bluuebunny/crossref_metadata_2025 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).
SU‐F‐J‐153: ACR MRI Phantom Test On a 1.5T MR‐Simulator with Flexible Coils Setting and Performance Comparison to Volumetric Head Coil Setting
Authors: Yuan J , Wong O , Cheung K , Yu S
Published: July 2016

Purpose:

To accommodate head‐and‐neck (HN) RT simulation scan with immobilization, sub‐optimized flexible radiofrequency coils have to be used on an MR‐sim rather than a volumetric head coil for diagnostic radiological (DR) applications. In this study, we present and compare ACR MRI phantom test with flexible coils setting (RT‐setting) and volumetric head coil setting (DR‐setting).

Methods:

Two 8‐channel array coils were wrapped close to an ACR MRI phantom placed on a flat couch‐top in RT‐setting for acquisition. ACR MRI phantom tests were conducted 10 times for each setting on a 1.5T MR‐sim. Sagittal localizer (TE/TR=20/200ms), axial T1 (TE/TR=20/500ms) and T2 scans (2TEs/TR=20,80/2000ms) were acquired (NEX=1). Acqusition and image analysis were conducted following ACR guidelines. Extra 10 RT‐setting acquisitions were obtained by enabling prescan normalization.

Results:

For RT‐setting without prescan normalization, all tests passed the ACR recommended criteria but image intensity uniformity. Geometric accuracy was 147.8±0.3mm and 191.0±0.4mm. Spatial resolution was 0.9mm. Slice thickness was 5.2mm±0.1mm (T1) and 5.1±0.1mm (T2). Slice position accuracy was 1.4±0.6mm, −2.2±0.3mm (T1), and 1.5±0.2mm, −2.2±0.2mm (T2). Image uniformity was 80.6%±2.6% (T1) and 80.2%±3.1% (T2) (criteria: ≥87.5% for 1.5T). Ghosting ratio was 0.0006±0.0004. Low contrast detectability was 30.7±1.7 (T1) and 22.6±3.0 (T2). Image uniformity (91.4%±4.2% and 91.8%±4.3%) and low contrast detectability (36.5±1.4 and 31.6±2.2) of DR‐setting were better than RT‐setting. Prescan normalization substantially improved image uniformity to 93.4%±0.2% and 93.4%±0.3%, but slightly compromised ghosting (0.0033±0.0004) and spatial resolution (0.9mm or 1.0mm) for RT‐setting.

Conclusion:

Flexible coils setting for HN‐RT simulation scan could successfully pass ACR criteria (prescan normalization enabled) and generally achieve comparable performance to volumetric coil setting, although compromise on low contrast detectability was observed probably due to the lower signal‐to‐noise ratio of the flexible coils. Our results could also serve as a reference baseline of high‐field MR‐sim QA performance under ACR guideline.
SU‐F‐J‐161: Prostate Contouring in Patients with Bilateral Hip Prostheses: Impact of Using Artifact‐Reduced CT Images and MRI
Authors: Elzibak A , Loblaw A , Morton G , Vesprini D , Liu S , Chung H , Davidson M
Published: July 2016

Purpose:

To investigate the usefulness of metal artifact reduction in CT images of patients with bilateral hip prostheses (BHP) for contouring the prostate and determine if the inclusion of MR images provides additional benefits.

Methods:

Five patients with BHP were CT scanned using our clinical protocol (140kV, 300mAs, 3mm slices, 1.5mm increment, Philips Medical Systems, OH). Images were reconstructed with the orthopaedic metal artifact reduction (O‐MAR) algorithm. MRI scanning was then performed (1.5T, GE Healthcare, WI) with a flat table‐top (T2‐weighted, inherent body coil, FRFSE, 3mm slices with 0mm gap). All images were transferred to Pinnacle (Version 9.2, Philips Medical Systems). For each patient, two data sets were produced: one containing the O‐MAR‐corrected CT images and another containing fused MRI and O‐MAR‐corrected CT images. Four genito‐urinary radiation oncologists contoured the prostate of each patient on the O‐MAR‐corrected CT data. Two weeks later, they contoured the prostate on the fused data set, blinded to all other contours. During each contouring session, the oncologists reported their confidence in the contours (1=very confident, 3=not confident) and the contouring difficulty that they experienced (1=really easy, 4=very challenging). Prostate volumes were computed from the contours and the conformity index was used to evaluate inter‐observer variability.

Results:

Larger prostate volumes were found on the O‐MAR‐corrected CT set than on the fused set (p< 0.05, median=36.9cm3 vs. 26.63 cm3). No significant differences were noted in the inter‐observer variability between the two data sets (p=0.3). Contouring difficulty decreased with the addition of MRI (p<0.05) while the radiation oncologists reported more confidence in their contours when MRI was fused with the O‐MAR‐corrected CT data (p<0.05).

Conclusion:

This preliminary work demonstrated that, while O‐MAR correction to CT images improves visualization of anatomy, the addition of MRI enhanced the oncologists’ confidence in contouring the prostate in patients with BHP.
SU‐F‐J‐168: Dosimetric Impact of MR Image Distortion in Treatment Planning
Authors: Yan Y , Yang J , Beddar S , Ibbott G , Balter P , Kudchadker R , Krishnan S , Fuller C , Wang J
Published: July 2016

Purpose:

To evaluate the dosimetric impact of MR image distortion in treatment planning.

Methods:

Based on the realistic MRI distortion measurement data from an integrated MRI‐Linac system, we created a generalized distortion model and applied it to CT images to simulate distorted MRI images. Ten patients with IMRT plans generated in Pinnacle treatment planning system in 5 anatomical cancer sites (lung, prostate, spinal cord, liver, and pancreas) were retrospectively selected for the simulation. The distortion model was applied to the planning CT image and contours. A distorted plan was created in Pinnacle for each patient. The dose‐volume‐histogram (DVH) of targets and critical structures were compared between the original and distorted plans. For a fair comparison, the same field sizes and intensity‐modulated radiation therapy (IMRT) parameters were used in generating the distorted plan.

Results:

The DVH of organs at risk (OARs) within a distance of 5cm to the imaging center did not show significant difference between the original and distorted plans. For certain OARs such as the spinal cord, the seminal vesicle (SV), and the larynx, with a distance greater than 5cm to the imaging center, larger deviations were observed between the distorted and original plans. The maximum mean dose difference was 1.92Gy (proximal SV, prescribed dose is 40Gy). Similar target coverage was observed between the distorted plans and the original plans for the 10 patients. One lung case had the maximum difference of the target mean dose between the original and distorted plans of 1.63Gy (prescribed dose is 72Gy).

Conclusion:

The MRI distortion did not lead to significant dosimetric difference compared to the original plans in most situations. However, OARs farther than 5cm from the imaging center showed larger dosimetric difference due to the distortion. Safety margin may need to account for the distortion in treatment planning.

One of the authors receive cooperate funding from the Elekta.
SU‐F‐J‐169: A Feasibility Study of Using MRI Alone in Abdominal Radiotherapy
Authors: Zawisza I , Hsu S , Peng Q , Tome W
Published: July 2016

Purpose:

To demonstrate the feasibility of a MRI alone workflow to support treatment planning and image guidance for abdominal radiotherapy.

Methods:

Abdominal MR images (in‐phase/out‐phase/fat/water) were acquired for a patient with breath‐hold using a Dixon pulse sequence. Air masks were created on in‐phase images using intensity thresholding and morphological processing methods in order to separate air from bone. Pseudo‐CT and DRRs were generated using a published method. To investigate the effect of heterogeneity corrections on dose calculations using pseudo‐CT, three different plans (3‐field 3D, 5‐field IMRT and 2‐arc VMAT) were performed to mimic pancreatic treatments (1.8Gy/fraction over 28 fractions).

Results:

The DRRs created from pseudo‐CT were of comparable quality as those created from CT. Comparing dose calculations with and without heterogeneity corrections between the 3 different plans, the biggest dosimetric differences were seen in the VMAT plan where modulation must occur across air‐tissue interfaces such as those of the stomach and bowel. The DVHs for the VMAT plan showed ∼84cc difference at V50Gy in the small bowel. In terms of pseudo‐CT quality, some small volumes of air in the bowel and stomach were misclassified as bone. The VMAT plan was re‐optimized on pseudo‐CT with 0 HU in the misclassified areas. The V50Gy in the small bowel differed by ∼90cc between the new VMAT plan with and without heterogeneity corrections.

Conclusion:

We found that the use of MRI alone is feasible for abdominal treatment planning and image guidance. A difference between calculations with and without heterogeneity corrections was found that is most pronounced for VMAT where the traversal of air‐tissue interfaces is unavoidable. Future work will be performed to minimize misclassification between bone and air.
SU‐F‐J‐189: A Method to Improve the Spatial Resolution of Prompt Gamma Based Compton Imaging for Proton Range Verification
Authors: Draeger E , Mackin D , Peterson S , Chen H , Beddar S , Polf J
Published: July 2016

Purpose:

To test two new techniques, the distance‐of‐closest approach (DCA) and Compton line (CL) filters, developed as a means of improving the spatial resolution of Compton camera (CC) imaging.

Methods:

Gammas emitted from 22Na, 137Cs, and 60Co point sources were measured with a prototype 3‐stage CC. The energy deposited and position of each interaction in each stage were recorded and used to calculate a “cone‐of‐origin” for each gamma that scattered twice in the CC. A DCA filter was developed which finds the shortest distance from the gamma's cone‐of‐origin surface to the location of the gamma source. The DCA filter was applied to the data to determine the initial energy of the gamma and to remove “bad” interactions that only contribute noise to the image. Additionally, a CL filter, which removes gamma events that do not follow the theoretical predictions of the Compton scatter equation, was used to further remove “bad” interactions from the measured data. Then images were reconstructed with raw, unfiltered data, DCA filtered data, and DCA+CL filtered data and the achievable image resolution of each dataset was compared.

Results:

Spatial resolutions of ∼2 mm, and better than 2 mm, were achievable with the DCA and DCA+CL filtered data, respectively, compared to > 5 mm for the raw, unfiltered data.

Conclusion:

In many special cases in medical imaging where information about the source position may be known, such as proton radiotherapy range verification, the application of the DCA and CL filters can result in considerable improvements in the achievable spatial resolutions of Compton imaging.
SU‐F‐J‐192: A Quick and Effective Method to Validate Patient's Daily Setup and Geometry Changes Prior to Proton Treatment Delivery Based On Water Equivalent Thickness Projection Imaging (WETPI) for Head Neck Cancer (HNC) Patient
Authors: Liu G , Qin A , Zhang J , Li X , Zhou J , Yan D , Teo B , Chen P , Krauss D , Kabolizadeh P , Guerrero T , Stevens C , Liang J , Ding X
Published: July 2016

Purpose:

With the implementation of Cone‐beam Computed‐Tomography (CBCT) in proton treatment, we introduces a quick and effective tool to verify the patient's daily setup and geometry changes based on the Water‐Equivalent‐Thickness Projection‐Image(WETPI) from individual beam angle.

Methods:

A bilateral head neck cancer(HNC) patient previously treated via VMAT was used in this study. The patient received 35 daily CBCT during the whole treatment and there is no significant weight change. The CT numbers of daily CBCTs were corrected by mapping the CT numbers from simulation CT via Deformable Image Registration(DIR). IMPT plan was generated using 4‐field IMPT robust optimization (3.5% range and 3mm setup uncertainties) with beam angle 60, 135, 300, 225 degree. WETPI within CTV through all beam directions were calculated. 3%/3mm gamma index(GI) were used to provide a quantitative comparison between initial sim‐CT and mapped daily CBCT. To simulate an extreme case where human error is involved, a couch bar was manually inserted in front of beam angle 225 degree of one CBCT. WETPI was compared in this scenario.

Results:

The average of GI passing rate of this patient from different beam angles throughout the treatment course is 91.5 ± 8.6. In the cases with low passing rate, it was found that the difference between shoulder and neck angle as well as the head rest often causes major deviation. This indicates that the most challenge in treating HNC is the setup around neck area. In the extreme case where a couch bar is accidently inserted in the beam line, GI passing rate drops to 52 from 95.

Conclusion:

WETPI and quantitative gamma analysis give clinicians, therapists and physicists a quick feedback of the patient's setup accuracy or geometry changes. The tool could effectively avoid some human errors. Furthermore, this tool could be used potentially as an initial signal to trigger plan adaptation.
SU‐F‐J‐207: Non‐Small Cell Lung Cancer Patient Survival Prediction with Quantitative Tumor Textures Analysis in Baseline CT
Authors: Wu Y , Zou J , Murillo P , Nosher J , Amorosa J , Bramwit M , Yue N , Jabbour S , Foran D
Published: July 2016

Purpose:

Chemo‐radiation therapy (CRT) is widely used in treating patients with locally advanced non‐small cell lung cancer (NSCLC). Determination of the likelihood of patient response to treatment and optimization of treatment regime is of clinical significance. Up to date, no imaging biomarker has reliably correlated to NSCLC patient survival rate. This pilot study is to extract CT texture information from tumor regions for patient survival prediction.

Methods:

Thirteen patients with stage II‐III NSCLC were treated using CRT with a median dose of 6210 cGy. Non‐contrast‐enhanced CT images were acquired for treatment planning and retrospectively collected for this study. Texture analysis was applied in segmented tumor regions using the Local Binary Pattern method (LBP). By comparing its HU with neighboring voxels, the LBPs of a voxel were measured in multiple scales with different group radiuses and numbers of neighbors. The LBP histograms formed a multi‐dimensional texture vector for each patient, which was then used to establish and test a Support Vector Machine (SVM) model to predict patients’ one year survival. The leave‐one‐out cross validation strategy was used recursively to enlarge the training set and derive a reliable predictor. The predictions were compared with the true clinical outcomes.

Results:

A 10‐dimensional LBP histogram was extracted from 3D segmented tumor region for each of the 13 patients. Using the SVM model with the leave‐one‐out strategy, only 1 out of 13 patients was misclassified. The experiments showed an accuracy of 93%, sensitivity of 100%, and specificity of 86%.

Conclusion:

Within the framework of a Support Vector Machine based model, the Local Binary Pattern method is able to extract a quantitative imaging biomarker in the prediction of NSCLC patient survival. More patients are to be included in the study.
SU‐F‐J‐209: Quantification of Image‐Guidance Benefit in Image‐Guided Radiotherapy of Cancers
Authors: Zhou L , Deng J
Published: July 2016

Purpose:

Image‐guidance has been widely used in radiation oncology for accurate radiotherapy. The goal of this study is to quantify the benefit of image‐guidance in image‐guided radiotherapy (IGRT) of cancers.

Methods:

In this study, a new index termed image‐guidance benefit (IGB), was proposed to quantify the benefit of image‐guidance in cancer radiotherapy. It is calculated as a ratio of the square sum of dose differences between planning dose matrix and actual delivery dose matrix post image‐guidance to the square sum of dose summation between the two matrixes, summing over all dose scoring voxels. Ranging from 0 to 1, larger IGB values indicate larger benefit out of image‐guidance. With IRB approval, the DICOM RT files and 3D couch shifts applied during IGRT of 2219 patients were collected, based on which patient‐specific IGB values were calculated with an in‐house MATLAB code.

Results:

In this study, the mean IGB value was found to be 0.0398 (0.000583–0.999) with a positive correlation between IGB value and 3D couch shift vector at 0.0435 per cm (P<0.0001). With 2 mm shift as a threshold above which an image‐guidance is deemed clinically necessary, the corresponding mean IGB value was 0.00457, much less than 0.0398 (P<0.001). However, the IGB values of 56 cases based on couch shifts were less than those based on 2 mm shift.

Conclusion:

The IGB values were patient‐specific and site‐dependent. Using 2 mm shifts as criterion for applying image‐guidance, the applied image‐guidance procedures were found clinically necessary and highly beneficial in 97.5% of cancer patients. However, image‐guidance procedures were found over‐used in about 2.5% of cancer patients in our current practices of IGRT, which should be avoided as they added no benefit in improving delivery accuracy while increasing cancer risk.
SU‐F‐J‐227: Accuracy of Passive Magnetic Ultrasound Needle Guidance in High‐ Fidelity Conventional and Novel Simulated Block Approach Phantoms
Authors: Johnson A
Published: July 2016

Purpose:

The objective of this research was to demonstrate accuracy of a real‐time passive ultrasound magnetic needle guidance technology (NGT) and target localization algorithm using conventional anechogenic contact phantoms and a novel fluid‐filled hyperechogenic phantom simulating nerve block technique.

Methods:

Accuracy (mm to phantom target) was assessed by observing 35 medical practitioners (16 anesthesiologists and 19 residents) performing 560 needle procedures in high‐fidelity ex vivo porcine tissue phantoms. Each practitioner performed 8 tasks with GE Venue 50 magnetic NGT system with PinPoint GT (Bard Access Sys.) and 8 conventional echogenic needle (control) procedures under various conditions (#18/#22 needle gauge, IP/OOP approach, and hyperechogenic simulated block approach targets or anechogenic solid targets). Passes, user feedback, and ergonomics were also assessed.

Results:

Overlaid visual aids produced in real time (<300 mS delay) by NGT enabled users to consistently perform with better accuracy than control echogenic needle guidance. Accuracy improved by 51.2% at 95% CI [29.8%, 66.7%] (P = 0.0008) among block approach phantoms and 51.4% at 95% CI [34.9%, 64.0%] (P < 0.0001) among placement phantoms. Further, inadvertent contact with targets was reduced by NGT visualizations versus controls in both anesthesiologists (0 vs. 8 contacts; accuracy 2.0±1.7 vs. 4.13±6.7 mm) and novice users (3 vs. 12 contacts; accuracy 2.2±2.3 vs. 2.9±3.7 mm), respectively. Among novice users, NGT visualizations notably reduced quality‐compromising ergonomic observations compared to controls under equivalent conditions.

Conclusion:

NGT systems employing magnetic field generation and electromagnetic sensors to track needle position and orientation relative to a sonoanatomical target within a magnetic field have the potential to enable greater accuracy for complex needle placements and reduce unintentional needle contact, particularly in novice users. Further, NGT visualizations of needle tip and projected trajectory contribute to positive ergonomics and reducing quality‐compromising behaviors among operators, potentially reducing fatigue and needle progression error.

This work was supported by funding provided by the GE Healthcare Ultrasound Business, Milwaukee, WI.
SU‐F‐T‐07: Dosimetric Impact of the Dwell Position Inaccuracy in HDR Ring and Tandem Treatments with VarisourceIX Afterloader
Authors: Veltchev I , Price R , Anderson P , Ma C
Published: July 2016

Purpose:

The dwell positions in the VariSourceIX HDR ring applicator are known to be somewhat inaccurate with observed deviations from the planned position of up to 5mm. The details of how to correct this issue are suggested by the vendor and the dosimetric impact on volumetric HDR plans varies from patient to patient. In this study we present our experience with correcting this issue, and discuss the impact on plan quality if the planned dwell positions were left unchanged.

Methods:

A 60 degree ring was characterized using gafchromic film with the applicator in treatment orientation. The offsets as a function of dwell position in the ring were deduced. The variability in each observed dwell position was determined from three consecutive runs. A total of 10 ring and tandem treatments were analyzed in this work. The PTV and organs at risk were outlined and dose‐volume histograms were produced. The patient plans were modified for delivery according to the average shift determined in the characterization stage. D2cc for the organs at risk (rectum, bladder, and sigmoid) were used as dosimetric end‐points in this study. The dose at the locations of the ICRU points A was analyzed as well.

Results:

Each dwell position was corrected according to the measured offsets. For each fraction, three plans were produced: dosimetric plan with ideal dwell positions, treatment plan with corrected dwell positions, and a test plan with opposite offsets for evaluation of dose differences for organs at risk and PTV. Maximum and average dose deviations were deduced for each organ at risk. For rectum, sigmoid, and bladder the maximum D2cc dose deviations were 7.6%, 5.3%, and 1.5%, respectively.

Conclusion:

Correcting dwell position inaccuracy in an HDR ring is essential for maintaining quality of treatment. The dose differences are significant in the organs at risk.
SU‐F‐T‐08: Brachytherapy Film Dosimetry in a Water Phantom for a Ring and Tandem HDR Applicator
Authors: Lee B , Grelewicz Z , Kang Z , Cutright D , Gopalakrishnan M , Sathiaseelan V , Zhang H
Published: July 2016

Purpose:

The feasibility of dose measurement using new generation EBT3 film was explored in a water phantom for a ring and tandem HDR applicator for measurements tracking mucosal dose during cervical brachytherapy.

Methods:

An experimental fixture was assembled to position the applicator in a water phantom. Prior to measurement, calibration curves for EBT3 film in water and in solidwater were verified. EBT3 film was placed at different known locations around the applicator in the water tank. A CT scan of the phantom with applicator was performed using clinical protocol. A typical cervical cancer treatment plan was then generated by Oncentra brachytherapy planning system. A dose of 500 cGy was prescribed to point A (2 cm, 2 cm). Locations measured by film included the outer surface of the ring, measurement point A_m (2.2 cm, 2.2 cm), and profiles extending from point A_m parallel to the tandem. Three independent measurements were conducted. The doses recorded by film were carefully analyzed and compared with values calculated by the treatment planning system.

Results:

Assessment of the EBT3 films indicate that the dose at point A matches the values predicted by the planning system. Dose to the point A_m was 411.5 cGy, and the outer circumferential surface dose of the ring was between 500 and 1150 cGy. It was found that from the point A_m, the dose drops 60% within 4.5 cm on the line parallel to the tandem. The measurement doses agree with the treatment planning system.

Conclusion:

Use of EBT3 film is feasible for in‐water measurements for brachytherapy. A carefully machined apparatus will likely improve measurement accuracy. In a typical plan, our study found that the ring surface dose can be 2.5 times larger than the point A prescription dose. EBT3 film can be used to monitor mucosal dose in brachytherapy treatments.