bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐F‐T‐64: An Alternative Approach to Determining the Reference Air‐Kerma Rate from Extrapolation Chamber Measurements
Authors: Schneider T 
Published: July 2016

Purpose:Since 2008 the Physikalisch‐Technische Bundesanstalt (PTB) has been offering the calibration of 125I‐brachytherapy sources in terms of the reference air‐kerma rate (RAKR). The primary standard is a large air‐filled parallel‐plate extrapolation chamber. The measurement principle is based on the fact that the air‐kerma rate is proportional to the increment of ionization per increment of chamber volume at chamber depths greater than the range of secondary electrons originating from the electrode x0.Methods:Two methods for deriving the RAKR from the measured ionization charges are: (1) to determine the RAKR from the slope of the linear fit to the so‐called 'extrapolation curve’, the measured ionization charges Q vs. plate separations x or (2) to differentiate Q(x) and to derive the RAKR by a linear extrapolation towards zero plate separation. For both methods, correcting the measured data for all known influencing effects before the evaluation method is applied is a precondition. However, the discrepancy of their results is larger than the uncertainty given for the determination of the RAKR with both methods.Results:A new approach to derive the RAKR from the measurements is investigated as an alternative. The method was developed from the ground up, based on radiation transport theory. A conversion factor C(x1, x2) is applied to the difference of charges measured at the two plate separations x1 and x2. This factor is composed of quotients of three air‐kerma values calculated for different plate separations in the chamber: the air kerma Ka(0) for plate separation zero, and the mean air kermas at the plate separations x1 and x2, respectively. The RAKR determined with method (1) yields 4.877 µGy/h, and with method (2) 4.596 µGy/h. The application of the alternative approach results in 4.810 µGy/h.Conclusion:The alternative method shall be established in the future.
SU‐F‐T‐66: Characteristics of Electron Beams From Varian Trubeam
Authors: Dimofte A , Kennedy C , Zhu T 
Published: July 2016

Purpose:The purpose of this study was to compare the electron beam data between Truebeam and 2300ix Varian accelerators for percent depth dose for broad beam and small circular cutouts, cone factors, head scatter factor as a function of cone size and SSD, phantom scatter factor, blocking factor, distance factor and virtual source position.Methods:Measurements were performed for Truebeam and 2300ix Varian accelerators. The main energies used were: 6, 9, 12, 16 and 20 MeV. PDD was measured at SSD = 100 cm for open beam and small circular cutouts (r = 0.5, 1.0, 1.5, 2.0, 3.0, 4.0 and 6.6cm) for different energies. Measurements to determine the head scatter factor (H) were done as a function of radius for six representative energies and five cone sizes (6, 10, 15, 20 and 25cm2). The phantom scatter factor (PSF) is defined as the ratio of blocking factor in water at reference depth and head scatter factor in air. PSF was measured as a function of radius and electron energy. Distance factor was measured for all energies and cones for three SSD's (100, 110 and 120cm).Results:The percent depth dose (PDD) was measured for small cutouts of radius r = 0.5, 1.0, 1.5, 2.0, 3.0, 4.0, 5.0 and 5.6cm. Blocking factor (BF) was measured for Truebeam and 2300ix accelerators, for different circular cutouts and energies for a 10×10 cone. Cone factors were compared between the two accelerators for different energies and applicator sizes.Conclusion:Cone factors measured for the two accelerator types differ by up to 5% for the largest applicator size. Blocking factors differs by up to 3%, with the largest variation for the smallest field size (0.5cm). Distance factor for different SSD's differ by up to 4.5%.
SU‐F‐T‐67: Correction Factors for Monitor Unit Verification of Clinical Electron Beams
Authors: Haywood J 
Published: July 2016

Purpose:Monitor units calculated by electron Monte Carlo treatment planning systems are often higher than TG‐71 hand calculations for a majority of patients. Here I've calculated tables of geometry and heterogeneity correction factors for correcting electron hand calculations.Method:A flat water phantom with spherical volumes having radii ranging from 3 to 15 cm was created. The spheres were centered with respect to the flat water phantom, and all shapes shared a surface at 100 cm SSD. Dmax dose at 100 cm SSD was calculated for each cone and energy on the flat phantom and for the spherical volumes in the absence of the flat phantom. The ratio of dose in the sphere to dose in the flat phantom defined the geometrical correction factor. The heterogeneity factors were then calculated from the unrestricted collisional stopping power for tissues encountered in electron beam treatments. These factors were then used in patient second check calculations. Patient curvature was estimated by the largest sphere that aligns to the patient contour, and appropriate tissue density was read from the physical properties provided by the CT. The resulting MU were compared to those calculated by the treatment planning system and TG‐71 hand calculations.Results:The geometry and heterogeneity correction factors range from ∼(0.8–1.0) and ∼(0.9–1.01) respectively for the energies and cones presented. Percent differences for TG‐71 hand calculations drop from ∼(3–14)% to ∼(0–2)%.Conclusion:Monitor units calculated with the correction factors typically decrease the percent difference to under actionable levels, < 5%. While these correction factors work for a majority of patients, there are some patient anatomies that do not fit the assumptions made. Using these factors in hand calculations is a first step in bringing the verification monitor units into agreement with the treatment planning system MU.
SU‐F‐T‐73: Experimental Determination of the Effective Point of Measurement in Electron Beams Using a Commercial Scintillation Detector
Authors: Simiele E , Smith B , Culberson W 
Published: July 2016

Purpose:The aim of this work was to determine experimentally the effective point of measurement (EPOM) in clinical electron beams for three cylindrical ionization chambers using a commercial scintillation detector as a reference detector.Methods:Percent depth dose (PDD) curves were measured using an Exradin W1 scintillation detector and were used as a representative PDD to water. Depth dose curves were measured with the Exradin A18, A1SL, and A28 ionization chambers. The raw ionization chamber curve data were corrected by the chamber fluence perturbation correction factor and restricted mass collisional stopping power ratio at each depth to obtain a percent depth dose curve to the gas volume (PDDGV) of the detector. Ratios of the W1 PDD to the ion chamber PDDGV were calculated for each measurement depth. The W1 PDD curve was shifted by small depth increments, Δz, until the ratio of the W1 PDD to the ion chamber PDDGV was depth‐independent (optimal Δz). A MATLAB routine was developed to determine the optimal Δz value.Results:The optimal Δz shift was used as an estimate of the EPOM for each chamber. The average calculated EPOM shifts (expressed as a fraction of the chamber cavity radius) for the A18, A1SL, and A28 ionization chambers were 0.21 ± 0.04, 0.10 ± 0.05, and 0.22 ± 0.03, respectively.Conclusion:The experimentally determined EPOM values for the A18 and A1SL in this work agreed with the simulated values of Muir and Rogers (MedPhys 2014). The results also indicate that the Exradin W1 scintillator is water equivalent for electron energies of 6 MeV, 9 MeV, 12 MeV, and 16 MeV. In addition, we confirmed that the AAPM TG51 recommended EPOM shift of 0.5 times the cavity radius is not accurate for the A18 and A1SL chambers.
SU‐F‐T‐76: Total Skin Electron Therapy: An‐End‐To‐End Examination of the Absolute Dosimetry with a Rando Phantom
Authors: Cui G , Ha J , Zhou S , Cui J , Shiu A 
Published: July 2016

Purpose:To examine and validate the absolute dose for total skin electron therapy (TSET) through an end‐to‐end test with a Rando phantom using optically stimulated luminescent dosimeters (OSLDs) and EBT3 radiochromic films.Methods:A Varian Trilogy linear accelerator equipped with the special procedure 6 MeV HDTSe‐ was used to perform TSET irradiations using a modified Stanford 6‐dual‐field technique. The absolute dose was calibrated using a Markus ion chamber at a reference depth of 1.3cm at 100 cm SSD with a field size of 36 × 36 cm at the isocenter in solid water slabs. The absolute dose was cross validated by a farmer ion chamber. Then the dose rate in the unit of cGy/Mu was calibrated using the Markus chamber at the treatment position. OSLDs were used to independently verify the dose using the calibrated dose rate. Finally, a patient treatment plan (200 cGy/cycle) was delivered in the QA mode to a Rando phantom, which had 16 pairs of OSLDs and EBT3 films taped onto its surface at different anatomical positions. The doses recorded were read out to validate the absolute dosimetry for TSET.Results:The OSLD measurements were within 7% agreement with the planned dose except the shoulder areas, where the doses recorded were 23% lower on average than those of the planned. The EBT3 film measurements were within 10% agreement with the planned dose except the shoulder and the scalp vertex areas, where the respective doses recorded were 18% and 14% lower on average than those of the planned. The OSLDs gave more consistent dose measurements than those of the EBT3 films.Conclusion:The absolute dosimetry for TSET was validated by an end‐to‐end test with a Rando phantom using the OSLDs and EBT3 films. The beam calibration and monitor unit calculations were confirmed.
SU‐F‐T‐80: A Mobile Application for Intra‐Operative Electron Radiotherapy Treatment Planning
Authors: Williams C , Crowley E , Wolfgang J 
Published: July 2016

Purpose:Intraoperative electron radiotherapy (IORT) poses a unique set of challenges for treatment planning. Planning must be performed in a busy operating room environment over a short timeframe often with little advance knowledge of the treatment depth or applicator size. Furthermore, IORT accelerators can have a large number of possible applicators, requiring extensive databooks that must be searched for the appropriate dosimetric parameters. The goal of this work is to develop a software tool to assist in the planning process that is suited to the challenges faced in the IORT environment.Methods:We developed a mobile application using HTML5 and Javascript that can be deployed to tablet devices suitable for use in the operating room. The user selects the desired treatment parameters cone diameter, bevel angle, and energy (a total of 141 datasets) and desired bolus. The application generates an interactive display that allows the user to dynamically select points on the depth‐dose curve and to visualize the shape of the corresponding isodose contours. The user can indicate a prescription isodose line or depth. The software performs a monitor unit calculation and generates a PDF report.Results:We present our application, which is now used routinely in our IORT practice. It has been employed successfully in over 23 cases. The interactivity of the isodose distributions was found to be of particular use to physicians who are less‐frequent IORT users, as well as for the education of residents and trainees.Conclusion:This software has served as a useful tool in IORT planning, and demonstrates the need for treatment planning tools that are designed for the specialized challenges encountered in IORT. This software is the subject of a license agreement with the IntraOp Medical Corporation.This software is the subject of a license agreement between Massachusetts General Hospital / Partners Healthcare and the IntraOp Medical Corporation. CLW is consulting on software development with the IntraOp Medical Corporation.
SU‐F‐T‐81: Treating Nose Skin Using Energy and Intensity Modulated Electron Beams with Monte Carlo Based Dose Calculation
Authors: Jin L , Fan J , Eldib A , Price R , Ma C 
Published: July 2016

Purpose:Treating nose skin with an electron beam is of a substantial challenge due to uneven nose surfaces and tissue heterogeneity, and consequently could have a great uncertainty of dose accuracy on the target. This work explored the method using Monte Carlo (MC)‐based energy and intensity modulated electron radiotherapy (MERT), which would be delivered with a photon MLC in a standard medical linac (Artiste).Methods:The traditional treatment on the nose skin involves the usage of a bolus, often with a single energy electron beam. This work avoided using the bolus, and utilized mixed energies of electron beams. An in‐house developed Monte Carlo (MC)‐based dose calculation/optimization planning system was employed for treatment planning. Phase space data (6, 9, 12 and 15 MeV) were used as an input source for MC dose calculations for the linac. To reduce the scatter‐caused penumbra, a short SSD (61 cm) was used. A clinical case of the nose skin, which was previously treated with a single 9 MeV electron beam, was replanned with the MERT method. The resultant dose distributions were compared with the plan previously clinically used. The dose volume histogram of the MERT plan is calculated to examine the coverage of the planning target volume (PTV) and critical structure doses.Results:The target coverage and conformality in the MERT plan are improved as compared to the conventional plan. The MERT can provide more sufficient target coverage and less normal tissue dose underneath the nose skin.Conclusion:Compared to the conventional treatment technique, using MERT for the nose skin treatment has shown the dosimetric advantages in the PTV coverage and conformality. In addition, this technique eliminates the necessity of the cutout and bolus, which makes the treatment more efficient and accurate.
SU‐F‐T‐86: Electron Dosimetric Effects of Bolus and Lens Shielding in Treating Superficial Eye Lesions
Authors: Young L , Wootton L , Gopan O , Liao J 
Published: July 2016

Purpose:Electron therapy for the treatment of ocular lymphomas requires the lens to be shielded to prevent secondary cataracts. This work evaluates the dosimetry under a suspended eyeshield with and without bolus for low energy electron fields.Methods:Film (GafChromic EBT3) dosimetry and relative output factors were measured for 6, 8, and 10 MeV electron energies. A customized 5 cm diameter circle electron orbital cutout was constructed for a 6×6 cm applicator with a lens shield, 1 cm diameter Cerrobend cylinder with 2.2 cm length, suspended from an XV film covering the open field. Relative output factors were measured using a Scanditronix electron diode in a solid water phantom. Depth dose profiles were collected for bolus thicknesses of 0, 3, and 5 mm in solid water at a source to surface distance (SSD) of 100 cm. These measurements were repeated in a Rando phantom.Results:At 5 mm, the approximate distance of the lens from the surface of the cornea, the estimated dose in solid water under the suspended lens shield was reduced to 16%, 14%, and 13% of the unblocked dose at the same depth, for electron energies of 6, 8, and 10 MeV, respectively. Applying bolus increased estimated doses under the block to 22% for 3‐mm and 32% for 5‐mm thicknesses for a 6 MeV incident electron beam. This effect is reduced for higher energies where the corresponding values were 15.5% and 18% for 3‐mm and 5‐mm for an 8 MeV electron beam.Conclusion:The application of bolus to treat superficial eye lesions of the conjunctiva increases lens dose at a depth of 5‐mm under the shielding block with decreasing electron energy. Careful selection of electron energy is needed to account for electron scatter under the lens shield with the application of bolus in order to prevent cataracts.
SU‐F‐T‐90: Patterns of Electron IORT Treatments in the U.S., Europe and Asia
Authors: Adamczyk S , Goer D , Ash R 
Published: July 2016

Purpose:We analyzed data collected from worldwide centers active in electron IORT with a focus on the technical variables of the treatment. Particular attention was given to the dominant tumor sites.Methods:54 Mobetron users from 14 countries in clinical operation prior to December 31, 2014, were invited to participate in this study. 29 centers contributed to this survey in sufficient detail to be included in this report. 6,035 patients were treated since 1997. Parameters were analyzed separately for each treatment site. However, special attention was given to the breast cancer, which turned out to be dominant tumor site.Results:The average number of patients treated per year in each center was 41 and exceeded 100 patients/year in 3 centers. For data received, 70% of patients worldwide were treated for breast cancer (93% in Europe, 14% in the U.S. and 21% in Asia). In 31% of cases electron IORT was the only breast irradiation. In breast patients, 9 MeV was used in 50% cases; 4MeV, 6MeV and 12MeV in 2%, 25% and 23% of cases respectively. 85% of patients were treated with field sizes between 4 and 6 cm and 35% of them were treated with 1/2 cm sized applicators. Beveled applicators (0°, 15° and 30° tips) were used in 51%, 33% and 16% of cases respectively. In 55% cases bolus was required with 5mm bolus used twice as often as 10mm. Chest‐wall protectors were used in 53% of treatment procedures. For Non‐breast data, main sites were: colorectal tumors (31%), pancreatic cancers (20%), extremity sarcomas (13%) and retroperitoneal sarcomas (5%).Conclusion:A large variety of tumors have been treated with IORT, with breast, colorectal, pancreas and sarcomas being the most frequently treated sites. This survey shows the most common applicators and energies used to treat each tumor site.
SU‐F‐T‐103: Analysis of Hepatitis B Virus Reactivation After Conformal Radiotherapy in Patients with Hepatocellular Carcinoma Using the Lyman NTCP Model
Authors: Li Z , Huang W , Li H , Li B 
Published: July 2016

Purpose:The aim of this research was to investigate the feasibility of Lyman‐Kutcher‐Burman (LKB) normal tissue complication probability (NTCP) model in analyzing hepatitis B virus (HBV) reactivation in patients receiving conformal radiotherapy for patients with hepatocellular carcinoma (HCC).Methods:Between June 2009 and June 2012, 108 HBV‐related HCC patients (90 were specifically selected and 18 patients were excluded) treated with conformal RT at three centers were enrolled in this retrospective study. They were all diagnosed as HCC by pathology or cytology. All 90 patients were followed up to September 2013 with a median follow‐up time of 25.2 months. The parameters (TD50 (1), n, and m) of the modified LKB NTCP model were derived using maximum likelihood estimation. Bootstrap and leave‐one‐out were employed to test the generalizability of the results for use in a general population.Results:The incidences of complications in the study population were as follows: radiation‐induced liver diseases (RILD) were 17.6%, HBV reactivation was 24.8%, and HBV reactivation‐induced hepatitis was 22.7%, respectively. In multivariate analysis, the NTCP (p<0.001), and V20 were associated with HBV reactivation. TD50 (1), m and n were 42.9Gy (95% CI) (38.2–46.8), 0.14 (0.12–0.15) and 0.30 (0.2–0.33), respectively, for HBV reactivation. Bootstrap and leave‐one‐out results showed that the HBV parameter fits were extremely robust.Conclusion:A modified LKB NTCP model has been established to predict HBV reactivation for patients with HCC receiving conformal RT. The finding derives parameters set to predict potential endpoints of HBV reactivation.
SU‐F‐T‐106: A Dosimetric Study of Intensity Modulated Radiation Therapy to Decrease Radiation Dose to the Thoracic Vertebral Bodies in Patients Receiving Concurrent Chemoradiation for Lung Cancer
Authors: DiCostanzo Dominic , Barney Christian L. , Bazan Jose G. 
Published: July 2016

Purpose:Recent clinical studies have shown a correlation between radiation dose to the thoracic vertebral bodies (TVB) and the development of hematologic toxicity (HT) in patients receiving chemoradiation (CRT) for lung cancer (LuCa). The feasibility of a bone‐marrow sparing (BMS) approach in this group of patients is unknown. We hypothesized that radiation dose to the TVB can be reduced with an intensity modulated radiation therapy(IMRT)/volumetric modulated arc radiotherapy(VMAT) without affecting plan quality.Methods:We identified LuCa cases treated with curative intent CRT using IMRT/VMAT from 4/2009 to 2/2015. The TVBs from T1–T10 were retrospectively contoured. No constraints were placed on the TVB structure initially. A subset were re‐planned with BMS‐IMRT/VMAT with an objective or reducing the mean TVB dose to <23 Gy. The following data were collected on the initial and BMS plans: mean dose to planning target volume (PTV), lungs‐PTV, esophagus, heart; lung V20; cord max dose. Pairwise comparisons were performed using the signed rank test.Results:94 cases received CRT with IMRT/VMAT. We selected 11 cases (7 IMRT, 4 VMAT) with a range of initial mean TVB doses (median 35.7 Gy, range 18.9–41.4 Gy). Median prescription dose was 60 Gy. BMS‐IMRT/VMAT significantly reduced the mean TVB dose by a median of 10.2 Gy (range, 1.0–16.7 Gy, p=0.001) and reduced the cord max dose by 2.9 Gy (p=0.014). BMS‐IMRT/VMAT had no impact on lung mean (median +17 cGy, p=0.700), lung V20 (median +0.5%, p=0.898), esophagus mean (median +13 cGy, p=1.000) or heart mean (median +16 cGy, p=0.365). PTV‐mean dose was not affected by BMS‐IMRT/VMAT (median +13 cGy, p=0.653).Conclusion:BMS‐IMRT/VMAT was able to significantly reduce radiation dose to the TVB without compromising plan quality. Prospective evaluation of BMS‐IMRT/VMAT in patients receiving CRT for LuCa is warranted to determine if this approach results in clinically significant reductions in HT.
SU‐F‐T‐110: LKB Modeling of Acute Hematologic Toxicity in Rectal Cancer
Authors: Deng H , Cheng K , Wan X 
Published: July 2016

Purpose:To investigate dosimetric parameters correlated with acute hematologic toxicity (HT) in patients with rectal cancer treated with IMRT and concurrent chemotherapy.Methods:We analyzed 127 rectal cancer patients receiving IMRT and concurrent chemotherapy. Whole pelvic bone marrow (PBM) was contoured for each patient including lumbosacral spine (LSSP), ilium and lower pelvic (LP). The equivalent uniform dose (EUD) of each region and the PBM were calculated. Endpoints for HT is grade ≥3 (HT3+) leukopenia, neutropenia or thrombocytopenia. Normal tissue complication probability (NTCP) was evaluated with the Lyman‐Kutcher‐Burman (LKB) model. On the basis of our NTCP modeling, we get the value of TD5, TD10, TD50 and other predictors of hematologic toxicity.Results:Twenty six patients experienced HT3+. Constrained optimization of the LKB model for HT3+ yielded the parameters m=0.583, n=1, and TD50=59.6Gy. With this model, mean PBM doses of 1.5Gy, 15Gy, 30.5Gy, 42Gy and 51Gy result in a 5%, 10%, 20%, 30% and 40% risk of HT3+, respectively. Our model suggested chemotherapy alone induced a HT3+ complication rate of about 4.6%.Conclusion:LKB modeling indicates that PBM acts like a parallel organ, implying that the mean dose to the organ is a useful predictor for toxicity. Compared with a Stanford study about anal cancer patients, the patients of anal cancer received chemotherapy with MMC and 5‐FU which can cause much more severe HT than 5‐FU or FOLFOX in our rectal cancer study. Therefore, the incidence of HT3+ is much higher in anal cancer and resulted in a much lower TD50 than our study.