bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐T‐450: Dosimetric Impact of Rotational Error On Multiple‐Target Intensity‐Modulated Radiosurgery (IMRS) with Single‐Isocenter
Authors: Jang S , Huq M 
Published: July 2014

Purpose:Evaluating the dosimetric‐impact on multiple‐targets placed away from the isocenter‐target with varying rotational‐error introduced by initial setup uncertainty and/or intrafractional‐movementMethods:CyberKnife‐Phantom was scanned with the Intracranial SRS‐protocol of 1.25mm slice‐thickness and the multiple‐targets(GTV) of 1mm and 10mm in diameter were contoured on the Eclipse. PTV for distal‐target only was drawn with 1mm expansion around the GTV to find out how much margin is needed to compensate for the rotational‐error. The separation between the isocenter‐target and distal‐target was varied from 3cm to 7cm. RapidArc‐based IMRS plans of 16Gy single‐fraction were generated with five non‐coplanar arcs by using Varian TrueBeam‐STx equipped with high resolution MLC leaves of 2.5mm at center and with dose‐rate of 1400MU/min at 6MV for flatteringfilter‐ free(FFF). An identical CT image with intentionally introduced 1° rotational‐error was registered with the planning CT image, and the isodose distribution and Dose‐Volume‐Histogram(DVH) were compared with the original plans. Additionally, the dosimetric‐impact of rotational error was evaluated with that of 6X photon energy which was generated with the same target‐coverage.Results:For the 1mm‐target with 6X‐FFF, PTV‐coverage(D100) of the distal‐target with 1° rotational‐error decreased from 1.00 to 0.35 as the separation between isocenter‐target and distal‐target increased from 3cm to 7cm. However, GTV‐coverage(D100) was 1.0 except that of 7cm‐separation(0.55), which resulted from the 1mm‐margin around the distal‐target. For 6X photon, GTV‐coverage remained at 1.0 regardless of the separation of targets, showing that the dosimetric‐impact of rotational error depends on the degree of rotational‐error, separation of targets, and dose distribution around targets. For 10mm‐target, PTV‐coverage of distaltarget located 3cm‐away was better than that of 1mm‐target(0.93 versus 0.7) and GTV‐coverage was 1.0 regardless of 6X‐FFF/6X photon beams.Conclusion:RapidArc‐based Multiple‐target IMRS may Resultin a compromised outcome due to the setup‐error for distal‐targets. With 1mm‐margin, GTV‐coverage of distal‐target was 1.0 although the separation of targets was up to 5cm.
SU‐E‐T‐451: Accuracy and Application of the Standard Imaging W1 Scintillator Dosimeter
Authors: Kowalski M , McEwen M 
Published: July 2014

Purpose:To evaluate the Standard Imaging W1 scintillator dosimeter in a range of clinical radiation beams to determine its range of possible applications.Methods:The W1 scintillator is a small perturbation‐free dosimeter which is of interest in absolute and relative clinical dosimetry due to its small size and water equivalence. A single version of this detector was evaluated in Co‐60 and linac photon and electron beams to investigate the following: linearity, sensitivity, precision, and dependence on electrometer type. In addition, depth‐dose and cross‐plane profiles were obtained in both photon and electron beams and compared with data obtained with wellbehaved ionization chambers.Results:In linac beams the precision and linearity was very impressive, with typical values of 0.3% and 0.1% respectively. Performance in a Co‐60 beam was much poorer (approximately three times worse) and it is not clear whether this is due to the lower signal current or the effect of the continuous beam (rather than pulsed beam of the linac measurements). There was no significant difference in the detector reading when using either the recommended SI Supermax electrometer or two independent high‐quality electrometers, except for low signal levels, where the Supermax exhibited an apparent threshold effect, preventing the measurement of the bremsstrahlung background in electron depth‐dose curves. Comparisons with ion chamber measurements in linac beams were somewhat variable: good agreement was seen for cross‐profiles (photon and electron beams) and electron beam depth‐dose curves, generally within the 0.3% precision of the scintillator but systematic differences were observed as a function of measurement depth in photon beam depth‐dose curves.Conclusion:A first look would suggest that the W1 scintillator has applications beyond small field dosimetry but performance appears to be limited to higher doserate and/or pulsed radiation beams. Further work is required to resolve discrepancies compared to ion chambers.
SU‐E‐T‐452: Impact of Respiratory Motion On Robustly‐Optimized Intensity‐Modulated Proton Therapy to Treat Lung Cancers
Authors: Liu W , Liao Z , Schild S , Park P , Li H , Li Y , Li X , Shen J , Anand A , Sahoo N , Dong L , Bues M , Zhu X , Mohan R 
Published: July 2014

Purpose:We compared conventionally optimized intensity‐modulated proton therapy (IMPT) treatment plans against the worst‐case robustly optimized treatment plans for lung cancer. The comparison of the two IMPT optimization strategies focused on the resulting plans' ability to retain dose objectives under the influence of patient set‐up, inherent proton range uncertainty, and dose perturbation caused by respiratory motion.Methods:For each of the 9 lung cancer cases two treatment plans were created accounting for treatment uncertainties in two different ways: the first used the conventional Method: delivery of prescribed dose to the planning target volume (PTV) that is geometrically expanded from the internal target volume (ITV). The second employed the worst‐case robust optimization scheme that addressed set‐up and range uncertainties through beamlet optimization. The plan optimality and plan robustness were calculated and compared. Furthermore, the effects on dose distributions of the changes in patient anatomy due to respiratory motion was investigated for both strategies by comparing the corresponding plan evaluation metrics at the end‐inspiration and end‐expiration phase and absolute differences between these phases. The mean plan evaluation metrics of the two groups were compared using two‐sided paired t‐tests.Results:Without respiratory motion considered, we affirmed that worst‐case robust optimization is superior to PTV‐based conventional optimization in terms of plan robustness and optimality. With respiratory motion considered, robust optimization still leads to more robust dose distributions to respiratory motion for targets and comparable or even better plan optimality [D95% ITV: 96.6% versus 96.1% (p=0.26), D5% – D95% ITV: 10.0% versus 12.3% (p=0.082), D1% spinal cord: 31.8% versus 36.5% (p =0.035)].Conclusion:Worst‐case robust optimization led to superior solutions for lung IMPT. Despite of the fact that robust optimization did not explicitly account for respiratory motion it produced motion‐resistant treatment plans. However, further research is needed to incorporate respiratory motion into IMPT robust optimization.
SU‐E‐T‐453: A Novel Daily QA System for Robotic Image Guided Radiosurgery with Variable Aperture Collimator
Authors: Wang L , Nelson B 
Published: July 2014

Purpose:A novel end‐to‐end system using a CCD camera and a scintillator based phantom that is capable of measuring the beam‐by‐beam delivery accuracy of Robotic Radiosurgery has been developed and reported in our previous work. This work investigates its application to end‐to‐end type daily QA for Robotic Radiosurgery (Cyberknife) with Variable Aperture Collimator (Iris).Methods:The phantom was first scanned with a CT scanner at 0.625 slice thickness and exported to the Cyberknife Muliplan (v4.6) treatment planning system. An isocentric treatment plan was created consisting of ten beams of 25 Monitor Units each using Iris apertures of 7.5, 10, 15, 20, and 25 mm. The plan was delivered six times in two days on the Cyberknife G4 system with fiducial tracking on the four metal fiducials embedded in phantom with re‐positioning between the measurements. The beam vectors (X, Y, Z) are measured and compared with the plan from the machine delivery file (XML file). The Iris apertures (FWHM) were measured from the beam flux map and compared with the commissioning data.Results:The average beam positioning accuracies of the six deliveries are 0.71 ± 0.40 mm, 0.72 ± 0.44 mm, 0.74 ± 0.42 mm, 0.70 ± 0.40 mm, 0.79 ± 0.44 mm and 0.69 ± 0.41 mm respectively. Radiation beam width (FWHM) variations are within ±0.05 mm, and they agree with the commissioning data within 0.22 mm. The delivery time for the plan is about 7 minutes and the results are given instantly.Conclusion:The experimental results agree with stated sub‐millimeter delivery accuracy of Cyberknife system. Beam FWHM variations comply with the 0.2 mm accuracy of the Iris collimator at SAD. The XRV‐100 system has proven to be a powerful tool in performing end‐to‐end type tests for Robotic Image Guided Radiosurgery Daily QA.
SU‐E‐T‐454: Impact of Calculation Grid Size On Dosimetry and Radiobiological Parameters for Head and Neck IMRT
Authors: Srivastava S , Cheng C , Das I 
Published: July 2014

Purpose:IMRT has become standard of care for complex treatments to optimize dose to target and spare normal tissues. However, the impact of calculation grid size is not widely known especially dose distribution, tumor control probability (TCP) and normal tissue complication probability (NTCP) which is investigated in this study.Methods:Ten head and neck IMRT patients treated with 6 MV photons were chosen for this study. Using Eclipse TPS, treatment plans were generated for different grid sizes in the range 1–5 mm for the same optimization criterion with specific dose‐volume constraints. The dose volume histogram (DVH) was calculated for all IMRT plans and dosimetric data were compared. ICRU‐83 dose points such as D2%, D50%, D98%, as well as the homogeneity and conformity indices (HI, CI) were calculated. In addition, TCP and NTCP were calculated from DVH data.Results:The PTV mean dose and TCP decreases with increasing grid size with an average decrease in mean dose by 2% and TCP by 3% respectively. Increasing grid size from 1–5 mm grid size, the average mean dose and NTCP for left parotid was increased by 6.0% and 8.0% respectively. Similar patterns were observed for other OARs such as cochlea, parotids and spinal cord. The HI increases up to 60% and CI decreases on average by 3.5% between 1 and 5 mm grid that resulted in decreased TCP and increased NTCP values. The number of points meeting the gamma criteria of ±3% dose difference and ±3mm DTA was higher with a 1 mm on average (97.2%) than with a 5 mm grid (91.3%).Conclusion:A smaller calculation grid provides superior dosimetry with improved TCP and reduced NTCP values. The effect is more pronounced for smaller OARs. Thus, the smallest possible grid size should be used for accurate dose calculation especially in H&N planning.
SU‐E‐T‐455: Characterization of 3D Printed Materials for Proton Beam Therapy
Authors: Zou W , McDonough J , Yin L , Fisher T , Siderits R , McKenna M , Khan A , Yue N , Teo B 
Published: July 2014

Purpose:The widespread availability of low cost 3D printing technologies provides an alternative fabrication method for customized proton range modifying accessories such as compensators and boluses. However the material properties of the printed object are dependent on the printing technology used. In order to facilitate the application of 3D printing in proton therapy, this study investigated the stopping power of several printed materials using both proton pencil beam measurements and Monte Carlo simulations.Methods:Five 3–4 cm cubes fabricated using three 3D printing technologies (selective laser sintering, fused‐deposition modeling and stereolithography) from five printers were investigated. The cubes were scanned on a CT scanner and the depth dose curves for a mono‐energetic pencil beam passing through the material were measured using a large parallel plate ion chamber in a water tank. Each cube was measured from two directions (perpendicular and parallel to printing plane) to evaluate the effects of the anisotropic material layout. The results were compared with GEANT4 Monte Carlo simulation using the manufacturer specified material density and chemical composition data.Results:Compared with water, the differences from the range pull back by the printed blocks varied and corresponded well with the material CT Hounsfield unit. The measurement results were in agreement with Monte Carlo simulation. However, depending on the technology, inhomogeneity existed in the printed cubes evidenced from CT images. The effect of such inhomogeneity on the proton beam is to be investigated.Conclusion:Printed blocks by three different 3D printing technologies were characterized for proton beam with measurements and Monte Carlo simulation. The effects of the printing technologies in proton range and stopping power were studied. The derived results can be applied when specific devices are used in proton radiotherapy.
SU‐E‐T‐456: Development of An EPID‐Based Output Measurement and Dosimetric Verification Tool for Electron Beam Therapy
Authors: Ding A , Han B , Xing L 
Published: July 2014

Purpose:To develop an efficient and robust method for output and absolute dosimetric measurements of electron beam therapy by using a high spatialresolution and high frame‐rate amorphous silicon flat‐panel electronic portal imaging device (EPID).Methods:A previously‐established EPID dosimetry system was extended to measure the output factors of electron beams of various sizes and their planar dose distributions at reference depths. Specific EPID responses to different electron energies were derived from Monte Carlo (MC) simulations to de‐convolve the EPID raw images to the incident electron fluence map. To reconstruct the 2D water‐based dose distribution map at reference depths for different energies, the fluence map was further convolved with a MC simulated pencil beam kernel. Different energies of 6, 9, 12, 16, and 20 MeV from a Varian C‐series linac were tested. Standard square fields ranging from 2×2 to 15×15 cm2 were measured and validated against film/ion chamber measurements. Small fields of different patient cases with irregular cutout shapes were also tested.Results:The EPIDmeasured output factors for 2×2, 3×3, 6×6, and 10×10 cm2 fields with all electron energies agree with the film/ion chamber data within 2.7%. The average discrepancy between EPID and film/ion chamber measurements was 1.4%. The differences for the three patient cases were 0.1%, 2.1%, and 1.6%. Deliveries with different monitor units were tested and the results exhibited good linearity. Measurements with different dose rate showed that the dose rate dependence was less than 1%. Using the proposed method, 2D absolute dose maps were created from the EPID raw images and the results were consistent with film measurements.Conclusion:The efficient data readout and portability of the newly developed EPID system provides an efficient and accurate solution for electron beam therapy. It addresses an important unmet clinical need for a fast and reliable small field output factor measurement.
SU‐E‐T‐457: Design and Characterization of An Economical 192Ir Hemi‐Brain Small Animal Irradiator
Authors: Grams M , Wilson Z , Sio T , Beltran C , Tryggestad E , Gupta S , Blackwell C , McCollough K , Sarkaria J , Furutani K 
Published: July 2014

Purpose:To describe the design and dosimetric characterization of a simple and economical small animal irradiator.Methods:A high dose rate 192Ir brachytherapy source from a commercially available afterloader was used with a 1.3 centimeter thick tungsten collimator to provide sharp beam penumbra suitable for hemi‐brain irradiation of mice. The unit is equipped with continuous gas anesthesia to allow robust animal immobilization. Dosimetric characterization of the device was performed with Gafchromic film. The penumbra from the small animal irradiator was compared under similar collimating conditions to the penumbra from 6 MV photons, 6 MeV electrons, and 20 MeV electrons from a linear accelerator as well as 300 kVp photons from an orthovoltage unit and Monte Carlo simulated 90 MeV protons.Results:The tungsten collimator provides a sharp penumbra suitable for hemi‐brain irradiation, and dose rates on the order of 200 cGy/minute were achieved. The sharpness of the penumbra attainable with this device compares favorably to those measured experimentally for 6 MV photons, and 6 and 20 MeV electron beams from a linear accelerator. Additionally, the penumbra was comparable to those measured for a 300 kVp orthovoltage beam and a Monte Carlo simulated 90 MeV proton beam.Conclusions:The small animal irradiator described here can be built for under $1,000 and used in conjunction with any commercial brachytherapy afterloader to provide a convenient and cost‐effective option for small animal irradiation experiments. The unit offers high dose rate delivery and sharp penumbra, which is ideal for hemi‐brain irradiation of mice. With slight modifications to the design, irradiation of sites other than the brain could be accomplished easily. Due to its simplicity and low cost, the apparatus described is an attractive alternative for small animal irradiation experiments requiring a sharp penumbra.
SU‐E‐T‐458: Determining Threshold‐Of‐Failure for Dead Pixel Rows in EPID‐Based Dosimetry
Authors: Gersh J , Wiant D 
Published: July 2014

Purpose:A pixel correction map is applied to all EPID‐based applications on the TrueBeam (Varian Medical Systems, Palo Alto, CA). When dead pixels are detected, an interpolative smoothing algorithm is applied using neighboring‐pixel information to supplement missing‐pixel information. The vendor suggests that when the number of dead pixels exceeds 70,000, the panel should be replaced. It is common for entire detector rows to be dead, as well as their neighboring rows. Approximately 70 rows can be dead before the panel reaches this threshold. This study determines the number of neighboring dead‐pixel rows that would create a large enough deviation in measured fluence to cause failures in portal dosimetry (PD).Methods:Four clinical two‐arc VMAT plans were generated using Eclipse's AXB algorithm and PD plans were created using the PDIP algorithm. These plans were chosen to represent those commonly encountered in the clinic: prostate, lung, abdomen, and neck treatments. During each iteration of this study, an increasing number of dead‐pixel rows are artificially applied to the correction map and a fluence QA is performed using the EPID (corrected with this map). To provide a worst‐case‐scenario, the dead‐pixel rows are chosen so that they present artifacts in the highfluence region of the field.Results:For all eight arc‐fields deemed acceptable via a 3%/3mm gamma analysis (pass rate greater than 99%), VMAT QA yielded identical results with a 5 pixel‐width dead zone. When 10 dead lines were present, half of the fields had pass rates below the 99% pass rate. With increasing dead rows, the pass rates were reduced substantially.Conclusion:While the vendor still suggests to request service at the point where 70,000 dead rows are measured (as recommended by the vendor), the authors suggest that service should be requested when there are greater than 5 consecutive dead rows.
SU‐E‐T‐459: Dosimetric Consequences of Rotated Elliptical Proton Spots in Modeling In‐Air Proton Fluence for Calculating Doses in Water of Proton Pencil Beams
Authors: Matysiak W , Hsi W , Yeung D 
Published: July 2014

Purpose:We present a study of dosimetric consequences on doses in water in modeling in‐air proton fluence independently along principle axes for rotated elliptical spots.Methods:Phase‐space parameters for modeling in‐air fluence are the position sigma for the spatial distribution, the angle sigma for the angular distribution, and the correlation between position and angle distributions. Proton spots of the McLaren proton therapy system were measured at five locations near the isocenter for the energies of 180 MeV and 250 MeV. An elongated elliptical spot rotated with respect to the principle axes was observed for the 180 MeV, while a circular‐like spot was observed for the 250 MeV. In the first approach, the phase‐space parameters were derived in the principle axes without rotation. In the second approach, the phase space parameters were derived in the reference frame with axes rotated to coincide with the major axes of the elliptical spot. Monte‐Carlo simulations with derived phase‐space parameters using both approaches to tally doses in water were performed and analyzed.Results:For the rotated elliptical 180 MeV spots, the position sigmas were 3.6 mm and 3.2 mm in principle axes, but were 4.3 mm and 2.0 mm when the reference frame was rotated. Measured spots fitted poorly the uncorrelated 2D Gaussian, but the quality of fit was significantly improved after the reference frame was rotated. As a Result, phase space parameters in the rotated frame were more appropriate for modeling in‐air proton fluence of 180 MeV protons. Considerable differences were observed in Monte Carlo simulated dose distributions in water with phase‐space parameters obtained with the two approaches.Conclusion:For rotated elliptical proton spots, phase‐space parameters obtained in the rotated reference frame are better for modeling in‐air proton fluence, and can be introduced into treatment planning systems.
SU‐E‐T‐460: Comparison of Proton and IMRT Planning for Head and Neck Cancer
Authors: Fontenla S , Zhou Y , Mah D , Kowalski A , Leven T , Cahlon O , Lee N , Hunt M , Mechalakos J 
Published: July 2014

Purpose:A retrospective study comparing proton and intensity‐modulated radiation therapy (IMRT) for head and neck cancerMethods:This study consists of six H&N cancer patients that underwent proton as well as IMRT planning. Patients analyzed had unilateral target volumes, one had prior RT. 3D‐conformal proton therapy (3D‐CPT) plans with multiple field uniform scanning were generated for delivery on the inclined beam line. IMRT was planned using fixed field sliding window. Final plan evaluations were performed by a radiation oncologist and a physicist. Metrics for comparison included tumor coverage, organ sparing with respect to spinal cord, brainstem, parotids, submandibulars, oral cavity, larynx, brachial plexus, cochleas, normal brain tissue, and skin using relevant indices for these structures. Dose volume histograms were generated as well as a qualitative comparison of isodose distributions between the two modalities. Planning and treatment delivery times were compared.Results:Results showed that IMRT plans offered better conformality in the high dose region as demonstrated by the conformality index for each plan. Ipsilateral cochlea, submandibular gland, and skin doses were lower with IMRT than proton therapy. There was significant sparing of larynx, oral cavity, and brainstem with proton therapy compared to IMRT. This translated into direct patient benefit with no evidence of hoarseness, mucositis, or nausea. Contralateral parotid and submandibular glands were equally spared. IMRT had shorter planning/parts fabrication and treatment times which needs to be taken into account when deciding modality.Conclusion:Sparing of clinically significant normal tissue structures such as oral cavity and larynx for unilateral H&N cancers was seen with 3D‐CPT versus IMRT. However, this is at the expense of less conformality at the high dose region and higher skin dose. Future studies are needed with full gantry systems and pencil beam scanning as these deliveries would be expected to further improve conformality and normal tissue sparing.