bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐T‐284: Revisiting Reference Dosimetry for the Model S700 Axxent 50 KVp Electronic Brachytherapy Source
Authors: Hiatt JR , Rivard MJ 
Published: July 2014

Purpose:The model S700 Axxent electronic brachytherapy source by Xoft was characterized in 2006 by Rivard et al. The source design was modified in 2006 to include a plastic centering insert at the source tip to more accurately position the anode. The objectives of the current study were to establish an accurate Monte Carlo source model for simulation purposes, to dosimetrically characterize the new source and obtain its TG‐43 brachytherapy dosimetry parameters, and to determine dose differences between the source with and without the centering insert.Methods:Design information from dissected sources and vendor‐supplied CAD drawings were used to devise the source model for radiation transport simulations of dose distributions in a water phantom. Collision kerma was estimated as a function of radial distance, r, and polar angle, θ, for determination of reference TG‐43 dosimetry parameters. Simulations were run for 1010 histories, resulting in statistical uncertainties on the transverse plane of 0.03% at r=1 cm and 0.08% at r=10 cm.Results:The dose rate distribution the transverse plane did not change beyond 2% between the 2006 model and the current study. While differences exceeding 15% were observed near the source distal tip, these diminished to within 2% for r>1.5 cm. Differences exceeding a factor of two were observed near θ=150° and in contact with the source, but diminished to within 20% at r=10 cm.Conclusions:Changes in source design influenced the overall dose rate and distribution by more than 2% over a third of the available solid angle external from the source. For clinical applications using balloons or applicators with tissue located within 5 cm from the source, dose differences exceeding 2% were observed only for θ>110°. This study carefully examined the current source geometry and presents a modern reference TG‐43 dosimetry dataset for the model S700 source.
SU‐E‐T‐285: Revisiting the Nomogram for Intra‐Operative Planning Based Pd‐103 Brachytherapy
Authors: Narayanan S , Cho P 
Published: July 2014

Purpose:The seed implant technique at our institution involves using a published nomogram for seed ordering based on CT based volume studies of the prostate. Ultrasound volume studies are subsequently used in the operating room for planning a modified peripheral loading with urethra sparing seed implant. The purpose of this study is to determine the appropriate modality for prostate volume measurement and creating an updated nomogram for intra‐operative planning specific to our technique for pd‐103 brachytherapy for efficient seed ordering.Methods:Prostate volumes based on pre‐implant CT (Pre‐CT), intra‐operative ultrasound (TRUS), and post‐implant CT (post‐CT) studies as well as the total airkerma strength (AKS) of the implants were analyzed for 135 seed implant cases (69 monotherapy, 66 boost). Regression analysis was performed to derive the relationship between the total AKS and pre‐CT and TRUS volumes. The correlation between TRUS and pre‐CT volumes and TRUS and post‐CT volumes were also studied.Results:Ultrasound based prostate volume exhibited a stronger correlation with total AKS than the pre‐implant CT volume (R2 = 0.97 vs 0.88 for monotherapy and 0.96 vs 0.89 for boost). In general the pre‐CT overestimated the prostate volume leading to ordering of a larger number of seeds and thus leading to higher number of unused/wasted seeds. Newly derived TRUS based nomogram was better suited for our technique than the published data. The post‐implant CT volume closely followed the ultrasound volume (R2 = 0.88) as compared to pre‐implant CT volumes (R2 = 0.57).Conclusion:In an era of costconscious health care where waste reduction is of utmost importance, an updated technique‐specific nomogram is useful for ordering optimal number of seeds resulting in significant cost savings. In addition, our study shows that ultrasound based prostate volume is a better predictor for seed ordering for intra‐operative planning than pre‐implant CT.
SU‐E‐T‐286: Robustness of One‐ Versus Two‐Isocenter SBRT for Two Lung Lesions with Rotational Setup Errors
Authors: Palefsky S , Roper J , Dhabaan A 
Published: July 2014

Purpose:Evaluate the robustness of two different planning techniques for SBRT patients with two lung lesions: with both PTVs treated simultaneously with one isocenter, or separately with an isocenter for each PTV.Methods:One‐ and two‐isocenter IMRT and VMAT SBRT plans were created in Varian Eclipse for five patients who each had two lung lesions. PTV coverage for the one‐ and two‐isocenter plans was similar when possible. Rotational setup errors were simulated using couch rotations of various angles, and the resulting dose distributions were calculated.Results:With a 2° setup error, the average decrease in PTV volume receiving at least the prescribed dose (V100%) was 1.66% for the oneisocenter plans, and 0.05% for the two‐isocenter plans. The changes in V100% ranged from +0.33% to 4.06% for one‐isocenter plans, and from +0.23% to −0.30% for two‐isocenter plans. With a 5° setup error, the average decrease in V100% was 6.46% for a one‐isocenter plan (range: −0.19% to −13.18%), and 0.42% for a two‐isocenter plan (range: +0.21% to −1.33%). For one‐isocenter plans, the decrease in V100% tended to increase as PTV separation increased. The three patients with PTV separation less than 10 cm each showed a decrease in V100% of less than 1% for a 2° error, while the two patients with larger PTV separations showed decreases of more than 3%.Conclusion:As could be predicted by geometric calculations, when a rotational setup error occurs, the PTV coverage decreased more for a one‐isocenter plan than for a two‐isocenter plan. These findings suggest that, in general, for lung SBRT patients with two lesions, the two‐isocenter technique may be preferable. However, they may also suggest that if the PTVs are separated by less than 10 cm, and there is high confidence that setup errors are small (≤ 2°), a one‐isocenter plan may deliver similar coverage.
SU‐E‐T‐287: Robustness Study of Passive‐Scattering Proton Therapy in Lung: Is Range and Setup Uncertainty Calculation On the Initial CT Enough to Predict the Plan Robustness?
Authors: Ding X , Dormer J , Kenton O , Liu H , Simone C , Solberg T , Lin L 
Published: July 2014

Purpose:Plan robustness of the passive‐scattering proton therapy treatment of lung tumors has been studied previously using combined uncertainties of 3.5% in CT number and 3 mm geometric shifts. In this study, we investigate whether this method is sufficient to predict proton plan robustness by comparing to plans performed on weekly verification CT scans.Methods:Ten lung cancer patients treated with passive‐scattering proton therapy were randomly selected. All plans were prescribed 6660cGy in 37 fractions. Each initial plan was calculated using +/− 3.5% range and +/− 0.3cm setup uncertainty in x, y and z directions in Eclipse TPS(Method‐A). Throughout the treatment course, patients received weekly verification CT scans to assess the daily treatment variation(Method‐B). After contours and imaging registrations are verified by the physician, the initial plan with the same beamline and compensator was mapped into the verification CT. Dose volume histograms (DVH) were evaluated for robustness study.Results:Differences are observed between method A and B in terms of iCTV coverage and lung dose. Method‐A shows all the iCTV D95 are within +/− 1% difference, while 20% of cases fall outside +/−1% range in Method‐B. In the worst case scenario(WCS), the iCTV D95 is reduced by 2.5%. All lung V5 and V20 are within +/−5% in Method‐A while 15% of V5 and 10% of V20 fall outside of +/−5% in Method‐B. In the WCS, Lung V5 increased by 15% and V20 increased by 9%. Method A and B show good agreement with regard to cord maximum and Esophagus mean dose.Conclusion:This study suggests that using range and setup uncertainty calculation (+/−3.5% and +/−3mm) may not be sufficient to predict the WCS. In the absence of regular verification scans, expanding the conventional uncertainty parameters(e.g., to +/−3.5% and +/−4mm) may be needed to better reflect plan actual robustness.
SU‐E‐T‐289: Scintillating Fiber Based In‐Vivo Dose Monitoring System to the Rectum in Proton Therapy of Prostate Cancer: A Geant4 Monte Carlo Simulation
Authors: Tesfamicael B , Gueye P , Mahesh M , Avery S , Lyons D 
Published: July 2014

Purpose:To construct a dose monitoring system based on an endorectal balloon coupled to thin scintillating fibers to study the dose delivered to the rectum during prostate cancer proton therapyMethods:The Geant4 Monte Carlo toolkit version 9.6p02 was used to simulate prostate cancer proton therapy treatments of an endorectal balloon (for immobilization of a 2.9 cm diameter prostate gland) and a set of 34 scintillating fibers symmetrically placed around the balloon and perpendicular to the proton beam direction (for dosimetry measurements)Results:A linear response of the fibers to the dose delivered was observed within <2%, a property that makes them good candidates for real time dosimetry. Results obtained show that the closest fiber recorded about 1/3 of the dose to the target with a 1/r2 decrease in the dose distribution as one goes toward the frontal and distal top fibers. Very low dose was recorded by the bottom fibers (about 45 times comparatively), which is a clear indication that the overall volume of the rectal wall that is exposed to a higher dose is relatively minimized. Further analysis indicated a simple scaling relationship between the dose to the prostate and the dose to the top fibers (a linear fit gave a slope of −0.07±0.07 MeV per treatment Gy)Conclusion:Thin (1 mm × 1 mm × 100 cm) long scintillating fibers were found to be ideal for real time in‐vivo dose measurement to the rectum for prostate cancer proton therapy. The linear response of the fibers to the dose delivered makes them good candidates of dosimeters. With thorough calibration and the ability to define a good correlation between the dose to the target and the dose to the fibers, such dosimeters can be used for real time dose verification to the target
SU‐E‐T‐291: Sensitivity of a Simple 2D EPID in Vivo Dosimetry
Authors: Peca S , Brown D 
Published: July 2014

Purpose:As radiotherapy (RT) increases in complexity, so does motivation for in vivo dosimetry (IVD), which may detect errors such as: setup, beam shaping and dose delivered. We have recently developed an easy‐toimplement method for two‐dimensional IVD based on images taken with the electronic portal imaging device (EPID) in cine mode during treatment. The purpose of this work is to characterize its sensitivity to possible RT delivery errors.Methods:We introduced a series of modifications to a simple RT field (10×10, 100MU, 300RR, 20cm homogeneous phantom) to simulate errors. These modifications included multi‐leaf collimator (MLC) position, number of MUs, and collimator angle. We quantified the sensitivity to inhomogeneities by inserting variable amounts of solid lung and bone. Finally we delivered realistic fields to an anthropomorphic phantom to estimate sensitivity to gantry angle and setup errors.Results:Our EPIDIVD is sensitive to MLC positioning errors of 1mm and 3mm in the closed and open directions respectively, and to 3% MU variations. Sensitivity to collimator angle depends on field shape irregularity; in the case of a 10×10 field, we are sensitive to errors of 0.8°. The sensitivity to inhomogeneities is limited by the nature of MV imaging: approximately 1% signal change is noted when switching 5cm of water to equal amounts of bone or lung. This suggests that the EPID‐IVD is likely not sensitive to small setup or gantry angle errors, as confirmed by anthropomorphic tests.Conclusion:We have characterized a simple method of 2D dose reconstruction at isocenter depth inside the patient, which is sensitive to possible RT delivery errors. This method may be useful as a secondary safety check, to prevent large errors from being carried on to following fractions, and to record delivered dose. By using readily available hardware, it is easily implemented and may prove especially useful in centers with limited resources.
SU‐E‐T‐297: Small Field Dosimetry for Superficial Lesions
Authors: Ying J , Casto B , Wang S , Talyor T , Wichman A , Taylor M , Ku L 
Published: July 2014

Purpose:Kilo‐voltage (kV) photons and low megavoltage (MeV) electrons are the most common options for treating small superficial lesions, but they present complex dosimetry. Using a tertiary lead shield may protect the surrounding critical structures. Our goal was to quantitatively evaluate the dosimetric impact resulting from applying tertiary shields on superficial lesions.Method:We directly compared the beam characteristics of 80 kV (0.8 mm Al) photon setup abutting the water phantom surface and 6 MeV electron setup at 100 cm SSD. Profiles and depth doses were acquired using a 3D scanning water tank and an ion chamber (active volume 0.01 cm^3). Beam profiles were scanned at Dmax. Three lead sheets (2 mm thickness) with 2.7, 2.2, and 1.6, cm diameter circular cutouts were fabricated and placed at the water surface for both photon and electron fields.Results:The penumbra (80% – 20%) of the open 4×4 cm^2 electron insert was 10.7 mm, compared to an average of 7.2 mm with the tertiary cutouts. The penumbra of the open kV photon beam was 2.8 mm compared to an average of 1.8 mm with the tertiary cutouts. For field widths 2.7, 2.2, and 1.6 cm, the flatness of the electron beams was 16%, 17.3%, and 21%, respectively, and for the kV photon beams was 1.4%, 2.3%, 3.3%, respectively. The electron depth dose (PDD) shifted shallower and the photon PDD shifted deeper as the field size became smaller.Conclusion:The penumbra of small electron fields can be improved by adding tertiary lead shields. Both modalities are clinically feasible; however, kV photons still offer sharper penumbra and better flatness than that of 6 MeV electrons with tertiary shielding. Thus, kV photons may still be a superior option for small superficial lesions.
SU‐E‐T‐308: Systematic Characterization of the Energy Response of Different LiF TLD Crystals for Dosimetry Applications
Authors: Pena E , Caprile P , Sanchez‐Nieto B 
Published: July 2014

Purpose:The thermoluminiscense dosimeters (TLDs) are widely used in personal and clinical dosimetry due to its small size, good sensitivity and tissue equivalence, among other advantages. This study presents the characterization of Lithium Fluoride based TLDs, in terms of their absorbed dose response to successive irradiation cycles in a broad range of beam energies, measured under reference conditions.Methods:Four types of Harshaw TLD chips were used: TLD‐100, TLD‐600 TLD‐700 and 100‐H. They were irradiated with 10 photon beams of different energy spectrums, from 28 kVp to 18MV (in 30 consecutive cycles for 6 and 18 MV).Results:It was found that the response of the dosimetric system was stabilized (less than ±3%) after 10 cycles for TLD‐600 and TLD‐700. In the case of TLD‐100 and TLD‐100H this dependence was not observed. A decreased response to increasing beam energy in terms of absorbed dose to water was observed, as expected, except for TLD‐100H which showed the opposite behavior. The less energy dependent detector was the TLD‐100H exhibiting a maximum deviation of 12%. The highest variation observed was 33% for TLD‐100. The study allowed the determination of calibration factors in absorbed dose for a wide range of energies and materials for different dosimetric applications, such as in‐vivo dosimetry during imaging and radiotherapy.Conclusion:The study allowed the determination of calibration factors in absorbed dose for a wide range of energies and materials for different dosimetric applications, such as in‐vivo dosimetry during imaging and radiotherapy.
SU‐E‐T‐309: Tangential Modulated Arc Therapy: A Novel Technique for the Treatment of Superficial Disease
Authors: Hadsell M , Chin E , Li R , Xing L , Bush K 
Published: July 2014

Purpose:We propose a new type of treatment that employs a modulated and sliding tangential photon field to provide superior coverage of superficial targets when compared to other commonly employed methods while drastically reducing dose to the underlying sensitive structures often present in these cases.Methods:Modulated treatment plans were formulated for a set of three representative cases. The first was a revised treatment of a scalp sarcoma, while the second was a treatment of a right posterior chest wall sarcoma. For these cases, asymmetric jaw placement, angular limitations, and central isocenter placements were used to force the optimization algorithm into finding solutions with beamlines that were not perpendicular to the body surface. The final case targeted the chest wall of a breast cancer patient, in which standard treatments were compared to the use of modulated fields with multiple isocenters along the chest wall.Results:When compared with unrestricted modulated arcs, the tangential arc scalp treatment reduced the max and mean doses delivered to the brain by 33Gy (from 55 to 22Gy) and 6Gy (from 14Gy to 8Gy), respectively. In the right posterior chest wall case, the V10 in the ipsilateral lung was kept below 5% while retaining a Rx dose (45Gy) target coverage of over 97%. For the breast case, the modulated plan achieved reductions in high dose to the ipsilateral lung and heart by a factor of 2–3 when compared to classic laterally opposed tangents and reduced the V5 by 40% when compared to standard modulated arcs.Conclusion:Tangential modulated arc therapy has outperformed the conventional modalities of treatment for superficial lesions used in our clinic. We hope that with the advent of digitally controlled linear accelerators, we can uncover further benefits of this new technique and extend its applicability to a wider section of the patient population.
SU‐E‐T‐310: Targeting Safety Improvements Through Analysis of Near‐Miss Error Detection Points in An Incident Learning Database
Authors: Novak A , Nyflot M , Sponseller P , Howard J , Logan W , Holland L , Jordan L , Carlson J , Ermoian R , Kane G , Ford E , Zeng J 
Published: July 2014

Purpose:Radiation treatment planning involves a complex workflow that can make safety improvement efforts challenging. This study utilizes an incident reporting system to identify detection points of near‐miss errors, in order to guide our departmental safety improvement efforts. Previous studies have examined where errors arise, but not where they are detected or their patterns.Methods:1377 incidents were analyzed from a departmental nearmiss error reporting system from 3/2012–10/2013. All incidents were prospectively reviewed weekly by a multi‐disciplinary team, and assigned a near‐miss severity score ranging from 0–4 reflecting potential harm (no harm to critical). A 98‐step consensus workflow was used to determine origination and detection points of near‐miss errors, categorized into 7 major steps (patient assessment/orders, simulation, contouring/treatment planning, pre‐treatment plan checks, therapist/on‐treatment review, post‐treatment checks, and equipment issues). Categories were compared using ANOVA.Results:In the 7‐step workflow, 23% of near‐miss errors were detected within the same step in the workflow, while an additional 37% were detected by the next step in the workflow, and 23% were detected two steps downstream. Errors detected further from origination were more severe (p<.001; Figure 1). The most common source of near‐miss errors was treatment planning/contouring, with 476 near misses (35%). Of those 476, only 72(15%) were found before leaving treatment planning, 213(45%) were found at physics plan checks, and 191(40%) were caught at the therapist pre‐treatment chart review or on portal imaging. Errors that passed through physics plan checks and were detected by therapists were more severe than other errors originating in contouring/treatment planning (1.81 vs 1.33, p<0.001).Conclusion:Errors caught by radiation treatment therapists tend to be more severe than errors caught earlier in the workflow, highlighting the importance of safety checks in dosimetry and physics. We are utilizing our findings to improve manual and automated checklists for dosimetry and physics.
SU‐E‐T‐311: Technical Aspects of Credentialing for the NSABP B‐51 / RTOG 1304 Trial
Authors: Lowenstein J , Nguyen H , Hollan A , Galvin J , Followill D 
Published: July 2014

Purpose:For each of this trials 3 treatment scenarios an institution must be credentialed. The purpose of credentialing is to verify all personnel involved with treatment planning have read the protocol and can follow the protocol specifications prior to placing a patient on protocol with the end result of limiting the number of protocol deviations. Credentialing also provides feedback to an institution prior to treatment of a patient on trial to correct any mistakes that may occur.Methods:An institution needs to update their Facility Questionnaire and download the 3 CT benchmark cases representing the 3 treatment groups (1A, 2A and 2B) of the study from the RPCs website. The institution may decide which modality (3DCRT/IMRT) to use for each benchmark, however at least one benchmark must be completed for each modality for which the institution wants to be credentialed. The RPC reviews these benchmarks using MIM for verification that dose requirements are per protocol.Results:Presently, 101 institutions have initiated the credentialing process. 94 institutions have submitted their benchmarks, 7% failed and never resubmitted a benchmark for re‐review. The breakdown of credentialed techniques is; 4% IMRT only, 52% 3DCRT only and 44% 3DCRT/IMRT. Of those sites that have been credentialed: 6% of the institutions failed the benchmark for 1A, 11% failed for 2B and 40% failed for 2A at least once, before being credentialed. 9% of the institutions failed 2A twice and 1 institution failed three times.Conclusion:Currently 87 institutions have been credentialed for this study. The protocol has accrued 9 patients which have all been pre‐treatment reviews where 2 of them had to be re‐submitted for a re‐review due to volume contouring.This work was supported by PHS grant CA 10953 awarded by NCI, DHHS.