Double Scattering Research Articles

WE‐D‐BRB‐04: Clinical Applications of CBCT 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.

WE‐D‐BRB‐00: Basics 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.

SU‐F‐T‐154: An Evaluation and Quantification of Secondary Neutron Radiation Dose Due to Double Scatter and Pencil Beam Scanning Proton Therapy

Proton radiation therapy can deliver high radiation doses to tumors while sparing normal tissue. However, protons yield secondary neutron and gamma radiation that is difficult to detect, small in comparison to the prescribed dose, and not accounted for in most treatment planning systems. The risk for secondary malignancies after proton therapy may be dependent on the quality of this dose. Consequently, there is interest in characterizing the secondary radiation. Previously, we used the dual ionization chamber method to measure the separate absorbed dose from gamma‐rays and neutrons secondary to the proton beam1, relying on characterization of ionization chamber response in the unknown neutron spectrum from Monte Carlo simulation. We developed a procedure to use Shieldwerx activation foils, with neutron activation energies ranging from 0.025 eV to 13.5 MeV, to measure the neutron energy spectrum from double scattering (DS) and pencil beam scanning (PBS) protons outside of the treatment volume in a water tank. The activated foils are transferred to a NaI well chamber for gamma‐ray spectroscopy and activity measurement. Since PBS treats in layers, the switching time between layers is used to correct for the decay of the activated foils and the relative dose per layer is assumed to be proportional to the neutron fluence per layer. MATLAB code was developed to incorporate the layer delivery and switching time into a calculation of foil activity, which is then used to determine the neutron energy fluence from tabulated foil activation energy thresholds.1. Diffenderfer et. al., Med. Phys., 38(11) 2011.

SU‐F‐T‐142: An Analytical Model to Correct the Aperture Scattered Dose in Clinical Proton Beams

Purpose:Apertures or collimators are used to laterally shape proton beams in double scattering (DS) delivery and to sharpen the penumbra in pencil beam (PB) delivery. However, aperture‐scattered dose is not included in the current dose calculations of treatment planning system (TPS). The purpose of this study is to provide a method to correct the aperture‐scattered dose based on an analytical model.Methods:A DS beam with a non‐divergent aperture was delivered using a single‐room proton machine. Dose profiles were measured with an ion‐chamber scanning in water and a 2‐D ion chamber matrix with solid‐water buildup at various depths. The measured doses were considered as the sum of the non‐contaminated dose and the aperture‐scattered dose. The non‐contaminated dose was calculated by TPS and subtracted from the measured dose. Aperture scattered‐dose was modeled as a 1D Gaussian distribution. For 2‐D fields, to calculate the scatter‐dose from all the edges of aperture, a sum of weighted distance was used in the model based on the distance from calculation point to aperture edge. The gamma index was calculated between the measured and calculated dose with and without scatter correction.Results:For a beam with range of 23 cm and aperture size of 20 cm, the contribution of the scatter horn was ∼8% of the total dose at 4 cm depth and diminished to 0 at 15 cm depth. The amplitude of scatter‐dose decreased linearly with the depth increase. The 1D gamma index (2%/2 mm) between the calculated and measured profiles increased from 63% to 98% for 4 cm depth and from 83% to 98% at 13 cm depth. The 2D gamma index (2%/2 mm) at 4 cm depth has improved from 78% to 94%.Conclusion:Using the simple analytical method the discrepancy between the measured and calculated dose has significantly improved.

SU‐F‐J‐64: Comparison of Dosimetric Robustness Between Proton Therapy and IMRT Plans Following Tumor Regression for Locally Advanced Non‐Small Cell Lung Cancer (NSCLC)

Purpose:In the light of tumor regression and normal tissue changes, dose distributions can deviate undesirably from what was planned. As a consequence, replanning is sometimes necessary during treatment to ensure continued tumor coverage or to avoid overdosing organs at risk (OARs). Proton plans are generally thought to be less robust than photon plans because of the proton beam's higher sensitivity to changes in tissue composition, suggesting also a higher likely replanning rate due to tumor regression. The purpose of this study is to compare dosimetric deviations between forward‐calculated double scattering (DS) proton plans with IMRT plans upon tumor regression, and assesses their impact on clinical replanning decisions.Methods:Ten consecutive locally advanced NSCLC patients whose tumors shrank > 50% in volume and who received four or more CT scans during radiotherapy were analyzed. All the patients received proton radiotherapy (6660 cGy, 180 cGy/fx). Dosimetric robustness during therapy was characterized by changes in the planning objective metrics as well as by point‐by‐point root‐mean‐squared differences for the entire PTV, ITV, and OARs (heart, cord, esophagus, brachial plexus and lungs) DVHs.Results:Sixty‐four pairs of DVHs were reviewed by three clinicians, who requested a replanning rate of 16.7% and 18.6% for DS and IMRT plans, respectively, with a high agreement between providers. Robustness of clinical indicators was found to depend on the beam orientation and dose level on the DVH curve. Proton dose increased most in OARs distal to the PTV along the beam path, but these changes were primarily in the mid to low dose levels. In contrast, the variation in IMRT plans occurred primarily in the high dose region.Conclusion:Robustness of clinical indicators depends where on the DVH curves comparisons are made. Similar replanning rates were observed for DS and IMRT plans upon large tumor regression.

SU‐F‐I‐70: Investigation of Gafchromic EBT3 Film Energy Dependence Using Proton, Photon, and Electron Beams

Purpose:To investigate the energy dependence of Gafchromic EBT3 film over a range of clinically used proton, photon and electron energies.Methods:Proton beam energies of 117 and 204 MeV, corresponding respectively to ranges in water of 10 cm and 27 cm from a Mevion S250 double scatter system unit were used. Electron energies of 6 and 20 MeV and photon energies of 6 and 18 MV from a Varian Clinac 21EX Linac were used. Two pieces of film (5×5 cm2) were irradiated sequentially for doses of 100, 500, and 1000 cGy for all energies and modalities. Films were placed on the central beam axis for a 10×10 cm2 field size in the middle of spread out Bragg peak (SOBP) for proton and in respective dmax for photon and electron energies. Films were scanned on a flatbed Epson Expression 10000 XL scanner on the central region of the scanning window using 48‐bit, 300 dpi, and landscape orientation after 48 hours post‐irradiation of film to account for optical density (OD) stabilization. Film analysis of the red channel was performed using ImageJ 1.48v (National Institutes of Health).Results:The energy dependency of EBT3 among all energies and modalities for all doses studied was small within measurement uncertainties (1σ = ± 4.1%). The mean net OD in red channel for films receiving the same dose in the same energy modality had standard deviations within 0.9% for photons, 4.9% for electrons and 1.8% for protons. It was observed that film pieces were activated during proton irradiation, e.g., 7 mR/hr at surface after 30 minutes of irradiation, lasting for 2 hours post irradiation.Conclusion:EBT3 energy dependency was evaluated for clinically used proton, photon, and electron energies. The film self‐activation may have contributed to fog and negligible dose.

Prospective MRI-based imaging study to assess feasibility of proton therapy for post-prostatectomy radiation

Purpose/Objectives: To optimize delivery of post-prostatectomy radiation (PPRT) with protons by examining dosimetric effects of variations in physician contouring, organ motion, and patient alignment during a course of PPRT. Material and methods: We enrolled 10 patients receiving PPRT in a prospective imaging study. All patients underwent combined computed tomography (CT)/magnetic resonance imaging (MRI) simulation with endorectal balloon (ERB) and received intensity modulated radiation therapy (IMRT) per institutional standards. Study patients underwent weekly MRI verification scans in the treatment position. Three radiation oncologists contoured clinical target volumes (CTV) on initial and verification scans using two consensus guidelines (RTOG and EORTC). We generated IMRT, double scattering (DS), and pencil beam scanning (PBS) proton plans and examined the dosimetric impact of contour variations, inter-fraction motion, and patient alignment techniques. Results: Inter-observer variations in contouring reduced median CTV coverage (D100) by 0.9% for IMRT plans, 2.8% for DS proton plans, 3.4–4.9% for PBS Proton Plans. Inter-fraction changes in target volumes due to internal organ motion resulted in a median loss of target dose coverage (D98) of 0% with IMRT, 3.5% with DS, and 8.1–8.3% with PBS. Median bladder V65Gy increased during the treatment course with all techniques (6.0–7.5%). Changes in the median rectal V60Gy remained small regardless of the treatment technique (0.5–3.1% increase). Alignment to the ERB after cranio-caudal bony alignment reduced CTV displacement compared to bony alignment alone, and as a result CTV coverage (D98) changed <2% with IMRT, DS, and PBS. Conclusion: Proton-based treatments are more sensitive to changes in inter-fraction organ motion during PPRT compared to IMRT, and therefore motion management and patient alignment methods are critical. Patient alignment using bony anatomy as well as the ERB minimizes displacement of the CTV, and reduces variation in target dose coverage particularly for PBS proton therapy.

Robust Detection of Single and Double Persistent Scatterers in Urban Built Environments

In this paper, we develop a synthetic aperture radar (SAR) tomography-based persistent scatterer interferometry (Tomo-PSInSAR) method to detect single and double persistent scatterers (PSs) in urban built environments. By constructing a two-tier network, we can jointly detect single and double PSs with no need for preliminary removal of the atmospheric phase screen (APS) in the whole area. This technique is more applicable in high-rise built environments (e.g., Hong Kong) with cloudy and rainy weather, where there is much uncertainty when removing the APS. In the first-tier network, we aim to detect the most reliable single PSs (SPSs) by constructing a Delaunay triangulation network. To improve the robustness of estimation, we combine beamforming with an M-estimator for parameter estimation at the arcs and introduce a ridge estimator for network adjustment. In the second-tier network, we detect the remaining SPSs and all of the double PSs (DPSs) by constructing local star networks that use the SPSs detected in the first-tier network as reference points. To simplify the detection of DPSs, we employ a local maximum ratio method for extracting overlaid DPSs. Finally, 56 Hong Kong TerraSAR-X images are used to validate the Tomo-PSInSAR method.

A Monte Carlo study on the collimation of pencil beam scanning proton therapy beams.

The lateral edge of a proton therapy beam is commonly used to achieve conformality to the treatment volume where critical structures reside close to the target. However, when treating shallow depths, the lateral edge of a pencil beam scanning (PBS) system may be broader than that of a double scattered (DS) system. Use of a range-shifter to degrade the beam and allow treatment of very shallow depths further blurs the lateral edge. The authors investigate the potential use of a collimator with a PBS system for delivery of 3D uniform dose-volumes to a water-tank phantom, identifying the key factors controlling the width of the lateral edge. The geant4 application for tomographic emission (gate) Monte Carlo (MC) environment was used, following validation against previously published data. Key parameters for PBS beams were investigated to assess their impact on the lateral edge of both monoenergetic beams and uniform dose-volumes. These parameters included nozzle-to-surface distance (NSD), vacuum window-to-surface distance (VSD), use of a range-shifter, and spot optimization parameters. The lateral edge of an uncollimated PBS beam is particularly sensitive to VSD and NSD. While use of a range-shifter blurs the lateral edge, collimation allows the edge to be sharpened to between 2 and 4 mm depending on the depth of the target. Optimization of the spot weightings alone can provide a penumbral width close to that of a single spot, but also leads to poorer uniformity near the edge of the target volume. Collimation of PBS beams should be considered for superficial targets particularly for beams delivered through a range-shifter, since the resultant sharpening of the lateral edge will allow improved sparing of adjacent normal tissues. Further work is needed to develop collimators which are integrated into both nozzle designs and planning system optimization algorithms.

一种双层散射介质中间目标单像素成像系统研究

一种双层散射介质中间目标单像素成像系统研究

Analysis of scattering mechanisms over sea oil slicks based on eigenvalues of simplified coherence matrix

Analytical forms of eigenvalues are given based on the coherence matrix simplified under the hypothesis of reflection symmetry, and three parameters P S , P D , and P M representing the individual contribution of single, double, and multiple scattering mechanisms to the total backscattering are defined. The single scattering is confirmed as a direct description of the Bragg scattering while the double and multiple scatterings are supposed to be classified as non-Bragg scattering. Experiments using quad-polarization single look complex C-band RADARSAT-2 SAR images indicate that the oil slick mainly dampens the Bragg scattering, due to the reduction of single scattering over oil-covered sea surfaces. The decrease of P S results in the corresponding increase of P D and P M , and the values of P S over clean sea surfaces are higher than those of oil slicks on the P S image. Therefore, P S can be selected to discriminate oil slicks from clean sea surfaces. By comparing the two imagery experiments, we also note that the relative contribution of Bragg scattering to the backscattering over oil-covered surfaces is highly dependent on the local wind field.

Simultaneous distribution between the deflection angle and the lateral displacement under the Molière theory of multiple scattering

Simultaneous distribution between the deflection angle and the lateral displacement of fast charged particles traversing through matter is derived by applying numerical inverse Fourier transforms on the Fourier spectral density solved analytically under the Moliere theory of multiple scattering, taking account of ionization loss. Our results show the simultaneous Gaussian distribution at the region of both small deflection angle and lateral displacement, though they show the characteristic contour patterns of probability density specific to the single and the double scatterings at the regions of large deflection angle and/or lateral displacement. The influences of ionization loss on the distribution are also investigated. An exact simultaneous distribution is derived under the fixed energy condition based on a well-known model of screened single scattering, which indicates the limit of validity of the Moliere theory applied to the simultaneous distribution. The simultaneous distribution will be valuable for improving the accuracy and the efficiency of experimental analyses and simulation studies relating to charged particle transports.

J/ψ-pair production at large momenta: Indications for double parton scatterings and large [formula omitted] contributions

We demonstrate that the recent studies of J/ψ-pair production by CMS at the LHC and by D0 at the Tevatron reveal the presence of different production mechanisms in different kinematical regions. We find out that next-to-leading-order single parton scattering contributions at αs5 dominate the yield at large transverse momenta of the pair. Our analysis further emphasises the importance of double parton scatterings – which are expected to dominate the yield at large J/ψ-rapidity differences – at large invariant masses of the pair in the CMS acceptance, and thereby solve a large discrepancy between the theory and the CMS data. In addition, we provide the first exact – gauge-invariant and infrared-safe – evaluation of a class of leading-PT (PT−4) next-to-next-to-leading-order contributions at αs6, which can be relevant in the region of large values of PTmin=min⁡(PT1,PT2). Finally, we derive simple relations for the feed-down fractions from the production of an excited charmonium state with a J/ψ in the case of the dominance of the double parton scatterings, which significantly deviate from those for single parton scatterings. Such relations can be used to discriminate these extreme scenarios, either DPS or SPS dominance.

Beam-specific planning target volumes incorporating 4D CT for pencil beam scanning proton therapy of thoracic tumors.

The purpose of this study is to determine whether organ sparing and target coverage can be simultaneously maintained for pencil beam scanning (PBS) proton therapy treatment of thoracic tumors in the presence of motion, stopping power uncertainties, and patient setup variations. Ten consecutive patients that were previously treated with proton therapy to 66.6/1.8 Gy (RBE) using double scattering (DS) were replanned with PBS. Minimum and maximum intensity images from 4D CT were used to introduce flexible smearing in the determination of the beam specific PTV (BSPTV). Datasets from eight 4D CT phases, using ±3% uncertainty in stopping power and ±3 mm uncertainty in patient setup in each direction, were used to create 8×12×10=960 PBS plans for the evaluation of 10 patients. Plans were normalized to provide identical coverage between DS and PBS. The average lung V20, V5, and mean doses were reduced from 29.0%, 35.0%, and 16.4 Gy with DS to 24.6%, 30.6%, and 14.1 Gy with PBS, respectively. The average heart V30 and V45 were reduced from 10.4% and 7.5% in DS to 8.1% and 5.4% for PBS, respectively. Furthermore, the maximum spinal cord, esophagus, and heart doses were decreased from 37.1 Gy, 71.7 Gy, and 69.2 Gy with DS to 31.3 Gy, 67.9 Gy, and 64.6 Gy with PBS. The conformity index (CI), homogeneity index (HI), and global maximal dose were improved from 3.2, 0.08, 77.4 Gy with DS to 2.8, 0.04, and 72.1 Gy with PBS. All differences are statistically significant, with p‐values <0.05, with the exception of the heart V45 (p=0.146). PBS with BSPTV achieves better organ sparing and improves target coverage using a repainting method for the treatment of thoracic tumors. Incorporating motion‐related uncertainties is essential.PACS number: 87.55.D

SU‐F‐BRD‐02: Incorporating Uncertainty Analysis in Plan Comparison of VMAT, Double Scattering Proton Plan and IMPT for Lung Irradiation

Purpose:We investigate the effect of residual setup and motion errors in lung irradiation for VMAT, double scattering (DS) proton beams and spot scanning (IMPT) in a case study.Methods:The CT image and contour sets of a lung patient treated with 6 MV VMAT is re‐planned with DS as well as IMPT subject to the same constraints; V20(lung), V10(lung) and V5(lung)&lt; 15%, 20% and 25% respectively, V20(heart)&lt;25% and V100%(PTV)≥95%. In addition, uncertainty analysis in the form of isocenter shifts (±1–3mm) was incorporated in the DVH calculations to assess the plan robustness.Results:Only the IMPT plan satisfies all the specified constraints. The 3D‐conformal DS proton plan is able to achieve better sparing of the lung and heart dose compared to VMAT. For the lung, V20, V10 and V5 are 13%, 19% and 25% respectively for IMPT, 18%, 23% and 30% respectively for DS, and 20%, 30% and 42% respectively for VMAT. For heart: 0.6% for IMPT, 2.4% for DS and 30% for VMAT. When incorporating isocenter shifts in DVH calculations, the maximum changes in V20, V10 and V5 for lung are 14%, 21% and 28% respectively for IMPT. The corresponding max changes are19%, 24% and 32% respectively for DS, and 22%, 32% and 44% respectively for VMAT. The largest change occurs in the PTV coverage. For IMPT, V100%(PTV) varies between 88–96%, while V100%(PTV) for VMAT suffers a larger change compared to DS (Δ=5.5% vs 3.3%).Conclusion:While only IMPT satisfies the stringent dose‐volume constraints for the lung irradiation, it is not as robust as the 3D conformal DS plan. DS also has better sparing in lung and heart compared to VMAT and similar PTV coverage. By including isocenter shifts in dose‐volume calculations in treatment planning of lung, DS appears to be more robust than VMAT.

SU‐E‐T‐638: Proton Beam Delivery to a Moving Lung Tumor and Monte Carlo Simulation with TOPAS

Purpose:To estimate the dose delivered to a moving lung tumor by proton therapy beams of different modulation types, and compare with Monte Carlo predictions.Methods:A radiology support devices (RSD) phantom was irradiated with therapeutic proton radiation beams using two different types of modulation: uniform scanning (US) and double scattered (DS). The Eclipse© dose plan was designed to deliver 1.00Gy to the isocenter of a static ∼3×3×3cm (27cc) tumor in the phantom with 100% coverage. The peak to peak amplitude of tumor motion varied from 0.0 to 2.5cm. The radiation dose was measured with an ion‐chamber (CC‐13) located within the tumor. The time required to deliver the radiation dose varied from an average of 65s for the DS beams to an average of 95s for the US beams.Results:The amount of radiation dose varied from 100% (both US and DS) to the static tumor down to approximately 92% for the moving tumor. The ratio of US dose to DS dose ranged from approximately 1.01 for the static tumor, down to 0.99 for the 2.5cm moving tumor. A Monte Carlo simulation using TOPAS included a lung tumor with 4.0cm of peak to peak motion. In this simulation, the dose received by the tumor varied by ∼40% as the period of this motion varied from 1s to 4s.Conclusion:The radiation dose deposited to a moving tumor was less than for a static tumor, as expected. At large (2.5cm) amplitudes, the DS proton beams gave a dose closer to the desired dose than the US beams, but equal within experimental uncertainty. TOPAS Monte Carlo simulation can give insight into the moving tumor — dose relationship.This work was supported in part by the Philips corporation.

TH‐AB‐BRD‐00: Proton Therapy

The goal of this session is to introduce the audience to the physics, dosimetry, treatment planning techniques, and quality assurances (QA) procedures used 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. Challenges involved in the motion management in proton therapy will also be discussed. It will also include the methodology for proton beam dosimetry for clinical commissioning, beam calibration, and quality assurance checks.Learning Objectives: Gain knowledge on physics, dosimetry, and treatment planning for proton therapy including intensity modulated proton therapy. Be acquainted with the procedures involved in machine and patient treatment field specific QA. Understand the uncertainties associated with proton therapy and currently used strategies for their mitigation in treatment planning.

TH‐AB‐BRD‐01: Basic Physics and Quality Assurance of Proton Therapy

The goal of this session is to introduce the audience to the physics, dosimetry, treatment planning techniques, and quality assurances (QA) procedures used 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. Challenges involved in the motion management in proton therapy will also be discussed. It will also include the methodology for proton beam dosimetry for clinical commissioning, beam calibration, and quality assurance checks.Learning Objectives: Gain knowledge on physics, dosimetry, and treatment planning for proton therapy including intensity modulated proton therapy. Be acquainted with the procedures involved in machine and patient treatment field specific QA. Understand the uncertainties associated with proton therapy and currently used strategies for their mitigation in treatment planning.

TH‐AB‐BRD‐02: Proton Treatment Planning

The goal of this session is to introduce the audience to the physics, dosimetry, treatment planning techniques, and quality assurances (QA) procedures used 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. Challenges involved in the motion management in proton therapy will also be discussed. It will also include the methodology for proton beam dosimetry for clinical commissioning, beam calibration, and quality assurance checks.Learning Objectives: Gain knowledge on physics, dosimetry, and treatment planning for proton therapy including intensity modulated proton therapy. Be acquainted with the procedures involved in machine and patient treatment field specific QA. Understand the uncertainties associated with proton therapy and currently used strategies for their mitigation in treatment planning.

SU‐E‐T‐147: Beam Specific Planning Target Volumes Incorporating 4DCT for Pencil Beam Scanning Proton Therapy of Thoracic Tumors

Purpose:The purpose of this study is to determine whether organ sparing and target coverage can be simultaneously maintained for pencil beam scanning (PBS) proton therapy treatment of thoracic tumors in the presence of motion, stopping power uncertainties and patient setup variations.Methods:Ten consecutive patients that were previously treated with proton therapy to 66.6/1.8 Gy (RBE) using double scattering (DS) were replanned with PBS. Minimum and maximum intensity images from 4DCT were used to introduce flexible smearing in the determination of the beam specific PTV (BSPTV). Datasets from eight 4DCT phases, using ±3% uncertainty in stopping power, and ±3 mm uncertainty in patient setup in each direction were used to create 8*12*10=960 PBS plans for the evaluation of ten patients. Plans were normalized to provide identical coverage between DS and PBS.Results:The average lung V20, V5, and mean doses were reduced from 29.0%, 35.0%, and 16.4 Gy with DS to 24.6%, 30.6%, and 14.1 Gy with PBS, respectively. The average heart V30 and V45 were reduced from 10.4% and 7.5% in DS to 8.1% and 5.4% for PBS, respectively. Furthermore, the maximum spinal cord, esophagus and heart dose were decreased from 37.1 Gy, 71.7 Gy and 69.2 Gy with DS to 31.3 Gy, 67.9 Gy and 64.6 Gy with PBS. The conformity index (CI), homogeneity index (HI), and global maximal dose were improved from 3.2, 0.08, 77.4 Gy with DS to 2.8, 0.04 and 72.1 Gy with PBS. All differences are statistically significant, with p values &lt;0.05, with the exception of the heart V45 (p= 0.146).Conclusion:PBS with BSPTV achieves better organ sparing and improves target coverage using a repainting method for the treatment of thoracic tumors. Incorporating motion‐related uncertainties is essentialThis work was supported by the US Army Medical Research and Materiel Command under Contract Agreement No. DAMD17‐W81XWH‐07‐2‐0121 and W81XWH‐09‐2‐0174.