicator size and, to a lesser extent, inversely related to the number of nearby organs at risk. Distributions of treatment times observed for each combination of applicator size and organs at risk category are depicted in Figure 1. The tabular nomogram featuring average treatment times with standard deviations is presented in Table 1.

Conclusion:

Strutbased APBI treatment times were observed to depend in a consistent manner on applicator size and number of nearby organs at risk. Information provided in the nomogram presented here represents several hundred treatments performed at multiple institutions. This data can serve as guidance or quality assurance for institutions with limited experience using strut‐based APBI applicators.
SU‐E‐T‐773: Use of a Commercial TPS for Deriving Exit Dose Distribution for Patient Specific QA with An EPID
Authors: Haering P , Lang C , Splinter M
Published: June 2015

Purpose:

A method to derive exit dose distributions with a commercial treatment planning system for comparison to Epid measured doses.

Methods:

In contrast to published methods, we present an approach that uses a treatment planning system (Raystation, Raysearch) to calculate exit dose patterns based on a modified patient CT dataset. The EPID is assumed as water equivalent and therefore is represented as water filled ring in the images. This is done by: ‐Export a renamed copy of the patient CT and plan data set. —Manipulate the CT‐data to a field of view of 1000 mm. — Insert the water filled cylinder ring, centered to the target point. — Manipulate plan file with the new target and dose prescription point. — Import and recalculate dose on the manipulated data set. — Export and extract exit field dose matrix from the cylinder (optional entrance dose). — Calibrate matrix to size and rebin data from the cylinder to EPID equivalent data. — Correct Epid measurement for scatter, position and field size. ‐Evaluate and compare data in Verisoft (PTW). Data manipulation and extraction is done by a simple tool (IDL, Exelis).

Results:

This method was tested on a Siemens Artiste 6MV for field sizes up to 27×27cm2 limited by used geometry and EPID size. First phantom measurements show good results for fields up to 20×20cm (pass rate > 95% for 3%, 3mm Gamma index) while larger fields have higher discrepancies towards the field edges. This might Result from off axis softening of the beam and the higher sensitivity of the detector to beam scatter.

Conclusion:

This method might simplify the use of exit dosimetry with the EPID for patient specific QA as it uses the dose calculation of a commercial treatment planning system. The concept was proven by phantom data sets, giving acceptable results.
SU‐E‐T‐774: Use of a Scintillator‐Mirror‐Camera System for the Measurement of MLC Leakage Radiation with the CyberKnife M6 System
Authors: Goggin L , Kilby W , Noll M , Maurer C
Published: June 2015

Purpose:

A technique using a scintillator‐mirror‐camera system to measure MLC leakage was developed to provide an efficient alternative to film dosimetry while maintaining high spatial resolution. This work describes the technique together with measurement uncertainties.

Methods:

Leakage measurements were made for the InCise™ MLC using the Logos XRV‐2020A device. For each measurement approximately 170 leakage and background images were acquired using optimized camera settings. Average background was subtracted from each leakage frame before filtering the integrated leakage image to replace anomalous pixels. Pixel value to dose conversion was performed using a calibration image. Mean leakage was calculated within an ROI corresponding to the primary beam, and maximum leakage was determined by binning the image into overlapping 1mm × 1mm ROIs. 48 measurements were performed using 3 cameras and multiple MLC‐linac combinations in varying beam orientations, with each compared to film dosimetry. Optical and environmental influences were also investigated.

Results:

Measurement time with the XRV‐2020A was 8 minutes vs. 50 minutes using radiochromic film, and results were available immediately. Camera radiation exposure degraded measurement accuracy. With a relatively undamaged camera, mean leakage agreed with film measurement to ≤0.02% in 92% cases, ≤0.03% in 100% (for maximum leakage the values were 88% and 96%) relative to reference open field dose. The estimated camera lifetime over which this agreement is maintained is at least 150 measurements, and can be monitored using reference field exposures. A dependency on camera temperature was identified and a reduction in sensitivity with distance from image center due to optical distortion was characterized.

Conclusion:

With periodic monitoring of the degree of camera radiation damage, the XRV‐2020A system can be used to measure MLC leakage. This represents a significant time saving when compared to the traditional film‐based approach without any substantial reduction in accuracy.
SU‐E‐T‐776: Use of Quality Metrics for a New Hypo‐Fractionated Pre‐Surgical Mesothelioma Protocol
Authors: Richardson S , Mehta V
Published: June 2015

Purpose:

The “SMART” (Surgery for Mesothelioma After Radiation Therapy) approach involves hypo‐fractionated radiotherapy of the lung pleura to 25Gy over 5 days followed by surgical resection within 7. Early clinical results suggest that this approach is very promising, but also logistically challenging due to the multidisciplinary involvement. Due to the compressed schedule, high dose, and shortened planning time, the delivery of the planned doses were monitored for safety with quality metric software.

Methods:

Hypo‐fractionated IMRT treatment plans were developed for all patients and exported to Quality Reports™ software. Plan quality metrics or PQMs™ were created to calculate an objective scoring function for each plan. This allows for an objective assessment of the quality of the plan and a benchmark for plan improvement for subsequent patients. The priorities of various components were incorporated based on similar hypo‐fractionated protocols such as lung SBRT treatments.

Results:

Five patients have been treated at our institution using this approach. The plans were developed, QA performed, and ready within 5 days of simulation. Plan Quality metrics utilized in scoring included doses to OAR and target coverage. All patients tolerated treatment well and proceeded to surgery as scheduled. Reported toxicity included grade 1 nausea (n=1), grade 1 esophagitis (n=1), grade 2 fatigue (n=3). One patient had recurrent fluid accumulation following surgery. No patients experienced any pulmonary toxicity prior to surgery.

Conclusion:

An accelerated course of pre‐operative high dose radiation for mesothelioma is an innovative and promising new protocol. Without historical data, one must proceed cautiously and monitor the data carefully. The development of quality metrics and scoring functions for these treatments allows us to benchmark our plans and monitor improvement. If subsequent toxicities occur, these will be easy to investigate and incorporate into the metrics. This will improve the safe delivery of large doses for these patients.
SU‐E‐T‐777: Use of Tennis Racket and Air Gap Between the Body and Carbon Fiber Couch for Skin Sparing in Radiation Therapy of Prone Breast
Authors: Lief E
Published: June 2015

Purpose:

To reduce the skin dose from the carbon fiber couch scatter in radiation treatment of breast cancer in the prone position. If this issue is not addressed, the prone breast touching the solid carbon fiber couch can absorb significant dose to the skin and cause the skin reaction.

Methods:

1. Use of “tennis racket” instead of the solid couch. To check this hypothesis, we measured the dose at the depth of 5 mm in solid water phantom placed on the couch, using a Farmer chamber. A plan for a patient with 6MV beams, gantry angles of 113 and 286 degrees Varian scale was used. It was found that treatment with “tennis racket” instead of the solid carbon fiber couch reduces the surface dose by 5–7%, depending on the beam direction. 2. Use of the air gap between the couch and the body was analyzed using radiochromic film on the surface of the solid water phantom 10 cm thick. Initially the phantom was placed on the couch with the film sandwiched in between. Two fields at the angles of 135 and 315 degrees were used. The measurements were repeated for the air gap of 2 and 5 cm and 6 and 15 MV beams.

Results:

It was found that a 2‐cm gap decreased the surface dose by 3% for a 6 MV beam and by 5.5% for a 15 MV beam. A 5‐cm gap reduced the dose by 9% for 6 MV and 13.5% for 15 MV.

Conclusion:

Use of both methods (combined if possible) can significantly reduce the surface dose in radiation therapy of the prone breast and possible skin reaction. We plan to explore dependence of the dose reduction upon the angle of incidence.
SU‐E‐T‐779: Use of the Varian Eclipse Scripting API to Collect Volumetric Modulated Arc Therapy Plan Data
Authors: Janes L A , Anderson C J R , Matuszak M M , Roberts D A , Moran J M , Younge K C
Published: June 2015

Purpose:

We have introduced an automated script into the VMAT planning process to visualize and understand plan characteristics in comparison to past plans including number of arcs, arc weighting, and arc modulation.

Methods:

Varian's Eclipse Scripting Application Programming Interface (API) was used to create a script to compare new VMAT plans to past clinical VMAT plans, during and after the planning process. A graphical user interface was developed to display the results for straightforward analysis and interpretation. Analysis of previously treated plans from the past two years was used to design the data layout and organizational categories. In addition, a method was developed to automatically update the script as new plans are generated.

Results:

Plan data are represented in a histogram format, which is updateable with additional treatment plans by uploading a comma separated value file with the new patients’ information. The current script has the ability to display the number of arcs, the MU per arc and per control point, and the degree of modulation in each control point compared to all past VMAT plans. The user can filter the histogram by treatment site to easily compare the current plan to other plans of the same site, or to all sites. The histogram also contains the total number of plans being compared, the average value of the metric being examined, and the standard deviation of that metric. The script has been built with a modular framework such that additional plan metrics can be added as they are developed.

Conclusions:

The script interface provides easy to understand feedback on quality metrics of VMAT plans compared to other plans for the same body site. The script enables dosimetrists to ensure consistent plan quality, and assists physicists in checking plans prior to pre‐treatment quality assurance measurements.

This project was supported in part by P01CA059827.
SU‐E‐T‐780: Use Robustness Optimization (RO) Method to Improve the Planning Efficiency for Pencil Beam Scanning Cranial Spinal Irradiation
Authors: Ding X , Traneus E , Zhang J , Lin H , Zhai H , Rosen L , Wu H
Published: June 2015

Purpose:

We evaluate the feasibility of using robustness optimization (RO) function to improve the planning efficiency of pencil beam scanning (PBS) craniospinal irradiation (CSI) with gradient matching technique.

Methods:

A CSI patient was planned with 2 lateral brain fields and 4 posterior fields to cover the entire spine to maximal field of 24 cm × 20 cm on a compact PBS gantry, ProteusONE. CSI plans were generated using traditional volumetric gradient dose optimization (VGDO) and robustness optimization (RO) method respectively. In traditional VGDO, besides the sectioned spine target volumes, gradient volume (GV) were generated as 4 equally spaced structures e.g. 80%, 60%, 40%, and 20% of prescription dose. In RO method, only sectioned spine target volumes with an overlap of 4cm were created. In the robustness optimization settings, 5mm uncertainty in superior and inferior direction was defined for auto gradient optimization. Dosimetric metrics of conformity number (CN), homogeneity index (HI), and maximal cord doses were compared in Raystation version 4.6.100.6.

Results:

In VGDO method, total 16 GV structures and five 100% dose level target structures were contoured compared to total 5 target structures in RO method which saves 30 min in contour. With the same PTV coverage (95% volume receive 30.6Gy prescription dose), maximum cord dose is 32.64Gy in VGDO and 31.94Gy in RO. HI is 1.03 and 1.04 for VGDO and RO respectively. CN is 0.93 and 0.94 for VGDO and RO respectively.

Conclusions:

The dosimetric comparison demonstrated both methods are equivalent in terms of plan quality. With robust optimization for CSI gradient matching, it efficiently reduces the amount of planning target contour structure by factor of 4 and thus improves the planning efficiency especially for 4 or more gradient junction area.
SU‐E‐T‐784: Using MLC Log Files for Daily IMRT Delivery Verification
Authors: Stathakis S , Defoor D , Linden P , Kirby N , Papanikolaou N
Published: June 2015

Purpose:

To verify daily intensity modulated radiation therapy (IMRT) treatments using multi‐leaf collimator (MLC) log files.

Methods:

The MLC log files from a NovalisTX Varian linear accelerator were used in this study. The MLC files were recorded daily for all patients undergoing IMRT or volumetric modulated arc therapy (VMAT). The first record of each patient was used as reference and all records for subsequent days were compared against the reference. An in house MATLAB software code was used for the comparisons. Each MLC log file was converted to a fluence map (FM) and a gamma index (γ) analysis was used for the evaluation of each daily delivery for every patient. The tolerance for the gamma index was set to 2% dose difference and 2mm distance to agreement while points with signal of 10% or lower of the maximum value were excluded from the comparisons.

Results:

The γ between each of the reference FMs and the consecutive daily fraction FMs had an average value of 99.1% (ranged from 98.2 to 100.0%). The FM images were reconstructed at various resolutions in order to study the effect of the resolution on the γ and at the same time reduce the time for processing the images. We found that the comparison of images with the highest resolution (768×1024) yielded on average a lower γ (99.1%) than the ones with low resolution (192×256) (γ 99.5%).

Conclusion:

We developed an in‐house software that allows us to monitor the quality of daily IMRT and VMAT treatment deliveries using information from the MLC log files of the linear accelerator. The information can be analyzed and evaluated as early as after the completion of each daily treatment. Such tool can be valuable to assess the effect of MLC positioning on plan quality, especially in the context of adaptive radiotherapy.
SU‐E‐T‐788: Validating the Use of Surfacing Mapping Tools for Motion and Irregular Breathing Pattern Monitoring On Lung SBRT Patients
Authors: Xie X , Cao D , Mehta V , Shepard D
Published: June 2015

Validating the Use of Surfacing Mapping Tools for Monitoring Motion and Irregular Breathing Patterns for Lung SBRT Patients

Purpose:

In this study, we have examined the utility of surface mapping in the treatment of lung SBRT patients. We examined the extent to which intra‐fraction patient motion and irregular breathing patterns impact the accuracy of treatment deliveries.

Materials and Methods:

The C‐RAD Catalyst, an optical surface mapping system was used to track the intra‐fractional isocenter motion of five lung SBRT patients treated with VMAT. A respiratory tracking tool was used to track the breathing pattern of these patients and to correlate the breathing pattern to the isocenter motion.

Results:

For 2 of the 5 patients the isocenter displacement exceeding the 5mm planning margin for a portion of the treatment delivery with the time outside of tolerance at 2.2%, and 2.5%.

Conclusions:

1) Breathing patterns may change between different fractions for the same patient; 2)Breathing patterns can change from the beginning to the end of the same fraction; 3) Not only amplitude, but also the baseline of breathing may change during an individual fraction; 4) We cannot predict which patients will have a stable isocenter in treatment even after the simulation study; and5)Real‐time motion monitoring with surface‐mapping tools and respiratory gating (free breathing or breath‐hold) may provide clinically valuable solution in motion management for lung SBRT patients.

The research is supported by funding from Elekta.
SU‐E‐T‐792: Validation of a Secondary TPS for IROC‐H Recalculation of Anthropomorphic Phantoms
Authors: Kerns J , Howell R , Followill D , Melancon A , Stingo F , Kry S
Published: June 2015

Purpose:

To validate a secondary treatment planning system (sTPS) for use by the Imaging & Radiation Oncology Core‐Houston (IROC‐H). The TPS will recalculate phantom irradiations submitted by institutions to IROC‐H and compare plan results of the institution to the sTPS.

Methods:

In‐field dosimetric data was collected by IROC‐H for numerous linacs at 6, 10, 15, and 18 MV. The data was aggregated and used to define reference linac classes; each class was then modeled in the sTPS (Mobius3D) by matching the in‐field characteristics. Fields used to collect IROC‐H data were recreated and recalculated using Mobius3D. The same dosimetric points were measured in the recalculation and compared to the initial collection data. Additionally, a 6MV Monte Carlo beam configuration was used to compare penumbrae in the Mobius3D models. Finally, a handful of IROC‐H head and neck phantoms were recalculated using Mobius3D.

Results:

Recalculation and quantification of differences between reference data and Mobius3D values resulted in a relative matching score of 12.45 (0 is a perfect match) for the default 6MV Mobius3D beam configuration. By adjusting beam configuration options, iterations resulted in scores of 8.45, 6.32, and 3.52, showing that customization could have a dramatic effect on beam configuration. After in‐field optimization, penumbra was compared between Monte Carlo and Mobius3D for the reference fields. For open jaw fields, FWHM field widths and penumbra widths were different by <0.6 and <1mm respectively; for MLC open fields the penumbra widths were up to 1.5mm different. Phantom recalculations showed good agreement, having an average of 0.6% error per beam.

Conclusion:

A secondary TPS has been validated for simple irradiation geometries using reference data collected by IROC‐H. The beam was customized to the reference data iteratively and resulted in a good match. This system can provide independent recalculation of phantom plans based on independent reference data.
SU‐E‐T‐797: Variations of Cardiac Dose at Different Respiratory Status in CyberKnife M6â„¢ Treatment Plans for Accelerated Partial Breast Irradiation (APBI)
Authors: Long S , Shang C , Evans G , Leventouri T
Published: June 2015

Purpose:

Cyberknife robotic assisted radiation delivery has become a choice for accelerated breast RT, while a slightly increased cardiac dose has been reported. The dose dynamics throughout the respiration cycle has scarcely been explored. This study was designed to investigate the dose changes at each respiratory phase or status during respiration cycle.

Methods:

Six patients with 4DCT studies and six patients with a pair of free‐breathing and deep breath‐hold CT sets were used for dosimetry comparisons. 4DCT sets were obtained by Siemens™ CT and its respiratory gating system, comprising of 8 phases. Standard APBI plan at 340 cGy was done per fraction per NSABP B‐39/RTOG 0413 and modulated with Cyberknife M6™ on MultiPlan™5.1.2. For the purpose of this study, the tumor volume was outlined in the media‐lower quadrant of the left breast.

Results:

Except for D5cc in plans with 4DCT, cardiac doses are significantly different between respiratory phases in well inhaled breathing phases, and more significantly in plans with BH CT. Mean cardiac doses in 100% inhalation phase were often found to be 5–15% (p< 0.02) less than those in other phases.

Conclusion:

Although ineligible cardiac doses are noted in APBI plans using 4D free‐breathing CT and instantaneous free breathing CT series, a reduction in cardiac dose was seen for the well‐inhaled phases. This provides practical guidance for cardiac dose reduction applicable with CK M6 APBR.
SU‐E‐T‐798: Verification of 3DVH Dose Distribution Before Clinical Implementation for Patient‐Specific IMRT QA
Authors: McFadden D
Published: June 2015

Purpose:

In recent years patient‐specific IMRT QA has transitioned from film and chamber measurements to beam‐by‐beam 2D array measurements. 3DVH takes this transition a step further by estimating the 3D dose distribution delivered using 2D per beam diode array measurements. In this study, the 3D dose distribution generated by 3DVH is compared to film and chamber measurements. In addition, the accuracy ROI volume and error detection is investigated.

Methods:

Composite film and ion chamber measurements in a solid water phantom were performed for 9 IMRT PINNACLE patient plans for 4 treatment sites. The film and chamber measurements were compared to the dose distribution predicted by 3DVH using MAPCHECK2 per beam measurements. The absolute point dose measurement (CAX) was extracted from the predicted 3DVH and PINNACLE dose distribution and was compared by taking the ratio of measured to predicted doses. The dose distribution measured with film was compared to the distribution in the corresponding plane (AX, SAG, COR) extracted from predicted dose distribution by 3DVH and PINNACLE using a 2D gamma analysis. Gamma analysis was performed with 2% dose, 2 mm DTA, 20% threshold, and global normalization. In addition, the percent difference between 3DVH and PINNACLE ROI volumes was calculated.

Results:

The average ratio of the measured point dose vs the 3DVH predicted dose was 1.017 (σ=0.011). The average gamma passing rate for measured vs 3DVH dose distributions was 95.1% (σ=2.53%). The average percent difference of 3DVH vs PINNACLE ROI volume was 2.29% (σ=2.5%).

Conclusion:

The dose distributions predicted by 3DVH using MAPCHECK2 measurements are the same as the distributions that would have been obtained using film and chamber. The ROI volumes used in 3DVH are not an exact match to those in PINNACLE; the effect requires more investigation. The accuracy of error detection by 3DVH is currently being investigated.
SU‐E‐T‐804: Verification of the BJR‐25 Method of KQ Determination for CyberKnife Absolute Dosimetry
Authors: Gersh J , Willett B
Published: June 2015

Purpose:

Absolute calibration of the CyberKnife is performed using a 6cm‐diameter cone defined at 80cm SAD. Since kQ is defined using PDD values determined using 10×10 cm fields at 100cm SSD, the PDD must be corrected in order to correctly apply the quality conversion factor. The accepted method is based on equivalent field‐size conversions of PDD values using BJR25. Using the new InCise MLC system, the CK is capable of generating a rectangular field equivalent to 10×10 cm square field. In this study, a comparison is made between kQ values determined using the traditional BJR25 method and the MLC method introduced herein.

Methods:

First, kQ(BJR) is determined: a PDD is acquired using a 6cm circular field at 100cm SSD, its field size converted to an equivalent square, and PDD converted to a 10×10cm field using the appropriate BJR25 table. Maintaining a consistent setup, the collimator is changed, and the MLC method is used. Finally, kQ is determined using PDDs acquired with a 9.71×10.31cm at 100cm SSD. This field is produced by setting the field to a size of 7.77×8.25cm (since it is defined at 80cm SAD). An exact 10×10cm field since field size is relegated to increments of its leaf width (0.25cm). This comparison is made using an Exradin A1SL, IBA CC08, IBA CC13, and an Exradin A19. For each detector and collimator type, the beam injector was adjusted to give 5 different beam qualities; representing a range of clinical systems.

Results:

Averaging across all beam qualities, kQ(MLC) differed from kQ(BJR) by less than 0.15%. The difference between the values increased with detector volume.

Conclusion:

For CK users with standard cone collimators, the BJR25 method has been verified. For CK users the MLC system, a technique is described to determine kQ.

Primary author is the President/Owner of Spectrum Medical Physics, LLC, a company which maintains contracts with Siemens Healthcare and Standard Imaging, Inc.
SU‐E‐T‐805: Verification of the Simplified Monte Carlo Method for Simulation in An Inhomogeneous Phantom
Authors: Mizutani S , Takada Y , Kohno R , Hotta K , Akimoto T
Published: June 2015

Purpose:

A simplified Monte Carlo (SMC) method has been developed to obtain fast and accurate dose calculation in heterogeneous tissues to improve the accuracy of dose calculation. We have applied the SMC method to calculation of dose kernels for the pencil beam scanning. While the SMC method tracks individual primary protons in medium, it simplifies the dose calculation by using a measured depth‐dose distribution instead of considering nuclear reactions and tracking secondary particles. To verify the accuracy of SMC calculation, we compared a dose‐calculation Result using the SMC method with that using the Full Monte Carlo (FMC) method in an inhomogeneous phantom.

Methods:

As a model of the inhomogeneous media, we considered a phantom complied of a rectangular acrylic block of size 150*300*200 mm 3 immersed in water within a virtual container with a size of 300*300*400 mm3.

Results:

We found excellent agreement of overall dose distributions between the SMC and FMC methods. As for the laterally integrated depth‐dose distributions, slight difference was found in front of the second Bragg‐Peak between the two algorithms. While it took 25717.0 s on 2.7 GHz Intel Core i7 for the FMC method to complete the calculation, it took 15.4 s for the SMC method to complete it. The SMC method can calculate the dose distribution approximately 1675 times faster than the FMC method.

Conclusion:

The dose distribution obtained by SMC method agreed well that obtained by the FMC method in a simple inhomogeneous phantom. In contrast, calculation time by the SMC method has been reduced by three orders in magnitude compared with the FMC method.
SU‐E‐T‐810: Volumetric Modulated Arc Therapy and Conventional Intensity‐Modulated Radiotherapy for Non‐Small‐Cell Lung Cancer with Simultaneously Integrated Boost Radiation Therapy: A Planning Comparison Study
Authors: Liu T , Chen J , Zhang G , Sun T
Published: June 2015

Purpose:

To compare and analyze the characteristics of intensity‐modulated arc therapy(IMAT) versus fixed‐gantry intensity‐modulated radiotherapy(IMRT) in treatment of non‐small‐cell lung cancer.

Methods:

Twelve patients treated in our radiotherapy center were selected for this study. The patient subsequently underwent 4D‐CT simulation.Margins of 5mm and 10mm were added to the ITV to generate the CTV and PTV respectively. Three treatment plans (IMRT,one single arc (RA1),double arcs (RA2))were generated with Eclipse ver.8.6 planning systems. Using a dose level of 75Gy in 15fractions to the ITV,60Gy in 15fractions to the CTV and 45Gy in 15fractions to the PTV respectively. The target and normol tissue volumes were compared,as were the dosimetry parameters.

Results:

There were no significant differences in CI of ITV,PTV,HI of ITV,CTV and PTV, V5,V10,V15,V20,V25,V30,V45,V50 of total‐lung and mean lung dose (all p>0.05). However, the differences were significant in terms of CI of CTV,V5 of B‐P (all p<0.05). On the MU, IMRT=1540MU,RA1=1006 MU and RA2=1096 MU. (F=12.00,P=0.000).On the treatment time, IMRT= 13.5min,RA1= 1.5min,and RA2=2.5 min (F= 30.11,P=0.000 ).

Conclusion:

IMAT is equal to IMRT in dosimetril evaluation. Due to much less Mu and delivery time,IMAT is an ideal technique in treating patients by reduceing the uncomfortable influnce which could effect the treatment.
SU‐E‐T‐815: In Vivo Dosimetry and Daily Arc Junction Verification Using EBT3 Gafchromic Film for Pediatric Cranio‐Spinal Irradiation
Authors: Saleh H , Ferjani S , Masssey V , Howlin T , Pokhrel D
Published: June 2015

Purpose:

Perform dosimetric comparison between planned and delivered dose in the junction area, measure daily dose variation in the arc junction area for pediatric patients treated for medulloblastoma using Craniospinal axis irradiation(CSI)

Material and methods

Dose comparison in the junction area, daily dose variation in the arc junction area for a Rando Phantom and 5 pediatric patients treated using CSI technique were analyzed. Plans were created using the Eclipse treatment planning system. Two arcs for cranium and 1 arc for spine region were used. Planar dose matrix was created by projecting phantom and patient plan into the ArcCheck phantom. EBT3 film was placed in the middle of ArcCheck plug to measure dose distribution in the junction areaDuring patient treatment, strip of EBT3 film was placed daily at each junction area for verification. EBT3 films were scanned using a flatbed scanner, Epson Expression 10000 XL. Film QA pro software was used to analyze film. Scanning and analysis was performed according to vendor recommendations and AAPM TG‐55 report. Films were scanned and analyzed daily after each treatment and at the end of treatment course. Planar dose distributions from films were compared with planar dose distribution from treatment planning system.

Results:

Comparison of planned vs. measured dose distributions for patients have passing rates of 90%–100% with 3% and 3 mm gamma analysis. In some of the treatment fractions, daily setup film showed variation in dose distribution in the junction area.

Conclusion:

It is critical to measure dose distribution in the arc junction area and use additional quality assurance measures to verify daily setup for CSI patient where one or more junctions are present. EBT3 film prove to be a good tool to achieve this task considering flexibility associated with the film such as symmetry, self‐developing and ease of use
SU‐F‐BRD‐07: Fast Monte Carlo‐Based Biological Optimization of Proton Therapy Treatment Plans for Thyroid Tumors
Authors: Wan Chan Tseung H , Ma J , Ma D , Beltran C
Published: June 2015

Purpose:

To demonstrate the feasibility of fast Monte Carlo (MC) based biological planning for the treatment of thyroid tumors in spot‐scanning proton therapy.

Methods:

Recently, we developed a fast and accurate GPU‐based MC simulation of proton transport that was benchmarked against Geant4.9.6 and used as the dose calculation engine in a clinically‐applicable GPU‐accelerated IMPT optimizer. Besides dose, it can simultaneously score the dose‐averaged LET (LETd), which makes fast biological dose (BD) estimates possible. To convert from LETd to BD, we used a linear relation based on cellular irradiation data. Given a thyroid patient with a 93cc tumor volume, we created a 2‐field IMPT plan in Eclipse (Varian Medical Systems). This plan was re‐calculated with our MC to obtain the BD distribution. A second 5‐field plan was made with our in‐house optimizer, using pre‐generated MC dose and LETd maps. Constraints were placed to maintain the target dose to within 25% of the prescription, while maximizing the BD. The plan optimization and calculation of dose and LETd maps were performed on a GPU cluster. The conventional IMPT and biologically‐optimized plans were compared.

Results:

The mean target physical and biological doses from our biologically‐optimized plan were, respectively, 5% and 14% higher than those from the MC re‐calculation of the IMPT plan. Dose sparing to critical structures in our plan was also improved. The biological optimization, including the initial dose and LETd map calculations, can be completed in a clinically viable time (∼30 minutes) on a cluster of 25 GPUs.

Conclusion:

Taking advantage of GPU acceleration, we created a MC‐based, biologically optimized treatment plan for a thyroid patient. Compared to a standard IMPT plan, a 5% increase in the target's physical dose resulted in ∼3 times as much increase in the BD. Biological planning was thus effective in escalating the target BD.