bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐F‐T‐551: Beam Hardening and Attenuation of Photon Beams Using Integral Quality Monitor in Radiotherapy
Authors: Casar B , Carot I Mendez , Peterlin P 
Published: July 2016

Purpose:Aim of the multi‐centre study was to analyse beam hardening effect of the Integral Quality Monitor (IQM) for high energy photon beams used in radiotherapy with linear accelerators. Generic values for attenuation coefficient k(IQM) of IQM system were additionally investigated.Methods:Beam hardening effect of the IQM system was studied for a set of standard nominal photon energies (6 MV–18 MV) and two flattening filter free (FFF) energies (6 MV FFF and 10 MV FFF). PDD curves were measured and analysed for various square radiation fields, with and without IQM in place. Differences between PDD curves were statistically analysed through comparison of respective PDD_20,10 values. Attenuation coefficients k(IQM) were determined for the same range of photon energies.Results:Statistically significant differences in beam qualities for all evaluated high energy photon beams were found, comparing PDD_20,10 values derived from PDD curves with and without IQM in place. Significance of beam hardening effect was statistically proven with high confidence (p < 0,01) for all analysed photon beams except for 15 MV (p = 0,078), although relative differences in beam qualities were minimal, ranging from 0,1 % to 0,5 %. Attenuation of the IQM system showed negligible dependence on radiation field size. However, clinically important dependence of kIQM versus TPRs20,10 was found: 0,941 for 6 MV photon beams, to 0,959 for 18 MV photon beams, with highest uncertainty below 0,006. k(IQM) versus TPRs were tabulated and polynomial equation for the determination of k(IQM) is suggested for clinical use.Conclusion:There was no clinically relevant beam hardening, when IQM system was on linear accelerators. Consequently, no additional commissioning is needed for the IQM system regarding the determination of beam qualities. Generic values for k(IQM) are proposed and can be used as tray factors for complete range of examined photon beam energies.
SU‐F‐T‐559: High‐Resolution Scintillating Fiber Array for In‐Vivo Real‐Time SRS and SBRT Patient QA
Authors: Knewtson T , Pokhrel S , Loyalka S , Izaguirre E 
Published: July 2016

Purpose:A high‐resolution scintillating fiber detector was built for in‐vivo real‐time patient specific quality assurance (QA). The detector is designed for stereotactic body radiotherapy (SBRT) and stereotactic radiosurgery (SRS) to monitor treatment delivery and detect real‐time deviations from planned dose to increase patient safety and treatment accuracy.Methods:The detector consists of two high‐density scintillating fiber arrays layered to form an X‐Y grid which can be attached to the accessory tray of a medical linac for SBRT and cone SRS treatment QA. Fiber arrays consist of 128 scintillating fibers embedded within a precision‐machined, high‐transmission polymer substrate with 0.8mm pitch. The fibers are coupled on both ends to high‐sensitivity photodetectors and the output is recorded through a high‐speed analog‐to‐digital converter to capture the linac pulse sequence as treatment delivery progresses. The detector has a software controlled 360 degree rotational system to capture angular beam projections for high‐resolution beam profile reconstruction.Results:The detector was validated using SRS cone sizes from 6mm to 34mm and MLC defined field sizes from 5×5mm2 to 100×100mm2. The detector output response is linear with dose and is dose rate independent. Each field can be reconstructed accurately with a spatial resolution of 0.8mm and the current beam output is displayed every 50msec. Dosimetric errors of 1% with respect to the treatment plan can be identified and clinically significant deviations from the expected treatment can be displayed in real‐time to alert the therapists.Conclusion:The high resolution detector is capable of reconstructing beam profiles in real‐time with submillimeter resolution and 1% dose resolution. This system has the ability to project in‐vivo both spatial and dosimetric errors during SBRT and SRS treatments when only a non‐clinically significant fraction of the intended dose was delivered. The device has the potential to establish new standards for in‐vivo patient specific QA.
SU‐F‐T‐627: A Conformity Index Study of SBRT Plans for Lung Cancer Patient
Authors: Zhu Dengsong , Fan Guoqing , Peng Chong , Austerlitz Carlos 
Published: July 2016

Purpose:To evaluate the conformity index for SBRT lung plan in Eclipse (version 11) treatment planning system.Methods:In the Eclipse treatment planning system the conformity index was defined as VRI/TV, where VRI is prescription isodose surface, and TV is the target volume. In 1997, Van't Riet et al introduced TVRI/TV × TVRI/VRI as a conformal index, where TVRI is the target volume closed by the prescription isodose surface. We chose a lung cancer patient who was assigned to be treated with SBRT. SBRT immobilization device was used and non‐gated CT/4DCT was performed. The tumor movement was less than 1 cm based on 4DCT. A MIP image set was generated and used to delineate the internal target volume (ITV). A 5 mm margin was added on the ITV to generate the PTV. The prescription was 5000 cGy in 5 fractions and 100% prescription dose covered 95% of the PTV. A VMAT plan (plan I) was made to achieve the physician's goal. Then a high dose structure was generated by VRI subtracting the TV, a low dose structure was generated by TV subtracting VRI, and medium dose structure was named for the overlapping area between VRI and TV. The other VMAT plan (plan II) was made by adding constraints to high/low/medium dose structures, respectively. The conformity index was determined and compared between plan I and plan II.Results:For plan I, the Eclipse's conformal index was 1.06; the Van't Riet's conformal index was 0.82. For plan II, the Eclipse's conformal index was 1.02; the Van't Riet's conformal index was 0.85. The conformal index was improved in plan II.Conclusion:The high/low dose/medium dose structures may be useful to make more conformal plans to treat lung area using SBRT based on the conformal index values.
SU‐F‐T‐632: On the Use of Intensity Modulated Arc Therapy for Thoracic Vertebral Metastases SBRT Treatment
Authors: Pokhrel D , Mallory M , Badkul R , Jiang H , Saleh H , Wang F , Lominska C 
Published: July 2016

Purpose:To retrospectively evaluate quality, efficiency and delivery accuracy of intensity modulated arc therapy (IMAT) plans for thoracic‐vertebral metastases using stereotactic body radiotherapy (SBRT).Methods:After obtaining approval of RPC‐benchmark plan, seven previously treated thoracic‐vertebral metastases patients with non‐coplanar hybrid arcs(NC‐HA)using 1–2 3D‐dynamic conformal partial‐arcs plus 7–9 IMRT‐beams were re‐optimized with IMAT using 3 full co‐planar arcs. Tumors were located between T2–T7. T1/T2‐weighted MRI images were co‐registered with planning‐CT. PTVs were between 24.3–240.1cc(median=48.1cc). Prescription was 30Gy in 5 fractions with 6‐MV beams at Novalis‐TX consisting of HD‐MLC.Plans were compared for target coverage:conformality index(CI),homogeneity index(HI),PTVD90. Organs‐at‐risks(OARs)was evaluated for spinal cord(Dmax, D0.35cc, and D1.2cc), esophagus(Dmax and D5cc),heart(Dmax, D15cc)and lung(V5 and V10). Dose delivery efficiency and accuracy of each IMAT plan was assessed via quality assurance(QA) plan. Beam‐on time was recorded and a gamma index was used to compare agreement between planned and measured doses.Results:SBRT IMAT plans resulted in superior CI(1.02 vs. 1.36, p=0.05) and HI (0.14 vs. 0.27, p=0.01). PTVD90 was improved but statistically insignificant (31.0 vs. 30.4Gy, p=0.38). IMAT resulted in statistically significant improvements in OARs sparing: esophagus max(22.5 vs. 27.0Gy, p=0.03), esophagus 5cc (17.6 vs. 21.5Gy, p=0.02) and heart max(13.1 vs. 15.8Gy, p=0.03). Spinal cord,lung V5 and V10 were lower but statistically insignificant. Average total MU and beam‐on time were 2598±354 vs. 3542±495 and 4.7±0.6 min vs. 7.1±1.0min for IMAT vs. NC‐HA (without accounting for couch kicks time for NC‐HA). IMAT plans demonstrated an accurate dose delivery of 95.5±1.0% for clinical gamma passing‐rate of 2%/2mm criteria on MapCHECK, that was comparable to NC‐HA plans.Conclusion:IMAT plans provided highly conformal and homogeneous dose distributions to target and reduced OARs doses compared to NC‐HA. Total MU was reduced by a factor of 1.4 and subsequently decreased treatment times significantly ‐ potentially minimizing intra‐fraction motion error and owing to patient comfort. SBRT using IMAT planning for single fraction thoracic‐vertebrae metastases will be investigated.
SU‐F‐T‐637: Single‐Isocenter Versus Multiple‐Isocenter VMAT SRS for Unusual Multiple Metastasis Case with Two Widely Separated Lesions
Authors: Thomas EM , Popple RA , Fiveash JB 
Published: July 2016

Purpose:Single‐isocenter (SI) volumetric modulated arc therapy has been shown to be an effective and efficient approach to multiple metastasis radiosurgery. However, certain extreme cases raise the question of whether multiple‐isocenter (MI) approaches can still generate superior plans. In this study, we ask this question with respect to a clinical case with two very widely separated lesions.Methods:A patient with two widely separated (d = 12cm) tumors was treated with SI‐VMAT SRS using 10MV flattening filter free (FFF) beam with high‐definition multi‐leaf collimator (HD‐MLC, 2.5/5mm) in two non‐coplanar arcs using concentric rings to enforce steep gradient. Because of lesion positioning with respect to collimator angle selection, lesions were treated by 5mm leaves. We re‐planned the case with a congruent arc arrangement but separate isocenter for each lesion. In this manner, lesions were treated by 2.5mm leaves. Conformity index (CI), V50%, and mean brain dose were compared.Results:Neither conformity (CI_SI = 1.12, CI_MI = 1.08) nor V50% (V50%_SI =8.82cc, V50%_MI =8.81cc) were improved by utilizing a separate isocenter for each lesion. Mean brain dose was slightly reduced (dmean_SI = 118.4 cGy, dmean_MI = 88.7 cGy) by using multiple isocenters.Conclusion:For this case with a lesion at the apex of the brain and another distantly located at the base of skull, employing a separate isocenter for each target did not meaningfully improve plan quality. Single‐isocenter VMAT has been shown feasible and equivalent to multiple‐isocenter VMAT for multiple metastasis cases in general. In this extreme case, single‐ and multiple‐ isocenter VMAT were also equivalent. If rotational setup errors are appropriately corrected, the increased delivery efficiency of the single‐isocenter approach renders it preferable to the multiple isocenter approach.Dr's Thomas, Popple, and Fiveash have all received honoraria from Varian Medical Systems for discussing their experiences with stereotactic radiosurgery.
SU‐F‐T‐638: Is There A Need For Immobilization in SRS?
Authors: Masterova K , Sethi A , Anderson D , Prabhu V , Rusu I , Gros S , Melian E 
Published: July 2016

Purpose:Frameless Stereotactic radiosurgery (SRS) is increasingly used in the clinic. Cone‐Beam CT (CBCT) to simulation‐CT match has replaced the 3‐dimensional coordinate based set up using a stereotactic localizing frame. The SRS frame however served as both a localizing and immobilizing device. We seek to measure the quality of frameless (mask based) and frame based immobilization and evaluate its impact on target dose.Methods:Each SRS patient was set up by kV on‐board imaging (OBI) and then fine‐tuned with CBCT. A second CBCT was done at treatment‐end to ascertain intrafraction motion. We compared pre‐ vs post‐treatment CBCT shifts for both frameless and frame based SRS patients. CBCT to sim‐CT fusion was repeated for each patient off‐line to assess systematic residual image registration error. Each patient was re‐planned with measured shifts to assess effects on target dose.Results:We analyzed 11 patients (12 lesions) treated with frameless SRS and 6 patients (11 lesions) with a fixed frame system. Average intra‐fraction iso‐center positioning errors for frameless and frame‐based treatments were 1.24 ± 0.57 mm and 0.28 ± 0.08 mm (mean ± s.d.) respectively. Residual error in CBCT registration was 0.24 mm. The frameless positioning uncertainties led to target dose errors in Dmin and D95 of 15.5 ± 18.4% and 6.6 ± 9.1% respectively. The corresponding errors in fixed frame SRS were much lower with Dmin and D95 reduced by 4.2 ± 6.5% and D95 2.5 ± 3.8% respectively.Conclusion:Frameless mask provides good immobilization with average patient motion of 1.2 mm during treatment. This exceeds MRI voxel dimensions (∼0.43mm) used for target delineation. Frame‐based SRS provides superior patient immobilization with measureable movement no greater than the background noise of the CBCT registration. Small lesions requiring submm precision are better served with a frame based SRS.
SU‐F‐T‐646: SBRT Lung: Moving Beyond the 3D Conformal Paradigm with An Elekta VersaHD Accelerator
Authors: Dalhart A , Hyer D , Allen B , Flynn R , Johnston H 
Published: July 2016

Purpose:To develop a volumetric modulated arc therapy (VMAT) planning and delivery methodology for lung stereotactic body radiation therapy (SBRT) that addresses the unique geometric challenges presented when using an Elekta VersaHD linear accelerator.Methods:The Elekta VersaHD imaging panels are fixed at 160cm SID when deployed, limiting the ability to perform non‐coplanar treatments due to collisions with the treatment table. The panels can be folded in a stored position for non‐coplanar treatments, but in this configuration, longitudinal table travel is restricted by the space required for the folded panels. To overcome these design features, a non‐coplanar VMAT technique was designed and evaluated for 6 patients that uses a superiorly placed isocenter near the apex of the lung. A coplanar VMAT technique with isocenter placement within the target was also assessed for each patient. Non‐coplanar plans included three arcs, totalling 340° of arc angle, while coplanar plans included two arcs, totalling 280° of arc angle. Each technique avoided the contralateral lung and major overlap on patient skin. Corresponding 3DCRT plans were used as a baseline for each patient in evaluating VMAT plans.Results:Coplanar and noncoplanar VMAT plans yielded a high dose conformity index (CI) improvement of 6% and low dose CI improvements of 9% and 11%, respectively, over corresponding 3DCRT plans. While both VMAT techniques provided greater skin sparing compared to 3DCRT, the non‐coplanar technique offered an improvement of 20% over the coplanar approach. Treatment time with for VMAT was ∼2.5 minutes compared to ∼10 minutes for 3DCRT.Conclusion:Two VMAT techniques were developed for lung SBRT that account for machine design limitations and provide greater dose conformity and normal tissue sparing than 3DCRT plans. The non‐coplanar VMAT plans showed a marginal improvement over coplanar VMAT plans and may not warrant the additional complexity.
SU‐F‐T‐652: Verification of Inter‐Fractional Tumor Motion Using Daily Fiducial Length Measurement for Pancreatic SBRT
Authors: Jang S , Hwang M , Michalski D , Lalonde R , Huq M 
Published: July 2016

Purpose:To evaluate possible inter‐fractional tumor motion variability for pancreatic SBRT with length measurement of the fiducial depiction on the scan and to develop an empirical correlation using a moving phantom and fiducials for adjusting gating window on a daily basisMethods:In this retrospective study, motion data for fifty pancreatic SBRT patients with fiducials were selected to find the tumor motion statistics. Three gold fiducials of 5mm were placed around a solid target inside the Quasar Phantom and the 4D CT images of the Phantom were acquired with tumor motion of 1cm in superior‐inferior direction. The breathing period was set to 4 seconds with a sinusoidal breathing form. After 4D‐CT acquisition, CT50% images were imported into the Eclipse and setup fields were created for acquiring CBCT images. CBCT images were acquired by using the TrueBeam‐STx and Pelvis technique. For sinusoidal tumor motions, CBCT images were acquired with tumor motion from zero to 2cm with 0.5cm increment along SI direction. The breathing period was varied from 2∼6 seconds with 2‐second increment. Also, real patients’ breathing files acquired from Varian‐RPM system were used to simulate real patients’ breathing patterns. Then length of fiducial depiction was measured with a HU threshold of zero and was used to find its correlation with real tumor motion.Results:Tumor motions in SI, AP, and LR directions were 0.7±0.5cm, 0.2±0.3cm, and 0.1±0.2cm, respectively. Breathing period was 4.3±0.8seconds. For a sinusoidal breathing form, there was a significant correlation between length of fiducial and real tumor motions with R2 of 0.98. However, the length of fiducial was independent of varying breathing periods. For a real patient's breathing file, the correlation between fiducial length(Y) and tumor motion(X) was Y=1.1268X+0.2696 with R2 of 0.99.Conclusion:With daily fiducial length measurement, we can evaluate possible changes in the inter‐fractional tumor motion in pancreatic SBRT.
SU‐F‐T‐653: Radiation Exposure from Cs‐131 Permanent Seed Implants
Authors: Giaddui T , Hardin M , To D , Kremmel E , Peng C , Hann P , Richardson S , Yu Y , Harrison A , Doyle L 
Published: July 2016

Purpose:Permanent seed implants have traditionally been used to treat prostate, lung and head or neck cancers using I‐125 and Pd‐103. Cs‐131, which has higher dose rate is being used to treat brain, head and/or neck cancers in our clinic, therefore, we chose to monitor the dose received by surgeons during the extensive procedure. The aims of this work are to assess the level of radiation exposure to surgeons and the instantaneous exposure at bedside and 1 m from patients.Methods:Ten patients received Cs‐131 implants for recurrent brain,head and/or neck cancer; the median implanted activity, number of implanted seeds and prescription dose at 0.5 cm from the perpendicular plane of the implant were: 54.3 mCi (14.52 – 77); 19 (4 – 24) and 60 Gy (range 42 – 60) respectively. Radiation exposure was recorded at bedside and 1 m from the patient using Victoreen ion chamber (Fluke Biomedical, Cleveland, OH). Exposure to surgeons was measured using TLD (Mirion Technologies (GDS), Inc., USA).Results:The median equivalent dose rate at 1 m and bedside immediately following implantation were 1.49×10‐2 mSv/h (8.77×10‐3–2.63×10‐2) and 7.76×10‐2 mSv/h (3.1×10‐2– 1.53×10‐1) respectively. Median equivalent dose to surgeons’ hands was 0.60 mSv (0.33 – 1.48) and no doses were detected for whole‐body. Surgical reconstruction for one patient was performed 71 days post‐implant and resulted in zero exposure to surgeons.Conclusion:The recorded exposure rates were low when compared with the literature. Post procedure surveys at bed site and 1 m indicated that all patients were within safe limits for discharge (< 0.05 mSv/h at 1 m). However, as a precautionary measure, patients were advised to avoid direct contact with children and pregnant women within four weeks of the implant and stay at least at 3 ft from other people. Surgeons doses were well within occupational dose limits.
SU‐F‐T‐658: Out‐Of‐Field Dose Comparison for TrueBeam Low Energy Beams for Extended Distances: Measurement Vs Monte Carlo Simulation
Authors: Wijesooriya K , Liyanage N , Kaluarachchi M , Sawkey D 
Published: July 2016

Purpose:Patient dose far from the treatment field is comprised of scatter from within the patient, and treatment head leakage. We quantify the treatment head leakage for TrueBeam linear accelerator for 6X and 6X‐FFF beams by comparing measurements to Monte Carlo simulations for a variety of jaw sizes and collimator rotations. This work is conceptually similar to that of Kry et al. (Medical Physics 2006; 33: 4405), who considered a Clinac linear accelerator.Methods:Measurements were made using an EXRADIN A101 ion chamber positioned in the patient plane, at distances up to 100 cm from isocenter. Simulations were done using VirtuaLinac, the GEANT4‐based Monte Carlo model of the TrueBeam treatment head, and an in‐house (U. Virginia) GEANT4‐based code. In‐house code modelled an ion chamber with build‐up, based on a CT scan of the chamber. VirtuaLinac included a detailed model of the treatment head shielding, and was run on the Amazon Web Services cloud to generate spherical phase space files surrounding the treatment head. These phase space files were imported into the in‐house code.Results:Initial comparisons between measurements and simulation showed an excess of dose in the in‐plane direction, away from the gantry, in the simulations. This was traced to an incomplete model of the shielding—specifically, the component holding the primary collimator was smaller in the model than in the TrueBeam. Modifications were made to VirtuaLinac to more closely match the engineering drawings. In the in‐plane direction, the lowest out of field dose was away from gantry (negative abscissa values) at around 60 cm from isocenter, for fields smaller than 10×10 cm2. Out of field dose decreased with decreasing jaw size. Flattening‐filter free beam produced out‐of‐field doses as low as 65% of those with flattened beam.Conclusion:Doses determined from simulation and measurement were in close agreement.Funding support from the Jefferson Trust Foundation
SU‐F‐T‐666: Molecular‐Targeted Gold Nanorods Enhances the RBE of Proton Therapy
Authors: Khoo A , Sahoo N , Krishnan S , Diagaradjane P 
Published: July 2016

Purpose:In recent years, proton beam radiation therapy (PBRT) has gained significant attention in the treatment of tumors in anatomically complex locations. However, the therapeutic benefit of PBRT is limited by a relative biological effectiveness (RBE) of just 1.1. The purpose of this study is to evaluate whether this limitation can be overcome by artificially enhancing the RBE using molecular‐targeted gold nanorods (GNRs).Methods:Molecular‐targeting of GNRs was accomplished using Cetuximab (antibody specific to epidermal growth factor receptor that is over‐expressed in tumors) conjugated GNRs (cGNRs) and their binding affinity to Head and Neck cancer cells was confirmed using dark field microscopy and Transmission Electron Microscopy (TEM). The radiosensitization potential of cGNRs when irradiated with photon (6MV) and proton (100 and 160 MeV) beams was determined using clonogenic assays. The RBE at 10% surviving fraction (RBE10) for proton therapies at central and distal locations of SOBP was calculated with respect to 6 MV photons. IgGconjugated GNRs (iGNRs) were used as controls in all experiments.Results:cGNRs demonstrated significant radiosensitization when compared to iGNRs for 6MV photons (1.14 vs 1.04), 100 MeV protons (1.19 vs 1.04), and 160 MeV protons (1.17 vs 1.04). While RBE10 for proton beams at the center of SOBP revealed similar effects for both 100 and 160 MeV (RBE10=1.39 vs 1.38; p>0.05), enhanced radiosensitization was observed at the distal SOBP with 100 MeV beams demonstrating greater effect than 160 MeV beams (RBE10=1.79 vs 1.6; p<0.05).Conclusion:EGFR‐targeting GNRs significantly enhance the RBE of protons well above the accepted 1.1 value. The enhanced RBE observed for lower energy protons (100 MeV) and at the distal SOBP suggests that low energy components may play a role in the observed radiosensitization effect. This strategy holds promise for clinical translation and could evolve as a paradigm‐changing approach in the field of radiation oncology.The UT MD Anderson Cancer Center's Institutional Research Grant funding to P. Diagaradjane