bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐F‐J‐61: The Effect of CBCT Volume Cutoff On Dose Calculations for Adaptive Planning
Authors: Byers K , Godley A 
Published: July 2016

Purpose:In adaptive re‐planning, the CBCT is used to recalculate the dose and adjust the treatment plan accordingly. The limited field of view of a CBCT can cause external volume cutoff of the patient, which may cause the dose in re‐planning to be miscalculated. This research determined how often this volume cutoff occurs, and how much the dose calculations are affected by this cutoff.Methods:30 consecutive prostate patients treated on the Synergy S (Elekta AB, Stockholm, Sweden) and 28 treated on the Edge (Varian, Palo Alto, CA) linacs were included. For three patients, external contours were added to the original CTs. The external contours added included the true external volume and five others created to mimic the cutoff seen in the CBCTs. The original treatment plans were recalculated using these cutoff contours.Results:30% of Synergy patients were affected by volume cutoff in their CBCTs, in which 75% of their CBCTs had volume cutoff that was less than 700cc, or 6% of the total patient volume imaged. At this 6% change in volume the target dose increases by <2% although there is up to a 13% increase in organ at risk dose. 11% of Edge patients were affected by volume cutoff, all of these CBCTs were affected by a volume cutoff less than 300cc, or 3% of the total imaged volume. At this 3% change in volume the target dose increases by <1% and there is up to a 7% increase in organ at risk dose. The Edge CBCT field of view diameter is 46 cm, whereas the Synergy is only 41 cm, which explains this discrepancy.Conclusion:There is no cutoff observed for 79% of patients studied. For 76% of the patients with cutoff, the target dose increases by <2%. Godley receives research grant from Elekta
SU‐F‐J‐62: Assessment of Dose Changes Due to Anterior‐Posterior Patient Separation During Daily MVCT Scans
Authors: Leney M , Nalichowski A , Patel S 
Published: July 2016

Purpose:To determine the effects of patient separation on absolute dose and dose distribution in patients undergoing pelvic radiotherapy on TomoTherapy.Methods:An Alderson RANDO phantom with 4cm of bolus was imaged on a CT simulator and the resulting scans were contoured as a whole pelvic case. Using TomoTherapy Planning Station, the plan was designed to give 45 Gy to 95% of the treatment volume in 25 fractions. TomoTherapy MVCT scans were performed on the RANDO phantom with 2cm and 4cm of bolus removed to simulate visible changes in a patient's anatomy. The MVCT images were rigidly registered with planning CT images on TomoTherapy Planned Adaptive. The original fluence was recalculated on the MVCT images and changes in dose distribution due to patient separation were quantified by the changes in DVHs for the target volume and the organs at risk.Results:Patient separation difference equivalent to 2cm and 4cm in anterior‐posterior direction resulted in an increase of the PTV D50 and maximum PTV dose of 5.6%, 6.2% for 2cm and 7.7%, 10.4% for 4cm, respectively. For the 2cm change, D50 and maximum doses to organs at risk increased by 6.5%, 7.1% in the bladder, 4.9%, 4.8% in the rectum, and 5.3%, 6.6% in the bowel. For the 4cm change, D50 and maximum doses increased by 10.7%, 12.2% in the bladder, 5.9%, 6.1% in the rectum, and 7.7%, 10.1% in the bowel.Conclusion:This research indicates that, without any changes to the structures, patient separation in the anterior‐posterior direction can affect the dose distribution for the PTV and organs at risk. These results can assist physicians in determining if obtaining a new CT simulation set and replanning is necessary for pelvic patients on TomoTherapy.
SU‐F‐J‐63: Abdominal Diameter Changes in Children During Volumetric Modulated Arc Therapy (VMAT): Is Re‐Planning Needed?
Authors: Guerreiro F , Janssens G , Seravalli E , Raaymakers B 
Published: July 2016

Purpose:To investigate the dosimetric impact of daily changes in patient's diameter, due to weight gain/loss and air in the bowel, based on CBCT information during radiotherapy treatment of pediatric abdominal tumors.Methods:10 pediatric patients with neuroblastoma (n=6) and Wilms’ (n=4) tumors were included. Available CBCTs were affinely registered to the planning CT for daily set‐up variations corrections. A density override approach assigning air‐density to the random air pockets and water‐density to the remaining anatomy was used to determine the CBCT and CT dose. Clinical VMAT plans, with a PTV prescribed dose ranging between (14.4‐ 36) Gy, were re‐optimized on the density override CT and re‐calculated on each CBCT. Dose‐volume statistics of the PTV and kidneys, delineated on each CBCT, were used to compare the daily and cumulative CBCT dose with the reference CT dose.Results:The average patient diameter variation was (0.5 ± 0.7) cm (maximum daily difference of 2.3 cm). The average PTV mean dose difference (MDD) between the CT and the cumulative CBCT plans was (0.1 ± 1.1) % (maximum daily MDD of 2%). A reduction in target coverage up to 3% and 7% was observed for the cumulative and daily CBCT plans, respectively. The average kidneys’ cumulative MDD was (−2.7 ± 3.6) % (maximum daily MDD of −12%), corresponding to an overdosage.Conclusion:Due to patient's diameter changes, a target underdosage was assessed. Given the high local tumor control of neuroblastoma and Wilms’ diseases, the need of re‐planning might be discarded. However, the assessed kidneys overdosage could represent a problem when the normal tissue tolerance is reached. The necessity of re‐planning should then be considered to reduce the risk of long‐term renal complications. Due to the poor softtissue contrast on CBCT, MRI‐guidance is required to obtain a better assessment of the accumulated dose on the remaining OARs.
SU‐F‐J‐66: Anatomy Deformation Based Comparison Between One‐Step and Two‐Step Optimization for Online ART
Authors: Feng Z , Yu G , Qin S , Ma C , Zhu J , Yin Y , Li D 
Published: July 2016

Purpose:This study investigated that how the quality of adapted plan was affected by inter‐fractional anatomy deformation by using one‐step and two‐step optimization for on line adaptive radiotherapy (ART) procedure.Methods:10 lung carcinoma patients were chosen randomly to produce IMRT plan by one‐step and two‐step algorithms respectively, and the prescribed dose was set as 60 Gy on the planning target volume (PTV) for all patients. To simulate inter‐fractional target deformation, four specific cases were created by systematic anatomy variation; including target superior shift 0.5 cm, 0.3cm contraction, 0.3 cm expansion and 45‐degree rotation. Based on these four anatomy deformation, adapted plan, regenerated plan and non‐adapted plan were created to evaluate quality of adaptation. Adapted plans were generated automatically by using one‐step and two‐step algorithms respectively to optimize original plans, and regenerated plans were manually created by experience physicists. Non‐adapted plans were produced by recalculating the dose distribution based on corresponding original plans. The deviations among these three plans were statistically analyzed by paired T‐test.Results:In PTV superior shift case, adapted plans had significantly better PTV coverage by using two‐step algorithm compared with one‐step one, and meanwhile there was a significant difference of V95 by comparison with adapted and non‐adapted plans (p=0.0025). In target contraction deformation, with almost same PTV coverage, the total lung received lower dose using one‐step algorithm than two‐step algorithm (p=0.0143,0.0126 for V20, Dmean respectively). In other two deformation cases, there were no significant differences observed by both two optimized algorithms.Conclusion:In geometry deformation such as target contraction, with comparable PTV coverage, one‐step algorithm gave better OAR sparing than two‐step algorithm. Reversely, the adaptation by using two‐step algorithm had higher efficiency and accuracy as target occurred position displacement.We want to thank Dr. Lei Xing and Dr. Yong Yang in the Stanford University School of Medicine for this work. This work was jointly supported by NSFC (61471226), Natural Science Foundation for Distinguished Young Scholars of Shandong Province (JQ201516), and China Postdoctoral Science Foundation (2015T80739, 2014M551949).
SU‐F‐J‐70: Monte Carlo Study On a Cone‐Beam Computed Tomography Using a Cross‐Type Carbon Fiber Antiscatter Grid
Authors: Usui K , Inoue T , Kurokawa C , Sugimoto S , Sasai K , Ogawa K 
Published: July 2016

Purpose:If a cone‐beam computed tomography (CBCT) image can be used for adaptive radiotherapy (ART), an irradiated actual dose distribution can be verified on every treatment day. However, a CBCT image is commonly degraded by scattered photons and thus cannot be directly used for dose calculation. The purpose of the present study is to evaluate whether a cross‐type carbon fiber antiscatter grid improves CBCT image quality using a Monte Carlo (MC) method for achieving CBCT‐based ART.Methods:We designed a new carbon fiber (C6H10O5) interspaced grid, which allows the grid ratio to be increased while maintaining the transmission of primary photons. The grid ratio was 20:1, and the grid frequency was 20 lp/cm, with lead strips oriented along the cone beam projections. The MC method was used to simulate a projection data acquisition system of a material phantom (water, lung, bone, cartilage, and adipose) with a bow‐tie filter. The parameters used to evaluate the image quality were uniformity, contrast, and contrast‐to‐noise ratio (CNR). Moreover, to evaluate the accuracy of the CT number, we compared CT numbers between images reconstructed by only primary photons and those obtained using grids.Results:The proposed grid had a beneficial impact on the image quality and accuracy of the CT number. The uniformity was improved by approximately 70% compared to the case without the grid. The average contrast and CNR improved by 14.2% and 22.6%, respectively, when using the proposed grid. CT numbers using the proposed grid were most consistent with nominal CT numbers obtained with only primary photons.Conclusion:The proposed cross‐type carbon fiber grid improves CBCT image quality and achieves an accurate CT number, without increasing the imaging doses. Therefore, the cross‐type carbon fiber antiscatter grid should be considered to achieve CBCT‐based ART.This work was supported by Japan Society for the Promotion of Science KAKENHI.Grant Number 15K19211.
SU‐F‐J‐78: Characterization of Deformable Image Registration for the Pelvic Region Based On Prostate Shifting, Image Noise and the Existence of Implanted Fiducial Markers
Authors: Ikeda T , Takemura A , Shinichi U , Kojima H , Noto K 
Published: July 2016

Purpose:To assess the impact of prostate shifting, image noise and the existence of fiducial markers on deformable image registration (DIR) performance in the pelvic region using original digital phantoms.Methods:A digital phantom of the pelvic region of a prostate cancer patient was created using contoured anatomy as a base image set. Two simulated fiducial markers were implanted at the apex and base of the prostate. With and without markers, the prostate was shifted by 6.00 and 10.0 mm superior, 5.63 and 9.38 mm posterior, and 5.63 and 9.38 mm left, respectively. We also added image noise with a standard deviation (SD) of 9, 21, or 28. A phantom with a noise SD of 9 and zero prostate shift was defined as the target, and the other phantoms were defined as the sources. DIR was performed using MIM Maestro (MIM Software Inc., Cleveland, OH, USA) on the digital phantoms. A dice similarity coefficient (DSC) was used as the index of correspondence level of the prostates on the target images and the results of the DIR. Also, we calculated the motion distance of the fiducial markers.Results:The DSC decreased with increasing prostate distance. The degree of correspondence of the fiducial markers and the DIR performance were worse when the bladder volume changed after the prostate shifted in the superior direction than when it shifted in the other directions. Changes in the image noise and the existence of fiducial markers produced minimal impact on the DIR results.Conclusion:We found that DIR was not affected by image noise, and the reproduction of prostate position by maintaining the bladder volume was important to preserve DIR performance. Further, the existence of two fiducial markers had no impact on DIR performance.This work was supported by Japan Society for the Promotion of Science (JSPS) KAKEN Grant‐in‐Aid for Scientific Research (C) Grant number 26460724.
SU‐F‐J‐101: Stereotactic Body Radiation Therapy Planning for Primary Prostate Cancer with Selective Intraprostatic Boost Determined by 18F‐Choline PET/CT
Authors: Wu L , Wang H , Hirata E , Kwee S , Kuang Y 
Published: July 2016

Purpose:To investigate the utility of 18F‐choline positron emission tomography (PET) scans guidance for SBRT dose painting in patients with prostate cancer and its impact on tumor control probability (TCP) and normal tissue complication probability (NTCP).Methods:Twenty seven patients with localized prostate cancer who had 18F‐choline PET/CT scan prior to treatment were included. A pair of nested intraprostatic dominant lesion (IDL) contours (IDLsuv60% and IDLsuv70%) were generated for each patient based on 60% and 70% of maximum prostate uptake on the 18F‐choline PET images. GTVreg was delineated on prostate according to the gland boundary seen on CT images. The PTVs (PTVsuv60% and PTVsuv70%) were defined as respective IDLs with a 3‐mm margin posteriorly and 5 mm in all other dimensions. Two 5‐fraction SBRT plans using VMAT technique along with 10 MV FFF beams, plan36Gy and plan50–55Gy, were generated for each patient. All plans included a dose of 36.25 Gy prescribed to PTVreg. The Plan50–55Gy also included a simultaneous boost dose of 50 Gy and 55 Gy prescribed to the PTVsuv60% and PTVsuv70%, respectively. The utility of 18F‐Choline PET‐guided SBRT dose escalation was evaluated by its ability to achieve the prescription dose objectives while adhering to organ‐at‐risk (OAR) dose constraints. The TCP and NTCP calculated by radiological models were also compared between two plans for each patient.Results:In all 54 SBRT plans generated, the planning objectives and dose constraints were met without exception. Plan50–55Gy had a significantly higher dose in PTVsuv60% and PTVsuv70% than those in Plan36Gy (p < 0.05), respectively, while still maintaining a safe OAR sparing profile. In addition, plan50–55Gy had significantly higher TCP than plan36Gy.Conclusion:Using VMAT with FFF beams to incorporate a simultaneous 18F‐choline PET‐guided radiation boost dose up to 55 Gy into a SBRT plan is technically feasible.This work was supported in part by Congressionally Directed Medical Research Programs Prostate Cancer Research Program grant PC04130, National Institutes of Health/National Cancer Institute grant R41CA110121, and the UNLV Lincy Endowed Assistant Professorship.
SU‐F‐J‐102: Lower Esophagus Margin Implications Based On Rapid Computational Algorithm for SBRT
Authors: Cardenas M , Mazur T , Li H , Mutic S , Bradley J , Tsien C , Green O 
Published: July 2016

Purpose:To quantify inter‐fraction esophagus‐variation.Methods:Computed tomography and daily on‐treatment 0.3‐T MRI data sets for 7 patients were analyzed using a novel Matlab‐based (Mathworks, Natick, MA) rapid computational method. Rigid registration was performed from the cricoid to the gastro‐esophageal junction. CT and MR‐based contours were compared at slice intervals of 3mm. Variation was quantified by “expansion,” defined as additional length in any radial direction from CT contour to MR contour. Expansion computations were performed with 360° of freedom in each axial slice. We partitioned expansions into left anterior, right anterior, right posterior, and left posterior quadrants (LA, RA, RP, and LP, respectively). Sample means were compared by analysis of variance (ANOVA) and Fisher's Protected Least Significant Difference test.Results:Fifteen fractions and 1121 axial slices from 7 patients undergoing SBRT for primary lung cancer (3) and metastatic lung disease (4) were analyzed, generating 41,970 measurements. Mean LA, RA, RP, and LP expansions were 4.30±0.05 mm, 3.71±0.05mm, 3.17±0.07, and 3.98±0.06mm, respectively. 50.13% of all axial slices showed variation > 5 mm in one or more directions. Variation was greatest in lower esophagus with mean LA, RA, RP, and LP expansion (5.98±0.09 mm, 4.59±0.09 mm, 4.04±0.16 mm, and 5.41±0.16 mm, respectively). The difference was significant compared to mid and upper esophagus (p<.0001). The 95th percentiles of expansion for LA, RA, RP, LP were 13.36 mm, 9.97 mm, 11.29 mm, and 12.19 mm, respectively.Conclusion:Analysis of on‐treatment MR imaging of the lower esophagus during thoracic SBRT suggests margin expansions of 13.36 mm LA, 9.97 mm RA, 11.29 mm RP, 12.19 mm LP would account for 95% of measurements. Our novel algorithm for rapid assessment of margin expansion for critical structures with 360° of freedom in each axial slice enables continuously adaptive patient‐specific margins which may reduce overlap with high‐dose regions.
SU‐F‐J‐108: TMR Correction Factor Based Online Adaptive Radiotherapy for Stereotactic Radiosurgery (SRS) of L‐Spine Tumors Using Cone Beam CT
Authors: Ghaffar I , Balik S , Zhuang T , Chao S , Xia P 
Published: July 2016

Purpose:To investigate the feasibility of using TMR ratio correction factors for a fast online adaptive plan to compensate for anatomical changes in stereotactic radiosurgery (SRS) of L‐spine tumors.Methods:Three coplanar treatment plans were made for 11 patients: Uniform (9 IMRT beams equally distributed around the patient); Posterior (IMRT with 9 posterior beams every 20 degree) and VMAT (2 360° arcs). For each patient, the external body and bowel gas were contoured on the planning CT and pre‐treatment CBCT. After registering CBCT and the planning CT by aligning to the tumor, the CBCT contours were transferred to the planning CT. To estimate the actual delivered dose while considering patient's anatomy of the treatment day, a hybrid CT was created by overriding densities in planning CT using the differences between CT and CBCT external and bowel gas contours. Correction factors (CF) were calculated using the effective depth information obtained from the planning system using the hybrid CT: CF = TMR (delivery)/TMR (planning). The adaptive plan was generated by multiplying the planned Monitor Units with the CFs.Results:The mean absolute difference (MAD) in V16Gy of the target between planned and estimated delivery with and without TMR correction was 0.8 ± 0.7% vs. 2.4 ± 1.3% for Uniform and 1.0 ± 0.9% vs. 2.6 ± 1.3% for VMAT plans(p<0.05), respectively. For V12Gy of cauda‐equina with and without TMR correction, MAD was 0.24 ± 0.19% vs. 1.2 ± 1.02% for Uniform and 0.23 ± 0.20% vs. 0.78 ± 0.79% for VMAT plans(p<0.05), respectively. The differences between adaptive and original plans were not significant for posterior plans.Conclusion:The online adaptive strategy using TMR ratios and pre‐treatment CBCT information was feasible strategy to compensate for anatomical changes for the patients treated for L‐spine tumors, particularly for equally spaced IMRT and VMAT plans.
SU‐F‐J‐111: A Novel Distance‐Dose Weighting Method for Label Fusion in Multi‐ Atlas Segmentation for Prostate Radiation Therapy
Authors: Chang J , Gu X , Lu W , Song T , Jiang S 
Published: July 2016

Purpose:A novel distance‐dose weighting method for label fusion was developed to increase segmentation accuracy in dosimetrically important regions for prostate radiation therapy.Methods:Label fusion as implemented in the original SIMPLE (OS) for multi‐atlas segmentation relies iteratively on the majority vote to generate an estimated ground truth and DICE similarity measure to screen candidates. The proposed distance‐dose weighting puts more values on dosimetrically important regions when calculating similarity measure. Specifically, we introduced distance‐to‐dose error (DDE), which converts distance to dosimetric importance, in performance evaluation. The DDE calculates an estimated DE error derived from surface distance differences between the candidate and estimated ground truth label by multiplying a regression coefficient. To determine the coefficient at each simulation point on the rectum, we fitted DE error with respect to simulated voxel shift. The DEs were calculated by the multi‐OAR geometry‐dosimetry training model previously developed in our research group.Results:For both the OS and the distance‐dose weighted SIMPLE (WS) results, the evaluation metrics for twenty patients were calculated using the ground truth segmentation. The mean difference of DICE, Hausdorff distance, and mean absolute distance (MAD) between OS and WS have shown 0, 0.10, and 0.11, respectively. In partial MAD of WS which calculates MAD within a certain PTV expansion voxel distance, the lower MADs were observed at the closer distances from 1 to 8 than those of OS. The DE results showed that the segmentation from WS produced more accurate results than OS. The mean DE error of V75, V70, V65, and V60 were decreased by 1.16%, 1.17%, 1.14%, and 1.12%, respectively.Conclusion:We have demonstrated that the method can increase the segmentation accuracy in rectum regions adjacent to PTV. As a result, segmentation using WS have shown improved dosimetric accuracy than OS. The WS will provide dosimetrically important label selection strategy in multi‐atlas segmentation.CPRIT grant RP150485
SU‐F‐J‐112: Clinical Feasibility Test of An RF Pulse‐Based MRI Method for the Quantitative Fat‐Water Segmentation
Authors: Yee S , Wloch J , Pirkola M 
Published: July 2016

Purpose:Quantitative fat‐water segmentation is important not only because of the clinical utility of fat‐suppressed MRI images in better detecting lesions of clinical significance (in the midst of bright fat signal) but also because of the possible physical need, in which CT‐like images based on the materials’ photon attenuation properties may have to be generated from MR images; particularly, as in the case of MR‐only radiation oncology environment to obtain radiation dose calculation or as in the case of hybrid PET/MR modality to obtain attenuation correction map for the quantitative PET reconstruction. The majority of such fat‐water quantitative segmentations have been performed by utilizing the Dixon's method and its variations, which have to enforce the proper settings (often predefined) of echo time (TE) in the pulse sequences. Therefore, such methods have been unable to be directly combined with those ultrashort TE (UTE) sequences that, taking the advantage of very low TE values (∼ 10's microsecond), might be beneficial to directly detect bones. Recently, an RF pulse‐based method (http://dx.doi.org/10.1016/j.mri.2015.11.006), termed as PROD pulse method, was introduced as a method of quantitative fat‐water segmentation that does not have to depend on predefined TE settings. Here, the clinical feasibility of this method is verified in brain tumor patients by combining the PROD pulse with several sequences.Methods:In a clinical 3T MRI, the PROD pulse was combined with turbo spin echo (e.g. TR=1500, TE=16 or 60, ETL=15) or turbo field echo (e.g. TR=5.6, TE=2.8, ETL=12) sequences without specifying TE values.Results:The fat‐water segmentation was possible without having to set specific TE values.Conclusion:The PROD pulse method is clinically feasible. Although not yet combined with UTE sequences in our laboratory, the method is potentially compatible with UTE sequences, and thus, might be useful to directly segment fat, water, bone and air.