bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐T‐404: Evaluation of the Effect of Spine Hardware for CyberKnife Spinal Stereotactic Radiosurgery
Authors: Yuan J , Zhang Y , Zheng Y , Wessels B , Machtay M , Yao M , Lo S 
Published: June 2015

Purpose:Spine hardware made of high‐Z materials such as titanium has the potential to affect the dose distribution around the metal rods in CyberKnife spinal stereotactic radiosurgery (SRS) treatments. The purpose of this work was to evaluate the magnitude of such effect retrospectively for clinical CyberKnife plans.Methods:The dose calculation was performed within the MultiPlan treatment planning system using the ray tracing (RT) and Monte Carlo (MC) method. A custom density model was created by extending the CT‐to‐Density table to titanium density of 4.5 g/cm3 with the CT number of 4095. To understand the dose perturbation caused by the titanium rod, a simple beam setup (7.5 mm IRIS collimator) was used to irradiate a mimic rod (5 mm) with overridden high density. Five patient spinal SRS cases were found chronologically from 2010 to 2015 in our institution. For each case, the hardware was contoured manually. The original plan was re‐calculated using both RT and MC methods with and without rod density override without changing clinical beam parameters.Results:The simple beam irradiation shows that there is 10% dose increase at the interface because of electron backscattering and 7% decrease behind the rod because of photon attenuation. For actual clinical plans, the iso‐dose lines and DVHs are almost identical (<2%) for calculations with and without density override for both RT and MC methods. However, there is a difference of more than 10% for D90 between RT and MC method.Conclusion:Although the dose perturbation around the metal rods can be as large as 10% for a single beam irradiation, for clinical treatments with complex beam composition the effect of spinal hardware to the PTV and spinal dose is minimal. As such, the MC dose algorithm without rod density override for CyberKnife spinal SRS is acceptable.
SU‐E‐T‐408: Evaluation of the Type and Frequency of Variations Discovered During Routine Secondary Patient Chart Review
Authors: Hardin M , Harrison A , Lockamy V , Li J , Peng C , Potrebko P , Yu Y , Doyle L , Cao J 
Published: June 2015

Purpose:Desire to improve efficiency and throughput inspired a review of our physics chart check procedures. Departmental policy mandates plan checks pre‐treatment, after first treatment and weekly every 3–5 days. This study examined the effectiveness of the “after first” check with respect to improving patient safety and clinical efficiency. Type and frequency of variations discovered during this redundant secondary review was examined over seven months.Methods:A community spreadsheet was created to record variations in care discovered during chart review following the first fraction of treatment and before the second fraction (each plan reviewed prior to treatment). Entries were recorded from August 2014 through February 2015, amounting to 43 recorded variations out of 906 reviewed charts. The variations were divided into categories and frequencies were assessed month‐to‐month.Results:Analysis of recorded variations indicates an overall variation rate of 4.7%. The initial rate was 13.5%; months 2–7 average 3.7%. The majority of variations related to discrepancies in documentation at 46.5%, followed by prescription, plan deficiency, and dose tracking related variations at 25.5%, 12.8%, and 12.8%, respectively. Minor variations (negligible consequence on patient treatment) outweighed major variations 3 to 1.Conclusion:This work indicates that this redundant secondary check is effective. The first month spike in rates could be due to the Hawthorne/observer effect, but the consistent 4% variation rate suggests the need for periodical re‐training on variations noted as frequent to improve awareness and quality of the initial chart review process, which may lead to improved treatment quality, patient safety and increased clinical efficiency. Utilizing these results, a continuous quality improvement process following Deming's Plan‐Do‐Study‐Act (PDSA) methodology was generated. The first iteration of this PDSA was adding a specific dose tracking checklist item in the pre‐treatment plan check assessment; the ramification of which will be assessed in future data.
SU‐E‐T‐409: Evaluation of Tissue Composition Effect On Dose Distribution in Radiotherapy with 6 MV Photon Beam of a Medical Linac
Authors: Ghorbani M , Tabatabaei Z , Noghreiyan A Vejdani , Meigooni A Soleimani 
Published: June 2015

Purpose:The aim of this study is to evaluate soft tissue composition effect on dose distribution for various soft tissues and various depths in radiotherapy with 6 MV photon beam of a medical linac.Methods:A phantom and Siemens Primus linear accelerator were simulated using MCNPX Monte Carlo code. In a homogeneous cubic phantom, six types of soft tissue and three types of tissue‐equivalent materials were defined separately. The soft tissues were muscle (skeletal), adipose tissue, blood (whole), breast tissue, soft tissue (9‐component) and soft tissue (4‐component). The tissue‐equivalent materials included: water, A‐150 tissue‐equivalent plastic and perspex. Photon dose relative to dose in 9‐component soft tissue at various depths on the beam's central axis was determined for the 6 MV photon beam. The relative dose was also calculated and compared for various MCNPX tallies including,F8, F6 and,F4.Results:The results of the relative photon dose in various materials relative to dose in 9‐component soft tissue and using different tallies are reported in the form of tabulated data. Minor differences between dose distributions in various soft tissues and tissue‐equivalent materials were observed. The results from F6 and F4 were practically the same but different with,F8 tally.Conclusion:Based on the calculations performed, the differences in dose distributions in various soft tissues and tissue‐equivalent materials are minor but they could be corrected in radiotherapy calculations to upgrade the accuracy of the dosimetric calculations.
SU‐E‐T‐414: Experimental Correction of High‐Z Electrode Effect in Mini‐Ionization Chambers for Small Beam Dosimetry
Authors: Larraga‐Gutierrez J 
Published: June 2015

Purpose:To correct for the over‐response of mini‐ionization chambers with high‐Z central electrodes. The hypothesis is that by applying a negative/reverse voltage, it is possible to suppress the signal generated in the high‐Z central electrode by low‐energy photons.Methods:The mini‐ionization chambers used in the experiments were a PTW‐31014, PTW‐31006 and IBA‐CC01. The PTW‐31014 has an aluminum central electrode while the PTW‐31006 and IBA‐CC01 have a steel one. Total scatter factors (Scp) were measured for a 6 MV photon beam down to a square field size of 0.5 cm. The measurements were performed in water at 10 cm depth with SAD of 100 cm. The Scp were measured with the dosimeters with +400V bias voltage. In the case of the PTW‐31006 and IBA‐CC01, the measurements were repeated with −400V bias voltage. Also, the field factors in water were calculated with Monte Carlo simulations for comparison.Results:The measured Scp at +400V with the PTW‐31006 and IBA‐CC01 detectors were in agreement within 0.2% down to a field size of 1.5 cm. Both dosimeters shown a systematic difference about 2.5% with the Scp measured with the PTW‐31014 and the Monte Carlo calculated field factors. The measured Scp at −400V with the PTW‐31006 and IBA‐CC01 detectors were in close agreement with the PTW‐31014 measured Scp and the field factors within 0.3 and 1.0%, respectively. In the case of the IBA‐CC01 it was found a good agreement (1%) down to field size of 1.0 cm. All the dosimeters shown differences up to 17% between the measured Scp and the field factor for the 0.5 cm field size.Conclusion:By applying a negative/reverse voltage to the mini‐ionization chambers with high‐Z central electrode it was possible to correct for their over‐response to low energy photons.
SU‐E‐T‐415: Experimental Determination of the Relative Stopping Power of TRUFILL N‐BCA Liquid Embolic System in a Clinical Proton Beam
Authors: Mandapaka A , Ghebremedhin A , Patyal B 
Published: June 2015

Purpose:Patients who undergo n‐BCA glue embolization as part of treatment for AVMs are later referred for proton therapy. Knowing the relative stopping power of the glue accurately allows us to perform accurate dose calculations. In this study we experimentally determine the relative stopping power of an n‐BCA mixture in a 126 MeV and 149.6 MeV proton beams.Methods:One unit of the TRUFILL™ n‐BCA liquid embolic system consists of 1g unit of n‐BCA, 1g unit of Tantalum powder and one 10mL vial of Ethiodized oil. The physician mixed 3:1 Ethiodized oil to n‐BCA. Five units (20cc) of the n‐BCA liquid embolic glue were prepared and placed in a 6cm × 3cm x3cm Lucite container. The container was placed in front of a water tank in the proton beam path. A diamond detector (active volume 0.004mm3) was used to measure distal edge of depth dose of a modulated 126 MeV proton beam collimated using a 3cm brass aperture. The procedure was repeated with a container carrying the same amount of water placed in front of the water tank. The difference in the depth dose measured with glue and with water was used to determine the relative stopping power of the glue. The same determination was done earlier at 149.6 MeV using a different smaller sample (4cc) of n‐BCA.Results:The relative stopping power of this particular n‐BCA mixture was determined to be 1.06 at both 126 MeV and 149.6 MeV. We are working on obtaining the composition data of the n‐BCA glue so we can perform Monte Carlo calculations.Conclusion:Accurate value of the stopping power of the n‐BCA glue in the proton beam was determined to be 1.06. It will improve the accuracy of dose calculations in proton radiosurgery procedures on AVM patients with n‐BCA embolization.
SU‐E‐T‐417: Experimental Verification of Robustness Optimized Intensity Modulated Proton Therapy Plans for Craniospinal Irradiation
Authors: Yu J , Liao L , Sahoo N , Zhu X , Gillin M , Zhang X 
Published: June 2015

Purpose:The robustness‐optimized intensity modulated proton therapy (RO‐IMPT) plans takes into account the setup errors to eliminate the hot/cold spots caused by setup errors at the junction for craniospinal (CSI) irradiation fields. The RO‐IMPT requires a large area for the junction of two fields. This work is to verify the treatment planning system calculated dose with introduction of setup errors by two‐dimensional (2D) dose measurement. Two fields of total lengths of 45 cm with junctions of 21 cm were measured.Methods:2D dose distributions in the coronal plane were measured by a commercial 2D ion‐chamber‐array detector in a cubic solid water phantom. A total spine field consisting of an upper and a lower spine field was measured at the depths of 5.4 and 6.9 cm. The active area for the measurement was 24×24 cm22. The junction and the area outside the junction of the spine fields were measured separately to complete the verification for the total field. Six different amounts of set‐up errors along the superior‐inferior direction up to 1.4 cm were intentionally applied. The measured dose with and without set‐up errors were compared with the calculated dose with and without set‐up errors using Gamma‐index analysis. 3%/3mm and 2%/2mm dose/distance agreement criteria were used. The point dose at the center of the junction was also compared.Results:For all fields with various introduced setup errors, 100 % of pixels passed the 3%/3mm criteria and on average 96% of pixels passed 2%/2mm criteria. Differences in the measured and calculated doses were within 1.1%.Conclusion:The efficacy of the robustness for the CSI RO‐IMPT plans were verified by measurement. The measurement method can be used for patient treatment field specific QA for CSI RO‐IMPT plans in our institution in the near future.
SU‐E‐T‐418: Explore the Sensitive of the Planar Quality Assurance to the MLC Error with Different Beam Complexity in Intensity‐Modulate Radiation Therapy
Authors: Wang J , Peng J , Xie J , Hu W 
Published: June 2015

Purpose:The purpose of this study is to investigate the sensitivity of the planar quality assurance to MLC errors with different beam complexities in intensity‐modulate radiation therapy.Methods:sixteen patients’ planar quality assurance (QA) plans in our institution were enrolled in this study, including 10 dynamic MLC (DMLC) IMRT plans measured by Portal Dosimetry and 6 static MLC (SMLC) IMRT plans measured by Mapcheck. The gamma pass rate was calculated using vender's software. The field numbers were 74 and 40 for DMLC and SMLC, respectively. A random error was generated and introduced to these fields. The modified gamma pass rate was calculated by comparing the original measured fluence and modified fields’ fluence. A decreasing gamma pass rate was acquired using the original gamma pass rate minus the modified gamma pass rate. Eight complexity scores were calculated in MATLAB based on the fluence and MLC sequence of these fields. The complexity scores include fractal dimension, monitor unit of field, modulation index, fluence map complexity, weighted average of field area, weighted average of field perimeter, and small aperture ratio ( <5cm2 and <50cm2). The Spearman's rank correlation coefficient was implemented to analyze the correlation between these scores and decreasing gamma rate.Results:The relation between the decreasing gamma pass rate and field complexity was insignificant for most complexity scores. The most significant complexity score was fluence map complexity for SMLC, which have ρ =0.4274 (p‐value=0.0063). For DMLC, the most significant complex score was fractal dimension, which have ρ=−0.3068 (p‐value=0.0081).Conclusions:According to the primarily Result of this study, the sensitivity gamma pass rate was not strongly relate to the field complexity.
SU‐E‐T‐419: Fabricating Cerrobend Grids with 3D Printing for Spatially Modulated Radiation Therapy: A Feasibility Study
Authors: Zhu X , Driewer J , Lei Y , Zheng D , Li S , Cullip T , Chang S , Zhang Q , Zhang M , Zhou S 
Published: June 2015

Purpose:Grid therapy has promising applications in the radiation treatment of bulky and large tumors. However, research and applications of grid therapy is limited by the accessibility of the specialized blocks that produce the grid of pencil‐like radiation beams. In this study, a Cerrobend grid block was fabricated using a 3D printing technique.Methods:A grid block mold was designed with divergent tubes following beam central rays. The mold was printed using a resin with the working temperature below 230 °C. The melted Cerrobend liquid at 120°oC was cast into the resin mold to yield a block with a thickness of 7.4 cm. The grid had a hexagonal pattern, with each pencil beam diameter of 1.4 cm at the iso‐center plane; the distance between the beam centers was 2 cm. The dosimetric properties of the grid block were studied using radiographic film and small field dosimeters.Results:the grid block was fabricated to be mounted at the third accessory mount of a Siemens Oncor linear accelerator. Fabricating a grid block using 3D printing is similar to making cutouts for traditional radiotherapy photon blocks, with the difference being that the mold was created by a 3D printer rather than foam. In this study, the valley‐to‐peak ratio for a 6MV photon grid beam was 20% at dmax, and 30% at 10 cm depth, respectively.Conclusion:We have demonstrated a novel process for implementing grid radiotherapy using 3D printing techniques. Compared to existing approaches, our technique combines reduced cost, accessibility, and flexibility in customization with efficient delivery. This lays the groundwork for future studies to improve our understanding of the efficacy of grid therapy and apply it to improve cancer treatment.
SU‐E‐T‐434: Fixed Margin Or Online Adaptation for Intermediate‐Risk Prostate Stereotactic Body Radiation Therapy? A Dosimetric Study
Authors: Sheng Y , Li T , Yin F , Wu Q 
Published: June 2015

Purpose:To investigate the choice of fixed margin or online adaptation when treating intermediate‐risk prostate cancer including seminal vesicles (SV) using stereotactic body radiation therapy (SBRT).Methods:9 prostate SBRT patients were retrospectively studied. All patients were implanted with fiducial markers in the prostate for daily localization and verification. Each patient had 5 pairs of pre‐treatment and post‐treatment cone‐beam CT (CBCT) per protocol. SVs were contoured on planning CT and all CBCTs by one attending physician. Simultaneous integral boost (SIB) IMRT plans were developed to deliver 25Gy/5fx to the SV while delivering 37Gy/5fx to the prostate. A 3mm isotropic margin was added to the prostate while a 5 mm isotropic margin was used for the SV. The planning CT was registered to daily pre‐treatment and post‐treatment CBCT based on fiducial markers in the prostate to mimic online prostate localization; and the SV on daily CBCT was transferred to the CT structure set after the prostates were aligned. Daily pre‐treatment and post‐treatment SV dose coverage and the organ‐at‐risk (OAR) sparing were evaluated for the SIB regimen. At least 95% of the SV need to receive the prescription dose (5Gy per fraction).Results:For the total of 90 daily SVs analyzed (ten CBCTs for each of nine patients), only 45 daily SVs (50%) were able to meet the coverage that 95% of the SV received 25Gy. The OAR sparing performance was acceptable for most of the dosimetric constraints in low‐risk prostate SBRT protocol with only two exceptions in bladder V100 (cc).Conclusion:A fixed 5mm margin for SV is not sufficient to provide consistent daily dose coverage due to SV's substantial inter‐ and intra‐fractional motion relative to the prostate.This finding calls for innovative strategies in margin design as well as online treatment adaptation.This work is partially supported a master research grant from Varian Medical Systems.
SU‐E‐T‐436: Fluence‐Based Trajectory Optimization for Non‐Coplanar VMAT
Authors: Smyth G , Evans PM , Bamber JC , Saran FH , Mandeville HC , Bedford JL 
Published: June 2015

Purpose:To investigate a fluence‐based trajectory optimization technique for non‐coplanar VMAT for brain cancer.Methods:Single‐arc non‐coplanar VMAT trajectories were determined using a heuristic technique for five patients. Organ at risk (OAR) volume intersected during raytracing was minimized for two cases: absolute volume and the sum of relative volumes weighted by OAR importance. These trajectories and coplanar VMAT formed starting points for the fluence‐based optimization method. Iterative least squares optimization was performed on control points 24° apart in gantry rotation. Optimization minimized the root‐mean‐square (RMS) deviation of PTV dose from the prescription (relative importance 100), maximum dose to the brainstem (10), optic chiasm (5), globes (5) and optic nerves (5), plus mean dose to the lenses (5), hippocampi (3), temporal lobes (2), cochleae (1) and brain excluding other regions of interest (1). Control point couch rotations were varied in steps of up to 10° and accepted if the cost function improved. Final treatment plans were optimized with the same objectives in an in‐house planning system and evaluated using a composite metric ‐ the sum of optimization metrics weighted by importance.Results:The composite metric decreased with fluence‐based optimization in 14 of the 15 plans. In the remaining case its overall value, and the PTV and OAR components, were unchanged but the balance of OAR sparing differed. PTV RMS deviation was improved in 13 cases and unchanged in two. The OAR component was reduced in 13 plans. In one case the OAR component increased but the composite metric decreased ‐ a 4 Gy increase in OAR metrics was balanced by a reduction in PTV RMS deviation from 2.8% to 2.6%.Conclusion:Fluence‐based trajectory optimization improved plan quality as defined by the composite metric. While dose differences were case specific, fluence‐based optimization improved both PTV and OAR dosimetry in 80% of cases.
SU‐E‐T‐438: Frameless Cranial Stereotactic Radiosurgery Immobilization Effectiveness Evaluation
Authors: Tseng T , Green S , Sheu R , Lo Y 
Published: June 2015

Purpose:To evaluate immobilization effectiveness of Brainlab frameless mask in cranial stereotactic radiosurgery (SRS).Methods:Two sets of setup images were collected pre‐and post‐treatment for 24 frameless SRS cases. The pre‐treatment images were obtained after applying 2D‐2D kV image‐guided shifts with patients in treatment position and approved by physicians; the post‐treatment images were taken immediately after treatment completion. All cases were treated on a Novalis linac with ExacTrac positioning system and Exact Couch. The two image sets were compared with the correctional shifts measured by ExacTrac 6D auto‐fusion. The shift differences were considered patient motion within the frameless mask and were used to evaluate its effectiveness for immobilization. Two‐tailed paired t‐test was applied for significance comparison.Results:The correctional shifts (mean±STD, median) of pre‐and post‐treatment images were 0.33±0.27mm, 0.26mm and 0.34±0.27mm, 0.23mm (p=0.740) in lateral direction; 0.32±0.29mm, 0.22mm and 0.48±0.30mm, 0.50mm (p=0.012) in longitudinal direction; 0.31±0.22mm, 0.24mm and 0.33±0.21mm, 0.36mm (p=0.623) in vertical direction. The radial correctional shifts (mean±STD, median) of pre ‐and post‐treatment images were 0.60±0.38mm, 0.45mm and 0.75±0.31mm, 0.66mm (p=0.033). The shift differences (mean±STD, median, maximum) were 0.35±0.28mm, 0.3mm, 1.05mm, 0.34±0.28mm, 0.3mm, 1.00mm, 0.24±0.15mm, 0.21mm, 0.60mm and 0.61±0.32mm, 0.57mm, 1.40mm in lateral, longitudinal, vertical and radial direction, respectively. Two shifts greater than 1 mm (1.06mm and 1.02mm) were acquired from post‐treatment images. However, the shift differences were only 0.09 and 0.19mm for these two shifts. Two patients with shift differences greater than 1mm (1.05 and 1.04mm) were observed and didn't coincide with those two who had post‐correctional shifts greater than 1mm.Conclusion:Image‐guided SRS allowed us to set up patients with sub‐millimeter accuracy relative to simulation position. However, patient motion during treatment could affect treatment accuracy. Our Result shows that Brainlab frameless mask provides reasonable patient immobilization and maintains the mean post‐treatment position within sub‐millimeter accuracy with some borderline results observed.