bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐689: Semi‐Automated GPU‐Based Monte Carlo Dose Calculation for Total Body Irradiation
Authors: Folkerts M , Ouyang L , Jia X , Jiang S , Gu X
Published: June 2015

Purpose:

To enable fast and accurate TBI dose calculations for research and clinical applications.

Methods:

We adapted GPU‐based Monte Carlo (MC) dose calculation library written for patient specific IMRT quality assurance to enable us to compute dose delivered to a patient during total body irradiation (TBI). The full CT dataset of the patient is loaded into the system along with organ contours, specifically, the body and lung contours, as well as rectangular contours denoting compensator sizes and locations. The CT data is automatically cropped by setting all values outside of the body contour to air HU value. The lung and compensator contours are automatically voxelized, projected and rotated by 45 degrees onto the 40×40 cm fluence map plane and weighted by the appropriate attenuation value. The mirror image of the fluence map is also computed for the opposite beam configuration (P‐A for A‐P, or R‐L for L‐R). The fluence maps are then included as input, along with the auto‐segmented material types and density values from the CT dataset, into the GPU‐based MC calculation. The Result is the full body MC calculated TBI dose for the patient which can then be used for various research studies. The users upload their data to the GPU server using FTP. The interface to the calculation software is in the form of an iPython Notebook, enabling the user to access the GPU server through a common web browser to input various parameters, monitor the process, and analyze results.

Results:

The developed software enables researchers and clinicians to compute MC TBI dose results in less than 2 minutes given lung and body contours and compensator transmission coefficients.

Conclusion:

We successfully designed and developed a semi‐automated MC TBI dose calculation software to enable research and clinical studies.
SU‐E‐T‐694: Significant Skin Dose Differences Between IMRT and VMAT and Between Boost and Integrated Treatment Regimens for Treating Head and Neck and Other Cancer Site Patients
Authors: Penoncello G , Ding G
Published: June 2015

Purpose:

The purpose of this study is to evaluate 1) dose to skin between VMAT and IMRT treatment techniques for targets in the head and neck, pelvis, and brain; 2) to determine if the treatment dose and fractionation regimen impacts the skin dose between traditional sequential boost and integrated boost regimens for head and neck patients.Methods and Materials: A total of 19 patients and 48 plans were evaluated. Eclipse (v11) treatment planning system was used to plan nine head and neck patients, five Prostate patients and five Brain patients with VMAT and static field IMRT. The mean skin dose and the maximum dose to a contiguous 2 cm^3 volume for head and neck plans and brain plans and a contiguous 5 cm^3 volume for pelvis plans, was compared for each treatment technique. Three of nine head and neck patients utilized an integrated boost regimen. One integrated boost plan was re‐planned with IMRT and VMAT using a traditional boost regimen.

Results:

For targets located in the head and neck VMAT reduced the mean dose and contiguous hot spot most noticeably in the shoulder region, by 5.6% and 5.4% respectively. When using an integrated boost regimen the contiguous hot spot skin dose in the shoulder was larger on average than a traditional boost pattern by 26.5% and the mean skin dose was larger by 1.7%. VMAT techniques largely decrease the contiguous hot spot in skin in the pelvis by an average of 36% compared with IMRT.

Conclusions:

For the same target coverage, VMAT can reduce the skin dose in all regions of the body, but more noticeably in pelvis and the shoulders in head and neck patients. In head and neck patients using integrated boost regimens lead to higher shoulder skin doses compared to traditional boost regimens.
SU‐E‐T‐695: Silicon Diode Measurements of Output Field Size Factors for Proton Pencil Beam Scanning with a Dedicated Nozzle
Authors: McGlade J , Lin L , Solberg T
Published: June 2015

Purpose:

Proton irradiation degrades solid state detectors, producing high recombination and leakage currents and ultimately rendering them unusable for dosimetry. In this work we evaluate the performance of a new p‐type silicon diode under proton beam irradiation.

Methods:

A novel p‐type silicon diode with improved radiation hardness has recently been developed (IBA Dosimetry, Schwarzenbruck, Germany). The dosimetric properties of the devices were assessed for application in pencil beam scanning (PBS) proton irradiation. Using PBS fields with 4 mm spaced, uniform intensity spots, dose and dose rate linearity were evaluated over a clinical range. Output factors were measured at energies of 100, 180, and 225 MeV and for field sizes ranging from 4×4 – 20×20 cm2. Measurements were performed at the center of the square fields at varying depths upstream from the Bragg peak and compared with previously published results.

Results:

At shallow depths, the diode exhibits linear behavior (0.1%) over the clinical range of doses and dose rates; the sensitivity of the diode in this region is ∼6.0 nC/Gy. As the depth of measurement approaches within 2 cm of each Bragg peak, the deviation from linearity becomes greater (±2–6%). The diode shows less response with small fields and ‐ over responds with large fields.ConclusionAt depths more than 2 cm upstream from the Bragg Peak, the diode shows very good agreement with ion chamber and calculated results for output factors. This demonstrates that diodes can be used for relative measurements at shallow depths, but should be used with caution at deeper depths and for higher energy. Measurements at all depths exhibit an energy dependence that is characteristic of silicon diodes and requires correction.

Detectors provided by IBA Dosimetry GmbH, Schwarzenbruck, Germany
SU‐E‐T‐703: Site Specific Image‐Guided Radiotherapy (IGRT) Tolerances for Patient Safety
Authors: Wijesooriya K , Seitter K , Dharia I , Read P , Larner J
Published: June 2015

Purpose:

To present our single institution experience of a very large pool of data, for all treatment sites, with image‐guided radiotherapy, comparing patient's external tattoo marks, kV or MV orthogonals to align to bony anatomy, and CBCT for soft tissue registration of the tumor volumes. To present measurement based tolerances for daily imaging registration shifts that could be used as guidelines.

Methods:

From March 2013 to March 2014, 17197 patient treatment fields were analyzed for the treatment of brain, chest‐wall, esophagus, head and neck, lung, pelvis, prostate, spine, extremities, and breast. TrueBeam trajectory log files for all imaging types as well as all treatment types were accessed, and couch parameters compared. Three types of shifts are evaluated: i) kV, or MV orthogonal imaging shifts from patient's tattoo marks to bony anatomy surrounding the tumor, ii) CBCT imaging shifts from patients bony alignment to soft tissue alignment of tumor, iii) CBCT imaging shifts from patients tattoo marks to soft tissue alignment of tumor. Shifts in the anterior‐posterior (AP), superior‐inferior (SI), and left‐right (LR) dimensions were recorded. Site specific mean and standard deviation of absolute differences were also compared.

Results:

Site specific observed imaging tolerances are: brain (1.82 cm), chest‐wall (1.26 cm), esophagus (1.60 cm), head and neck (1.2 cm), lung (1.97 cm), pelvis (3.65 cm), prostate (2.64 cm), spine (1.38 cm), extremities (3.96 cm).

Conclusion:

These site specific imaging tolerances could be used as guidelines for raising a red flag when exceeded.
SU‐E‐T‐706: Small Field Dosimetry: Output Factors for Fixed Cones, Iris Collimator and MLC Fields for the CyberKnife M6™ System with Newly Released InCise™ Multileaf Collimator
Authors: Huq M Saiful , Zhang Y , Ozhasoglu C , Jang S , Heron D , Lalonde R
Published: June 2015

Purpose:

Accuray has recently released a new collimator, the InCise™ Multileaf Collimator (MLC), for clinical use with the CyberKnife M6™ System. This work reports the results of measurements of output factors (OF) for fields shaped by the InCise™ Multileaf collimator, Iris collimator and fixed cones.

Methods:

The MLC consists of 41 pairs of 2.5 mm wide leaves projecting a minimum and maximum field size of 7.6 mm × 7.5 mm and 110 mm × 97.5 mm at 800 mm SAD. OF measurements were made using 6 different detectors: PTW stereotactic and electron diodes, PTW microDiamond detector, Sun Nuclear Edge diode, IBA SFD diode and PFD 3G photon diode. Measurements were made for 14 MLC field sizes and 12 cone/Iris field sizes (5mm to 60 mm diameter field sizes). All measurements were made in a Wellhofer water tank at the depth of maximum dose. Correction factors from Francescon et al (PMB 59, 2014, N11‐N17; 17, 2012 3741–3748) were used to correct the diode responses for the fixed cone and Iris measurements.

Results:

For the MLC fields no correction factors are currently available. For the cones and Iris collimator, the average of corrected OF for all diodes ranged from 0.651 ± 0.014 (5mm cone) to 0.994 ± 0.001 (50 mm cone); for the Iris collimator the corresponding values are 0.510 ±0.004 and 0.997 ±0.000 respectively. The OF for the MLC field sizes ranged from 0.806 ±0.009 for the 7.6 mm × 7.5 mm field to 1.023± 0.003 for the 110 mm × 97.5 mm field size.

Conclusion:

The present results are the first set of output factor data reported for the InCise™ MLC, Iris collimator and the fixed cones for the CyberKnife M6™ system. Good agreement is obtained among all the corrected data for the cones and Iris data.
SU‐E‐T‐709: Spatial Resolution Requirements for Fragment Identification in a Carbon Ion Spread Out Bragg Peak
Authors: McBeth R , Borak T
Published: June 2015

Purpose:

To determine spatial resolution for detectors used to identify charged fragments in a carbon ion therapy spread out Bragg peak.

Methods:

The Geant4 Monte Carlo toolkit was used to simulate a 2 × 2 cm2 broad beam of carbon ions incident on a 30 × 30 × 12 cm3 water phantom. The carbon ion energies ranged from 165 MeV/n to 220 MeV/n and intensities were selected in order to simulate a SOBP extending from 6 to 10 cm in depth. Scoring of secondary fragments was performed for different pixel sizes at 3 depths in water. The analysis was designed to identify situations where two or more fragments intercept a pixel coincidently.

Results:

Initial results show that increased depths in the phantom require smaller pixel sizes due to increases in fragment population. At a pixel size of 1 × 1 cm2, a detector pixel was intercepted by two or more particles 16%, 14% and 30% percent of the time at depths of 6, 8 and 10 cm respectively. The probability of coincident hits decreases with smaller pixel size. At a pixel size of 0.05 × 0.05 cm2 a detector pixel was intercepted by two or more particles 0.7%, 0.9%, and 2% of the time at depths of 6, 8 and 10 cm respectively.

Conclusion:

Accurate characterization of carbon ion beams requires the consideration of secondary charged particles that have different radiobiological effectiveness. A method for accurate identification in a clinical setting could lead to improved models for treatment planning. This work investigated the spatial resolution requirements for a detector that could be used to perform secondary fragment identification in a spread out Bragg peak. These preliminary results show that detectors with pixel size on the order of 0.5 × 0.5 mm2 may be sufficient.

This work was supported through research grant NNX13AD19G for Early Stage Innovations (ESI) administered through the NASA Space Technology Research Grants Program. No conflict of interest.
SU‐E‐T‐710: Study of Dosimetric Leaf Gap and Transmission Factor Variations Affecting Common Clinical QA Tools
Authors: Monroe J , Bull C
Published: June 2015

Purpose:

To determine if clinical variations in the Dosimetric Leaf Gap (DLG) or Transmission Factor (TF) are detectable in a 3D secondary calculation, 1D secondary calculation, log file‐based analysis or hardware‐based quality assurance of realistic patient plans.

Methods:

DLG values and TF values were selected based on clinical surveys of 17 clinics. The minimum, maximum, and representative values were used in the generation of 30 6MV plans. Six patients were created in Eclipse 11 and planned for three sites: SBRT Lung, Prostate, and Prostate with Lymph Nodes(P/S/L). Each site was planned utilizing two different techniques: IMRT and VMAT. Variations in the DLG used were 0.02cm, 0.1748cm, 0.17208cm (SBRT), and 0.2cm while holding the TF at 0.015 and 0.0148 (SBRT). The TF values used were 0.0135, 0.015, 0.0148 (SBRT), and 0.0215 while holding the DLG at 0.1748cm or 0.17208cm(SBRT).Plans used the Analytic Anisotropic Algorithm. Consistency in planning included controlling objectives, iterations, priorities, and normalizations. Plans were delivered on a Varian Trilogy with Millennium 120 MLCs. Plans were analyzed with: Mobius3D using Collapsed Cone Convolution/Superposition Algorithm (CCCS) reference beam model, RadCalc using a modified Clarkson scatter integration lookup tables, a gantry‐mounted MapCHECK2 using a 2‐D diode array, and MobiusFX log file‐based CCCS analysis. Gamma analysis in Mobius3D, MobiusFX, and MapCHECK2 used a gamma criteria of 95%/3%/3mm. No efforts were made to improve any outcome by searching for improved agreement.

Results:

The prostate IMRT plans were not affected by any variation. IMRT Lung showed mixed results. VMAT Prostate plans were not affected. The VMAT P/S/L was flagged by Mobius3D and Fx, while the VMAT Lung DLG 0.02cm was flagged by RadCalc as well as the IMRT Lung TF=0.0215.

Conclusion:

The variations in clinical DLG values and TF values were only detectable in extreme cases (DLG=0.02cm or TF=0.0215) in a few select plan variations tested here.

Mobius Systems supplied by Mobius Medical, LP. C Bull is an employee of Mobius Medical, LP
SU‐E‐T‐712: Study of the Linear‐Quadratic‐Linear and Universal‐Survival‐ Curve Models for Lung SBRT Using BED and EQD2 Concepts
Authors: Kehwar T.S. , Chopra K.L. , Sood B.
Published: June 2015

Purpose:

Linear‐quadratic‐linear(LQ‐L) and Universal‐Survival‐Curve(USC) models are investigated for the changes in biologically effective dose(BED) and equivalent dose at 2Gy/fraction(EQD2) for SBRT.

Method:

Survival data were extracted from published reports for 5 small‐cell(SC) and 6 non‐small cell(NSC) lung cancer cell lines. The best‐fit regression and chi‐square fit used to compute α and β of LQ, D0, and n of multitarget(MT) and y of LQ‐L models, and used to calculate BED and EQD2 for lung SBRT.

Results:

The value of parameters α and β was determined by best‐fit regression for low dose survival data(R2≥0.97) and by interactive‐inspection and chi‐square best‐fit to initial curvature points for LQ model, respectively. D0 and n were calculated by best‐fit regression to final slope points. Mean value of α, α/β, D0 and n with 95%CI was 0.756±0.152Gy‐1, 16.31±7.78Gy, 1.014±0.308Gy and 1.688±0.696, respectively, for SC; and 0.18±0.081Gy‐1, 7.74±5.893Gy, 2.90±1.704Gy and 3.69±3.36, for NSC, respectively. Mean value of α, α/β, D0 and n for lung tumors, averaging parameter values for all cell lines, was 0.442±0.194Gy‐1, 11.63±5.241Gy, 1.28±1.07Gy and 2.78±1.88, respectively. BED and EQD2 for LQ, LQ‐L and USC models calculated for dose levels I‐IX of RTOG0813 protocol were 67.52–121.59Gy and 57.61–104.02Gy, 78.25–132.55Gy and 66.77–113.10Gy, 59.14–94.49Gy and 50.46–80.62Gy, respectively. USC curves closely overlap to survival data. For transition dose Dt=2α/β (α/β>6Gy) LQ‐L curves have significant difference at higher doses than USC and survival data. When Dt(LQ‐L)‐Dt(USC), LQ‐L curves exceptionally close to USC and experimental data. In SBRT doses, BED and EQD2 calculated by LQ and LQ‐L(α/β>6Gy) are higher than that of USC model.

Conclusion:

USC curves closely match with experimental data. BED and EQD2 for dose levels of RTOG0813 protocol for LQ and LQ‐L(α/β>6Gy) have significant difference than USC values. BED matching for designing SBRT treatment should consider comprehensive calculations to include BED of USC model.
SU‐E‐T‐714: Study On Set‐Up Accuracy of Three Different Immobilization Methods in Radiotherapy for Thoracic Cancer
Authors: Chen J , Chen L , Yin Y
Published: June 2015

Purpose:

Using VARIAN Clinac ix cone beam CT to evaluate the different immobilization methods in thoracic cancer radiotherapy positioning accuracy.

Methods:

Ninety thoracic cancer patients were selected and were divided into 3 group randomly according to immobilization method, with Body fixed film, vacuum mat, Arm bracket joint vacuum mat. All of the patients in the first three times before radiotherapy with OBI system KV CBCT scanning,plan to get the volume of the image was treated with CT image comparison,two image space position deviation. After treatment of CBCT position verification once a week.

Results:

Body fixed way setup errors X, Y, Z axis deviation mean respectively (2.038±1.416)mm, (2.267±1.568)mm, (1.412±1.408)mm. vacuum mat fixed way respectively (2.395±1.576)mm, 2.721±1.764)mm,(2.419±1.516)mm. Arm bracket joint vacuum mat fixed way respectively (2.325±1.419)mm,(1.837±0.814)mm, (1.674±1.213)mm. Body fixed group Compared with the vacuum mat group P<0.05. Arm bracket joint vacuum mat fixed group Compared with the vacuum mat group P<0.05. Arm bracket joint vacuum mat fixed group Compared with the Body fixed group P<0.05.

Conclusion:

Thoracic tumor radiotherapy using Arm bracket joint vacuum mat fixed patients can significantly reduce the position error,improve the positioning accuracy,precise radiotherapy to provide quality assurance
SU‐E‐T‐717: Surface Coating for Prevention of Metallic Seed Migration in Tissues
Authors: Lee H , Lee W , Park J , Choy Y , Ye S
Published: June 2015

Purpose:

In radiotherapy, metallic implants often detach from their deposited sites and migrate to other locations. This undesirable migration could cause inadequate dose coverage for permanent brachytherapy and difficulties in image‐guided radiation delivery for patients. To prevent migration of implanted seeds, we propose a potential strategy to use of a biocompatible and tissue‐adhesive material called polydopamine.

Methods:

In this study, non‐radioactive dummy seeds that have the same geometry and composition as commercial I‐125 seeds were coated in polydopamine. Using scanning electron microscopy and X‐ray photoelectron spectroscopy, the surface of the polydopamine‐coated and non‐coated seeds was characterized. The detachment stress between the two types of seeds and the tissue was measured. The efficacy of polydopamine‐coated seed was investigated through in‐vitro migration tests by tracing the seed location after tissue implantation and shaking for given times. The cytotoxicity of the polydopamine coating was also evaluated.

Results:

The results of the coating characterization have shown that polydopamine was successfully coated on the surface of the seeds. In the adhesion test, the polydopamine‐coated seeds had 2.1‐fold greater detachment stress than non‐coated seeds. From the in‐vitro test, it was determined that the polydopamine‐coated seed migrated shorter distances than the non‐coated seed. This difference was increased with a greater length of time after implantation.

Conclusion:

We suggest that polydopamine coating is an effective technique to prevent migration of implanted seeds, especially for permanent prostate brachytherapy.
SU‐E‐T‐718: Surface Dose and Build‐Up Dose Comparison of 6MV and 10MV Flattened with 6MV FFF and 10MV FFF Photon Beams with Different Detectors
Authors: Nambiraj Arunai , Sigamani Ashokkumar , Kaviarasu K , Rajesh T , Karthikeyan S , Subramanian Narayanan , Meerza Kazem
Published: June 2015

Purpose:

To compare measured surface dose and build‐up dose for 6MV and 10MV flattened(FB) with 6MV FFF and 10MV FFF photon beams with different detectors

Methods:

The surface dose for flattened and FFF photon beams from a Varian True beam medical linear accelerator were measured for square field sizes of 5Χ5 to 30Χ30 cm2 using Scanditronix NACP ion chamber, CC 13, and Stereotactic field Detectors (SFD) along the central axis of the beam at 100 cm source to surface distance with IBA blue phantom and solid phantom

Results:

The consistency between the measured percentage depth dose data from all three detector types were observed for depths beyond the depth of the maximum dose, but were all clearly different from each other data in the build‐up region this is observed for both 6 and 10 MV flattened and FFF photon beams. The measured percentage surface doses obtained using the NACP parallel plate chamber, CC 13 and SFD without any correction factor values are varies from 0.322 to 0.519 and 0.524 to 0.709 and 0.370 to 0.585 for 6MV FB and 0.434 to 0.564 and 0.616 to 0.724 and 0.510 to 0.665 for 6MV FFF respectively for field sizes of 5Χ5 to 30Χ30 cm2 for the 6MV FB photon beams and 0.166 to 0.415 and 0.335 to 0.602 and 0.321 to 0.565 for 10MV FB and 0.268 to 0.473 and 0.406 to 0.550 and 0.372 to 0.523 for the 10MV FFF photon beams

Conclusion:

The measured surface dose clearly increases with increasing field size, regardless of the detector used in the measurement for both 6MV and 10MV flattened and FFF photon beams. Compare to NACP parallel plate chamber CC13 chamber is showing over response and SFD is showing lesser surface dose. Removal of flattening filter increases the surface dose irrespective of beam energy
SU‐E‐T‐720: Surface Electronic Brachytherapy Dosimetry: Comparison and Uncertainty Evaluation of Different Calibration Protocols and Ionization Chambers
Authors: Candela‐Juan C , Garcia‐Martinez T , Niatsetski Y , Schuurman J , Nauta G , Vijande J , Ouhib Z , Ballester F , Perez‐Calatayud J
Published: June 2015

Purpose:

The Esteya electronic brachytherapy system (Elekta Brachytherapy, The Netherlands) has been recently developed for HDR brachytherapy treatment of skin lesions, using a 69.5 kVp x‐ray source and a set of applicators that generate beams of 1 to 3 cm diameter. The purpose of this study was to evaluate the surface dose rate of the Esteya (and its estimated uncertainty) by using different detectors and calibration protocols.

Methods:

The surface dose rates for the different applicators were measured with the plane parallel ionization chamber T34013 (PTW‐Freiburg, Germany) and the parallel plate ionization chamber Exradin A20 (Standard Imaging Inc., USA). The first one was calibrated in both air and water, whereas the second one was provided with calibration in air. Two different chambers of each type were used to evaluate detector reproducibility. Measurements in air were performed according to dosimetric protocol established by the TG‐61 of the AAPM, whereas measurements in water were performed in a CIRS Plastic Water LR phantom, using the methodology proposed by the TRS‐398 of IAEA. The correction factors of each protocol and ionization chamber were carefully evaluated.

Results:

Differences between surface dose rates measured in‐air and in‐water using the T34013 chamber range from 1.6% to 3.3%. Differences are below 3.7% when measurements with the A20 and the T34013 chambers calibrated in air are compared. However, absorbed dose rates measured with the A20 chamber in air and the T34013 chamber in water differ up to 6%. Estimated uncertainties are of the order of 2.5% (with coverage factor k=1). The output factors measured with the PTW chambers differ by less than 1.1% when compared to the values measured with the A20 chamber.

Conclusion:

The two ionization chambers and the two dosimetric protocols provide consistent results considering the combined uncertainties. Both chambers have negligible stem effect.

This study was supported in part by Generalitat Valenciana under Project PROMETEOII/2013/010 and by Spanish Government under Project No. FIS2013‐42156. Funding was also received by Elekta and PTW.
SU‐E‐T‐721: Systematic Dose Discrepancy of Diode Based In‐Vivo Dosimetry Due to Short Source‐To‐Surface Distance and Oblique Beam Angle Incidence
Authors: Chen F , Rao M , Cao D , Wu J , Ye J
Published: June 2015

Purpose:

The diode detectors for photon beam In‐Vivo dose (IVD) measurement are usually manufactured with intrinsic buildup, which may cause the IVD respond differently from the predicted dose when the source‐to‐surface distance (SSD) and/or the beam incident angle changes, such as that in breast or chest wall irradiations. This work is to evaluate this systematic discrepancy.

Methods:

In‐Vivo dose was measured on a solid water phantom as a function of varying SSD and beam oblique incidence. The cylindrical IVD detectors were calibrated to 100cGy at nominal gantry angle, 100MU, 10×10cm field, 100 SAD with isocenter at dmax. To study SSD dependence, beams were delivered from nominal gantry angle at SSDs from 105 to 75cm. Doses calculated at the dmax were used as the predicted values. To study the oblique incidence responses, measurements were performed at fixed 100 SSD with gantry angles ranging from the nominal angle (0 degree) to horizontal (90 degree). Two calculation points were used for comparison, one at dmax from nominal angle, a second one at dmax along the oblique beam ray. For both setup, IVD was positioned at the beam CAX on the phantom surface.

Results:

Dose discrepancy increases with decreasing SSD and is more pronounced with high photon energy. This discrepancy is as high as 4.6% for an 18MV beam at 75SSD. For oblique measurements, both calculated values decrease as the oblique angle increases; however, the measured IVD doses exhibited little changes, which introduce significant systematic errors (∼20% at 80 degree) for incident angles larger than 60 degrees.

Conclusion:

Significant systematic dose discrepancies are observed between IVD measurements and the predicted values for short SSD and oblique incident angles. Cautions must be taken in evaluating IVD results at short SSD and at oblique incidence angles larger than 60 degrees.
SU‐E‐T‐723: Testing Critical Structure Avoidance: End‐To‐End Verification Using the MAX‐HD Phantom
Authors: Shay K , Myers D , Gersh J
Published: June 2015

Purpose:

End‐to‐end tests should be performed prior to implementation of any major component in the treatment workflow. Each facet of the workflow should be tested; simulation, planning, image‐guided alignment, and delivery. This study demonstrates the use of the MAX‐HD Phantom (Integrated Medical Technologies, Troy, NY) for multi‐system QA prior to clinical implementation of a new LINAC. This anthropomorphic cranial phantom contains multiple targets which can be localized during simulation and planning. During delivery, the dose to these targets can be measured using detectors and dose distribution measured using radiochromic film. While dose to the PTV is an important test, as‐important is the verification of critical structure avoidance. This phantom allows for placement of detectors in several critical structure regions, yielding a subsequent verification of the fidelity of avoidance algorithms.

Methods:

The described end‐to‐end tests evaluate cranial RapidArc treatments planned using Eclipse (AAA and Acuros) delivered using a Varian TrueBeam (Varian Medical Systems, Palo Alto, CA). A 2.5cm‐diameter spherical volume serves as the PTV while a peripherally‐located region (3cm‐offset) serves as the avoidance structure. The planning CT was performed with an “imaging insert,” which is identical to the “detector insert,” however lacks detector bore holes. Prior to delivery, CBCT is used for alignment. Two deliveries were performed for each plan; one with the detector placed within the PTV and the other within the avoidance structure.

Results:

Ten plans were tested; varying the energy, fluence mode, and algorithm. The dose to the PTV differed on average by 0.66% while the dose to the avoidance structure differed by 0.27%.

Conclusion:

The MAX‐HD allowed for the verification of treatment workflow (simulation, treatment planning, image‐guided alignment, and delivery), concentrating not only on absolute dose to the PTV, but the dose to an avoidance structure.

Presenting 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‐727: The Application of Regularization‐Based Multi‐Channel Radiochromic Film Dosimetry for Patient‐Specific QA of Stereotactic Body Radiation Therapy (SBRT) Treatment
Authors: Li Darrell T H , Chan Kenny S K , Lee Louis K Y , Chan Anthony T C
Published: June 2015

Purpose:

To examine the feasibility of using radiochromic film with advanced calibration techniques for absolute and relative dose measurement in patient‐specific SBRT QA.

Methods:

Ten SBRT cases were randomly selected. The treatment plans were mapped to a cylindrical Perspex phantom for QA measurement. A radiochromic film of 8”x10” was cut into a large piece of 20×21cm2 and 2 small pieces of 4×4cm2 each. The large piece was inserted in the mid‐plane of the phantom which was irradiated with the treatment beam. One of the small pieces was irradiated with known dose. All irradiated films were allowed to stabilize for 24 hours before scanning. The protocol of single‐scan with recalibration was followed and the 2 small films were used to adjust the calibration curve. The treatment film was calibrated with the dose gradient regularization method by an in‐house developed MATLab program. The calculated dose planes were then exported to RIT113V4.4. Both treatment films and planned dose planes were normalized to the corresponding prescribed fractional dose for analysis.

Results:

The analysis was performed by normalizing both the treatment film and the planned dose planes to the prescribed fractional dose. Isodose line comparison was performed to visually check the alignment of the isodose level of steep dose gradient regions. Good agreements were observed in all 10 cases. Gamma index analysis with tolerance of 3% and 2mm was also carried out for quantitative analysis. All 10 cases were reported with a gamma index passing percentage of at least 98.9%, which were higher than the institute's passing criteria of over 95%.

Conclusion:

By employing recalibration and regularization‐based calibration techniques, radiochromic film can measure both the absolute and relative dose of SBRT treatment plans. This study suggested that radiochromic film, with proper application of advanced calibration methods, can be a promising tool for patient‐specific SBRT QA.
SU‐E‐T‐728: The Comparison of Risk of Secondary Malignancies Arising From Five Different Whole Breast Radiation Treatments
Authors: Kim D , Han E , Paudel N , Hardee M , Chung W , Sung J , Yoon M
Published: June 2015

Purpose:

This study aimed to compare estimates of secondary cancer risks using five radiotherapy modalities to treat breast cancer: intensity‐modulated radiotherapy (IMRT), 3‐dimensional conformal radiation therapy (3D‐CRT), field‐in‐field forward‐planned intensity‐modulated radiation (FinF), volumetric modulated arc therapy (VMAT), and TomoHDA (TOMO).

Methods:

Each of 10 selected breast patients was re‐planned with the five different modalities. The planning target volume (PTV) was defined as the contoured breast subtracted 5 mm from the skin, and lungs, heart, and contralateral breast were contoured as OARs. The prescription (Rx) was 50.4 Gy in 28 fractions, which covered 95% of the PTV. Dose constraints for the contralateral lung of volumes receiving 20 Gy and 10 Gy (V20Gy and V10Gy) were less than 20% and 40%, respectively, a maximum cord dose less than 45 Gy and for the rest. Qrgan equivalent doses (OEDs), dose characteristics, and lifetime attributable risks (LARs) were derived from dose‐volume histograms for in‐field regions and radio‐photoluminescence glass dosimeter (RPLGD) measurements for out‐of‐field regions.

Results:

TOMO had a better target dose distribution than 3D‐CRT and FinF. OEDs for TOMO were similar to those of 3D‐CRT in in‐field region but increased as distance from the field boundary increased. LARs of the lung and contralateral breast were highest for VMAT, followed by IMRT, FinF, 3D‐CRT, and TOMO. IMRT and VMAT had a 40–50% lower in V20Gy than 3D‐CRT.

Conclusion:

Our results indicate that TOMO provides comparable plan quality for breast cancer radiotherapy compared to IMRT/VMAT, and, at the same time, the lowest cancer risk in in‐field regions among all studied treatment modalities. Therefore TOMO could be a better alternative treatment modality than 3D‐CRT for breast cancer patients.
SU‐E‐T‐733: The Effects of Duty Cycle On Gated VMAT Delivery
Authors: Song C , Xue C , Li R , Xue T
Published: June 2015

Purpose:

When delivering gated VMAT treatments, the gantry moves back and forth after each beam interruption. There are more beam interruptions with smaller duty cycles. This is a study of the effects of gating and duty cycle on the dose output from the treatment machine.

Methods:

5 previously‐treated SBRT lung patients with 6X FFF RapidArc plans and 4 previously‐treated lung patients with 6X RapidArc plans are used for this study. The treatment machine is a TrueBeam STx with HD‐MLC. A sinusoidal motion generator is used to gate the beam. A MapCheck, and a 0.6 cc ion chamber sandwiched in solid water phantom are used for dose measurements. The MapCheck is used to measure non‐gated, gated with 50% and 30% duty cycles. The ion chamber is used to measure non‐gated and gated with 30% duty cycles.

Results:

For the 5 SBRT lung plans with 6X FFF, the average percentage of diodes with dose difference less than 0.1% is 99.5% between non‐gated and 50% duty cycle, and 99.7% between non‐gated and 30% duty cycle. For the 4 lung plans with 6X, the average percentage of diodes with dose difference less than 0.1% is 99.5% between non‐gated and 50% duty cycle, and 98.9% between non‐gated and 30% duty cycle. Using the ion chamber, the measured dose difference between non‐gated and 30% duty cycle is within 0.1% for all 10 SBRT arcs and within 0.2% for all 10 non‐SBRT arcs.

Conclusion:

On a TrueBeam machine, the VMAT dose delivery difference is within 0.2% between non‐gated and gated treatments. This difference decreases with the increase of duty cycle, also decreases with the decrease of target volume.
SU‐E‐T‐734: The Feasibility of Using Polymer Gel Dosimetry to Measure the Dose Around Thin High Z Materials Irradiated with High Energy Photon Beams
Authors: Warmington L , Watanabe Y
Published: June 2015

Purpose:

The purpose of this study is to investigate the feasibility of 3D dose measurements near thin high z materials using high energy photon beams.

Methods:

A MAGAT‐type polymer gel was manufactured in‐house. Lead foils of dimensions 1cm × 1cm × 0.5mm were encapsulated in 0.06mm thick tape and placed in two foil supports with 4cm depth and 0.7cm separation. The foils and supports were placed in a 500ml polystyrene container and the gel was poured into the phantom. The phantom was irradiated with a 18MV photon beam of 5cm × 5cm field size perpendicular to the foil at 100cm SSD. The gel was imaged with a Siemens 3T MRI scanner using the CPMG pulse sequence. DOSXYZnrc was used to calculate the expected dose and the Monte Carlo dose was compared with the gel. Enough histories were simulated so that the average error was less than 1%. The percentage difference of the dose between the heterogeneous gel and the homogeneous water was computed along and perpendicular to the beam axis.

Results:

Depth dose measurements made on the central axis showed increased dose upstream and between the foils, but had a decreased dose downstream. The range of increased dose was 1.8cm above and 0.7cm below the foils. The minimum dose point between the foils had an enhancement of 7.4%. The dose reduction downstream averaged around 5%. There was very good agreement between the Monte Carlo measurements and the gel doses. The gel and Monte Carlo results were within 2% at the minimum point.

Conclusion:

It was demonstrated that the MAGAT polymer‐gel can be used to measure the fine structures around small metallic objects. The results suggest that the dose of a 18MV photon beam can be increased in between thin high Z foils while reducing the dose downstream.
SU‐E‐T‐735: The Feasibility of Using A Knowledge Base of Prior Treatment Plans in Cervical Cancer: A Dosimetric Comparision with Original Plans
Authors: Ma C , Yin Y
Published: June 2015

Purpose:

To demonstrate the feasibility of using a knowledge base of prior treatment plans to generate new cervical intensity modulated radiation therapy (IMRT) plans. Dosimetric diffeerences were investigated between knowledge‐based IMRT rapidplans and original plans.

Methods:

A database of 20 cervical IMRT treatment plans were assembled to create a knowledge‐based IMRT rapidplan model. Another 19 clinical cases were randomly selected to test the model. A comparision of the difference in the dose‐volume histograms(DVH) between the semiautomated treatment plans and the original treatment plans were analyzed.

Results:

On average, the new knowledge‐based rapidplans are capable of achieving very comparable planning target volume coverage as the original plan, to within 1% as evaluated for D98, D95, and D1. For the rectum, the mean and standard deviation of the dose percentage differences for D20, D30, and D50 are3.79%±8.31%, 4.00%±9.87%, and 1.52±10.89%, respectively. For the bladder, the mean and standard deviation of the dose percentage differences for D20, D30, and D50 are −2.43%±9.40%, −2.03%±10.17% and −2.94%±12.30%, respectively. For the femoral heads, the mean and standard deviation of the dose percentage differences for the left and right are 3.15%±18.29% and −3.18%±13.79%. A negative percentage difference indicates that the new plan has greater dose sparing as compared to the original plan.

Conclusion:

We demonstrate a knowledge‐based IMRT model in cervical cancer can generate clinically acceptable treatment plans of high quality. This semiautomated approach can improve the efficiency of the treatment planning process while ensuring that high quality plans are developed.
SU‐E‐T‐740: The Optimization in Segment Numbers for Nasopharyngeal Carcinoma (NPC) Treated by Intensity Modulated
Authors: Qiu R , Wang Y , Chi Z
Published: June 2015

Purpose:

In premise of uninfluenced to dose distribution of tumor target and organ at risk(OAR) in Nasopharyngeal carcinoma (NPC),the number of segment was changed to increase efficacy and optimize treatment method by designing different plan of intensity modulated radiotherapy(IMRT).

Methods:

10 cases of NPC were confirmed in pathology and treated with step and shoot IMRT. The target volumes were defined: GVT‐T (the primary tumor); GVT‐N (the metastasis lymph nodes in neck); CTV‐T and CTV‐N (the clinical targets of GVT‐T and GTV‐N); and PTV (incidental lymph nodal region). Dose of GTV/CTV/PTV was 70/64/54Gy for 30 fractions.Every patient was designed 7 treatment plans of IMRT by Pinnacle 8.0m planning system,each plan was used with 9 beams of uniform distribution and fixing incidence direction(200°,240°,280°,320°,0°,40°,80°,120°and 160°respectively),and designed for delivery on Elekta Synergy linear accelerator.All plans were optimized with the direct machine parameter optimization(DMPO) algorithm.Minimum MU in each segment was defined at 4MU,and minimal segment area was 4cm2.Number of maximum segment field was defined at 120,110,100,90,80,70,60, respectively.Coverage and conformity of GTV/CTV/PTV,sparing of OARs(spinal cord, brain, parotids, lens and optic nerves) were compared.

Results:

In this group,mean volume of GTV(GTV‐T+GTV‐N),CTV(CTV‐T+CTV‐N)and PTV were 91.39±71.13cm3,177.27±92.16cm3 and 1028.05±167.03cm3,.respectively. Compared with the number of segment decreased from 120 to 60, there were no difference in MU(p>0.05),and the dose distribution of targets(GTV/CTV/PTV),OARs and CI were not different too(p>0.05).But when the segment number was <60, CI of PTV was changed compared with others(p<0.05).

Conclusion:

The minimal segment number of IMRT plan designed by Pinnacle 8.0m planning system in NPC should be decreased reasonably and the limit of minimal segment number was recommended by 70.
SU‐E‐T‐745: The Use of Electron Dense Materials for Quality Assurance Testing in a Magnetic Field
Authors: van Zijp H , van Asselen B , de Vries W , Ishakoglu K , Beld E , Kok J , Wolthaus J , Lagendijk J , Raaymakers B
Published: June 2015

Purpose:

Due to the effect of the magnetic field on the dose deposition (skewing the beam), machine quality assurance (QA) tests for the MR‐linac (MRI combined with a linear accelerator) need to be redesigned. In this work we focus on the redesign of QA tests that address geometrical accuracy of the system.

Methods:

Using electron dense materials (e.g. copper in our experiment) the dose kernel is minimized and thereby the effect of the magnetic field on the dose distribution. This approach is supported by Monte‐Carlo simulations and can be used in practice with film measurements. Two examples of QA tests are presented: beam profile and star‐shot measurements.

Results:

The novel method was verified by performing both measurements on a conventional linac and the MR‐linac with a film that was sandwiched between copper layers. Measurements were compared with a reference setup which was similar to setup used in clinical practice. On a conventional linac the experimental outcome showed good agreement between the reference and the new setup for both QA tests. The results from the MR‐linac showed that the symmetry of the beam profile was restored in presence of the copper layers in the setup and that the isocenter size can be determined accurately with the introduced star‐shot setup (see supporting material).

Conclusion:

The use of electron dense materials for QA tests was shown to be a simple and effective method to remove the effects on the dose distribution enabling assessment of geometrical accuracy of a MR‐linac system. The use of high dense materials is not limited to the presented QA tests only, but has a broad applicability for beam specific QA tests in presence of a magnetic field.
SU‐E‐T‐746: The Use of Radiochromic Film Analyzed with Three Channel Dosimetry as a Secondary Patient‐Specific QA Tool for Small SBRT Fields
Authors: Hadsell M , Holcombe C , Chin E , Hsu A
Published: June 2015

Introduction:

As diagnostic techniques become more sensitive and targeting methods grow in accuracy, target volumes continue to shrink and SBRT becomes more prevalent. Due to this fact, patient‐specific QA must also enhance resolution and accuracy in order to verify dose delivery in these volumes. It has been suggested that when measuring small fields at least two separate detectors be used to verify delivered dose. Therefore, we have instituted a secondary patient QA verification for small (<3cm) SBRT fields using Gafchromic EBT2 film.

Methods:

Films were cross‐calibrated using a Farmer chamber in plastic water at reference conditions as defined by TG‐51. Films were scanned, and an RGB calibration curve was created according to best practices published by Ashland, Inc. Four SBRT cases were evaluated both with the Scandidos Delta4 and with EBT2 films sandwiched in plastic water. Raw values obtained from the film were converted to dose using an in‐house algorithm employing all three color channels to increase accuracy and dosimetric range. Gamma and dose profile comparisons to Eclipse dose calculations were obtained using RIT and compared to values obtained with the Delta4.

Results:

Film gamma pass rates at 2% and 2mm were similar to those obtained with the Delta4. However, dose difference histograms showed better absolute dose agreement, with the average mean film dose agreeing with calculation to 0.3% and the Delta4 only agreeing to 3.1% across the cases. Additionally, films provided more resolution than the Delta4 and thus their dose profiles better succeeded in diagnosing dose calculation inaccuracies.

Conclusion:

We believe that the implementation of secondary patient QA using EBT2 film analyzed with all three color channels is an invaluable tool for evaluation of small SBRT fields. Furthermore, we have shown that this method can sometimes provide a more detailed and faithful reproduction of plan dose than the Delta4.
SU‐E‐T‐747: The Use of the EQD2 Formalism and Repair Estimates in the Re‐Irradiation Setting and Correlation with Patient Follow‐Up Data
Authors: Price R , Meyer J , Horwitz E , Ma C
Published: June 2015

Purpose:

Medical advances have resulted in cancer patients living longer as evidenced by the number of patients seen for possible re‐irradiation. Original normal tissue dose volume constraints remain in the re‐irradiation setting to minimize normal tissue toxicity. This work correlates estimates of equivalent dose and repair with sequelae.

Methods:

CNS and GI tract re‐irradiation patient follow‐up records (including imaging studies) were reviewed with side effects correlated with the calculated EQD2 and repair estimates.

Results:

Follow‐up records for 16 re‐irradiation patients with potential overlap to the spinal cord were analyzed. The mean time interval between 1st and last courses was 76.6 months. Three patients underwent a 3rd course of radiotherapy with a mean time interval between 2nd and final courses of 19.7 months. The mean values for assumed repair were 18.8% and 8.3%, respectively. The calculated total EQD2 doses were 48.09Gy and 50.98Gy with and without repair. At a mean follow‐up time of 5.0 months, 6 patients were deceased and no records indicate radiation related neurological deficits. The records for 11 patients with potential overlap to the bowel were also analyzed. The mean time interval between 1st and last courses was 105.9 months. The mean value for assumed repair was 15.9%. The calculated total EQD2 doses were 64.96Gy and 70.80Gy with and without repair. At a mean follow‐up time of 4.9 months, 6 patients were deceased, one having a potential enteric fistulization of the bladder. Clinical review of the case determined that the fistula was caused by tumor progression and not a side effect of radiotherapy treatments.

Conclusion:

Application of the EQD2 method in the re‐irradiation setting using conservative estimates of repair is presented. Adhering to accepted dose volume limits following this application is demonstrated to be safe through empirical records as limited by this small patient cohort and short follow‐up.