bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐400: SBRT Dose Verification Using Monte Carlo Simulation
Authors: Luo W , Xie X , McGarry R , Molloy J
Published: June 2012

Purpose: To verify the SBRT plans on CMS Xio treatment planning system using the Monte Carlo simulation and investigate the related issues. Methods: The SBRT plans with 6 MV were created on CMS Xio treatment planning system with superposition algorithm. The same patient's CT, beam geometry and MUs were used in the Monte Carlo simulation (MC) on MCSIM. MCSIM is an EGS4‐based MC dose calculation system for photon and electron beams. The Monte Carlo plans were compared with the Xio plans to verify Xio superposition algorithm for SBRT. The electron disequilibrium was particularly investigated by comparing the DVHs for a 2‐mm thick peel of the GTV. The beam energy was changed from 6 MV to 10 MV for MC to test energy effect on SBRT dosimetry. Results: Six SBRT lung plans created on Xio and delivered on Varian 21 EX linac were included in this study. The tumor GTV ranged from 1.4 cc to 11 cc and the dose ranged from 1950 cGy to 5400 cGy. The comparisons were made in terms of DVHs, mean doses, minimal doses, and maximal doses for GTV. The results showed all the dose values of Xio plans agreed with MC to within 2% with only two exceptions of 3% and 5%. The dose distribution in the peel of GTV followed the same pattern as the whole GTV. This indicated the Xio superposition algorithm has well accounted for electron disequilibrium. The 10‐MV beams had both hot and cold spots from DVH comparison. This may be due to the large build‐up region for high energy beams. Conclusions: The Xio superposition algorithm has adequately accounted for electron disequilibrium and can perform accurate dose calculation for SBRT. Compared to high energy beams, 6 MV is preferable in terms of the GTV coverage and dose homogeneity.
SU‐E‐T‐403: Delivery Efficiency of StereoArc Stereotactic Body Radiotherapy (SBRT)
Authors: Kinsey E , Yang X , Prado K , Feigenberg S , Yi B
Published: June 2012

Purpose: Traditional SBRT employs approximately 10 static beams with up to 20 Gy per fraction, requiring lengthy treatments which can be difficult for patients to tolerate, increasing the risk of movement, and causing discrepancies in the reproducibility of the breathing cycle. Commercial VMAT systems offer shorter treatment times with modulated beams; however, modulation is often not necessary or desired for small fields. Conformai arc therapy offers efficient beam delivery, but with only one aperture shape and constant beam weighting over all gantry angles. This study evaluates the efficiency of a new SBRT delivery Method: a conformai arc with multiple aperture shapes and variable dose rate. Methods: Three clinical SBRT cases were chosen for this study. Each static field was converted into an arc segment to create a StereoArc plan. Gantry angle ranges were determined from the clinical monitor units, with the MU/degree chosen to maximize the dose rate. All segments were merged into a single arc with variable dose rate. Dose distributions from the StereoArc plans were compared to the clinical static field plans using Pinnacle. Delivery times were compared between the static SBRT plans, both with and without Beam Automation, and equivalent StereoArc plans. All plans were delivered on a Varian TrueBeam using a dose rate of 1000 MU/min. Results: Dose differences between StereoArc and static plans were minimal. Delivery times for the static plans were 5–8 minutes, while delivery time with StereoArc was less than 3 minutes for all cases, which was equivalent to delivering the static plans with Beam Automation. Conclusions: Delivery efficiency was improved up to 60%: from 8 minutes for static fields, to less than 3 minutes for StereoArc. StereoArc appears to be both an effective and efficient way of delivering SBRT for centers not wishing to modulate SBRT and without access to Beam Automation. This study is partially supported by NIH grant 1R01CA133539‐01A2.
SU‐E‐T‐410: Spine Radiosurgery Imaging Guidance Using ExacTrac and CT on rails
Authors: Yang J , Wang X , Zhao Z , Brown P
Published: June 2012

Purpose: To evaluate the patient setup accuracy and effectiveness using ExacTrac and CT_on_rails systems. Methods: We used Brainlab's Exactrac system and Varian/GE's CT_on_rails for spine radiosurgery patient setup. Once the patient was setup using the ExacTrac and couch position was recorded, fiducially markers were placed on stable surfaces based on the room laser to indicate the linac iso for the CT images. CT images were acquired using the on‐rail CT with the couch rotated 180 degrees. The couch was returned to 0 degree position, and verification X‐ray images were taken and corrections were made by ExacTrac. The treatment CT images were registered with the planning CT using the in‐house CAT software and it displays the correct couch position based on CT which can be compared with ExacTrac setup. The corrected couch positions from CT registration are compared to those from ExacTrac. The translational discrepancies needed to be within 2 mm for confirmation. If a discrepancy was greater than 2 mm, investigation or re‐setup was required. The rotation deviations were also evaluated by ExacTrac and confirmed by the treatment CT images. We would also re‐setup patient if Exactrac detected more than 3 degree rotation, or treatment CT images showed significant target rotation compared to planning CT. The use of the CTonrails took little extra time, but make the overall evaluation process easier, faster and with more confidence. Results: for 171 treatment sessions using this approach, the mean discrepancies between CTonrails and ExacTrac setup is: x=0.0±1.0 mm, y=−0. 1±0.9 mm, z=0.2±0.9 mm; for rotations, about 3% of the cases required re‐setup patient due to significant rotation displayed by the treatment CT on the CAT system. Conclusions: The combined use of ExacTrac and CT_on_Rails systems can improve the overall setup accuracy and increase the confidence in setup for spine radiosurgery treatments.
SU‐E‐T‐411: Dosimetric Comparison Between Two Multileaf Collimator Systems for Stereotactic Radiosurgery and Radiotherapy
Authors: Asnaashari K , Chow J , Heydarian M
Published: June 2012

Purpose: This aim of this study is to compare the dosimetric parameters of two multileaf collimator (MLC) systems: (1) the beam modulator (BM), which is the MLC commercial name for Elekta ‘Synergy S’ linear accelerator; and (2) Radionics micro‐MLC (MMLC). Methods: Dosimetric parameters of percentage depth dose (PDD), in‐plane and cross‐plane beam profile, penumbra, MLC leakage and transmission for a 6 MV photon beam with different field sizes and depths were measured using ionization chamber, film, solid water phantom and water tank. At the same time, the BM and MMLC were modeled using the BEAMnrc code and the above dosimetric parameters were calculated using Monte Carlo simulations. Energy fluence spectra for the two MLC were determined using the BEAMnrc and BEAMDP. Results: We found that dosimetric parameters (PDD, beam profile, energy fluence spectra, leakage and transmission) of the two MLC were similar, except for penumbra. The leaf‐side and leaf‐end 20%–80% penumbras at 10 cm depth for a 10×10 cm2 field were 4.8 and 5.1 mm for the MMLC and 5.3 mm and 6.3 mm for the BM, respectively. The maximum percentage of the leakage for the BM and MMLC are 1.3% and 1.2%, while the average percentage of leakage for the BM and MMLC are 0.9% and 1%. Conclusions: Based on their dosimetric characteristics for stereotactic radiosurgery and radiotherapy, it can be concluded that both the BM and MMLC can be used effectively, though the latter showed slightly sharper dose penumbra especially in the leaf‐end direction. However, the BM has the advantages of producing considerably larger field at isocenter and having a greater isocenter clearance compared to the MMLC. The dosimetric data in this study should help radiotherapy staff to appreciate dependence of dosimetry on the MLC design and configuration for stereotactic radiosurgery and radiotherapy. Actual or potential conflicts of interest do not exist.
SU‐E‐T‐427: Effect of Contrast in Radiadyne Alatus Balloon Packing System on Bladder and Rectal Doses in Gynecological Brachytherapy
Authors: Libby B , Ding K , Reardon K , Crandley E , Andrew C , Schneider B
Published: June 2012

Purpose: Vaginal packing for gynecological brachytherapy is used to immobilize the applicator and reduce doses to the bladder and rectum by increasing the separation from the applicator. With the introduction of theRadiadyne Alatus™ balloon packing system, we evaluate further reductions in dose to these structures by increasing the concentration of contrast in the balloon, increasing its attenuation. This evaluation has been performed using the Acuros™ dose calculation algorithm. Methods: A patient with cervical cancer was treated with HDR Ir‐192 by insertion of a tandem and ovoid applicator, with the Alatus™ balloon system used for vaginal packing instead of wet gauze. The balloons were filled with distilled water containing 10% Omnipaque contrast. Retrospectively, the balloons were contoured in the BrachyVision™ planning system, and the CT number of the structure set was adjusted to determine the effect of the concentration of the contrast in the balloons on bladder and rectal doses after heterogeneity correction using the Acuros™ algorithm. Results: Use of 10% Omnipaque solution reduced the bladder and rectal point doses by 6% and 9.5%, respectively, with similar reductions in the D2cc and D1cc for each structure. Overriding the density of the balloon showed that a 50% solution would reduce the doses by 8% and 30%, respectively, due to the positions of the balloons with respect to the applicator dwell positions. Conclusions: Use of the Alatus™ balloon packing system allows reduction of the bladder and rectal doses both by increasing the distance between the bladder and rectum and the applicators and by increased attenuation of the dose by the use of contrast solution. Optimal dilution of the contrast should take into account both the positive protective effect of the solution as well as any negative artifact that the solution causes in the CT scan, which might obscure the patient's anatomy patient.
SU‐E‐T‐438: Optimal Proton Beam Energy to Treat Adult CNS, Adult Head and Neck, and Pediatric Cancers
Authors: Kainz K , Firat S , Wilson J , Li X
Published: June 2012

Purpose: Proton therapy machines with lower beam energy requirements are expected to be easier and more cost‐efficient to design, construct, and operate, particularly when using novel proton acceleration technology (e.g., dielectric wall). We determine, for adult central nervous system (CNS) and head and neck (HN) and pediatric cases, the optimal proton beam energies that can lead to clinically acceptable plan quality. Methods: Proton treatment plans for various adult CNS and HN and pediatric cases, previously treated at our institution using helical tomotherapy, were generated using a commercial planning system (XiO, v. 4.62, Elekta) with a passively‐scattered proton beam model. Proton beam orientations were chosen such that the distance from the skin to the distal target edge was minimal; however, beams could not pass through areas with significant surface irregularity (e.g. ear), nor through OARs with strict dose limitations (e.g. lens). For a given beam direction, the planning system would calculate an optimum range and modulation to cover a given target volume. Beam weights were adjusted so that 95% of the target volume received the prescribed dose. All plans were limited to two proton beams. Results: An optimal proton energy exists for each case studied. Among all cases, target dose conformity (the ratio of target volume to volume encompassed by theprescribed dose) ranged from 0.74 to 0.94, and target dose uniformity (the ratio of the D5 and D95 doses) ranged from 1.01 to 1.04, with the optimal proton energies. Among the CNS and HN cases and for most pediatric cases, the maximum proton energy required was 133 MeV. For a pediatric abdomen case, 159 MeV protons were required. Conclusions: For protontreatment of most adult CNS and HN and pediatric cases, the optimal energies that are capable of generating good quality plans are only as high as 130 MeV.
SU‐E‐T‐440: Dosimetry Parameter Comparison between Field‐In‐Field Technique and Conventional Physical Wedge Technique for Whole Breast Radiation Treatment
Authors: Su M , Ayzenberg V , Li W
Published: June 2012

Purpose: To compare an advantage/disadvantage between Field‐in‐Field (FIF) technique and conventional physical wedge (PW) technique for a whole breast (WB) tangential field irradiation. Methods and Materials: Total 86 patients were included in this study. 46 of them were left breast cancer cases. FIF/PW plans were created by Eclipse (V7.3, Varian) with 6MV or 6MV mixed with 18MV. Plans had a same ioscenter location, beam setup and normalized isodose line selection for each case. Varian 21EX Linac with 120 MLC was used for beam delivery. Two plans were compared by PTV encompassed by 95% isodose line (V95), dose inhomogeneity (DI), dose received by 10% volume of lung (D10), mean lung dose (MLD), dose received by 5% volume of heart (D5), Mean heart dose (MHD), total MU, maximum dose in the plan and the number of field needed for each fraction. Results: Comparing with PW plan, FIF plan showed an average percentage improvement of V95 was 0.1±1.6, DI was 0.6±5.0, MLD was 1.5±4.2, D5 was 2.0±8.8, MHD was 3.2±4.6. However, D10 increased by 1.4%±0.050. FIF lowered an average daily MU by 28.5%±0.080, maximum dose by 0.5%±0.018, and increased number of treatment field by 1.50±0.356. There were 12 cases treated with mixed beam in PW technique vs 10 in FIF technique. Conclusion: The advantages of FIF technique included: (1) Reduce radiation contamination to contra lateral breast and Linac room induced activity by remove the PW, lower MU and diminish a higher energy. (2) Time saving was not only from less MU but also from not need go into the treatment room for a wedge adjustment. (3) Reduced the therapist work load. (4) Regular MU 2nd check was applied because there was not FIF merge involved in the treatment field. With a MLC to shape the field and treatment record/verification system to control the treatment, increasing number of treatment field didn't show as a problem.
SU‐E‐T‐464: Impact of the Treatment Margin on Tumor Control and Normal Tissue Complication for Prostate Treatment
Authors: Li JS , Lin M‐H , Ma C‐M
Published: June 2012

Purpose: To investigate the consequence of treatment margin reduction on normal tissue complication probability (NTCP) and tumor control probability (TCP) of prostate external beam treatment. Methods: Intensity modulated rotational radiotherapy plans were generated for 10 prostate patients with 6 different posterior margin sizes from 5mm to 0. The prescription dose is 80Gy for 40 treatment fractions. The dose distributions were recalculated with consideration of the intrafractional motion and the localization error. The statistical uncertainties of the intrafractional motion and the localization error were derived based on the motion tracking data recorded by the Calypso 4D localization system for a large patient population. The TCP and NTCP were calculated based on the dose volume histograms (DVH) of prostate and rectum for plans with different margins using an equivalent uniform dose (EUD) based biological model. The 50% tumor control dose (TCD50) of 60Gy for prostate and the median toxic dose (TD50) of 55Gy for rectum were used in the calculation. Results: The minimum dose of the prostate and the mean dose of the rectum dropped with the decrease of the treatment margin. When the posterior treatment margin was reduced from 5mm to zero, the EUD of prostate decreased from 83Gy (±0.5Gy) to 81Gy (±0.5Gy) and the TCP dropped from 93.2% (±0.1%) to 91.7% (±0.1%), the EUD of the rectum decreased more significantly from 48.9Gy (±0.4Gy) to 32.5Gy (±0.5Gy) and the NTCP dropped from 13.3% (±1.5%) to 0.03% (± 0.01%). Conclusions: The treatment margin size affects the dose to the target and the nearby critical structure. More significant impact on NTCP has been observed than on TCP. This gives us some room to consider the quality of the patient's after‐treatment life. A wise choice of treatment margin can be made based on physician's opinion and patient's preference on the tumor control and the quality of life.
SU‐E‐T‐467: Monte Carlo Dosimetric Study of the New Flexisource Co‐60 High Dose Rate Source
Authors: Vijande J , Granero D , Perez‐Calatayud J , Ballester F
Published: June 2012

Purpose: Recently, a new HDR 60Co brachytherapy source, Flexisource Co‐60, has been developed (Nucletron B.V.). This study aims to obtain quality dosimetric data for this source for its use in clinical practice as required by AAPM and ESTRO. Methods: Penelope2008 and GEANT4 Monte Carlo codes were used to dosimetrically characterize this source. Water composition and mass density was that recommended by AAPM. Due to the high energy of the 60Co, dose for small distances cannot be approximated by collisional kerma. Therefore, we have considered absorbed dose to water for r<0.75 cm and collisional kerma from 0.75<r<20 cm. To provide adequate spatial resolution, cells were 0.01 cm in thickness for r<2 cm from the source and a factor of 10 thicker for 2<r<20 cm respectively. Angular sampling was taken every 2°. Additional simulations were performed to obtain SK as recommended by AAPM. Mass‐energy absorption coefficients in water and air were consistently derived and used to calculate collisional kerma. Along‐away tables and TG‐43 formalism parameters and functions were derived. Dosimetric data were also provided following the primary and scatter dose separation for the collapsed cone technique. Results: TG‐43 dosimetry parameters with L = 0.35 cm were obtained. Results performed with both radiation transport codes showed agreement typically within 0.2% for r > 0.8 cm and up to 2% closer to the source. Using Penelope2008 and GEANT4, an average of Î> = 1.085±0.003 cGy/(h U) (with k = 1, Type A uncertainties) was obtained. Dose rate constant, radial dose function and anisotropy functions for the Flexisource Co‐60 are compared with published data for other Co‐60 sources. Conclusions: Dosimetric data are provided for the new Flexisource Co‐60 source not studied previously in the literature. Using the data provided by this study in the treatment planning systems, it can be used in clinical practice. This project has been funded by Nucletron BV
SU‐E‐T‐468: Gamma Knife Perfexion Dosimetry: A Monte Carlo Model of One Sector
Authors: Best R , Gersh J , Wiant D , Bourland J
Published: June 2012

Purpose: We have implemented a Monte Carlo (MC) based dose computation model of one sector of the Gamma Knife Perfexion (GK PFX) using the Penelope MC dosimetry codes. The single sector simulation was rotated about the z‐axis to model all eight GK sectors. GK dosimetric aspects examined include: 1) output factors (OF) for each of the three GK collimator sizes (4, 8, 16 mm), 2) OFs for each source row and collimator size, and 3) dose distribution profiles along the x‐ and z‐axes, compared to film measurements and dose calculations from the Leksell GammaPlan (LGP) workstation. Methods: We defined the internal GK PFX geometry in Penelope with the aid of vendor‐supplied proprietary information. A single source per row was modeled for five rows for each of the 3 collimators (15 beams modeled). MC simulations were carried out on a Linux cluster. Phase space files (PSFs) were collected for the 15 modeled collimators then rotated about the z‐axis to model the sector of 24 sources per collimator. 3D dose distributions from the MC model, film, and LGP DICOM‐RT dose exports were analyzed using Matlab. For OF calculations, a 16 cm diameter dosimetry sphere was modeled with a virtual detector volume at its center. Results: Good agreement is found for row‐ and total‐output factors (greatest deviation of any type < 4%) compared to reference values. Off‐axis factors closely follow LGP predicted dose distributions along the x‐axis and differ on the inferior side of the z‐axis. Conclusions: Detailed geometric representations (radiation source, device components) of the GK PFX are required for high fidelity MC simulations. Calculated GK PFX OF values depend on the simulated detector volume size (4 mm OF most dependent). Our model shows strong agreement for the GK PFX OFs and dose profile curves compared to reference values. Non‐disclosure agreement for proprietary information with Elekta AB. No financial contribution.
SU‐E‐T‐469: The Effects of Patient Anatomy and Parallel Magnetic Fields on Beamlet Dose Distributions
Authors: Keyvanloo A , Warkentin B , Fallone BG , Field GC
Published: June 2012

Purpose: Beamlets are generated in a patient geometry in the presence of a magnetic field to investigate the effects of tissue density and magnetic field on beamlet dose distributions, which is important for the optimization of photon fluence to be delivered by a linac‐MR system. Methods: 50×50 mm2 fields were placed with isocenter in the middle of a patient's right lung. Each treatment field was decomposed into 100 beamlets (each 5×5 mm2). BEAMnrc scored the particle phase space at 100.2 cm from the source in the linac‐MR geometry (isocentre at 126 cm) with parallel magnetic fields of 0, 0.56, and 3T. DOSXYZnrc was modified to score the energy deposited by particles from this phase space as a function of the beamlet the particle passed through. The calculation volume of 70×46×64 voxels encompassed the patient with a voxel size of 3×3×3 mm3. Each beamlet was normalized to the dose calculated to a 3×3×3 mm3 voxel with isocenter at 5cm depth in a flat water tank without a magnetic field. Results: Beamlet files were calculated on Western Canada's high performance computing cluster (Westgrid) using 100 processors, enabling simulation of 109 histories in less than 3 hours. The resulting files, which contained 3D dose distributions for all 100 beamlets, were 81 MB per field. The Monte Carlo uncertainty was also stored. The gyroradii for 1 MeV electron traversing field lines at 20 degrees are 2.9mm and 0.5mm for 0.56 and 3T fields respectively. The 0.56T parallel magnetic field has a small effect compared to the distortion of the beamlet introduced by the presence of lung. Conclusions: The effect of tissue heterogeneities is more significant than the effect of a 0.56T parallel magnetic field. A 3T field refocuses the dose in lung to the beamlet path and significantly reduces the lateral electron scatter.
SU‐E‐T‐480: Updating the Planar Patterson‐Parker Table Using the TG‐43U1 Recommended Dosimetric Parameters
Authors: Naghshnezhad Z , Faghihi R , Meigooni A
Published: June 2012

Purpose: In this project, the Patterson‐Parker Table has been updated for Cs‐137 and Ir‐192 sources using their recent TG‐43U1 dosimetric data. In addition, dose uniformity for the different loading schemes as a function of implant area has been verified. Methods: The updated Paterson‐Parker tables have been generated for planar implants with Cs‐137 and Ir‐192 sources using their published TG‐43U1 dosimetric parameters. Accuracies of the updated tables were examined by two independent methods, namely, Monte Carlo simulation technique and using a commercially available treatment planning system. In addition to the dose values along the central axis of the implant, dose profiles along two orthogonal directions have been evaluated for selection of the optimum radioactivity distribution in each implant geometry. Results: The results of these investigations show that for the same implant size the mg.hr required for delivery of a given dose with Cs‐137 is not identical to that of Ir‐192. In addition, some differences between the updated Table and the published Paterson‐Parkers Tables have been observed. Independent Monte Carlo simulations and treatment planning data for multi‐seed implant indicated the accuracy (less than ±5%) of the updated Table. Conclusions: This work gives complete updated Paterson‐Parker Tables for two of the commonly utilized brachytherapy sources. For delivery of a given dose, significant differences (approximately 35%) have been observed between the traditional Paterson‐Parker Table and the updated Tables. These differences are attributed to the differences of tissue attenuation, 2D anisotropy functions as well as the availability of the new source dosimetry.
SU‐E‐T‐492: The Dosimetric and Clinical Impact of the Metallic Dental Implants on Radiation Dose Distributions in IMRT Head and Neck Cancer Patients
Authors: Wang L , Xing L , Le Q
Published: June 2012

Purpose: In H&N cancer patients, the development of oral mucositis is related closely to the radiation dose to the oral cavity. It is generally presumed that the existence of metallic dental implants makes it worse due to the scattering effect of the metal. This study investigates the effects of the dental implants on radiation doses to PTV, tongue mucosa, and other structures for IMRT H&N cancer patients by Monte Carlo (MC) dose calculations. Methods: Two H&N cancer patients who have dental implant and are treated by IMRT technique are selected for the purpose. The BEAMnrc/DOSXYZnrc MC codes are employed for the CT‐image based dose calculations. The radiation sources are the validated Varian phase‐space files for 6MV linac beams. The CT image artifacts caused by the dental fillings are replaced by tissue material. Two sets of MC calculations for each patient are performed at a calculation statistics of 1%: one treats all dental implants as bones, the other substitutes the implants by metal of either titanium or gold with correct density. Doses in PTV and various tissue structures are compared for the two scenarios. Results: With titanium implant, there is no significant difference in doses to PTV and tongue mucosa from that when treating implant as bone. With gold implant, the mean dose to PTV is slightly lowered by 1%; the mean dose to tongue mucosa is reduced by less than 0.5%, although the maximum dose is increased by 5%. Conclusions: The scattering dose from titanium implants is not of concern for H&N patients irradiated by 6MV IMRT beams. For gold implants, the scattering dose to tongue mucosa is not as severe as presumed; and the dose to PTV could be slightly compromised due to the attenuation effect of the metal. This work was supported in part by Varian Medical Systems.
SU‐E‐T‐497: Study of Restricted Mass Stopping Power Ratio in Small Electron Tube Fields
Authors: Sugimoto S , Ozawa S , Takatou H , Tokuyama K , Maruyama H , Yamagishi T , Baba R , Ebe K , Sasai K
Published: June 2012

Purpose: Electron tubes with small radii are useful to treat narrow regions which cannot accommodate normal electron applicators. In small electron fields, it is not trivial to estimate restricted mass stopping power ratio (MSR), which is needed to evaluate dose from ion chamber measurement. We studied MSRs in small electron tube fields using the Monte Carlo simulation. Methods: Electron tubes with radii, 3 and 2.5 cm, were used in this study. Nominal electron energies were 6 and 9 MeV. There were two types of tubes. One has a normal cut but the other has a 45‐degree cut. For the normal cut tube, percent depth dose (PDD) in water was evaluated along the center of axis (CAX) of a beam. For the 45‐degree cut tube, PDD was evaluated along the vertical line from the intersection of the CAX and the phantom surface with 45‐degree gantry angle. The MSRs and mean electron energies were calculated using the Monte Carlo simulation. Results: We found good agreement between the measured and calculated PDDs. The changes of mean energies from those in the 10×10 cm2 field at the depth of maximum dose (dmax) were very small for the normal cut electron tubes. For the 45‐degree cut tubes, the changes of mean energies at dmax were less than 1 MeV. The MSRs in the normal cut tube fields were almost the same as those in the 10×10 cm2 field at the corresponding depths. The MSRs for the 45‐degree cut tubes deviated from those in the 10×10 cm2 by about 1% (1.5 % at most). Conclusions: We evaluated the mean energies and MSRs in small electron tube fields. The deviations of them from the values in the 10×10 cm2 were small. The maximum difference of MSR was 1.5% in 45‐degree cut tube fields. This work was supported by KAKENHI (23791449), Japan Society for the Promotion of Science, and Cancer Professional Training Plan, The Ministry of Education, Culture, Sports, Science and Technology, Japan.
SU‐E‐T‐534: Beam and MLC Commissioning and Assessment of Three Commercial Treatment Planning Systems
Authors: Lim S , LoSasso T
Published: June 2012

Purpose: To assess and compare the open beam and multi‐leaf collimator modeling of Pinnacle, Ecilpse (AAA and Acuros) and RayStation planning systems. Method and Materials: The 6MV photon beam of a Varian TrueBeam with Millennium 120 MLC was used for this study. Measurements made with combinations of ion chamber, radiochromic film, and diodes in water and plastic phantoms. Depth and crossplane profiles of open square fields shaped by jaws or MLC ranged from 3×3 to 40×40cm2 and from 0 to 20 cm depth. Depth dose, flatness (80% of FWHM), and penumbra (20–80%) of calculated and measured profiles were compared. Various MLC test patterns were calculated and compared with measurements to assess the modeling of the round leaf edge, tongue‐and‐groove, and interleaf transmissions. Results: Calculated depth doses are within 1.0% and flatness is within 2% for all field sizes and depths. Jaw penumbrae are within 2mm and 3mm for 20×20 and 30×30cm2 at 10cm depth respectively. MLC penumbrae (20−80%) of the three systems are within 0.3mm and 1.0mm for a 3×3cm2 and 10×10cm2 MLC apertures. Notably, to match the measured MLC round‐edge transmission, the half thickness (10% transmission) leaf‐tip width of the current RayStation MLC model has to be broadened to 10mm. All three systems appear to adequately model the tongue‐and‐groove. Pinnacle explicitly models the interleaf transmission while Eclipse and RayStation simply use average MLC transmission. Conclusions: All three systems are capable of generating clinically acceptable beam models for open fields. Based upon the round‐edge profile, Eclipse and Pinnacle provide better MLC models than RayStation. Among the three systems, Eclipse took the least time and effort to commission these features.
SU‐E‐T‐557: A Planning Strategy of Volumetric Modulated Arc Therapy with Simultaneous Integrated Boost for Intracranial Stereotactic Radiotherapy
Authors: Ono K , Fujimoto S , Furukawa K , Kudo T , Akagi Y , Hirokawa Y
Published: June 2012

Purpose: The purpose of this planning study was to evaluate the dosimetric effect of dose escalation for intracranial stereotactic radiotherapy by volumetric modulated arc therapy (RapidArc) with simultaneous integrated boost (SIB‐VMAT). Methods: Dynamic conformal arc therapy (DCA), VMAT, and SIB‐VMAT plans using Novalis Tx (Varian/BrainLAB) were performed for twenty target volumes in patients with intracranial metastases with median PTV of 16.0 cm3 (range 2.4–35.2 cm3). PTV was created with 2 mm expansion from GTV. All plans were generated with a prescribed dose of 35 Gy in 5 fractions to the PTV (D95 = 95%), and dose escalation up to 40 Gy (SIB‐VMAT40) and 45 Gy (SIB‐VMAT45) was performed only to the PTV‐boost (PTV shrunk by 5 mm) for SIB‐VMAT. Each plan was compared using conformity parameters. Results: The average Paddick conformity index (CI) was 0.78, 0.90, 0.91, and 0.89 for DCA, VMAT, SIB‐VMAT40, and SIB‐VMAT45, respectively. The average healthy tissue overdosage factor (HTOF), suggested by SALT was 0.118, 0.006, 0.007, and 0.011 for DCA, VMAT, SIB‐VMAT40, and SIB‐VMAT45, respectively. The average V30, V20, and V10 of normal brain for VMAT and SIB‐VMAT decreased by 3.0 cm3 (range 0.1–8.2 cm3), 3.0 cm3 (range 0.1–8.7 cm@@@3@@), and 7.5 cm@@@3@@ (range 0.3–26.2 cm@@@3@@), respectively, compared to DCA depending on the target volume. Conclusions: SIB‐VMAT improved dose conformity to the PTV for intracranial stereotactic radiotherapy, and decreased high and low dose volume of normal brain compared to DCA. SIB‐VMAT offers the ability of dose escalation due to high conformity of high dose regions inside the target volume.
MO‐G‐213AB‐02: A Gated IMRT Study Based on Comparative 2D and 3D Dose Measurements
Authors: Dvorak P , Stevens S , McQuaid M , Dawes S , Richmond A
Published: June 2012

Purpose: To perform a quantitative study of Varian RPM gating modes and parameters on a gated IMRT of esophagus cancer case using both 2D and 3D dose measurements. Methods: A 4DCT scan reconstructed into a 10‐phase series was acquired. For each of 7 IMRT fields, the target trajectory, due to respiratory and also cardiac motion, perpendicular to the beam axis was recorded. An alternative set of smoothed trajectories was also processed to form closed hysteresis‐like curves. Each trajectory was replicated using a MotionSim phantom in the plane perpendicular to beam axis. Motion was correlated to the position of a surrogate platform, monitored using a reflective marker block and RPM gating system. Dose planes were measured using a MapCheck2 detector placed upon the MotionSim phantom. Dynamic delivery was performed for non‐gated, narrow window (2mm or 40–60% in amplitude or phase of breathing cycle, respectively) and wide window (5mm or 30–70% in amplitude or phase of breathing cycle, respectively) gated delivery. Corresponding 3D dose distributions were obtained using 2D maps of dose difference between reference and measurement, backprojected in the direction of the given field onto the original reference 3D dose distribution. Results: Results based on 2D dose analysis do not always correlate with results based on reconstructed 3D doses, e.g. using narrow gating was found superior to wide gating based on conventional gamma 2D analysis. However, CTV DVH analysis did not show a significant difference. On other hand, both 2D and 3D approaches favour phase‐over amplitude‐based gating. Both methods also showed better results for adjusted smoother trajectories. Conclusions: Interpreting dose measurements using three‐dimensional reconstructed dose directly on patient model and volume structures provides more relevant information than conventional 2D dose‐to‐dose approaches and has potential to uncover different trends and the magnitude of a given effect as indicated in this study.
TU‐A‐BRB‐01: Groundbreaking 2D and 3D Dosimetry Techniques Using Scintillating Fibers and Tomographic Reconstruction
Authors: Goulet M , Archambault L , Beaulieu L , Gingras L
Published: June 2012

Purpose: To present the novel concept of tomodosimetry, i.e. the tomographic reconstruction of the dose projections obtained using long scintillating fibers, and its application to 2D and 3D dosimetry. Methods: 2D configuration: 50 scintillating fibers were aligned on a 20cm diameter disk inside a 30cm diameter rotating masonite phantom. 18 dose projections (8 MU each) were measured for each radiation field over a 180 degrees rotation of the phantom. 3D configuration: 128 long scintillating fibers were simulated inside a 20cm diameter, 20cm long cylindrical water‐equivalent phantom. The fibers were placed at various angles on the surface of two cylindrical regions of radius 7.5 and 3.75cm. Using the predicted dose from Pinnacle3, we simulated a 360 degrees rotation of the phantom along its principal axis, collecting the scintillation light from the fibers at each 5 degrees. Both prototypes: the dose in each scintillating fiber plane was reconstructed using a total variation minimization reconstruction iterative algorithm at a resolution of 1×1mm2, and was interpolated in the 3D volume between in each cylindrical plane in the 3D prototype. Results: Absolute measured dose differences in the 2D configuration were on average below 1% in the high dose low gradient region of each field. Absolute doses differences calculated inside the inner cylindrical region were on average of 0.5% and 1.3% of the isocenter dose for a 10×10cm2 field and an IMRT segment, respectively. 3%/3mm gamma tests conducted in both configurations in the isocenter plane achieved a success rate of more than 99% of the dose pixels for the region over 50% of the maximum dose. Conclusions: This work demonstrates the potential of scintillating fiber based tomographic 2D and 3D dosimeters. This methodology allows for millimeter resolution dosimetry in a whole 2D plane or 3D volumes in realtime using only a limited number of detectors.
TU‐A‐BRB‐03: Realization of the Unit of Absorbed Dose to Water for I‐125 Interstitial Brachytherapy Sources
Authors: Schneider T , Selbach H
Published: June 2012

Purpose: To establish a primary standard for I‐125 interstitial brachytherapy sources in terms of absorbed dose to water and thereby to improve the accuracy and effectiveness of the dosimetry for brachytherapy. Methods: The primary standard is a large, air‐filled, parallel‐plate extrapolation chamber in a phantom of water‐equivalent material (RW1). The thickness of the entrance plate defines the measurement depth within the water phantom and the inner side of the front plate the reference plane of the chamber. The method of evaluation was derived analytically based on radiation transport theory. A conversion factor has to be applied to the difference of ionization charges measured at two plate separations. This factor is composed of quotients of kerma values calculated for different plate separations in the chamber. In a recent publication it has been shown that this conversion factor is robust against uncertainties of database and spectra in comparison to conversion factors needed to convert the Reference Air Kerma Rate (RAKR) into Dw. With this measure the relative uncertainties of the conversion into Dw could be reduced from 10% to 1 %. Results: Dw and RAKR of four ‘BEBIG Symmetra I25.S16’‐ seeds were determined by means of primary standards. With this an experimentally determined dose rate constant was obtained, which could be compared to literature data. The uncertainty of the experimentally determined dose‐rate constant results to 1.6% as the uncertainties of the determination of Dw is 1.3% and of the RAKR is 0.9%. The mean value of the determined dose rate constants amounts to 1.021×10−4 m‐2 and is in good agreement with the TG‐43 consensus value of 1.012×10−4 m‐2. Conclusions: A primary standard was developed which is able to determine the absorbed dose to water for I‐125 interstitial brachytherapy sources with an uncertainty of 1.3%. The research within this EURAMET joint research project leading to these results has received funding from the European Community's Seventh Framework Programme, ERA‐NET Plus, under Grant Agreement No. 217257.
TU‐A‐BRB‐09: Ion Recombination in a Liquid‐Filled Ionization Chamber in High‐Energy Photon Beams
Authors: Chung E , Davis S , Seuntjens J
Published: June 2012

Purpose: To characterize the ion recombination effect of a liquid‐filled ionization chamber (LIC) in high‐energy photon beams. Methods: The ion recombination effect on the response of a PTW micro liquid ion chamber model 31018 (microLion) was investigated with a 6 MV photon beam in normal and SRS modes produced from a Varian Novalis Tx linear accelerator. Repetition rates were set to 100, 400 and 1000 MU/min, which correspond to pulse repetition frequencies of 60, 240 and 600 Hz, respectively. Polarization voltages applied to the microLion were +800 V and +400 V. The collection efficiency of the microLion as a function of dose per pulse was experimentally measured and theoretically calculated with changing polarization voltage and repetition rate. Results: The relative collection efficiency of the microLion decreased with increasing dose per pulse or pulse repetition frequency from the linear accelerator, or with decreasing polarization voltage to the microLion because of more ion recombination in the liquid. For repetition rates of 100, 400 and 1000 MU/min, the collection efficiency decreased by up to 0.62%, 0.71% and 1.9%, respectively, in a range of dose per pulse from 0.062 to 0.429 mGy/pulse with the polarization voltage of +800 V. For +400 V, the collection efficiency decrease was by up to 0.92%, 2.0% and 5.8% at 100, 400 and 1000 MU/min, respectively. For pulsed radiation with high repetition rate, the experimental relative collection efficiency for all polarization voltages tends to the theoretically calculated efficiency for continuous beams because of low ion mobility in the liquid. We proposed a correction technique for differences in recombination between different radiation fields. Conclusions: Ion recombination effects in a LIC were quantified and a practical correction method was proposed thereby enabling the use of the LIC for accurate measurements of output factors and relative doses in small and nonstandard fields.
TU‐A‐BRA‐05: Lung Cancer Patient Feasibility Study for Emission Guided Radiation Therapy
Authors: Mazin S , Nanduri A , Yang J , Yamamoto T , Loo B , Graves E
Published: June 2012

Purpose: Emission guided radiation therapy (EGRT) is a new concept that allows for online biological targeting with radioactive tracers. The concept was previously demonstrated in phantom experiments involving free breathing trajectories. This study involves the first patient imaging data to assess feasibility and estimate performance in a more realistic context. Methods: A proposed EGRT geometry involves rotating two PET detector arcs with a linear accelerator and binary multi‐leaf collimator on a CT gantry to deliver beamlets of radiation dynamically along detected PET emission paths. A lung cancer patient underwent PET‐CT as part of radiotherapy planning. PET list‐mode data were retrospectively used as an input to simulate the EGRT system's response and Monte Carlo simulations were used to calculate the dose to the patient. The gross target volume (GTV) was contoured based on the PET‐CT images and the planning volume (PTV) was defined as a 10 mm extension of the GTV in all directions. The EGRT method was compared to uniformly irradiating the same PTV (IMRT), with both methods normalized for the same integral dose to the chest wall. Physiologic motion was ignored during the dose calculations as the tumor exhibited < 2 mm motion. Results: The dose peaks towards the center of the GTV with the EGRT method. However, even in the presence of this inhomogeneity, the EGRT method resulted in 18% relative increase in dose to 95% of the GTV, and 45% increase in dose to 50% of the GTV, compared to the IMRT method. Both methods were normalized for the same integral dose to the chest wall. Conclusions: The feasibility of EGRT has been demonstrated with PET data from a lung cancer patient. Future work will analyze the ability of EGRT to compensate for motion in PET‐CT patient studies which will include breathing traces to estimate ground truth. RefleXion Medical is a company commercializing PET‐guided radiotherapy. SRM and ASN have financial interest in the company.
TU‐A‐BRA‐10: Real‐Time Markerless Tumor Tracking with MV Imaging and a Dynamic Multi‐Leaf Collimator (DMLC)
Authors: Rottmann J , Keall P , Yue Y , Berbeco R
Published: June 2012

Purpose: The implementation of a real‐time adaptive therapy system. Automatic soft tissue localization (STiL) is used to drive DMLC adaptation maintaining the position of the dynamic treatment aperture relative to the tumor location during the entire breathing cycle. The STiL component utilizes electronic portal images and operates without the need for fiducial markers. The proposed system has the potential to improve treatment accuracy, dose conformity and sparing of healthy tissue. Methods: The system is implemented and tested on a clinical linear accelerator featuring an electronic portal imaging device (EPID) and a DMLC control system. EPID images are continuously acquired at a frame rate of 12.86 Hz. The STiL component processes the images in real‐time, sending its output ‐ the current tumor position ‐ to the DMLC component, which moves the aperture to that position. Image transfer, tumor position calculation and DMLC motion introduce a time lag between tumor position at acquisition time and at the time the treatment aperture reaches this position. We analyze this latency with a dynamic chest phantom driving a 1D sinusoidal motion (20mm superior‐inferior motion range and 4.5s period). We estimate the resulting average geometric systematic error in a clinical setting by driving the phantom with several patient traces (recorded from fiducial tracking during lung SBRT). Results: The individual geometric errors of the StiL and the DMLC component are each smaller than 1 mm. The overall system latency was found to be 210 ms. The average rms‐error of 11 patients traces (172 beams) was found to be (1.8 ± 0.8) mm with this latency. Conclusions: We have implemented a real‐time adaptive therapy system integrating automatic soft tissue tumor localization with DMLC adaptation of the treatment aperture. The functionality of the combined system was tested successfully and the systemic latency and resulting rms error measured. Varian Medical Systems Inc., NCI grant CA93626
TU‐A‐213CD‐01: GDRR: A GPU Tool for Cone‐Beam CT Projection Simulations
Authors: Jia X , Yan H , Folkerts M , Jiang S
Published: June 2012

Purpose: Realistic calculations of x‐ray projection images play an important role in many projects related to CBCT, such as the design of scanners and reconstruction algorithms. However, to yield a desired level of realism it usually requires a tremendously long computational time, which hinders the research process. The purpose of this project is to develop a realistic x‐ray projection image simulation package, gDRR, on a computer graphics processing unit (GPU) to achieve both high accuracy and efficiency. Methods: Primary signals in a projection is computed by GPU‐based ray‐tracing algorithms, with many features considered, e.g. source energy spectrum, fluence map due to a bowtie filter, and detector response. Scatter signals are obtained by Monte Carlo (MC) simulations on GPU under the aforementioned realistic setup followed by a denoising step. Noise signals are calculated by taking the difference between the MC simulated primary and the ray‐tracing primary signals, and the difference between the MC simulated scatter signals and the denoised scatter signals. The noise level is calibrated according to the mAs level in a scan. Results: The primary signals agree well with results from MC simulations. As for the scatter signals, our MC results for real patient cases are in good agreement with those from EGSnrc with less than 2% relative error using 10 million source photons. Various realistic artifacts can be observed in CBCT images reconstructed from the simulated projections, e.g. beam hardening, scatter, and noise. The computation time per projection is ∼20ms for primary signal per energy channel, ∼4sec for scatter signal, and 1∼2sec for all other steps. Conclusions: We have developed a complete simulation package on GPU to compute x‐ray projections in CBCT. Primary, scatter, and noise signals can be calculated with a high level of realism at a high efficiency. This work is supported in part by NIH (1R01CA154747‐01), Varian Medical Systems through a Master Research Agreement, and the Thrasher Research Fund.