bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐T‐43: Analytical Model for Photon Peripheral Dose in Radiotherapy Treatments
Authors: Nieto B Sanchez , El far R , Romero‐Exposito M , Lagares J , Mateo JC , Terron JA , Irazola L , Sanchez‐Doblado F 
Published: July 2014

Purpose:The higher survival rate of radiotherapy patients entails a growing concern on second cancers associated to peripheral doses. Currently, dosimetry of out‐of field doses is still under development. Our group has developed a methodology to estimate neutron equivalent dose in organs (1,2). We aimed to propose a model to estimate out‐of‐field photon doses in isocentric treatments from basic clinical data.Methods:The proposed function models the dose as the sum of leakage and scatter terms. The latter is modeled as a virtual source at the collimator, which suffers from attenuation in air and tissue, corrected by the inverse‐square‐law. The model was parameterized using experimental measurements with TLD700 chips placed inside an anthropomorphic phantom (6–18MV) irradiated with conformal and modulated techniques in Elekta, Siemens and Varian linacs. This model provides photon dose at a point as a function of clinical parameters as prescription dose/UM, PTV volume, distance to the field edge, height of the MLC leaves and distance from the the MLC to the isocenter. Model was tested against independent measurements (TLD100) for a VMAT treatment on a Elekta. Dose to organs is modeled from dose to points along the head‐to‐feet axis of the organ of a “standard man” escalated by patient height.Results:Our semi‐empirical model depends on 3 given parameters (leakage parameter can be individualized). A novelty of our model, over other models (e.g., PERIDOSE), arises from its applicability to any technique (independently of the number of MU needed to deliver a dose). Differences between predictions and measurements were < 0.005mSv/UM.Conclusion:We have proposed a unique model which successfully account for photon peripheral organ dose. This model can be applied in the day‐to‐day clinic as it only needs a few basic parameters which are readily accessible.1. Radiother. Oncol. 107:234–243, 2013. 2. Phys. Med. Biol. 57:6167–6191, 2012.
SU‐E‐T‐45: Antibody Mean Residence Time in Blood and Its Correlation with Protein Molecular Weight
Authors: Kwok C , Williams L 
Published: July 2014

Purpose:Animal biodistribution data are required prior to introducing a new radiopharmaceutical into clinical trials. Protein engineering, using recombinant DNA techniques can produce a large number of related (cognate) antibodies to a given molecular target. Thus, it is important that these constructs be numerically related to one another via a single criterion. In the following, we use the mean residence time (MRT) in murine blood as this criterion.Methods:Five cognate anti‐CEA (Carcinoembryonic Antigen) antibodies were compared with regard to their MRT in whole blood of CEA‐positive tumor‐bearing (LS174T) mice. MRT was defined by blood AUC (area under the curve) divided by the initial blood uptake value; all in units of percent injected dose per gram (%ID/g). Cognates included single chain scFv (25 kDa), diabody (50 kDa), minibody (80 kDa), F(ab')2 (120 kDa), and intact (155 kDa) forms of the murine cT84.66 antibody against CEA. All were labeled with radioactive iodine.Results:The agents, in the sequence listed, exhibited MRT values of 1.16 +/‐ 0.01 h, 0.99 h, 5.06 +/‐ 0.70 h, 6.61 +/‐ 0.36 h, and 59.3 +/‐ 2.4 h respectively. Because of the monotonic nature of the sequence, a linear correlation analysis was performed between molecular weight (MW) and MRT or ln(MRT) of the 5 proteins. Probability of random correlation was 0.10 for MRT and 0.01 for ln(MRT).Conclusion:MRT values of cognate anti‐CEA antibodies were found to be a monotonically increasing sequence with respect to MW. Cognate MW values correlated best to ln(MRT) of the protein species. Thus MRT was proportional to an exponential function of molecular weight. The extended intact antibody circulation time presumably reflected its relatively maximal MW. Presence of an intact FC segment on this native antibody may also have influenced these results.
SU‐E‐T‐46: Application of a Twin‐Detector Method for the Determination of the Mean Photon Energy Em at Points of Measurement in a Water Phantom Surrounding a GammaMed HDR 192Ir Brachytherapy Source
Authors: Chofor N , Nebah F , Harder D , Poppe B 
Published: July 2014

Purpose:In a brachytherapy photon field in water the fluence‐averaged mean photon energy Em at the point of measurement correlates with the radiation quality correction factor kQ of a non water‐equivalent detector. To support the experimental assessment of Em, we show that the normalized signal ratio NSR of a pair of radiation detectors, an unshielded silicon diode and a diamond detector can serve to measure quantity Em in a water phantom at a Ir‐192 unit.Methods:Photon fluence spectra were computed in EGSnrc based on a detailed model of the GammaMed source. Factor kQ was calculated as the ratio of the detector's spectrum‐weighted responses under calibration conditions at a 60Co unit and under brachytherapy conditions at various radial distances from the source. The NSR was investigated for a pair of a p‐type unshielded silicon diode 60012 and a synthetic single crystal diamond detector 60019 (both PTW Freiburg). Each detector was positioned according to its effective point of measurement, with its axis facing the source. Lateral signal profiles were scanned under complete scatter conditions, and the NSR was determined as the quotient of the signal ratio under application conditions x and that at position r_ref = 1 cm.Results:The radiation quality correction factor kQ shows a close correlation with the mean photon energy Em. The NSR of the diode/diamond pair changes by a factor of two from 0–18 cm from the source, while Em drops from 350 to 150 keV. Theoretical and measured NSR profiles agree by ± 2 % for points within 5 cm from the source.Conclusion:In the presence of the close correlation between radiation quality correction factor kQ and photon mean energy Em, the NSR provides a practical means of assessing Em under clinical conditions. Precise detector positioning is the major challenge.
SU‐E‐T‐50: Automatic Validation of Megavoltage Beams Modeled for Clinical Use in Radiation Therapy
Authors: Melchior M , Aranda F Salinas , Sciutto S , Dodat D , Larragueta N 
Published: July 2014

Purpose:To automatically validate megavoltage beams modeled in XiO™ 4.50 (Elekta, Stockholm, Sweden) and Varian Eclipse™ Treatment Planning Systems (TPS) (Varian Associates, Palo Alto, CA, USA), reducing validation time before beam‐on for clinical use.Methods:A software application that can automatically read and analyze DICOM RT Dose and W2CAD files was developed using MatLab integrated development environment. TPS calculated dose distributions, in DICOM RT Dose format, and dose values measured in different Varian Clinac beams, in W2CAD format, were compared. Experimental beam data used were those acquired for beam commissioning, collected on a water phantom with a 2D automatic beam scanning system. Two methods were chosen to evaluate dose distributions fitting: gamma analysis and point tests described in Appendix E of IAEA TECDOC‐1583. Depth dose curves and beam profiles were evaluated for both open and wedged beams. Tolerance parameters chosen for gamma analysis are 3% and 3 mm dose and distance, respectively.Absolute dose was measured independently at points proposed in Appendix E of TECDOC‐1583 to validate software results.Results:TPS calculated depth dose distributions agree with measured beam data under fixed precision values at all depths analyzed. Measured beam dose profiles match TPS calculated doses with high accuracy in both open and wedged beams. Depth and profile dose distributions fitting analysis show gamma values < 1. Relative errors at points proposed in Appendix E of TECDOC‐1583 meet therein recommended tolerances.Independent absolute dose measurements at points proposed in Appendix E of TECDOC‐1583 confirm software results.Conclusion:Automatic validation of megavoltage beams modeled for their use in the clinic was accomplished. The software tool developed proved efficient, giving users a convenient and reliable environment to decide whether to accept or not a beam model for clinical use. Validation time before beam‐on for clinical use was reduced to a few hours.
SU‐E‐T‐55: Biological Equivalent Dose (BED) Comparison Between Permanent Interstitial Brachytherapy and Conventional External Beam Radiotherapy for Prostate Cancer
Authors: Liu X , Rahimian J , Cosmatos H , Goy B , Heywood C , Qian Y 
Published: July 2014

Purpose:The goal of this research is to calculate and compare the Biological Equivalent Dose (BED) between permanent prostate Iodine‐125 implant brachytherapy as monotherapy with the BED of conventional external beam radiation therapy (EBRT).Methods:A retrospective study of 605 patients treated with Iodine‐125 seed implant was performed in which physician A treated 274 patients and physician B treated 331 patients. All the Brachytherapy treatment plans were created using VariSeed 8 planning system. The Iodine‐125 seed source activities and loading patterns varied slightly between the two physicians. The prescription dose is 145 Gy to PTV for each patient. The BED and Tumor Control Probability (TCP) were calculated based on the TG 137 formulas. The BED for conventional EBRT of the prostate given in our institution in 2Gy per fraction for 38 fractions was calculated and compared.Results:Physician A treated 274 patients with an average BED of 123.92±0.87 Gy and an average TCP of 99.20%; Physician B treated 331 patients with an average BED of 124.87±1.12 Gy and an average TCP of 99.30%. There are no statistically significant differences (T‐Test) between the BED and TCP values calculated for these two group patients. The BED of the patients undergoing conventional EBRT is calculated to be 126.92Gy. The BED of the patients treated with permanent implant brachytherapy and EBRT are comparable. Our BED and TCP values are higher than the reported values by TG 137 due to higher Iodine‐125 seed activity used in our institution.Conclusion:We calculated the BED,a surrogate of the biological response to a permanent prostate brachytherapy using TG 137 formulas and recommendation. The TCP of better than 99% is calculated for these patients. A clinical outcome study of these patients correlating the BED and TCP values with PSA and Gleason Levels as well as patient survival is warranted.
SU‐E‐T‐56: Brain Metastasis Treatment Plans for Contrast‐Enhanced Synchrotron Radiation Therapy
Authors: Obeid L , Tessier A , Vautrin M , Sihanath R , Benkebil M , Adam J 
Published: July 2014

Purpose:Iodine‐enhanced radiotherapy is an innovative treatment combining the selective accumulation of an iodinated contrast agent in brain tumors with irradiations using monochromatic medium energy x‐rays. The aim of this study is to compare dynamic stereotactic arc‐therapy and iodineenhanced SSRT.Methods:Five patients bearing brain metastasis received a standard helical 3D‐scan without iodine. A second scan was acquired 13 min after an 80 g iodine infusion. Two SSRT treatment plans (with/without iodine) were performed for each patient using a dedicated Monte Carlo (MC) treatment planning system (TPS) based on the ISOgray TPS. Ten coplanar beams (6×6 cm2, shaped with collimator) were simulated. MC statistical error objective was less than 5% in the 50% isodose. The dynamic arc‐therapy plan was achieved on the Iplan Brainlab TPS. The treatment plan validation criteria were fixed such that 100% of the prescribed dose is delivered at the beam isocentre and the 70% isodose contains the whole target volume. The comparison elements were the 70% isodose volume, the average and maximum doses delivered to organs at risk (OAR): brainstem, optical nerves, chiasma, eyes, skull bone and healthy brain parenchyma.Results:The stereotactic dynamic arc‐therapy remains the best technique in terms of dose conformation. Iodine‐enhanced SSRT presents similar performances to dynamic arc‐therapy with increased brainstem and brain parenchyma sparing. One disadvantage of SSRT is the high dose to the skull bone. Iodine accumulation in metastasis may increase the dose by 20–30%, allowing a normal tissue sparing effect at constant prescribed dose. Treatment without any iodine enhancement (medium‐energy stereotactic radiotherapy) is not relevant with degraded HDVs (brain, parenchyma and skull bone) comparing to stereotactic dynamic arc‐therapy.Conclusion:Iodine‐enhanced SSRT exhibits a good potential for brain metastasis treatment regarding the dose distribution and OAR criteria.
SU‐E‐T‐236: Monte Carlo Calculations for Radiosurgery of the Clivus
Authors: Ho A , Gibbs I , Chang S , Soltys S 
Published: July 2014

Purpose:We sought to determine if dosimetric differences exist between Ray‐Trace (RT) and Monte‐Carlo (MC) calculation algorithms for radiosurgery for tumors of the clivus, given their proximity to air‐tissue inhomogeneity.Methods:We retrospectively identified 10 patients with a tumor of the clivus where the target was located near an air‐tissue interface. CyberKnife treatment was delivered in 1 to 5 fractions. Plans originally calculated with the RT algorithm were re‐calculated with the same monitor units (MU) with the MC algorithm. Similarly, plans originally calculated with MC were recalculated with RT. MC calculations were performed using High Resolution with 2% uncertainty on the MultiPlan 4.6 planning system. If the RT plans were originally calculated using water‐air density model, they were re‐calculated with Body standard density model, and then compared with MC plans computed with Body standard density model. The maximum dose (Dmax) to the planning target volumes (PTV) and critical structures, minimum dose (Dmin) and coverage percentage for the PTV were calculated.Results:For 8 cases, MC PTV Dmin was a median 5% (range 0–10%) and Dmax a median 6% (range 3–9%) higher than for RT. For 2 cases, MC PTV Dmin was 6 and 2% and Dmax was 1 and 3% lower than for RT. MC PTV Dmin and Dmax maybe higher or lower than for RT even though the target coverage for MC was less than for RT (median 4%, range 0–13%) with the same MU used. The degree of differences depends on the location of the target relative to the air‐tissue inhomogeneity. Examples are shown that the targets are underdosed near the air‐tissue inhomogenity.Conclusion:Monte Carlo dose calculations are recommended for targets near tissue homogeneity such as the clivus. Assuming that Monte Carlo more closely approximates the true dosimetry, the use of Ray Trace could overestimate target coverage.
SU‐E‐T‐245: MR Guided Focused Ultrasound Increased PARP Related Apoptosis On Prostate Cancer in Vivo
Authors: Chen L , Chen X , Cvetkovic D , Gupta R , Yang D , Ma C 
Published: July 2014

Purpose:Our previous study demonstrated that significant tumor growth delay was observed in the mice treated with pulsed high intensity focused ultrasound (pHIFU). The purpose of this study is to understand the cell killing mechanisms of pHIFU.Methods:Prostate cancer cells (LNCaP), were grown orthotopically in 17 nude mice. Tumor‐bearing mice were treated using pHIFU with an acoustic power of 25W, pulse width 100msec and 300 pulses in one sonication under MR guidance. Mutiple sonications were used to cover the whole tumor volume. Temperature (less than 40 degree centigrade in the focal spot) was monitored using MR thermometry. Animals were euthanized at pre‐determined time points (n=2) after treatment: 0 hours; 6 hrs; 24 hrs; 48 hrs; 4 days and 7 days. Two tumorbearing mice were used as control. Three tumor‐bearing mice were treated with radiation (RT, 2 Gy) using 6 MV photon beams. RT treated mice were euthanized at 0 hr, 6 hrs and 24 hrs. The tumors were processed for immunohistochemical (IHC) staining for PARP (a surrogate of apoptosis). A multispectral imaging analysis system was used to quantify the expression of PARP staining. Cell apoptosis was calculated based on the PARP expression level, which is the intensity of the DAB reaction.Results:Our data showed that PARP related apoptosis peaked at 48 hrs and 7 days in pHIFU treated mice, which is comparable to that for the RT group at 24 hrs. The preliminary results from this study were consistent with our previous study on tumor growth delay using pHIFU.Conclusion:Our results demonstrated that non‐thermal pHIFU increased apoptotic tumor cell death through the PARP related pathway. MR guided pHIFU may have a great potential as a safe, noninvasive treatment modality for cancer therapy. This treatment modality might be able to synergize with PARP inhibitors to achieve better result.
SU‐E‐T‐246: MU Model Implementation for a Passively Scattered Proton Beam: Inclusion of the Bolus Gap and Nozzle Extension Factors
Authors: Simpson R , Ghebremedhin A , Gordon I , Patyal B , Piskulich F. , LeMaster Brett 
Published: July 2014

Purpose:To develop and implement an MU model for a passively scattered proton beam, and eliminate the need for patient specific calibrations for field sizes from 3cm to 15cm. This would enable consistent and timely calibrations for a wide variety of patient portals, streamlining the treatment process.Methods:Measurements were initially made using a Standard Imaging A‐16 ion chamber and a modified water tank to determine the bolus gap factors (BGF) for multiple combinations of aperture size, bolus thickness, and air gap. The BGF was then separated into two component factors: the bolus thickness factor (BTF) and the nozzle extension factor (NEF). Polynomial curves were generated using the measured data to produce BTF tables for air gaps from 0cm to 30cm and for bolus thicknesses from 0cm to 10cm, and NEF tables for the full range of clinically used nozzle extensions. Additionally, data tables were created for every factor that affects beam output in the MU model. The MUs were then modeled for 487 patient portals and retrospectively compared to the MUs generated from the physical calibrations previously performed.Results:Of the 487 patient portals tested, 100% of the portals used for the comparison were within 2.5% from the MUs generated using a physical calibration, and 95.9% of the MU model portals tested were within 2%. The patient portals tested had field sizes ranging from 2.1cm to 10.1cm, with air gaps from 2cm to 25cm. Output factors for field sizes below 3cm with irregularly shaped fields demonstrated inconsistent results and will be further studied.Conclusion:The most problematic output factor, the BGF, was modeled accurately and consistently using the lowest order polynomial curve fits and interpolation between measured data. The study results demonstrate the robustness of the MU model and the potential for saving valuable personnel and beam time.
SU‐E‐T‐248: Near Real‐Time Analysis of Radiation Delivery and Imaging, Accuracy to Ensure Patient Safety
Authors: Wijesooriya K , Seitter K , Desai V , Read P , Larner J 
Published: July 2014

Purpose:To develop and optimize an effective software method for comparing planned to delivered control point machine parameters for all VARIAN TrueBeam treatments so as to permit (1) assessment of a large patient pool throughout their treatment course to quantify treatment technique specific systematic and random uncertainty of observables, (2) quantify the site specific daily imaging shifts required for target alignment, and (3) define tolerance levels for mechanical parameters and imaging parameters based on statistical analysis data gathered, and the dosimetric impact of variations.Methods:Treatment and imaging log files were directly compared to plan parameters for Eclipse and Pinnacle planned treatments via 3D, IMRT, control point, RapidArc, and electrons. Each control point from all beams/arcs (7984) for all fractions (1940) of all patients treated over six months were analyzed. At each control point gantry angle, collimator angle, couch angle, jaw positions, MLC positions, MU were compared. Additionally per‐treatment isocenter shifts were calculated.Results were analyzed as a whole in treatment type subsets:IMRT, 3D, RapidArc; and in treatment site subsets: brain, chest/mediastinum, esophagus, H&N, lung, pelvis, prostate. Results: Daily imaging isocenter shifts from initial external tattoo alignment were dependent on the treatment site with < 0.5 cm translational shifts for H&N, Brain, and lung SBRT, while pelvis, esophagus shifts were ∼1 cm. Mechanical delivery parameters were within tolerance levels for all sub‐beams. The largest variations were for RapidArc plans: gantry angle 0.11±0.12,collimator angle 0.00±0.00, jaw positions 0.48±0.26, MLC leaf positions 0.66±0.08, MU 0.14±0.34.Conclusion:Per‐control point validation reveals deviations between planned and delivered parameters. If used in a near real‐time error checking system, patient safety can be improved by equipping the treatment delivery system with additional forcing functions which by‐pass human error avenues.
SU‐E‐T‐252: On the Evaluation of Patient Specific IMRT QA Using EPID, Dynalog Files and Patient Anatomy
Authors: Defoor D , Vazquez Quino L , Stathakis S , Mavroidis P , Papanikolaou N 
Published: July 2014

Purpose:This research, investigates the viability of using the Electronic portal imaging device (EPID) coupled with the treatment planning system (TPS), to calculate the doses delivered and verify agreement with the treatment plan. The results of QA analysis using the EPID, Delta4 and fluence calculations using the multi‐leaf collimator (MLC) dynalog files on 10 IMRT patients are presented in this study.Methods:EPID Fluence Images in integrated mode and Dynalog files for each field were acquired for 10 IMRT (6MV) patients and processed through an in house MatLab program to create an opening density matrix (ODM) which was used as the input fluence for dose calculation with the TPS (Pinnacle3, Philips). The EPID used in this study was the aSi1000 Varian on a Novalis TX linac equipped with high definition MLC. The resulting dose distributions were then exported to VeriSoft (PTW) where a 3D gamma was calculated using 3mm‐3% criteria. The Scandidos Delta4 phantom was also used to measure a 2D dose distribution for all 10 patients and a 2D gamma was calculated for each patient using the Delta4 software.Results:The average 3D gamma for all 10 patients using the EPID images was 98.2% ± 2.6%. The average 3D gamma using the dynalog files was 94.6% ± 4.9%. The average 2D gamma from the Delta4 was 98.1% ± 2.5%. The minimum 3D gamma for the EPID and dynalog reconstructed dose distributions was found on the same patient which had a very large PTV, requiring the jaws to open to the maximum field size.Conclusion:Use of the EPID, combined with a TPS is a viable method for QA of IMRT plans. A larger ODM size can be implemented to accommodate larger field sizes. An adaptation of this process to Volumetric Arc Therapy (VMAT) is currently under way.