bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐T‐600: Patient Specific IMRT Verification Using a Phosphor‐Screen Based Geometric QA System: A Preliminary Study
Authors: Lee M , Hu E , Yi B 
Published: June 2015

Purpose:Raven QA (JPLC, MD) is a unified and comprehensive quality assurance system for QA of TG‐142, which use a phosphor screen, a mirror system and a camera. It is to test if this device can be used for IMRT QA dosimetry.Methods:A lung IMRT case is used deliver dose to Raven QA. Accuracy of dose distribution of 5cm slab phantom using Eclipse planning system (Varian) has been confirmed both from a Monte Carlo Simulation and from a MapCheck (SunNuclear) measurement. Geometric distortion and variation of spatial dose response are corrected after background subtraction. A pin‐hole grid plate is designed and used to determine the light scatter in the Raven QA box and the spatial dose response. Optic scatter model was not applied in this preliminary study. Dose is normalized to the response of the 10×10 field and the TMR of 5cm depth was considered.Results:Time to setup the device for IMRT QA takes less than 5 minutes as other commercially available devices. It shows excellent dose linearity and dose rate independent, less than 1 %. Background signal, however, changes for different field sizes. It is believed to be due to inaccurate correction of optic scatter. Absolute gamma (5%, 5mm) passing rate was higher than 95%.Conclusion:This study proves that the Raven QA can be used for a patient specific IMRT verification.Part of this study is supported by the Maryland Industrial Partnership Grant.
SU‐E‐T‐602: Patient‐Specific Online Dose Verification Based On Transmission Detector Measurements
Authors: Thoelking J , Yuvaraj S , Jens F , Lohr F , Wenz F , Wertz H , Wertz H 
Published: June 2015

Purpose:Intensity modulated radiotherapy requires a comprehensive quality assurance program in general and ideally independent verification of dose delivery. Since conventional 2D detector arrays allow only pre‐treatment verification, there is a debate concerning the need of online dose verification. This study presents the clinical performance, including dosimetric plan verification in 2D as well as in 3D and the error detection abilities of a new transmission detector (TD) for online dose verification of 6MV photon beam.Methods:To validate the dosimetric performance of the new device, dose reconstruction based on TD measurements were compared to a conventional pre‐treatment verification method (reference) and treatment planning system (TPS) for 18 IMRT and VMAT treatment plans. Furthermore, dose reconstruction inside the patient based on TD read‐out was evaluated by comparing various dose volume indices and 3D gamma evaluations against independent dose computation and TPS. To investigate the sensitivity of the new device, different types of systematic and random errors for leaf positions and linac output were introduced in IMRT treatment sequences.Results:The 2D gamma index evaluation of transmission detector based dose reconstruction showed an excellent agreement for all IMRT and VMAT plans compared to reference measurements (99.3±1.2)% and TPS (99.1±0.7)%. Good agreement was also obtained for 3D dose reconstruction based on TD read‐out compared to dose computation (mean gamma value of PTV = 0.27±0.04). Only a minimal dose underestimation within the target volume was observed when analyzing DVH indices (<1%). Positional errors in leaf banks larger than 1mm and errors in linac output larger than 2% could clearly identified with the TD.Conclusion:Since 2D and 3D evaluations for all IMRT and VMAT treatment plans were in excellent agreement with reference measurements and dose computation, the new TD is suitable to qualify for routine treatment plan verification.Funding Support, Disclosures, and Conflict of Interest: COIs: Frank Lohr: Elekta: research grant, travel grants, teaching honoraria IBA: research grant, travel grants, teaching honoraria, advisory board C‐Rad: board honoraria, travel grants Frederik Wenz: Elekta: research grant, teaching honoraria, consultant, advisory board Zeiss: research grant, teaching honoraria, patent Hansjoerg Wertz: Elekta: research grant, teaching honoraria IBA: research grant
SU‐E‐T‐603: PBS Prostate Plan Robustness: A Tool for Patient Specific Setup Tolerance
Authors: Tang S , Song L , Chen C , Chang C , Chon B , Tsai H , Soffen E , Cahlon O , Mah D 
Published: June 2015

Purpose:Fiducial markers are commonly used for setup of prostate patients using orthogonal radiographs. After aligned with the markers, the displacement of the bony anatomy relative to the planned DRR can be up to 10 mm. Such offset can potentially have significant dosimetric effects because it changes the radiological path length of protons in differing amounts of bone. It is imperative to develop a method to evaluate its impact on target coverage and hence establish patient specific setup tolerance for prostate proton PBS treatment.Methods:Prostate patients were planned in RayStation according to the PCG protocol with bi‐lateral beams. The primary planning objectives are: (1) 100% of CTV receives full prescription dose; (2) 98% of the prescription dose covers at least 98% of the PTV; (3) OARs meet criteria per protocol. For each patient 108 dose perturbations were automatically generated using an in‐house script, which considered the isocenter shifting in S‐I and A‐P directions (up to ±15 mm with an interval of 6mm) as well as the range uncertainty (±3.5%). The target coverage was evaluated on the contour shifted along with prostate to mimic the daily treatment.Results:The minimum CTV coverage as a function of offsets in S‐I and A‐P directions is presented in a 2D contour map. The offsets along A‐P direction generally have greater impact than along S‐I direction. Both the CTV D98%>98% or CTV V98%>98% are achievable for most patients if the offset is <10 mm in either direction despite of range uncertainties.Conclusion:We developed a method to evaluate the plan robustness for proton PBS prostate treatment. It can provide patient specific setup tolerance of bony structure offset. For our current planning approach, a 1 cm displacement is acceptable. This approach can be generalized to other target structures that move relative to bony anatomy.
SU‐E‐T‐605: Performance Evaluation of MLC Leaf‐Sequencing Algorithms in Head‐And‐Neck IMRT
Authors: Jing J , Lin H , Chow J 
Published: June 2015

Purpose:To investigate the efficiency of three multileaf collimator (MLC) leaf‐sequencing algorithms proposed by Galvin et al, Chen et al and Siochi et al using external beam treatment plans for head‐and‐neck intensity modulated radiation therapy (IMRT).Methods:IMRT plans for head‐and‐neck were created using the CORVUS treatment planning system. The plans were optimized and the fluence maps for all photon beams determined. Three different MLC leaf‐sequencing algorithms based on Galvin et al, Chen et al and Siochi et al were used to calculate the final photon segmental fields and their monitor units in delivery. For comparison purpose, the maximum intensity of fluence map was kept constant in different plans. The number of beam segments and total number of monitor units were calculated for the three algorithms.Results:From results of number of beam segments and total number of monitor units, we found that algorithm of Galvin et al had the largest number of monitor unit which was about 70% larger than the other two algorithms. Moreover, both algorithms of Galvin et al and Siochi et al have relatively lower number of beam segment compared to Chen et al. Although values of number of beam segment and total number of monitor unit calculated by different algorithms varied with the head‐and‐neck plans, it can be seen that algorithms of Galvin et al and Siochi et al performed well with a lower number of beam segment, though algorithm of Galvin et al had a larger total number of monitor units than Siochi et al.Conclusion:Although performance of the leaf‐sequencing algorithm varied with different IMRT plans having different fluence maps, an evaluation is possible based on the calculated number of beam segment and monitor unit. In this study, algorithm by Siochi et al was found to be more efficient in the head‐and‐neck IMRT.The Project Sponsored by the Fundamental Research Funds for the Central Universities (J2014HGXJ0094) and the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry.
SU‐E‐T‐606: Performance of MR‐Based 3D FXG Dosimetry for Preclinical Irradiation
Authors: Welch M , Jaffray D 
Published: June 2015

Purpose:Technological advances have revolutionized preclinical radiation research to enable precise radiation delivery in preclinical models. Kilovoltage x‐rays and complex geometries in preclinical radiation studies challenge conventional dosimetry methods. Previously developed gel‐based dosimetry provides a viable means of accommodating complex geometries and accurately reporting dose at kV energies. This paper will describe the development and evaluation of gel‐based ferrous xylenol‐orange (FXG) dosimetry using a 7T preclinical imaging system.Methods:To confirm water equivalence, Zeff values were calculated for the FXG material, water and ICRU defined soft tissue. Proton T1 relaxivity response in FXG was measured using a preclinical 7T MR and a small animal irradiator for a dose range of 1–22 Gy. FXG was contained in 50 ml centrifuge tubes and irradiated with a 225 kVp x‐ray beam at a nominal dose rate of 2.3 Gy/min. Pre and post irradiation maps of the T1 relaxivity were collected using variable TR spin‐echo imaging (TE 6.65 ms; TR 500, 750, 1000, 1500, 2000, 3000 and 5000 ms) with 2 mm thick slices, 0.325 mm/pixel, 3 averages and an acquisition time of 26 minutes. A linear fit to the change in relaxation rate (1/T1) for the delivered doses reported the gel sensitivity in units of ms‐1Gy‐1. Irradiation and imaging studies were repeated using three batches of gel over 72 hrs.Results:FXG has a Zeff of 3.8 for the 225 kVp spectrum used; differing from water and ICRU defined soft tissue by 0.5% and 2.5%, respectively. The average sensitivity for the FXG dosimeter was 31.5 ± 0.7 ms‐1Gy‐1 (R2 = 0.9957) with a y‐intercept of −29.4 ± 9.0 ms‐1.Conclusion:Preliminary results for the FXG dosimeter properties, sensitivity, and dose linearity at preclinical energies is promising. Future work will explore anatomically relevant tissue inclusions to test MR performance.Student funding provided by The Terry Fox Foundation Strategic Initiative for Excellence in Radiation Research for the 21st Century at CIHR and the Gifford Ontario Student Opportunity Trust Fund.
SU‐E‐T‐609: Perturbation Effects of Pedicle Screws On Radiotherapy Dose Distributions
Authors: Bar‐Deroma R , Borzov E , Nevelsky A 
Published: June 2015

Purpose:Radiation therapy in conjunction with surgical implant fixation is a common combined treatment in case of bone metastases. However, metal implants generally used in orthopedic implants perturb radiation dose distributions. Carbon‐Fiber Reinforced (CFR) PEEK material has been recently introduced for production of intramedullary screws and plates. Gold powder can be added to the CFR‐PEEK material in order to enhance visibility of the screws during intraoperative imaging procedures. In this work, we investigated the perturbation effects of the pedicle screws made of CFR‐PEEK, CFR‐PEEK with added gold powder (CFR‐PEEK‐AU) and Titanium (Ti) on radiotherapy dose distributions.Methods:Monte Carlo (MC) simulations were performed using the EGSnrc code package for 6MV beams with 10×10 fields at SSD=100cm. By means of MC simulations, dose distributions around titanium, CFR‐ PEEK and CFR‐PEEK‐AU screws (manufactured by Carbo‐Fix Orthopedics LTD, Israel) placed in a water phantom were calculated. The screw axis was either parallel or perpendicular to the beam axis. Dose perturbation (relative to dose in homogeneous water phantom) was assessed.Results:Maximum overdose due to backscatter was 10% for the Ti screws, 5% for the CFR‐PEEK‐AU screws and effectively zero for the CFR‐PEEK screws. Maximum underdose due to attenuation was 25% for the Ti screws, 15% for the CFR‐PEEK‐AU screws and 5% for the CFR‐PEEK screws. Conclusion: Titanium screws introduce the largest distortion on the radiation dose distribution. The gold powder added to the CFR‐PEEK material improves visibility at the cost of increased dose perturbation. CFR‐PEEK screws caused minimal alteration on the dose distribution. This can decrease possible over and underdose of adjacent tissue and thus favorably influence treatment efficiency. The use of such implants has potential clinical advantage in the treatment of neoplastic bone disease.
SU‐E‐T‐611: Photon and Neutron Peripheral Dose Ratio for Low (6 MV) and High (15 MV) Energy for Treatment Selection
Authors: Irazola L , Terron J , Sanchez‐Nieto B , Ortiz‐Seidel M , Sanchez‐Doblado F 
Published: June 2015

Purpose:Differences between radiotherapy techniques and energies, can offer improvements in tumor coverage and organs at risk preservation. However, a more complete decision should include peripheral doses delivered to the patient. The purpose of this work is the balance of photon and neutron peripheral doses for a prostate case solved with 6 different treatment modalities.Methods:Inverse and Forward IMRT and 3D‐CRT in 6 and 15 MV for a Siemens Primus linac, using the same CT data set and contours. The methodology described in [1], was used with the TNRD thermal neutron detector [2] for neutron peripheral dose estimation at 7 relevant organs (colon, esophagus, stomach, liver, lung, thyroid and skin). Photon doses were estimated for these organs by terms of the algorithm proposed in [3]. Plans were optimized with the same restrictions and limited to 30 segments in the Inverse case.Results:A similar photon peripheral dose was found comparing 6 and 15 MV cases with slightly higher values of (1.9 ± 1.6) % in mean, for the 6 MV cases. Neutron presence when using 15 MV, represents an increase in peripheral dose of (18 ± 17) % in average. Due to the higher number of MU used in Inverse IMRT, an increasing of (22 ± 3) % in neutron dose is found related to Forward and 3D‐CRT plans. This corresponds to photon doses within 44 and 255 mSv along the organs, for a dose prescription of 68 Gy at the isocenter.Conclusion:Neutron and photon peripheral doses for a prostate treatment planified in 6 different techniques have been analyzed. 6 MV plans are slightly more demanding in terms of photon peripheral doses. Inverse technique in 15 MV has Result to be the most demanding one in terms of total peripheral doses, including neutrons and photons. [1]Phys.Med.Biol,2012;57:6167–6191.[2]Med.Phys.,2014;41(112105)1–5.[3]Phys.Medica,2014;30:e33.
SU‐E‐T‐612: Photonuclear Activation of Prosthetic Hips in Radiotherapy
Authors: Keehan S , Smith R , Millar J , Esser M , Taylor M , Kron T , Franich R 
Published: June 2015

Purpose:To measure the neutron induced activation of a prosthetic hip when exposed to an 18 MV radiotherapy linac beam to assess the potential dose to patients.Methods:A prosthetic hip (Thackray, UK) was placed in a water phantom and irradiated (both in‐field and out‐of‐field) with an 18 MV linac beam. Gamma spectroscopy was used to identify the radioisotopes produced. Following the in‐field irradiation where the induced activity is higher, high sensitivity lithium fluoride Thermoluminescence Dosimeters (TLD‐100H) (Harshaw, USA) were placed on the surface to measure the dose which would be deposited to nearby tissue resulting from the induced radioactivity.Results:The radioisotopes produced in the hip prosthesis have been identified as 52V, 53Fe, and 56Mn which have half‐lives of 3.74, 8.51 and minutes respectively. The 378 and 511 keV characteristic peaks of 53Fe do not appear in the spectra collected from hips irradiated in the out‐of‐field region. This isotope is produced by photonuclear interactions within the hip itself. 52V and 56Mn appear in spectra collected from hips irradiated either within the photon beam or in the nearby out‐of‐field region, implying that they are produced by incident neutron radiation produced in components of the linear accelerator.The integrated dose which would be deposited in the tissue immediately surrounding the hip after four hours (1.5 half‐lives of the longest lived product) was measured as approximately 100 µGy, following a 10,000 MU irradiation of the prosthesis. A highly accurate measurement of the dose is challenging because of the irregular shape of the prosthesis.Conclusion:The cumulative dose measured at the surface of the hip is 0.0001% of the in‐field dose, and is therefore negligible compared with the doses the patient receives as a consequence of their treatment.
SU‐E‐T‐617: Plan Quality Estimation of Intensity‐Modulated Radiotherapy Cases for Lung Cancer
Authors: Koo J , Yoon M , Chung W , Kim D 
Published: June 2015

Purpose:To estimate the planning quality of intensity‐modulated radiotherapy in lung cancer cases and to provide preliminary data for the development of a planning quality assurance algorithm.Methods:42 IMRT plans previously used in cases of solitary lung cancers were collected. Organs in or near the thoracic cavity, such as lung (ipsilateral, contralateral), heart, liver, esophagus, cord and bronchus were considered as organs at risk (OARs) in this study. The coverage index (CVI), conformity index (CI), homogeneity index (HI), volume, irregularity (standard deviation of center‐surface distance) were used to compare PTV dose characteristics. The effective uniform dose (EUD), V10Gy, and V20Gy of the OARs were used to compare OAR dose characteristics.Results:Average CVI, CI, HI values were 0.9, 0.8, 0.1, respectively. CVI and CI had narrow Gaussian distribution curves without a singular value, but one case had a relatively high (0.25) HI because of location and irregular shape (Irregularity of 18.5 when average was 12.5) of PTV. EUDs tended to decrease as OAR‐PTV distance increased and OAR‐PTV overlap volume decreased.Conclusion:This work indicates the potential for significant plan quality deviation of similar lung cancer cases. Considering that this study were from a single department, differences in the treatment results for a given patient would be much more pronounced if multiple departments (and therefore more planners) were involved. Therefore, further examination of QA protocols is needed to reduce deviations in radiation treatment planning.
SU‐E‐T‐623: Polarity Effects for Small Volume Ionization Chambers in Cobalt‐60 Beams
Authors: Xu Y , Bhatnagar J , Huq M Saiful 
Published: June 2015

Purpose:To investigate the polarity effects for small volume ionization chambers in 60Co gamma‐ray beams using the Leksell Gamma Knife Perfexion.Methods:Measurements were made for 7 small volume ionization chambers (a PTW 31016, an Exradin A14, 2 Capintec PR0‐5P, and 3 Exradin A16) using a PTW UNIDOSwebline Universal Dosemeter and an ELEKTA solid water phantom with proper inserts. For each ion chamber, the temperature/pressure corrected electric charge readings were obtained for 16 voltage values (±50V, ±100V, ±200V, ±300V, ±400V, ±500V, ±600V, ±700V). For each voltage, a five‐minute leakage charge reading and a series of 2‐minute readings were continuously taken during irradiation until 5 stable signals (less than 0.05% variation) were obtained. The average of the 5 reading was then used for the calculation of the polarity corrections at the voltage and for generating the saturation curves.Results:The polarity effects are more pronounced at high or low voltages than at the medium voltages for all chambers studied. The voltage dependence of the 3 Exradin A16 chambers is similar in shape. The polarity corrections for the Exradin A16 chambers changes rapidly from about 1 at 500V to about 0.98 at 700V. The polarity corrections for the 7 ion chambers at 300V are in the range from 0.9925 (for the PTW31016) to 1.0035 (for an Exradin A16).Conclusion:The polarity corrections for certain micro‐chambers are large even at normal operating voltage.
SU‐E‐T‐626: Practical Method to Implement Arc Therapy Using Scanned Particle Beams
Authors: Eley J , Mehta M , Molitoris J , Langner U , Langen K 
Published: June 2015

Purpose:The purpose of this study was to propose a method to implement arc therapy that is compatible with existing particle therapy systems having gantries and pencil‐beam scanning capacities. Furthermore, we sought to demonstrate expected benefits of this method for selected clival chordoma patients.Methods:We propose that a desired particle arc treatment plan can be discretized into a finite number of fixed beams and that only one (or a subset) of these beams be delivered in any single treatment fraction; the target should receive uniform dose during each fraction. For 3 clival‐chordoma patients, robust‐optimized, scanned proton beams were simulated to deliver 78 Gy (RBE) to clinical target volumes (CTVs), using either a single‐field plan with a posterior‐anterior (PA) beam or a discrete‐arc plan with 16 beams that were equally spaced throughout a 360‐degree axial arc. Dose‐volume metrics were compared with emphasis on the brainstem, since risk of radiation necrosis there can often restrict application of tumoricidal doses for chordomas.Results:The mean volume of brainstem receiving a dose of 60 Gy (RBE) or higher (V60Gy) was 10.3±0.9 cm3 for the single‐field plan and 4.7±1.8 cm3 for the discrete‐arc plan, a reduction of 55% in favor of arcs. The mean dose to the brainstem was also reduced using arcs, by 18%, while the maximum dose was nearly identical for both methods. For the whole brain, V60Gy was reduced by 23%, in favor of arcs. Mean dose to the CTVs were nearly identical for both strategies, within 0.3%.Conclusion:Discrete arc treatments can be implemented using existing scanned particle‐beam facilities. Aside from the physical advantages, the biological uncertainties of particle therapy, particularly high in the distal edge, can be reduced by arc therapy via rotational smearing, which may be of benefit for tumors near the brainstem.