bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐180: Clinical Implementation of Hybrid Density Override Planning for Lung SBRT
Authors: Siddique H , Sintay B , Maurer J , Liu H , Hayes L , Wiant D
Published: June 2015

Purpose:

Hybrid density override schemes have been shown to yield more accurate dose modeling for lung SBRT than plans calculated on free breathing (FB) or time average (AVG) CT scans. Before hybrid schemes are clinically implemented, comparisons are needed between dose delivered to a moving gross tumor volume (GTV) by plans calculated on hybrid scans (HP) and plans calculated on FB and AVG scans.

Methods:

Volumetric arc therapy plans were created on HP, FB, and AVG scans for 10 patients with FB and 4D‐CT scans. Five of the cases had target volumes contained entirely in lung, 5 had target volumes that included chestwall. The HP were created by overriding the internal target volume (ITV) to GTV density, and the planning target volume minus ITV shell to a density between GTV and lung. If chestwall was in the target its density was not changed. Plans were copied to the 10 4D‐CT phases and recalculated to evaluate the impact of tumor motion on each technique. The GTV doses from the initial plans were compared to mean doses over the 4D‐CT phases. Doses were calculated with the anisotropic analytical algorithm.

Results:

The minimum GTV dose ratios from the 4D to initial plans were 0.95 +/−0.11, 0.97 +/−0.11, 0.94 +/−0.13 (2 SD), for the FB, AVG, and HP plans, respectively. The mean GTV dose ratios were 1.00 +/−0.07, 1.01 +/−0.03, 0.97 +/−0.09, for the FB, AVG, and HP plans, respectively. The individual minimum dose ratios for HP to FB or AVG were all < 10%, the mean ratios agreed < 10% for 90% of the comparisons.

Conclusion:

The FB, AVG, and HP plans showed consistent results when considering motion. The interpretation of the planning system dose and prescription definition with HP techniques should be similar to current practices.
SU‐E‐T‐183: Clinical Quality Assurance Workflow for Dynamic Tumor Tracking Radiation Dose Delivery
Authors: Mamalui‐Hunter M , Su Z , Li Z
Published: June 2015

Purpose:

One of the most important aspects of implementation of new treatment modalities is an ‘end‐to‐end’ verification of the treatment process. Radiation treatment based on dynamic tracking of a tumor is highly patient‐specific, therefore, special attention should be paid to quality assurance of the treatment delivery. Our goal was to design the clinical workflow that ensures accurate delivery of the planned dose using the Dynamic Target Tracking option of VeroTM (BrainLab,MHI) linac.

Methods:

A patient simulation is designed to include a pre‐treatment session to verify whether the system can reliably track the motion of the implanted marker and build the 4D model of the target motion. The external surrogate and target motion patterns are recorded in the ExactracTM log files. In this work, a spectrum of custom marker and external surrogate motion trajectories closely resembling the patient specific motion patterns was used. 1mm thick/11mm long VisicoilTM marker was placed 15 and 20mm from the center of the spherical tissue equivalent target (centroid to centroid distance) in the 4D motion phantom (CIRSTM). 3D conformal (3 mm block margin) SBRT plans were delivered to 2 moving targets in the phantom: 1) 20mm diameter target that allows ion chamber dose measurement and 2) 25mm target that allows using film to measure CAX dose (GafchromicTM EBT3 used). The measured dose was compared to the iPlanTM TPS results using MonteCarlo algorithm (1% variance, Dose‐to‐water).

Results:

On average, film shows 98.9% pass using gamma criterion for 2% and 2mm DTA, 94.3% match for 2% and 1 mm DTA, 98% pass for 1% and 2 mm DTA however only 88% points passing for 1% and 1 mm DTA. Ion chamber measurements agreed with the calculation within 1.5%.

Conclusion:

The clinical QA workflow was designed for SBRT delivery using real‐time tumor tracking on VeroTM linac.
SU‐E‐T‐187: Collimation Methods in Spot Scanning Proton Therapy: A Treatment Plan Comparison Between a Fixed Aperture and a Dynamic Collimation System
Authors: Smith B , Gelover E , Wang D , Moignier A , Flynn R , Lin L , Kirk M , Solberg T , Hyer D
Published: June 2015

Purpose:

Low‐energy treatments during spot scanning proton therapy (SSPT) suffer from poor conformity due to increased spot size. Collimation devices can reduce the lateral penumbra of a proton therapy dose distribution and improve the overall plan quality. The purpose of this work was to study the advantages of individual energy‐layer collimation, which is unique to a recently proposed Dynamic Collimation System (DCS), in comparison to a standard, fixed aperture that allows only a single shape for all energy layers.

Methods:

Three brain patients previously planned and treated with SSPT were re‐planned using an in‐house treatment planning system capable of modeling collimated and un‐collimated proton beamlets. The un‐collimated plans, which served as a baseline for comparison, reproduced the target coverage of the clinically delivered plans. The collimator opening for the aperture based plans included a 0.6 cm expansion of the largest cross section of the target in the Beam's Eye View, while the DCS based plans were created by optimizing the collimator position for beam spots near the periphery of the target in each energy layer.

Results:

The reduction of mean dose to normal tissue adjacent to the target, as defined by a 10 mm ring, averaged 9.13% and 3.48% for the DCS and aperture plans, respectively. The conformity index, as defined by the ratio of the volume of the 50% isodose line to the target volume, yielded an average improvement of 16.42% and 8.16% for the DCS and aperture plans, respectively.

Conclusion:

Collimation reduces the dose to normal tissue adjacent to the target and increases dose conformity to the target region for low‐energy SSPT. The ability of the DCS to provide collimation to each energy layer yields better conformity in comparison to fixed aperture plans.

This work was partially funded by IBA (Ion Beam Applications S.A.).
SU‐E‐T‐188: Commission of World 1st Commercial Compact PBS Proton System
Authors: Ding X , Patel B , Song X , Syh J , Syh J , Zhang J , Freund D , Rosen L , Wu H
Published: June 2015

Purpose:

ProteusONE is the 1st commercial compact PBS proton system with an upstream scanning gantry and C230 cyclotron. We commissioned XiO and Raystation TPS simultaneously. This is a summary of beam data collection, modeling, and verification and comparison without range shiter for this unique system with both TPS.

Methods:

Both Raystation and XiO requires the same measurements data: (i) integral depth dose(IDDs) of single central spot measured in water tank; (ii) absolute dose calibration measured at 2cm depth of water with mono‐energetic 10×10 cm2 field with spot spacing 4mm, 1MU per spot; and (iii) beam spot characteristics in air at 0cm and ± 20cm away from ISO. To verify the beam model for both TPS, same 15 cube plans were created to simulate different treatment sites, target volumes and positions. PDDs of each plan were measured using a Multi‐layer Ionization Chamber(MLIC), absolute point dose verification were measured using PPC05 in water tank and patient‐specific QA were measured using MatriXX PT, a 2D ion chamber array.

Results:

All the point dose measurements at midSOBP were within 2% for both XiO and Raystation. However, up to 5% deviations were observed in XiO's plans at shallow depth while within 2% in Raystation plans. 100% of the ranges measured were within 1 mm with maximum deviation of 0.5 mm. 20 patient specific plan were generated and measured in 3 planes (distal, proximal and midSOBP) in Raystation. The average of gamma index is 98.7%±3% with minimum 94%

Conclusions:

Both TPS were successfully commissioned and can be safely deployed for clinical use for ProteusONE. Based on our clinical experience in PBS planning, user interface, function and workflow, we preferably use Raystation as our main clinical TPS. Gamma Index >95% at 3%/3 mm criteria is our institution action level for patient specific plan QAs.
SU‐E‐T‐190: Commissioning An Elekta VersaHD Linear Accelerator
Authors: Narayanasamy G , Saenz D , Cruz W , Mavroidis P , Papanikolaou N , Stathakis S
Published: June 2015

Purpose:

The purpose of this study is to report the dosimetric aspects of commissioning performed on an Elekta VersaHD linear accelerator with high dose rate flattening‐filter‐free (FFF) photon modes and electron modes.

Methods:

Acceptance and commissioning was performed on an Elekta VersaHD linac with 5 photon energies (6MV, 10MV, 18MV, 6FFF, 10FFF), 4 electron energies (6MeV, 9MeV, 12MeV, 15MeV) and 160 leaf (5mm wide) multi‐leaf collimators (MLCs). Mechanical and dosimetric data was measured and evaluated. The measurements include percent depth doses (PDDs), inplane and crossplane profiles, head scatter factor (Sc), relative photon output factors (Scp), universal wedge transmission factor, MLC transmission factors, and electron cone factors.

Results:

Gantry, collimator, couch isocentricity measurements were within 1mm, 0.7mm and 0.7mm diameter respectively. The PDDs of 6FFF and 10FFF beams show deeper dmax and steeper fall‐off with depth than the corresponding flattened beams. While flatness values of 6FFF and 10FFF normalized profiles were higher than the corresponding flattened beams, the symmetry values were almost identical. The crossplane penumbra values were higher than the inplane penumbra values for all the energies. The MLC transmission values were 0.5%, 0.6% and 0.6% for 6MV, 10MV, and 18MV photon beams. The electron PDDs, profiles and cone factors is validated by literature.

Conclusion:

The outcome of radiation treatment is directly related to the accuracy in the dose modeled in the treatment planning system which is based on the commissioned data. Commissioning data provided us a valuable insight into the dosimetric characteristics of the beam. This set of commissioning data can provide comparison data to others performing VersaHD commissioning thus improving patient safety.
SU‐E‐T‐192: Commissioning of a Commercial 3D Dose Calculation Program
Authors: Langen K , Guerrero M , Killefer M , Xu H , Zhou J , Zhang B , Chen S
Published: June 2015

Purpose:

To commission a commercial software package (CSP) that is used as secondary dose calculation check. The CSP uses an independent golden data beam model. However, some parameters can be modified to generate a customer specific model. Plan comparisons and point dose measurements were performed to test if and to what extent the beam model needed adjustment to optimize results.

Methods:

Beam parameter configurations were compared between the CSP and both TPS. Twelve phantom test plans ranging from simple to complex were generated in two treatment planning systems (TPS). Tests included small field, off axis, EDW, IMRT and VMAT plans. For each plan a point dose was measured to establish ground truth. Lastly, patient plans were compared for both TPS systems and the CSP.

Results:

Beam parameters agreed within 2%. The output factors for small fields were changed for the 15 MV beam by 2 and 1.5 % for the 1 cm and 2 cm field sizes, respectively. For the 6 MV beam output factors were adjusted by 3−0.8% for field sizes ranging from 1 to 5 cm. The MLC dynamic leaf gap was adjusted by 1.5 mm for 18 MV beam. Differences between the CSP and the TPS were noted in the built‐up region. These differences affected the gamma pass rate in the surface region, however this effect is reduced with increasing number of beam angles and does not affect point dose calculations at depth. All IMRT and VMAT plans agreed with the CSP using a gamma pass rate of 95% (3%, 3mm).

Conclusion:

The CSP is used to verify point doses for all 3D plans generated in our clinic for the last 6 months. No point dose mismatches were encountered since the CSP was implemented. Next, the CSP will be adapted for secondary checks of all IMRT plans.

KL had a beta tester agreement with Mobius Medical for an in‐kind equipment and software loan.
SU‐E‐T‐194: Commissioning of Monaco Treatment Planning System On An Elekta VersaHD Linear Accelerator
Authors: Narayanasamy G , Bosse C , Saenz D , Cruz W , Mavroidis P , Papanikolaou N , Stathakis S
Published: June 2015

Purpose:

The Monaco treatment planning system (TPS) uses a Monte‐Carlo algorithm based dose computation engine to model the photon beams of a linear accelerator. The aim is to perform verification of Monaco TPS beam modeling of a Elekta VersaHD linac with 6MV, 6MV FFF, 10 MV, 10MV FFF, 18MV photon beams and 160 multileaf collimators (MLC) with a projected width of 5‐mm at the isocenter.

Methods:

A series of dosimetric tests were performed to validate Monaco calculated beams including point dose measurement in water with and without heterogeneity and 2‐dimensional dose distributions on a Delta4 bi‐planar diode dosimeter array (Scandidos, Uppsala, Sweden). 3D conformal beams of different field sizes, source‐to‐surface distances, wedges, and gantry angles were delivered onto a phantom consisting of several plastic water and Styrofoam slabs. Point dose measurements were verified with a PTW 31013 Semiflex 0.3 cc ionization chamber (PTW, Freiburg, Germany). In addition, 8 step and shoot intensity modulated radiotherapy (IMRT) and volumetric modulated arc radiotherapy (VMAT) beams included in the Monaco TPS commissioning suite were verified against measurements on Delta4 to test and fine tune parameters in the beam model. IMRT verification was computed using gamma analysis with dose difference and distance‐to‐agreement criteria of 3%/3mm with a dose threshold of 10%.

Results:

Point dose measurements agreed within 2% in the homogeneous phantom and within 3% in the heterogeneous phantom for all photon energies. IMRT beams yielded a passing percentage of 99.1±1.1% in the gamma analysis which is well above the institutional passing threshold of 90%.

Conclusion:

Monaco TPS commissioning was successfully performed for all the photon energies on the Elekta VersaHD linac prior to clinical usage.
SU‐E‐T‐196: Comparative Analysis of Surface Dose Measurements Using MOSFET Detector and Dose Predicted by Eclipse ‐ AAA with Varying Dose Calculation Grid Size
Authors: Badkul R , Nejaiman S , Pokhrel D , Jiang H , Kumar P
Published: June 2015

Purpose:

Skin dose can be the limiting factor and fairly common reason to interrupt the treatment, especially for treating head‐and‐neck with Intensity‐modulated‐radiation‐therapy(IMRT) or Volumetrically‐modulated ‐ arc‐therapy (VMAT) and breast with tangentially‐directed‐beams. Aim of this study was to investigate accuracy of near‐surface dose predicted by Eclipse treatment‐planning‐system (TPS) using Anisotropic‐Analytic Algorithm (AAA)with varying calculation grid‐size and comparing with metal‐oxide‐semiconductor‐field‐effect‐transistors(MOSFETs)measurements for a range of clinical‐conditions (open‐field,dynamic‐wedge, physical‐wedge, IMRT,VMAT).

Methods:

QUASAR™‐Body‐Phantom was used in this study with oval curved‐surfaces to mimic breast, chest wall and head‐and‐neck sites.A CT‐scan was obtained with five radio‐opaque markers(ROM) placed on the surface of phantom to mimic the range of incident angles for measurements and dose prediction using 2mm slice thickness.At each ROM, small structure(1mmx2mm) were contoured to obtain mean‐doses from TPS.Calculations were performed for open‐field,dynamic‐wedge,physical‐wedge,IMRT and VMAT using Varian‐21EX,6&15MV photons using twogrid‐sizes:2.5mm and 1mm.Calibration checks were performed to ensure that MOSFETs response were within ±5%.Surface‐doses were measured at five locations and compared with TPS calculations.

Results:

For 6MV: 2.5mm grid‐size,mean calculated doses(MCD)were higher by 10%(±7.6),10%(±7.6),20%(±8.5),40%(±7.5),30%(±6.9) and for 1mm grid‐size MCD were higher by 0%(±5.7),0%(±4.2),0%(±5.5),1.2%(±5.0),1.1% (±7.8) for open‐field,dynamic‐wedge,physical‐wedge,IMRT,VMAT respectively.For 15MV: 2.5mm grid‐size,MCD were higher by 30%(±14.6),30%(±14.6),30%(±14.0),40%(±11.0),30%(±3.5)and for 1mm grid‐size MCD were higher by 10% (±10.6), 10%(±9.8),10%(±8.0),30%(±7.8),10%(±3.8) for open‐field, dynamic‐wedge, physical‐wedge, IMRT, VMAT respectively.For 6MV, 86% and 56% of all measured values agreed better than ±20% for 1mm and 2.5mm grid‐sizes respectively. For 18MV, 56% and 18% of all measured‐values agreed better than ±20% for 1mm and 2.5mm grid‐sizes respectively.

Conclusion:

Reliable Skin‐dose calculations by TPS can be very difficult due to steep dose‐gradient and inaccurate beam‐modelling in buildup region.Our results showed that Eclipse over‐estimates surface‐dose.Impact of grid‐size is also significant,surface‐dose increased up to 40% from 1mm to 2.5mm,however, 1mm calculated‐values closely agrees with measurements. Due to large uncertnities in skin‐dose predictions from TPS,outmost caution must be exercised when skin dose is evaluated,a sufficiently smaller grid‐size(1mm)can improve the accuracy and MOSFETs can be used for verification.
SU‐E‐T‐198: Comparison Between a PTW MicroDiamond Dosimeter and a Markus Chamber in a 62 MeV/n Carbon Ion Beam
Authors: Rossomme S , Hopfgartner J , Delor A , Vynckier S , Palmans H
Published: June 2015

Purpose:

To investigate the linear energy transfer (LET) dependence of a PTW Freiburg microDiamond dosimeter, we compared its response to the response of a plane‐parallel Markus chamber in a 62 MeV/n mono‐energetic carbon ion beam.

Methods:

The response of both detectors has been studied as a function of depth in graphite by adding or removing graphite plates in front of the detectors. To account for fluctuations of the beam, we used two setups with different monitor chambers. The depth of the effective point of measurement of both detectors has been converted into a graphite equivalent depth using ICRU Report 73 data. As recommended by IAEA TRS‐398, the response of the Markus chamber has been corrected for temperature, pressure, polarity effects and ion recombination. The latter required an additional experiment; to quantify the effect of volume recombination and initial recombination, measurements have been performed at different voltages and different dose rates.

Results:

As expected, the dominant process leading to ion recombination for carbon ion beam is the initial recombination. At the entrance, the ion recombination correction equals 1.1% and the value is approximately constant in the plateau region. Due to the increase of the LET in the Bragg peak region, we observe a strong increase of the ion recombination correction, up to 6.1% at the distal edge. Comparison between the microDiamond response and the Markus chamber response shows good agreement in the plateau region. However, we observe a 13.6% under response of the microDiamond in the Bragg peak.

Conclusion:

Increasing between 1% and 6%, the depth dependent ion recombination correction has to be applied to the Markus response. The comparison between the microDiamond and the Markus chamber indicates that there is an under‐response of the microDiamond in the vicinity of the Bragg peak due to the increased LET.
SU‐E‐T‐203: Comparison of a Commercial MRI‐Linear Accelerator Based Monte Carlo Dose Calculation Algorithm and Geant4
Authors: Ahmad S , Sarfehnia A , Paudel M , Sahgal A , Hissoiny S , Keller B
Published: June 2015

Purpose:

An MRI‐linear accelerator is currently being developed by the vendor Elekta™. The treatment planning system that will be used to model dose for this unit uses a Monte Carlo dose calculation algorithm, GPUMCD, that allows for the application of a magnetic field. We tested this radiation transport code against an independent Monte‐Carlo toolkit Geant4 (v.4.10.01) both with and without the magnetic field applied.

Methods:

The setup comprised a 6 MeV mono‐energetic photon beam emerging from a point source impinging on a homogeneous water phantom at 100 cm SSD. The comparisons were drawn from the percentage depth doses (PDD) for three different field sizes (1.5 × 1.5 cm2, 5 × 5 cm2, 10 × 10 cm2) and dose profiles at various depths. A 1.5 T magnetic field was applied perpendicular to the direction of the beam. The transport thresholds were kept the same for both codes.

Results:

All of the normalized PDDs and profiles agreed within ± 1 %. In the presence of the magnetic field, PDDs rise more quickly reducing the depth of maximum dose. Near the beam exit point in the phantom a hot spot is created due to the electron return effect. This effect is more pronounced for the larger field sizes. Profiles selected parallel to the external field show no effect, however, the ones selected perpendicular to the direction of the applied magnetic field are shifted towards the direction of the Lorentz force applied by the magnetic field on the secondary electrons. It is observed that these profiles are not symmetric which indicates a lateral build up of the dose.

Conclusion:

There is a good general agreement between the PDDs/profiles calculated by both algorithms thus far. We are proceeding towards clinically relevant comparisons in a heterogeneous phantom for polyenergetic beams.

Funding for this work has been provided by Elekta.
SU‐E‐T‐204: Comparison of Absorbed‐Dose to Water in High‐Energy Photon Beams Based On Addendum AAPM TG‐51, IAEA TRS‐398, and JSMP 12
Authors: Kinoshita N , Oguchi H , Kita A , Yoshioka C , Sasamoto K , Nishimoto Y , Adachi T , Shioura H , Kimura H
Published: June 2015

Purpose:

Several clinical reference dosimetry protocols for absorbed‐dose to water have recently been published: The American Association of Physicists in Medicine (AAPM) published an Addendum to the AAPM's TG‐51 (Addendum TG‐51) in April 2014, and the Japan Society of Medical Physics (JSMP) published the Japan Society of Medical Physics 12 (JSMP12), a clinical reference dosimetry protocol, in September 2012. This investigation compared and evaluated the absorbed‐dose to water of high‐energy photon beams according to Addendum TG‐51, International Atomic Energy Agency Technical Report Series No. 398 (TRS‐398), and JSMP12.

Methods:

Differences in the respective beam quality conversion factors with Addendum TG‐51, TRS‐398, and JSMP12 were analyzed and the absorbed‐dose to water using 6‐ and 10‐MV photon beams was measured according to the protocols recommended in Addendum TG‐51, TRS‐398, and JSMP12. The measurements were conducted using two Farmer‐type ionization chambers, Exradin A12 and PTW 30013.

Results:

The beam quality conversion factors for both the 6‐ and 10‐MV photon beams with Addendum TG‐51 were within 0.6%, in agreement with the beam quality conversion factors with TRS‐398 and JSMP12. The Exradin A12 provided an absorbed‐dose to water ratio from 1.003 to 1.006 with TRS‐398 / Addendum TG‐51 and from 1.004 to 1.005 with JSMP 12 / Addendum TG‐51, whereas the PTW 30013 provided a ratio of 1.001 with TRS‐398 / Addendum TG‐51 and a range from 0.997 to 0.999 with JSMP 12 / Addendum TG‐51.

Conclusion:

Despite differences in the beam quality conversion factor, no major differences were seen in the absorbed‐dose to water with Addendum TG‐51, TRS‐398, and JSMP12. However, Addendum TG‐51 provides the most recent data for beam quality conversion factors based on Monte Carlo simulation and greater detail for the measurement protocol. Therefore, the absorbed‐dose to water measured with Addendum TG‐51 is an estimate with less uncertainty.
SU‐E‐T‐209: Comparison of Plan Quality Between Arm Avoidance (AA) Vs. Non Arm Avoidance VMAT Planning Techniques for Breast Cancer Patients with Bilateral Implant Reconstructions Receiving Postmastectomy Radiation
Authors: Kuo L , Ballangrud A , Ho A , Mechalakos J , Li G , Hong L
Published: June 2015

Purpose:

Breast cancer patients with bilateral implant reconstructions who require postmastectomy radiotherapy can pose unique treatment planning challenges. The use of VMAT may provide advantages over conventional tangent or multi‐beam IMRT techniques. Moreover, daily setup uncertainly of the arm position, however, could have significant impact on accurate dose delivery. This study compares the plan qualities between non‐AA and AA VMAT techniques.

Methods:

Three breast cancer patients receiving left chest wall and regional nodal irradiation with bilateral implant reconstructions were studied. PTV included chest wall and IMNs (PTV‐CW), and supraclavicular and axillary lymph nodes (PTV‐SCV). For each patient, one non‐AA VMAT plan (VMAT‐S) with 4 partial arcs encompassing the ipsilateral arm and three AA VMAT plans where no arcs were entering or existing through the ipsilateral arm were generated. VMAT‐AA1 uses 2 arcs for PTV‐CW and 2 arcs for PTV‐SCV. VMAT‐AA2 used two static fields for PTV‐SCV with 2 arcs for PTV‐CW. VMAT‐AA3 used 2 narrow arcs for PTV‐CW and 2 long arcs for all PTVs. Prescription dose (PD) was 50 Gy (25 fractions). All plans were normalized to have 95% of PD to 95 % of PTV. PTV dose inhomogeneity and dose to the heart, left lung, right thyroid dose and left humerus were evaluated.

Results:

For VMAT‐S, VMAT‐AA1, VMAT‐AA2 and VMAT‐AA3, respectively, the average and standard deviation (in Gy unless specified otherwise) of PTV D05 are 54.7±0.9, 55.9±0.4, 56.7±0.7 and 55.7±0.4; mean Heart dose: 7.1±0.7, 7.2±0.8, 7.3±0.9 and 6.9±1.0; left lung V20Gy (in %): 28.1±1.0, 28.8+2.2, 32.2±4.1 and 27.8±2.0; mean right thyroid dose: 8.1±0.6, 5.1±2.1, 2.1±0.4 and 5.0±2.0; mean left humerus dose: 20.0±4.4,15.6±4.4, 15.2±8.2 and 15.3±4.6.

Conclusion:

AA VMAT can produce acceptable clinical plans while eliminating dosimetric impact related to arm setup uncertainty. These data require validation in larger planning studies prior to routine clinical implantation.
SU‐E‐T‐219: Comprehensive Validation of the Electron Monte Carlo Dose Calculation Algorithm in RayStation Treatment Planning System for An Elekta Linear Accelerator with AgilityTM Treatment Head
Authors: Wang Yi , Park Yang‐Kyun , Doppke Karen P.
Published: June 2015

Purpose:

This study evaluated the performance of the electron Monte Carlo dose calculation algorithm in RayStation v4.0 for an Elekta machine with Agility™ treatment head.

Methods:

The machine has five electron energies (6–8 MeV) and five applicators (6×6 to 25×25 cm 2). The dose (cGy/MU at dmax), depth dose and profiles were measured in water using an electron diode at 100 cm SSD for nine square fields ≥2×2 cm2 and four complex fields at normal incidence, and a 14×14 cm2 field at 15° and 30° incidence. The dose was also measured for three square fields ≥4×4 cm2 at 98, 105 and 110 cm SSD. Using selected energies, the EBT3 radiochromic film was used for dose measurements in slab‐shaped inhomogeneous phantoms and a breast phantom with surface curvature. The measured and calculated doses were analyzed using a gamma criterion of 3%/3 mm.

Results:

The calculated and measured doses varied by <3% for 116 of the 120 points, and <5% for the 4×4 cm2 field at 110 cm SSD at 9–18 MeV. The gamma analysis comparing the 105 pairs of in‐water isodoses passed by >98.1%. The planar doses measured from films placed at 0.5 cm below a lung/tissue layer (12 MeV) and 1.0 cm below a bone/air layer (15 MeV) showed excellent agreement with calculations, with gamma passing by 99.9% and 98.5%, respectively. At the breast‐tissue interface, the gamma passing rate is >98.8% at 12–18 MeV. The film results directly validated the accuracy of MU calculation and spatial dose distribution in presence of tissue inhomogeneity and surface curvature ‐ situations challenging for simpler pencil‐beam algorithms.

Conclusion:

The electron Monte Carlo algorithm in RayStation v4.0 is fully validated for clinical use for the Elekta Agility™ machine. The comprehensive validation included small fields, complex fields, oblique beams, extended distance, tissue inhomogeneity and surface curvature.
SU‐E‐T‐220: Computational Accuracy of Adaptive Convolution (AC) and Collapsed Cone Convolution (CCC) Algorithms in the Presence of Air Gaps
Authors: Oyewale S , Pokharel S , Rana S
Published: June 2015

Purpose:

To compare the percentage depth dose (PDD) computational accuracy of Adaptive Convolution (AC) and Collapsed Cone Convolution (CCC) algorithms in the presence of air gaps.

Methods:

A 30×30×30 cm3 solid water phantom with two 5cm air gaps was scanned with a CT simulator unit and exported into the Phillips Pinnacle™ treatment planning system. PDDs were computed using the AC and CCC algorithms. Photon energy of 6 MV was used with field sizes of 3×3 cm2, 5×5 cm2, 10×10 cm2, 15×15 cm2, and 20×20 cm2. Ionization chamber readings were taken at different depths in water for all the field sizes. The percentage differences in the PDDs were computed with normalization to the depth of maximum dose (dmax). The calculated PDDs were then compared with measured PDDs.

Results:

In the first buildup region, both algorithms overpredicted the dose for all field sizes and under‐predicted for all other subsequent buildup regions. After dmax in the three water media, AC under‐predicted the dose for field sizes 3×3 and 5×5 cm2 and overpredicted for larger field sizes, whereas CCC under‐predicted for all field sizes. Upon traversing the first air gap, AC showed maximum differences of –3.9%, −1.4%, 2.0%, 2.5%, 2.9% and CCC had maximum differences of −3.9%, −3.0%,–3.1%, −2.7%, −1.8% for field sizes 3×3, 5×5, 10×10, 15×15, and 20×20 cm2 respectively.

Conclusion:

The effect of air gaps causes a significant difference in the PDDs computed by both the AC and CCC algorithms in secondary build‐up regions. AC computed larger values for the PDDs except at smaller field sizes. For CCC, the size of the errors in prediction of the PDDs has an inverse relationship with respect to field size. These effects should be considered in treatment planning where significant air gaps are encountered.
SU‐E‐T‐221: Computational Evaluation of Proton Induced Gain in a Portable Faraday Cup
Authors: Marshall S , Hodgdon A , Currier B
Published: June 2015

Purpose:

The design of a new Portable Faraday Cup (PFC) used to calibrate proton accelerators was evaluated for energies between 50 and 220 MeV. Monte Carlo simulations performed in Geant4–10.0 were used to evaluate experimental results and reduce the relative detector error for this vacuum‐less and low mass system, and invalidate current MCNP releases.

Methods:

The detector construction consisted of a copper conductor coated with an insulator and grounded with silver. Monte Carlo calculations in Geant4 were used to determine the net charge per proton input (gain) as a function of insulator thickness and beam energy. Kapton was chosen as the insulating material and was designed to capture backscattered electrons. Charge displacement from/into Kapton was assumed to follow a linear proportionality to the origin/terminus depth toward the outer ground layer. Kapton thicknesses ranged from 0 to 200 microns, proton energies were set to match empirical studies ranging from 70 to 250 MeV. Each setup was averaged over 1 million events using the FTFP_BERT 2.0 physics list.

Results:

With increasing proton energy, the gain of Cu+KA gradually converges to the limit of pure copper, with relative error between 1.52% and 0.72%. The Ag layer created a more diverging behavior, accelerating the flux of negative charge into the device and increasing relative error when compared to pure copper from 1.21% to 1.63%.

Conclusion:

Gain vs. beam energy signatures were acquired for each device. Further analysis reveals proportionality between insulator thickness and measured gain, albeit an inverse proportionality between beam energy and in‐flux of electrons. Increased silver grounding layer thickness also decreases gain, though the relative error expands with beam energy, contrary to the Kapton layer.
SU‐E‐T‐222: Computational Optimization of Monte Carlo Simulation On 4D Treatment Planning Using the Cloud Computing Technology
Authors: Chow J
Published: June 2015

Purpose:

This study evaluated the efficiency of 4D lung radiation treatment planning using Monte Carlo simulation on the cloud. The EGSnrc Monte Carlo code was used in dose calculation on the 4D‐CT image set.

Methods:

4D lung radiation treatment plan was created by the DOSCTP linked to the cloud, based on the Amazon elastic compute cloud platform. Dose calculation was carried out by Monte Carlo simulation on the 4D‐CT image set on the cloud, and results were sent to the FFD4D image deformation program for dose reconstruction. The dependence of computing time for treatment plan on the number of compute node was optimized with variations of the number of CT image set in the breathing cycle and dose reconstruction time of the FFD4D.

Results:

It is found that the dependence of computing time on the number of compute node was affected by the diminishing return of the number of node used in Monte Carlo simulation. Moreover, the performance of the 4D treatment planning could be optimized by using smaller than 10 compute nodes on the cloud. The effects of the number of image set and dose reconstruction time on the dependence of computing time on the number of node were not significant, as more than 15 compute nodes were used in Monte Carlo simulations.

Conclusion:

The issue of long computing time in 4D treatment plan, requiring Monte Carlo dose calculations in all CT image sets in the breathing cycle, can be solved using the cloud computing technology. It is concluded that the optimized number of compute node selected in simulation should be between 5 and 15, as the dependence of computing time on the number of node is significant.
SU‐E‐T‐229: Craniospinal Radiotherapy Planning with VMAT, Two First Years Experience
Authors: Lliso F , Carmona V , Gimeno J , Candela‐Juan C , Bautista J , Richart J , Perez‐Calatayud J
Published: June 2015

Purpose:

To describe how we moved to VMAT in the craniospinal radiotherapy planning process, the actual procedure details, and the results for the patients treated.

Methods:

Twelve patients underwent craniospinal irradiation with the new procedure, based on the paper by Lee et al. (IJROBP 82, 2012), with some additional modifications. Patients were treated in supine position in Varian Clinac iX linacs with 6 MV RapidArc; prescription doses ranged from 23.4 to 40 Gy (13 to 20 fractions); depending on the PTV length, 2 or 3 isocenters were used, all coordinates being equal except the longitudinal one, setting a few centimeter‐long overlapping region; 2 arcs (RA) sharing isocentre for the cranial region, RA1 encompassing cranium and superior spinal region, and RA2 intended to improve conformity, only for cranium; for spine, 1 or 2 isocenters were employed; optimization was performed with Eclipse (V 13.0) using AAA algorithm, establishing sets of optimization parameters to give high conformity while sparing OAR. In pediatric patients, homogeneous irradiation of the vertebrae was also required.Conformity (CI) and heterogeneity (HI) indices (same as Lee et al.), and mean and maximum doses for OAR were calculated. Several pre‐treatment verification methods were used: Octavius4D (PTW) for each isocentre, point dose at the junction region, Portal Dosimetry (when possible), and independent MU verification software (Diamond, PTW).

Results:

CI median value was 1.02 (0.99–1.07) and HI, 1.07 (1.06–1.09); a great reduction was observed for CI and OAR mean doses with respect to Lee et al. data; median maximum eye lens dose was 7.3 Gy (4.0–12.0); mean LungV20Gy was 1.9%; in children, vertebrae were homogeneously irradiated (D95%=20.8 Gy, Dmean= 23.2 Gy).All pre‐treatment verifications were found within our action levels except for Portal Dosimetry.

Conclusion:

A RapidArc planning process for craniospinal axis irradiation has been implemented with significant advantages on conformity, homogeneity, feasibility and efficiency. and increase brain tissue sparing. Variations in volume decrease may be related to shape or location of the tumor.
SU‐E‐T‐236: Deconvolution of the Total Nuclear Cross‐Sections of Therapeutic Protons and the Characterization of the Reaction Channels
Authors: Ulmer W.
Published: June 2015

Purpose:

The knowledge of the total nuclear cross‐section Qtot(E) of therapeutic protons Qtot(E) provides important information in advanced radiotherapy with protons, such as the decrease of fluence of primary protons, the release of secondary particles (neutrons, protons, deuterons, etc.), and the production of nuclear fragments (heavy recoils), which usually undergo β+/− decay by emission of γ‐quanta. Therefore determination of Qtot(E) is an important tool for sophisticated calculation algorithms of dose distributions. This cross‐section can be determined by a linear combination of shifted Gaussian kernels and an error‐function. The resonances resulting from deconvolutions in the energy space can be associated with typical nuclear reactions.

Methods:

The described method of the determination of Qtot(E) results from an extension of the Breit‐Wigner formula and a rather extended version of the nuclear shell theory to include nuclear correlation effects, clusters and highly excited/virtually excited nuclear states. The elastic energy transfer of protons to nucleons (the quantum numbers of the target nucleus remain constant) can be removed by the mentioned deconvolution.

Results:

The deconvolution of the term related to the error‐function of the type cerf*er((E‐ETh)/σerf] is the main contribution to obtain various nuclear reactions as resonances, since the elastic part of energy transfer is removed. The nuclear products of various elements of therapeutic interest like oxygen, calcium are classified and calculated.

Conclusions:

The release of neutrons is completely underrated, in particular, for low‐energy protons. The transport of seconary particles, e.g. cluster formation by deuterium, tritium and α‐particles, show an essential contribution to secondary particles, and the heavy recoils, which create γ‐quanta by decay reactions, lead to broadening of the scatter profiles. These contributions cannot be accounted for by one single Gaussian kernel for the description of lateral scatter.
SU‐E‐T‐244: Designing Low‐Z Targets To Enhance Surface Dose: A Monte Carlo Simulation
Authors: Kelly R , Robar J , Parsons D
Published: June 2015

Purpose:

Recent developments in The Varian Truebeam linac platform allows for the introduction of low‐Z targets into the beam line for the imaging purposes. We have proposed using a low‐Z target for radiation therapy purposes to enhance the surface dose during radiation treatment. The target arm of the Varian Truebeam accelerator consists of multiple targets with are linearly translated into the beam line. We have designed two Low‐Z targets made of carbon: 1) a step target consisting of three steps of 15%, 30% and 60% CSDA range for 2.5 MeV electrons Figure 1a; 2) and a ramp target, an incline plane 2cm long with thicknesses ranging from 0% to 60% CSDA range, Figure 1b. The purpose of this work will determine the spectral characteristics of these target designs and determine if they have practical clinical applications for enhancing surface dose.

Methods:

To calculate the spectral characteristics of these targets, a standard Monte Carlo model of a Varian Clinac accelerator was used. Simulations were performed with a carbon step target, and a carbon ramp target, located at the same position as the electron foil in the rotating carousel. Simulations were carried out using a 2.5 MeV electron beam.

Results:

The step target design produced spectral characteristics which were similar to spectral model using a single disk target of the same thickness. The ramp target provides a means to have positional variation of the spectral components of the beam, however, the electron component as 60% CSDA us much broader than the step target.

Conclusion:

The carbon step‐target provides a spectral distribution which is similar to a carbon disk of comparable thickness. The spectral distribution from the ramp‐target can be modified as a function of position to provide a wide range of low energy electrons for surface dose enhancement.
SU‐E‐T‐323: Dosimetric Evaluation of Small Fields for SBRT Treatment
Authors: Gupta R , Eldib A , Wang B , Ma C , Li J
Published: June 2015

Purpose:

Stereotactic body radiation therapy (SBRT) is commonly employed to treat small targets for effective tumor control with radiation beams of small field sizes. The goal of this work was to evaluate dosimetrically a treatment planning system (TPS) by comparing the calculated dose for SBRT treatment with ion‐chamber measurements.

Methods:

3D images of a solid‐water phantom with a pinpoint ion‐chamber (0.015cm3) inside were acquired with a CT scanner. Active volume of the ion‐chamber was delineated on CT images. Targets with a diameter of 1.5cm, 2cm, 3cm, 4cm and 5cm were drawn around the chamber. 3DCRT plans were generated for each target size with centrally opened 6MV beams and off‐axis beams by changing the isocenter location, respectively, using a TPS with the Analytical Anisotropic Algorithm. A 21iX linear accelerator was employed for plan delivery. The measured and calculated doses were compared. To evaluate the dose calculations in heterogeneity for small fields SBRT treatment, similar plans were also generated and delivered on a heterogeneous thoracic phantom for 5 different size targets in the lung.

Results:

Dose comparisons between measurements and calculations showed 5.2%, 1.88%, 1.34%, 1.01% and 0.85% difference for SBRT plans with small central axis beams and 0.96%, 0.15%, 0.58%, 0.22% and 0.77% difference for plans with off‐axis beams for five different size targets. For the thoracic phantom, the differences on dose between measurements and calculations are bigger, which are 8%, 5.9%, 4.5%, 3.9% and 4.5%, respectively.

Conclusion:

Dose verification for small fields used in the SBRT treatment has been performed based on ion‐chamber measurements in both homogenous and heterogeneous phantoms. More than a 5% difference has been observed in the heterogeneous phantom, especially for very small fields. To meet the ICRU recommendation on a dose difference of no more than 5%, some corrections on the commissioning parameters of the TPS are needed.
SU‐E‐T‐336: Dosimetric Properties of a New Solid Water High Equivalency Phantom for High‐Energy Photon Beams
Authors: Araki F , Ohno T , Onitsuka R , Shimohigashi Y
Published: June 2015

Purpose:

To investigate dosimetric properties in high‐energy photon beams for a Solid Water High Equivalency (SWHE, SW557) phantom (Gammex) which was newly developed as water mimicking material.

Methods:

The mass density of SWHE and SWHE/water electron density ratio are 1.032 g/cm3 and 1.005 according to the manufacturer information, respectively. SWHE is more water equivalent material in physical characteristics and uniformity than conventional SW457. This study calculated the relative ionization ratio of water and SWHE as a function of depth from the cavity dose in PTW30013 and Exradin A19 Farmer‐type ionization chambers using Monte Caro simulations. The simulation was performed with a 10 × 10 cm2 field at SAD of 100 cm for 4, 6, 10, 15, and 18 MV photons. The ionization ratio was also measured with the PTW30013 chamber for 6 and 15 MV photons. In addition, the overall perturbation factor of both chambers was calculated for both phantoms.

Results:

The relative ionization ratio curves for water and SWHE was in good agreement for all photon energies. The ionization ratio of water/SWHE for both chambers was 0.999–1.002, 0.999–1.002, 1.001–1.004, 1.004–1.007, and 1.006–1.010 at depths of over the buildup region for 4, 6, 10, 15, and 18 MV photons, respectively. The ionization ratio of water/SWHE increased up to 1% with increasing the photon energy. The measured ionization ratio of water/SWHE for 6 and 15 MV photons agreed well with calculated values. The overall perturbation factor for both chambers was 0.983–0.988 and 0.978–0.983 for water and SWHE, respectively, in a range from 4 MV to 18 MV.

Conclusion:

The depth scaling factor of water/SWHE was equal to unity for all photon energies. The ionization ratio of water/SWHE at a reference depth was equal to unity for 4 and 6 MV and larger up to 0.7% than unity for 18 MV.
SU‐E‐T‐337: Dosimetric Study of TMI Using Helical Tomotherapy
Authors: Phurailatpam R , Swamidas J , Sastri J , Josi K , Mathankar M , Paul S , Sawant M , Moundekar P
Published: June 2015

Purpose:

The purpose of this study is to evaluate the dosimtry of TMI using Helical Tomotherapy (HT).

Methods:

Whole body CT data sets of 4 patients (median age : range:12–37 years) with 5mm slice thickness were used for planning in HT (TPS version 4.2.3). The contouring of the target and organ at risks (OAR) were delineated ( Oncentra Master Plan v 4.1). Two plans were generated using 5cm and 2.5 cm field widths.The modulation factor and pitch was 3 and 0.3 respectively. Dose to PTV, OARs and the dose homogeneity were evaluated. The doses obtained were compared with the existimg literature. Dose delivery verification was carried out by point dose and 2D array measurements with ion chamber and Arc check dosimetry (Sun NuclearTM) system repectively. The prescribed dose was 14.4 Gy in 8 fractions.

Results:

The mean PTV volume was 7341.28cc (sd=2353) The dose homogeneity index of PTV was 12.03(sd=2.98) for 2.5cm_FW and 14.61 (sd=1.33) for 5cm_FW.The conformation number for 2.5 and 5 cm plans are 0.6328(sd=0.09) and 0.5915 (sd=0.0376) respectively. The mean dose(Gy) to the OARs were as follows for 2.5cm_FW : eyes, lens, lungs, kidneys, heart, liver,thyroid and testes for are 4.12,1.9,6.61,4.04,4.85,6.06,7.17 and 1.27. The mean dose(Gy) to the OARs were as follows for 5cm_FW :eyes, lens, lungs, kidneys, heart, liver,thyroid and testes for are 4.45,3.14,6.79,4.02,5.01,6.01,10.8 and 1.33. The mean variation of the point dose as compared to the expected dose was within 2% and the gamma analysis was at 91%.

Conclusion:

It was concluded that 5cm field width plans produces optimal dose volume parameters with deliverable treatment time. From this initial dissymmetric study, it was concluded that the treatment planning and the dose delivery verification was feasible considering the complexity of the TMI.
SU‐E‐T‐338: Dosimetric Study of Volumetric Modulated Arc Therapy (VMAT) and Intensity Modulated Radiation Therapy (IMRT) for Stereotactic Body Radiation Therapy (SBRT) in Early Stage Lung Cancer
Authors: Ahmad I , Yah R , Quinn K , Seebach A , Wang H
Published: June 2015

Purpose:

This study evaluates the dosimetric differences using volumetric modulated arc therapy (VMAT) in patients previously treated with intensity modulated radiation therapy IMRT for stereotactic body radiotherapy (SBRT) in early stage lung cancer.

Methods:

We evaluated 9 consecutive medically inoperable lung cancer patients at the start of the SBRT program who were treated with IMRT from November 2010 to October 2011. These patients were treated using 6 MV energy. The 9 cases were then re‐planned with VMAT performed with arc therapy using 6 MV flattening filter free (FFF) energy with the same organs at risk (OARS) constraints. Data collected for the treatment plans included target coverage, beam on time, dose to OARS and gamma pass rate.

Results:

Five patients were T1N0 and four patients were T2N0 with all tumors less than 5 cm. The average GTV was 13.02 cm3 (0.83–40.87) and average PTV was 44.65 cm3 (14.06–118.08). The IMRT plans had a mean of 7.2 angles (6–9) and 5.4 minutes (3.6–11.1) per plan. The VMAT plans had a mean of 2.8 arcs (2–3) and 4.0 minutes (2.2–6.0) per plan. VMAT had slightly more target coverage than IMRT with average increase in D95 of 2.68% (1.24–5.73) and D99 of 3.65% (0.88–8.77). VMAT produced lower doses to all OARs. The largest reductions were in maximum doses to the spinal cord with an average reduction of 24.1%, esophagus with an average reduction of 22.1%, and lung with an average reduction in the V20 of 16.3% The mean gamma pass rate was 99.8% (99.2–100) at 3 mm and 3% for VMAT with comparable values for IMRT.

Conclusion:

These findings suggest that using VMAT for SBRT in early stage lung cancer is superior to IMRT in terms of dose coverage, OAR dose and a lower treatment delivery time with a similar gamma pass rate.