bluuebunny/crossref_metadata_2025_split huggingface dataset:
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.