bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐F‐T‐51: Investigating the Effect of Eye Size and Eccentricity On Normal Tissue Doses From Eye Plaque Brachytherapy
Authors: Polsdofer E , Crilly R
Published: July 2016

Purpose:

This study investigates the effect of eye size and eccentricity on doses to critical tissues by simulating doses in the Plaque Simulator (v. 6.3.1) software. Present OHSU plaque brachytherapy treatment focuses on delivering radiation to the tumor measured with ocular ultrasound plus a small margin and assumes the orbit has the dimensions of a “standard eye.” Accurately modeling the dimensions of the orbit requires a high resolution ocular CT. This study quantifies how standard differences in equatorial diameters and eccentricity affect calculated doses to critical structures in order to query the justification of the additional CT scan to the treatment planning process.

Methods:

Tumors of 10 mm × 10 mm × 5 mm were modeled at the 12:00:00 hour with a latitude of 45 degrees. Right eyes were modeled at a number of equatorial diameters from 17.5 to 28 mm for each of the standard non‐notched COMS plaques with silastic inserts. The COMS plaques were fully loaded with uniform activity, centered on the tumor, and prescribed to a common tumor dose (85 Gy/100 hours). Variations in the calculated doses to normal structures were examined to see if the changes were significant.

Results:

The calculated dose to normal structures show a marked dependence on eye geometry. This is exemplified by fovea dose which more than doubled in the smaller eyes and nearly halved in the larger model. Additional significant dependence was found in plaque size on the calculated dose in spite of all plaques giving the same dose to the prescription point.

Conclusion:

The variation in dose with eye dimension fully justifies the addition of a high resolution ocular CT to the planning technique. Additional attention must be made to plaque size beyond simply covering the tumor when considering normal tissue dose
SU‐F‐T‐53: Treatment Planning with Inhomogeneity Correction for Intraoperative Radiotherapy Using KV X‐Ray Beams
Authors: Chen Y , Ghaly M , Souri S , Wang L , Diaz F , Cao Y , Klein E , Jamshidi A
Published: July 2016

Purpose:

The current standard in dose calculation for intraoperative radiotherapy (IORT) using the ZEISS Intrabeam 50 kV x‐ray system is based on depth dose measurements in water and no heterogeneous tissue effect has been taken into account. We propose an algorithm for pre‐treatment planning including inhomogeneity correction based on data of depth dose measurements in various tissue phantoms for kV x‐rays.

Methods:

Direct depth dose measurements were made in air, water, inner bone and cortical bone phantoms for the Intrabeam 50 kV x‐rays with a needle applicator. The data were modelled by a function of power law combining exponential with different parameters. Those phantom slabs used in the measurements were scanned to obtain CT numbers. The x‐ray beam initiated from the source isocenter is ray‐traced through tissues. The corresponding doses will be deposited/assigned at different depths. On the boundary of tissue/organ changes, the x‐ray beam will be re‐traced in new tissue/organ starting at an equivalent depth with the same dose. In principle, a volumetric dose distribution can be generated if enough directional beams are traced. In practice, a several typical rays traced may be adequate in providing estimates of maximum dose to the organ at risk and minimum dose in the target volume.

Results:

Depth dose measurements and modeling are shown in Figure 1. The dose versus CT number is shown in Figure 2. A computer program has been written for Kypho‐IORT planning using those data. A direct measurement through 2 mm solid water, 2 mm inner bone, and 1 mm solid water yields a dose rate of 7.7 Gy/min. Our calculation shows 8.1±0.4 Gy/min, consistent with the measurement within 5%.

Conclusion:

The proposed method can be used to more accurately calculate the dose by taking into account the heterogeneous effect. The further validation includes comparison with Monte Carlo simulation.
SU‐F‐T‐55: Reproducibility of Interstitial HDR Brachytherapy Plans
Authors: Lee S , Ellis R , Traughber B , Podder T
Published: July 2016

Purpose:

Treating gynecological cancers with interstitial high‐dose‐rate (HDR) brachytherapy requires precise reconstruction of catheter positions to obtain accurate dosimetric plans. In this study, we investigated the degree of reproducibility of dosimetric plans for Syed HDR brachytherapy.

Methods:

We randomly selected five patients having cervix‐vaginal cancer who were recently treated in our clinic with interstitial HDR brachytherapy with a prescription dose of 25–30 Gy in five fractions. Interstitial needles/catheters were placed under fluoroscopic guidance and intra‐operative 3T MRI scan was performed to confirm the desired catheter placement for adequate target volume coverage. A CT scan was performed and fused with the MRI for delineating high‐risk CTV (HR‐CTV), intermediate‐risk CTV (IR‐CTV) and OARs. HDR treatment plans were generated using Oncentra planning software. A single plan was used for all five fractions of treatment for each patient. For this study, we took the original clinical plan and removed all the reconstructed catheters from the plan keeping the original contours unchanged. Then, we manually reconstructed all the catheters and entered the same dwell time from the first original clinical plan. The dosimetric parameters studied were: D90 for HR‐CTV and IR‐CV, and D2cc for bladder, rectum, sigmoid and bowel.

Results:

The mean of absolute differences in dosimetric coverage (D90) were (range): 1.3% (1.0–2.0%) and 2.0% (0.9–3.6%) for HR‐CTV and IR‐CTV, respectively. In case of OARs, the mean of absolute variations in D2cc were (range): 4.7% (0.7–8.9%) for bladder, 1.60% (0.3–3.2%) for rectum, 1.6% (0–3.9%) for sigmoid, and 1.8% (0–5.1%) for bowel.

Conclusion:

Overall, the reproducibility of interstitial HDR plans was within clinically acceptable limit. Observed maximum variation in D2cc for bladder. If number of catchers and dwell points were relatively low or any one catheter was heavily loaded, then reproducibility of the plan was more sensitive to the accuracy of catheter reconstruction.
SU‐F‐T‐56: Dosimetric Characterization of the INTRABEAM 50 KV X‐Ray System with a Needle Applicator in Heterogeneous Tissues
Authors: Chen Y , Souri S , Qian X , Wang L , Ghaly M , Cao Y , Jamshidi A
Published: July 2016

Purpose:

We report the depth dose measurements in air, in solid water, and in bone materials for the Intrabeam 50 kV x‐rays with a needle applicator.

Methods:

The absolute dose was measured using a PTW TN34013W soft x‐ray ion chamber. Gammex tissue equivalent materials of solid water, inner bone, and cortical bone slabs (minimum thickness of 2 mm) were used. In addition, the PTW solid water slabs with a minimum thickness of 1 mm were used. The manufactory calibrated depth dose data in water were compared. The x‐ray source together with a needle applicator was secured on an Intrabeam stand. The slabs lay on a 6 degrees of freedom treatment couch with a digitally controlled minimum step size of 0.1 mm. The depth of the source to the ion chamber was accurately and reproducibly adjusted by moving the couch up and down.

Results:

The depth dose measurements for the Intrabeam 50 kV x‐rays with a needle applicator were conducted up to 20 mm in depth. The values for the PTW solid water were close to those for water. The Gammex solid water demonstrated lower values compared to water, consistent with the observation of its positive CT number. At a depth of 10 mm, the dose rates of the system are 29.6, 3.6, 1.2, and 0.24 Gy/min in air, in water, in inner bone, and in cortical bone, respectively. The 10 mm water equivalent depths in inner and cortical bone are about 6.4 and 4.1 mm. A function of power law combining exponential was used to fit and interpolate data well.

Conclusion:

Direct depth dose measurements in different materials provide a basis for treatment calculation and planning taking into account the heterogeneous effect. The results can be used for verification of analytical and/or Monte Carlo dose calculation methods as well.
SU‐F‐T‐61: Treatment Planning Observations for the CivaSheet Directional Brachytherapy Device Using VariSeed 9.0
Authors: Rivard MJ , Rothley DJ
Published: July 2016

Purpose:

The VariSeed 9.0 brachytherapy TPS is recently available and has new features such as ability to rotate a brachytherapy source away from normal to the imaging plane. Consequently, a dosimetric analysis was performed for a directional brachytherapy source (CivaSheet) with tests of this functionality and experiences from clinical treatment planning were documented. These observations contribute to safe, practical, and accurate use of such new software features.

Methods:

Several tests were established to evaluate the new rotational feature, specific to the CivaSheet for the first patients treated using this new brachytherapy device. These included suitability of imaging slice‐thickness and in‐plane resolution, window/level adjustments for brachytherapy source visualization, commissioning the source physical length for performing rotations, and using different planar and 3D window views to identify source orientation. Additional CivaSheet‐specific tests were performed to determine the dosimetric influence on target coverage: changing the source tilt angle, source positioning in the treatment plan based on the CivaSheet rectangular array of CivaDots, and influence of prescription depth on the necessary treatment margin for adequate target coverage.

Results:

Higher imaging‐resolution produced better accuracy for source orientation and positioning, with sub‐millimeter CT slice‐thickness and in‐plane resolution preferred. Source rotation was possible only in sagittal or coronal views. The process for validating source orientation required iteratively altering rotations then checking them in the 3D view, which was cumbersome given the absence of quantitative plan documentation to indicate orientation. Given the small Pd‐103 source size, influence of source tilt within 30° was negligible for <1.0 cm. Influence of source position was important when the source was positioned in/out of the adjacent source plane, causing changes of 15%, 7%, and 3% at depths of 0.5, 0.7, and 1.0 cm.

Conclusion:

The new TPS rotational feature worked well, but several issues were identified to improve the treatment planning process.

Research supported in part by CivaTech Oncology, Inc. for Dr. Rivard.
SU‐F‐T‐62: Three‐Dimensional Dosimetric Gamma Analysis for Impacts of Tissue Inhomogeneity Using Monte Carlo Simulation in Intracavitary Brachytheray for Cervix Carcinoma
Authors: Nguyen Tran Thi Thao , Arimura Hidetaka , Oku Yoshifumi , Nakamoto Takahiro , Shibayama Yusuke , Yoshiura Takashi
Published: July 2016

Purpose:

The aim of this study was to investigate the impacts of tissue inhomogeneity on dose distributions using a three‐dimensional (3D) gamma analysis in cervical intracavitary brachytherapy using Monte Carlo (MC) simulations.

Methods:

MC simulations for comparison of dose calculations were performed in a water phantom and a series of CT images of a cervical cancer patient (stage: Ib; age: 27) by employing a MC code, Particle and Heavy Ion Transport Code System (PHIT) version 2.73. The 192Ir source was set at fifteen dwell positions, according to clinical practice, in an applicator consisting of a tandem and two ovoids. Dosimetric comparisons were performed for the dose distributions in the water phantom and CT images by using gamma index image and gamma pass rate (%). The gamma index is the minimum Euclidean distance between two 3D spatial dose distributions of the water phantom and CT images in a same space. The gamma pass rates (%) indicate the percentage of agreement points, which mean that two dose distributions are similar, within an acceptance criteria (3 mm/3%). The volumes of physical and clinical interests for the gamma analysis were a whole calculated volume and a region larger than t% of a dose (close to a target), respectively.

Results:

The gamma pass rates were 77.1% for a whole calculated volume and 92.1% for a region within 1% dose region. The differences of 7.7% to 22.9 % between two dose distributions in the water phantom and CT images were found around the applicator region and near the target.

Conclusion:

This work revealed the large difference on the dose distributions near the target in the presence of the tissue inhomogeneity. Therefore, the tissue inhomogeneity should be corrected in the dose calculation for clinical treatment.
SU‐F‐T‐65: AutomaticTreatment Planning for High‐Dose Rate (HDR) Brachytherapy with a VaginalCylinder Applicator
Authors: Zhou Y , Tan J , Jiang S , Albuquerque K , Jia X
Published: July 2016

Purpose:

High dose rate (HDR) brachytherapy treatment planning is conventionally performed in a manual fashion. Yet it is highly desirable to perform computerized automated planning to improve treatment planning efficiency, eliminate human errors, and reduce plan quality variation. The goal of this research is to develop an automatic treatment planning tool for HDR brachytherapy with a cylinder applicator for vaginal cancer.

Methods:

After inserting the cylinder applicator into the patient, a CT scan was acquired and was loaded to an in‐house developed treatment planning software. The cylinder applicator was automatically segmented using image‐processing techniques. CTV was generated based on user‐specified treatment depth and length. Locations of relevant points (apex point, prescription point, and vaginal surface point), central applicator channel coordinates, and dwell positions were determined according to their geometric relations with the applicator. Dwell time was computed through an inverse optimization process. The planning information was written into DICOM‐RT plan and structure files to transfer the automatically generated plan to a commercial treatment planning system for plan verification and delivery.

Results:

We have tested the system retrospectively in nine patients treated with vaginal cylinder applicator. These cases were selected with different treatment prescriptions, lengths, depths, and cylinder diameters to represent a large patient population. Our system was able to generate treatment plans for these cases with clinically acceptable quality. Computation time varied from 3–6 min.

Conclusion:

We have developed a system to perform automated treatment planning for HDR brachytherapy with a cylinder applicator. Such a novel system has greatly improved treatment planning efficiency and reduced plan quality variation. It also served as a testbed to demonstrate the feasibility of automatic HDR treatment planning for more complicated cases.
SU‐F‐T‐70: A High Dose Rate Total Skin Electron Irradiation Technique with A Specific Inter‐Film Variation Correction Method for Very Large Electron Beam Fields
Authors: Yang X , Rosenfield J , Dong X , Elder E , Dhabaan A
Published: July 2016

Purpose:

Rotational total skin electron irradiation (RTSEI) is used in the treatment of cutaneous T‐cell lymphoma. Due to inter‐film uniformity variations the dosimetry measurement of a large electron beam of a very low energy is challenging. This work provides a method to improve the accuracy of flatness and symmetry for a very large treatment field of low electron energy used in dual beam RTSEI.

Methods:

RTSEI is delivered by dual angles field a gantry of ±20 degrees of 270 to cover the upper and the lower halves of the patient body with acceptable beam uniformity. The field size is in the order of 230cm in vertical height and 120 cm in horizontal width and beam energy is a degraded 6 MeV (6 mm of PMMA spoiler). We utilized parallel plate chambers, Gafchromic films and OSLDs as a measuring devices for absolute dose, B‐Factor, stationary and rotational percent depth dose and beam uniformity. To reduce inter‐film dosimetric variation we introduced a new specific correction method to analyze beam uniformity. This correction method uses some image processing techniques combining film value before and after radiation dose to compensate the inter‐variation dose response differences among films.

Results:

Stationary and rotational depth of dose demonstrated that the Rp is 2 cm for rotational and the maximum dose is shifted toward the surface (3mm). The dosimetry for the phantom showed that dose uniformity reduced to 3.01% for the vertical flatness and 2.35% for horizontal flatness after correction thus achieving better flatness and uniformity. The absolute dose readings of calibrated films after our correction matched with the readings from OSLD.

Conclusion:

The proposed correction method for Gafchromic films will be a useful tool to correct inter‐film dosimetric variation for the future clinical film dosimetry verification in very large fields, allowing the optimizations of other parameters.
SU‐F‐T‐71: A Practical Method for Evaluation of Electron Virtual Source Position
Authors: Huang Z , Jiang W , Stuart B , Leu S , Liu T , Feng Y
Published: July 2016

Purpose:

Since electrons are easily scattered, the virtual source position for electrons is expected to locate below the x‐ray target of Medical Linacs. However, the effective SSD method yields the electron virtual position above the x‐ray target for some applicators for some energy in Siemens Linacs. In this study, we propose to use IC Profiler (Sun Nuclear) for evaluating the electron virtual source position for the standard electron applicators for various electron energies.

Methods:

The profile measurements for various nominal source‐to‐detector distances (SDDs) of 100–115 cm were carried out for electron beam energies of 6–18 MeV. Two methods were used: one was to use a 0.125 cc ion chamber (PTW, Type 31010) with buildup mounted in a PTW water tank without water filled; and the other was to use IC Profiler with a buildup to achieve charge particle equilibrium. The full width at half‐maximum (FWHM) method was used to determine the field sizes for the measured profiles. Backprojecting (by a straight line) the distance between the 50% points on the beam profiles for the various SDDs, yielded the virtual source position for each applicator.

Results:

The profiles were obtained and the field sizes were determined by FWHM. The virtual source positions were determined through backprojection of profiles for applicators (5, 10, 15, 20, 25). For instance, they were 96.415 cm (IC Profiler) vs 95.844 cm (scanning ion chamber) for 9 MeV electrons with 10×10 cm applicator and 97.160 cm vs 97.161 cm for 12 MeV electrons with 10×10 cm applicator. The differences in the virtual source positions between IC profiler and scanning ion chamber were within 1.5%.

Conclusion:

IC Profiler provides a practical method for determining the electron virtual source position and its results are consistent with those obtained by profiles of scanning ion chamber with buildup.
SU‐F‐T‐78: Minimum Data Set of Measurements for TG 71 Based Electron Monitor‐Unit Calculations
Authors: Xu H , Guerrero M , Prado K , Yi B
Published: July 2016

Purpose:

Building up a TG‐71 based electron monitor‐unit (MU) calculation protocol usually involves massive measurements. This work investigates a minimum data set of measurements and its calculation accuracy and measurement time.

Methods:

For 6, 9, 12, 16, and 20 MeV of our Varian Clinac‐Series linear accelerators, the complete measurements were performed at different depth using 5 square applicators (6, 10, 15, 20 and 25 cm) with different cutouts (2, 3, 4, 6, 10, 15 and 20 cm up to applicator size) for 5 different SSD's. For each energy, there were 8 PDD scans and 150 point measurements for applicator factors, cutout factors and effective SSDs that were then converted to air‐gap factors for SSD 99–110cm. The dependence of each dosimetric quantity on field size and SSD was examined to determine the minimum data set of measurements as a subset of the complete measurements. The “missing” data excluded in the minimum data set were approximated by linear or polynomial fitting functions based on the included data. The total measurement time and the calculated electron MU using the minimum and the complete data sets were compared.

Results:

The minimum data set includes 4 or 5 PDD's and 51 to 66 point measurements for each electron energy, and more PDD's and fewer point measurements are generally needed as energy increases. Using only <50% of complete measurement time, the minimum data set generates acceptable MU calculation results compared to those with the complete data set. The PDD difference is within 1 mm and the calculated MU difference is less than 1.5%.

Conclusion:

Data set measurement for TG‐71 electron MU calculations can be minimized based on the knowledge of how each dosimetric quantity depends on various setup parameters. The suggested minimum data set allows acceptable MU calculation accuracy and shortens measurement time by a few hours.
SU‐F‐T‐84: Measurement and Monte‐Carlo Simulation of Electron Phase Spaces Using a Wide Angle Magnetic Electron Spectrometer
Authors: Englbrecht F , Lindner F , Bin J , Wislsperger A , Reiner M , Kamp F , Belka C , Dedes G , Schreiber J , Parodi K
Published: July 2016

Purpose:

To measure and simulate well‐defined electron spectra using a linear accelerator and a permanent‐magnetic wide‐angle spectrometer to test the performance of a novel reconstruction algorithm for retrieval of unknown electron‐sources, in view of application to diagnostics of laser‐driven particle acceleration.

Methods:

Six electron energies (6, 9, 12, 15, 18 and 21 MeV, 40cm × 40cm field‐size) delivered by a Siemens Oncor linear accelerator were recorded using a permanent‐magnetic wide‐angle electron spectrometer (150mT) with a one dimensional slit (0.2mm × 5cm). Two dimensional maps representing beam‐energy and entrance‐position along the slit were measured using different scintillating screens, read by an online CMOS detector of high resolution (0.048mm × 0.048mm pixels) and large field of view (5cm × 10cm). Measured energy‐slit position maps were compared to forward FLUKA simulations of electron transport through the spectrometer, starting from IAEA phase‐spaces of the accelerator. The latter ones were validated against measured depth‐dose and lateral profiles in water. Agreement of forward simulation and measurement was quantified in terms of position and shape of the signal distribution on the detector.

Results:

Measured depth‐dose distributions and lateral profiles in the water phantom showed good agreement with forward simulations of IAEA phase‐spaces, thus supporting usage of this simulation source in the study. Measured energy‐slit position maps and those obtained by forward Monte‐Carlo simulations showed satisfactory agreement in shape and position.

Conclusion:

Well‐defined electron beams of known energy and shape will provide an ideal scenario to study the performance of a novel reconstruction algorithm using measured and simulated signal. Future work will increase the stability and convergence of the reconstruction‐algorithm for unknown electron sources, towards final application to the electrons which drive the interaction of TW‐class laser pulses with nanometer thin target foils to accelerate protons and ions to multi‐MeV kinetic energy.

Cluster of Excellence of the German Research Foundation (DFG) “Munich‐Centre for Advanced Photonics”
SU‐F‐T‐85: Energy Modulated Electron Postmastectomy Unreconstructed (PU) Chest Wall (CW) Irradiation Technique to Achieve Heart Sparing
Authors: Hong L , Ballangrud A , McCormick B , Mechalakos J
Published: July 2016

Purpose:

For left‐sided PU patients requiring CW and nodal irradiation, sometimes partial wide tangents (PWT) are not feasible due to abnormal chest wall contour or heart position close to the anterior chest wall or unusual wide excision scar. We developed an energy modulated electron chest wall irradiation technique that will achieve heart sparing.

Methods:

Ten left‐sided PU patients were selected for this dosimetry study. If PWT were used, the amount of the ipsilateral lung would be ranged 3.4 to 4.4 cm, and the amount of heart would be ranged 1.3 to 3.8 cm. We used electron paired fields that matched on the skin to achieve dose conformity to the chest wall. The enface electron fields were designed at extended SSD from a single isocenter and gantry angle with different energy beams using different cutout. Lower energy was used in the central chest wall part and higher energy was used in the periphery of the chest wall. Bolus was used for the electron fields to ensure adequate skin dose coverage. The electron fields were matched to the photon supra‐clavicle field in the superior region. Daily field junctions were used to feather the match lines between all the fields. Target volumes and normal tissues were drawn according to institutional protocols. Prescription dose was 2Gy per fraction for a total 50Gy. Dose calculations were done with Eclipse EMC_11031 for Electron and AAA_11031 for photons.

Results:

Six patients were planned using 6/9MeV, three using 9/12MeV and one 6/12MeV. Target volumes achieved adequate coverage. For heart, V30Gy, V20Gy and Mean Dose were 0.6%±0.6%, 2.7%±1.7%, and 3.0Gy±0.8Gy respectively. For ipsilateral lung, V50Gy, V20Gy, V10Gy and V5Gy were 0.9%±1.1%, 34.3%±5.1%, 51.6%±6.3% and 64.1%±7.5% respectively.

Conclusion:

For left‐sided PU patients with unusual anatomy, energy modulated electron CW irradiation technique can achieve heart sparing with acceptable lung dose.
SU‐F‐T‐87: Comparison of Advanced Radiotherapy Techniques for Post‐ Mastectomy Breast Cancer Patients
Authors: Heins D , Zhang R , Hogstrom K , Sanders M
Published: July 2016

Purpose:

To determine if bolus electron conformal therapy (Bolus‐ECT) combined with intensity modulated x‐ray therapy (IMXT) and flattening filter free volumetric modulated arc therapy (FFF‐VMAT (6x and 10x)) can maintain equal or better dose coverage than standard volumetric modulated arc therapy (Std‐VMAT) while reducing doses to organs at risk (OARs).

Methods:

Bolus‐ECT with IMXT, FFF‐VMAT, and Std‐VMAT treatment plans were produced for ten post‐mastectomy radiotherapy (PMRT) patients previously treated at our clinic. The treatment plans were created on commercially available treatment planning system (TPS) and all completed treatment plans were reviewed and approved by a radiation oncologist. The plans were evaluated based on planning target volume (PTV) coverage, tumor control probability (TCP), dose homogeneity index (DHI), conformity index (CI), and dose to organs at risk (OAR).

Results:

All techniques produced clinically acceptable PMRT plans. Overall, Bolus‐ECT with IMXT exhibited higher maximum dose compared to all VMAT techniques. Bolus‐ECT with IMXT and FFF‐VMAT10x had slightly improved TCP over FFF‐VMAT6x and Std‐VMAT. However, all VMAT techniques showed improved CI and DHI over Bolus‐ECT with IMXT. All techniques showed very similar mean lung dose. Bolus‐ECT with IMXT exhibited a reduced mean heart dose over Std‐VMAT. Both FFF‐VMAT techniques had higher mean heart dose compared to Std‐VMAT. In addition, Bolus‐ECT with IMXT was able to reduce mean dose to the contralateral breast compared to Std‐VMAT and both FFF‐VMAT techniques had comparable but slightly reduced dose compared to Std‐VMAT.

Conclusion:

This work has shown that Bolus‐ECT with IMXT produces clinically acceptable plans while reducing OAR doses. Both FFF‐VMAT techniques are comparable to Std‐VMAT with slight improvements. Even though all VMAT techniques produce more homogenous and conformal dose distributions, Bolus‐ECT with IMXT is a viable option for treating post‐mastectomy patients possibly leading to reduced risks of normal tissue complications.
SU‐F‐T‐89: Investigation of Simultaneous Optimization of Photon and Electron Apertures for Mixed Beam Radiotherapy Based On An Academic Case
Authors: Mueller S , Joosten A , Fix MK , Henzen D , Volken W , Frei D , Stampanoni MFM , Manser P
Published: July 2016

Purpose:

To estimate the dosimetric potential of mixed beam radiotherapy (MBRT) by using a single process optimizing the shape and weight of photon and electron apertures simultaneously based on Monte Carlo beamlet dose distributions.

Methods:

A simulated annealing based direct aperture optimization capable to perform simultaneous optimization was developed to generate treatment plans for MERT, photon‐IMRT and MBRT. Both photon and electron apertures are collimated with the photon‐MLC and are delivered in a segmented manner. For dosimetric comparison and for investigating the dependency on the number of apertures, photon‐IMRT, MERT and MBRT plans were generated for an academic case consisting of a water phantom containing two shallow PTVs differing in the maximal depth of 5 and 7 cm, respectively and two OARs in distal and lateral direction to the PTVs.

Results:

For the superficial PTV, the dose homogeneity (V95%–V107%) and the mean dose (in percent of the prescribed dose) to the distal and the lateral OARs of the MBRT plan (94.9%, 16.9%, 17.8%) are superior or comparable to those for the MERT (74%, 18.4%, 15.4%) and the photon‐IMRT plan (89.4%, 20.8%, 24.7%). For the enlarged PTV, the dosimetric superiority of MBRT compared to MERT and photon‐IMRT is even more pronounced. Furthermore, an MBRT plan with 12 electron and 10 photon apertures lead to an objective function value 38% lower than that of a photon‐IMRT plan with 40 apertures.

Conclusion:

The results of simultaneous optimization for MBRT are promising with regards to further OAR sparing and improved dose coverage to the PTV compared to photon‐IMRT and MERT. Especially superficial targets with deeper subparts (>5 cm) could substantially benefit. Moreover, MBRT seems to be a possible solution of two downsides of photon‐IMRT, namely the extended low dose bath and the requirement of numerous apertures. This work was supported by Varian Medical Systems.

This work was supported by Varian Medical Systems.
SU‐F‐T‐93: Breast Surface Dose Enhancement Using a Clinical Prone Breast Board
Authors: Guerra M , Jozsef G
Published: July 2016

Purpose:

The use of specialized patient set‐up devices in radiotherapy, such as prone breast boards, may have unwanted dosimetric effects. The goal of this study was to evaluate the effect of a clinically used prone breast board on skin dose due to buildup.

Methods:

GafChromic film (EBT3) was used for dose measurements on the surface of a solid water phantom shaped to mimic the curvature of the breast. We investigated two setup scenarios: the medial field border placed at the medial edge of the board and 1 cm contralaterally from that edge. A strip of film was taped to the medial surface of the phantom. Gantry angles varied from 10 to 30 degrees below the lateral gantry position, representing anterior oblique fields. The measurements were performed with and without the presence of the board; the ratio of their corresponding doses (dose enhancement) was evaluated.

Results:

For the cases where the field edge is at the edge of the board, the dose enhancement is negligible for all the tested angles. When the field edge is 1 cm inside the board, the maximum surface dose enhancement varies depending on the gantry angle between 2.2 for 30 degrees and 3.2 for 20 degrees. The length on the film at which the presence of the board is detectable (i.e. where there is dose enhancement) is longer for the shallower angles.

Conclusion:

Even the low‐density, thin carbon fiber board with a thin soft foam pad on the top can produce significant dose enhancement on the skin in prone breast treatment due to loss of buildup. However, it happens only when the patient mid‐sternum is over the board, i.e. the medial edge of the field traverses through the board and pad. Even then, the effect occurs only at the field edge, i.e. the penumbral region.
SU‐F‐T‐95: An Automatic Data Verification Method During An Eclipse/Aria Version Upgrade Using Cryptographic Secure Hash Algorithm
Authors: Xu Z , Baker J , Ryu S
Published: July 2016

Purpose:

To develop an efficient way to verify that patient plan and dose information does not change during an Eclipse/Aria database version upgrade.

Methods:

Eclipse Scripting Application Programming Interface (ESAPI) was used to create a script to retrieve plan information from the Eclipse database before and after the database upgrade for each patient on treatment. Using Cryptographic Secure Hash Algorithm (SHA256), fixed length digest hash values are generated from the plan parameters for each patient. The script is run twice to create two hash values, HVbefore and HVafter, before and after the Aria database upgrade. Separately, the delivered dose information for all patients was verified by comparing two hash values based on a crystal report summary for all patients treated within a date range. Lastly, an Excel macro is used to import the generated hash values for comparison.

Results:

If HVbefore is the same as HVafter, then the database is considered unchanged based on the collision resistant property of the cryptographic hash function. Otherwise, we conclude that the patient data may have been altered during the upgrade process. In testing the process, all patients passed the comparison. Without using this method, the time to verify a single patient's information was about five minutes. This would result in five hours of work for sixty patients. With this method, we can verify sixty patients in less than thirty minutes before and after the upgrade. This results in time savings of four hours.

Conclusion:

An automatic database verification method has been developed using ESAPI, SHA‐256 Cryptographic Hash Algorithm and Microsoft Excel. We found that the time to verify the database for sixty patients is less than one hour. The scripts can be integrated into Eclipse or can be run as a stand‐alone executable program for a more automated process and increased time savings.
SU‐F‐T‐102: Automatic Curation for a Scalable Registry Using Machine Learning
Authors: Ruan D , Shao W , Wong J , Veruttipong D , Steinberg M , Low D , Kupelian P
Published: July 2016

Purpose:

growing partnership and contributors to registry efforts an efficient way to perform data integration, de‐duplication, and cleansing, amongst other tasks. This project aims to develop an automatic curation module to discover, clean, and transform new data, and semantically integrate them with the composite hosting registry upon de‐duplication.

Methods:

We have investigated various similarity metrics for various attributes and value types in the registry. More specifically, cosine word similarity, cosine term frequency‐inverse document frequency, cosine trigram similarity are used to measure similarity between free text fields; Jaccard similarity and histogram matching are used for categorical values, Naive Bayesian probability in combination with Welch's t‐test values are used to measure likelihood of matching for numerical fields. A supervised learning framework is then adopted where these similarity values are used as input to regress out a decision of amongst {“automatic aggregation with high confidence”, “no match (hence expand current registry)”, and “likely match upon confirmation”}. Multi‐class logistic regression, and classification and regression tree (CART) techniques were used. Seven previous rolling versions of the registry with variations in terminology and data duration were used in a cross‐validation setting to test the applicability of the proposed approach.

Results:

Initial results showed that automatic curation can properly label more than 80% of the label and data fields, significantly alleviating the burden of human operator and the risk of human error. The major limitation of the current approach is ambiguity, e.g., an input tag “MRI” yields multiple potential match. We are investigating the incorporation of context knowledge to reduce such ambiguity to facilitate both automatic curation and human confirmation.

Conclusion:

(Semi‐)automatic curation provides a sustainable pathway to integrate data both longitudinally and across multiple institutions and data sources. Our preliminary effort has demonstrated the feasibility and potential efficacy of utilizing machine learning techniques for such purposes.

This work is supported in part by a Varian research grant.
SU‐F‐T‐107: Correlations Between Dosimetric Indices of Pharyngeal Constrictors and Proximal Esophagus with Associated Patient‐Reported Outcomes Six Months After Radiation Therapy for Head and Neck Cancer
Authors: Chera B , Price A , Kostich M , Amdur R , Mendenhall W , Sheets N , Green R , Marks L , Das S , Mavroidis P
Published: July 2016

Purpose:

To compare the correlations between different dosimetric indices derived from the pharyngeal constrictor muscles and proximal esophagus with patient‐reported difficulty in swallowing 6 months post radiotherapy using a novel patient reported outcome version of CTCAE (PRO‐CTCAE).

Methods:

Forty‐three patients with oropharyngeal squamous cell carcinoma were treated on a prospective multi‐institutional study. All patients received de‐intensified 60 Gy intensity modulated radiotherapy. We investigated correlations of individual patient dosimetric data of the superior (SPC), middle (MPC), inferior (IPC) pharyngeal constrictor muscles, the superior esophagus (SES), and the inferior esophagus (IES) to their self‐reported 6 month post‐treatment swallowing difficulty responses. Mild (≥ Grade 1) swallowing difficulty responses were used as the clinical endpoint indicating response. The predictive efficacy of Dmean and dose‐volume (VD) points were assessed through the area under the Receiver Operating Characteristic curve (ROC) and Odds Ratio (OR).

Results:

The SES and SPC had more favorable area under the curves (AUC) for the Dmean (0.62 and 0.70) while the Dmean to the IPC, MPC, and IES produced suboptimal AUCs (0.42, 0.48, and 0.52). Additionally, over the range of VD, the V54 and V55 for the SES and SPC demonstrated the highest AUCs: AUC(SES) = 0.76–0.73 and AUC(SPC) = 0.72–0.69, respectively. The IES, IPC, and MPC had worse AUC results over the range of VD. An optimal OR can be found when V54 = 96% for the SPC, where OR = 3.96 (1.07–14.62).

Conclusion:

The V45 and V55 of the SES and SPC had the highest correlation to the clinical endpoint compared to the commonly used dosimetric index, Dmean for both the esophagus and constrictor muscles. The reported dosimetric data demonstrates that new dosimetric indices may need to be considered in the setting of dose de‐escalation and self‐reported outcomes.
SU‐F‐T‐115: Uncertainty in the Esophagus Dose in Retrospective Epidemiological Study of Breast Cancer Radiotherapy Patients
Authors: Mosher E , Kim S , Lee C , Pelletier C , Jung J , Jones E , Lee C
Published: July 2016

Purpose:

Epidemiological studies of second cancer risks in breast cancer radiotherapy patients often use generic patient anatomy to reconstruct normal tissue doses when CT images of patients are not available. To evaluate the uncertainty involved in the dosimetry approach, we evaluated the esophagus dose in five sample patients by simulating breast cancer treatments.

Methods:

We obtained the diagnostic CT images of five anonymized adult female patients in different Body Mass Index (BMI) categories (16– 36kg/m2) from National Institutes of Health Clinical Center. We contoured the esophagus on the CT images and imported them into a Treatment Planning System (TPS) to create treatment plans and calculate esophagus doses. Esophagus dose was calculated once again via experimentally‐validated Monte Carlo (MC) transport code, XVMC under the same geometries. We compared the esophagus doses from TPS and the MC method. We also investigated the degree of variation in the esophagus dose across the five patients and also the relationship between the patient characteristics and the esophagus doses.

Results:

Eclipse TPS using Analytical Anisotropic Algorithm (AAA) significantly underestimates the esophagus dose in breast cancer radiotherapy compared to MC. In the worst case, the esophagus dose from AAA was only 40% of the MC dose. The Coefficient of Variation across the patients was 48%. We found that the maximum esophagus dose was up to 2.7 times greater than the minimum. We finally observed linear relationship (Dose = 0.0218 × BMI – 0.1, R2=0.54) between patient's BMI and the esophagus doses.

Conclusion:

We quantified the degree of uncertainty in the esophagus dose in five sample breast radiotherapy patients. The results of the study underscore the importance of individualized dose reconstruction for the study cohort to avoid misclassification in the risk analysis of second cancer. We are currently extending the number of patients up to 30.
SU‐F‐T‐119: Development of Heart Prediction Model to Increase Accuracy of Dose Reconstruction for Radiotherapy Patients
Authors: Mosher E , Choi M , Jones E , Lee C
Published: July 2016

Purpose:

To assess individual variation in heart volume and location in order to develop a prediction model of the heart. This heart prediction model will be used to calculate individualized heart doses for radiotherapy patients in epidemiological studies.

Methods:

Chest CT images for 30 adult male and 30 adult female patients were obtained from NIH Clinical Center. Image‐analysis computer programs were used to segment the whole heart and 8 sub‐regions and to measure the volume of each sub‐ region and the dimension of the whole heart. An analytical dosimetry method was used for the 30 adult female patients to estimate mean heart dose during conventional left breast radiotherapy.

Results:

The average volumes of the whole heart were 803.37 cm3 (COV 18.8%) and 570.19 cm3 (COV 18.8%) for adult male and female patients, respectively, which are comparable with the international reference volumes of 807.69 cm3 for males and 596.15 cm3 for females. Some patient characteristics were strongly correlated (R2>0.5) with heart volume and heart dimensions (e.g., Body Mass Index vs. heart depth in males: R2=0.54; weight vs. heart width in the adult females: R2=0.63). We found that the mean heart dose 3.805 Gy (assuming prescribed dose of 50 Gy) in the breast radiotherapy simulations of the 30 adult females could be an underestimate (up to 1.6‐fold) or overestimate (up to 1.8‐fold) of the patient‐specific heart dose.

Conclusion:

The study showed the significant variation in patient heart volumes and dimensions, resulting in substantial dose errors when a single average heart model is used for retrospective dose reconstruction. We are completing a multivariate analysis to develop a prediction model of the heart. This model will increase accuracy in dose reconstruction for radiotherapy patients and allow us to individualize heart dose calculations for patients whose CT images are not available.
SU‐F‐T‐120: How Many and Which Respiratory Phases Should Be Included During the 4D Robust Optimization Process
Authors: Ge S , Wang X , Mohan R
Published: July 2016

Purpose:

To study how many and which respiratory phases should be included to conduct an efficient 4D robust optimization since contouring CTV and critical organs at all 10 phases are time consuming.

Methods:

A 4D robust optimization algorithm which simultaneously optimizes dose distributions for all 10 respiratory phases has been developed to desensitize plan quality to various uncertainties. To study the possibility of reducing number of phases included during the optimization process while keep the plan quality, four strategies have been conducted and compared: A. including 2 phases: 0% and 50%; B. including 4 phases: 0%, 20%, 50% and 80%. C. including 5 phases: 0%, 20%, 50%, 60% and 80%; D. including all 10 phases during the optimization process. The resulting plans for two patients were evaluated at all 10 respiratory phases.

Results:

For patient one, reducing the number of phases included in optimization process will degrade CTV coverage while improve the normal tissue sparing. The possible worst CTV coverage at prescription dose (74Gy) for IMPT plans optimized for strategy A, B, C, D was 98.13%, 98.29%, 99.00% and 99.05% respectively. The CTV coverage is almost the same when including 5 phases compared to including 10 phases. For patient 2, reducing the number of phases included in optimization process will degrade CTV coverage, while the normal tissue sparing is not affected too much. The possible worst CTV coverage at prescription dose for IMPT plans optimized for strategy A, B, C, D was 95.85%, 99.01%, 99.18% and 99.72% respectively. The CTV coverage is similar when including 4 phases or 5 phases compared to including 10 phases.

Conclusion:

The preliminary data shows that at least 4 phases or 5 phases should be included during optimization process to achieve a high quality IMPT plan considering CTV coverage and normal tissue sparing.
SU‐F‐T‐121: Abdominal Compression Effectively Reduces the Interplay Effect and Enables Pencil Beam Scanning Proton Therapy of Liver Tumors
Authors: Souris K , Glick A , Kang M , Janssens G , Sterpin E , Lin H , McDonough J , Simone C , Solberg T , Ben‐Josef E , Lee J , Lin L
Published: July 2016

Purpose:

To study if abdominal compression can reduce breathing motion and mitigate interplay effect in pencil beam scanning proton therapy (PBSPT) treatment of liver tumors in order to better spare healthy liver volumes compared with photon therapy.

Methods:

Ten patients, six having large tumors initially treated with IMRT and four having small tumors treated with SBRT, were replanned for PBSPT. ITV and beam‐specific PTVs based on 4D‐CT were used to ensure target coverage in PBSPT. The use of an abdominal compression belt and volumetric repainting was investigated to mitigate the interplay effect between breathing motion and PBSPT dynamic delivery. An in‐house Matlab script has been developed to simulate this interplay effect. The dose is computed on each phase individually by sorting all spots according to their simulated delivery timing. The final dose distribution is then obtained by accumulating all dose maps to a reference phase.

Results:

For equivalent target coverage PBSPT reduced average healthy liver dose by 9.5% of the prescription dose compared with IMRT/SBRT. Abdominal compression of 113.2±42.2 mmHg was effective for all 10 patients and reduced average motion by 2.25 mm. As a result, the average ITV volume decreased from 128.2% to 123.1% of CTV volume. Similarly, the average beam‐specific PTV volume decreased from 193.2% to 183.3%. For 8 of the 10 patients, the average motion was reduced below 5 mm, and up to 3 repainting were sufficient to mitigate interplay. For the other two patients with larger residual motion, 4–5 repainting were needed.

Conclusion:

We recommend evaluation of the 4DCT motion histogram following simulation and the interplay effect following treatment planning in order to personalize the use of compression and volumetric repainting for each patient. Abdominal compression enables safe and more effective PBS treatment of liver tumors by reduction of motion and interplay effect.

Kevin Souris is supported by IBA and Televie Grant from F.R.S.‐FNRS. Liyong Lin is partially supported by Varian.