bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐F‐J‐151: Evaluation of a Magnetic Resonance Image Gated Radiotherapy System Using a Motion Phantom and Radiochromic Film
Authors: Lamb J , Ginn J , O'Connell D , Thomas D , Agazaryan N , Cao M , Yang Y , Low D
Published: July 2016

Purpose:

Magnetic resonance image (MRI) guided radiotherapy enables gating directly on target position for soft‐tissue targets in the lung and abdomen. We present a dosimetric evaluation of a commercially‐available FDA‐approved MRI‐guided radiotherapy system's gating performance using a MRI‐compatible respiratory motion phantom and radiochromic film.

Methods:

The MRI‐compatible phantom was capable of one‐dimensional motion. The phantom consisted of a target rod containing high‐contrast target inserts which moved inside a body structure containing background contrast material. The target rod was equipped with a radiochromic film insert. Treatment plans were generated for a 3 cm diameter spherical target, and delivered to the phantom at rest and in motion with and without gating. Both sinusoidal and actual tumor trajectories (two free‐breathing trajectories and one repeated‐breath hold) were used. Gamma comparison at 5%/3mm was used to measure fidelity to the static target dose distribution.

Results:

Without gating, gamma pass rates were 24–47% depending on motion trajectory. Using our clinical standard of repeated breath holds and a gating window of 3 mm with 10% of the target allowed outside the gating boundary, the gamma pass rate was 99.6%. Relaxing the gating window to 5 mm resulted in gamma pass rate of 98.6% with repeated breath holds. For all motion trajectories gated with 3 mm margin and 10% allowed out, gamma pass rates were between 64–100% (mean:87.5%). For a 5 mm margin and 10% allowed out, gamma pass rates were between 57–98% (mean: 82.49%), significantly lower than for 3 mm by paired t‐test (p=0.01).

Conclusion:

We validated the performance of respiratory gating based on real‐time cine MRI images with the only FDA‐approved MRI‐guided radiotherapy system. Our results suggest that repeated breath hold gating should be used when possible for best accuracy. A 3 mm gating margin is statistically significantly more accurate than a 5 mm gating margin.
SU‐F‐J‐154: Harmonic Analysis for Arbitrary 3D MR Image Distortion Fields
Authors: Stanescu T , Jaffray D
Published: July 2016

Purpose:

To study the practical feasibility of harmonic analysis for the full quantification of 3D MR image distortion fields associated with arbitrarily‐shaped regions of interest.

Methods:

The 3D scanner‐related distortion field (F) is innate to the MR image data. Since it is implicitly related to the magnetic fields required to perform MR imaging, F is in a steady‐state and can be described by a boundary value problem in which the Laplace's equation is solved with Dirichlet boundary conditions. Specifically, to fully derive a unique solution for F inside an arbitrarily‐shaped domain (D) the minimum input data required is given by the boundary of D. In practice, the data that needs to be measured by means of image acquisition and post‐processing is on the 3D surface of D (e.g. ellipsoid, cylinder, cuboid). Data from a large FOV phantom with a dense grid structure was used as a reference to explore multiple scenarios. The harmonic analysis solver was based on a finite element method and the domains were defined as binary STL structures for robust meshing. Simple and complex (non‐)quadratic shapes were analyzed to test the applicability of the harmonic approach. The harmonic solution and reference data were compared inside D using histograms and typical metrics such as max/mean/stdev using a residual error threshold set by the accuracy of the reference data (i.e. 1 mm).

Results:

The harmonic analysis showed good performance for all cases investigated. The percentage of control points inside D exhibiting residual values above 1 mm was lower than 1%.

Conclusion:

Harmonic analysis can be used to characterize geometric distortions inside arbitrary volumes given availability of the surface data with a certain accuracy.
SU‐F‐J‐156: The Feasibility of MR‐Only IMRT Planning for Prostate Anatomy
Authors: Vaitheeswaran R , Sivaramakrishnan KR , Kumar Prashant , Gattamaneni Raja , Kumar Girish
Published: July 2016

Purpose:

For prostate anatomy, previous investigations have shown that simulated CT (sCT) generated from MR images can be used for accurate dose computation. In this study, we demonstrate the feasibility of MR‐only IMRT planning for prostate case.

Methods:

Regular CT (rCT) and MR images of the same patient were acquired for prostate anatomy. Regions‐of‐interest (ROIs) i.e. target and risk structures are delineated on the rCT. A simulated CT (sCT) is generated from the MR image using the method described by Schadewaldt N et al. Their work establishes the clinical acceptability of dose calculation results on the sCT when compared to rCT. rCT and sCT are rigidly registered to ensure proper alignment between the two images. rCT and sCT are overlaid on each other and slice‐wise visual inspection confirms excellent agreement between the two images. ROIs on the rCT are copied over to sCT. Philips AutoPlanning solution is used for generating treatment plans. The same treatment technique protocol (plan parameters and clinical goals) is used to generate AutoPlan‐rCT and AutoPlan‐sCT respectively for rCT and and sCT. DVH comparison on ROIs and slice‐wise evaluation of dose is performed between AutoPlan‐rCT and AutoPlan‐sCT. Delivery parameters i.e. beam and corresponding segments from the AutoPlan‐sCT are copied over to rCT and dose is computed to get AutoPlan‐sCT‐on‐rCT.

Results:

Plan evaluation is done based on Dose Volume Histogram (DVH) of ROIs and manual slice‐wise inspection of dose distribution. Both AutoPlan‐rCT and AutoPlan‐sCT provide a clinically acceptable plan. Also, AutoPlan‐sCT‐on‐rCT shows excellent agreement with AutoPlan‐sCT.

Conclusion:

The study demonstrates that it is feasible to do IMRT planning on the simulated CT image obtained from MR image for prostate anatomy.

The research is supported by Philips India Ltd
SU‐F‐J‐160: Clinical Evaluation of Targeting Accuracy in Radiosurgery Using Tractography
Authors: Juh R , Suh T , Han J , Kim C , Oh C
Published: July 2016

Purpose:

Focal radiosurgery is a common treatment modality for trigeminal neuralgia (TN), a neuropathic facial pain condition. Assessment of treatment effectiveness is primarily clinical, given the paucity of investigational tools to assess trigeminal nerve changes. The efficiency of radiosurgery is related to its highly precise targeting. We assessed clinically the targeting accuracy of radiosurgery with Gamma knife. We hypothesized that trigeminal tractography provides more information than 2D‐MR imaging, allowing detection of unique, focal changes in the target area after radiosurgery.

Methods:

Sixteen TN patients (2 females, 4 males, average age 65.3 years) treated with Gamma Knife radiosurgery, 40 Gy/50% isodose line underwent 1.5Tesla MR trigeminal nerve. Target accuracy was assessed from deviation of the coordinates of the target compared with the center of enhancement on post MRI. Radiation dose delivered at the borders of contrast enhancement was evaluated.

Results:

The median deviation of the coordinates between the intended target and the center of contrast enhancement was within 1mm. The radiation doses fitting within the borders of the contrast enhancement the target ranged from 37.5 to 40 Gy. Trigeminal tractography accurately detected the radiosurgical target. Radiosurgery resulted in 47% drop in FA values at the target with no significant change in FA outside the target, suggesting that radiosurgery primarily affects myelin. Tractography was more sensitive, since FA changes were detected regardless of trigeminal nerve enhancement.

Conclusion:

The median deviation found in clinical assessment of gamma knife treatment for TN Is low and compatible with its high rate of efficiency. DTI parameters accurately detect the effects of focal radiosurgery on the trigeminal nerve, serving as an in vivo imaging tool to study TN. This study is a proof of principle for further assessment of DTI parameters to understand the pathophysiology of TN and treatment effects.
SU‐F‐J‐166: Volumetric Spatial Distortions Comparison for 1.5 Tesla Versus 3 Tesla MRI for Gamma Knife Radiosurgery Scans Using Frame Marker Fusion and Co‐Registration Modes
Authors: Neyman G
Published: July 2016

Purpose:

To compare typical volumetric spatial distortions for 1.5 Tesla versus 3 Tesla MRI Gamma Knife radiosurgery scans in the frame marker fusion and co‐registration frame‐less modes.

Methods:

Quasar phantom by Modus Medical Devices Inc. with GRID image distortion software was used for measurements of volumetric distortions. 3D volumetric T1 weighted scans of the phantom were produced on 1.5 T Avanto and 3 T Skyra MRI Siemens scanners. The analysis was done two ways: for scans with localizer markers from the Leksell frame and relatively to the phantom only (simulated co‐registration technique). The phantom grid contained a total of 2002 vertices or control points that were used in the assessment of volumetric geometric distortion for all scans.

Results:

Volumetric mean absolute spatial deviations relatively to the frame localizer markers for 1.5 and 3 Tesla machine were: 1.39 ± 0.15 and 1.63 ± 0.28 mm with max errors of 1.86 and 2.65 mm correspondingly. Mean 2D errors from the Gamma Plan were 0.3 and 1.0 mm. For simulated co‐registration technique the volumetric mean absolute spatial deviations relatively to the phantom for 1.5 and 3 Tesla machine were: 0.36 ± 0.08 and 0.62 ± 0.13 mm with max errors of 0.57 and 1.22 mm correspondingly.

Conclusion:

Volumetric spatial distortions are lower for 1.5 Tesla versus 3 Tesla MRI machines localized with markers on frames and significantly lower for co‐registration techniques with no frame localization. The results show the advantage of using co‐registration technique for minimizing MRI volumetric spatial distortions which can be especially important for steep dose gradient fields typically used in Gamma Knife radiosurgery.

Consultant for Elekta AB
SU‐F‐J‐173: Online Replanning for Dose Painting Based On Changing ADC Map of Pancreas Cancer
Authors: Ates O , Ahunbay E , Erickson B , Li X
Published: July 2016

Purpose:

The introduction of MR‐guided radiation therapy (RT), e.g., MR‐Linac, would allow dose painting to adapt spatial RT response revealed from MRI data during the RT delivery. The purpose of this study is to investigate the use of an online replanning method to adapt dose painting from the MRI Apparent Diffusion Coefficient (ADC) map acquired during the delivery of RT for pancreatic cancers.

Methods:

Original dose painting plans were created based on multi‐parametric simulation MRI including T1, T2 and ADC, using a treatment planning system (MONACO, Elekta) equipped with an online replanning algorithm (WSO, warm start optimization). Multiple GTVs, identified based on various ADC levels were prescribed to different doses ranging from 50–70 Gy with simultaneous integrated boost in 28 fractions. The MRI acquired after RT were used to mimic weekly MRI, on which the changing GTVs, pancreatic head and other organs‐at‐risk (OAR) (duodenum, stomach, small bowel) were delineated. The adaptive plan was generated by applying WSO algorithm starting from the deformed original plan based on the weekly MRI using a deformable image registration (DIR) software (ADMIRE, Elekta). The online replanning method takes <10 min. including DIR, target delineation, WSO execution and final dose calculation. Standard IGRT repositioning and full‐blown reoptimization plans were also generated to compare with the adaptive plans.

Results:

The online replanning method significantly improved the multiple target coverages and OAR sparing for pancreatic cancers. For example, for a case with two GTVs with prescriptions of 60 and 70 Gy in pancreatic head, V100‐GTV70 (the volume covered by 100% of prescription dose for GTV with 70 Gy)/V100‐GTV60/V100‐CTV50/V45‐duodenum were (95.1/22.2/69.5/85.7), (95.0/97.0/98.6/34.3), and (95.0/98.1/100.0/38.7) for the IGRT, adaptive and reoptimization plans, respectively.

Conclusion:

The introduced online adaptive replanning method can effectively account for interfractional changes including tumor spatial response during MR‐guided RT delivery, allowing precise delivery of dose painting.

This study was partially supported by Elekta Inc.
SU‐F‐J‐185: Detection of Low Contrast Objects: Optimization of CT Simulation Reconstruction Protocol Parameters
Authors: Alani S , Schlocker A , Honig N , Corn B
Published: July 2016

Purpose:

CT simulation has become an integral component of modern RT planning and therefore must be continually optimized. We evaluated the detection of small and low‐contrast regions in images obtained during CT simulation.

Methods:

A CT phantom containing a contrast detail modulus for detection of low‐contrast structures was used to optimize the CT reconstruction protocol for abdomen. The parameters (A) Pitch, (B) Reconstruction Filter, and (C) Rotation Time type were varied for assessment of image quality.Three factors, three levels, and nine experiments were identified. According to the Taguchi approach an L9 orthogonal array was selected. The reconstruction parameters of the CT scanner (Brilliance Big Bore), Pitch, Reconstruction Filter type, and Rotation Time, were iteratively scanned according to the orthogonal array. A Catphan 604 CT phantom was used to characterize low‐contrast resolution (CPT730 module). All CT scan images were analyzed by IMAGE‐OWL software. The objective of the study was to identify parameters that maximize the low‐contrast resolution of the images. The ANOVA and F‐tests were used to analyze results using JMP statistical software.

Results:

The optimal settings and predicted optimal values for low‐contrast resolution were determined. The ANOVA was used to determine the optimum combination of process parameters more accurately by investigating the relative importance of each process parameter. We determined that Pitch (61.4%) had the most significant influence on low contrast resolution, followed by the Reconstruction Filter type (29.7%). The optimal setting level is A1‐B1‐C3, 0.68 pitch, smooth filter, and gantry rotation time 1.5sec., respectively. Additional measurements were made to confirm the prediction error model is justified and the results are validated.

Conclusion:

These experiments have several implications for CT imaging, especially for clinical detection of small, low‐contrast lesions in liver or pancreas. In the phantom model of this study, optimal Contrast Detail Values were determined to be: 1% contrast, 2mm; 0.5% contrast, 4mm; 0.3% contrast, 7mm.
SU‐F‐J‐188: Clinical Implementation of in Room Mobile CT for Image Guided Proton Therapy
Authors: Li H , Wu R , Poenisch F , Zhang L , Palmer M , Gautam A , Sahoo N , Zhang X , Balter P , Gillin M , Gunn B , Frank S , Zhu X
Published: July 2016

Purpose:

To implement soft‐tissue image‐guided proton therapy using inroom mobile CT.

Methods:

Anthropomorphic phantom was first used to determine the setup accuracy using in‐ room mobile CT. Laser and bbs were used for the initial setup (marked isocenter). CT data was then acquired with in‐room mobile CT (daily CT). The shift between the marked isocenter and the planned isocenter (final isocenter) was determined from the daily CT using in‐house Computer Assisted Targeting (CAT) software. Orthogonal DRRs of the day was also generated from the daily CT. The phantom was then transferred on the treatment couch top to the treatment machine using a transportation system, and again aligned to the marked isocenter. Couch shifts were made to align the phantom to the final isocenter using the shifts as determined using the CAT software, and verified using orthogonal X‐ray images with the daily DRRs.

Results:

Phantom data suggests that following the setup procedure as described above, targeting accuracy could be within 1 mm. Patient data are being acquired and analyzed.

Conclusion:

In‐room mobile CT is capable of providing soft‐tissue image‐guided proton therapy.
SU‐F‐J‐194: Development of Dose‐Based Image Guided Proton Therapy Workflow
Authors: Pham R , Sun B , Zhao T , Li H , Yang D , Grantham K , Goddu S , Santanam L , Bradley J , Mutic S , Kandlakunta P , Zhang T
Published: July 2016

Purpose:

To implement image‐guided proton therapy (IGPT) based on daily proton dose distribution.

Methods:

Unlike x‐ray therapy, simple alignment based on anatomy cannot ensure proper dose coverage in proton therapy. Anatomy changes along the beam path may lead to underdosing the target, or overdosing the organ‐at‐risk (OAR). With an in‐room mobile computed tomography (CT) system, we are developing a dose‐based IGPT software tool that allows patient positioning and treatment adaption based on daily dose distributions. During an IGPT treatment, daily CT images are acquired in treatment position. After initial positioning based on rigid image registration, proton dose distribution is calculated on daily CT images. The target and OARs are automatically delineated via deformable image registration. Dose distributions are evaluated to decide if repositioning or plan adaptation is necessary in order to achieve proper coverage of the target and sparing of OARs. Besides online dose‐based image guidance, the software tool can also map daily treatment doses to the treatment planning CT images for offline adaptive treatment.

Results:

An in‐room helical CT system is commissioned for IGPT purposes. It produces accurate CT numbers that allow proton dose calculation. GPU‐based deformable image registration algorithms are developed and evaluated for automatic ROI‐delineation and dose mapping. The online and offline IGPT functionalities are evaluated with daily CT images of the proton patients.

Conclusion:

The online and offline IGPT software tool may improve the safety and quality of proton treatment by allowing dose‐based IGPT and adaptive proton treatments.

Research is partially supported by Mevion Medical Systems.
SU‐F‐J‐196: A Prototype System for Portal Imaging for Intensity Modulated Neutron Therapy
Authors: St. James S , Moffitt G , Argento D , DeWitt D , Miyaoka R , Stewart R
Published: July 2016

Purpose:

Fast neutron therapy is offered at the University of Washington Medical Center for treatment of selected cancers. The hardware and control systems of the UW Clinical Neutron Therapy System are undergoing upgrades to enable delivery of IMNT. To clinically implement IMNT, dose verification tools need to be developed. We propose a portal imaging system that relies on the creation of positron emitting isotopes (11C and 15O) through (n, 2n) reactions with a PMMA plate placed below the patient. After field delivery, the plate is retrieved from the vault and imaged using a reader that detects the annihilation photons. The pattern of activity produced in the plate provides information to reconstruct the neutron fluence map that can be compared to fluence maps from Monte Carlo (MCNP) simulations to verify treatment delivery. We have previously performed Monte Carlo simulations of the portal imaging system (GATE simulations) and the beam line (MCNP simulations). In this work, initial measurements using a prototype system are presented.

Methods:

Custom electronics were developed for BGO detectors read out with photomultiplier tubes (previous generation PET detectors from a CTI ECAT 953 scanner). Two detectors were placed in coincidence, with a detector separation of 2 cm. Custom software was developed to create the crystal look up tables and perform a limited angle planar reconstruction with a stochastic normalization. To test the initial capabilities of the system, PMMA squares were irradiated with neutrons at a depth of 1.5 cm and read out using the prototype system. Doses ranging from 10–200 cGy were delivered.

Results:

Using the prototype system, dose differences in the therapeutic range could be determined.

Conclusion:

The prototype portal imaging system is capable of detecting neutron doses as low as 10–50 cGy and shows great promise as a patient QA tool for IMNT.
SU‐F‐T‐32: Evaluation of the Performance of a Multiple‐Array‐Diode Detector for Quality Assurance Tests in High‐Dose‐Rate Brachytherapy with Ir‐192 Source
Authors: Harpool K , De La Fuente Herman T , Ahmad S , Ali I
Published: July 2016

Purpose:

To evaluate the performance of a two‐dimensional (2D) array‐diode‐ detector for geometric and dosimetric quality assurance (QA) tests of high‐dose‐rate (HDR) brachytherapy with an Ir‐192‐source.

Methods:

A phantom setup was designed that encapsulated a two‐dimensional (2D) array‐diode‐detector (MapCheck2) and a catheter for the HDR brachytherapy Ir‐192 source. This setup was used to perform both geometric and dosimetric quality assurance for the HDR‐Ir192 source. The geometric tests included: (a) measurement of the position of the source and (b) spacing between different dwell positions. The dosimteric tests include: (a) linearity of output with time, (b) end effect and (c) relative dose verification. The 2D‐dose distribution measured with MapCheck2 was used to perform the previous tests. The results of MapCheck2 were compared with the corresponding quality assurance testes performed with Gafchromic‐film and well‐ionization‐chamber.

Results:

The position of the source and the spacing between different dwell‐positions were reproducible within 1 mm accuracy by measuring the position of maximal dose using MapCheck2 in contrast to the film which showed a blurred image of the dwell positions due to limited film sensitivity to irradiation. The linearity of the dose with dwell times measured from MapCheck2 was superior to the linearity measured with ionization chamber due to higher signal‐to‐noise ratio of the diode readings. MapCheck2 provided more accurate measurement of the end effect with uncertainty < 1.5% in comparison with the ionization chamber uncertainty of 3%. Although MapCheck2 did not provide absolute calibration dosimeter for the activity of the source, it provided accurate tool for relative dose verification in HDR‐brachytherapy.

Conclusion:

The 2D‐array‐diode‐detector provides a practical, compact and accurate tool to perform quality assurance for HDR‐brachytherapy with an Ir‐192 source. The diodes in MapCheck2 have high radiation sensitivity and linearity that is superior to Gafchromic‐films and ionization chamber used for geometric and dosimetric QA in HDR‐brachytherapy, respectively.
SU‐F‐T‐36: Dosimetric Comparison of Point Based Vs. Target Based Prescription for Intracavitary Brachytherapy in Cancer of the Cervix
Authors: Ashenafi M , McDonald D , Peng J , Mart C , Koch N , Cooper L , Vanek K
Published: July 2016

Purpose:

Improved patient imaging used for planning the treatment of cervical cancer with Tandem and Ovoid (T&O) Intracavitary high‐dose‐rate brachytherapy (HDR) now allows for 3D delineation of target volumes and organs‐at‐risk. However, historical data relies on the conventional point A‐based planning technique. A comparative dosimetric study was performed by generating both target‐based (TBP) and point‐based (PBP) plans for ten clinical patients.

Methods:

Treatment plans created using Elekta Oncentra v. 4.3 for ten consecutive cervical cancer patients were analyzed. All patients were treated with HDR using the Utrecht T&O applicator. Both CT and MRI imaging modalities were utilized to delineate clinical target volume (CTV) and organs‐at‐risk (rectum, sigmoid, bladder, and small bowel). Point A (left and right), vaginal mucosa, and ICRU rectum and bladder points were defined on CT. Two plans were generated for each patient using two prescription methods (PBP and TBP). 7Gy was prescribed to each point A for each PBP plan and to the target D90% for each TBP plan. Target V90%, V100%, and V200% were evaluated. In addition, D0.1cc and D2cc were analyzed for each organ‐at‐risk. Differences were assessed for statistical significance (p<0.05) by use of Student's t‐test.

Results:

Target coverage was comparable for both planning methods, with each method providing adequate target coverage. TBP showed lower absolute dose to the target volume than PBP (D90% = 7.0Gy vs. 7.4Gy, p=0.028), (V200% = 10.9cc vs. 12.8cc, p=0.014), (ALeft = 6.4Gy vs. 7Gy, p=0.009), and (ARight = 6.4Gy vs. 7Gy, p=0.013). TBP also showed a statistically significant reduction in bladder, rectum, small bowel, and sigmoid doses compared to PBP. There was no statistically significant difference in vaginal mucosa or ICRU‐defined rectum and bladder dose.

Conclusion:

Target based prescription resulted in substantially lower dose to delineated organs‐at‐risk compared to point based prescription, while maintaining similar target coverage.
SU‐F‐T‐38: How Much Dose Is Given in MR Guided Cervical Cancer Brachytherapy with the Ring and Tandem Applicators?
Authors: Zhang H
Published: July 2016

Purpose:

To evaluate the dosimetric metrics of HDR Ring and Tandem applicator Brachytherapy for primary cervical cancers.

Methods:

The dosimetric metrics of high‐risk clinical target volumes (HDR‐CTV) of 12 patients (in total 60 fractions/plans) treated with the HDR ring and tandem applicators were retrospectively analyzed. Ring diameter is from 2.6 to 3.4 cm, tandem length is from 4 to 6 cm, and the angle is either 45 or 60 degrees. The first fraction plan was MR guided, the MR images were then used as a reference for contouring the HR‐CTV in CT images of following 4 fractions. The nominal prescription dose was between 5.2 and 5.8 Gy at the point A. The plans were adjusted to cover at least 90% of the HR‐CTV by 90% of the prescription dose and to reduce the doses to the bladder, rectum and bowel‐bag. Minimum target dose of D100 and D90 were converted into the biologically equivalent EBRT dose D90‐iso and D100‐iso (using α/β=10 Gy, 2 Gy/fx). Equivalent uniform doses (EUD) based on the average cancer killing across the target volume were calculated by the modified linear quadratic model (MLQ) from the differential dose volume histogram (DVH) tables.

Results:

The average D90iso of all plans is 8.1 Gy (ranging from 6.2 to 15 Gy, median 7.8 Gy); the average D100iso is just 4.1 Gy (ranging from 1.8 to 7.8 Gy; median 3.9 Gy). The average EUD is 7.0 Gy (ranging from 6.1 to 9.6 Gy, median 6.9 Gy), which is 87% of the D90iso, and 170% of the D100iso.

Conclusion:

The EUDs is smaller than D90iso but greater than D100iso. Because the EUD takes into account the intensive cancer cell killing in the high dose zone of HR‐CTV, MLQ calculated EUD apparently is more relevant than D90 and D100 to describe the HDR brachytherapy treatment quality.
SU‐F‐T‐40: Can CBCT Images Be Used for Volume Studies of Prostate Seed Implants for Boost Treatment?
Authors: Xu H , Lee S , Diwanji T , Amin P , Krudys K , Guerrero M
Published: July 2016

Purpose:

In our clinic, the planning CT is used for definitive and boost low‐dose‐rate (LDR) brachytherapy treatments to determine the ultrasound volume in the operating room (OR) at the time of the implant. While the CT overestimation of OR volume is known, a larger estimation discrepancy has been observed for boost treatments. A possible reason is the prostate size reduction during EBRT for boost patients. Since cone‐beam CT (CBCT) is often used as routine imaging guidance of EBRT, this prostate volume change may be captured. This study investigates if CBCT taken during EBRT includes the volume change information and therefore beats CT in estimating the prostate OR volumes.

Methods:

9 prostate patients treated with EBRT (45Gy in 1.8Gy per fractions to the whole pelvis) and I‐125 seed implants (108Gy) were involved in this study. During EBRT, CBCT image guidance was performed on a weekly basis. For each patient, the prostate volumes on the first and the last available CBCT images were manually contoured by a physician. These volumes were then compared to each other and with the contoured volumes from the planning CT and from the ultrasound images in the OR.

Results:

The first and the last CBCT images did not show significant prostate volume change. Their average +/− standard deviation of prostate volumes were 24.4cc+/−14.6cc and 29.9cc+/−16.1cc, respectively (T‐test p=0.68). The ratio of the OR volume to the last CBCT (0.71+/−0.21) was not significantly different from the ratio of OR volumes to the planning CT (0.61+/−0.13) (p=0.25).

Conclusion:

In this study, CBCT does not show significant prostate volume changes during EBRT. CBCT and CT volumes are quite consistent and no improvement of volume estimation using CBCT is observed. The advantage of CBCT as a replacement of CT for volume study of boost LDR brachytherapy is limited.
SU‐F‐T‐44: A Comparison of the Pre‐Plan, Intra‐Operative Plan, and Post‐Implant Dosimetry for a Prostate Implant Case Using Prefabricated Linear Polymer‐Encapsulated Pd‐103
Authors: Sheu R , Powers A , McGee H , Stock R , Lo Y
Published: July 2016

Purpose:

To investigate the reproducibility and limitations of Pd‐103 prostate brachytherapy using fixed length linear sources (CivaString).

Methods:

An LDR prostate brachytherapy case which was preplanned on MR images with prefabricated linear polymer‐encapsulated Pd‐103 sources (CivaString) was studied and compared with ultrasound based intra‐operative planning and CT based post‐implant dosimetry. We evaluated the following parameters among the three studies: prostate geometry (volume and cross sectional area), needle position and alignment deviations, and dosimetry parameters (D90).

Results:

The prostate volumes and axial cross sectional areas at center of prostate were measured as 41.8, 39.3 and 36.8 cc, and 14.9, 14.3, and 11.3 respectively on pre‐plan MR, inter‐op US, and post‐implant CT studies. The deviation of prostate volumes and axial cross sectional areas measured on pre‐planning MR and intra‐operative US were within 5%. 17 out of 19 pre‐planned needles were positioned within 5mm (the template grid size). One needle location was adjusted intra‐operatively and another needle was removed due to proximity to urethra. The needle pathways were not always parallel to the trans‐rectal probe due to the flexibility of CivaString. The angle of deviation was up to 10 degrees. Two pairs of needles were exchanged to better fit the length of prostate at the time of implant. This resulted in a prostate D90 of 153.8 Gy (124%) and 131.4 Gy (106.7%) for intra‐op and PID respectively.

Conclusion:

Preplanning is a necessary part of implants performed with prefabricated linear polymer sources. However, as is often the case, there were real‐time deviations from the pre‐plan. Intra‐op planning provides the ability conform to anatomy at the time of implant. Therefore, we propose to develop a systematic way to order extra strings of different length to provide the flexibility to perform intra‐operative planning with fixed length strands.
SU‐F‐T‐58: Dosimetric Evaluation of Breast Tissue Composition for Electronic Brachytherapy (BET) Source In High Dose Rate Accelerated Partial Breast (APBI) Irradiation
Authors: Taylor W , Johnson D , Ahmad S , Chen Y
Published: July 2016

Purpose:

To quantitatively evaluate the dosimetric impact of differing breast tissue compositions for electronic brachytherapy source for high dose rate accelerated partial breast irradiation.

Methods:

A series of Monte Carlo Simulation were created using the GEANT4 toolkit (version 10.0). The breast phantom was modeled as a semi‐circle with a radius of 5.0 cm. A water balloon with a radius of 1.5 cm was located in the phantom with the Xoft AxxentTM EBT source placed at center as a point source. A mixed of two tissue types (adipose and glandular tissue) was assigned as the materials for the breast phantom with different weight ratios. The proportionality of glandular and adipose tissue was simulated in four different fashions, 80/20, 70/30, 50/50 and 30/70 respectively. The custom energy spectrum for the 50 kVp XOFT source was provided via the manufacturer and used to generate incident photons. The dose distributions were recorded using a parallel three dimensional mesh with a size of 30 × 30 × 30 cm3 with 1 × 1 × 1 mm3 voxels. The simulated doses absorbed along the transverse axis were normalized at the distance of 1 cm and then compared with the calculations using standard TG‐43 formalism.

Results:

All simulations showed underestimation of dose beyond balloon surface compared to standard TG‐43 calculations. The maximum percentage differences within 2 cm distance from balloon surface were found to be 18%, 11%, 10% and 8% for the fat breast (30/70), standard breast (50/50), dense breast (70/30 and 80/20), respectively.

Conclusion:

The accuracy of dose calculations for low energy EBT source was limited when considering tissue heterogeneous composition. The impact of atomic number on photo‐electric effect for lower energy Brachytherapy source is not accounted for and resulting in significant errors in dose calculation.
SU‐F‐T‐59: The Effect of Radiotherapy Dose On Immunoadjuvants
Authors: Moreau M , Yasmin‐Karim S , Hao Y , Ngwa W
Published: July 2016

Purpose:

Combining radiotherapy with immunotherapy is a promising approach to enhance treatment outcomes for cancer patients. This in‐vitro study investigated which radiotherapy doses could adversely affect the function of anti‐CD40 mAb, which is one of the key immunoadjuvants under investigations for priming such combination therapy.

Methods:

Human monocyte derived THP‐1 cells were treated with 100ng/mL of PMA in chamber slides to differentiate into macrophage. The THP‐1 differentiated macrophages were treated with 2uL/ml of the anti‐CD40 mAb and incubated at 37°C and 5% CO2 for 24 hours. Anti‐CD40 mAb treated cells were then irradiated at different doses of x‐rays: (0, 2, 4, 6, 8, and 12) Gy using the Small Animal Radiotherapy Research Platform (SARRP). After radiation, the cells were left at 4°C for 2 hours followed by immunofluorescence assay. A Nikon inverted live‐cell imaging system with fluorescence microscope was used to image the cells mounted on a slide fixed with Dapi. For comparison, an ELISA assay was performed with the antibody added to 3mL of PBS in multiple 10mm dishes. The 10mm dishes were irradiated at different x‐ray dose: (0, 2, 4, 6, 8. 10, 12, and 15) Gy using the SARRP.

Results:

The anti‐CD40 mAb activating the macrophages starts to lose their viability due to radiation dose between 8Gy to 12Gy as indicated by the immunofluorescence assay. The ELISA assay, also indicated that such high doses could lead to loss of the mAb's viability.

Conclusion:

This work suggests that high doses like those employed during Stereotactic Ablative Radiotherapy may affect the viability of immunoadjuvants such as anti‐CD 40. This study avails in‐vivo experiments combining radiotherapy with anti‐cd40 to get synergistic outcomes, including in the treatment of metastatic disease.
SU‐F‐T‐60: A Quick Dose Calculation Check for Accuboost Breast Treatment
Authors: Sen A
Published: July 2016

Purpose:

Accuboost treatment planning uses dwell times from a nomogram designed with Monte Carlo calculations for round and D‐shaped applicators. A quick dose calculation method has been developed for verification of the HDR Brachytherapy dose as a second check.

Methods:

Accuboost breast treatment uses several round and D‐shaped applicators to be used non‐invasively with an Ir‐192 source from a HDR Brachytherapy afterloader after the breast is compressed in a mammographic unit for localization. The breast thickness, source activity, the prescription dose and the applicator size are entered into a nomogram spreadsheet which gives the dwell times to be manually entered into the delivery computer. Approximating the HDR Ir‐192 as a point source, and knowing the geometry of the round and D‐applicators, the distances from the source positions to the midpoint of the central plane are calculated. Using the exposure constant of Ir‐192 and medium as human tissue, the dose at a point is calculated as: D(cGy) = 1.254 × A × t/R2, where A is the activity in Ci, t is the dwell time in sec and R is the distance in cm. The dose from each dwell position is added to get the total dose.

Results:

Each fraction is delivered in two compressions: cranio‐caudally and medial‐laterally. A typical APBI treatment in 10 fractions requires 20 compressions. For a patient treated with D45 applicators and an average of 5.22 cm thickness, this calculation was 1.63 % higher than the prescription. For another patient using D53 applicators in the CC direction and 7 cm SDO applicators in the ML direction, this calculation was 1.31 % lower than the prescription.

Conclusion:

This is a simple and quick method to double check the dose on the central plane for Accuboost treatment.
SU‐F‐T‐68: Characterizes of Microdetectors in Electron Beam Dosimetry
Authors: Das I , Andersen A , Akino Y
Published: July 2016

Purpose:

Electron beam dosimetry requires high resolution data due to finite range that can be accomplished with small volume detectors. The small‐field used in advance technologies in photon beam has created a market for microdetectors, however characteristics are significantly variable in photon beams and relatively unknown in electron beam that is investigated in this study.

Methods:

Among nearly 2 dozen microdetectors that have been investigated in small fields of photon beam, two popular detectors (microDiamond 60019 (PTW)) and W1 plastic scintillator detector (Standard Imaging)) that are tissue equivalent and have very small sensitive volume are selected. Electron beams from Varian linear accelerators were used to investigate dose linearity dose rate dependence, energy dependence, depth dose and profiles in a reference condition in a water phantom. For W1 that has its own Supermax electrometer point by point measurements were performed. For microDiamond, a PTW‐scanning tank was used for both scanning and point dose measurements.

Results:

W1 detector showed excellent dose linearity (r2 =1.0) from 5–500 MU either with variation of dose rate or beam energy. Similar findings were also observed for microdiamond with r2=1.0. Percent variations in dose/MU for W1 and microDiamond were 0.2–1.1% and 0.4–1.2%, respectively among dose rate and beam energy. This variation was random for microDiamond, whereas it decreased with beam energy and dose rate for W1. The depth dose and profiles were within ±1 mm for both detectors. Both detectors did not show any energy dependence in electron beams.

Conclusion:

Both microDiamond and W1 detectors provided superior characteristics of beam parameters in electron beam including dose, dose rate linearity and energy independence. Both can be used in electron beam except W1 require point by point measurements and microdiamond requires 1500 MU for initial quenching.
SU‐F‐T‐75: Dosimetry Considerations in the Use of Hanging‐Eye Block for Lesions of the Conjunctiva
Authors: Grelewicz Z , Lee B , Cutright D , Kang Z , Gopalakrishnan M , Sathiaseelan V , Zhang H
Published: July 2016

Purpose:

Superficial lesions in the conjunctiva are frequently treated with en face electrons, using a hanging block to spare dose to the lens of the eye. Dose to the tumor and lens depend on the design and setup of the block and supporting apparatus. We performed in phantom measurements in order to characterize the dose sparing effects of the block as well as the under‐dosing effect under the supporting apparatus for 6 MeV treatment.

Methods:

The commercial hanging block studied uses a 1.2 cm diameter tungsten cylinder supported by a 3 mm diameter acrylic rod. Point dose measurements under the hanging block, under an unblocked part of the field, and under the acrylic rod were performed using MOSFET detectors. In addition, EBT3 film was used for both PDD and profile measurements at a depth in phantom of 3 mm for both 105 and 103 cm SSD.

Results:

MOSFET measurements reported a dose reduction of 95% under the tungsten block when using an SSD of 103 cm, and 86% when using an SSD of 105 cm at a depth in phantom of 3 mm. Film measurements showed that the area under the acrylic rod may be under‐dosed by as much as 30% when using 103 SSD. MOSFET measurements confirmed that when using an SSD of 103 cm, the area under the acrylic rod is under‐dosed by up to 30% at 3mm depth, compared to the unblocked part of the field.

Conclusion:

The effectiveness of the commercial hanging block apparatus depends on setup, with 95% lens sparing possible with an SSD of 103 cm. This short SSD is necessary for sharp penumbra. At this SSD, substantial under‐dosing under the acrylic support rod is possible. This must be mitigated with either feathering, or using an alternative method of support for the tungsten block.
SU‐F‐T‐77: A Novel Test for Coincidence Between Light Fields and Electron Radiation Fields
Authors: Gibbard G , Shang C , Khanal S
Published: July 2016

Purpose:

To validate a novel real time quality assurance device, as a means to test coincidence of light fields to electron radiation fields. Method and Materials: Use a Raven™ (LAP of America Laser Applications) detector, both light fields and electron radiation fields of various electron cones and cutouts from two Clinacs (Varian Medical) were sensed by the phosphor screen and registered by a CCD camera of the device. During measurements, the screen surface of Raven was placed at ISO center level facing the radiation field at any setup angle. Subsequently the light field and the electron radiation field (with 100 MU) were captured separately by the device. The measurements were then analyzed using the Raven software with a maximal 25 by 25 cm^2 field size and 0.25 mm resolution. The results were further compared against those using chromic graphic film (EBT3). To ensure consistence only the dimensions through the central axis were recorded. All the films were analyzed with Dose Lab Pro™ v6.70. Coincidence comparisons were done within the tests on one Clinac and between the two Clinacs.

Results:

The similar difference means of the field coincidence are indicated from the 18 samples by EBT films and 34 by the Raven as 1.33 ± 0.87 mm verses 1.06 ± 0.58 mm (p = 0.74). The mean differences of the field coincidence between the two Clinacs, 1.16 ± 0.68 mm (n=16) and 1.16 ± 0.48 mm (n=18) respectively, also suggest no statistical difference (p= 0.40).

Conclusion:

The Raven™ is a comparable quality verification device to the chromic graphic film (EBT3) in checking the coincidence between light and electron radiation fields. In this investigation, the Raven device provided highly reproducible results with real time analysis. Further improvements in its resolution and automatic analyzing capability are warranted.
SU‐F‐T‐83: Infant Total Skin Electron Therapy Using Five Fields Technique
Authors: Saleh H , Howlin T , Massey V
Published: July 2016

Purpose:

We were presented with a 9 month old boy with Relapsed Acute Myeloid Leukemia (AML) involving the skin. The plan was to treat the entire skin using 6 MeV electrons with the infant under complete anesthesia. The purpose of this work is to commission the 6 MeV electron beam and to develop a technique that can be used to deliver total skin dose to infants with minimal patient immobilization.

Methods:

A baby mannequin phantom that mimics the child's length was used to determine the best technique to treat the infant. The 76 cm long phantom was placed on the floor. The phantom was placed in four unique immobilization devices to simulate four different treatment positions (anterior, posterior, left lateral and right lateral). Radiochromic films were used to determine beam profile in both axial and radial directions, and percent depth dose (PDD). Absolute calibration of the machine output at 214 cm distance was measured using an Exradin A11 parallel‐plate ion chamber. A 1.0 cm plexiglass scatter plate was inserted in the collimator. Mosfet dosimeters were used for dose verification for phantom and and patient.

Results:

At 214 cm source to surface distance (SSD) using gantry angle of + 20o from vertical beam flatness is + 10% in the radial direction over a region of 70 cm and + 4% in the axial direction over 60 cm. A five field arrangement was determined to optimally deliver the desired dose with > 90% uniformity. The fifth field was used to boost the head vertex.

Conclusion:

It is possible to treat sedated infants with total skin dose using five positions. Four positions were enough to cover the body and the fifth position boosts the vertex of the head. All fractions can be reproduced accurately daily because of the patient's stable immobilization.
SU‐F‐T‐88: Field's Metal for Electron Beam Inserts and Blocks
Authors: Ha J , Gallogly A , Cui J , Jennelle R
Published: July 2016

Purpose:

The aim of this work is to show that Field's metal can be used as a viable alternative material to lead‐based low‐melting temperature alloys (e.g., Cerrobend) for electron beam inserts and blocks. The goal is to eliminate exposure risks associated with lead and cadmium.

Methods:

Field's metal (51% Indium, 32.5% Bismuth, 16.5% Tin) is a low‐melting point eutectic alloy, and is proposed as a lead‐free replacement for Cadmium‐free alloy (52.5% Bismuth, 32% Lead, 15.5% Tin). The experiments were done using a Varian 21EX linac equipped with 6, 9, 12, and 16 MeV beams. The 10×10 cone was used with 1.8cm thick insert made of Fields metal, Cd‐Free alloy or open field. The transmitted radiation was measured using a diode at various depths in water. Block transmission factor (BTF) is determined as the ratio of maximum transmission radiation dose over the dose at dmax of the open field.

Results:

The data shows BTFs for both alloys are very similar, well below 5% for 6, 9, and 12 MeV beams. For 16 MeV, the BTF of the Fields metal is about 5.3%; the Cd‐free metal 4.2%. The peak dose of the transmitted radiation occurs less than 1 cm below the water surface, at a much shallower depth than the dmax of the electron beam in the open field. The beam profile shows the maximum block transmission is along the central axis of the beam.

Conclusion:

The present study shows that Fields metal can be used to make electron cutouts and blocks for 6, 9, 12, and 16 MeV beams. Because it has a similar density as other lead‐based alloys, the same thickness of Fields metal would be adequate for shielding the electron beams. This means that it can be used as a replacement without modification to the existing block holder.