bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐F‐J‐115: Target Volume and Artifact Evaluation of a New Device‐Less 4D CT Algorithm
Authors: Martin R , Pan T 
Published: July 2016

Purpose:4DCT is often used in radiation therapy treatment planning to define the extent of motion of the visible tumor (IGTV). Recent available software allows 4DCT images to be created without the use of an external motion surrogate. This study aims to compare this device‐less algorithm to a standard device‐driven technique (RPM) in regards to artifacts and the creation of treatment volumes.Methods:34 lung cancer patients who had previously received a cine 4DCT scan on a GE scanner with an RPM determined respiratory signal were selected. Cine images were sorted into 10 phases based on both the RPM signal and the device‐less algorithm. Contours were created on standard and device‐less maximum intensity projection (MIP) images using a region growing algorithm and manual adjustment to remove other structures. Variations in measurements due to intra‐observer differences in contouring were assessed by repeating a subset of 6 patients 2 additional times. Artifacts in each phase image were assessed using normalized cross correlation at each bed position transition. A score between +1 (artifacts “better” in all phases for device‐less) and −1 (RPM similarly better) was assigned for each patient based on these results.Results:Device‐less IGTV contours were 2.1 ± 1.0% smaller than standard IGTV contours (not significant, p = 0.15). The Dice similarity coefficient (DSC) was 0.950 ± 0.006 indicating good similarity between the contours. Intra‐observer variation resulted in standard deviations of 1.2 percentage points in percent volume difference and 0.005 in DSC measurements. Only two patients had improved artifacts with RPM, and the average artifact score (0.40) was significantly greater than zero.Conclusion:Device‐less 4DCT can be used in place of the standard method for target definition due to no observed difference between standard and device‐less IGTVs. Phase image artifacts were significantly reduced with the device‐less method.
SU‐F‐J‐116: Clinical Experience‐Based Verification and Improvement of a 4DCT Program
Authors: Fogg P , West M , Aland T 
Published: July 2016

Purpose:To demonstrate the role of continuous improvement fulfilled by the Medical Physicist in clinical 4DCT and CBCT scanning.Methods:Lung (SABR and Standard) patients’ 4D respiratory motion and image data were reviewed over a 3, 6 and 12 month period following commissioning testing. By identifying trends of clinically relevant parameters and respiratory motions, variables were tested with a programmable motion phantom and assessed. Patient traces were imported to a motion phantom and 4DCT and CBCT imaging were performed. Cos6 surrogate and sup‐inf motion was also programmed into the phantom to simulate the long exhale of patients for image contrast tests.Results:Patient surrogate motion amplitudes were 9.9+5.2mm (3–35) at 18+6bpm (6–30). Expiration/Inspiration time ratios of 1.4+0.5second (0.6–2.9) showed image contrast effects evident in the AveCT and 3DCBCT images. Small differences were found for patients with multiple 4DCT data sets. Patient motion assessments were simulated and verified with the phantom within 2mm. Initial image reviews to check for reconstructed artefacts and data loss identified a small number of patients with irregularities in the automatic placement of inspiration and expiration points.Conclusion:The Physicist's involvement in the continuous improvements of a clinically commissioned technique, processes and workflows continues beyond the commissioning stage of a project. Our experience with our clinical 4DCT program shows that Physics presence is required at the clinical 4DCT scan to assist with technical aspects of the scan and also for clinical image quality assessment prior to voluming. The results of this work enabled the sharing of information from the Medical Physics group with the Radiation Oncologists and Radiation Therapists. This results in an improved awareness of clinical patient respiration variables and how they may affect 4D simulation images and also may also affect the treatment verification images.
SU‐F‐J‐120: Evaluation of the Combined Effect of Body Orientation and Breathing On Organ Movement in Thorax Using Multi‐Step Deformable Image Registration
Authors: Guy C , Weiss E , Che S , Sleeman W , Mukhopadhyay N , Rosu M 
Published: July 2016

Purpose:Use deformable registration to map more complex anatomies that include changes associated with both different body positions and breathing, and evaluate the resultant respiratory excursions for tumors and relevant organs at risk.Methods:Same‐day exhale and inhale datasets from prone and supine 4D CT scans of lung cancer patients have been registered using the Elastix software package through a 3 step process: (1) rigid registration for bony alignment (2) deformable multiresolution B‐Spline registration of entire anatomy (3) deformable multiresolution B‐Spline registration of lung parenchyma (to improve lung vasculature alignment).Manual contours were propagated from the supine‐inhale phase to supine‐exhale, prone‐exhale and prone‐inhale, via the resulting registration transformations. Motion excursions between exhale and inhale for both body orientations were computed for tumors, heart, esophagus, vertebrae (T2, T5, T12).Results:The registration accuracy was evaluated by visual inspection of the deformed contours by physicians and minimal contour adjustments were made where deemed appropriate. The average supine [mm] / prone [mm] motion amplitudes for the initial 5‐patient sample are as follows: Tumor – 5.8/6.5, T5 – 1.4/2.0, T2 – 0.5/1.6, T12 – 1.7/2.9, Heart– 4.9/9.0, Upper esophagus – 1.6/3.8, Middle esophagus – 3.8/5.0, Lower esophagus – 4.1/6.7. Differences between prone and supine excursions for heart, esophagus, T2 and T12 were significant at 95% level (one‐sided Wilcoxon Mann‐Whitney test).On average, the right and left lung volumes increased by 10% at inhale prone and by 5% at exhale prone from their respective values in supine position.Conclusion:A multi‐step deformable registration sequence was implemented and successfully used for supine‐prone image registration of thorax. In prone position, lungs are larger, likely owing to increased pulmonary compliance and decreased compressive force of the heart on lungs when prone. Breathing motion excursion is enhanced in prone, possible consequence of rib cage stabilization and increased diaphragmatic motion.Elisabeth Weiss: Research support from Philips Healthcare and National Institutes of Health; Licensing agreement with Varian Medical Systems, UpToDate royalties.
SU‐F‐J‐122: Rectal Sparing Reproducibility in Prostate Cancer Patients Treated with Hydrogel Spacer and Proton Therapy
Authors: Hedrick S , Case S , Robison B , Blakey M , Artz M , Renegar J , Schreuder A , Fagundes M 
Published: July 2016

Purpose:Rectal hydrogel spacer has been shown to improve rectal sparing in prostate radiotherapy. The purpose of this study was to determine the reproducibility of rectal sparing throughout treatment in patients undergoing proton therapy.Methods:At our facility, prostate cancer patients are treated with pencil beam scanning proton therapy, utilizing an endorectal balloon (ERB) or rectal spacer hydrogel (Gel) “SpaceOAR” implant. All patients were treated with a full bladder and empty rectum (low residue diet and stool softeners). A quality assurance CT (QACT) was performed periodically throughout treatment to ensure rectal filling consistency and sparing in 41 patients treated with Gel. The treatment planning (TP) dose was calculated on each QACT and the rectum V90%, V75%, V65%, V50%, and V40% were recorded. QACT scans were acquired on day 0, week 1, week 3, and week 5.Results:144 QACT scans were analyzed, each patient receiving 3–4 QACTs. Rectum V90% was within +/−1% of the TP dose in 70% of the QACTs and within +/−5% in 95% of scans. From previous data analyses, our ERB rectum V90% average is 6%. This value was used as an upper threshold for the Gel QACT analysis. 5 of the 41 patients (12%), corresponding to 7 QACTs, had a rectum V90% that exceeded 6% on one or more QACTs. However, the average rectal V90% measured over multiple QACTs never exceeded 6%. 55% of the QACTs had a rectum volume within 5cc of the TPCT volume, 68% were within 10cc.Conclusion:In this study, we have shown that a majority of our prostate patients can maintain consistent rectal sparing when treated with a hydrogel spacer. QACT rectal V90% exceeding our threshold was most often related to increased rectal filling and gas, which was addressed with improved dietary compliance and the intensification of stool softeners or laxatives.
SU‐F‐J‐125: Effects of Couch Position Variability On Dosimetric Accuracy with An MRI‐Guided Co‐60 Radiation Therapy Machine
Authors: Chow P , Thomas D , Agazaryan N , Cao M , Low D , Yang Y , Lamb J 
Published: July 2016

Purpose:Magnetic resonance imaging (MRI) guidance in radiation therapy brings real‐time imaging and adaptive planning into the treatment vault where it can account for interfraction and intrafraction movement of soft tissue. The only commercially‐available MRI‐guided radiation therapy device is a three‐head 60Co and MRI system with an integrated treatment planning system (TPS). An up to 20% attenuation of the beam by the couch is well modeled in the TPS. However, variations in the patient's day‐to‐day position introduce discrepancies in the actual couch position relative its location as modeled in the treatment plan. For this reason, our institution avoids plans with beams that pass through or near the couch edges. This study looks at plans without restriction on beam angles and investigates the effects of couch shift by simulating shifts of the couch relative to the patient, in order to determine whether couch edge avoidance restrictions can be lifted.Methods:A total of 27 plans from 23 patients were investigated. Couch shifts of 1 and 2 cm were introduced in combinations of lateral and vertical direction to simulate variations in patient positioning on the couch giving 16 shifted plans per reference plan. The shift values of 1 and 2 cm were based on shifts recorded in 320 treatment fractions.Results:Measured couch attenuation versus TPS modeled agreed within 2.1%. Planning Target Volume (PTV) D95 changed less than 1% for 1 and 2 cm couch shifts in only the x‐direction and less than 3% for all directions.Conclusion:The dosimetry of all plans with shifts up to ±2 cm was within reasonable clinical tolerances. Robustness of a plan to couch shifts can be tested in the TPS. Inclusion of beams traversing the couch edges should be considered if an improvement in plan quality or delivery time can be achieved.
SU‐F‐J‐126: Influence of Six Dimensional Motions in Frameless Stereotactic Dosimetry Incorporating Rotational Shifts as Equivalent Translational Shifts: A Feasibility Study for Elekta‐BrainLAB Stereotactic System
Authors: Sarkar B , Manikandan A , Jassal K , Ganesh T , Munshi A , Mohanti B , Pradhan A 
Published: July 2016

Purpose:Six dimensional positional shifts (translational and rotational) determined by a volumetric imaging system were mathematically combined and incorporated as simple translational shifts and the resultant impact on dose characteristics was studied.Methods:Thirty patients who underwent either single fraction (12 Gy) or five fractions (5 Gy per fraction) stereotactic treatments were included in this study. They were immobilized using a double layered thermoplastic mask from BrainLAB. Isocenter matching was done using infrared marker of ExacTrac. An initial cone beam CT (CBCT) gave positional shifts in 6‐dimensions that were applied through 6‐D motion enabled couch. A verification CBCT was done following corrections before treatment. These 6‐D positional shifts determined at each imaging session from the first CBCT were mathematically combined to give three simple translational shifts. Doses were recalculated in the patient matrix with these positional errors present by moving the whole image dataset. Doses were also recalculated after second CBCT with only residual errors present. PTV dose statistics were compared.Results:For the approved plans V100%(PTV), V100%(GTV), D95%(PTV), D95%(GTV), D1%(PTV) and D1%(GTV) were 96.2±3.0%, 98.2±1.4%, 102%±1.7%, 103±1.2%, 107.9±8.9% and 109.3±7.5% of prescription dose respectively. With the positional errors present (after 1st CBCT) the corresponding values were 86.7±4.9%, 91.3±2.9%, 89.6±4.2%, 95.9±3.7%, 108.3±9.9% and 108.6±4.5%. Post‐correction (after 2nd CBCT) with only residual errors present, values were 94.5±5.7%, 97.3±2.9%, 99.3%±3.2%, 102%±2.1%, 107.6±8.5% and 109.0±7.6% respectively. Significant and nominal OAR dose variation was observed between pre‐ and post‐table corrections.Conclusion:Positional errors significantly affect PTV dose statistics. They need to be corrected before delivery of stereotactic treatments although the magnitude of dose changes can vary from patient‐to‐patient depending on the tumor location. As expected after the table corrections, residual errors result in insignificant dose deviations. For frameless stereotactic treatments having a six‐dimensional motion enabled couch is highly recommended to reduce quantum of dose deviations.
SU‐F‐J‐127: Multi‐Institutional Evaluation of Setup, Organ Deformation, Precision Dosimetry in Total Marrow Irradiation
Authors: Zuro D , Hui S 
Published: July 2016

Purpose:Totals Marrow Irradiation (TMI) is a highly focused radiation delivery to the human skeleton structure therefore requiring a high amount of precision and accuracy for a quality treatment. Not much is known on how the patient position varies across multiple treatment fractions and how that positioning impacts the dose delivery. Currently TMI is studied as an international collaboration with multiple centers around the world; however, many of these centers used different pretreatment techniques. The goal of this work is to measure the accuracy of patient positioning, its impact on dose delivery and compare the impact of each technique for multiple institutions.Methods:Using Tomotherapy pretreatment MVCTs and the planning KVCTs measurements are made of the 3D setup uncertainties of the TMI treatment. Then, using the dose and plan files of the treatment impact of patient position on dose can be measured. Measurement of organ deformation and center of mass change were done using the Velocity AI program from Varian. We are looking at four the boney targets (skull, spine, pelvis, and femur) and three key sensitive tissues (eyes, lungs, kidneys).Results:Position measurements have been made for 3 different institutions using 3 different pre‐treatment techniques. Comparing the translation motion we can observe the greatest change in the Y and Z direction of patient set up. For intra‐fractional motion the shoulder and clavicle represent the greatest potential for motion and therefore most likely to have a dose change.Conclusion:All centers use different techniques for their treatment and this study shows that these techniques do not produce the same pretreatment results. We hope to expand this study further. Currently we have 3 centers participating in this study with more centers joining every day.
SU‐F‐J‐128: Dosimetric Impact of Esophagus Motion in Spine Stereotactic Body Radiotherapy
Authors: Yang J , Wang X , Zhao Z , Yang J , Zhang Y , Court L , Li J , Brown P , Ghia A 
Published: July 2016

Purpose:Acute esophageal toxicity is a common side effect in spine stereotactic body radiotherapy (SBRT). The respiratory motion may alter esophageal position from the planning scan resulting in excessive esophageal dose. Here we assessed the dosimetric impact resulting from the esophageal motion using 4DCT.Methods:Nine patients treated to their thoracic spines in one fraction of 24 Gy were identified for this study. The original plan on a free breathing CT was copied to each phase image of a 4DCT scan, recalculated, scaled, and accumulated to the free breathing CT using deformable image registration. A segment of esophagus was contoured in the vicinity of treatment target. Esophagus dose volume histogram (DVH) was generated for both the original planned dose and the accumulated 4D dose for comparison. In parallel, we performed a chained deformable registration of 4DCT phase images to estimate the motion magnitude of the esophagus in a breathing cycle. We examined the correlation between the motion magnitude and the dosimetric deviation.Results:The esophageal motion mostly exhibited in the superior‐inferior direction. The cross‐sectional motion was small. Esophagus motion at T1 vertebra level (0.7 mm) is much smaller than that at T11 vertebra level (6.5 mm). The difference of Dmax between the original and 4D dose distributions ranged from 9.1 cGy (esophagus motion: 5.6 mm) to 231.1 cGy (esophagus motion: 3.1 mm). The difference of D(5cc) ranged from 5 cGy (esophagus motion: 3.1 mm) to 85 cGy (esophagus motion: 3.3 mm). There was no correlation between the dosimetric deviation and the motion magnitude. The V(11.9Gy)<5cc constraint was met for each patient when examining the DVH calculated from the 4D dose.Conclusion:Respiratory motion did not result in substantial dose increase to esophagus in spine SBRT. 4DCT simulation may not be necessary with regards to esophageal dose assessment.
SU‐F‐J‐132: Evaluation of CTV‐To‐PTV Expansion for Whole Breast Radiotherapy
Authors: Burgdorf B , Freedman G , Teo B 
Published: July 2016

Purpose:The current standard CTV‐to‐PTV expansion for whole breast radiotherapy (WBRT) is 7mm, as recommended by RTOG‐1005.This expansion is derived from the uncertainty due to patient positioning (±5mm) and respiratory motion (±5mm). We evaluated the expansion needed for respiratory motion uncertainty using 4DCT. After determining the appropriate expansion margins, RT plans were generated to evaluate the reduction in heart and lung dose.Methods:4DCT images were acquired during treatment simulation and retrospectively analyzed for 34 WBRT patients. Breast CTVs were contoured on the maximum inhale and exhale phase. Breast CTV displacement was measured in the L‐R, A‐P, and SUP‐INF directions using rigid registration between phase images. Averaging over the 34 patients, we determined the margin due to respiratory motion. Plans were generated for 10 left‐sided cases comparing the new expansion with the 7mm PTV expansion.Results:The results for respiratory motion uncertainty are shown in Table 1. Drawing on previous work by White et al at Princess Margaret Hospital (1) (see supporting document for reference) which studied the uncertainty due to patient positioning, we concluded that, in total, a 5mm expansion was sufficient. The results for our suggested PTV margin are shown in Table 2, combining the patient positioning results from White et al with our respiratory motion results. The planning results demonstrating the heart and lung dose differences in the 5mm CTV‐to‐PTV expanded plan compared to the 7mm plan are shown in Table 3.Conclusion:Our work evaluating the expansion needed for respiratory motion along with previous work evaluating the expansion needed for setup uncertainty shows that a CTV‐to‐PTV expansion of 5mm is acceptable and conservative. By reducing the PTV expansion, significant dose reduction to the heart and lung are achievable.
SU‐F‐J‐141: Real‐Time Position Management (RPM) System as a Valuable Tool to Predict Tumor Position Deviation in SBRT Lung and Liver Patients with Breath Hold Using Active Breathing Coordinator (ABC)
Authors: Shen Z , Andrews M , Balik S , Magnelli A , Stephans K , Videtic G , Abazeed M , Zhuang T , Xia P 
Published: July 2016

Purpose:ABC is a breath‐hold technique for SBRT treatments. At our institution, three CTs with ABC are acquired at simulation to check the breath‐hold consistency because tumor position may deviate among three scans. The purpose of this study was to determine whether RPM can predict tumor position deviation in SBRT breath‐hold treatments with ABC.Methods:Five SBRT lung and five SBRT liver patients were selected. An RPM block was placed on the patients between the xiphoid and the umbilicus. RPM recorded patients’ anterior‐posterior skin surface positions during breath holds with ABC. For each patient, three CTs (ABC1, ABC2, ABC3) were acquired at the same breath‐hold level. ABC2 and ABC3 CTs were rigidly registered to ABC1 CT. Tumor position deviations were measured on the fused CTs (ABC2 with ABC1, ABC3 with ABC1) and compared to the corresponding RPM position shifts. Linear regression, k‐means clustering, and decision tree classifier were used to determine the relationship between RPM position shifts and tumor position deviations.Results:Tumor position deviations were 0.4–8.7 mm for lung patients and 1.6–9.1 mm for liver patients. There were no significant linear correlations between RPM position shifts and tumor position deviations for both lung (R2=0.20) and liver (R2=0.45) patients. In contrast, decision tree classification showed that the RPM position shift of 3.45 mm or more indicated tumor position deviation >5 mm for lower lobe lung tumors and liver tumors that are close to the diaphragm.Conclusion:RPM position shifts are not linearly correlated with tumor position deviations. However, RPM can be used to predict large tumor position deviations (>5 mm) among three ABC CTs in SBRT for lower lobe lung tumors and liver tumors and to validate the breath‐hold consistency with the ABC technique. Therefore, RPM has the potential to replace the additional verification CT scans.
SU‐F‐J‐147: Magnetic Field Dose Response Considerations for a Linac Monitor Chamber
Authors: Reynolds M , Fallone B 
Published: July 2016

Purpose:The impact of magnetic fields on the readings of a linac monitor chamber have not yet been investigated. Herein we examine the total dose response as well as any deviations in the beam parameters of flatness and symmetry when a Varian monitor chamber is irradiated within an applied magnetic field. This work has direct application to the development of Linac‐MR systems worldwide.Methods:A Varian monitor chamber was modeled in the Monte Carlo code PENELOPE and irradiated in the presence of a magnetic field with a phase space generated from a model of a Linac‐MR prototype system. The magnetic field strength was stepped from 0 to 3.0T in both parallel and perpendicular directions with respect to the normal surface of the phase space. Dose to each of the four regions in the monitor chamber were scored separately for every magnetic field adaptation to evaluate the effect of the magnetic field on flatness and symmetry.Results:When the magnetic field is perpendicular to the phase space normal we see a change in dose response with a maximal deviation (10–25% depending on the chamber region) near 0.75T. In the direction of electron deflection we expectedly see opposite responses in chamber regions leading to a measured asymmetry. With a magnetic field parallel to the phase space normal we see no measured asymmetries, however there is a monotonic rise in dose response leveling off at about +12% near 2.5T.Conclusion:Attention must be given to correct for the strength and direction of the magnetic field at the location of the linac monitor chamber in hybrid Linac‐MR devices. Elsewise the dose sampled by these chambers may not represent the actual dose expected at isocentre; additionally there may be a need to correct for the symmetry of the beam recorded by the monitor chamber.Fallone is a co‐founder and CEO of MagnetTx Oncology Solutions (under discussions to license Alberta bi‐planar linac MR for commercialization).