bluuebunny/crossref_metadata_2025_split huggingface dataset:
TH‐AB‐201‐05: Determining the Direction Distribution of the Primary Radiation for a Cyberknife‐M6
Authors: Henzen D , C Zanella C , Schmidhalter D , Volken W , Mackeprang P‐H , Malthaner M , K Fix M , Manser P 
Published: July 2016

Purpose:Radiation protection regulatory differentiates between primary and scatter radiation. Whereas for conventional clinical linear accelerators the solid angle for primary radiation is planar, the Cyberknife (Accuray Inc., Sunnyvale, CA) may point its beam in all spatial directions. In order to be able to judge on radiation protection calculations for a Cyberknife‐M6 vault, the direction distribution for delivered plans was evaluated based on clinical experiences.Methods:The log‐files of 121 delivered patient treatment plans were exported, divided into cranial and extra‐cranial treatments and the delivered monitor units (MU) together with the corresponding beam directions were analyzed. This MU‐weighted spatial distribution was then projected to a 9.5 × 5.9 × 3.9 m3 vault, generating an “intensity map” using a binning of 50 × 50 cm2. The factor of direction (FOD) is reported as a fraction of the total applied MUs to the walls, ceiling and floor in the perspective of a patient lying in head‐first‐supine position on the couch. In this study, the term intFOD refers to the integral FOD and maxFOD refers to the maximal FOD for a single bin.Results:For all kind of treatments and collimators, intFOD and maxFOD for the wall behind the patient's head is 0.0. The intFOD for the floor varies between 0.65 and 0.74. For the ceiling, maxFOD is 0.002 and 0.0 for cranial and extra‐cranial cases, respectively. The intFOD for the wall at the patient's feet, is 0.094 for cranial and 0.005 for extra‐cranial cases. There is nearly no difference between the maxFOD of the right and left wall for cranial cases, whereas for extra‐cranial cases these numbers differ by a factor of 1.75.Conclusion:The varying FODs for the Cyberknife were quantified based on delivered treatment plans. These findings are helpful regarding the design of Cyberknife vaults.
TH‐AB‐201‐10: Portal Dosimetry with Elekta IViewDose:Performance of the Simplified Commissioning Approach Versus Full Commissioning
Authors: Kydonieos M , Folgueras A , Florescu L , Cybulski T , Marinos N , Thompson G , Sayeed A , Rozendaal R , Olaciregui‐Ruiz I , Subiel A , Patallo I Silvestre 
Published: July 2016

Purpose:Elekta recently developed a solution for in‐vivo EPID dosimetry (iViewDose, Elekta AB, Stockholm, Sweden) in conjunction with the Netherlands Cancer Institute (NKI). This uses a simplified commissioning approach via Template Commissioning Models (TCMs), consisting of a subset of linac‐independent pre‐defined parameters. This work compares the performance of iViewDose using a TCM commissioning approach with that corresponding to full commissioning. Additionally, the dose reconstruction based on the simplified commissioning approach is validated via independent dose measurements.Methods:Measurements were performed at the NKI on a VersaHD™ (Elekta AB, Stockholm, Sweden). Treatment plans were generated with Pinnacle 9.8 (Philips Medical Systems, Eindhoven, The Netherlands). A farmer chamber dose measurement and two EPID images were used to create a linac‐specific commissioning model based on a TCM. A complete set of commissioning measurements was collected and a full commissioning model was created.The performance of iViewDose based on the two commissioning approaches was compared via a series of set‐to‐work tests in a slab phantom. In these tests, iViewDose reconstructs and compares EPID to TPS dose for square fields, IMRT and VMAT plans via global gamma analysis and isocentre dose difference. A clinical VMAT plan was delivered to a homogeneous Octavius 4D phantom (PTW, Freiburg, Germany). Dose was measured with the Octavius 1500 array and VeriSoft software was used for 3D dose reconstruction. EPID images were acquired. TCM‐based iViewDose and 3D Octavius dose distributions were compared against the TPS.Results:For both the TCM‐based and the full commissioning approaches, the pass rate, mean γ and dose difference were >97%, <0.5 and <2.5%, respectively. Equivalent gamma analysis results were obtained for iViewDose (TCM approach) and Octavius for a VMAT plan.Conclusion:iViewDose produces similar results with the simplified and full commissioning approaches. Good agreement is obtained between iViewDose (simplified approach) and the independent measurement tool.This research is funded by Elekta Limited
TH‐AB‐201‐12: Using Machine Log‐Files for Treatment Planning and Delivery QA
Authors: Stanhope C , Liang J , Drake D , Yan D 
Published: July 2016

Purpose:To determine the segment reduction and dose resolution necessary for machine log‐files to effectively replace current phantom‐based patient‐specific quality assurance, while minimizing computational cost.Methods:Elekta's Log File Convertor R3.2 records linac delivery parameters (dose rate, gantry angle, leaf position) every 40ms. Five VMAT plans [4 H&N, 1 Pulsed Brain] comprised of 2 arcs each were delivered on the ArcCHECK phantom. Log‐files were reconstructed in Pinnacle on the phantom geometry using 1/2/3/4° control point spacing and 2/3/4mm dose grid resolution. Reconstruction effectiveness was quantified by comparing 2%/2mm gamma passing rates of the original and log‐file plans. Modulation complexity scores (MCS) were calculated for each beam to correlate reconstruction accuracy and beam modulation. Percent error in absolute dose for each plan‐pair combination (log‐file vs. ArcCHECK, original vs. ArcCHECK, log‐file vs. original) was calculated for each arc and every diode greater than 10% of the maximum measured dose (per beam). Comparing standard deviations of the three plan‐pair distributions, relative noise of the ArcCHECK and log‐file systems was elucidated.Results:The original plans exhibit a mean passing rate of 95.1±1.3%. The eight more modulated H&N arcs [MCS=0.088±0.014] and two less modulated brain arcs [MCS=0.291±0.004] yielded log‐file pass rates most similar to the original plan when using 1°/2mm [0.05%±1.3% lower] and 2°/3mm [0.35±0.64% higher] log‐file reconstructions respectively. Log‐file and original plans displayed percent diode dose errors 4.29±6.27% and 3.61±6.57% higher than measurement. Excluding the phantom eliminates diode miscalibration and setup errors; log‐file dose errors were 0.72±3.06% higher than the original plans – significantly less noisy.Conclusion:For log‐file reconstructed VMAT arcs, 1° control point spacing and 2mm dose resolution is recommended, however, less modulated arcs may allow less stringent reconstructions. Following the aforementioned reconstruction recommendations, the log‐file technique is capable of detecting delivery errors with equivalent accuracy and less noise than ArcCHECK QA.I am funded by an Elekta Research Grant
TH‐AB‐BRB‐01: Trajectory Modulated Arc Therapy: Application to Partial Breast Irradiation
Authors: Hristov D. 
Published: July 2016

Current state‐of‐the art digital C‐arm medical linear accelerators are capable of delivering radiation treatments with high level of automation, which affords coordinated motions of gantry, couch, and multileaf collimator (MLC) with dose rate modulations. The new machine capacity has shown the potential to bring substantially improved radiation dosimetry and/or delivery efficiency to many challenging diseases. Combining an integrated beam orientation optimization algorithm with automated machine navigation, markedly improved dose conformity has been achieved using 4ρ therapy. Trajectory modulated radiation therapy (TMAT) can be used to deliver highly conformal dose to partial breast or to carve complex dose distribution for therapy involving extended volumes such as total marrow and total lymph node treatment. Dynamic electron arc radiotherapy (DEAR) not only overcomes the deficiencies of conventional electron therapy in dose conformity and homogeneity but also achieves so without patient‐specific shields. The combination of MLC and couch tracking provides improved motion management of thoracic and abdominal tumors. A substantial body of work has been done in these technological advances for clinical translation. The proposed symposium will provide a timely review of these exciting opportunities.

Learning Objectives:
Recognize the potential of using digitally controlled linacs for clinically significant improvements in delivered dose distributions for various treatment sites.
Identify existing approaches to treatment planning, optimization and delivery for treatment techniques utilizing the advanced functions of digital linacs and venues for further development and improvement.
Understand methods for testing and validating delivery system performance.
Identify tools available on current delivery systems for implementation and control for such treatments.
Obtain the update in clinical applications, trials and regulatory approval.K. Sheng, NIH U19AI067769, NIH R43CA183390, NIH R01CA188300, Varian Medical SystemsV. Yu, Varian Medical Systems, AAPM Summer Undergraduate Fellowship, NSF graduate fellowshipS. Nill, Elekta AB. Cancer Research UK under Programme C33589/A19727, NIHR Biomedical Research Centre at The Royal Marsden and The Institute of Cancer Research.
TH‐CD‐207A‐11: Sensitivity Analysis of Action Limits for Real‐Time EPID‐Based Delivery Verification System Using Artificial Clinical Relevant Error Simulations
Authors: Fuangrod T , Simpson J , Middleton R , Greer P 
Published: July 2016

Purpose:A real‐time patient treatment delivery verification system using EPID (Watchdog) has been developed as an advanced patient safety tool. In a pilot study data was acquired for 119 prostate and head and neck (HN) IMRT patient deliveries to generate body‐site specific action limits using statistical process control. The purpose of this study is to determine the sensitivity of Watchdog to detect clinically significant errors during treatment delivery.Methods:Watchdog utilizes a physics‐based model to generate a series of predicted transit cine EPID images as a reference data set, and compares these in real‐time to measured transit cine‐EPID images acquired during treatment using chi comparison (4%, 4mm criteria) after the initial 2s of treatment to allow for dose ramp‐up. Four study cases were used; dosimetric (monitor unit) errors in prostate (7 fields) and HN (9 fields) IMRT treatments of (5%, 7%, 10%) and positioning (systematic displacement) errors in the same treatments of (5mm, 7mm, 10mm). These errors were introduced by modifying the patient CT scan and re‐calculating the predicted EPID data set. The error embedded predicted EPID data sets were compared to the measured EPID data acquired during patient treatment. The treatment delivery percentage (measured from 2s) where Watchdog detected the error was determined.Results:Watchdog detected all simulated errors for all fields during delivery. The dosimetric errors were detected at average treatment delivery percentage of (4%, 0%, 0%) and (7%, 0%, 0%) for prostate and HN respectively. For patient positional errors, the average treatment delivery percentage was (52%, 43%, 25%) and (39%, 16%, 6%).Conclusion:These results suggest that Watchdog can detect significant dosimetric and positioning errors in prostate and HN IMRT treatments in real‐time allowing for treatment interruption. Displacements of the patient require longer to detect however incorrect body site or very large geographic misses will be detected rapidly.
TH‐CD‐207A‐12: Impacts of Inter‐ and Intra‐Fractional Organ Motion for High‐Risk Prostate Cancer Stereotactic Body Radiation Therapy
Authors: Hassan Rezaeian N , Chi Y , Zhou Y , Tian Z , Jiang S , Hannan R , Jia X 
Published: July 2016

Purpose:We are conducting a clinical trial on stereotactic body radiation therapy (SBRT) for high‐risk prostate cancer. Doses to three targets, prostate, intra‐prostatic lesion, and pelvic lymph node (PLN) region, are escalated to three different levels via simultaneous integrated boost technique. Inter‐/intra‐fractional organ motions deteriorate planned dose distribution. This study aims at developing a dose reconstruction system to comprehensively understand the impacts of organ motion in our clinical trial.Methods:A 4D dose reconstruction system has been developed for this study. Using a GPU‐based Monte‐Carlo dose engine and delivery log file, the system is able to reconstruct dose on static or dynamic anatomy. For prostate and intra‐prostatic targets, intra‐fractional motion is the main concern. Motion trajectory acquired from Calypso in previously treated SBRT patients were used to perform 4D dose reconstructions. For pelvic target, inter‐fractional motion is one concern. Eight patients, each with four cone beam CTs, were used to derive fractional motion. The delivered dose was reconstructed on the deformed anatomy. Dosimetric parameters for delivered dose distributions of the three targets were extracted and compared with planned levels.Results:For prostate intra‐fractional motion, the mean 3D motion amplitude during beam delivery ranged from 1.5mm to 5.0mm and the average among all patients was 2.61mm. Inter‐fractional motion for the PLN target was more significant. The average amplitude among patients was 4mm with the largest amplitude up to 9.6mm. The D95% deviation from planned level for prostate PTVs and GTVs are on average less than<0.1% and this deviation for intra‐prostatic lesion PTVs and GTVs were more prominent. The dose at PLN was significantly affected with D95% reduced by up to 44%.Conclusion:Intra‐/inter‐fractional organ motion is a concern for high‐risk prostate SBRT, particularly for the PLN target. Our dose reconstruction approach can also serve as the basis to guide treatment adaptation.
TH‐CD‐206‐03: Evaluation of a New Method to Improve Atlas Based Segmentation for the Bladder and Rectum
Authors: Nelson A , Pirozzi S , Chung S 
Published: July 2016

Purpose:Atlas segmentation for the bladder and rectum pose particular challenges due to variability in bladder filling and variability in rectal contents including air and fecal matter. Previously we evaluated atlas segmentation for high risk prostate cancer including the bladder and rectum. In the current study we sought to further improve automated segmentation results by utilizing a customized post‐processing workflow for the bladder and rectum.Methods:Pelvic CT scans for 32 subjects with prostate cancer were chosen and the bladder and rectum were first segmented using the Multi‐5 atlas‐based approach described in Pirozzi et al (IJROBP 2012). The post‐processing workflow for the bladder limited the HU range to include only water and soft tissue density voxels (Multi‐5 PP). For the rectum, air in the image was masked to soft tissue density and an atlas masked with the same approach was used to segment the rectum. Next, the rectal contours were restricted to exclude voxels in the fat HU range (Masked Multi‐5 PP). Multi‐5, Multi‐5 PP, and Masked Multi‐5 PP were compared to manually defined contours using Hausdorff distance and the Dice Similarity Index (DSI).Results:The average dice and Hausdorff distance for the bladder for Multi‐5 and Multi‐5 PP was 0.83, 0.46 and 0.86, 0.39 respectively, significantly increasing dice while decreasing Hausdorff distance (p < 0.0005). Multi‐5 PP for the rectum improved significantly over Multi‐5 alone with DSI and Hausdorff distances of 0.79, 0.31 and 0.68, 0.43 respectively (p‐value < 0.0005).Conclusion:Customized workflows applying post‐processing steps to atlas‐segmented bladders and rectal masking significantly increase the accuracy of contours when compared to manual contours. These automated steps should be incorporated into the atlas based segmentation workflow of the bladder and rectum.Aaron Nelson is a part owner and employee of MIM Software Inc.; Sara Pirozzi is an employee of MIM Software Inc.; Stephanie Chung is an employee of MIM Software Inc.
TH‐CD‐209‐07: Preliminary Experimental Comparison of Spot‐ and Continuous Line Scanning with Or Without Rescanning for Gated Proton Therapy
Authors: Fattori G , Klimpki G , Safai S , Weber D , Lomax A , Psoroulas S 
Published: July 2016

Purpose:We aim to compare the performance of discrete spot‐ or continuous line scanning combined with rescanning in mitigating residual organ motion during gated proton therapy treatments.Methods:The Quasar respiratory phantom was used to move a 2D scintillation detector on a linear trajectory with sinusoidal motion pattern (sin4), 20 mm peak‐to‐peak amplitude and 5 sec period. Its motion was monitored using a customized solution based on optical tracking technology. We compared spot and line scanning plans for a monoenergetic 150 MeV circular field, 50.4 mm radius at isocenter. Transverse dose distributions at 13 cm depth in PMMA (15.47 mm water equivalent) were measured to compare three options for motion mitigation: rescanning (10× factor), gating and their combination. The gating window was centered in the trajectory plateau to simulate end‐exhale gated treatment in presence of 2 mm and 4 mm residual motion, parallel or perpendicular to the primary scanning direction.Results:When the target moves perpendicular to the primary scanning direction, large dose deviations are measured (γ3%/3mm=47%) without mitigation techniques. Beam gating combined with rescanning restores target coverage (γ3%/3mm=91%). For parallel target motion, observed dose distortions in the non‐compensated irradiation are smaller (γ3%/3mm=77%). Beam gating alone recovers the 100% gamma pass‐rate at 3%/3mm. Continuous line scanning reduces delivery time by up to 60% with respect to discrete spot scanning in presence of motion mitigation, and improves homogeneity when rescanning is applied (up to 20%, perpendicular motion, 4 mm residual motion).Conclusion:The direction of motion has a large impact on the target dose coverage. Nevertheless, even in the worst case scenario, gating combined with rescanning could mitigate the impact of motion on dose deposition. Moreover, continuous line rescanning improves the robustness against residual motion in the gating window.This study has received funding from the European Community's Seventh Framework Programme (FP7/2007–2013) under grant agreement n.290605 (PSI‐FELLOW/COFUND) and ‘Giuliana and Giorgio Stefanini Foundation’
TH‐CD‐209‐11: Simulation Study of Real‐Time‐Image Gating On Spot Scanning Proton Therapy for Lung Tumors
Authors: Kanehira T , Matsuura T , Takao S , Matsuzaki Y , Fujii Y , Fujii T , Miyamoto N , Inoue T , Katoh N , Shimizu S , Umegaki K , Shirato H 
Published: July 2016

Purpose:To study the impact of a real‐time‐image gating on spot scanning proton therapy for lung tumors and to examine the suitable size of the gating window (GW).Methods:We investigated a real‐time‐image gated proton therapy (RGPT), in which two fluoroscopic units monitor a gold sphere fiducial in real‐time, and the proton beam is irradiated only when the marker enters within the pre‐assigned GW. We designed 5 treatment plans for 7 lung cancer patients: RGPT with a GW of ±1, 2, 5, and 8 mm and free‐breathing proton therapy (FBPT) using the end‐exhale and average images of 4‐dimensional (4D) CT, respectively. 70 Gy(RBE)/10fr was prescribed to 99% of the targets. The time‐series data of the three‐dimensional marker positions (RTRT data) were grouped into 10 phases to associate with the phases of 4DCT. The 4D dose distributions were calculated using the plan information, RTRT Data, 4DCT, and modeled accelerator pattern. The dose distribution in each respiratory phase was deformed into the end‐exhale CT. The D99 and D5‐95 of CTV (with a criteria of D99>95% and D5‐95<5%), V20 of Lung‐GTV, and treatment times were evaluated.Results:GWs ≤ ±2 mm satisfied the criteria of CTV in all cases, whereas GWs ≥ ±5 mm did not satisfy the criteria in some cases. The V20 was reduced by more than 18.9% (relative to FBPT) for GW ≤ ±2 mm, but equaled or even surpassed the FBPT for GWs ≥ ±5 mm. The irradiation times for the ±1, 2, 5, and 8 mm GWs and FBPT were 372.4±208.3, 215.2±51.5, 180.9±31.6, 178.4±21.2, and 140.1±15.2 s, respectively. The GW of ±1 mm caused large variation in irradiation time among the patients.Conclusion:In RGPT for lung cancer, the most suitable GW, in terms of good dose preservation without prolonging the therapeutic beam delivery, is ±2 mm.
TH‐CD‐207B‐05: Measurement of CT Bow‐Tie Profiles Using a Linear Array Detector
Authors: Yang K , Li X , Liu B 
Published: July 2016

Purpose:To accurately measure CT bow‐tie profiles from various manufacturers and to provide non‐proprietary information for CT system modeling.Methods:A GOS‐based linear detector (0.8 mm per pixel and 51.2 cm in length) with a fast data sampling speed (0.24 ms/sample) was used to measure the relative profiles of bow‐tie filters from a collection of eight CT scanners by three different vendors, GE (LS Xtra, LS VCT, Discovery HD750), Siemens (Sensation 64, Edge, Flash, Force), and Philips (iBrilliance 256). The linear detector was first calibrated for its energy response within typical CT beam quality ranges and compared with an ion chamber and analytical modeling (SPECTRA and TASMIP). A geometrical calibration process was developed to determine key parameters including the distance from the focal spot to the linear detector, the angular increment of the gantry at each data sampling, the location of the central x‐ray on the linear detector, and the angular response of the detector pixel. Measurements were performed under axial‐scan modes for most representative bow‐tie filters and kV selections from each scanner. Bow‐tie profiles were determined by re‐binning the measured rotational data with an angular accuracy of 0.1 degree using the calibrated geometrical parameters.Results:The linear detector demonstrated an energy response as a solid state detector, which is close to the CT imaging detector. The geometrical calibration was proven to be sufficiently accurate (< 1mm in error for distances >550 mm) and the bow‐tie profiles measured from rotational mode matched closely to those from the gantry‐stationary mode. Accurate profiles were determined for a total of 21 bow‐tie filters and 83 filter/kV combinations from the abovementioned scanner models.Conclusion:A new improved approach of CT bow‐tie measurement was proposed and accurate bow‐tie profiles were provided for a broad list of CT scanner models.