Double Scattering Research Articles

TOPAS Monte Carlo simulation for double scattering proton therapy and dosimetric evaluation

PurposeTo construct and commission a double scattering (DS) proton beam model in TOPAS Monte Carlo (MC) code. Dose comparisons of MC calculations to the measured and treatment planning system (TPS) calculated dose were performed. MethodsThe TOPAS nozzle model was based on the manufacturer blueprints. Nozzle set-up and beam current modulations were calculated using room-specific calibration data. This model was implemented to reproduce pristine peaks, spread-out Bragg peaks (SOBP) and lateral profiles. A stair-shaped target plan in water phantom was calculated and compared to measured data to verify range compensator (RC) modeling. ResultsTOPAS calculated pristine peaks agreed well with measurements, with accuracies of 0.03 cm for range R90 and 0.05 cm for distal dose fall-off (DDF). The calculated SOBP range, modulation width and DDF differences between MC calculations and measurements were within 0.05 cm, 0.5 cm and 0.03 cm respectively. MC calculated lateral penumbra agreed well with measured data, with difference less than 0.05 cm. For RC calculation, TPS underestimated the additional depth dose tail due to the nuclear halo effect. Lateral doses by TPS were 10% lower than measurement outside the target, while maximum difference of MC calculation was within 2%. At deeper depths inside the target volume, TPS overestimated doses by up to 25% while TOPAS predicted the dose to within 5% of measurements. ConclusionWe have successfully developed and commissioned a MC based DS nozzle model. The performance of dose accuracy by TOPAS was superior to TPS, especially for highly inhomogeneous compensator.

Optimization of PSInSAR networks with application to TomoSAR for full detection of single and double persistent scatterers

ABSTRACTIn this paper, we develop an optimized network to achieve the full detection of single and double persistent scatterers (PSs) in SAR tomography (TomoSAR). The two-tier network used in persistent scatterer interferometry (PSInSAR) is applied to TomoSAR. Adaptive network densification is constructed to improve global connectivity in the first-tier network. This optimization contributes to improving the connectivity of different clusters by sacrificing computational efficiency slightly. In the second-tier network, we develop an omnidirectional point extension method by progressively constructing local networks and multi-directional extension. This contributes to identifying scatterers that are far away from the reference points in the first-tier network. This improved point extension method can achieve the full extraction of single and double PSs, which is especially applicable in areas with unevenly and sparsely distributed PSs. To validate these improvements, we applied the method to the western reclaimed area of Shenzhen, China with offshore islands and facilities using 30 COSMO-SkyMed images.

Abstract P3-12-16: Five year outcomes of a prospective study of proton radiotherapy for breast cancer regional nodal irradiation

Abstract Purpose: Through improved nodal coverage and decreased dose to the heart and lung, proton therapy (PT) may improve the therapeutic ratio for treatment of breast cancer requiring regional nodal irradiation (RNI). The purpose of this study is to report 5 year disease control and toxicity. Methods: From May 2012 to February 2014, 18 women (stage IIA-IIIB) prospectively enrolled on a pilot study. Median age was 52 years (range, 42-73), with equal division between breast-conserving therapy (BCT) and mastectomy and right and left-sided cancers. Median number of positive nodes among the 16 node-positive patients was 2 (range, 1-14). Five patients had ≥ 10 nodes positive on axillary dissection (N3a). Treatment targets (CTVs for breast/chest wall, supraclavicular, axillary, internal mammary nodes (IMNs)) and organs at risk were delineated on CT scans. Double scatter PT alone was used for 10 patients (9 post-mastectomy, 1 after BCT) and combined proton-photon in 8 (all BCT). Toxicity was prospectively recorded using CTCAE v4.0. Results: Median follow-up was 4 years (range, 0.3 – 6). 5 year overall survival was 82% and locoregional control was 100%. 5 year distant metastases-free survival was 82%. No grade 4+ toxicity developed. Four patients developed grade 3 cellulitis, which was the only grade 3 toxicity. One patient had a reconstructive failure associated with a post-surgical cellulitis. A right-sided patient was diagnosed with CHF within 2 months of completion of PT, following diagnosis of a pulmonary embolus 1 month prior. She had an elevated BNP (1101) prior to PT following adriamycin-based chemotherapy. Mean heart dose was 0 Gy and cardiac V5 0%. Atrial fibrillation developed in two patients. One patient developed grade 2 pneumonitis (she received concurrent chemotherapy). One patient, with a history of rib fractures prior to PT, developed an ipsilateral rib fracture 7 months after PT. Conclusion: In a population of women with locally advanced breast cancer, PT for RNI has proven feasible after either mastectomy (with or without reconstruction) or BCT with excellent locoregional control. PT allows for highly conformal radiation delivery without compromise of target coverage or excess exposure of normal tissue. Documentation of the ultimate benefits of PT in this population, freedom from radiation induced cardiac disease and breast cancer recurrence will require prospective study of a larger numbers of patients. Citation Format: Bradley JA, Dagan R, Liang X, Ho MW, Rutenberg M, Mailhot R, Morris C, Mendenhall NP. Five year outcomes of a prospective study of proton radiotherapy for breast cancer regional nodal irradiation [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P3-12-16.

Non-hot-image-plane intense fringe from double scatterers in an intense laser beam through cascaded Kerr medium disks.

We theoretically investigate beam properties in a laser system of two scatterers with cascaded Kerr medium disks. A non-hot-image-plane intense fringe may appear when an intense laser beam passes through cascaded Kerr medium disks, which is modulated by double scatterers. It is found that besides generating hot images at expected positions, a new intense fringe appears at a position of about tens of centimeters downstream of the hot-image plane. The intensity of this intense fringe is greater than that of the first hot image, and it is sufficient to damage the optical elements. The effects of object distance, wavelength, and width of scatterer on the properties of this intense fringe are investigated, and we find that this intense fringe appears under certain conditions. Its intensity is closely related to several factors, such as the distance from the scatterer to the first Kerr medium disk, the scatterer width, and the wavelength of the incident beam, as well as the position of this intense fringe, which is not varied with the object distance.

Comparison of Persistent Scatterer Interferometry and SAR Tomography Using Sentinel-1 in Urban Environment

In this paper, persistent scatterer interferometry and Synthetic Aperture Radar (SAR) tomography have been applied to Sentinel-1 data for urban monitoring. The paper analyses the applicability of SAR tomography to Sentinel-1 data, which is not granted, due to the reduced range and azimuth resolutions and the low resolution in elevation. In a first part of the paper, two implementations of the two techniques are described. In the experimental part, the two techniques are used in parallel to process the same Sentinel-1 data over two test areas. An intercomparison of the results from persistent scatterer interferometry and SAR tomography is carried out, comparing the main parameters estimated by the two techniques. Finally, the paper addresses the complementarity of the two techniques, and in particular it assesses the increase of measurement density that can be achieved by adding the double scatterers from SAR tomography to the persistent scatterer interferometry measurements.

Motion effects in proton treatments of hepatocellular carcinoma—4D robustly optimised pencil beam scanning plans versus double scattering plans

Pencil beam scanning (PBS) proton therapy enables better dose conformality for complex anatomical geometries than passive proton scattering techniques, but is more susceptible to organ motion. This becomes an issue when treating moving tumours in the thorax or abdomen. Novel four-dimensional treatment planning approaches have been developed to increase the robustness of PBS plans against motion. However, their efficacy still needs to be examined by means of 4D dynamically accumulated dose (4DDD) analyses.This study investigates the potential use of 4D robust optimisation to maintain sufficient target coverage in the presence of organ motion, while sparing surrounding healthy tissue, for hepatocellular carcinoma (HCC). The liver is particularly suited to study motion interplay effects since the treatment region exhibits smaller density gradients and more homogeneous tissue than targets in the thorax, making it less prone to range errors. A facility-specific beam time model, developed and experimentally validated previously, was used for the clinical evaluation.4DDD analyses of eleven target volumes did not show a significant improvement of the target coverage using 4D robust optimisation, but a reduction of the dose to close-by organs at risk. Interplay effects were averaged out for the applied fractionation scheme of 15 fractions. Contrary to PBS, passive double scattering (DS) plans yielded homogeneous 4DDD dose distributions in a single fraction. But, in some cases, they exceeded organ at risk dose limits, which were only satisfied in PBS. The average normal liver dose could be decreased by almost 6% compared to non-robustly optimised PBS plans and by 16% compared to DS plans when implementing 4D robust optimisation.Except for some very small tumours with large motion amplitudes, 4D robustly optimised PBS plans were found to be clinically acceptable even without supplementary motion mitigation techniques.

Multi-Look in GLRT-Based Detection of Single and Double Persistent Scatterers

Persistent scatterer (PS) interferometry and more recently synthetic aperture radar tomography have shown to be powerful tools in urban scenarios for providing 3-D point clouds in the reconstruction of buildings as well as in the monitoring of their possible slow temporal deformations. The detection of PSs represents a fundamental aspect, which in the literature has been mainly addressed at full resolution (single-look detection), thus considering only the scatterer coherence properties along the different acquisitions. In this paper, we investigate the benefits offered by the usage of multiple observation looks. Multi-look generalized likelihood ratio test detection schemes are derived and analyzed in terms of detection performances. The analysis shows that even a slight multi-look can provide a dramatic improvement on the detection capability both on simulated and real data, especially in the areas characterized by a low signal-to-noise ratio and in the presence of a limited number of acquisitions.

Indication for double parton scatterings in W+ prompt J/ψ production at the LHC

We re-analyse the associated production of a prompt J/ψ and a W boson in pp collisions at the LHC following the results of the ATLAS Collaboration. We perform the first study of the Single-Parton-Scattering (SPS) contributions at the Next-to-Leading Order (NLO) in αs in the Colour-Evaporation Model (CEM), an approach based on the quark–hadron-duality. Our study provides clear indications for Double-Parton-Scattering (DPS) contributions, in particular at low transverse momenta, since our SPS CEM evaluation, which can be viewed as a conservative upper limit of the SPS yields, falls short compared to the ATLAS experimental data by 3.1 standard deviations. We also determine a finite allowed region for σeff, inversely proportional to the size of the DPS yields, corresponding to the otherwise opposed hypotheses, namely our NLO CEM evaluation and the LO direct Colour-Singlet (CS) Model contribution. In both cases, the resulting DPS yields are significantly larger than that initially assumed by ATLAS based on jet-related analyses but is consistent with their observed raw-yield azimuthal distribution and with their prompt J/ψ+J/ψ and Z+ prompt J/ψ data.

Sensitivity of a prompt-gamma slit-camera to detect range shifts for proton treatment verification

Background and purposeA prompt-gamma imaging (PGI) slit-camera was recently applied successfully in clinical proton treatments using pencil beam scanning (PBS) and double scattering (DS). However, its full capability under clinical conditions has still to be systematically evaluated. Here, the performance of the slit-camera is systematically assessed in well-defined error scenarios using realistic treatment deliveries to an anthropomorphic head phantom. Materials and methodsThe sensitivity and accuracy to detect introduced global and local range shifts with the slit-camera was investigated in PBS and DS irradiations. For PBS, measured PGI information of shifted geometries were compared spot-wise with un-shifted PGI information derived from either a reference measurement or a treatment-plan-based simulation. Furthermore, for DS and PBS the integral PGI signal of the whole field was evaluated. ResultsDeviations from the treatment plan were detected with an accuracy better than 2 mm in PBS. The PGI simulation accuracy was well below 1 mm. Interfractional comparisons are more affected by measurement noise. The field-integral PGI sum signal allows the detection of global shifts in DS. ConclusionsDetection of global and local range shifts under close-to-clinical conditions is possible with the PGI slit-camera. Especially for PBS, high sensitivity and high accuracy in shift detection were found.

Characterization of proton pencil beam scanning and passive beam using a high spatial resolution solid-state microdosimeter.

This work aims to characterize a proton pencil beam scanning (PBS) and passive double scattering (DS) systems as well as to measure parameters relevant to the relative biological effectiveness (RBE) of the beam using a silicon on insulator (SOI) microdosimeter with well-defined 3D sensitive volumes (SV). The dose equivalent downstream and laterally outside of a clinical PBS treatment field was assessed and compared to that of a DS beam. A novel silicon microdosimeter with well-defined 3D SVs was used in this study. It was connected to low noise electronics, allowing for detection of lineal energies as low as 0.15keV/μm. The microdosimeter was placed at various depths in a water phantom along the central axis of the proton beam, and at the distal part of the spread-out Bragg peak (SOBP) in 0.5mm increments. The RBE values of the pristine Bragg peak (BP) and SOBP were derived using the measured microdosimetric lineal energy spectra as inputs to the modified microdosimetric kinetic model (MKM). Geant4 simulations were performed in order to verify the calculated depth-dose distribution from the treatment planning system (TPS) and to compare the simulated dose-mean lineal energy to the experimental results. For a 131MeV PBS spot (124.6mm R90 range in water), the measured dose-mean lineal energy yD¯ increased from 2keV/μm at the entrance to 8keV/μm in the BP, with a maximum value of 10keV/μm at the distal edge. The derived RBE distribution for the PBS beam slowly increased from 0.97±0.14 at the entrance to 1.04±0.09 proximal to the BP, then to 1.1±0.08 in the BP, and steeply rose to 1.57±0.19 at the distal part of the BP. The RBE distribution for the DS SOBP beam was approximately 0.96±0.16 to 1.01±0.16 at shallow depths, and 1.01±0.16 to 1.28±0.17 within the SOBP. The RBE significantly increased from 1.29±0.17 to 1.43±0.18 at the distal edge of the SOBP. The SOI microdosimeter with its well-defined 3D SV has applicability in characterizing proton radiation fields and can measure relevant physical parameters to model the RBE with submillimeter spatial resolution. It has been shown that for a physical dose of 1.82Gy at the BP, the derived RBE based on the MKM model increased from 1.14 to 1.6 in the BP and its distal part. Good agreement was observed between the experimental and simulation results, confirming the potential application of SOI microdosimeter with 3D SV for quality assurance in proton therapy.

Evaluation of Proton Arc Therapy Using a Double Scattering System with a Single, Pre-Cut Aperture with no Compensator

To simulate and quantitatively evaluate dose from proton arc therapy using a double scattering proton therapy system with a single aperture and no compensator. Proton arc therapy was simulated with 5, 10 and 15 fields using the Mevion S250 double scattering proton therapy system and the Eclipse treatment planning system (TPS). A single aperture that provided the best conformal circular or rectangular apertures covering the tumor from the different angular views was used. No compensator was used to modulate the intensity of the fields. TPS calculated for each field the most efficient range and modulation providing the most conformal dose coverage of the target. To account for dose delivery uncertainties without a compensator, a planning-target-volume (PTV) was defined as the target. The PTV dose coverage from the arc plans were compared with the conventional proton plans prepared with 2 fields using conformal aperture and compensator for each field. Several dosimetric parameters (Dmin, Dmax, Dmean, D95, D90, D50) were used to evaluate the dose coverage of the PTV and sparing of normal tissues. The proton arc plans for spherical or rectangular regular shape targets provided superior conformal plans with lower skin and critical structure doses compared to conventional proton plans. This was due to the use of multiple beams that delivered low doses at the entrance depths and paths through normal tissues. In contrast, conventional plans with only 2 beams had relatively larger entrance and path doses, while the PTV minimum, maximum and mean doses were nearly equal in both arc and conventional plans (Table 1). The patient setup and dose delivery times were comparable with both arc and conventional plans. This has been achievable by only having to position and image the patient once for setup. Furthermore, the use of no field-specific compensator and using of one aperture size eliminated the need to enter the room and replace these devices for each field. Although, this approach of using proton arc plans had several dosimetric and delivery advantages for regular-shaped targets, the advantages has been limited for PTV with complicated shapes. Simulation of proton arc therapy shows that regular shaped targets can be treated with superior dose coverage of the PTV and sparing of critical structures using a single aperture, no compensator proton arc plans compared to conventional 2 beam proton plans with patient specific apertures and compensators. This proton arc therapy approach is superior for regular spherical or rectangular shaped targets.Abstract 3511; Table 1Comparison of different dose parameters between 2 fields conventional beam plan and proton arc beam plans simulated with 5, 10 and 15 fields with a single circular aperture and no compensatorBeamsStructureMinMaxMeanD95D90D502PTV (%)92105103100101103591106104101104109310610310110415921061041011072Lt Femur (cGy)108131692977-29123026551264712171052121410532595128768912381549248713599671303 Open table in a new tab

AUTOMATIC COREGISTRATION FOR MULTIVIEW SAR IMAGES IN URBAN AREAS

Abstract. Due to the high resolution property and the side-looking mechanism of SAR sensors, complex buildings structures make the registration of SAR images in urban areas becomes very hard. In order to solve the problem, an automatic and robust coregistration approach for multiview high resolution SAR images is proposed in the paper, which consists of three main modules. First, both the reference image and the sensed image are segmented into two parts, urban areas and nonurban areas. Urban areas caused by double or multiple scattering in a SAR image have a tendency to show higher local mean and local variance values compared with general homogeneous regions due to the complex structural information. Based on this criterion, building areas are extracted. After obtaining the target regions, L-shape structures are detected using the SAR phase congruency model and Hough transform. The double bounce scatterings formed by wall and ground are shown as strong L- or T-shapes, which are usually taken as the most reliable indicator for building detection. According to the assumption that buildings are rectangular and flat models, planimetric buildings are delineated using the L-shapes, then the reconstructed target areas are obtained. For the orignal areas and the reconstructed target areas, the SAR-SIFT matching algorithm is implemented. Finally, correct corresponding points are extracted by the fast sample consensus (FSC) and the transformation model is also derived. The experimental results on a pair of multiview TerraSAR images with 1-m resolution show that the proposed approach gives a robust and precise registration performance, compared with the orignal SAR-SIFT method.

Extension of a Fast GLRT Algorithm to 5D SAR Tomography of Urban Areas

This paper analyzes a method for Synthetic Aperture Radar (SAR) Tomographic (TomoSAR) imaging, allowing the detection of multiple scatterers that can exhibit time deformation and thermal dilation by using a CFAR (Constant False Alarm Rate) approach. In the last decade, several methods for TomoSAR have been proposed. The objective of this paper is to present the results obtained on high resolution tomographic SAR data of urban areas, by using a statistical test for detecting multiple scatterers that takes into account phase variations due to possible deformations and/or thermal dilation. The test can be evaluated in terms of probability of detection (PD) and probability of false alarm (PFA), and is based on an approximation of a Generalized Likelihood Ratio Test (GLRT), denoted as Fast-Sup-GLRT. It was already applied and validated by the authors in the 3D case, while here it is extended and experimented in the 5D case. Numerical experiments on simulated and on StripMap TerraSAR-X (TSX) data have been carried out. The presented results show that the adopted method allows the detection of a large number of scatterers and the estimation of their position with a good accuracy, and that the consideration of the thermal dilation and surface deformation helps in recovering more single and double scatterers, with respect to the case in which these contributions are not taken into account. Moreover, the capability of method to provide reliable estimates of the deformations in urban structure suggests its use in structure stress monitoring.

Single-View 3-D Reconstruction of Correlated Gamma-Neutron Sources

We describe a new method of 3D image reconstruction of neutron sources that emit correlated gammas (e.g. Cf-252, Am-Be). This category includes a vast majority of neutron sources important in nuclear threat search, safeguards and non-proliferation. Rather than requiring multiple views of the source this technique relies on the source's intrinsic property of coincidence gamma and neutron emission. As a result only a single-view measurement of the source is required to perform the 3D reconstruction. In principle, any scatter camera sensitive to gammas and neutrons with adequate timing and interaction location resolution can perform this reconstruction. Using a neutron double scatter technique, we can calculate a conical surface of possible source locations. By including the time to a correlated gamma we further constrain the source location in three-dimensions by solving for the source-to-detector distance along the surface of said cone. As a proof of concept we applied these reconstruction techniques on measurements taken with the the Mobile Imager of Neutrons for Emergency Responders (MINER). Two Cf-252 sources measured at 50 and 60 cm from the center of the detector were resolved in their varying depth with average radial distance relative resolution of 26%. To demonstrate the technique's potential with an optimized system we simulated the measurement in MCNPX-PoliMi assuming timing resolution of 200 ps (from 2 ns in the current system) and source interaction location resolution of 5 mm (from 3 cm). These simulated improvements in scatter camera performance resulted in radial distance relative resolution decreasing to an average of 11%.

Triple Parton Scatterings in High-Energy Proton-Proton Collisions.

A generic expression to compute triple parton scattering cross sections in high-energy proton-proton (pp) collisions is presented as a function of the corresponding single parton cross sections and the transverse parton profile of the proton encoded in an effective parameter σ_{eff,TPS}. The value of σ_{eff,TPS} is closely related to the similar effective cross section that characterizes double parton scatterings, and amounts to σ_{eff,TPS}=12.5±4.5 mb. Estimates for triple charm (cc[over ¯]) and bottom (bb[over ¯]) production in pp collisions at LHC and FCC energies are presented based on next-to-next-to-leading-order perturbative calculations for single cc[over ¯], bb[over ¯] cross sections. At sqrt[s]≈100 TeV, about 15% of the pp collisions produce three cc[over ¯] pairs from three different parton-parton scatterings.

Phenomenological analysis of associated production of Z0 + b in the b → J/ψX decay channel at the LHC

The ATLAS collaboration recently reported on the first observation of associated-production of a Z0 boson with a J/ψ. We recently claimed that the corresponding yield of the promptJ/ψ was dominated by double parton scatterings in the ATLAS acceptance with a somewhat small value of σeff. We also found out that single parton scatterings were only dominant at large transverse momenta. We present here the first phenomenological analysis of another part of the ATLAS data sample, namely of a Z0 boson plus a non-promptJ/ψ. Our study is performed at next-to-leading order in αs and includes parton-shower effects via the MadGraph5_aMC@NLO framework. We find out that the data, unlike the case of prompt J/ψ+Z0, do not hint at significant DPS contributions. Owing to the current experimental and theoretical uncertainties, there is still a room for these but with a lower limit of σeff close to 5 mb. We stress the importance of QCD corrections to account for the ATLAS data.

Single-Look SAR Tomography as an Add-On to PSI for Improved Deformation Analysis in Urban Areas

Persistent scatterer interferometry (PSI) is in operational use for spaceborne synthetic aperture radar (SAR)-based deformation analysis. A limitation inherently associated with PSI is that, by definition, a persistent scatterer (PS) is a single dominant scatterer. Therefore, pixels containing signal contributions from multiple scatterers, as in the case of a layover, are typically rejected in the PSI processing, which in turn limits deformation retrieval. SAR tomography has the ability to resolve layovers. This paper investigates the added value that can be achieved by operationally combining SAR tomography with a PSI approach toward the objective of improving deformation sampling in layover-affected urban areas. Different tomographic phase models are implemented and compared as regards their suitability in resolving layovers. Single-look beamforming-based tomographic inversion and a generalized likelihood ratio test (GLRT)-based detection strategy are used to detect single and double scatterers. The quantity of the detected scatterers is weighed against their quality as defined in terms of the phase deviation between the single-look complex (SLC) measurements and the tomographic model fit. The gain in deformation sampling that can be derived with tomography relative to a PSI-based analysis is quantitatively assessed, and alongside the quality of the scatterers obtained with tomography is compared with the quality of the PSs identified with a PSI approach. The experiments are performed on an interferometric stack of 50 TerraSAR-X stripmap images. The results obtained show that, although there is a tradeoff between the quantity and the quality of the detected scatterers, the tested SAR tomography approach leads to an improvement in deformation sampling in layover-affected areas.

Proton pencil beam scanning for mediastinal lymphoma: treatment planning and robustness assessment

ABSTRACTBackground: Modern radiotherapy (RT) for lymphoma is highly personalized. While advanced imaging is largely employed to define limited treatment volumes, the use of proton pencil beam scanning (PBS) for highly conformal lymphoma RT is still in its infancy. Here, we assess the dosimetric benefits and feasibility of PBS for mediastinal lymphoma (ML).Materials and methods: Ten patients were planned using PBS for involved-site RT. The initial plans were calculated on the average four-dimensional computed tomography (4D-CT). PBS plans were compared with 3D conformal radiotherapy (3D-CRT), intensity-modulated radiotherapy (IMRT), and proton double scattering (DS). In order to evaluate the feasibility of PBS and the plan robustness against inter- and intra-fractional uncertainties, the 4D dose was calculated on initial and verification CTs. The deviation of planned dose from delivered dose was measured. The same proton beamline was used for all patients, while another beamline with larger spots was employed for patients with large motion perpendicular to the beam.Results: PBS provided the lowest mean lung dose (MLD) and mean heart dose (MHD) for all patients in comparison with 3D-CRT, IMRT, and DS. For eight patients, internal target volume (ITV) D98% was degraded by <3%; and the MLD and MHD deviated by <10% of prescription over the course of treatment when the PBS field was painted twice in each session. For one patient with target motion perpendicular to the beam (>5 mm), the degradation of ITV D98% was 9%, which was effectively mitigated by employing large spots. One patient exhibited large dose degradation due to pericardial effusion, which required replanning across all modalities.Conclusions: This study demonstrates that PBS plans significantly reduce MLD and MHD relative to 3D-CRT, IMRT, and DS and identifies requirements for robust free-breathing ML PBS treatments, showing that PBS plan robustness can be maintained with repainting and/or large spots.

WE‐D‐BRB‐01: Basic Physics of Proton Therapy

The goal of this session is to review the physics of proton therapy, treatment planning techniques, and the use of volumetric imaging in proton therapy. The course material covers the physics of proton interaction with matter and physical characteristics of clinical proton beams. It will provide information on proton delivery systems and beam delivery techniques for double scattering (DS), uniform scanning (US), and pencil beam scanning (PBS). The session covers the treatment planning strategies used in DS, US, and PBS for various anatomical sites, methods to address uncertainties in proton therapy and uncertainty mitigation to generate robust treatment plans. It introduces the audience to the current status of image guided proton therapy and clinical applications of CBCT for proton therapy. It outlines the importance of volumetric imaging in proton therapy. Learning Objectives: Gain knowledge in proton therapy physics, and treatment planning for proton therapy including intensity modulated proton therapy. The current state of volumetric image guidance equipment in proton therapy. Clinical applications of CBCT and its advantage over orthogonal imaging for proton therapy.B. Teo, B.K Teo had received travel funds from IBA in 2015.

WE‐D‐BRB‐03: Current State of Volumetric Image Guidance for Proton Therapy

The goal of this session is to review the physics of proton therapy, treatment planning techniques, and the use of volumetric imaging in proton therapy. The course material covers the physics of proton interaction with matter and physical characteristics of clinical proton beams. It will provide information on proton delivery systems and beam delivery techniques for double scattering (DS), uniform scanning (US), and pencil beam scanning (PBS). The session covers the treatment planning strategies used in DS, US, and PBS for various anatomical sites, methods to address uncertainties in proton therapy and uncertainty mitigation to generate robust treatment plans. It introduces the audience to the current status of image guided proton therapy and clinical applications of CBCT for proton therapy. It outlines the importance of volumetric imaging in proton therapy. Learning Objectives: Gain knowledge in proton therapy physics, and treatment planning for proton therapy including intensity modulated proton therapy. The current state of volumetric image guidance equipment in proton therapy. Clinical applications of CBCT and its advantage over orthogonal imaging for proton therapy.B. Teo, B.K Teo had received travel funds from IBA in 2015.