bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐F‐BRD‐08: A Novel Technique to Derive a Clinically‐Acceptable Beam Model for Proton Pencil‐Beam Scanning in a Commercial Treatment Planning System
Authors: Scholey J. E. , Lin L. , Ainsley C. G.
Published: June 2015

Purpose:

To evaluate the accuracy and limitations of a commercially‐available treatment planning system's (TPS's) dose calculation algorithm for proton pencil‐beam scanning (PBS) and present a novel technique to efficiently derive a clinically‐acceptable beam model.

Methods:

In‐air fluence profiles of PBS spots were modeled in the TPS alternately as single‐(SG) and double‐Gaussian (DG) functions, based on fits to commissioning data. Uniform‐fluence, single‐energy‐layer square fields of various sizes and energies were calculated with both beam models and delivered to water. Dose was measured at several depths. Motivated by observed discrepancies in measured‐versus‐calculated dose comparisons, a third model was constructed based on double‐Gaussian parameters contrived through a novel technique developed to minimize these differences (DGC). Eleven cuboid‐dose‐distribution‐shaped fields with varying range/modulation and field size were subsequently generated in the TPS, using each of the three beam models described, and delivered to water. Dose was measured at the middle of each spread‐out Bragg peak.

Results:

For energies <160 MeV, the DG model fit square‐field measurements to <2% at all depths, while the SG model could disagree by >6%. For energies >160 MeV, both SG and DG models fit square‐field measurements to <1% at <4 cm depth, but could exceed 6% deeper. By comparison, disagreement with the DGC model was always <3%. For the cuboid plans, calculation‐versus‐measured percent dose differences exceeded 7% for the SG model, being larger for smaller fields. The DG model showed <3% disagreement for all field sizes in shorter‐range beams, although >5% differences for smaller fields persisted in longer‐range beams. In contrast, the DGC model predicted measurements to <2% for all beams.

Conclusion:

Neither the TPS's SG nor DG models, employed as intended, are ideally suited for routine clinical use. However, via a novel technique to be presented, its DG model can be tuned judiciously to yield acceptable results.
SU‐F‐BRD‐12: When Does Pencil Beam Scanning Become Superior to Passive Scattered Proton Therapy for Pediatric Head and Neck Cancers?
Authors: Moteabbed M , Depauw N , Kooy H , Yock T , Paganetti H
Published: June 2015

Purpose:

To investigate the dosimetric benefits of pencil beam scanning (PBS) compared with passive scattered (PS) proton therapy for treatment of pediatric head&neck patients as a function of the PBS spot size and explore the advantages of using apertures in PBS.

Methods:

Ten pediatric patients with head&neck cancers treated by PS proton therapy at our institution were retrospectively selected. The histologies included rhabdomyosarcoma, ependymoma, astrocytoma, craniopharyngioma and germinoma. The prescribed dose ranged from 36 to 54 Gy(RBE). Five PBS plans were created for each patient using variable spot size (average sigma at isocenter) and choice of beam specific apertures: (1) 10mm spots, (2) 10mm spots with apertures, (3) 6mm spots, (4) 6mm spots with apertures, and (5) 3mm spots. The plans were optimized for intensity modulated proton therapy (IMPT) with no single beam uniformity constraints. Dose volume indices as well as equivalent uniform dose (EUD) were compared between PS and PBS plans.

Results:

Although target coverage was clinically adequate for all cases, the plans with largest (10mm) spots provide inferior quality compared with PS in terms of dose to organs‐at‐risk (OAR). However, adding apertures to these plans ensured lower OAR dose than PS. The average EUD difference between PBS and PS plans over all patients and organs at risk were (1) 2.5%, (2) −5.1%, (3) ‐5%, (4) −7.8%, and (5) −9.5%. As the spot size decreased, more conformal plans were achieved that offered similar target coverage but lower dose to the neighboring healthy organs, while alleviating the need for using apertures.

Conclusion:

The application of PBS does not always translate to better plan qualities compared to PS depending on the available beam spot size. We recommend that institutions with spot size larger than ∼6mm at isocenter consider using apertures to guarantee clinically comparable or superior dosimetric efficacy to PS treatments.
SU‐F‐BRD‐14: Dose Weighted Linear Energy Transfer Analysis of Critical Structures in Proton Therapy of Pediatric Brain Tumor Patients
Authors: Pirlepesov F. , Shin J. , Moskvin V. P. , Gray J. , Li Z. , Hua C. , Gajjar A. , Krasin M. J. , Merchant T. E. , Farr J. B.
Published: June 2015

Purpose:

Dose weighted Linear Energy Transfer (LETd) analysis of critical structures may be useful in understanding the side effects of the proton therapy. The objective is to analyze the differences between LETd and dose distributions in brain tumor patients receiving double scattering proton therapy, to quantify LETd variation in critical organs, and to identify beam arrangements contributing to high LETd in critical organs.

Methods:

Monte Carlo simulations of 9 pediatric brain tumor patients were performed. The treatment plans were reconstructed with the TOPAS Monte Carlo code to calculate LETd and dose. The beam data were reconstructed proximal to the aperture of the double scattering nozzle. The dose and LETd to target and critical organs including brain stem, optic chiasm, lens, optic nerve, pituitary gland, and hypothalamus were computed for each beam.

Results:

Greater variability in LETd compared to dose was observed in the brainstem for patients with a variety of tumor types including 5 patients with tumors located in the posterior fossa. Approximately 20%–44% brainstem volume received LETd of 5kev/µm or greater from beams within gantry angles 180°±30° for 5 patients treated with a 3 beam arrangement. Critical organs received higher LETd when located in the vicinity of the beam distal edge.

Conclusion:

This study presents a novel strategy in the evaluation of the proton treatment impact on critical organs. While the dose to critical organs is confined below the required limits, the LETd may have significant variation. Critical organs in the vicinity of beam distal edge receive higher LETd and depended on beam arrangement, e.g. in posterior fossa tumor treatment, brainstem receive higher LETd from posterior‐anterior beams. This study shows importance of the LETd analysis of the radiation impact on the critical organs in proton therapy and may be used to explain clinical imaging observations after therapy.
SU‐F‐BRD‐16: Relative Biological Effectiveness of Double‐Strand Break Induction for Modeling Cell Survival in Pristine Proton Beams of Different Dose‐Averaged Linear Energy Transfers
Authors: Peeler C , Taleei R , Guan F , Bronk L , Patel D , Titt U , Mirkovic D , Stewart R , Grosshans D , Mohan R
Published: June 2015

Purpose:

High throughput in vitro experiments assessing cell survival following proton radiation indicate that both the alpha and the beta parameters of the linear quadratic model increase with increasing proton linear energy transfer (LET). We investigated the relative biological effectiveness (RBE) of double‐strand break (DSB) induction as a means of explaining the experimental results.

Methods:

Experiments were performed with two lung cancer cell lines and a range of proton LET values (0.94 – 19.4 keV/µm) using an experimental apparatus designed to irradiate cells in a 96 well plate such that each column encounters protons of different dose‐averaged LET (LETd). Traditional linear quadratic survival curve fitting was performed, and alpha, beta, and RBE values obtained. Survival curves were also fit with a model incorporating RBE of DSB induction as the sole fit parameter. Fitted values of the RBE of DSB induction were then compared to values obtained using Monte Carlo Damage Simulation (MCDS) software and energy spectra calculated with Geant4. Other parameters including alpha, beta, and number of DSBs were compared to those obtained from traditional fitting.

Results:

Survival curve fitting with RBE of DSB induction yielded alpha and beta parameters that increase with proton LETd, which follows from the standard method of fitting; however, relying on a single fit parameter provided more consistent trends. The fitted values of RBE of DSB induction increased beyond what is predicted from MCDS data above proton LETd of approximately 10 keV/µm.

Conclusion:

In order to accurately model in vitro proton irradiation experiments performed with high throughput methods, the RBE of DSB induction must increase more rapidly than predicted by MCDS above LETd of 10 keV/µm. This can be explained by considering the increased complexity of DSBs or the nature of intra‐track pairwise DSB interactions in this range of LETd values.

NIH Grant 2U19CA021239‐35
SU‐F‐BRB‐01: How Effective Is Abdominal Compression at Reducing Lung Motion? An Analysis Using Deformable Image Registration Within Different Sub‐Regions of the Lung
Authors: Paradiso D , Pearce A , Leszczynski K , Oliver M
Published: June 2015

Purpose:

To investigate the effectiveness of employing abdominal compression (AC) in reducing motion for the target region and sub‐regions of the lung as part of the planning process for radiation therapy.

Methods:

Fourteen patients with early lung cancer were scanned with 4DCT and it was determined that target motion exceeded our institutional limit of > 8 mm motion and received a repeat 4DCT with AC. For each 4DCT, deformable image registration (DIR) was used to map the max inhale to the max exhale phase to determine the deformation vector fields (DVF). DIR was performed with Morphons and Demons algorithms. The mean DVF was used to represent that sub‐region for each patient. The magnitudes of the mean DVF were quantified for the target and 12 sub‐regions in the AP, LR SI directions. The sub‐regions were contoured on each lung as (add prefix R or L for lung): Upper‐Anterior (UA), Upper‐Posterior (UP), Mid‐Anterior (MA), Mid‐Posterior (MP), Lower‐Anterior (LA) and Lower‐Posterior (LP).

Results:

The min/max SI motion for the target on the uncompressed 4DCT was 8mm/24.5 mm. The magnitude of decrease in SI was greatest in the RLP region (3.7±4.0mm) followed by target region (3.3±2.2mm) and finally the LLP region (3.0±3.5mm). The magnitude of decrease in 3D vector followed the same trend; RLP (3.5±2.2mm) then GTV (3.5±2.6mm) then LLP (2.7±3.8mm). 79% of the cases had a SI decrease of >12.5%, 43% had a SI decrease of >25% and 21% had a SI decrease of >50% as compared to the motion on the uncompressed 4DCT.

Conclusion:

AC is useful in reducing motion with the largest decreases observed in the lower posterior regions of the lungs. However, it should be noted that AC will not greatly decrease motion for all cases as 21% of cases did not reduce SI motion more than 12.5% of initial motion.
SU‐F‐BRB‐09: Measurement Based Dose‐Volume Metrics for the Quality Assurance of VMAT Plans‐Are We There Yet?
Authors: Arumugam S , Xing A , Young T , Blake S , Thwaites D , Holloway L
Published: June 2015

Purpose:

To validate ArcCHECK measurement‐based 3DVH dose‐volume metrics for use with volumetric modulated arc therapy (VMAT) plans.

Methods:

Five each of prostate and head and neck (H&N) VMAT plans were considered for this study. Three types of errors were introduced into the original plans: gantry angle independent MLC shift (ranging from −5mm to 5mm), gantry angle dependent MLC error (ranging from 1mm to 7mm) and gantry angle dependent dose error (ranging from 1% to 10%). The percentage difference in PTV‐D95 as estimated by 3DVH for the error‐introduced delivery was compared with a similar metric calculated by comparing the dose matrices of the error‐free and error‐introduced plans calculated in the TPS. The gamma analysis with 2%L/2mm and 3%L/3mm tolerance criteria was also calculated by comparing the dose matrices.

Results:

For MLC shift errors, the TPS dose matrix comparison showed that the PTV‐D95 for the prostate plans reduced by a maximum (SD) of −8.4(3.3)% for the 5mm error. The 3DVH‐estimated D95 reduced from −0.5(2.0) for no‐error plans to −1.0(3.3)% for the 5mm MLC shift. Similarly for H&N plans the TPS‐calculated PTV‐D95 reduced by −5.1(3.8)%, with the 3DVH‐estimated D95 reducing from −1.5(2.2)% to −3.2(5.8)%. For gantry dependent MLC errors, the TPS D95 of prostate plans reduced to a maximum of −14.1(8.5)%, while the 3DVH‐estimated D95 reduced to 0.6(4.2)%. For H&N plans the TPS D95 reduced to −1.7(1.7)%, while the 3DVH‐estimated D95 reduced to −4.0(4.1)%. No major change in D95 was observed for gantry dependent dose errors for the TPS or 3DVH. In all error scenarios the gamma pass rate decreased as the magnitude of error increased.

Conclusion:

The gamma comparison of dose matrices was shown to detect all type of errors considered. The 3DVH‐estimated D95 agreed with the TPS more closely in H&N plans than prostate plans.

This project was funded through a Cancer Council NSW Project Grant (RG14‐11)
SU‐F‐BRB‐10: A Statistical Voxel Based Normal Organ Dose Prediction Model for Coplanar and Non‐Coplanar Prostate Radiotherapy
Authors: Tran A , Yu V , Nguyen D , Woods K , Low D , Sheng K
Published: June 2015

Purpose:

Knowledge learned from previous plans can be used to guide future treatment planning. Existing knowledge‐based treatment planning methods study the correlation between organ geometry and dose volume histogram (DVH), which is a lossy representation of the complete dose distribution. A statistical voxel dose learning (SVDL) model was developed that includes the complete dose volume information. Its accuracy of predicting volumetric‐modulated arc therapy (VMAT) and non‐coplanar 4π radiotherapy was quantified. SVDL provided more isotropic dose gradients and may improve knowledge‐based planning.

Methods:

12 prostate SBRT patients originally treated using two full‐arc VMAT techniques were re‐planned with 4π using 20 intensity‐modulated non‐coplanar fields to a prescription dose of 40 Gy. The bladder and rectum voxels were binned based on their distances to the PTV. The dose distribution in each bin was resampled by convolving to a Gaussian kernel, resulting in 1000 data points in each bin that predicted the statistical dose information of a voxel with unknown dose in a new patient without triaging information that may be collectively important to a particular patient. We used this method to predict the DVHs, mean and max doses in a leave‐one‐out cross validation (LOOCV) test and compared its performance against lossy estimators including mean, median, mode, Poisson and Rayleigh of the voxelized dose distributions.

Results:

SVDL predicted the bladder and rectum doses more accurately than other estimators, giving mean percentile errors ranging from 13.35–19.46%, 4.81–19.47%, 22.49–28.69%, 23.35–30.5%, 21.05–53.93% for predicting mean, max dose, V20, V35, and V40 respectively, to OARs in both planning techniques. The prediction errors were generally lower for 4π than VMAT.

Conclusion:

By employing all dose volume information in the SVDL model, the OAR doses were more accurately predicted. 4π plans are better suited for knowledge‐based planning than the VMAT plans that are strongly biased in its dose gradient orientation.

This project is supported by Varian Medical Systems.
SU‐F‐BRB‐12: A Novel Haar Wavelet Based Approach to Deliver Non‐Coplanar Intensity Modulated Radiotherapy Using Sparse Orthogonal Collimators
Authors: Nguyen D , Ruan D , O'Connor D , Low D , Boucher S , Sheng K
Published: June 2015

Purpose:

Existing efforts to replace complex multileaf collimator (MLC) by simple jaws for intensity modulated radiation therapy (IMRT) resulted in unacceptable compromise in plan quality and delivery efficiency. We introduce a novel fluence map segmentation method based on compressed sensing for plan delivery using a simplified sparse orthogonal collimator (SOC) on the 4π non‐coplanar radiotherapy platform.

Methods:

4π plans with varying prescription doses were first created by automatically selecting and optimizing 20 non‐coplanar beams for 2 GBM, 2 head & neck, and 2 lung patients. To create deliverable 4π plans using SOC, which are two pairs of orthogonal collimators with 1 to 4 leaves in each collimator bank, a Haar Fluence Optimization (HFO) method was used to regulate the number of Haar wavelet coefficients while maximizing the dose fidelity to the ideal prescription. The plans were directly stratified utilizing the optimized Haar wavelet rectangular basis. A matching number of deliverable segments were stratified for the MLC‐based plans.

Results:

Compared to the MLC‐based 4π plans, the SOC‐based 4π plans increased the average PTV dose homogeneity from 0.811 to 0.913. PTV D98 and D99 were improved by 3.53% and 5.60% of the corresponding prescription doses. The average mean and maximal OAR doses slightly increased by 0.57% and 2.57% of the prescription doses. The average number of segments ranged between 5 and 30 per beam. The collimator travel time to create the segments decreased with increasing leaf numbers in the SOC. The two and four leaf designs were 1.71 and 1.93 times more efficient, on average, than the single leaf design.

Conclusion:

The innovative dose domain optimization based on compressed sensing enables uncompromised 4π non‐coplanar IMRT dose delivery using simple rectangular segments that are deliverable using a sparse orthogonal collimator, which only requires 8 to 16 leaves yet is unlimited in modulation resolution.

This work is supported in part by Varian Medical Systems, Inc. and NIH R43 CA18339.
SU‐F‐BRB‐13: Correlation of Improved Target and Organ‐At‐Risk Dosimetric Quantities and Clinical Outcomes for Helical Tomotherapy Treated Mesothelioma
Authors: Qi S , Kishan A , Alexander S , Lee P , Selch M , Kupelian P , Steiberg M , Low D
Published: June 2015

Purpose:

We have observed improved local control probability (LCP) for adjuvant mesothelioma radiotherapy following pleurectomy/decortication using Tomotherapy compared to the conventional 3D technique (p<0.05). This work assesses the correlation between the improved clinical outcomes against dosimetry quantities.

Methods:

Thirty‐eight mesothelioma cases consecutively treated at our clinic were retrospectively analyzed. Sixteen patients were treated using 3D technique planned on the Eclipse for c‐arm accelerators prior to 7/2012; the other 22 cases were treated on Tomotherapy using helical IMRT after 7/2012. Typical 3D plans consisting of 15 MV AP/PA photon fields prescribed to 10 cm depth followed by matching electron fields with energy ranging from 8–16 MeV. Tomotherapy plans were designed using 2.5cm jaw, 0.287 pitch with directional blocking of the contralateral lung. The same prescription of 45 Gy (1.8GyX25) was used for both techniques. The dosimetry metrics for the critical structures: ipsilateral‐/contralateral‐lung, heart, cord, esophagus, etc were compared between two techniques.

Results:

Superior LCP is closely associated with improved target coverage. Tomotherapy plans yielded dramatically better target coverage and less dose heterogeneity despite of more advanced/larger disease. The averaged PTV volumes were 2287.3±569.9 (Tomotherapy) vs. 1904.8±312.3cc (3D); V100s were: 91.1±4.0 (%) vs. 47.8±12.7 (%) with heterogeneity indices of 1.20±0.1 vs.1.37±0.38 and for the Tomotherapy and 3D plans, respectively. Compared to the 3D technique, we observed significant lower maximum cord doses (p<0.001), lower mean esophagus doses (p<0.002), and lower heart mean doses when tumor was left‐sided (p=0.002). For ipsilateral‐/contralateral‐lungs, however, the mean doses and V20, V5 of Tomotherapy plans were significantly higher than the 3D plans (p<0.01) regardless which sides of lung were treated. However, rates of radiation pneumonitis were no different.

Conclusion:

Tomotherapy achieved great improvement of plan quality including target coverage, resulting in significantly better local control over the traditional 3D technique for adjuvant radiotherapy for mesothelioma.
MO‐A‐BRB‐01: Review of TG‐262 Internal Survey of Practices in EMR for External Beam Therapy
Authors: Mechalakos J.
Published: June 2015

The process of converting to an electronic chart for radiation therapy can be daunting. It requires a dedicated committee to first research and choose appropriate software, to review the entire documentation policy and flow of the clinic, to convert this system to electronic form or if necessary, redesign the system to more easily conform to the electronic process. Those making the conversion and those who already use electronic charting would benefit from the shared experience of those who have been through the process in the past. Therefore TG262 was convened to provide guidance on electronic charting for external beam radiation therapy and brachytherapy.

This course will present the results of an internal survey of task group members on EMR practices in External Beam Radiation Therapy as well as discuss important issues in EMR development and structure for both EBRT and brachytherapy.

Learning Objectives:

Be familiarized with common practices and pitfalls in development and maintenance of an electronic chart in Radiation Oncology

Be familiarized with important issues related to electronic charting in External Beam Radiation Therapy

Be familiarized with important issues related to electronic charting in Brachytherapy
MO‐A‐BRB‐02: Considerations and Issues in Electronic Charting for Brachytherapy
Authors: Richardson S.
Published: June 2015

The process of converting to an electronic chart for radiation therapy can be daunting. It requires a dedicated committee to first research and choose appropriate software, to review the entire documentation policy and flow of the clinic, to convert this system to electronic form or if necessary, redesign the system to more easily conform to the electronic process. Those making the conversion and those who already use electronic charting would benefit from the shared experience of those who have been through the process in the past. Therefore TG262 was convened to provide guidance on electronic charting for external beam radiation therapy and brachytherapy.

This course will present the results of an internal survey of task group members on EMR practices in External Beam Radiation Therapy as well as discuss important issues in EMR development and structure for both EBRT and brachytherapy.

Learning Objectives:

Be familiarized with common practices and pitfalls in development and maintenance of an electronic chart in Radiation Oncology

Be familiarized with important issues related to electronic charting in External Beam Radiation Therapy

Be familiarized with important issues related to electronic charting in Brachytherapy
MO‐AB‐BRA‐01: A Novel Method to Objectively Quantify Normal Tissue Toxicity in the Esophagus
Authors: Niedzielski J , Yang J , Stingo F , Krafft S , Martel M , Briere T , Mohan R , Court L
Published: June 2015

Purpose:

Inconsistency between NTCP models for esophagitis prediction leads to reduced treatment efficacy, and arises from using subjective endpoints. We investigate esophageal swelling as an objective endpoint for NTCP modeling.

Methods:

A novel voxel‐based method was developed to quantify expansion in the esophagus. Utilizing deformable image registration (DIR) between a plan and serial CT image set, this technique calculates esophageal volume change from the Jacobian Map. This voxel‐volume change quantifies esophageal swelling. Next, a technique was developed to reduce uncertainty in esophageal volume change calculations due to physiological variation (i.e. swallowing, esophageal air pockets, etc.). The technique's effectiveness was evaluated by comparing expansion calculations on week01 CTs with and without corrections for 65 patients. This methodology was tested on sixty‐five patients with NSCLC that had esophagitis scoring (CTCAE3.0, 15 Grade3, 31 Grade2, 19 Grade0) and 6–8 weekly 4DCTs during treatment (IMRT). Esophageal swelling was analyzed for the treatment week of highest response. Dose was accumulated weekly using DIR. Logistic regression models were used to examine the relationship between expansion and grade3 esophagitis, and used to determine optimal binary endpoints of expansion. The relationship between dose and esophageal expansion as the endpoint was compared with dose to grade NTCP models. Performance of models was quantified with area under the curve (AUC) from ROC analysis.

Results:

Uncertainty in esophageal expansion calculations were reduced from 14.3% to 6.9%. The following expansion metrics were the most significantly correlated to grade3 esophagitis: maximum expansion (AUC=0.87,pval<0.001) and length of esophagus expanding>20% (LExp20%) (AUC=0.88,pval<0.01). The optimal expansion endpoint metrics were: Maximum Expansion>1.4 and LExp20%>50mm. Multivariate NTCP model with expansion endpoints outperformed NTCP model with grade endpoints: dose‐to‐expansion endpoint AUC=0.91, dose‐to‐grade endpoint AUC=0.81.

Conclusion:

Esophageal swelling is a continuous, objective, and in‐vivo metric of esophageal toxicity. Esophageal swelling endpoints can increase the performance of NTCP models.
MO‐AB‐BRA‐04: Correct Identification of Low‐Attenuation Intracranial Hemorrhage and Calcification Using Dual‐Energy Computed Tomography in a Phantom System
Authors: Nute J , Jacobsen M , Wei W , Baiu C , Popnoe D , Schellingerhout D , Cody D
Published: June 2015

Purpose:

Intracranial hemorrhage and calcification with Single‐Energy CT (SECT) attenuation below 100HU cannot be reliably identified using currently clinically available means. Calcification is typically benign but hemorrhage can carry a risk of intracranial bleeding and contraindicate use of anticoagulant therapies. A biologically‐relevant phantom was used to investigate identification of unknown intracranial lesions using dual‐energy CT (DECT) as a verification of prior lesion differentiation results.

Methods:

Prior phantom work investigating calcification and hemorrhage differentiation resulted in 3D‐DECT raw data (water density, calcium density, 68keV) for a range of DECT protocol variations: image thicknesses (1.25, 2.5, 3.75, 5mm), CTDIvol (36.7 to 132.6mGy) and reconstruction algorithms (Soft, Standard, Detail). Acquisition‐specific raw data were used to create a plane of optimal differentiation based on the geometric bisector of 3D‐linear regression of the two lesion distributions. Verification hemorrhage and calcification lesions, ranging in size from 0.5 to 1.5cm, were created at varying attenuation from 50 to 100HU. Lesions were inserted into a biologically‐relevant brain phantom and scanned using SECT (3.75mm images, Standard, 67mGy) and a range of DECT protocols (3.75mm images, Standard, [67, 105.6, 132.6mGy]). 3D‐DECT data were collected and blinded for analysis. The 3D‐DECT distribution of the lesion was then compared to the acquisition‐matched geometric bisector plane and the mean lesion value's position relative to the plane, indicating lesion identity, and the percentage of voxels on the identified side of the plane, indicating identification confidence, were derived.

Results:

98% of the 120 lesions investigated were identified correctly as hemorrhage or calcification. 74% were identified with greater than 80% confidence. Increases in CTDIvol and lesion diameter were associated with increased identification confidence.

Conclusion:

Intracranial lesions of unknown etiology were identified with 80% confidence for 74% of lesions investigated. These phantom data suggest that the identification of intracranial lesions below 100HU is clinically feasible using DECT.

This research was conducted at the MD Anderson Center for Advanced Biomedical Imaging in‐part with equipment support from General Electric Healthcare
MO‐AB‐BRA‐05: Monte Carlo Simulation of Glandular Breast Dose in Mammography Using Breast CT‐Derived Glandular Distributions
Authors: Hernandez A , Boone J , Seibert J
Published: June 2015

Purpose:

To determine the effect of breast CT‐derived fibroglandular distributions on glandular dose in mammography.

Methods:

Previously‐reported 3D glandular distributions, obtained from a large cohort of breast CT (bCT) data sets (N=219), were fit to bi‐Gaussian functions and used as probability density maps to assign glandular distributions within compressed breast models. Using a conventional mammography geometry, MCNPX was used to simulate monoenergetic normalized glandular dose “DgN(E)” values in compressed phantoms composed of either a homogeneous mixture of glandular and adipose tissue or heterogeneously distributed glandular tissue. The DgN(E) values were weighted by mammographic x‐ray spectra to produce polyenergetic DgN (pDgN) values for the homogeneous (pDgNhomo) and heterogeneous (pDgNhetero) tissue compositions. This work quantified the effect of permutations in glandular fraction, phantom size, x‐ray technique, and location of glandular distributions on pDgN values.

Results:

Averaged across all phantom sizes and glandular fractions, pDgNhetero values were 30.1% and 21.6% lower than the pDgNhomo values for the Mo and W x‐ray spectra, respectively, when the heterogeneous distributions were centered within the breast phantom. Displacement of the glandular distributions in the superior and inferior directions resulted in pDgNhetero values 5.7% and 49.4% lower than pDgNhomo values, respectively, for Mo x‐ray spectra. Lateral displacement of the glandular distributions resulted in no notable difference in pDgN values.

Conclusion:

This study demonstrates that glandular dose values in mammography are 20 to 30% lower than assumed using the homogeneous approximation resulting from overestimation of glandular tissue at the breast entrance where the dose deposition is higher. The sensitivity analysis also demonstrates that the differences depend on likely perturbations in the glandular distributions. While these results are robust because the glandular distributions are modeled from a large cohort of bCT data sets, future work will focus on improved quantification of the glandular distributions based on breast size and glandular fraction.
MO‐AB‐BRA‐06: Noise Index for Model Based Iterative Reconstruction (MBIR)? A Prospective Trial with 110 Human Subjects
Authors: Gomez‐Cardona D , Li K , Lubner M G , Pickhardt P J , Chen G‐H
Published: June 2015

Purpose:

Noise index (NI) enables the mAs to be automatically determined to achieve the desired CT noise level. The scientific foundation behind the use of NI is the linear relationship between noise variance (σ2) and the 1/mAs. This relationship has been severely violated by the use of the highly nonlinear MBIR algorithm, making the traditional NI system no longer valid. This work studied how the quantitative relationship between σ2 and mAs should be modified in MBIR so that a new NI‐mAs correspondence can be established.

Methods:

A comprehensive investigation using an anthropomorphic abdominal phantom, in‐vivo swine, and an IRB‐approved prospective human subject trial with a cohort of 110 subjects was performed. All scans were performed using a 64‐slice CT scanner (Discovery CT750 HD, GE Healthcare) with typical abdominal protocols. Several mAs levels were used for the phantom and swine (10–350 mAs), while for human subjects two mAs levels were used. Both FBP and MBIR (Veo, GE Healthcare) reconstructions were performed. Values of σ2 were measured in relatively uniform regions such as liver and fat. The measured variances were related to mAs through the power‐law relationship σ2 = α(mAs)^(−β).

Results:

For liver, β is 1.0±0.10 for FBP and 0.4±0.12 for MBIR. The difference in β between the two methods is statistically significant (p<0.001). For patients with a given size (effective diameter∼28 cm), the α value is 1.2×10⁵ for FBP and 600 for MBIR. The R2 value fitting was 0.96±0.03.

Conclusion:

As long as the noise magnitude of a standard dose FBP image is known, in addition to predicting the noise magnitude of the corresponding MBIR image at the same dose, one can also predict the noise magnitude of the MBIR image at reduced dose. Therefore, it is both plausible and necessary to establish a new NI‐mAs correspondence system for the MBIR.

This work was partially supported by an NIH grant R01CA169331 and GE Healthcare. K. Li, D. Gomez‐Cardona, M. G. Lubner: Nothing to disclose. P. J. Pickhardt: Co‐founder, VirtuoCTC, LLC Stockholder, Cellectar Biosciences, Inc. G.‐ H. Chen: Research funded, GE Healthcare; Research funded, Siemens AX.
MO‐AB‐BRA‐07: Prompt Gamma‐Ray Spectroscopy for Range Verification of Clinical Proton Beams
Authors: Verburg J , Bortfeld T , Seco J
Published: June 2015

Purpose:

We developed a pre‐clinical prototype system for range verification of proton pencil‐beam scanning fields. The system was evaluated using phantom treatment plans delivered with a clinical dose rate.

Methods:

The absolute range of proton pencil‐beams was verified through an optimization procedure, which matches energy‐ and time‐resolved prompt gamma‐ray measurements with models, based on cross sections for discrete prompt gamma‐ray line excitations. Phantom experiments were performed with a pre‐clinical prototype detector, using treatment plans delivered with a clinical pencil‐beam scanning system. The detector consisted of an actively shielded lanthanum(III) bromide scintillator. Tungsten was used to collimate the gamma‐rays. To support high event rates, the detector readout featured custom amplifiers and an active voltage divider for the photomultiplier. The detector signals were acquired by fast analog‐to‐digital converters and processed using digital algorithms. The data acquisition was also synchronized with the pencil‐beam scanning and dosimetry systems.

Results:

We successfully acquired prompt gamma‐ray spectra during the delivery of proton pencil‐beams with a clinical beam current of 2 nA at the exit of the treatment head. The number of events in the primary detector ranged from 1 × 10⁶ to 2 × 10⁶ per second. In phantom experiments, non‐uniform range errors were introduced by placing strips of plastic in the beam path. The magnitudes and positions of these range errors were correctly detected in two‐dimensional range maps that were generated from the measurements. With our small scale prototype, a 1.0 mm standard deviation on the absolute range required about 5 × 10⁸ protons per delivered pencil‐beam.

Conclusions:

Prompt gamma‐ray spectroscopy to verify the absolute range of proton beams was demonstrated under clinical pencil‐beam delivery conditions. A 1 mm to 2 mm range verification accuracy for a field delivering 1 Gy, appears feasible with a full scale system.

This work was supported by the Federal Share of program income earned on C06‐CA059267, Proton Therapy Research and Treatment Center.
MO‐AB‐BRA‐08: Rapid Treatment Field Uniformity Optimization for Total Skin Electron Beam Therapy Using Cherenkov Imaging
Authors: Andreozzi J , Jarvis L , Zhang R , Williams B , Glaser A , Pogue B , Gladstone D
Published: June 2015

Purpose:

To evaluate treatment field heterogeneity resulting from gantry angle choice in total skin electron beam therapy (TSEBT) following a modified Stanford dual‐field technique, and determine a relationship between source to surface distance (SSD) and optimized gantry angle spread.

Methods:

Cherenkov imaging was used to image 62 treatment fields on a sheet of 1.2m × 2.2m × 1.2cm polyethylene following standard TSEBT setup at our institution (6 MeV, 888 MU/min, no spoiler, SSD=441cm), where gantry angles spanned from 239.5° to 300.5° at 1° increments. Average Cherenkov intensity and coefficient of variation in the region of interest were compared for the set of composite Cherenkov images created by summing all unique combinations of angle pairs to simulate dual‐field treatment. The angle pair which produced the lowest coefficient of variation was further studied using an ionization chamber. The experiment was repeated at SSD=300cm, and SSD=370.5cm. Cherenkov imaging was also implemented during TSEBT of three patients.

Results:

The most uniform treatment region from a symmetric angle spread was achieved using gantry angles +/−17.5° about the horizontal axis at SSD=441cm, +/−18.5° at SSD=370.5cm, and +/−19.5° at SSD=300cm. Ionization chamber measurements comparing the original treatment spread (+/−14.5°) and the optimized angle pair (+/−17.5°) at SSD=441cm showed no significant deviation (r=0.999) in percent depth dose curves, and chamber measurements from nine locations within the field showed an improvement in dose uniformity from 24.41% to 9.75%. Ionization chamber measurements correlated strongly (r=0.981) with Cherenkov intensity measured concurrently on the flat Plastic Water phantom. Patient images and TLD results also showed modest uniformity improvements.

Conclusion:

A decreasing linear relationship between optimal angle spread and SSD was observed. Cherenkov imaging offers a new method of rapidly analyzing and optimizing TSEBT setup geometry by providing a 2D image of the treatment plane as a sum of the two fields.

This study has been funded by NIH grants R21EB17559 and R01CA109558 as well as Norris Cotton Cancer Center Pilot funding.
MO‐AB‐BRA‐10: Cancer Therapy Outcome Prediction Based On Dempster‐Shafer Theory and PET Imaging
Authors: Lian C , Li H , Denoeux T , Chen H , Robinson C. , Vera P , Ruan S
Published: June 2015

Purpose:

In cancer therapy, utilizing FDG‐18 PET image‐based features for accurate outcome prediction is challenging because of 1) limited discriminative information within a small number of PET image sets, and 2) fluctuant feature characteristics caused by the inferior spatial resolution and system noise of PET imaging. In this study, we proposed a new Dempster‐Shafer theory (DST) based approach, evidential low‐dimensional transformation with feature selection (ELT‐FS), to accurately predict cancer therapy outcome with both PET imaging features and clinical characteristics.

Methods:

First, a specific loss function with sparse penalty was developed to learn an adaptive low‐rank distance metric for representing the dissimilarity between different patients’ feature vectors. By minimizing this loss function, a linear low‐dimensional transformation of input features was achieved. Also, imprecise features were excluded simultaneously by applying a l2,1‐norm regularization of the learnt dissimilarity metric in the loss function. Finally, the learnt dissimilarity metric was applied in an evidential K‐nearest‐neighbor (EK‐ NN) classifier to predict treatment outcome.

Results:

Twenty‐five patients with stage II–III non‐small‐cell lung cancer and thirty‐six patients with esophageal squamous cell carcinomas treated with chemo‐radiotherapy were collected. For the two groups of patients, 52 and 29 features, respectively, were utilized. The leave‐one‐out cross‐validation (LOOCV) protocol was used for evaluation. Compared to three existing linear transformation methods (PCA, LDA, NCA), the proposed ELT‐FS leads to higher prediction accuracy for the training and testing sets both for lung‐cancer patients (100+/−0.0, 88.0+/−33.17) and for esophageal‐cancer patients (97.46+/−1.64, 83.33+/−37.8). The ELT‐FS also provides superior class separation in both test data sets.

Conclusion:

A novel DST‐ based approach has been proposed to predict cancer treatment outcome using PET image features and clinical characteristics. A specific loss function has been designed for robust accommodation of feature set incertitude and imprecision, facilitating adaptive learning of the dissimilarity metric for the EK‐NN classifier.
MO‐AB‐207‐01: ACR Update in CT
Authors: McNitt‐Gray M.
Published: June 2015

A goal of an imaging accreditation program is to ensure adequate image quality, verify appropriate staff qualifications, and to assure patient and personnel safety. Currently, more than 35,000 facilities in 10 modalities have been accredited by the American College of Radiology (ACR), making the ACR program one of the most prolific accreditation options in the U.S. In addition, ACR is one of the accepted accreditations required by some state laws, CMS/MIPPA insurance and others. Familiarity with the ACR accreditation process is therefore essential to clinical diagnostic medical physicists. Maintaining sufficient knowledge of the ACR program must include keeping up‐to‐date as the various modality requirements are refined to better serve the goals of the program and to accommodate newer technologies and practices. This session consists of presentations from authorities in four ACR accreditation modality programs, including magnetic resonance imaging, computed tomography, nuclear medicine, and mammography. Each speaker will discuss the general components of the modality program and address any recent changes to the requirements.

Learning Objectives:

To understand the requirements of the ACR MR Accreditation program. The discussion will include accreditation of whole‐body general purpose magnets, dedicated extremity systems well as breast MRI accreditation. Anticipated updates to the ACR MRI Quality Control Manual will also be reviewed.

To understand the requirements of the ACR CT accreditation program, including updates to the QC manual as well as updates through the FAQ process.

To understand the requirements of the ACR nuclear medicine accreditation program, and the role of the physicist in annual equipment surveys and the set up and supervision of the routine QC program.

To understand the current ACR MAP Accreditation requirement and present the concepts and structure of the forthcoming ACR Digital Mammography QC Manual and Program.
MO‐AB‐207‐04: ACR Update in Mammography
Authors: Berns E.
Published: June 2015

A goal of an imaging accreditation program is to ensure adequate image quality, verify appropriate staff qualifications, and to assure patient and personnel safety. Currently, more than 35,000 facilities in 10 modalities have been accredited by the American College of Radiology (ACR), making the ACR program one of the most prolific accreditation options in the U.S. In addition, ACR is one of the accepted accreditations required by some state laws, CMS/MIPPA insurance and others. Familiarity with the ACR accreditation process is therefore essential to clinical diagnostic medical physicists. Maintaining sufficient knowledge of the ACR program must include keeping up‐to‐date as the various modality requirements are refined to better serve the goals of the program and to accommodate newer technologies and practices. This session consists of presentations from authorities in four ACR accreditation modality programs, including magnetic resonance imaging, computed tomography, nuclear medicine, and mammography. Each speaker will discuss the general components of the modality program and address any recent changes to the requirements.

Learning Objectives:

To understand the requirements of the ACR MR Accreditation program. The discussion will include accreditation of whole‐body general purpose magnets, dedicated extremity systems well as breast MRI accreditation. Anticipated updates to the ACR MRI Quality Control Manual will also be reviewed.

To understand the requirements of the ACR CT accreditation program, including updates to the QC manual as well as updates through the FAQ process.

To understand the requirements of the ACR nuclear medicine accreditation program, and the role of the physicist in annual equipment surveys and the set up and supervision of the routine QC program.

To understand the current ACR MAP Accreditation requirement and present the concepts and structure of the forthcoming ACR Digital Mammography QC Manual and Program.
MO‐AB‐201‐00: Radiation Safety Officer Update
Authors: Kroger Linda
Published: June 2015

The role of the Radiation Safety Officer at a medical facility can be complicated. The complexity of the position is based on the breadth of services provided at the institution and the nature of the radioactive materials license. Medical practices are constantly changing and the use of ionizing radiation continues to rise in this area. Some of the newer medical applications involving radiation have unique regulatory and safety issues that must be addressed. Oversight of the uses of radiation start at the local level (radiation safety officer, radiation safety committee) and are heavily impacted by outside agencies (i.e. Nuclear Regulatory Commission, State Radiologic Health, The Joint Commission (TJC), etc).

This session will provide both an overview of regulatory oversight and essential compliance practices as well as practical ways to assess and introduce some of the new applications utilizing radioactive materials into your medical facility.

Learning Objectives:

Regulatory Compliance and Safety with New Radiotherapies: Spheres and Ra‐223 (Lance Phillips)

Understand the radioactive materials license amendment process to add new radiotherapies (i.e., SIR‐Spheres, Therasphere, Xofigo).

Understand the AU approval process for microspheres and Xofigo.

Examine the training and handling requirements for new procedures.

Understand the process involved with protocol development, SOP in order to define roles and responsibilities.

The RSO and The RSC: Challenges and Opportunities (Colin Dimock)

Understand how to form an effective Committee.

Examine what the Committee does for the Program and the RSO.

Understand the importance of Committee engagement.

Discuss the balance of the complimentary roles of the RSO and the Committee.

The Alphabet Soup of Regulatory Compliance: Being Prepared for Inspections (Linda Kroger)

Recognize the various regulatory bodies and organizations with oversight or impact in Nuclear Medicine, Radiology and Radiation Oncology.

Examine 10CFR35 requirements as they relate to the everyday practice of Nuclear Medicine and Radiation Oncology.

Understand the nature of available guidance documents (e.g., NUREG 1556).

Examine the commonalities between TJC and CMS preparedness.
MO‐AB‐201‐02: The RSO and The RSC: Challenges and Opportunities
Authors: Dimock C.
Published: June 2015

The role of the Radiation Safety Officer at a medical facility can be complicated. The complexity of the position is based on the breadth of services provided at the institution and the nature of the radioactive materials license. Medical practices are constantly changing and the use of ionizing radiation continues to rise in this area. Some of the newer medical applications involving radiation have unique regulatory and safety issues that must be addressed. Oversight of the uses of radiation start at the local level (radiation safety officer, radiation safety committee) and are heavily impacted by outside agencies (i.e. Nuclear Regulatory Commission, State Radiologic Health, The Joint Commission (TJC), etc).

This session will provide both an overview of regulatory oversight and essential compliance practices as well as practical ways to assess and introduce some of the new applications utilizing radioactive materials into your medical facility.

Learning Objectives:

Regulatory Compliance and Safety with New Radiotherapies: Spheres and Ra‐223 (Lance Phillips)

Understand the radioactive materials license amendment process to add new radiotherapies (i.e., SIR‐Spheres, Therasphere, Xofigo).

Understand the AU approval process for microspheres and Xofigo.

Examine the training and handling requirements for new procedures.

Understand the process involved with protocol development, SOP in order to define roles and responsibilities.

The RSO and The RSC: Challenges and Opportunities (Colin Dimock)

Understand how to form an effective Committee.

Examine what the Committee does for the Program and the RSO.

Understand the importance of Committee engagement.

Discuss the balance of the complimentary roles of the RSO and the Committee.

The Alphabet Soup of Regulatory Compliance: Being Prepared for Inspections (Linda Kroger)

Recognize the various regulatory bodies and organizations with oversight or impact in Nuclear Medicine, Radiology and Radiation Oncology.

Examine 10CFR35 requirements as they relate to the everyday practice of Nuclear Medicine and Radiation Oncology.

Understand the nature of available guidance documents (e.g., NUREG 1556).

Examine the commonalities between TJC and CMS preparedness.