bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐F‐T‐320: Assessing Placement Error of Optically Stimulated Luminescent in Vivo Dosimeters Using Cone‐Beam Computed Tomography
Authors: Riegel A , Tariq M , Gomez C , Klein E 
Published: July 2016

Purpose:Optically‐stimulated luminescent dosimeters (OSLDs) are increasingly utilized for in vivo dosimetry of complex radiation delivery techniques such as intensity‐modulated radiation therapy (IMRT) and volumetric‐modulated arc therapy (VMAT). Evaluation of clinical uncertainties such as placement error has not been performed. This work retrospectively investigates the magnitude of placement error using conebeam computed tomography (CBCT) and its effect on measured/planned dose agreement.Methods:Each OSLD was placed at a physicist‐designated location on the patient surface on a weekly basis. The location was given in terms of a gantry angle and two‐dimensional offset from central axis. The OSLDs were placed before daily image guidance. We identified 77 CBCTs from 25 head‐and‐neck patients who received IMRT or VMAT, where OSLDs were visible on the CT image. Grossly misplaced OSLDs were excluded (e.g. wrong laterality). CBCTs were registered with the treatment plan and the distance between the planned and actual OSLD location was calculated in two dimensions in the beam's eye view. Distances were correlated with measured/planned dose percent differences.Results:OSLDs were grossly misplaced for 5 CBCTs (6.4%). For the remaining 72 CBCTs, average placement error was 7.0±6.0 mm. These errors were not correlated with measured/planned dose percent differences (R2=0.0153). Generalizing the dosimetric effect of placement errors may be unreliable.Conclusion:Correct placement of OSLDs for IMRT and VMAT treatments is critical to accurate and precise in vivo dosimetry. Small placement errors could produce large disagreement between measured and planned dose. Further work includes expansion to other treatment sites, examination of planned dose at the actual point of OSLD placement, and the influence of imageguided shifts on measured/planned dose agreement.
SU‐F‐T‐321: The Effect of an Electromagnetic Array Used for Patient Localization and Tumor Tracking On OSLD in Vivo Dosimetry
Authors: Rea A , Kuruvilla A , Gill G , Riegel A , Klein E 
Published: July 2016

Purpose:The purpose of this study was to observe the effect of an electromagnetic array used for patient localization and tumor tracking on optically‐stimulated luminescent in‐vivo dosimetry.Methods:A linear accelerator equipped with four photon energies was used to irradiate optically stimulated luminescent dosimeters (OSLDs) at the respective dmax depths and in the buildup region, with and without the presence of an electromagnetic array used for tumor tracking and patient localization. The OSLDs were placed on solid water slabs under 5 mm bolus and on each face of an octagonal phantom, and irradiated using both static beam and arc geometry, with and without the electromagnetic array under our setup. The electromagnetic array was placed 6 cm above the phantom to coincide with similar distances used during patient treatment. Ionization chamber measurements in a water phantom were also taken initially for comparison with the simple geometry OSLD measurements and published data.Results:Under simple geometry, a negligible change was observed at dmax for all energies when the electromagnetic array was placed over the setup. When measuring at five millimeter depth, increases of 1.3/3.1/16/18% were observed for energies 4X/6X/10X/15X respectively when the electromagnetic array was in place. Measurements using the octagonal phantom yielded scattered results for the lateral and posterior oblique fields, and showed increases in dose to the OSLDs placed on the anterior and lateral anterior faces of the phantom.Conclusion:Placing the electromagnetic array very close to the patient's surface acts as a beam spoiler in the buildup region (at 5 mm depth), which in turn causes an increase in the measured dose reading of the OSLD. This increase in dose is more pronounced when the OSLD is placed directly underneath the electromagnetic array than off to one side or the other.
SU‐F‐T‐324: Experimental Measurement of Optically Stimulated Luminescence Detectors in a MR‐IGRT Environment Toward Assessing Magnetic Field Effects On These Devices and Their Use as An In‐Vivo Dosimeter
Authors: Reilly M , Curcuru A , Yaddanapudi S , Green O 
Published: July 2016

Purpose:To characterize magnetic field effects on Optically Stimulated Luminescence Detectors (OSLDs) for use as an in‐vivo dosimeter in an MRIGRT machine.Methods:Landauer OSLD nano‐dots and the MicroStar II reader were used to measure and record OSLDs exposed in and on a solid water phantom in a 10.5 × 10.5 cm2 field, Co‐60, 0.32‐Tesla MR‐IGRT machine ‐ with and without the presence of the magnetic field. Two orthogonal gantry angles were considered to assess orientation effects on the OSLDs with respect to the incident angle of the radiation beam and magnetic field. The same OSLDs were then used (after readout and bleaching) when the magnetic field was restored.Results:The measured surface dose decreased by 14.1 ± 1.8% when magnetic field was 'on’ due to contamination electrons being swept away by the field. Doses at both 0.5 cm and 5 cm depth increased by 6.5 ± 0.9% and 8.8 ± 0.5% respectively when the magnetic field was present and the OSLDs oriented with their long axis parallel with the incident beam. This contrasts with an increased dose of 2.7 ± 1.1% when the magnetic field was present and the OSLDs were oriented with their long axis perpendicular to the incident beam.Conclusion:Previous works have shown that OSLDs have a dependence on beam incidence angle. Our current work suggests an additional dependence on the presence of the magnetic field when the beam is not perpendicular to the plane of the detector and this effect needs to be considered. Furthermore, the use of an in‐vivo dosimeter was shown to have no effect on image quality during the use of MR guidance. Future work will focus on the use of an electromagnet with a linear accelerator to further characterize these effects.
SU‐F‐T‐325: On the Use of Bolus in Dosimetry and Dose Reduction for Pacemaker and Defibrillator
Authors: Liu W , Zhu D , Trumpore S , Kenneth R , Higgins S , Nath R , Chen Z 
Published: July 2016

Purpose:Special attention is required in planning and administering radiation therapy to patients with cardiac implantable electronic devices (CIEDs), such as pacemaker and defibrillator. The range of dose to CIEDs that can induce malfunction is very large among CIEDs. Significant defects have been reported at dose as low as 0.15Gy. Failures causing discomfort have been reported at dose as low as 0.05Gy. Therefore, accurate estimation of dose to CIED and dose reduction are both important even if the dose is expected to be less than the often‐used 2Gy limit. We investigate the use of bolus in in vivo dosimetry for CIEDs.Methods:In our clinic, high‐energy beams (>10MV) are not used for patients with CIED due to neutron production. Solid water phantom measurements of out‐of‐field dose for a 6MV beam were performed using parallel plate chamber at different depth with and without 2cm bolus covering the chamber. In vivo dosimetry at skin surface above the pacemaker was performed with and without bolus for 3 patients with pacemaker <5cm from the field edge.Results:Chamber measured dose at depth ∼1 to 1.5cm below the skin surface, where the CIED is normally located, was reduced by ∼6% – 20% with bolus. The dose reduction became smaller at deeper depth. In vivo dosimetry at skin surface also yielded ∼20% – 60% lower dose when using bolus for the 3 patients. In general, TPS calculation underestimated the dose. The dose measured with bolus is closer to the dose at the depth of the pacemaker and less affected by contaminant electrons and linac head leakage.Conclusion:In vivo CIED dose measurements should be performed with 1 to 2cm bolus covering the dosimeter on the skin above the CIED for more accurate CIED dose estimation. The use of bolus also reduces the dose delivered to CIED.
SU‐F‐T‐393: Using Commercially Available Software to Prove That Providing Planning Objectives to the Planner Improves Plan Quality
Authors: Younan F , Arnold A , Patel S , Clouser E 
Published: July 2016

Purpose:Use commercially available software to evaluate whether providing planning objectives during the treatment planning process improves overall plan quality in head and neck casesMethods:The commercially available software, PlanIQ, was used to evaluate the plan quality of head and neck cases before and after the introduction of an inhouse developed evaluation tool, Integrated Clinical Information System (ICIS). Twenty patients were selected; ten from before the introduction of ICIS and ten that used ICIS during the treatment planning process. These plans only included oropharynx cases. All plans were two or three arc VMAT cases prescribed at two dose levels, 60 Gy and 54 Gy. A PlanIQ algorithm was created with the assistance of physician input. The algorithm consisted of seventy‐four PTV and OAR plan quality metrics and objectives. Each plan was scored based on meeting the objectives provided. Plans were then evaluated by looking at the Plan Quality Metric (PQM) and Adjusted Plan Quality Metric (APQM) score. The PQM score is the overall score which evaluated the treatment plan against the PlanIQ algorithm. The APQM score was customized to the patient‐specific feasibility analysis, adjusting the PQM scores to account for unique challenges like patient‐specific anatomical challenges.Results:After introducing ICIS into the workflow, PlanIQ scores improved. On average, target coverage remained the same (p>.05). Individual OAR sparing differed when looking at plans evaluated before ICIS versus plans created with the assistance of the ICIS template. PQM scores increased from 65.16% to 74.07% (p=.004), while the APQM scores increased from 78.26% to 84.05% (p=.008). Overall plan quality improved after providing planners with additional information during the treatment planning process.Conclusion:Overall plan quality improves when providing the treatment planner with additional information and guidance during the treatment planning process.
SU‐F‐T‐395: Evaluation of Best Dosimetry Achievable with VMAT and IMRT Treatment Techniques Targeting Borderline Resectable Pancreatic Cancer
Authors: Harpool K , Schnell E , Herman T , Ahmad S , De La Fuente Herman T 
Published: July 2016

Purpose:To determine from retrospective study the most appropriate technique for targeting small borderline operable pancreatic cancer surrounding blood vessels by evaluating the dosimetry and normal tissue sparing achievable using Volumetric Modulated Arc Therapy (VMAT) and Intensity Modulated Radiation Therapy (IMRT).Methods:Treatment plans from ten patients who have undergone treatment with a prescribed dose of 4950 cGy, at 275 cGy per fraction, were analyzed. All plans were replanned using Eclipse TPS (Varian Medical Systems, Palo Alto, CA) with complementary VMAT or IMRT techniques to obtain paired data sets for comparison. The coverage to at least 95% of the planned target volume (PTV) was normalized to receive 100% of the prescription dose. The normal tissue constraints followed the quantitative analysis of normal tissue effects in the clinic (QUANTEC) guidelines and the organs at risks (OARs) were liver, kidneys, spinal cord and bowel. The plan evaluation was based on conformity index (CI), homogeneity index (HI), uniformity index (UI), DVH parameters, and student's‐t statistics (2 tails).Results:The VMAT technique delivered less maximum dose to the right kidney, left kidney, total kidney, liver, spinal cord, and bowel by 9.3%, 5.9%, 6.7%, 3.9%, 15.1%, 3.9%, and 4.3%, respectively. The averaged V15 for the total kidney was 10.21% for IMRT and 7.29% for VMAT. The averaged V20 for the bowel was 19.89% for IMRT and 14.06% for VMAT. On average, the CI for IMRT was 1.20 and 1.16 for VMAT (p = 0.20). The HI was 0.08 for both techniques (p = 0.91) and UI was 1.05 and 1.06 for IMRT and VMAT respectively (p = 0.59).Conclusion:Both techniques achieve adequate PTV coverage. Although VMAT techniques show better normal tissue sparing from excessive dose, no significant differences were observed. Slight discrepancies may rise from different versions of calculation algorithms.
SU‐F‐T‐398: Improving Radiotherapy Treatment Planning Using Dual Energy Computed Tomography Based Tissue Characterization
Authors: Tomic N , Bekerat H , Seuntjens J , Forghani R , DeBlois F , Devic S 
Published: July 2016

Purpose:Both kVp settings and geometric distribution of various materials lead to significant change of the HU values, showing the largest discrepancy for high‐Z materials and for the lowest CT scanning kVp setting. On the other hand, the dose distributions around low‐energy brachytherapy sources are highly dependent on the architecture and composition of tissue heterogeneities in and around the implant. Both measurements and Monte Carlo calculations show that improper tissue characterization may lead to calculated dose errors of 90% for low energy and around 10% for higher energy photons. We investigated the ability of dual‐energy CT (DECT) to characterize more accurately tissue equivalent materials.Methods:We used the RMI‐467 heterogeneity phantom scanned in DECT mode with 3 different set‐ups: first, we placed high electron density (ED) plugs within the outer ring of the phantom; then we arranged high ED plugs within the inner ring; and finally ED plugs were randomly distributed. All three setups were scanned with the same DECT technique using a single‐source DECT scanner with fast kVp switching (Discovery CT750HD; GE Healthcare). Images were transferred to a GE Advantage workstation for DECT analysis. Spectral Hounsfield unit curves (SHUACs) were then generated from 50 to 140‐keV, in 10‐keV increments, for each plug.Results:The dynamic range of Hounsfield units shrinks with increased photon energy as the attenuation coefficients decrease. Our results show that the spread of HUs for the three different geometrical setups is the smallest at 80 keV. Furthermore, among all the energies and all materials presented, the largest difference appears at high Z tissue equivalent plugs.Conclusion:Our results suggest that dose calculations at both megavoltage and low photon energies could benefit in the vicinity of bony structures if the 80 keV reconstructed monochromatic CT image is used with the DECT protocol utilized in this work.
SU‐F‐T‐401: Three‐Dimensional Conformal Planning Using Low‐Segment Multi‐Criteria Optimization for Hippocampal Avoidance Whole Brain Radiotherapy
Authors: Zhang X , Penagaricano J , Narayanasamy G , Griffin R , Maraboyina S , Paudel N , Peter C , Morrill S 
Published: July 2016

Purpose:Hippocampus avoidance whole brain radiotherapy (HA‐WBRT) has been shown to reduce the risk of neurocognitive dysfunction. This type of treatment has the potential of insurance company payment denial due to increased cost of intensity modulated radiotherapy (IMRT), while the accepted modality for WBRT is three‐dimensional conformal radiotherapy (3DCRT). The purpose of this study is to assess HA‐WBRT treatment plans using 3DCRT and multi‐criteria optimization (MCO) that meets the RTOG 0933 criteria.Methods:Ten patients with brain metastases at least 0.5cm away from the hippocampal avoidance region as defined in RTOG 0933 were selected in this study. HA‐WBRT treatment plans with MCO 3DCRT technique (MCO‐3D) was generated with beam arrangements and dose constraints following the RTOG 0933 guidelines. MCO‐3D plans were compared with plans using MCO IMRT techniques (MCO‐IMRT) with same beam arrangements and dose constraints. Evaluation parameters included D98% D2% and dose homogeneity index of PTV, and Dmax and D100% of the hippocampi. The OAR doses were also evaluated.Results:For MCO‐IMRT plans, PTV D2% and hippocampi Dmax and D100% met RTOG 0933 objectives in all ten patients (PTV D2%<37.5Gy; Hippocampi Dmax<16Gy and D100%<9Gy). One patient met the RTOG 0933 PTV D98% objective (PTV D98%>25Gy) and 9/10 patients met acceptable variation (PTV D98%<25Gy). For MCO‐3D plans, PTV D2% met RTOG 0933 objective for all patients; 1/10 patient for PTV D98% and 6/10 patients for Hippocampi Dmax and 7/10 patients for hippocampi D100% met RTOG 0933 objective. All the other patients met the RTOG 0933 acceptable variation requirement. (PTV D98%<25Gy; Hippocampi Dmax<17Gy and D100%<10Gy).Conclusion:All dosimetric parameters of MCO‐3D plans met the criteria of at least acceptable variation per RTOG 0933. This may be helpful in cases where there is denial of patient's medical insurance coverage due to the use of IMRT for HA‐WBRT.
SU‐F‐T‐403: Impact of Dose Reduction for Simulation CT On Radiation Therapy Treatment Planning
Authors: Liang Q , Shah P , Li S , Miyamoto C 
Published: July 2016

Purpose:To investigate the feasibility of applying ALARA principles to current treatment planning CT scans. The study aims to quantitatively verify lower dose scans does not alter treatment planning.Method:Gammex 467 tissue characterization phantom with inserts of 14 different materials was scanned at seven different mA levels (30∼300 mA). CT numbers of different inserts were measured. Auto contouring for bone and lung in treatment planning system (Pinnacle) was used to evaluate the effect of CT number accuracy from treatment planning aspect, on the 30 and 300 mA‐scanned images. A head CT scan intended for a 3D whole brain radiation treatment was evaluated. Dose calculations were performed on normal scanned images using clinical protocol (120 kVP, Smart mA, maximum 291 mA), and the images with added simulating noise mimicking a 70 mA scan. Plan parameters including isocenter, beam arrangements, block shapes, dose grid size and resolution, and prescriptions were kept the same for these two plans. The calculated monitor units (MUs) for these two plans were compared.Results:No significant degradation of CT number accuracy was found at lower dose levels from both the phantom scans, and the patient images with added noise. The CT numbers kept consistent when mA is higher than 60 mA. The auto contoured volumes for lung and cortical bone show 0.3% and 0.12% of differences between 30 mA and 300 mA respectively. The two forward plans created on regular and low dose images gave the same calculated MU, and 98.3% of points having <1% of dose difference.Conclusion:Both phantom and patient studies quantitatively verified low dose CT provides similar quality for treatment planning at 20–25% of regular scan dose. Therefore, there is the potential to optimize simulation CT scan protocol to fulfil the ALARA principle and limit unnecessary radiation exposure to non‐targeted tissues.
SU‐F‐T‐406: Verification of Total Body Irradiation Commissioned MU Lookup Table Accuracy Using Treatment Planning System for Wide Range of Patient Sizes
Authors: Lewis D , Chi P , Tailor R , Aristophanous M , Tung S 
Published: July 2016

Purpose:To verify the accuracy of total body irradiation (TBI) measurement commissioning data using the treatment planning system (TPS) for a wide range of patient separations.Methods:Our institution conducts TBI treatments with an 18MV photon beam at 380cm extended SSD using an AP/PA technique. Currently, the monitor units (MU) per field for patient treatments are determined using a lookup table generated from TMR measurements in a water phantom (75 × 41 × 30.5 cm3). The dose prescribed to an umbilicus midline point at spine level is determined based on patient separation, dose/ field and dose rate/MU. One‐dimensional heterogeneous dose calculations from Pinnacle TPS were validated with thermoluminescent dosimeters (TLD) placed in an average adult anthropomorphic phantom and also in‐vivo on four patients with large separations. Subsequently, twelve patients with various separations (17–47cm) were retrospectively analyzed. Computed tomography (CT) scans were acquired in the left and right decubitus positions from vertex to knee. A treatment plan for each patient was generated. The ratio of the lookup table MU to the heterogeneous TPS MU was compared.Results:TLD Measurements in the anthropomorphic phantom and large TBI patients agreed with Pinnacle calculated dose within 2.8% and 2%, respectively. The heterogeneous calculation compared to the lookup table agreed within 8.1% (ratio range: 1.014–1.081). A trend of reduced accuracy was observed when patient separation increases.Conclusion:The TPS dose calculation accuracy was confirmed by TLD measurements, showing that Pinnacle can model the extended SSD dose without commissioning a special beam model for the extended SSD geometry. The difference between the lookup table and TPS calculation potentially comes from lack of scatter during commissioning when compared to extreme patient sizes. The observed trend suggests the need for development of a correction factor between the lookup table and TPS dose calculations.
SU‐F‐T‐412: Spatiotemporal Distribution of Dose Rates in VMAT Plans
Authors: Mackeprang P , Volken W , Terribilini D , Frauchiger D , Klippel N , Zaugg K , Aebersold D M , Fix M K , Manser P 
Published: July 2016

Purpose:To assess dose rates in volumetric modulated arc therapy (VMAT) plans.Methods:For dose rate analysis, using Monte Carlo methods, dose distributions are calculated in sectors of consecutive DICOM control points and each multiplied with the MU‐rate obtaining dose rate distributions for every voxel at every time‐point during a treatment fraction. Dose rate distributions were calculated for a clinical head and neck, cranial (2 Gy fraction dose) and a SBRT liver treatment case (5 Gy per fraction). To assess optimizer influence on dose rate distributions, five conventionally fractionated head and neck cases were optimized using the progressive resolution optimizer (PRO) versions 2 and 3 (Varian Medical Systems, Palo Alto, CA).Results:Firstly, histograms of dose rates over the course of treatment delivery in volumes of interest were generated for the PTV and spine or brainstem of the clinical treatment plans. Secondly, dose rates were assessed as color wash overlay on top of CT slices, allowing the user to explore the dose rate variation over time. For the cases considered, dose rates were spread out over a continuous spectrum with a mean value in the lower half. PRO3 generated plans showed higher maximum dose rates compared to PRO2 (699.80 cGy/min vs. 543.46 cGy/min) and modulation of MU rates in blocks as opposed to gradual modulation.Conclusion:Calculation and visualization of dose rate distributions in VMAT have been performed. Dose rates in clinical relevant VMAT cases are spread out over a continuous spectrum with a mean in the lower part for both conventional and SBRT test cases. Different optimization algorithms may lead to substantially different dose rate distributions in the same cases. The development of the Swiss Monte Carlo Plan framework has been partially supported by Varian Medical Systems