bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐T‐332: Dosimetric Impact of Photon Energy and Treatment Technique When Knowledge Based Auto‐Planning Is Implemented in Radiotherapy of Localized Prostate Cancer
Authors: Liu Z , Larsen E , Salmon H , Grow A , Hayes C , Balamucki C , Thompson M , Kennedy A 
Published: June 2015

Purpose:The aim of this study was to investigate the dosimetric impact of the combination of photon energy and treatment technique on radiotherapy of localized prostate cancer when knowledge based planning was used.Methods:A total of 16 patients with localized prostate cancer were retrospectively retrieved from database and used for this study. For each patient, four types of treatment plans with different combinations of photon energy (6X and 10X) and treatment techniques (7‐field IMRT and 2‐arc VMAT) were created using a prostate DVH estimation model in RapidPlan™ and Eclipse treatment planning system (Varian Medical System). For any beam arrangement, DVH objectives and weighting priorities were generated based on the geometric relationship between the OAR and PTV. Photon optimization algorithm was used for plan optimization and AAA algorithm was used for final dose calculation. Plans were evaluated in terms of the pre‐defined dosimetric endpoints for PTV, rectum, bladder, penile bulb, and femur heads. A Student's paired t‐test was used for statistical analysis and p > 0.05 was considered statistically significant.Results:For PTV, V95 was statistically similar among all four types of plans, though the mean dose of 10X plans was higher than that of 6X plans. VMAT plans showed higher heterogeneity index than IMRT plans. No statistically significant difference in dosimetry metrics was observed for rectum, bladder, and penile bulb among plan types. For left and right femur, VMAT plans had a higher mean dose than IMRT plans regardless of photon energy, whereas the maximum dose was similar.Conclusion:Overall, the dosimetric endpoints were similar regardless of photon energy and treatment techniques when knowledge based auto planning was used. Given the similarity in dosimetry metrics of rectum, bladder, and penile bulb, the genitourinary and gastrointestinal toxicities should be comparable among the selections of photon energy and treatment techniques.
SU‐E‐T‐335: Dosimetric Investigation of An Advanced Rotating Gamma Ray System for Imaged Guided Radiation Therapy
Authors: Ma C , Eldib A , Li C , Chibani O , Mora G , Li J , Chen L 
Published: June 2015

Purpose:Co‐60 beams have unique dosimetric properties for cranial treatments and thoracic cancers. The conventional concern about the high surface dose is overcome by modern system designs with rotational treatment techniques. This work investigates a novel rotational Gamma ray system for image‐guided, external beam radiotherapy.Methods:The CybeRT system (Cyber Medical Corp., China) consists of a ring gantry with either one or two treatment heads containing a Gamma source and a multileaf collimator (MLC). The MLC has 60 paired leaves, and the maximum field size is either 40cmx40cm (40 pairs of 0.5cm central leaves, 20 pairs of 1cm outer leaves), or 22cmx40cm (32 pairs of 0.25cm central leaves, 28 pairs of 0.5cm outer leaves). The treatment head(s) can swing 35° superiorly and 8° inferiorly, allowing a total of 43° non‐coplanar beam incident. The treatment couch provides 6‐degrees‐of‐freedom motion compensation and the kV cone‐beam CT system has a spatial resolution of 0.4mm. Monte Carlo simulations were used to compute dose distributions and compare with measurements. A retrospective study of 98 previously treated patients was performed to compare CybeRT with existing RT systems.Results:Monte Carlo results confirmed the CybeRT design parameters including output factors and 3D dose distributions. Its beam penumbra/dose gradient was similar to or better than that of 6MV photon beams and its isocenter accuracy is 0.3mm. Co‐60 beams produce lower‐energy secondary electrons that exhibit better dose properties in low‐density lung tissues. Because of their rapid depth dose falloff, Co‐60 beams are favorable for peripheral lung tumors with half‐arc arrangements to spare the opposite lung and critical structures. Superior dose distributions were obtained for head and neck, breast, spine and lung tumors.Conclusion:Because of its accurate dose delivery and unique dosimetric properties of C‐60 sources, CybeRT is ideally suited for advanced SBRT as well as conventional RT.This work was partially supported by Cyber Medical Corp.
SU‐E‐T‐340: Dosimetry of a Small Field Electron Beam for Innovative Radiotherapy of Small Surface Or Internal Tumors
Authors: Reft C , Lu Z , Noonan J 
Published: June 2015

Purpose:An innovative small high intensity electron beams with energies from 6 to 12 MeV is being developed at Argonne National Laboratory to deliver an absorbed dose via a catheter to small malignant and nonmalignant lesions. This study reports on the initial dosimetric characteristics of this electron beam. These include output calibration, percent depth dose, beam profiles and leakage through the catheter.Methods:To simulate the narrow electron beam, the Argonne Wakefield Accelerator is used to produce high energy electron beams. The electron beam from the accelerator is monitored by measuring the current through a transmission coil while the beam shape is observed with a fluorescent screen. The dosimetry properties of the electron beam transmitting through bone and tissue‐like materials are measured with nanodot optically stimulated luminescent dosimeters and EDR radiographic film. The 6 MV photon beam from a Varian True beam linac is used to calibrate both the OSLDs and the film.Results:The beam characteristics of the 12 MeV beam were measured. The properties of the small diameter, 5 mm, beam differs from that of broad clinical electron beams from radiotherapy linacs. Due to the lack of scatter from the narrow beam, the maximum dose is at the surface and the depth of the 50% depth dose is 35 mm compared to 51 mm for a clinical 12 MeV. The widths of the 90% isodose measured at the surface and depths of 2, 6, 12, and 16 mm varied from 6.6 to 8.8 mm while the widths of the FWHM isodose varied from 7.8 to 25.5 mm.Conclusion:Initial beam measurements show favorable dosimetric properties for its use in treating either small surface or internal lesions, particularly to deliver radiation at the time of surgery to maximize the dose to the lesion and spare normal tissue.
SU‐E‐T‐341: DVH‐Based Comparison of True 3D Measurements to a Delta4 System
Authors: Crockett E , Oldham M , Ren L 
Published: June 2015

Purpose:Delta4 dosimetric software can be used to calculate DVH‐based metrics for patient‐specific quality assurance from measurements made by a Delta4 QA device. This study investigates the effectiveness of a novel transform method that transposes measurements made with a full‐density 3D dosimeter onto patient anatomy, enabling the calculation of DVHs. This allows for DVH comparisons from the transformed dose distribution, which are based on true 3D measurements, to those from the Delta4 system, which are based on semi‐3D measurements and interpolation.Methods:A double‐arc VMAT treatment for a head‐and‐neck case was delivered to a 1kg PRESAGE 3D dosimeter inserted into a polyurethane head phantom. The dosimeter was readout using an in‐house optical‐CT scanner to gather full‐density 3D dosimetric data. The transform method is achieved by multiplication of the measured doses with a “transformation matrix” which accounts for heterogeneities and differences in geometry between the patient and the phantom. The transformation matrix is a voxel‐by‐voxel division of the patient planned dose by the phantom planned dose, both calculated in the treatment planning system (Eclipse). The transformed distribution was then overlaid on the patient CT data, enabling the calculation of DVHs. The same VMAT treatment was delivered to the Delta4 phantom and DVH data was calculated using its associated software.Results:The transformed dose distribution showed good agreement with calculated patient values, determined by similarity in dose profiles between the two distributions and a 3D gamma index passing rate of 94.87% for 3%/3mm criteria. For every structure contained within the dosimeter volume, the transformed DVHs demonstrated better agreement than the Delta4 DVHs, when compared to the values calculated in the treatment planning system.Conclusion:The coupled technique of full‐density 3D dose measurements and the presented transform method enables clinical patient‐specific quality assurance data that is more accurate than the semi‐3D Delta4 system.This work was supported by NIH R01CA100835.
SU‐E‐T‐343: Dynamic Collimator Rotation for Volumetric Modulated Arc Therapy
Authors: Fix MK , Frei D , Volken W , Terribilini D , Manser P 
Published: June 2015

Purpose:Volumetric modulated arc therapy (VMAT) utilizes dynamic gantry rotation, dynamic MLC and varying dose rate. However, in addition the collimator angle could be changed dynamically, thus, increasing the degrees of freedom for the optimization, which might lead to improved dose distributions. This work investigates the feasibility of including a dynamic collimator rotation for VMAT.Methods:In this work a 20×20×20 cm3 water phantom with a cigar shaped target volume and a spherical shaped critical structure was used. By means of the Eclipse Research Scripting a predefined collimator rotation was included in a not yet optimized treatment plan, consisting of one partial arc, by assigning for each dicom control point a different collimator angle. Thereby the collimator rotation takes into account the physical limitations for the delivery. This treatment plan was then imported into Eclipse using the Eclipse Research Scripting interface and VMAT PRO3 optimization was performed in a research version of Eclipse. For the dose calculation of the optimized treatment plan the Swiss Monte Carlo Plan (SMCP) was used. Similarly, a dose distribution was determined using a static collimator angle as applied in VMAT. The resulting DVHs for the target and the critical structure were compared for the two treatment plans.Results:A VMAT treatment plan with dynamically moving collimator angle was successfully generated. The comparison of the DVHs for the target volume shows a slight improvement of the coverage and dose homogeneity for the treatment plan using dynamic collimator rotation. Additionally, the dose to the critical structure could be reduced when using the moving collimator rotation.Conclusion:The usage of dynamic collimator rotation for VMAT is feasible and has the potential to improve the dose distribution for the target while reducing the dose to critical structures. This work was supported by Varian Medical Systems.This work was supported by Varian Medical Systems.
SU‐E‐T‐344: Dynamic Electron Beam Therapy Using Multiple Apertures in a Single Cut‐Out
Authors: Rodrigues A , Yin F , Wu Q 
Published: June 2015

Purpose:Few leaf electron collimators (FLEC) or electron MLCs (eMLC) are highly desirable for dynamic electron beam therapies as they produce multiple apertures within a single delivery to achieve conformal dose distributions. However, their clinical implementation has been challenging. Alternatively, multiple small apertures in a single cut‐out with variable jaw sizes could be utilized in a single dynamic delivery. In this study, we investigate dosimetric characteristics of such arrangement.Methods:Monte Carlo (EGSnrc/BEAMnrc/DOSXYnrc) simulations utilized validated Varian TrueBeam phase spaces. Investigated quantities included: Energy (6 MeV), jaw size (1×1 to 22×22 cm 2; centered to aperture), applicator/cut‐out (15×15 cm2), aperture (1×1, 2×2, 3×3, 4×4 cm2), and aperture placement (on/off central axis). Three configurations were assessed: (1) single aperture on‐axis, (2) single aperture off‐axis, and (3) multiple apertures. Reference was configuration (1) with standard jaw size. Aperture placement and jaw size were optimized to maintain reference dosimetry and minimize leakage through unused apertures to <5%. Comparison metrics included depth dose and orthogonal profiles.Results:Configuration (1) and (2): Jaw openings were reduced to 10×10 cm2 without affecting dosimetry (gamma 2%/1mm) regardless of on‐ or off‐axis placement. For smaller jaw sizes, reduced surface (<2%, 5% for 1×1 cm2 aperture) and increased Bremsstrahlung (<2%, 10% for 1×1 cm2 aperture) dose was observed. Configuration (3): Optimal aperture placement was in the corners (order: 1×1, 4×4, 2×2, 3×3 cm2) and jaw sizes were 4×4, 4×4, 7×7, and 5×5 cm2 (apertures: 1×1, 2×2, 3×3, 4×4 cm2 ). Asymmetric leakage was found from upper and lower jaws. Leakage was generally within 5% with a maximum of 10% observed for the 1×1 cm2 aperture irradiation.Conclusion:Multiple apertures in a single cut‐out with variable jaw size can be used in a single dynamic delivery, providing a practical alternative to FLEC or eMLC. Future simulations will expand on all variables.
SU‐E‐T‐347: Effect of MLC Leaf Position Inaccuracy On Dose Distribution for Spinal SBRT with Different Energies and Dose Rates
Authors: You T , Dang J , Dai C , Yin F 
Published: June 2015

Purpose:To evaluate dosimetric impact of spinal SBRT when MLC leaf positions deviate from planning positions for different energies and doserates.Methods and Materials:18 localized spinal metastases patients were selected for SBRT using IMRT planning with 9 posterior beams delivered at gantry angles ranging between 100°–260°. A modern linear accelerator(Varian Turebeam STX with HDMLC 2.5 mm thick leaf at isocenter) IMRT plans were generated using both 6X and 6X_FFF(Flattening filter free) beams with a nominal prescription dose of 6 Gy/fraction to PTV. Doserates ranging from 200–600 MU/min for 6X and 400–1400 MU/min for 6X_FFF, with 200 increments were examined. A fixed amount(0.3, 0.5, 1, and 2 mm) of MLC‐leaf position deviation was simulated to each plan under following conditions: 1)only along X1 collimator; 2)with increments at both X1 and X2 collimator directions;3)with reductions at both X1 and X2 collimator directions. Dose was recalculated for each modified plans. Both original and modified plans were delivered using Turebeam STX machine and measured using both portal dosimetry and a 3D dosimeter(Delta4 of ScandiDos). Each field's Result were compared using following three parameters: the 95% iso‐dose level Conformal Index(95%CI), the spinal cord maximum dose(SCDmax), and the planned target volume(PTV) mean dose.Results:Dosimetric impacts on the 95%CI, SCDmax and the PTV mean dose are: 1)negligible if MLC‐leaf position deviation only along a single collimator direction ≥1.0 mm,2)substantial if MLC‐leaf position increment along both collimator directions ≥0.3 mm(95% CI decreases while SCDmax and PTV mean‐dose increase), 3)substantial if MLC‐leaf position reduction along both collimator directions ≥0.3 mm(95% CI first increases and then decreases while SCDmax and PTV mean‐dose decrease). Different energies and doserates demonstrated comparable dosimetric impacts.Conclusion:Substantial dose deviations could happen for spinal SBRT using IMRT plan with HD‐MLC if leaf position deviation ≥0.3 mm. The effects of different energy and doserate are negligible.
SU‐E‐T‐348: Effect of Treatment Table and Immobilization Devices On Surface Dose When Using a GRID Technique
Authors: Gajdos S , Donaghue J 
Published: June 2015

Purpose:To determine the increase of surface dose of MLC‐designed GRID therapy in the presence of immobilization devices and treatment table.Methods:To create a GRID field, our facility utilizes an MLC consisting of four millimeter wide leaves. The field is designed to have aperture sizes of 0.8 cm X 0.8 cm with inter‐aperture distance of 3.2 cm. Gafchromic EBT3 film was placed between the surface of a solid water phantom and the immobilization device. The treatment table was also present within the beam path. The devices consist of carbon fiber exterior shell. A piece of film was also placed at maximal depth for the photon energy of 10 MV. Image files were converted to dose per a calibration curve based on the selected red channel. The surface dose to maximum dose was established by comparing the ratio of seven centrally located aperture regions‐of‐interest and four adjacent inter‐aperture regions‐of‐interest were measured with the available software tools.Results:With no devices present in beam path, the ratio of surface dose to maximum dose was 11.5% ± 0.3% for aperture region and 7.0% ± 0.1% for inter‐aperture region. When devices are present, the ratio of surface dose to maximum dose was 45.2% ± 0.5% and 33.8% ± 1.1%, respectively. Due to the presence of devices, the surface dose increases in aperture region by 3.8 times or in the inter‐aperture region by 4.7 times.Conclusion:The purpose of using GRID technique is to deliver a single fractional dose in range of 15–20 Gy to a bulky lesion while also preserving skin tolerance. The increase of surface dose due to devices placed in beam path may increase the chance of skin toxicity in GRID therapy. Care should be used to determine best manageable patient immobilization while considering skin dose especially for posteriorly located lesions.
SU‐E‐T‐356: Efficient Segmentation of Flattening Filter Free Photon Beamsfor 3D‐Conformal SBRT Treatment Planning
Authors: Barbiere J , Beninati G , Ndlovu A 
Published: June 2015

Purpose:It has been argued that a 3D‐conformal technique (3DCRT) is suitable for SBRT due to its simplicity for non‐coplanar planning and delivery. It has also been hypothesized that a high dose delivered in a short time can enhance indirect cell death due to vascular damage as well as limiting intrafraction motion. Flattening Filter Free (FFF) photon beams are ideal for high dose rate treatment but their conical profiles are not ideal for 3DCRT. The purpose of our work is to present a method to efficiently segment an FFF beam for standard 3DCRT planning.Methods:A 10×10 cm Varian True Beam 6X FFF beam profile was analyzed using segmentation theory to determine the optimum segmentation intensity required to create an 8 cm uniform dose profile. Two segments were automatically created in sequence with a Varian Eclipse treatment planning system by converting isodoses corresponding to the calculated segmentation intensity to contours and applying the “fit and shield” tool. All segments were then added to the FFF beam to create a single merged field. Field blocking can be incorporated but was not used for clarity.Results:Calculation of the segmentation intensity using an algorithm originally proposed by Xia and Verhey indicated that each segment should extend to the 92% isodose. The original FFF beam with 100% at the isocenter at a depth of 10 cm was reduced to 80% at 4cm from the isocenter; the segmented beam had +/−2.5 % uniformity up to 4.4cm from the isocenter. An additional benefit of our method is a 50% decrease in the 80%‐20% penumbra of 0.6cm compared to 1.2cm in the original FFF beam.Conclusion:Creation of two optimum segments can flatten a FFF beam and also reduce its penumbra for clinical 3DCRT SBRT treatment.
SU‐E‐T‐360: End‐To‐End Dosimetric Testing of a Versa HD Linear Accelerator with the Agility Head Modeled in Pinnacle3
Authors: Saenz D , Narayanasamy G , Cruz W , Papanikolaou N , Stathakis S 
Published: June 2015

Purpose:The Versa HD incorporates a variety of upgrades, primarily including the Agility head. The distinct dosimetric properties of the head from its predecessors combined with flattening‐filter‐free (FFF) beams require a new investigation of modeling in planning systems and verification of modeling accuracy.Methods:A model was created in Pinnacle3 v9.8 with commissioned beam data. Leaf transmission was modeled as <0.5% with maximum leaf speed of 3 cm/s. Photon spectra were tuned for FFF beams, for which profiles were modeled with arbitrary profiles rather than with cones. For verification, a variety of plans with varied parameters were devised, and point dose measurements were compared to calculated values. A phantom of several plastic water and Styrofoam slabs was scanned and imported into Pinnacle3. Beams of different field sizes, SSD, wedges, and gantry angles were created. All available photon energies (6 MV, 10 MV, 18 MV, 6 FFF, 10 FFF) as well four clinical electron energies (6, 9, 12, and 15 MeV) were investigated. The plans were verified at a calculation point (8 cm deep for photons, variable for electrons) by measurement with a PTW Semiflex ionization chamber. In addition, IMRT testing was performed with three standard plans (step and shoot IMRT, small and large field VMAT plans). The plans were delivered on the Delta4 IMRT QA phantom (ScandiDos, Uppsala, Sweden).Results:Homogeneous point dose measurement agreed within 2% for all photon and electron beams. Open field photon measurements along the central axis at 100 cm SSD passed within 1%. Gamma passing rates were >99.5% for all plans with a 3%/3mm tolerance criteria. The IMRT QA results for the first 23 patients yielded gamma passing rates of 97.4±2.3%.Conclusion:The end‐to‐end testing ensured confidence in the ability of Pinnacle3 to model photon and electron beams with the Agility head.
SU‐E‐T‐362: Enhanced Dynamic Wedge Output Factors for Varian 2300CD and the Case for a Reference Database
Authors: Njeh C 
Published: June 2015

Purpose:Dose inhomogeneity in treatment planning can be compensated using physical wedges. Enhanced dynamic wedges (EDW) were introduced by Varian to overcome some of the short comings of physical wedges. The objectives of this study were to measure EDW output factors for 6 MV and 20 MV photon energies for a Varian 2300CD. Secondly to review the literature in terms of published enhanced dynamic wedge output factors (EDWOF) for different Varian models and thereby adding credence to the case of the validity of reference databases.Methods:The enhanced dynamic wedge output factors were measured for the Varian 2300CD for both 6 MV and 20 MV photon energies. Twelve papers with published EDWOF for different Varian Linac models were found in the literature.Results:The EDWOF for 6 MV varied from 0.980 for a 5×5 cm 10 degree wedge to 0.424 for 20×20 cm 60 degree wedge. Similarly for 20 MV, the EDWOF varied from 0.986 for 5×5 cm 10 degree wedge to 0.529 for 20×20 cm 60 degree wedge. EDWOF are highly dependent on field size. Comparing our results with the published mean, we found an excellent agreement for 6 MV EDWOF with the percentage differences ranging from 0.01% to 0.57% with a mean of 0.03%. The coefficient of variation of published EDWOF ranged from 0.17% to 0.85% and 0.1% to 0.9% for the for 6 MV and 18MV photon energies respectively. This paper provides the first published EDWOF for 20 MV photon energy. In addition, we have provided the first compendium of EDWOFs for different Varian linac models.Conclusion:The consistency of EDWOF across models and institution provide further support that, a standard data set of basic photon and electron dosimetry could be established, as a guide for future commissioning, beam modeling and quality assurance purposes.