bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐QI‐12: Morphometry Based Measurements of the Structural Response to Whole Brain Radiation
Authors: Fuentes D , Castillo R , Castillo E , Guerrero T
Published: July 2014

Purpose:

Although state of the art radiation therapy techniques for treating intracranial malignancies have eliminated acute brain injury, cognitive impairment occurs in 50–90% of patients who survive >6mo post irradiation. Quantitative characterization of therapy response is needed to facilitate therapeutic strategies to minimize radiation induced cognitive impairment [1]. Deformation based morphometry techniques [2, 3] are presented as a quantitative imaging biomarker of therapy response in patients receiving whole brain radiation for treating medulloblastoma.

Methods:

Post‐irradiation magnetic resonance imaging (MRI) data sets were retrospectively analyzed in N=15 patients, >60 MR image datasets. As seen in Fig 1(a), volume changes at multiple time points post‐irradiation were quantitatively measured in the cerebrum and ventricles with respect to pre‐irradiation MRI. A high resolution image Template, was registered to the pre‐irradiation MRI of each patient to create a brain atlas for the cerebrum, cerebellum, and ventricles. Skull stripped images for each patient were registered to the initial pre‐treatment scan. Average volume changes in the labeled regions were measured using the determinant of the displacement field Jacobian.

Results:

Longitudinal measurements, Fig 1(b‐c), show a negative correlation p=.06, of the cerebral volume change with the time interval from irradiation. A corresponding positive correlation, p=.01, between ventricular volume change and time interval from irradiation is seen. One sample t‐test for correlations were computed using a Spearman method. An average decrease in cerebral volume, p=.08, and increase in ventricular volume, p<.001, was observed. The radiation dose was seen directly proportional to the induced volume changes in the cerebrum, r=−.44, p<.001, Fig 1(d).

Conclusion:

Results indicate that morphometric monitoring of brain tissue volume changes may potentially be used to quantitatively assess toxicity and response to radiation and may provide insight in developing new therapeutic approaches and monitoring efficacy.
SU‐E‐QI‐13: Predictable Models for Radio‐Sensitizing Agent Kinetics: Application to Stereotactic Synchrotron Radiation Therapy
Authors: Obeid L , Schmitt M , Esteve F , Adam J
Published: July 2014

Purpose:

Iodine‐enhanced radiotherapy is an innovative treatment combining the selective accumulation of an iodinated contrast agent in brain tumors with irradiations using monochromatic medium energy x‐rays. The radiation dose enhancement depends on the time course of iodine in the tumors. A prolonged CT scanning (∼30 min) is required to follow‐up iodine kinetics for recruited patients. This protocol could lead to substantial radiation dose to the patient. A novel method is proposed to reduce the acquisition time.

Methods:

12 patients received an intravenous bolus of iodinated contrast agent, followed by a steady‐state infusion to ensure stable intra‐tumoral amounts of iodine during the treatment. Absolute iodine concentrations (IC) were derived from 40 multi‐slice dynamic conventional CT images of the brain. The impulse response function (IRF) to the bolus was estimated using the adiabatic approximation of the Johnson and Wilson's model. The arterial input function (AIF) of the steady‐state infusion was fitted with several models: Gamma, Gamma with recirculation and hybrid. Estimated IC were calculated by convolving the IRF with the modeled AIF and were compared to the measured data.

Results:

The gamma variate function was not relevant to model the AIF due to high differences with the measured AIF. The hybrid and the gamma with recirculation models provided differences below 8% during the whole acquisition time. The absolute difference between the measured and the estimated IC was lower than 0.5 mg/ml, which corresponds to 5% of dose enhancement error.

Conclusion:

The proposed method allows a good estimation of the iodine time course with reduced scanning delays (3 instead of 30 min) and dose to the patient. The results suggest that the dose errors may stay within the radiotherapy standards.
SU‐E‐QI‐14: Quantitative Variogram Detection of Mild, Unilateral Disease in Elastase‐Treated Rats
Authors: Jacob R , Carson J
Published: July 2014

Purpose:

Determining the presence of mild or early disease in the lungs can be challenging and subjective. We present a rapid and objective method for evaluating lung damage in a rat model of unilateral mild emphysema based on a new approach to heterogeneity assessment. We combined octree decomposition (used in three‐dimensional (3D) computer graphics) with variograms (used in geostatistics to assess spatial relationships) to evaluate 3D computed tomography (CT) lung images for disease.

Methods:

Male, Sprague‐Dawley rats (232 ± 7 g) were intratracheally dosed with 50 U/kg of elastase dissolved in 200 μL of saline to a single lobe (n=6) or with saline only (n=5). After four weeks, 3D micro‐CT images were acquired at end expiration on mechanically ventilated rats using prospective gating. Images were masked, and lungs were decomposed to homogeneous blocks of 2×2×2, 4×4×4, and 8×8×8 voxels using octree decomposition. The spatial variance – the square of the difference of signal intensity – between all pairs of the 8×8×8 blocks was calculated. Variograms – graphs of distance vs. variance – were made, and data were fit to a power law and the exponent determined. The mean HU values, coefficient of variation (CoV), and the emphysema index (EI) were calculated and compared to the variograms.

Results:

The variogram analysis showed that significant differences between groups existed (p<0.01), whereas the mean HU (p=0.07), CoV (p=0.24), and EI (p=0.08) did not. Calculation time for the variogram for a typical 1000 block decomposition was ∼6 seconds, and octree decomposition took ∼2 minutes. Decomposing the images prior to variogram calculation resulted in a ∼700x decrease in time as compared to other published approaches.

Conclusions:

Our results suggest that the approach combining octree decomposition and variogram analysis may be a rapid, non‐subjective, and sensitive imaging‐based biomarker for quantitative characterization of lung disease.
SU‐E‐QI‐15: Single Point Dosimetry by Means of Cerenkov Radiation Energy Transfer (CRET)
Authors: Volotskova O , Jenkins C , Xing L
Published: July 2014

Purpose:

Cerenkov light is generated when a charged particles with energy greater then 250 keV, moves faster than the speed of light in a given medium. Both x‐ray photons and electrons produce optical Cerenkov photons during the static megavoltage linear accelerator (LINAC) operational mode. Recently, Cerenkov radiation gained considerable interest as possible candidate as a new imaging modality. Optical signals generated by Cerenkov radiation may act as a surrogate for the absorbed superficial radiation dose. We demonstrated a novel single point dosimetry method for megavoltage photon and electron therapy utilizing down conversion of Cerenkov photons.

Methods:

The custom build signal characterization system was used: a sample holder (probe) with adjacent light tight compartments was connected via fiber‐optic cables to a photon counting photomultiplier tube (PMT). One compartment contains a medium only while the other contains medium and red‐shifting nano‐particles (Q‐dots, nanoclusters). By taking the difference between the two signals (Cerenkov photons and CRET photons) we obtain a measure of the down‐converted light, which we expect to be proportional to dose as measured with an adjacent ion chamber. Experimental results are compared to Monte Carlo simulations performed using the GEANT4 code.

Results:

The signal correlation between CR signal, CRET readings and dose produced by LINAC at a single point were investigated. The experimental results were compared with simulations. The dose linearity, signal to noise ratio and dose rate dependence were tested with custom build CRET based probe.

Conclusion:

Performance characteristics of the proposed single point CRET based probe were evaluated. The direct use of the induced Cerenkov emission and CRET in an irradiated single point volume as an indirect surrogate for the imparted dose was investigated. We conclude that CRET is a promising optical based dosimetry method that offers advantages over those already proposed.
SU‐E‐QI‐16: Reproducibility of Computed Tomography Quantitative Structural Features Using the FDA Thoracic Phantom Image Database
Authors: Budzevich M , Grove O , Balagurunathan Y , Gu Y , Wang H , Oliver J , Latifi K , Zhang G , Dilling T , Gillies R , Moros E , Lee H.
Published: July 2014

Purpose:

To assess the reproducibility of quantitative structural features using images from the computed tomography thoracic FDA phantom database under different scanning conditions.

Methods:

Development of quantitative image features to describe lesion shape and size, beyond conventional RECIST measures, is an evolving area of research in need of benchmarking standards. Gavrielides et al. (2010) scanned a FDA‐developed thoracic phantom with nodules of various Hounsfield units (HU) values, shapes and sizes close to vascular structures using several scanners and varying scanning conditions/parameters; these images are in the public domain. We tested six structural features, namely, Convexity, Perimeter, Major Axis, Minor Axis, Extent Mean and Eccentricity, to characterize lung nodules. Convexity measures lesion irregularity referenced to a convex surface. Previously, we showed it to have prognostic value in lung adenocarcinoma. The above metrics and RECIST measures were evaluated on three spiculated (8mm/‐300HU, 12mm/+30HU and 15mm/+30HU) and two non‐spiculated (8mm/+100HU and 10mm/+100HU) nodules (from layout 2) imaged at three different mAs values: 25, 100 and 200 mAs; on a Phillips scanner (16‐slice Mx8000‐IDT; 3mm slice thickness). The nodules were segmented semi‐automatically using a commercial software tool; the same HU range was used for all nodules.

Results:

Analysis showed convexity having the lowest maximum coefficient of variation (MCV): 1.1% and 0.6% for spiculated and non‐spiculated nodules, respectively, much lower compared to RECIST Major and Minor axes whose MCV were 10.1% and 13.4% for spiculated, and 1.9% and 2.3% for non‐spiculated nodules, respectively, across the various mAs. MCVs were consistently larger for speculated nodules. In general, the dependence of structural features on mAs (noise) was low.

Conclusion:

The FDA phantom CT database may be used for benchmarking of structural features for various scanners and scanning conditions; we used only a small fraction of available data. Our feature convexity outperformed other structural features including RECIST measures.
SU‐E‐QI‐17: Dependence of 3D/4D PET Quantitative Image Features On Noise
Authors: Oliver J , Budzevich M , Zhang G , Latifi K , Dilling T , Balagurunathan Y , Gu Y , Grove O , Feygelman V , Gillies R , Moros E , Lee H.
Published: July 2014

Purpose:

Quantitative imaging is a fast evolving discipline where a large number of features are extracted from images; i.e., radiomics. Some features have been shown to have diagnostic, prognostic and predictive value. However, they are sensitive to acquisition and processing factors; e.g., noise. In this study noise was added to positron emission tomography (PET) images to determine how features were affected by noise.

Methods:

Three levels of Gaussian noise were added to 8 lung cancer patients PET images acquired in 3D mode (static) and using respiratory tracking (4D); for the latter images from one of 10 phases were used. A total of 62 features: 14 shape, 19 intensity (1stO), 18 GLCM textures (2ndO; from grey level co‐occurrence matrices) and 11 RLM textures (2ndO; from run‐length matrices) features were extracted from segmented tumors. Dimensions of GLCM were 256×256, calculated using 3D images with a step size of 1 voxel in 13 directions. Grey levels were binned into 256 levels for RLM and features were calculated in all 13 directions.

Results:

Feature variation generally increased with noise. Shape features were the most stable while RLM were the most unstable. Intensity and GLCM features performed well; the latter being more robust. The most stable 1stO features were compactness, maximum and minimum length, standard deviation, root‐mean‐squared, I30, V10‐V90, and entropy. The most stable 2ndO features were entropy, sum‐average, sum‐entropy, difference‐average, difference‐variance, difference‐entropy, information‐correlation‐2, short‐run‐emphasis, long‐run‐emphasis, and run‐percentage. In general, features computed from images from one of the phases of 4D scans were more stable than from 3D scans.

Conclusion:

This study shows the need to characterize image features carefully before they are used in research and medical applications. It also shows that the performance of features, and thereby feature selection, may be assessed in part by noise analysis.
SU‐E‐QI‐18: QUATTRO: An Open‐Source Software Package for Quantitative Imaging Applications in Assessing Treatment Response
Authors: Bosca R , Johnson V , Jackson E
Published: July 2014

Purpose:

Quantitative imaging biomarkers are becoming increasingly utilized in early phase clinical trials as a means non‐invasively monitoring treatment response. However, such techniques require extensive data pipelines (e.g., image quantitation, image registration, ROI definition, statistical analyses) to capture and model longitudinal parameter changes. The aim of this study was to develop a comprehensive open‐source research software environment supporting such analyses with an emphasis on longitudinally assessing treatment response.

Methods:

Using the MATLAB programming environment, an intuitive graphical user interface (GUI) and associated advanced programming interface (API) were developed, providing an imaging study environment collectively titled Quantitative Utility for Assessing TreaTment RespOnse or QUATTRO. Standard tools were incorporated for importing/exporting common data formats such as DICOM 3.0 and associated RT contours, Pinnacle contours, and for performing ROI and voxel‐based modeling for a number of common quantitative MR imaging strategies (dynamic contrast‐enhanced, diffusion weighted, and dynamic susceptibility contrast, in addition to T1/T2 relaxometry). Advanced features for preforming longitudinal analyses were also developed, including image registration (provided by directly linked Insight Toolkit executables), ordinal and logistic regression analyses (utilizing a link with R), and a scripting framework.

Results:

QUATTRO has been successfully implemented and employed in a number of longitudinal phantom studies and quantitative imaging applications. Moreover, the software has facilitated the development and associated feasibility studies of a voxel‐by‐voxel statistical response model capable of generating probabilistic response maps by incorporating multiparametric quantitative imaging data.

Conclusion:

An open‐source software package, QUATTRO, has been developed for applications in assessing treatment response incorporating quantitative imaging. An intuitive GUI provides a front‐end tool for utilizing built‐in QUATTRO capabilities, while the API facilitates rapid prototyping of future applications, e.g., novel multimodality analyses, and links to the highly developed libraries of ITK and R enable development of advanced image processing and statistical tools, respectively.
SU‐E‐QI‐19: Evaluation of a Clinical 1.5T MRI for Prostate Cancer MRS Imaging Using a In Vivo Tumor Model
Authors: Chen X , Chen L , Hensley H , Cvetkovic D , Zhang C , Fan J , Ma C
Published: July 2014

Purpose:

Magnetic resonance spectroscopic (MRS) imaging may provide important bio‐markers to distinguish normal/cancerous prostate tissue. While MRS imaging requires a high uniform magnetic field, the ability of a clinical 1.5T MRI to achieve a comparable MRS signal is of interest for radiation treatment planning/assessment. This study is to evaluate the MRS imaging of a 1.5T clinical MRI for prostate cancers by comparing with a small animal 7T MRS scanner.

Methods:

A tumor model was developed by implanting LNCaP tumor cells in nude mice prostates. Tumor was monitored 3 weeks after implantation using MRI, and MRS imaging was performed on the tumor area when the tumor reached around 1cm in diameter. The 1.5T GE clinical MR scanner and the 7T Bruker small animal MR scanner were used for each mouse. MR spectrums acquired with these scanners were analyzed and compared. The signals of Choline and Citrate were considered.

Results:

The prostate tumor MR spectrum under the 1.5T clinical MRI showed a similar spectrum pattern to that acquired using the 7T animal MRI. The Choline signal (3.2ppm) is clear and there is no clear peak for Citrate (2.6ppm). However, the signal magnitude for Choline is not dominant compared to the background signal under 1.5T MRI. Typical cancerous prostate tissue MR spectrum with an increased Choline signal and a reduced Citrate signal was observed. In addition, signal variation is noticeable between repeated spectrum scans. The average of these scans showed a comparable and consistent spectrum to those under 7T MRI.

Conclusion:

The clinical 1.5T MRI is able to acquire a MR spectrum for prostate cancer comparable to those acquired using a dedicated 7T MRS scanner. However, to achieve a consistent and reliable spectrum, multiple repeated scans were necessary to get a statistical result and reduce the noise‐induced artifact.

This work was supported in part by the National Cancer Institute Grant R21 CA131979 and R01CA172638.
SU‐E‐QI‐20: A Review of Advanced PET and CT Image Features for the Evaluation of Tumor Response
Authors: Lu W
Published: July 2014

Purpose:

To review the literature in using quantitative PET and CT image features for the evaluation of tumor response.

Methods:

We reviewed and summarized more than fifty papers that use advanced, quantitative PET/CT image features for the evaluation of tumor response. We also discussed future works on extracting disease‐specific features, combining multiple and complementary features in response modeling, delineating tumor in multimodality images, and exploring biological explanations of these advanced features.

Results:

Advanced PET image features considering spatial information, such as tumor volume, tumor shape, total glycolytic volume, histogram distance, and texture features (characterizing spatial distribution of FDG uptake) have been found more informative than the traditional SUVmax for the prediction of tumor response. Advanced CT features, including volumetric, attenuation, morphologic, structure, and texture descriptors, have also been found advantage over the traditional RECIST and WHO criteria in certain tumor types.

Conclusions:

Advanced, quantitative FDG PET/CT image features have been shown promising for the evaluation of tumor response. With the emerging multi‐modality imaging performed at multiple time points for each patient, it becomes more important to analyze the serial images quantitatively, select and combine both complementary and contradictory information from various sources, for accurate and personalized evaluation of tumor response to therapy.
SU‐E‐QI‐21: Iodinated Contrast Agent Time Course In Human Brain Metastasis: A Study For Stereotactic Synchrotron Radiotherapy Clinical Trials
Authors: Obeid L , Tessier A , Balosso J , Esteve F , Adam J
Published: July 2014

Purpose:

Synchrotron stereotactic radiotherapy (SSRT) is an innovative treatment combining the selective accumulation of heavy elements in tumors with stereotactic irradiations using monochromatic medium energy x‐rays from a synchrotron source. Phase I/II clinical trials on brain metastasis are underway using venous infusion of iodinated contrast agents. The radiation dose enhancement depends on the amount of iodine in the tumor and its time course. In the present study, the reproducibility of iodine concentrations between the CT planning scan day (Day 0) and the treatment day (Day 10) was assessed in order to predict dose errors.

Methods:

For each of days 0 and 10, three patients received a biphasic intravenous injection of iodinated contrast agent (40 ml, 4 ml/s, followed by 160 ml, 0.5 ml/s) in order to ensure stable intra‐tumoral amounts of iodine during the treatment. Two volumetric CT scans (before and after iodine injection) and a multi‐slice dynamic CT of the brain were performed using conventional radiotherapy CT (Day 0) or quantitative synchrotron radiation CT (Day 10). A 3D rigid registration was processed between images. The absolute and relative differences of absolute iodine concentrations and their corresponding dose errors were evaluated in the GTV and PTV used for treatment planning.

Results:

The differences in iodine concentrations remained within the standard deviation limits. The 3D absolute differences followed a normal distribution centered at zero mg/ml with a variance (∼1 mg/ml) which is related to the image noise.

Conclusion:

The results suggest that dose errors depend only on the image noise. This study shows that stable amounts of iodine are achievable in brain metastasis for SSRT treatment in a 10 days interval.
SU‐E‐CAMPUS‐T‐01: Automation of the Winston‐Lutz Test for Stereotactic Radiosurgery
Authors: Litzenberg D , Irrer J , Keranen W , Kessler M , Lam K
Published: July 2014

Purpose:

To optimize clinical efficiency and shorten patient wait time by minimizing the time and effort required to perform the Winston‐Lutz test before stereotactic radiosurgery (SRS) through automation of the delivery, analysis, and documentation of results.

Methods:

The radiation fields of the Winston‐Lutz (WL) test were created in a “machine‐QA patient” saved in ARIA for use before SRS cases. Images of the BRW target ball placed at mechanical isocenter are captured with the portal imager for each of four, 2cm×2cm, MLC‐shaped beams. When the WL plan is delivered and closed, this event is detected by in‐house software called EventNet which automates subsequent processes with the aid of the ARIA web services. Images are automatically retrieved from the ARIA database and analyzed to determine the offset of the target ball from radiation isocenter. The results are posted to a website and a composite summary image of the results is pushed back into ImageBrowser for review and authenticated documentation.

Results:

The total time to perform the test was reduced from 20‐25 minutes to less than 4 minutes. The results were found to be more accurate and consistent than the previous method which used radiochromic film. The images were also analyzed with DoseLab for comparison. The difference between the film and automated WL results in the X and Y direction and the radius were (−0.17 +/− 0.28) mm, (0.21 +/− 0.20) mm and (−0.14 +/− 0.27) mm, respectively. The difference between the DoseLab and automated WL results were (−0.05 +/− 0.06) mm, (−0.01 +/− 0.02) mm and (0.01 +/− 0.07) mm, respectively.

Conclusions:

This process reduced patient wait times by 15–20 minutes making the treatment machine available to treat another patient. Accuracy and consistency of results were improved over the previous method and were comparable to other commercial solutions. Access to the ARIA web services is made possible through an Eclipse co‐development agreement with Varian Medical Systems.
SU‐E‐CAMPUS‐T‐02: Exploring Radiation Acoustics CT Dosimeter Design Aspects for Proton Therapy
Authors: Alsanea F , Moskvin V , Stantz K
Published: July 2014

Purpose:

Investigate the design aspects and imaging dose capabilities of the Radiation Acoustics Computed Tomography (RA CT) dosimeter for Proton induced acoustics, with the objective to characterize a pulsed pencil proton beam. The focus includes scanner geometry, transducer array, and transducer bandwidth on image quality.

Methods:

The geometry of the dosimeter is a cylindrical water phantom (length 40cm, radius 15cm) with 71 ultrasound transducers placed along the length and end of the cylinder to achieve a weighted set of projections with spherical sampling. A 3D filtered backprojection algorithm was used to reconstruct the dosimetric images and compared to MC dose distribution. First, 3D Monte Carlo (MC) Dose distributions for proton beam energies (range of 12cm, 16cm, 20cm, and 27cm) were used to simulate the acoustic pressure signal within this scanner for a pulsed proton beam of 1.8×107 protons, with a pulse width of 1 microsecond and a rise time of 0.1 microseconds. Dose comparison within the Bragg peak and distal edge were compared to MC analysis, where the integrated Gaussian was used to locate the 50% dose of the distal edge. To evaluate spatial fidelity, a set of point sources within the scanner field of view (15×15×15cm3) were simulated implementing a low‐pass bandwidth response function (0 to 1MHz) equivalent to a multiple frequency transducer array, and the FWHM of the point‐spread‐function determined.

Results:

From the reconstructed images, RACT and MC range values are within 0.5mm, and the average variation of the dose within the Bragg peak are within 2%. The spatial resolution tracked with transducer bandwidth and projection angle sampling, and can be kept at 1.5mm.

Conclusion:

This design is ready for fabrication to start acquiring measurements. The 15 cm FOV is an optimum size for imaging dosimetry. Currently, simulations comparing transducer sensitivity, bandwidth, and proton beam parameters are being evaluated to assess signal‐to‐noise.
SU‐E‐CAMPUS‐T‐03: Four‐Dimensional Dose Distribution Measurement Using Plastic Scintillator
Authors: Hashimoto M , Nishio T , Haga A , Hanada T , Kabuki S , Kozuka T , Oguchi M
Published: July 2014

Purpose:

To develop the detector for the four‐dimensional dose distribution measurement.

Methods:

We made the prototype detector for four‐dimensional dose distribution measurement using a cylindrical plastic scintillator (5 cm diameter) and a conical reflection grass. The plastic scintillator is used as a phantom. When the plastic scintillator is irradiated, the scintillation light was emitted according to absorbed dose distribution. The conical reflection grass was arranged to surround the plastic scintillator, which project to downstream the projection images of the scintillation light. Then, the projection image was reflected to 45 degree direction by flat reflection grass, and was recorded by camcorder. By reconstructing the three‐dimensional dose distribution from the projection image recorded in each frame, we could obtain the four‐dimensional dose distribution. First, we tested the characteristic according to the amount of emitted light. Then we compared of the light profile and the dose profile calculated with the radiotherapy treatment planning system.

Results:

The dose dependency of the amount of light showed linearity. The pixel detecting smaller amount of light had high sensitivity than the pixel detecting larger amount of light. However the difference of the sensitivity could be corrected from the amount of light detected in each pixel. Both of the depth light profile through the conical reflection grass and the depth dose profile showed the same attenuation in the region deeper than peak depth. In lateral direction, the difference of the both profiles was shown at outside field and penumbra region. We consider that the difference is occurred due to the scatter of the scintillation light in the plastic scintillator block.

Conclusion:

It was possible to obtain the amount of light corresponding to the absorbed dose distribution from the prototype detector. Four‐dimensional dose distributions can be reconstructed with high accuracy by the correction of the scattered light.
SU‐E‐CAMPUS‐T‐04: Measurement of Proton Pencil Beam Spot Profile Using Cherenkov Radiation in Two Dimensional Optical Fiber Arrays
Authors: Kim M , Son J , Hwang U , SHIN D , Park J , Lim Y , Lee S , Kim J
Published: July 2014

Purpose:

Proton therapy aims to deliver a high dose in a well‐defined target volume while sparing the healthy surrounding tissues thanks to their inherent depth dose characteristic (Bragg peak). In proton therapy, several techniques can be used to deliver the dose into the target volume. The one that allows the best conformity with the tumor, is called PBS (Pencil Beam Scanning). The measurement of the proton pencil beam spot profile (spot size) and position is very important for the accurate delivery of dose to the target volume with a good conformity.

Methods:

We have developed a fine segmented detector array to monitor the PBS. A prototype beam monitor using Cherenkov radiation in clear plastic optical fibers (cPOF) has been developed for continuous display of the pencil beam status during the therapeutic proton Pencil Beam Scanning mode operation. The benefit of using Cherenkov radiation is that the optical output is linear to the dose. Pedestal substraction and the gain adjustment between channels are performed. Spot profiles of various pencil beam energies(100 MeV to 226 MeV) are measured. Two dimensional gaussian fit is used to analyze the beam width and the spot center. The results are compared with that of Lynx(Scintillator‐based sensor with CCD camera) and EBT3 Film.

Results:

The measured gaussian widths using fiber array system changes from 13 to 5 mm for the beam energies from 100 to 226 MeV. The results agree well with Lynx and Film within the systematic error.

Conclusion:

The results demonstrate good monitoring capability of the system. Not only measuing the spot profile but also monitoring dose map by accumulating each spot measurement is available. The x‐y monitoing system with 128 channel readout will be mounted to the snout for the in‐situ real time monitoring.
SU‐E‐CAMPUS‐T‐05: Preliminary Results On a 2D Dosimetry System Based On the Optically Stimulated Luminescence of Al2O3
Authors: Ahmed M , Eller S , Schnell E , Ahmad S , Akselrod M , Hanson O , Yukihara E
Published: July 2014

Purpose:

To develop a precise 2D dose mapping technique based on the optically stimulated luminescence (OSL) from Al2O3 films for medical applications.

Methods:

A 2D laser scanning reader was developed using fast F+‐center (lifetime of <7 ns) and slow F‐center (lifetime of 35 ms) OSL emission from newly developed Al2O3 films (Landauer Inc.). An algorithm was developed to correct images for both material and system properties. Since greater contribution of the F??‐center emission in the recorded signal increases the readout efficiency and robustness of image corrections, Al2O3:C,Mg film samples are being investigated in addition to Al2O3:C samples. Preliminary investigations include exposure of the films to a 6 MV photon beam at 10 cm depth in solid water phantom with an SSD of 100 cm, using a 10 cm × 10 cm flat field or a 4 cm × 4 cm field with a 60° wedge filter. Kodak EDR2 radiographic film and EBT2 Gafchromic film were also exposed for comparison.

Results:

The results indicate that the algorithm is able to correct images and calculate 2D dose. For the wedge field irradiation, the calculated dose at the center of the field was 0.9 Gy for Al2O3:C and 0.87 Gy for Al2O3:C,Mg, whereas, the delivered dose was 0.95 Gy. A good qualitative agreement of the dose profiles was obtained between the OSL films and EDR2 and EBT2 films. Laboratory tests using a beta source suggest that a large dynamic range (10−2−102 Gy) can be achieved using this technique.

Conclusion:

A 2D dosimetry system and an in‐house image correction algorithm were developed for 2D film dosimetry in medical applications. The system is in the preliminary stage of development, but the data demonstrates the feasibility of this approach. This work was supported by Landauer, Inc.
SU‐E‐CAMPUS‐T‐06: Radiochromic Film Analysis Based On Principal Components
Authors: Wendt R
Published: July 2014

Purpose:

An algorithm to convert the color image of scanned EBT2 radiochromic film [Ashland, Covington KY] into a dose map was developed based upon a principal component analysis. The sensitive layer of the EBT2 film is colored so that the background streaks arising from variations in thickness and scanning imperfections may be distinguished by color from the dose in the exposed film.

Methods:

Doses of 0, 0.94, 1.9, 3.8, 7.8, 16, 32 and 64 Gy were delivered to radiochromic films by contact with a calibrated Sr‐90/Y‐90 source. They were digitized by a transparency scanner. Optical density images were calculated and analyzed by the method of principal components. The eigenimages of the 0.94 Gy film contained predominantly noise, predominantly background streaking, and background streaking plus the source, respectively, in order from the smallest to the largest eigenvalue. Weighting the second and third eigenimages by −0.574 and 0.819 respectively and summing them plus the constant 0.012 yielded a processed optical density image with negligible background streaking. This same weighted sum was transformed to the red, green and blue space of the scanned images and applied to all of the doses. The curve of processed density in the middle of the source versus applied dose was fit by a twophase association curve. A film was sandwiched between two polystyrene blocks and exposed edge‐on to a different Y‐90 source. This measurement was modeled with the GATE simulation toolkit [Version 6.2, OpenGATE Collaboration], and the on‐axis depth‐dose curves were compared.

Results:

The transformation defined using the principal component analysis of the 0.94 Gy film minimized streaking in the backgrounds of all of the films. The depth‐dose curves from the film measurement and simulation are indistinguishable.

Conclusion:

This algorithm accurately converts EBT2 film images to dose images while reducing noise and minimizing background streaking.

Supported by a sponsored research agreement from IsoTherapeutics Group, LLC.
SU‐E‐CAMPUS‐T‐01: Analysis of the Precision of Patient Set‐Up, and Fidelity of the Delivered Dose Distribution in Proton Therapy of Ocular Tumors
Authors: Trofimov A , Carpenter K , Shih HA
Published: July 2014

Purpose:

To quantify daily set‐up variations in fractionated proton therapy of ocular melanomas, and to assess the effect on the fidelity of delivered distribution to the plan.

Methods:

In a typical five‐fraction course, daily set‐up is achieved by matching the position of fiducial markers in orthogonal radiographs to the images generated by treatment planning program. A patient maintains the required gaze direction voluntarily, without the aid of fixation devices. Confirmation radiographs are acquired to assess intrafractional changes. For this study, daily radiographs were analyzed to determine the daily iso‐center position and apparent gaze direction, which were then transferred to the planning system to calculate the dose delivered in individual fractions, and accumulated dose for the entire course. Dose‐volume metrics were compared between the planned and accumulated distributions for the tumor and organs at risk, for representative cases that varied by location within the ocular globe.

Results:

The analysis of the first set of cases (3 posterior, 3 transequatorial and 4 anterior tumors) revealed varying dose deviation patterns, depending on the tumor location. For anterior and posterior tumors, the largest dose increases were observed in the lens and ciliary body, while for the equatorial tumors, macula, optic nerve and disk, were most often affected. The iso‐center position error was below 1.3 mm (95%‐confidence interval), and the standard deviation of daily polar and azimuthal gaze set‐up were 1.5 and 3 degrees, respectively.

Conclusion:

We quantified interfractional and intrafractional set‐up variation, and estimated their effect on the delivered dose for representative cases. Current safety margins are sufficient to maintain the target coverage, however, the dose delivered to critical structures often deviates from the plan. The ongoing analysis will further explore the patterns of dose deviation, and may help to identify particular treatment scenarios which are at a higher risk for such deviations.
SU‐E‐CAMPUS‐T‐02: Can Pre‐Treatment 4DCT‐Based Motion Margins Estimates Be Trusted for Proton Radiotherapy?
Authors: Seco J , Koybasi O , Mishra P , James S St. , Lewis J
Published: July 2014

Purpose:

Radiotherapy motion margins are generated using pre‐treatment 4DCT data. The purpose of this study is to assess if pre‐treatment 4DCT is sufficient in proton therapy to provide accurate estimate of motion margins. A dosimetric assessment is performed comparing pre‐treatment margins with daily‐customized margins.

Methods:

Gold fiducial markers implanted in lung tumors of patients were used to track the tumor. A spherical tumor of diameter 20 mm is inserted into a realistic digital respiratory phantom, where the tumor motion is based on real patient lung tumor trajectories recorded over multiple days. Using “Day 1” patient data, 100 ITVs were generated with 1 s interval between consecutive scan start times. Each ITV was made up by the union of 10 tumor positions obtained from 6 s scan time. Two ITV volumes were chosen for treatment planning: ITVmean‐σ and ITVmean+σ. The delivered dose was computed on i) 10 phases forming the planning ITV (“10‐phase” – simulating dose calculation based on 4DCT) and ii) 50 phantoms produced from 100 s of data from any other day with tumor positions sampled every 2 s (“dynamic” – simulating the dose that would actually be delivered).

Results:

For similar breathing patterns between “Day 1” and any other “Day N(>1)”, the 95% volume coverage (D95) for “dynamic” case was 8.13% lower than the “10‐phase” case for ITVmean+σ. For breathing patterns that were very different between “Day 1” and any other “Day N(>1)”, this difference was as high as 24.5% for ITVmean‐σ.

Conclusion:

Proton treatment planning based on pre‐treatment 4DCT can lead to under‐dosage of the tumor and over‐dosage of the surrounding tissues, because of inadequate estimate of the range of motion of the tumor. This is due to the shift of the Bragg peak compared to photon therapy in which the tumor is surrounded by an electron bath.
SU‐E‐CAMPUS‐T‐03: Development and Implementation of An Anthropomorphic Pediatric Spine Phantom for the Assessment of Craniospinal Irradiation Procedures in Proton Therapy
Authors: Lewis D , Summers P , Followill D , Sahoo N , Mahajan A , Stingo F , Kry S
Published: July 2014

Purpose:

To design an anthropomorphic pediatric spine phantom for use in the evaluation of proton therapy facilities for clinical trial participation by the Imaging and Radiation Oncology Core (IROC) Houston QA Center (formerly RPC).

Methods:

This phantom was designed to perform an end‐to‐end audit of the proton spine treatment process, including simulation, dose calculation by the treatment planning system (TPS), and proton treatment delivery. The design incorporated materials simulating the thoracic spinal column of a pediatric patient, along with two thermoluminescent dosimeter (TLD)‐100 capsules and radiochromic film embedded in the phantom for dose evaluation. Fourteen potential materials were tested to determine relative proton stopping power (RSP) and Hounsfield unit (HU) values. Each material was CT scanned at 120kVp, and the RSP was obtained from depth ionization scans using the Zebra multilayer ion chamber (MLIC) at two energies: 160 MeV and 250 MeV. To determine tissue equivalency, the measured RSP for each material was compared to the RSP calculated by the Eclipse TPS for a given HU.

Results:

The materials selected as bone, tissue, and cartilage substitutes were Techron HPV Bearing Grade (Boedeker Plastics, Inc.), solid water, and blue water, respectively. The RSP values did not differ by more than 1.8% between the two energies. The measured RSP for each selected material agreed with the RSP calculated by the Eclipse TPS within 1.2%.

Conclusion:

An anthropomorphic pediatric proton spine phantom was designed to evaluate proton therapy delivery. The inclusion of multiple tissue substitutes increases heterogeneity and the level of difficulty for institutions to successfully treat the phantom. The following attributes will be evaluated: absolute dose agreement, distal range, field width, junction match and right/left dose profile alignment. The phantom will be tested at several institutions using a 5% dose agreement criterion, and a 5%/3mm gamma analysis criterion for the film planes.

Work supported by grants CA10953, CA059267, and CA81647 (NCI, DHHS).
SU‐E‐CAMPUS‐T‐04: Statistical Process Control for Patient‐Specific QA in Proton Beams
Authors: LAH J , SHIN D , Kim G
Published: July 2014

Purpose:

To evaluate and improve the reliability of proton QA process, to provide an optimal customized level using the statistical process control (SPC) methodology. The aim is then to suggest the suitable guidelines for patient‐specific QA process.

Methods:

We investigated the constancy of the dose output and range to see whether it was within the tolerance level of daily QA process. This study analyzed the difference between the measured and calculated ranges along the central axis to suggest the suitable guidelines for patient‐specific QA in proton beam by using process capability indices. In this study, patient QA plans were classified into 6 treatment sites: head & neck (41 cases), spinal cord (29 cases), lung (28 cases), liver (30 cases), pancreas (26 cases), and prostate (24 cases).

Results:

The deviations for the dose output and range of daily QA process were ±0.84% and ±019%, respectively. Our results show that the patient‐specific range measurements are capable at a specification limit of ±2% in all treatment sites except spinal cord cases. In spinal cord cases, comparison of process capability indices (Cp, Cpm, Cpk ≥1, but Cpmk ≤1) indicated that the process is capable, but not centered, the process mean deviates from its target value. The UCL (upper control limit), CL (center line) and LCL (lower control limit) for spinal cord cases were 1.37%, −0.27% and −1.89%, respectively. On the other hands, the range differences in prostate cases were good agreement between calculated and measured values. The UCL, CL and LCL for prostate cases were 0.57%, −0.11% and −0.78%, respectively.

Conclusion:

SPC methodology has potential as a useful tool to customize an optimal tolerance levels and to suggest the suitable guidelines for patient‐specific QA in clinical proton beam.
SU‐E‐CAMPUS‐T‐05: Validation of High‐Resolution 3D Patient QA for Proton Pencil Beam Scanning and IMPT by Polymer Gel Dosimetry
Authors: Cardin A , Avery S , Maryanski M , Ding X , Kassaee A , Lin L
Published: July 2014

Purpose:

Validation of high‐resolution 3D patient QA for proton pencil beam scanning and IMPT by polymer gel dosimetry.

Methods:

Four BANG3Pro polymer gel dosimeters (manufactured by MGS Research Inc, Madison, CT) were used for patient QA at the Robert's Proton Therapy Center (RPTC, Philadelphia, PA). All dosimeters were sealed in identical thin‐wall Pyrex glass spheres. Each dosimeter contained a set of markers for 3D registration purposes. The dosimeters were mounted in a consistent and reproducible manner using a custom build holder. Two proton pencil beam scanning plans were designed using Varian Eclipse™ treatment planning system: 1) A two‐field intensity modulated proton therapy (IMPT) plan and 2) one single field uniform dose (SFUD) plan. The IMPT fields were evaluated as a composite plan and individual fields, the SFUD plan was delivered as a single field plan.Laser CT scanning was performed using the manufacturer's OCTOPUS‐IQ axial transmission laser CT scanner using a 1 mm slice thickness. 3D registration, analysis, and OD/cm to absorbed dose calibrations were perfomed using DICOM RT‐Dose and CT files, and software developed by the manufacturer. 3D delta index, a metric equivalent to the gamma tool, was used for dose comparison.

Results:

Very good agreement with single IMPT fields and with SFUD was obtained. Composite IMPT fields had a less satisfactory agreement. The single fields had 3D delta index passing rates (3% dose difference, 3 mm DTA) of 98.98% and 94.91%. The composite 3D delta index passing rate was 80.80%. The SFUD passing rate was 93.77%. Required shifts of the dose distributions were less than 4 mm.

Conclusion:

A formulation of the BANG3Pro polymer gel dosimeter, suitable for 3D QA of proton patient plans is established and validated. Likewise, the mailed QA analysis service provided by the manufacturer is a practical option when required resources are unavailable.

We fully disclose that the subject of this research regards a production of MGS Research, Inc.
SU‐E‐CAMPUS‐T‐06: Initial Experience of Patient‐Specific QA Using a Pencil Beam Scanning Proton Therapy System
Authors: Piskulich F , Zhang Y , Perles L , Mascia A , Lepage R , Giebeler A , Dong L
Published: July 2014

Purpose:

To illustrate patient QA results for the first 10 patients treated at Scripps Proton Center by comparing point dose measurement using an ion chamber and in‐house developed secondary MU program, and the measurement of 2D dose distribution using an ion chamber array.

Methods:

At the time of writing, 10 patient plans were approved for treatment using Varian ProBeam pencil beam scanning system and Eclipse treatment planning software. We used the IBA CC04 0.04 cm3 ion chamber and PTW Unidos E electrometer for point dose measurement in a small water tank (Sun Nuclear 1D scanner). We developed independent MU check software based on measured pencil beam dose profiles for various energies. We used PTW Octavius 729 XDR array to evaluate 2D planar dose distribution. The 3D gamma at 3%/3 mm local dose was used to compare a 3D calculated dose plan with a 2D measured dose distribution using PTW Verisoft software. All fields were exported to a verification phantom plan and delivered at 0 degrees for simplicity.

Results:

Comparisons between the CC04 ion chamber measurement and calculated dose agree well within 1%. The PTW Octavius 729 XDR array exhibited some dose rate dependence in high dose rate pencil beam delivery. Nevertheless, the results, used as a relative measurement, passed the gamma criteria of 3%/3mm for greater than 90% of area in all patient fields. Visual inspection showed good agreement between ion chamber dose profile and the calculated plan. The in‐house secondary check for MU agreed very well with the plan dose and measurement. The results will be updated with more patients treated.

Conclusion:

The initial patient specific QA results are encouraging for a new pencil beam scanning only proton therapy system.