bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐48: Automated Quality Assurance for XML Controlled Linacs
Authors: Valdes G , Morin O , Pouliot J , Chuang C
Published: July 2014

Purpose:

To automate routine imaging QA procedures so that complying with TG 142 and TG 179 can be efficient and reliable.

Methods:

Two QA tests for a True Beam Linac were automatized. A Winston Lutz test as described by Lutz et al1 using the Winston Lutz test kit from BrainLab, Germany and a CBCT Image Quality test as described in TG 179 using the EMMA phantom, Siemens Medical Physics, Germany were performed in our True Beam. For each QA procedure tested, a 3 step paradigm was used. First, the data was automatically acquired using True Beam Developer Mode and XML scripting. Second, the data acquired in the first step was automatically processed using in‐home grown Matlab GUIs. Third, Machine Learning algorithms were used to automatically classify the processed data and reports generated.

Results:

The Winston Luzt test could be performed by an experienced medical physicist in 29.0 ± 8.0 min. The same test, if automated using our paradigm, could be performed in 3.0 ± 0.1 min. In the same lieu, time could be substantially saved for image quality tests. In this case, the amount of time saved will depend on the phantoms used and the initial localization method. Additionally, machine learning algorithms could automatically identify the roots of the problems if any and possibly help reduce machine down time.

Conclusion:

Modern linear accelerators are equipped with advanced 2D and 3D imaging that are used for patient alignment substantially improving IGRT protocols. However, this extra complexity exponentially increases the number of QA tests needed. Using the new paradigm described above, not only bare minimum but best practice QA programs could be implemented with the same manpower.

This work is supported by Varian, Palo Alto, CA
SU‐E‐T‐52: Beam Data Comparison for 20 Linear Accelerators in One Network
Authors: LoSasso T , Lim S , Tang G , Chan M , Li J , Obcemea C , Song Y , Ma R , Yang G , Xiong W , Huang D , Burman C , Mechalakos J , Hunt M
Published: July 2014

Purpose:

To compare photon beam data for the 20 Varian linear accelerators (TrueBeam, iX, and EX models) in use at five centers in the same network with the intent to model with one set of beam data in Eclipsec.

Methods:

Varian linear accelerators, TrueBeam (3), 21 EX, iX, and Trilogy (14), and 6 EX (3), installed between 1999 and 2014 have their 6 MV and 15 MV x‐ray beams reevaluated. Full commissioning, including output factors (St), percent depth doses (PDD), and off‐axis profiles, was recently performed for a TrueBeam with a cc04 ion chamber in an IBA Blue phantom. Similarly, a subset of beam data for each of the other accelerators was measured recently as follows: for 3×3, 10×10, and 30×30 cm2 field sizes, flatness and penumbra (80–20%) were measured at dmax and 10 cm depths, PDD were measured at 10 and 20 cm depths, and St were measured at 5 cm depth. Measurement results for all machines were compared.

Results:

For 15 high‐energy (6 and 15 MV) and 3 low‐energy machines (6MV only): 1) PDD agreed within 1.4% at 10 and 20 cm depths; 2) penumbra agreed within 1.0 mm at dmax and 10 cm depths; 3) flatness was within 1.3% at dmax and 10 cm depths; and 4) with exception of the three low energy machines, output factors were within 1.1% and 0.5% for 3×3 and 30×30 cm2, respectively. Measurement uncertainty, not quantified here, accounts for some of these differences.

Conclusion:

Measured beam data from 15 high‐energy Varian linacs are consistent enough that they can be classified using one beam data set in Eclipse. Two additional high‐energy machines are removed from this group until their data are further confirmed. Three low‐energy machines will be in a separate class based upon differences in output factors (St).
SU‐E‐T‐53: Benchmarking a Monte Carlo Model for Patient Plane Leakage Calculations of Low Energy 6MV Unique Linacs
Authors: Constantin M , Sawkey D , Johnsen S , Hsu H
Published: July 2014

Purpose:

To validate the physics parameters of a Monte Carlo model for patient plane leakage calculations on the 6MV Unique linac by comparing the simulations against IEC patient plane leakage measurements. The benchmarked model can further be used for shielding design optimization, to predict leakage in the proximity of intended treatment fields, reduce the system weight and cost, and improve components reliability.

Methods:

The treatment head geometry of the Unique linac was simulated in Geant4 (v9.4.p02 with “Opt3” standard electromagnetic physics list) based on CAD drawings of all collimation and shielding components projected from the target to the area within 2m from isocenter. A 4×4m2 scorer was inserted 1m from the target in the patient plane and multiple phase space files were recorded by performing a 40‐node computing cluster simulation on the EC2 cloud. The photon energy fluence was calculated relative to the value at isocenter for a 10×10cm2 field using 10×10mm2 bins. Tungsten blocks were parked accordingly to represent MLC120. The secondary particle contamination to patient plane was eliminated by “killing” those particles prior to the primary collimator entrance using a “kill‐plane”, which represented the upper head shielding components not being modeled. Both IEC patient‐plane leakage and X/Y‐jaws transmission were simulated.

Results:

The contribution of photons to energy fluence was 0.064% on average, in excellent agreement with the experimental data available at 0.5, 1.0, and 1.5m from isocenter, characterized by an average leakage of 0.045% and a maximum leakage of 0.085%. X‐ and Y‐jaws transmissions of 0.43% and 0.44% were found in good agreement with measurements of 0.48% and 0.43%, respectively.

Conclusion:

A Geant4 model based on energy fluence calculations for the 6MV Unique linac was created and validated using IEC patient plane leakage measurements. The “kill‐plane” has effectively eliminated electron contamination to patient plane in these simulations.
SU‐E‐T‐243: MonteCarlo Simulation Study of Polymer and Radiochromic Gel for Three‐Dimensional Proton Dose Distribution
Authors: Park M , Jung H , Kim G , Ji Y , Kim K , Park S
Published: July 2014

Purpose:

To estimate the three dimensional dose distributions in a polymer gel and a radiochromic gel by comparing with the virtual water phantom exposed to proton beams by applying Monte Carlo simulation.

Methods:

The polymer gel dosimeter is the compositeness material of gelatin, methacrylic acid, hydroquinone, tetrakis, and distilled water. The radiochromic gel is PRESAGE product. The densities of polymer and radiochromic gel were 1.040 and 1.0005 g/cm3, respectively. The shape of water phantom was a hexahedron with the size of 13 × 13 × 15 cm3. The proton beam energies of 72 and 116 MeV were used in the simulation. Proton beam was directed to the top of the phantom with Z‐axis and the shape of beam was quadrangle with 10 × 10 cm2 dimension. The Percent depth dose and the dose distribution were evaluated for estimating the dose distribution of proton particle in two gel dosimeters, and compared with the virtual water phantom.

Results:

The Bragg‐peak for proton particles in two gel dosimeters was similar to the virtual water phantom. Bragg‐peak regions of polymer gel, radiochromic gel, and virtual water phantom were represented in the identical region (4.3 cm) for 72 MeV proton beam. For 116 MeV proton beam, the Bragg‐peak regions of polymer gel, radiochromic gel, and virtual water phantom were represented in 9.9, 9.9 and 9.7 cm, respectively. The dose distribution of proton particles in polymer gel, radiochromic gel, and virtual water phantom was approximately identical in the case of 72 and 116 MeV energies. The errors for the simulation were under 10%.

Conclusion:

This work indicates the evaluation of three dimensional dose distributions by exposing proton particles to polymer and radiochromic gel dosimeter by comparing with the water phantom. The polymer gel and the radiochromic gel dosimeter show similar dose distributions for the proton beams.
SU‐E‐T‐250: New IMRT Sequencing Strategy: Towards Intra‐Fraction Plan Adaptation for the MR‐Linac
Authors: Kontaxis C , Bol G , Lagendijk J , Raaymakers B
Published: July 2014

Purpose:

To develop a new sequencer for IMRT planning that during treatment makes the inclusion of external factors possible and by doing so accounts for intra‐fraction anatomy changes. Given a real‐time imaging modality that will provide the updated patient anatomy during delivery, this sequencer is able to take these changes into account during the calculation of subsequent segments.

Methods:

Pencil beams are generated for each beam angle of the treatment and a fluence optimization is performed. The pencil beams, together with the patient anatomy and the above optimal fluence form the input of our algorithm. During each iteration the following steps are performed: A fluence optimization is done and each beam's fluence is then split to discrete intensity levels. Deliverable segments are calculated for each one of these. Each segment's area multiplied by its intensity describes its efficiency. The most efficient segment among all beams is then chosen to deliver a part of the calculated fluence and the dose that will be delivered by this segment is calculated. This delivered dose is then subtracted from the remaining dose. This loop is repeated until 90% of the dose has been delivered and a final segment weight optimization is performed to reach full convergence.

Results:

This algorithm was tested in several prostate cases yielding results that meet all clinical constraints. Quality assurance was performed on Delta4 and film phantoms for one of these prostate cases and received clinical acceptance after passing both gamma analyses with the 3%/3mm criteria.

Conclusion:

A new sequencing algorithm was developed to facilitate the needs of intensity modulated treatment. The first results on static anatomy confirm that it can calculate clinical plans equivalent to those of the commercially available planning systems. We are now working towards 100% dose convergence which will allow us to handle anatomy deformations.

This work is financially supported by Elekta AB, Stockholm, Sweden.
SU‐E‐T‐251: Novel Multi‐Stage Stereotactic Radiosurgery Technique for Large Cerebral Arteriovenous Malformations Using the Gammaknife System
Authors: Ding C , Hrycushko B , Jiang S , Whitworth L , Timmerman R
Published: July 2014

Purpose:

To develop a multi‐stage stereotactic radiosurgery delivery technique for large intracranial arteriovenous malformations (AVM) using the Gammaknife treatment platform.

Methods:

Eleven patients having large (>15 cm3) cerebral AVMs were selected for this study. AVMs were contoured and divided into 3‐8 subtargets with volumes ranging from 3–7 cm3. Each subtarget is to be treated sequentially in 1–4 week intervals between stages. The prescription dose was 16–20 Gy depending on the target volume. Gammaknife plans were retrospectively generated to treat the entire AVM target with a simulated Extend frame system that can reposition patients within a 1mm accuracy. The coordinates of each shot from the initial plan were extracted based on the shot position within the Extend frame system. Shots were then grouped based on their relative position to individual subtarget contours to generate stage‐specific plans. The delivery time of each shot of a subtarget was corrected for decay of each stage to generate the same dose distribution as that of the original plan for the entire AVM. Conformality and dose‐volume analysis was performed to evaluate the PITV (ratio of prescription isodose volume to target volume), R50 (ratio of 50% isodose volume to target volume), and V12Gy (percentage of brain volume receiving 12Gy or greater).

Results:

The total accumulated dose for the multi‐staged treatments was shown to be equivalent to the initial plan of the entire AVM target. The Gammaknife plans resulted in an average of 95.8%±0.6 PTV coverage with a PITV of 1.06±0.07. The resulting V12Gy and R50 dose spillage values were 4.2%±2.0 and 3.2±0.4, respectively.

Conclusion:

With the Extend frame, the Gammaknife system can deliver a multi‐staged conformal dose to treat large AVMs. Target dose coverage and conformality as well as normal brain toxicity measures were shown to be similar compared to that of a single fraction treatment.
SU‐E‐T‐253: Open‐Source Automatic Software for Quantifying Biological Assays of Radiation Effects
Authors: Detappe A , Korideck H , Makrigiorgos G , Berbeco R
Published: July 2014

Purpose:

Clonogenic cell survival is a common assay for quantifying the effect of drugs and radiation. Manual counting of surviving colonies can take 30–90seconds per plate, a major limitation for large studies. Currently available automatic counting tools are not easily modified for radiation oncology research. Our goal is to provide an open‐source toolkit for precise, accurate and fast analysis of biological assays in radiation oncology.

Methods:

As an example analysis, we used HeLa cells incubated with gadolinium nanoparticles prior to irradiation. After treatment, the cells are grown for 14days to allow for colony formation. To analyze the colony growth, we capture images of each dish for archiving and automatic computer‐based analysis. A FujifilmX20 camera is placed at the top of a box setup, 20cm above the sample, which is backlit by a LED lamp placed at the bottom of the box. We use a Gaussian filter (width=1.3mm) and color threshold (19–255). The minimum size for a colony to be counted is 1mm. For this example, 20 dishes with a large range of colonies were analyzed. Each dish was counted 3 times manually by 3 different users and then compared to our counter.

Results:

Automatic counting of cell colonies takes an average of 7seconds, enabling the analysis process to be accelerated 4–12 times. The average precision of the automatic counter was 1.7%. The Student t‐test demonstrated the non‐significant differences between the two counting methods (p=0.64). The ICC demonstrated the reliability of each method with ICC>0.999 (automatic) and ICC=0.95 (manual).

Conclusion:

We developed an open‐source automatic toolkit for the analysis of biological assays in radiation oncology and demonstrated the accuracy, precision and effort savings for clonogenic cell survival quantification. This toolkit is currently being used in two laboratories for routine experimental analysis and will be made freely available on our departmental website.
SU‐E‐T‐270: Quality Control of Source Strength and Indexer Length in HDR Brachytherapy Using Sun Nuclear Mapcheck2
Authors: Morales J
Published: July 2014

Purpose:

The goal of this work was to evaluate Sun Nuclear MapCheck2 capability for quantitative determination of both HDR source strength and position. Predictive power of Mapcheck2 dose matrix, originated by a microSelectron_v2 source from 22mm distance, was investigated.

Methods:

A Mick MultiDoc phantom with the 1400mm indexer length mark aligned over MapCheck2 central detector plus two additional 5cm plastic slabs were used as a composite phantom. Dose readings were transformed by applying published source anisotropy corrections and experimentally established radial dose and relative sensitivity factors. Angular dependence was not considered. Only readings from diodes located 2cm around the central detector were evaluated. The reproducibility of a fit between transformed dose readings and the ratio of virtual source strength and the square of source‐detector distance was investigated. Four parameters were considered in the model: virtual source strength, lateral, longitudinal and vertical source positions. Final source strength calibration factor was calculated from the ratio of reference measurements and results from the fit.

Results:

Original lateral and longitudinal source position estimations had systematic errors of 0.39mm and 0.75mm. After subtracting these errors, both source positions were predicted with a standard deviation of 0.15mm. Results for vertical positions were reproducible with a standard deviation of 0.05mm. The difference between calculated and reference source strengths from 34 independent measurement setups had a standard deviation of 0.3%. The coefficient of determination for the linear regression between known indexer lengths and results from the fit in the range 1400mm ± 5mm was 0.985.

Conclusions:

ource strength can be estimated with MapCheck2 at appropriate accuracy levels for quality control. Verification of indexer length with present implementation is more accurate than visual alternatives. Results can be improved by designing a coupling catheter phantom and refining relative diode calibration. Diode angular dependence in MapCheck2 does not play significant role.
SU‐E‐T‐271: Quantitative Analysis of Correlations Between Patient Geometry and Dosimetric Variation for Prostate Cancer Cases Using PCA and Step‐Wise Regression
Authors: Song T , Folkerts M , Zhen H , Tian Z , Zhou L , Jia X , Jiang S , Gu X
Published: July 2014

Purpose:

To study the potential correlations between patient geometry information and corresponding plan dosimetric variation in terms of planning target volumes (PTVs) coverage and organs‐at‐risk (OARs) dose sparing for prostate cancer cases.

Methods:

We extracted dosimetric and geometrical data from twenty‐three clinically acceptable prostate treatment plans. Dosimetric data extracted from each patient was PTV dose‐volume historgram (DVH), and dose‐wall‐volume histograms (DWHs) for the bladder and rectum. Geometrical data extracted was the PTV volume, OAR volumes, and COP (closeness of OAR to PTV). COP is the weighted sum of the overlapping wall histogram (OWH). OWH is proposed to describe the complex spatial relationship between PTV and a hollow organ. Principal component analysis (PCA) was performed on the (inverted and downsampled) DVH and DWH data from all the patients. We then fit the patient geometry features to first 3 PCA scores using a step‐wise regression analysis. The fitting results in a mapping from plan geometry information to dosimetric features.

Results:

First 3 PCA modes were found corresponded to clinically relevant features, indicating a tradeoff between homogenous coverage of the PTV and higher OAR dose, higher average dose to the OARs and PTV, and bladder and rectum dose tradeoffs along the first, second and third principal component respectively. Step‐wise regression results show baldder surface volume and OAR COP more relevant to the 1st PCA modes score rather than other features with p‐value of 0.58 for bladder volume, 0.26 for bladder COP, 0.98 for rectum COP, and less than 0.025 for other features after t‐test.

Conclusion:

Quantitative correlations were established between patient geometry and corresponding plan dosimetric variation in terms of PTV coverage, trade‐offs between PTV coverage and OAR dose sparing and trade‐offs between different OAR dose sparing. Thus a new patient dosimetric variation tendency can be predicted and act as guidance for setting up planning goals.
SU‐E‐T‐274: Radiation Therapy with Very High‐Energy Electron (VHEE) Beams in the Presence of Metal Implants
Authors: Jensen C , Palma B , Qu B , Maxim P , Hardemark B , Hynning E , Loo B , Bazalova M
Published: July 2014

Purpose:

To evaluate the effect of metal implants on treatment plans for radiation therapy with very high‐energy electron (VHEE) beams.

Methods:

The DOSXYZnrc/BEAMnrc Monte Carlo (MC) codes were used to simulate 50–150MeV VHEE beam dose deposition and its effects on steel and titanium (Ti) heterogeneities in a water phantom. Heterogeneities of thicknesses ranging from 0.5cm to 2cm were placed at 10cm depth. MC was also used to calculate electron and photon spectra generated by the VHEE beams' interaction with metal heterogeneities. The original VMAT patient dose calculation was planned in Eclipse. Patient dose calculations with MC‐generated beamlets were planned using a Matlab GUI and research version of RayStation. VHEE MC treatment planning was performed on water‐only geometry and water with segmented prostheses (steel and Ti) geometries with 100MeV and 150MeV beams.

Results:

100MeV PDD 5cm behind steel/Ti heterogeneity was 51% less than in the water‐only phantom. For some cases, dose enhancement lateral to the borders of the phantom increased the dose by up to 22% in steel and 18% in Ti heterogeneities. The dose immediately behind steel heterogeneity decreased by an average of 6%, although for 150MeV, the steel heterogeneity created a 23% increase in dose directly behind it. The average dose immediately behind Ti heterogeneities increased 10%. The prostate VHEE plans resulted in mean dose decrease to the bowel (20%), bladder (7%), and the urethra (5%) compared to the 15MV VMAT plan. The average dose to the body with prosthetic implants was 5% higher than to the body without implants.

Conclusion:

Based on MC simulations, metallic implants introduce dose perturbations to VHEE beams from lateral scatter and backscatter. However, when performing clinical planning on a prostate case, the use of multiple beams and inverse planning still produces VHEE plans that are dosimetrically superior to photon VMAT plans.

BW Loo and P Maxim received research support from RaySearch laboratories; B Hardemark and E Hynning are employees of RaySearch.
SU‐E‐T‐278: Realization of Dose Verification Tool for IMRT Plan Based On DPM
Authors: Cai Jinfeng , LIN Hui , Cao Ruifen , Dai Yumei , Pei Xi , Zhang Jun , Hu Liqin ,   FDS Team
Published: July 2014

Purpose:

To build a Monte Carlo dose verification tool for IMRT Plan by implementing a irradiation source model into DPM code. Extend the ability of DPM to calculate any incident angles and irregular‐inhomogeneous fields.

Methods:

With the virtual source and the energy spectrum which unfolded from the accelerator measurement data,combined with optimized intensity maps to calculate the dose distribution of the irradiation irregular‐inhomogeneous field. The irradiation source model of accelerator was substituted by a grid‐based surface source. The contour and the intensity distribution of the surface source were optimized by ARTS (Accurate/Advanced Radiotherapy System) optimization module based on the tumor configuration. The weight of the emitter was decided by the grid intensity. The direction of the emitter was decided by the combination of the virtual source and the emitter emitting position. The photon energy spectrum unfolded from the accelerator measurement data was adjusted by compensating the contaminated electron source. For verification, measured data and realistic clinical IMRT plan were compared with DPM dose calculation.

Results:

The regular field was verified by comparing with the measured data. It was illustrated that the differences were acceptable (<2% inside the field, 2–3mm in the penumbra). The dose calculation of irregular field by DPM simulation was also compared with that of FSPB (Finite Size Pencil Beam) and the passing rate of gamma analysis was 95.1% for peripheral lung cancer. The regular field and the irregular rotational field were all within the range of permitting error. The computing time of regular fields were less than 2h, and the test of peripheral lung cancer was 160min. Through parallel processing, the adapted DPM could complete the calculation of IMRT plan within half an hour.

Conclusion:

The adapted parallelized DPM code with irradiation source model is faster than classic Monte Carlo codes. Its computational accuracy and speed satisfy the clinical requirement, and it is expectable to be a Monte Carlo dose verification tool for IMRT Plan.

Strategic Priority Research Program of the China Academy of Science(XDA03040000); National Natural Science Foundation of China (81101132)
SU‐E‐T‐295: Simultaneous Beam Sampling and Aperture Shape Optimization for Station Parameter Optimized Radiation Therapy (SPORT)
Authors: Zarepisheh M , Ye Y , Boyd S , Li R , Xing L
Published: July 2014

Purpose:

Station Parameter Optimized Radiation Therapy (SPORT) was recently proposed to fully utilize the technical capability of emerging digital LINACs, in which the station parameters of a delivery system, (such as aperture shape and weight, couch position/angle, gantry/collimator angle) are optimized altogether. SPORT promises to deliver unprecedented radiation dose distributions efficiently, yet there does not exist any optimization algorithm to implement it. The purpose of this work is to propose an optimization algorithm to simultaneously optimize the beam sampling and aperture shapes.

Methods:

We build a mathematical model whose variables are beam angles (including non‐coplanar and/or even nonisocentric beams) and aperture shapes. To solve the resulting large scale optimization problem, we devise an exact, convergent and fast optimization algorithm by integrating three advanced optimization techniques named column generation, gradient method, and pattern search. Column generation is used to find a good set of aperture shapes as an initial solution by adding apertures sequentially. Then we apply the gradient method to iteratively improve the current solution by reshaping the aperture shapes and updating the beam angles toward the gradient. Algorithm continues by pattern search method to explore the part of the search space that cannot be reached by the gradient method.

Results:

The proposed technique is applied to a series of patient cases and significantly improves the plan quality. In a head‐and‐neck case, for example, the left parotid gland mean‐dose, brainstem max‐dose, spinal cord max‐dose, and mandible mean‐dose are reduced by 10%, 7%, 24% and 12% respectively, compared to the conventional VMAT plan while maintaining the same PTV coverage.

Conclusion:

Combined use of column generation, gradient search and pattern search algorithms provide an effective way to optimize simultaneously the large collection of station parameters and significantly improves quality of resultant treatment plans as compared with conventional VMAT or IMRT treatments.
SU‐E‐T‐298: Small Field Total Scatter Factors Using a Commercial Scintillator Detector: Calibration Parameters Are Not Independent of Field Size
Authors: Jornet N , Carrasco de Fez P , Jordi O , Latorre‐Musoll A , Eudaldo T , Ruiz‐Martinez A , Ribas Morales M
Published: July 2014

Purpose:

To evaluate the accuracy in total scatter factor (Sc,p) determination for small fields using commercial plastic scintillator detector (PSD). The manufacturer's spectral discrimination method to subtract Cerenkov light from the signal is discussed.

Methods:

Sc,p for field sizes ranging from 0.5 to 10 cm were measured using PSD Exradin (Standard Imaging) connected to two channel electrometer measuring the signals in two different spectral regions to subtract the Cerenkov signal from the PSD signal. A Pinpoint ionisation chamber 31006 (PTW) and a non‐shielded semiconductor detector EFD (Scanditronix) were used for comparison. Measures were performed for a 6 MV X‐ray beam. The Sc,p are measured at 10 cm depth in water for a SSD=100 cm and normalized to a 10' 10 cm2 field size at the isocenter. All detectors were placed with their symmetry axis parallel to the beam axis.We followed the manufacturer's recommended calibration methodology to subtract the Cerenkov contribution to the signal as well as a modified method using smaller field sizes. The Sc,p calculated by using both calibration methodologies were compared.

Results:

Sc,p measured with the semiconductor and the PinPoint detectors agree, within 1.5%, for field sizes between 10' 10 and 1' 1 cm2. Sc,p measured with the PSD using the manufacturer's calibration methodology were systematically 4% higher than those measured with the semiconductor detector for field sizes smaller than 5' 5 cm2. By using a modified calibration methodology for smalls fields and keeping the manufacturer calibration methodology for fields larger than 5' 5cm2 field Sc,p matched semiconductor results within 2% field sizes larger than 1.5 cm.

Conclusion:

The calibration methodology proposed by the manufacturer is not appropriate for dose measurements in small fields. The calibration parameters are not independent of the incident radiation spectrum for this PSD. This work was partially financed by grant 2012 of Barcelona board of the AECC.
SU‐E‐T‐303: Spot Scanning Dose Delivery with Rapid Cycling Proton Beams From RCMS
Authors: Cheng C , Liu H , Lee S
Published: July 2014

Purpose:

A rapid cycling proton beam has several distinct characteristics superior to a slow extraction synchrotron: The beam energy and energy spread, beam intensity and spot size can be varied spot by spot. The feasibility of using a spot scanning beam from a rapidc‐ycling‐medical‐synchrotron (RCMS) at 10 Hz repetition frequency is investigated in this study for its application in proton therapy.

Methods:

The versatility of the beam is illustrated by two examples in water phantoms: (1) a cylindrical PTV irradiated by a single field and (2) a spherical PTV irradiated by two parallel opposed fields. A uniform dose distribution is to be delivered to the volumes. Geant4 Monte Carlo code is used to validate the dose distributions in each example.

Results:

Transverse algorithms are developed to produce uniform distributions in each transverseplane in the two examples with a cylindrical and a spherical PTV respectively. Longitudinally, different proton energies are used in successive transverse planes toproduce the SOBP required to cover the PTVs. In general, uniformity of dosedistribution within 3% is obtained for the cylinder and 3.5% for the sphere. The transversealgorithms requires only few hundred beam spots for each plane The algorithms may beapplied to larger volumes by increasing the intensity spot by spot for the same deliverytime of the same dose. The treatment time can be shorter than 1 minute for any fieldconfiguration and tumor shape.

Conclusion:

The unique beam characteristics of a spot scanning beam from a RCMS at 10 Hz repetitionfrequency are used to design transverse and longitudinal algorithms to produce uniformdistribution for any arbitrary shape and size of targets. The proposed spot scanning beam ismore versatile than existing spot scanning beams in proton therapy with better beamcontrol and lower neutron dose.

This work is supported in part by grants from the US Department of Energy under contract; DE‐FG02‐12ER41800 and the National Science Foundation NSF PHY‐1205431.
SU‐E‐T‐312: Test of the Generalized Tumor Dose (gTD) Model with An Independent Lung Tumor Dataset
Authors: Fontanella A , Robinson C , Zuniga A , Apte A , Thorstad W , Bradley J , Deasy J
Published: July 2014

Purpose:

We previously developed a novel approach to tumor response modeling which was inspired by the gEUD model of tumor cell kill under inhomogeneous dose profiles. The model assumes that the cell‐kill law is valid, but further adds a parameter analogous to the generalized equivalent uniform dose model to test the independence of response of tumor subvolumes. The purpose of this study was to test the resulting generalized tumor dose (gTD) model on an independent lung cancer subset.

Methods:

Niemierko's gEUD model of cell kill introduces a generalization term describing interactions among tumor sub‐volumes under non‐uniform dose distributions. This parameter effectively applies weights to sub‐volumes based off of tumor type‐specific sensitivities to variance in dose. We combine the gEUD with the cell‐kill based cEUD to form the “generalized tumor dose” (gTD) model, which is given by gTD=‐α−1*ln(Vt/Vref)‐ (α*a)−1*ln(Σi=1:subvolsM#subvols−1 *e (‐α*a*di)). This model was previously applied to lung and H&N data. Here, we apply the model to an independent lung dataset (N= 36).

Results:

We found that the model does not perform well for large tumors (volume > 70 cc.) However,. However, for tumors smaller than this volume, the model was well‐correlated with local control, with a normalized log‐likelihood value (log‐likelihood divided by the number of cases) of −0.604.

Conclusion:

The presented model continues to predict tumor response in this dataset, for tumors less than 70 cc. To date, no other TCP model has been validated on clinical datasets for tumors with varying volumes and dose distributions. More tests are needed to further refine and validate the model.
SU‐E‐T‐313: The Accuracy of the Acuros XB Advanced Dose Calculation Algorithm for IMRT Dose Distributions in Head and Neck
Authors: Araki F , Onizuka R , Ohno T , Tomiyama Y , Hioki K
Published: July 2014

Purpose:

To investigate the accuracy of the Acuros XB version 11 (AXB11) advanced dose calculation algorithm by comparing with Monte Caro (MC) calculations. The comparisons were performed with dose distributions for a virtual inhomogeneity phantom and intensity‐modulated radiotherapy (IMRT) in head and neck.

Methods:

Recently, AXB based on Linear Boltzmann Transport Equation has been installed in the Eclipse treatment planning system (Varian Medical Oncology System, USA). The dose calculation accuracy of AXB11 was tested by the EGSnrc‐MC calculations. In additions, AXB version 10 (AXB10) and Analytical Anisotropic Algorithm (AAA) were also used. First the accuracy of an inhomogeneity correction for AXB and AAA algorithms was evaluated by comparing with MC‐calculated dose distributions for a virtual inhomogeneity phantom that includes water, bone, air, adipose, muscle, and aluminum. Next the IMRT dose distributions for head and neck were compared with the AXB and AAA algorithms and MC by means of dose volume histograms and three dimensional gamma analysis for each structure (CTV, OAR, etc.).

Results:

For dose distributions with the virtual inhomogeneity phantom, AXB was in good agreement with those of MC, except the dose in air region. The dose in air region decreased in order of MC<AXB11<AXB10. This may be caused by the difference of the electron cut‐off energy for algorithms, ie: 0.700 MeV for MC, 0.711 MeV for AXB11, and 1.011 MeV for AXB 10. Since the AAA algorithm is based on the dose kernel of water, the doses in regions for air, bone, and aluminum considerably became higher than those of AXB and MC. The pass rates of the gamma analysis for IMRT dose distributions in head and neck were similar to those of MC in order of AXB11<AXB10<AAA.

Conclusion:

The dose calculation accuracy of AXB11 was almost equivalent to the MC dose calculation.
SU‐E‐T‐318: The Effect of Patient Positioning Errors On Target Coverage and Cochlear Dose in Stereotactic Radiosurgery Treatment of Acoustic Neuromas
Authors: Dellamonica D. , Luo G. , Ding G.
Published: July 2014

Purpose:

Setup errors on the order of millimeters may cause under‐dosing of targets and significant changes in dose to critical structures especially when planning with tight margins in stereotactic radiosurgery. This study evaluates the effects of these types of patient positioning uncertainties on planning target volume (PTV) coverage and cochlear dose for stereotactic treatments of acoustic neuromas.

Methods:

Twelve acoustic neuroma patient treatment plans were retrospectively evaluated in Brainlab iPlan RT Dose 4.1.3. All treatment beams were shaped by HDMLC from a Varian TX machine. Seven patients had planning margins of 2mm, five had 1–1.5mm. Six treatment plans were created for each patient simulating a 1mm setup error in six possible directions: anterior‐posterior, lateral, and superiorinferior. The arcs and HDMLC shapes were kept the same for each plan. Change in PTV coverage and mean dose to the cochlea was evaluated for each plan.

Results:

The average change in PTV coverage for the 72 simulated plans was −1.7% (range: −5 to +1.1%). The largest average change in coverage was observed for shifts in the patient's superior direction (−2.9%). The change in mean cochlear dose was highly dependent upon the direction of the shift. Shifts in the anterior and superior direction resulted in an average increase in dose of 13.5 and 3.8%, respectively, while shifts in the posterior and inferior direction resulted in an average decrease in dose of 17.9 and 10.2%. The average change in dose to the cochlea was 13.9% (range: 1.4 to 48.6%). No difference was observed based on the size of the planning margin.

Conclusion:

This study indicates that if the positioning uncertainty is kept within 1mm the setup errors may not result in significant under‐dosing of the acoustic neuroma target volumes. However, the change in mean cochlear dose is highly dependent upon the direction of the shift.
SU‐E‐T‐324: The Influence of Patient Positioning Uncertainties in Proton Radiotherapy On Proton Range and Dose Distributions
Authors: Liebl J , Paganetti H , Winey B
Published: July 2014

Purpose:

Proton radiotherapy allows radiation treatment delivery with high dose gradients. The nature of such dose distributions increases the influence of patient positioning uncertainties on their fidelity when compared to photon radiotherapy. The present work quantitatively analyzes the influence of setup uncertainties on proton range and dose distributions.

Methods:

38 clinical passive scattering treatment fields for small lesions in the head were studied. Dose distributions for shifted and rotated patient positions were Monte Carlo‐simulated. Proton range uncertainties at the 50% and 90%‐dose falloff position were calculated considering 18 arbitrary combinations of maximal patient position shifts and rotations for two patient positioning methods. Normal tissue complication probabilities (NTCPs), equivalent uniform doses (EUDs) and tumor control probabilities (TCPs) were studied for organs at risk (OARs) and target volumes of eight patients.

Results:

We identified a median 1σ proton range uncertainty at the 50%‐dose falloff of 2.8 mm for anatomy‐based patient positioning and 1.6 mm for fiducial‐based patient positioning as well as 7.2 mm and 5.8 mm for the 90%‐dose falloff position respectively. These range uncertainties were correlated to heterogeneity indices (HIs) calculated for each treatment field (38% < R2 < 50%). A NTCP increase of more than 10% (absolute) was observed for less than 2.9% (anatomy‐based positioning) and 1.2% (fiducial‐based positioning) of the studied OARs and patient shifts. TCP decreases larger than 10% (absolute) were seen for less than 2.2% of the target volumes or non‐existent. EUD changes were up to 178% for OARs and 35% for target volumes.

Conclusion:

The influence of patient positioning uncertainties on proton range in therapy of small lesions in the human brain and target and OAR dosimetry were studied. Observed range uncertainties were correlated with HIs. The clinical practice of using multiple compensator‐smeared treatment beams selected to avoid distal OAR sparing is considered to be safe.

J. L. was supported by a scholarship of the University of Vienna
SU‐F‐BRF‐06: Density Correction for Deformable Image Registration to Improve CT Number Mapping
Authors: Yang J , Zhang Y , Zhang L , Balter P , Court L
Published: July 2014

Purpose:

To improve the accuracy of CT number mapping inside the lung using deformable image registration for cases having substantially large lung volume differences.

Methods:

The deep‐inspiration‐breath‐hold (DIBH) CT image and the end‐of‐exhalation (EE) phase image in 4DCT of three thoracic cancer patients were enrolled in this study. The lung volumes were manually delineated and the lung volume ratio of DIBH‐CT over EECT is 1.7, 1.8, and 2.0 respectively, demonstrating large volume differences. A demons‐based deformable registration was first applied to register the EECT to the DIBH‐CT for each patient, and the resulting deformation field deformed the EE‐CT image to the DIBH‐CT space. Based on the assumption that the mass of lung remains the same during respiration, we created a mass preserving model to correlate the lung density variations with the lung volumetric changes, which were characterized by the Jacobian derived from the deformation field. The Jacobian is used to correct the lung CT number transferred from the EE‐CT image. The deformed images with and without the density correction were compared using absolute intensity difference created by subtracting the deformed image from the DIBH‐CT image.

Results:

The deformable registration could register the lung shape very well, but the CT numbers inside the lung could not be registered correctly. Without density correction, the mean and standard deviation of the absolute CT number difference inside the lung were 59±48, 69±49, and 71±42 for the three cases. After density correction, these numbers changed to 18±35, 20±35, and 14±29, respectively, demonstrating an improvement in the accuracy of CT number mapping. The accumulative histogram of the intensity difference also showed that density correction improved CT number mapping.

Conclusion:

Density correction improved the CT number mapping inside the lung using deformable image registration for difficult cases having large lung volume differences.

This work is partially supported by the CPRIT (Cancer Prevention Research Institute of Texas) grant RP110732.
SU‐F‐BRF‐14: Increasing the Accuracy of Dose Calculation On Cone‐Beam Imaging Using Deformable Image Registration in the Case of Prostate Translation
Authors: Fillion O , Gingras L , Archambault L
Published: July 2014

Purpose:

Artifacts can reduce the quality of dose re‐calculations on CBCT scans during a treatment. The aim of this project is to correct the CBCT images in order to allow for more accurate and exact dose calculations in the case of a translation of the tumor in prostate cancer.

Methods:

Our approach is to develop strategies based on deformable image registration algorithms using the elastix software (Klein et al., 2010) to register the treatment planning CT on a daily CBCT scan taken during treatment. Sets of images are provided by a 3D deformable phantom and comprise two CT and two CBCT scans: one of both with the reference anatomy and the others with known deformations (i.e. translations of the prostate). The reference CT is registered onto the deformed CBCT and the deformed CT serves as the control for dose calculation accuracy. The planned treatment used for the evaluation of dose calculation is a 2‐Gy fraction prescribed at the location of the reference prostate and assigned to 7 rectangular fields.

Results:

For a realistic 0.5‐cm translation of the prostate, the relative dose discrepancy between the CBCT and the CT control scan at the prostate's centroid is 8.9 ± 0.8 % while dose discrepancy between the registered CT and the control scan lessens to −2.4 ± 0.8 %. For a 2‐cm translation, clinical indices like the V90 and the D100 are more accurate by 0.7 ± 0.3 % and 8.0 ± 0.5 cGy respectively when using registered CT than when using CBCT for dose calculation.

Conclusion:

The results show that this strategy gives doses in agreement within a few percents with those from calculations on actual CT scans. In the future, various deformations of the phantom anatomy will allow a thorough characterization of the registration strategies needed for more complex anatomies.
SU‐F‐18C‐02: Evaluations of the Noise Power Spectrum of a CT Iterative Reconstruction Technique for Radiation Therapy
Authors: Dolly S , Chen H , Anastasio M , Mutic S , Li H
Published: July 2014

Purpose:

To quantitatively assess the noise power spectrum (NPS) of the new, commercially released CT iterative reconstruction technique, iDose4 from Philips, to compare it with filtered back‐projection techniques (FBP), and to provide clinical practice suggestions for radiation therapy.

Methods:

A uniform phantom was CT imaged with 120kVp tube potential over a range of mAs (250‐3333). The image sets were reconstructed using two reconstruction algorithms (FBP and iDose4 with noise reduction levels 1, 3, and 6) and three reconstruction filters (standard B, smooth A, and sharp C), after which NPS variations were analyzed and compared on region of interest (ROI) sizes (16×16 to 128×128 pixels), ROI radii (0–65 mm), reconstruction algorithms, reconstruction filters, and mAs.

Results:

The NPS magnitude and shape depended considerably on ROI size and location for both reconstruction algorithms. Regional noise variance became more stationary as ROI size decreased, minimizing NPS artifacts. The optimal 32×32‐pixel ROI size balanced the trade‐off between stationary noise and adequate sampling. NPS artifacts were greatest at the center of reconstruction space and decreased with increasing ROI distance from the center. The optimal ROI position was located near the phantom's radial midpoint (∼40mm). For sharper filters, the NPS magnitude and the maximum magnitude frequency increased. Higher dose scans yielded lower NPS magnitudes for both reconstruction algorithms and all filters. Compared to FBP, the iDose4 algorithm reduced the NPS magnitude while preferentially reducing noise at mid‐range spatial frequencies, altering noise texture. This reduction was more significant with increasing iDose4 noise reduction level.

Conclusion:

Compared to pixel standard deviation, NPS has greater clinical potential for task‐based image quality assessment, describing both the magnitude and spatial frequency characteristics of image noise. While iDose4 reduces the NPS magnitude more dramatically than FBP, further studies are needed to assess the impacts of noise texture alteration on its clinical usage.
SU‐F‐18C‐04: A Combination of Monoenergetic Reconstruction and Stoichiometric Calibration for Tissue Characterization Using Dual Energy Computed Tomography
Authors: Bedwani S , Tremblay J , Bouchard H
Published: July 2014

Purpose:

Dual energy computed tomography (DECT) pre‐reconstruction methods require the prior knowledge of the X‐ray source spectrum to allow extracting physical parameters needed for radiation therapy dose calculation, such as electron density (ED) and the effective atomic number (EAN). While DECT stoichiometric calibration may provide reliable performance for typical radiation therapy clinical conditions, it is yet to be adapted to prereconstruction methods. The presence of noise and inaccurate spectrum description may lead to systematic errors and artifacts which compromise the accuracy of treatment planning.

Methods:

A new technique is investigated which consists in applying a DECT stoichiometric calibration method to a set of monoenergetic images obtained with a DECT prereconstruction method. To evaluate the performance of this extended method, a simulation environment is developed to generate DECT scans under well controlled conditions, to reconstruct monoenergetic images of a tissue‐equivalent phantom from transformed sinograms and to extract ED and EAN maps using a DECT formalism.

Result:

Under simulated clinical conditions, the accuracy in determining ED with the extended method versus a pre‐reconstruction method alone is shown to be better than 0.35% versus 0.5%, respectively. In the presence of a realistic noise level, EAN determination presents a relative mean error that drops from 2.5% to 0.5% once the calibration is applied. Considering a spectrum alteration by a 1 mm Cu layer, EAN errors are up to 30% for the pre‐reconstruction method alone versus less than 3% for the extended method.

Conclusion:

This study shows that combining pre‐reconstruction DECT methods with a stoichiometric calibration considerably improves the accuracy and reliability of tissue characterization for radiation therapy in a clinical context. The presented method could potentially be adapted as gold standard for dose calculation methods based on DECT.