bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐F‐P‐25: Dosimetric Changes of Brainstem Caused by Weight Loss During Intensity‐Modulated Radiation Therapy for Nasopharyngeal Carcinoma
Authors: Hu W , Yu C , Cai Y , Zhou X , Wang W , Yang H
Published: July 2016

Purpose:

To explore dosimetric effects of brainstem (BS) caused by weight loss during the course of intensity‐modulated radiation therapy (IMRT) for nasopharyngeal carcinoma (NPC).

Methods:

Seventy‐seven patients who were diagnosed with NPC by pathology biopsy have been enrolled. Every patients should receive weight measurement weekly and three times of computed tomography (CT) scans and replanning, at the 15th and 25th fraction during the treatment, respectively. The vertical diameter at the level of odontoid process (d1) and cervical vertebra 3 (d2) be measured from CT images (Supporting document Figure 1). All IMRT plans were designed by inverse planning with commercial treatment planning systems (Corvus 6.2 version, NOMOS Corporation). The dose differences between plan and actual delivery were generated to compare.

Results:

The weight loss was more in week 4–5 (3.21±2.19kg) than in week 1–3 (1.79±1.83kg) (Supporting document Figure 2). The d1 and d2 decreased was more significantly in week 4–5 than week 1–3, 2.83±1.75mm vs. 0.55±0.75mm and 2.98±2.96mm vs. 1.23±2.09mm, respectively. The maximum dose to the brainstem (BS Dmax) and the percentage of brainstem volume receiving ≥50Gy (BS V50) increased more significantly in week 4–5 than week 1–3, −3.02±5.49Gy vs. −1.85 ±4.88Gy and −1.85±4.88% vs. −0.77±3.32%, respectively. The changes of d1 and d2 and the BS‐V50 and BS‐Dmax were closely related to weight loss (p≤0.001)(Supporting document Table 1).

Conclusion:

The study results indicate that weight loss leads to the vertical diameter reduction, which results has a close relationship with dose of the brainstem during IMRT of NPC.

This study was supported by Zhejiang Provincial Medicine and Health Foundation (2013KYB290) and Research Foundation of Science and Technology Department of Zhejiang Province 2015C33257
SU‐F‐P‐28: A Method of Maximize the Noncoplanar Beam Orientations and Assure the Beam Delivery Clearance for Stereotactic Body Radiation Therapy (SBRT)
Authors: Zhu J
Published: July 2016

Purpose:

Develop a method to maximize the noncoplanar beam orientations and assure the beam delivery clearance for SBRT, therefore, optimize the dose conformality to the target, increase the dose sparing to the critical normal organs and reduce the hot spots in the body.

Methods:

A SBRT body frame (Elekta, Stockholm, Sweden) was used for patient immobilization and target localization. The SBRT body frame has CT fiducials on its side frames. After patient's CT scan, the radiation treatment isocenter was defined and its coordinators referring to the body frame was calculated in the radiation treatment planning process. Meanwhile, initial beam orientations were designed based on the patient target and critical organ anatomy. The body frame was put on the linear accelerator couch and positioned to the calculated isocenter. Initially designed beam orientations were manually measured by tuning the body frame position on the couch, the gantry and couch angles. The finalized beam orientations were put into the treatment planning for dosimetric calculations.

Results:

Without patient presence, an optimal set of beam orientations were designed and validated. The radiation treatment plan was optimized and guaranteed for delivery clearance.

Conclusion:

The developed method is beneficial and effective in SBRT treatment planning for individual patient. It first allows maximizing the achievable noncoplanar beam orientation space, therefore, optimize the treatment plan for specific patient. It eliminates the risk that a plan needs to be modified due to the gantry and couch collision during patient setup.
SU‐F‐P‐31: Dosimetric Effects of Roll and Pitch Corrections Using Robotic Table
Authors: Mamalui M , Su Z , Flampouri S , Li Z
Published: July 2016

Purpose:

To quantify the dosimetric effect of roll and pitch corrections being performed by two types of robotic tables available at our institution: BrainLabTM 5DOF robotic table installed at VERO (BrainLab&MHI) dedicated SBRT linear accelerator and 6DOF robotic couch by IBA Proton Therapy with QFixTM couch top.

Methods:

Planning study used a thorax phantom (CIRSTM), scanned at 4DCT protocol; targets (IGTV, PTV) were determined according to the institutional lung site‐specific standards. 12 CT sets were generated with Pitch and Roll angles ranging from −4 to +4 degrees each. 2 table tops were placed onto the scans according to the modality‐specific patient treatment workflows. The pitched/rolled CT sets were fused to the original CT scan and the verification treatment plans were generated (12 photon SBRT plans and 12 proton conventional fractionation lung plans). Then the CT sets were fused again to simulate the effect of patient roll/pitch corrections by the robotic table. DVH sets were evaluated for all cases.

Results:

The effect of not correcting the phantom position for roll/pitch in photon SBRT cases was reducing the target coverage by 2% as maximum; correcting the positional errors by robotic table varied the target coverage within 0.7%. in case of proton treatment, not correcting the phantom position led to the coverage loss up to 4%, applying the corrections using robotic table reduced the coverage variation to less than 2% for PTV and within 1% for IGTV.

Conclusion:

correcting the patient position by using robotic tables is highly preferable, despite the small dosimetric changes introduced by the devices.
SU‐F‐R‐42: Association of Radiomic and Metabolic Tumor Volumes in Radiation Treatment of Glioblastoma Multiforme
Authors: Lopez C , Nagornaya N , Parra N , Kwon D , Ishkanian F , Markoe A , Maudsley A , Stoyanova R
Published: July 2016

Purpose:

High‐throughput extraction of imaging and metabolomic quantitative features from MRI and MR Spectroscopy Imaging (MRSI) of Glioblastoma Multiforme (GBM) results in tens of variables per patient. In radiotherapy (RT) of GBM, the relevant metabolic tumor volumes (MTVs) are related to aberrant levels of N‐acetyl Aspartate (NAA) and Choline (Cho). Corresponding Clinical Target Volumes (CTVs) for RT planning are based on Contrast Enhancing T1‐weighted MRI (CE‐T1w) and T2‐weighted/Fluid Attenuated Inversion Recovery (FLAIR) MRI. The objective is to build a framework for investigation of associations between imaging, CTV, and MTV features better understanding of the underlying information in the CTVs and dependencies between these volumes.

Methods:

Necrotic portions, enhancing lesion and edema were manually contoured on T1w/T2w images for 17 GBM patients. CTVs and MTVs for NAA (MTVNAA) and Cho (MTVCho) were constructed. Tumors were scored categorically for ten semantic imaging traits by neuroradiologist. All features were investigated for redundancy. Two‐way correlations between imaging and RT/MTV features were visualized as heat maps. Associations between MTVNAA, MTVCho and imaging features were studied using Spearman correlation.

Results:

39 imaging features were computed per patient. Half of the imaging traits were replaced with automatically extracted continuous variables. 21 features were extracted from MTVs/CTVs. There were a high number (43) of significant correlations of imaging with CTVs/MTVNAA while very few (10) significant correlations were with CTVs/MTVCho. MTVNAA was found to be closely associated with MRI volumes, MTVCho remains elusive for characterization with imaging.

Conclusion:

A framework for investigation of co‐dependency between MRI and RT/metabolic features is established. A series of semantic imaging traits were replaced with automatically extracted continuous variables. The approach will allow for exploration of relationships between sizes and intersection of imaging features of tumors, RT volumes, metabolite concentrations and comparing those to therapy outcome, quality of life evaluation and overall survival rate.

This publication was supported by Grant 10BN03 from Bankhead Coley Cancer Research Program, R01EB000822, R01EB016064, and R01CA172210 from the National Institutes of Health, and Indo‐US Science & Technology Forum award #20‐2009. Bhaswati Roy received financial assistance from University Grant Commission, New Delhi, India.
SU‐F‐I‐05: Dose Symmetry for CTDI Equivalent Measurements with Limited Angle CBCT
Authors: Singh V , McKenney S , Sunde P , Feng W , Bakalyar D
Published: July 2016

Purpose:

CTDI measurements, useful for characterizing the x‐ray output for multi‐detector CT (MDCT), require a 360° rotation of the gantry; this presents a problem for cone beam CT (CBCT) due to its limited angular rotation. The purpose of this work is to demonstrate a methodology for overcoming this limited angular rotation so that CTDI measurements can also be made on CBCT systems making it possible to compare the radiation output from both types of system with a common metric.

Methods:

The symmetry of the CTDI phantom allows a 360° CTDI measurement to be replaced with two 180° measurements. A pencil chamber with a real‐time digitizer was placed at the center of the head phantom (16 cm, PMMA) and the resulting exposure measurement from a 180° acquisition was doubled. A pair of edge measurements, each obtained with the gantry passing through the same 180 arc, was obtained with the pencil chamber at opposite edges of the diameter of the phantom and then summed. The method was demonstrated on a clinical CT scanner (Philips, Brilliance6) and then implemented on an interventional system (Siemens, Axiom Artis).

Results:

The equivalent CTDI measurement agreed with the conventional CTDI measurement within 8%. The discrepancy in the two measurements is largely attributed to uncertainties in cropping the waveform to a 180°acquisition. (Note: Because of the reduced fan angle in the CBCT, CTDI is not directly comparable to MDCT values when a 32 cm phantom is used.)

Conclusion:

The symmetry‐based CTDI measurement is an equivalent measurement to the conventional CTDI measurement when the fan angle is large enough to encompass the phantom diameter. This allows a familiar metric of radiation output to be employed on systems with a limited angular rotation.
SU‐F‐I‐29: Investigating the Impact of the Amount of Contrast Material Used in Abdominal CT Examinations Regarding the Diagnosis of Appendicolith
Authors: Lavdas E , Boci N , Sarantaenna L , Godevenos A , Ntavelis I , Theodoropoulos T , Zaimis G , Mavroidis P
Published: July 2016

Purpose:

The purpose of this study is to report the case of a young adult in which the incomplete oral administration of contrast material led to diagnosis of an appendicolith, which cause acute appendicitis.

Methods:

A male 34 years old underwent CT examination due to acute abdominal pain in the upper abdomen. An ultrasound examination of the upper abdomen and kidneys, an x‐ray examination of the abdomen and a CT scan of the entire abdomen and pelvis after both oral and IV administration of contrast material were performed. In the ultrasound examination, both kidneys gallbladder and spleen appeared normal and the x‐ray examination did not show any pathological findings. As part of the CT examination, the patient received oral contrast material less than 500 ml due to lack of cooperation by the patient as a result of his abdominal pain.

Results:

The CT abdomen revealed a severely inflamed appendix that was significantly dilated at 1.1 cm. Moreover, it demonstrated a 1.4 cm appendicolith. The portion of the oral contrast material that was injected to the patient covered the upper abdomen and as a result an appendicolith could be revealed in the lower abdomen. If the patient had received the 1,000ml of contrast material, the whole abdomen would have been covered with the contrast in danger to lose the appendicolith, which caused the inflammation.

Conclusion:

Based on the findings of this study, in suspicion of acute appendicitis nephrolithiasis and ureterolithiasis, we propose to start the CT protocol with a CT scan without oral contrast material and then proceed with oral and IV contrast not only to succeed gastric intestinal differentiation but also to avoid covering the lower abdomen and obscure any small stones that may exist.
SU‐F‐I‐56: High‐Precision Gamma‐Ray Analysis of Medical Isotopes
Authors: Chopra N , Chillery T , McCutchan E , Chowdhury P , Smith C , Lister C
Published: July 2016

Purpose:

Advanced, time‐resolved, Compton‐suppressed gamma‐ray spectroscopy with germanium detectors is implemented for assaying medical isotopes to study the radioactive decay process leading to a more accurate appraisal of the received dose and treatment planning. Lowell's Array for Radiological Assay (LARA), a detector array that is comprised of six Compton‐suppressed high‐purity germanium detectors, is currently under development at UMass‐Lowell which combines Compton‐suppression and time‐and‐angle correlations to allow for highly efficient and highly sensitive measurements.

Methods:

Two isotopes produced Brookhaven Linac Isotope Producer (BLIP) were investigated. 82Sr which is the parent isotope for producing 82Rb is often used in cardiac PET. 82Sr gamma‐ray spectrum is dominated by the 511keV photons from positron annihilation which prevent precise measurement of co‐produced contaminant isotopes. A second project was to investigate the production of platinum isotopes. Natural platinum was bombarded with protons from 53MeV to 200MeV. The resulting spectrum was complicated due to the large number of stable platinum isotopes in the target, the variety of open reaction channels (p,xn), (p,pxn), (p,axn).

Results:

By using face‐to‐face NaI(Tl) counters 90‐degrees to the Compton‐suppressed germaniums to detect the 511keV photons, a much cleaner and more sensitive measurement of 85Sr and other contaminants was obtained. For the platinum target, we identified the production of 188–189–191–195Pt, 191–192–193–194–195–196Au and 186–188–189–190–192–194–189–190–192–194Ir. For example, at the lower energies (53 and 65MeV), we measured 191Pt production cross‐sections of 144mb and 157mb. Considerable care was needed in following the process of dissolving and diluting the samples to get consistent results. The new LARA array will help us better ascertain the absolute efficiency of the counting system and more reliable production cross‐sections.

Conclusion:

Modern HPGe spectroscopic techniques provide enhanced sensitivity, promising precise quantification of the quality of radioisotopes used in medical physics. Using new decay information may have non‐trivial impact on treatment planning and dose‐assessment.
SU‐F‐I‐64: Comparison of Lipid Contents Using STEAM and PRESS with in Vivo High‐Resolution Spectra at 9.4 T
Authors: Song K‐H , Lim S‐I , Yoo C‐H , Choe B‐Y
Published: July 2016

Purpose:

The objective of this study is to compare lipid contents using localized point‐resolved spectroscopy (PRESS) and stimulated echo acquisition mode (STEAM) sequences to assess lipid resonances in the liver, using in vivo high‐resolution spectra at 9.4 T.

Methods:

The examinations were performed on a Bruker 9.4T scanner using 4‐channel animal coil for higher resolution. We used PRESS (repetition time [TR]/ TE = 3500/20 ms; number of signal averages [NSA] = 128; acquisition data points = 2048) and STEAM (TR/TM/TE = 3500/10/20 ms; NSA = 128; acquisition data points = 2048). Lipid relaxations in HF diet mice were estimated at a fixed TR of 5000 ms, and TEs of 20–70 ms. All spectra acquired were processed using the Advanced Method for Accurate, Robust, and Efficient Spectral (AMARES) fitting algorithm including in the Java‐based Magnetic Resonance User Interface (jMRUI) software package. Preprocessing was performed using an automatic frequency shift and the Hankel‐Lanczos Singular Value Decomposition (HLSVD) filter with subtraction of water peak (4.70 ppm).

Results:

To accurately quantify lipid content, a sequence was selected. The total lipid and total saturated fatty acid were differently changed in HF diet mice that underwent PRESS compared with those that underwent STEAM (total lipid, p < 0.05; total saturated fatty acid, p < 0.001). Compared with PRESS, STEAM showed different total unsaturated fatty acid value (p < 0.001). Compared with PRESS, STEAM showed different total unsaturated and poly unsaturated bonds (total unsaturated bond, p<0.001; poly unsaturated bond, p < 0.001).

Conclusion:

Due to stronger J‐coupling effects on the PRESS sequence, the accurate estimation could not be obtained. STEAM is less sensitive to J‐coupling and gives a theoretically more accurate estimate at 9.4T.
SU‐F‐J‐04: Automated Detection of Diabetic Retinopathy Using Deep Convolutional Neural Networks
Authors: XU Kele , ZHU Li , WANG Ruixing , LIU Chang , ZHAO Yi
Published: July 2016

Purpose:

In this work, we explore to use very deep convolutional neural network (CNN) for the automatic classification of diabetic retinopathy using color fundus image.

Methods:

We apply translation, stretching, rotation and flipping to the labeled dataset. The original number of labeled‐frames is 3000, while after augmentations, 6000 frames with labels are used for the CNN training task. Several different CNN architectures have been proposed and tested. The architecture of our network contains 18 layers with parameters, consists of 12 convolutional layers, some of which followed by max‐pooling layers, and two fully connected layers. For a given input, the networks output two probabilities sum to 1, one for each class (as our problem is a two class classification problem).

Results:

To make a comparison, the performance of CNN‐based are compared to previous automatic classification attempts using the hand‐crafted features, such as: hard exudates, red lesions, micro‐aneurysms and blood vessel detection. We obtained an accuracy of 94.54% on our dataset using CNN, which rank as the highest with the comparison with previous handcrafted features‐based classifiers.

Conclusion:

With limited number of medical staff, an automated system can significantly decrease the tedious manual labor involved in diagnosing large quantities of retinal images. In this work, we explore the potential usage of CNN in retinal image classification. The results are encouraging and a clinical evaluation will be undertaken in order to be able to integrate the presented algorithm in a tool to diagnosis of diabetic retinopathy.
SU‐F‐J‐17: Patient Localization Using MRI‐Guided Soft Tissue for Head‐And‐Neck Radiotherapy: Indication for Margin Reduction and Its Feasibility
Authors: Qi X , Yang Y , Jack N , Santhanam A , Yang L , Chen A , Low D
Published: July 2016

Purpose:

On‐board MRI provides superior soft‐tissue contrast, allowing patient alignment using tumor or nearby critical structures. This study aims to study H&N MRI‐guided IGRT to analyze inter‐fraction patient setup variations using soft‐tissue targets and design appropriate CTV‐to‐PTV margin and clinical implication.

Methods:

282 MR images for 10 H&N IMRT patients treated on a ViewRay system were retrospectively analyzed. Patients were immobilized using a thermoplastic mask on a customized headrest fitted in a radiofrequency coil and positioned to soft‐tissue targets. The inter‐fraction patient displacements were recorded to compute the PTV margins using the recipe: 2.5∑+0.7σ. New IMRT plans optimized on the revised PTVs were generated to evaluate the delivered dose distributions. An in‐house dose deformation registration tool was used to assess the resulting dosimetric consequences when margin adaption is performed based on weekly MR images. The cumulative doses were compared to the reduced margin plans for targets and critical structures.

Results:

The inter‐fraction displacements (and standard deviations), ∑ and σ were tabulated for MRI and compared to kVCBCT. The computed CTV‐to‐PTV margin was 3.5mm for soft‐tissue based registration. There were minimal differences between the planned and delivered doses when comparing clinical and the PTV reduced margin plans: the paired t‐tests yielded p=0.38 and 0.66 between the planned and delivered doses for the adapted margin plans for the maximum cord and mean parotid dose, respectively. Target V95 received comparable doses as planned for the reduced margin plans.

Conclusion:

The 0.35T MRI offers acceptable soft‐tissue contrast and good spatial resolution for patient alignment and target visualization. Better tumor conspicuity from MRI allows soft‐tissue based alignments with potentially improved accuracy, suggesting a benefit of margin reduction for H&N radiotherapy. The reduced margin plans (i.e., 2 mm) resulted in improved normal structure sparing and accurate dose delivery to achieve intended treatment goal under MR guidance.
SU‐F‐J‐18: Feasibility of Open Mask Immobilization with Optical Imaging Guidance (OIG) for H&N Radiotherapy
Authors: Zhao B , Maquilan G , Anders M , Jiang S , Schwartz D
Published: July 2016

Purpose:

Full face and neck thermoplastic masks provide standard‐of‐care immobilization for patients receiving H&N IMRT. However, these masks are uncomfortable and increase skin dose. The purpose of this pilot study was to investigate the feasibility and setup accuracy of open face and neck mask immobilization with OIG.

Methods:

Ten patients were consented and enrolled to this IRB‐approved protocol. Patients were immobilized with open masks securing only forehead and chin. Standard IMRT to 60–70 Gy in 30 fractions were delivered in all cases. Patient simulation information, including isocenter location and CT skin contours, were imported to a commercial OIG system. On the first day of treatment, patients were initially set up to surface markings and then OIG referenced to face and neck skin regions of interest (ROI) localized on simulation CT images, followed by in‐room CBCT. CBCTs were acquired at least weekly while planar OBI was acquired on the days without CBCT. Following 6D robotic couch correction with kV imaging, a new optical real‐time surface image was acquired to track intrafraction motion and to serve as a reference surface for setup at the next treatment fraction. Therapists manually recorded total treatment time as well as couch shifts based on kV imaging. Intrafractional ROI motion tracking was automatically recorded.

Results:

Setup accuracy of OIG was compared with CBCT results. The setup error based on OIG was represented as a 6D shift (vertical/longitudinal/lateral/rotation/pitch/roll). Mean error values were −0.70±3.04mm, −0.69±2.77mm, 0.33±2.67 mm, −0.14±0.94 o, −0.15±1.10o and 0.12±0.82o, respectively for the cohort. Average treatment time was 24.1±9.2 minutes, comparable to standard immobilization. The amplitude of intrafractional ROI motion was 0.69±0.36 mm, driven primarily by respiratory neck motion.

Conclusion:

OGI can potentially provide accurate setup and treatment tracking for open face and neck immobilization. Study accrual and patient/provider satisfaction survey collection remain ongoing.

This study is supported by VisionRT, Ltd
SU‐F‐J‐36: Comparison of Ball Bearing and Iso‐Cube Phantoms for KV‐MV Iso‐Center Coincidence Check
Authors: Markovich A , Yang C
Published: July 2016

Purpose:

To compare two different quality assurance tools for kV‐MV isocenter coincidence check.

Methods:

Ball‐Bearing device (BBD) (Elekta) provided along with a CBCT equipped LINAC and isocenter cube phantom (CP) (a commercial product of Modus Medical Devices) are utilized to check the coincidence between the MV and kV beam isocenters. The microstepping meter of the BBD allows precision adjustment to better than 0.01mm in three directions. The BBD is aligned to the MV‐isocenter with the lasers and followed by taking MV‐images of at two collimator angles at each cardinal gantry, then its position adjusted. This process takes in iterative steps until 0.25mm tolerance is achieved. Four planar kV‐images are taken at cardinal angles and deviations of BBD position from kVisocenter are evaluated. CP is positioned on the couch with the lasers at known offset from the isocenter. CBCT is utilized to set the cube to its kV isocenter with the precision of linac's couch (1mm). MV‐images are taken at various gantry, collimator, and couch angles and evaluated with the CP manufacturer provided QA software to determine coincidence of the 6mm steel ball at cube center with MV‐isocenter. Three sets of measurements, one after another, were performed on the same day for each phantom on the same linac.

Results:

Assuming little variation between kV and MV isocenters in a short time, BBD measurements are more reproducible than CP. With comparable conditions both methods agree within 0.5 mm in each direction, while for BBD average standard deviation was 0.07mm and for iso‐cube 0.3mm.

Conclusion:

Since BBD is more reliable and its results are more reproducible, it should be used during the monthly QA. Since CP is a more efficient device, it should be used for daily QA. A comparison study between the two devices should be periodically performed.
SU‐F‐J‐48: Effect of Scan Length On Magnitude of Imaging Dose in KV CBCT
Authors: Deshpande S , Dhote D , Naidu S , Sutar A , Kannan V
Published: July 2016

Purpose:

To study effect of scan length on magnitude of imaging dose deposition in Varian kV CBCT for head & neck and pelvis CBCT.

Methods:

To study effect of scan length we measured imaging dose at depth of 8 cm for head and neck Cone Beam Computed Tomography (CBCT) acquisition (X ray beam energy is used 100kV and 200 degree of gantry rotation) and at 16 cm depth for pelvis CBCT acquisition (X ray beam energy used is 125 kV and 360 degree of gantry rotation) in specially designed phantom. We used farmer chamber which was calibrated in kV X ray range for measurements .Dose was measured with default field size, and reducing field size along y direction to 10 cm and 5 cm.

Results:

As the energy of the beam decreases the scattered radiation increases and this contributes significantly to the dose deposited in the patient. By reducing the scan length to 10 Cm from default 20.6 cm we found a dose reduction of 14% for head and neck CBCT protocol and a reduction of 26% for pelvis CBCT protocol. Similarly for a scan length of 5cm compared to default the dose reduction in head and neck CBCT protocol is 36% while in the pelvis CBCT protocol the dose reduction is 50%.

Conclusion:

By limiting the scan length we can control the scatter radiation generated and hence the dose to the patient. However the variation in dose reduction for same length used in two protocols is because of the scan geometry. The pelvis CBCT protocol uses a full rotation and head and neck CBCT protocol uses partial rotation.
SU‐F‐J‐50: Study On the Magnetic Field Effect On the Exradin W1 Plastic Scintillation Detector
Authors: Wen Z , Therriault‐Proulx F , Owens C , Ibbott G , Beddar S
Published: July 2016

Purpose:

To study the response of the Exradin W1 plastic scintillator detector to a 6 MV photon field in the presence of a strong magnetic field (B).

Methods:

An Exradin W1 scintillator detector coupled to a SuperMax two‐channel electrometer, both manufactured by Standard Imaging, Inc., was first calibrated in a Co‐60 beam. The Cerenkov Light Ratio (CLR) was obtained following the procedure recommended by the manufacturer. Subtracting signal in channel 2 multiplied by CLR from the signal in channel 1 should lead to a Cerenkov‐free signal. The W1 scintillator was placed in a plastic phantom inside a dipole electromagnet (GMW Associates) that could produce a strong B field, and irradiated using a 6 MV beam from an Elekta Versa HD LINAC. Signals from both channels of the W1 scintillator were acquired as a function of B (0 ‐ 1.5 T).

Results:

The signals from both channels increased as a function of the B field strength. At 1.5 T, channel 1 increased by 11% compared to the baseline (B=0 T), while channel 2 increased by 22%. Applying the recommended Cerenkov correction led to a 2% difference between dose measurement with and without a magnetic field. The values between B=0.3 T and B=1.5 T remained constant.

Conclusion:

Signals from the Exradin W1 plastic scintillation detector increased as the B field increased. This increase mainly comes from a change in the amount of Cerenkov light coupled within the optical fiber. Removing the Cerenkov component following the procedure recommended by the manufacturer showed to be an effective way to measure dose accurately in strong magnetic fields. The cause for the residual 2% difference is currently under investigation.

We acknowledge research support from Elekta AB.
SU‐F‐J‐52: A Novel Approach to X‐Ray Tube Quality Assurance for CBCT Systems in Order to Better Assess the Patient Imaging Dose in a Large, Multi‐Unit Treatment Facility
Authors: Buckley L , Webb R , Lambert C , Nyiri B , Gerig L
Published: July 2016

Purpose:

To standardize the tube calibration for Elekta XVI cone beam CT (CBCT) systems in order to provide a meaningful estimate of the daily imaging dose and reduce the variation between units in a large centre with multiple treatment units.

Methods:

Initial measurements of the output from the CBCT systems were made using a Farmer chamber and standard CTDI phantom. The correlation between the measured CTDI and the tube current was confirmed using an Unfors Xi detector which was then used to perform a tube current calibration on each unit.

Results:

Initial measurements showed measured tube current variations of up to 25% between units for scans with the same image settings. In order to reasonably estimate the imaging dose, a systematic approach to x‐ray generator calibration was adopted to ensure that the imaging dose was consistent across all units at the centre and was adopted as part of the routine quality assurance program. Subsequent measurements show that the variation in measured dose across nine units is on the order of 5%.

Conclusion:

Increasingly, patients receiving radiation therapy have extended life expectancies and therefore the cumulative dose from daily imaging should not be ignored. In theory, an estimate of imaging dose can be made from the imaging parameters. However, measurements have shown that there are large differences in the x‐ray generator calibration as installed at the clinic. Current protocols recommend routine checks of dose to ensure constancy. The present study suggests that in addition to constancy checks on a single machine, a tube current calibration should be performed on every unit to ensure agreement across multiple machines. This is crucial at a large centre with multiple units in order to provide physicians with a meaningful estimate of the daily imaging dose.
SU‐F‐J‐73: Simple Approach for Quantification of Metal Artifact Reduction Capabalities of Dual‐Energy CT
Authors: Lamichhane N , Padgett K , Li X , Mihaylov I
Published: July 2016

Purpose:

To present a simple method for quantification of dual‐energy CT metal artifact reduction capabilities

Methods:

A phantom was constructed from solid water and a steel cylinder. Solid water is commonly used for radiotherapy QA, while steel cylinders are readily available in hardware stores. The phantom was scanned on Siemens Somatom 64‐slice dual‐energy CT system. Three CTs were acquired at energies of 80kV (low), 120kV (nominal), and 140kV (high). The low and high energy acquisitions were used to generate dual‐energy (DE) monoenergetic image sets, which also utilized metal artifact reduction algorithm (Maris). Several monoenergetic DE image sets, ranging from 70keV to 190keV were generated. The size of the metal artifact was measured by two different approaches. The first approach measured the distance from the center of the steel cylinder to a location with nominal (undisturbed by metal) HU value for the 120kV, DE 70keV, and DE 190keV image sets. In the second approach, the distance from the center of the cylinder to the edge of the air pocket for the above mentioned three image sets was measured.

Results:

The DE 190keV synthetic image set demonstrated the largest reduction of the metal artifacts. The size of the artifact was more than three times the actual size of the milled hole in the solid water in the DE 190keV, as compared to more than 7.5 times larger as estimated from the 120kV uncorrected image

Conclusion:

A simple phantom for quantification of dual‐energy CT metal artifact reduction capabilities was presented. This inexpensive phantom can be easily built from components available in every radiation oncology department. It allows quick assessment and quantification of the properties of different metal artifact reduction algorithms, available on modern dual‐energy CT scanners.
SU‐F‐J‐90: Effects of Optimization Cost Function On Ventilation in SBRT of NSCLC
Authors: Mihaylov I , Latifi K , De Ornelas‐Couto M , Moros E , Zhang G
Published: July 2016

Purpose:

To explore the effects of dose‐volume (Dvh) and dose‐mass (Dmh) inverse optimization approaches on the lung ventilation for SBRT in NSCLC.

Methods:

Six cases were studied. For each case ventilation was computed on voxel‐by‐voxel basis, derived from the time‐resolved (4D) CT scans. Ventilation is defined as voxel volume change between full inspiration and full expiration, divided by voxel volume. The ventilation volume was mapped to full expiration phase. For each patient case two IMRT plans were created ‐ one with Dvh and one with Dmh quadratic objective function, applied to the OARs. The OARs used as dose limiting structures were lung, spinal cord, esophagus, and heart. After obtaining the IMRT solutions average doses as well as 2000 cGy isovolumes and isomases were extracted for ventilation volumes of 0.5, 0.9, 1.1, 1.2, and 1.5. Ventilation volume of 0.5 incorporates all CT voxels having a voxel volume change (exhale‐to‐inhale) 50% and more. Similarly, ventilation volume of 1.5 encompasses all CT voxels with volume change of 150% and more. Thereby, ventilation volume of 0.5 encompasses almost the entire lung, while ventilation volume of 1.5 represents ∼1% of ventilation 0.5 volume. The doses, the isovolumes, and the isomasses derived from the Dvh optimization were used as references.

Results:

The results indicate that with decreasing ventilation (from 1.5 to 0.5) the differences between Dvh and Dmh derived tallied quantities decrease. For some cases the differences between the average doses for the different ventilation volumes are up to 20%. The changes in the isovolumes and the isomasses for the different ventilations are much more dramatic and can differ by a factor of 3.5.

Conclusion:

This is the first investigation on the effects of different optimization schemes on lung ventilation. The presented results indicate that the larger the ventilation the more dramatic the effects.

Supported in part by NIH R01 CA163360
SU‐F‐J‐96: Comparison of Frame‐Based and Mutual Information Registration Techniques for CT and MR Image Sets
Authors: Popple R , Bredel M , Brezovich I , Dobelbower M , Fisher W , Fiveash J , Guthrie B , Riley K , Wu X
Published: July 2016

Purpose:

To compare the accuracy of CT‐MR registration using a mutual information method with registration using a frame‐based localizer box.

Methods:

Ten patients having the Leksell head frame and scanned with a modality specific localizer box were imported into the treatment planning system. The fiducial rods of the localizer box were contoured on both the MR and CT scans. The skull was contoured on the CT images. The MR and CT images were registered by two methods. The frame‐based method used the transformation that minimized the mean square distance of the centroids of the contours of the fiducial rods from a mathematical model of the localizer. The mutual information method used automated image registration tools in the TPS and was restricted to a volume‐of‐interest defined by the skull contours with a 5 mm margin. For each case, the two registrations were adjusted by two evaluation teams, each comprised of an experienced radiation oncologist and neurosurgeon, to optimize alignment in the region of the brainstem. The teams were blinded to the registration method.

Results:

The mean adjustment was 0.4 mm (range 0 to 2 mm) and 0.2 mm (range 0 to 1 mm) for the frame and mutual information methods, respectively. The median difference between the frame and mutual information registrations was 0.3 mm, but was not statistically significant using the Wilcoxon signed rank test (p=0.37).

Conclusion:

The difference between frame and mutual information registration techniques was neither statistically significant nor, for most applications, clinically important. These results suggest that mutual information is equivalent to frame‐based image registration for radiosurgery. Work is ongoing to add additional evaluators and to assess the differences between evaluators.
SU‐F‐J‐117: Impact of Motion Artifacts On Image Quality and Accuracy of Tumor Motion Reconstruction in 4D CT‐On‐Rails and MV‐CBCT Scans: A Phantom Study
Authors: Lin T , Ma C
Published: July 2016

Purpose:

To compare and quantify respiratory motion artifacts in images from free breathing 4D‐CT‐on‐Rails(CTOR) and those from MV‐Cone‐beam‐CT(MVCB) and facilitate respiratory motion guided radiation therapy.

Methods:

4D‐CTOR: Siemens Somatom CT‐on‐Rails system with Anzai belt loaded with pressure sensor load cells. 4D scans were performed in helical mode, pitch 0.1, gantry rotation time 0.5s, 1.5mm slice thickness, 120kVp, 400 mAs. Normal and fast breathing (>12rpm) scanning protocols were investigated. Helical scan, AIP(average intensity projection) and MIP(maximum intensity projection) were generated from 4D‐CTOR scans with amplitude sorting into 10 phases.MVCB: Siemens Artiste diamond view(1MV)MVCB was performed with 5MU thorax protocol with 60 second of full rotation.Phantom: Anzai AZ‐733V respiratory phantom. The settings were set to normal and resp. modes with repetition rates at 15 rpm and 10 rpm. Surgical clips, acrylic, wooden, rubber and lung density, total six mock‐ups were scanned and compared in this study.Signal‐to‐noise ratio(SNR), contrast‐to‐noise ratio(CNR) and reconstructed motion volume were compared to different respiratory setups for the mock‐ups.

Results:

Reconstructed motion volume was compared to the real object volume for the six test mock‐ups. It shows that free breathing helical in all instances underestimates the object excursions largest to −67.4% and least −6.3%. Under normal breathing settings, MIP can predict very precise motion volume with minimum 0.4% and largest −13.9%. MVCB shows underestimate of the motion volume with −1.11% minimum and −18.0% maximum. With fast breathing, AIP provides bad representation of the object motion; however, the MIP can predict the motion volume with −2.0% to −11.4% underestimate.

Conclusion:

Respiratory motion guided radiation therapy requires good motion recording. This study shows that regular CTOR helical scans provides bad guidance, 4D CTOR AIP cannot represent the fast breathing pattern, MIP can represent the best motion volume, MVCBCT can only be used for normal breathing with acceptable uncertainties.
SU‐F‐J‐130: Margin Determination for Hypofractionated Partial Breast Irradiation
Authors: Geady C , Keller B , Ruschin M , Hahn E , Makhani N , Bosnic S , Vesprini D , Soliman H , Lee J , McCann C
Published: July 2016

Purpose:

To determine the Planning Target Volume (PTV) margin for Hypofractionated Partial Breast Irradiation (HPBI) using the van Herk formalism (M=2.5∑+0.7σ). HPBI is a novel technique intended to provide local control in breast cancer patients not eligible for surgical resection, using 40 Gy in 5 fractions prescribed to the gross disease.

Methods:

Setup uncertainties were quantified through retrospective analysis of cone‐beam computed tomography (CBCT) data sets, collected prior to (prefraction) and after (postfraction) treatment delivery. During simulation and treatment, patients were immobilized using a wing board and an evacuated bag. Prefraction CBCT was rigidly registered to planning 4‐dimensional computed tomography (4DCT) using the chest wall and tumor, and translational couch shifts were applied as needed. This clinical workflow was faithfully reproduced in Pinnacle (Philips Medical Systems) to yield residual setup and intrafractional error through translational shifts and rigid registrations (ribs and sternum) of prefraction CBCT to 4DCT and postfraction CBCT to prefraction CBCT, respectively. All ten patients included in this investigation were medically inoperable; the median age was 84 (range, 52–100) years.

Results:

Systematic (and random) setup uncertainties (in mm) detected for the left‐right, craniocaudal and anteroposterior directions were 0.4 (1.5), 0.8 (1.8) and 0.4 (1.0); net uncertainty was determined to be 0.7 (1.5). Rotations >2° in any axis occurred on 8/72 (11.1%) registrations.

Conclusion:

Preliminary results suggest a non‐uniform setup margin (in mm) of 2.2, 3.3 and 1.7 for the left‐right, craniocaudal and anteroposterior directions is required for HPBI, given its immobilization techniques and online setup verification protocol. This investigation is ongoing, though published results from similar studies are consistent with the above findings. Determination of margins in breast radiotherapy is a paradigm shift, but a necessary step in moving towards hypofractionated regiments, which may ultimately redefine the standard of care for this select patient population.
SU‐F‐J‐131: Reproducibility of Positioning Error Due to Temporarily Indwelled Urethral Catheter for Urethra‐Sparing Prostate IMRT
Authors: Hirose K , Sato M , Hatayama Y , Kawaguchi H , Aoki M , Akimoto H , Komai F , Souma M , Obara H , Suzuki M , Takai Y
Published: July 2016

Purpose:

The purpose of this study was to prospectively assess the reproducibility of positioning errors due to temporarily indwelled catheter in urethra‐sparing image‐guided (IG) IMRT.

Methods:

Ten patients received urethra‐sparing prostate IG‐IMRT with implanted fiducials. After the first CT scan was performed in supine position, 6‐Fr catheter was indwelled into urethra, and the second CT images were taken for planning. While the PTV received 80 Gy, 5% dose reduction was applied for the urethral PRV along the catheter. Additional CT scans were also performed at 5th and 30th fraction. Positions of interests (POIs) were set on posterior edge of prostate at beam isocenter level (POI1) and cranial and caudal edge of prostatic urethra on the post‐indwelled CT images. POIs were copied into the pre‐indwelled, 5th and 30th fraction's CT images after fiducial matching on these CT images. The deviation of each POI between pre‐ and post‐indwelled CT and the reproducibility of prostate displacement due to catheter were evaluated.

Results:

The deviation of POI1 caused by the indwelled catheter to the directions of RL/AP/SI (mm) was 0.20±0.27/−0.64±2.43/1.02±2.31, respectively, and the absolute distances (mm) were 3.15±1.41. The deviation tends to be larger if closer to the caudal edge of prostate. Compared with the pre‐indwelled CT scan, a median displacement of all POIs (mm) were 0.3±0.2/2.2±1.1/2.0±2.6 in the post‐indwelled, 0.4±0.4/3.4±2.1/2.3±2.6 in 5th, and 0.5±0.5/1.7±2.2/1.9±3.1 in 30th fraction's CT scan with a similar data distribution. There were 6 patients with 5‐mm‐over displacement in AP and/or CC directions.

Conclusion:

Reproducibility of positioning errors due to temporarily indwelling catheter was observed. Especially in case of patients with unusually large shifts by indwelling catheter at the planning process, treatment planning should be performed by using the pre‐indwelled CT images with transferred contour of the urethra identified by post‐indwelled CT images.
SU‐F‐J‐138: An Extension of PCA‐Based Respiratory Deformation Modeling Via Multi‐Linear Decomposition
Authors: Iliopoulos AS , Pitsianis N , Sun X , Yin FF , Ren L
Published: July 2016

Purpose:

To address and lift the limited degree of freedom (DoF) of globally bilinear motion components such as those based on principal components analysis (PCA), for encoding and modeling volumetric deformation motion.

Methods:

We provide a systematic approach to obtaining a multi‐linear decomposition (MLD) and associated motion model from deformation vector field (DVF) data. We had previously introduced MLD for capturing multi‐way relationships between DVF variables, without being restricted by the bilinear component format of PCA‐based models. PCA‐based modeling is commonly used for encoding patient‐specific deformation as per planning 4D‐CT images, and aiding on‐board motion estimation during radiotherapy. However, the bilinear space‐time decomposition inherently limits the DoF of such models by the small number of respiratory phases. While this limit is not reached in model studies using analytical or digital phantoms with low‐rank motion, it compromises modeling power in the presence of relative motion, asymmetries and hysteresis, etc, which are often observed in patient data. Specifically, a low‐DoF model will spuriously couple incoherent motion components, compromising its adaptability to on‐board deformation changes. By the multi‐linear format of extracted motion components, MLD‐based models can encode higher‐DoF deformation structure.

Results:

We conduct mathematical and experimental comparisons between PCA‐ and MLD‐based models. A set of temporally‐sampled analytical trajectories provides a synthetic, high‐rank DVF; trajectories correspond to respiratory and cardiac motion factors, including different relative frequencies and spatial variations. Additionally, a digital XCAT phantom is used to simulate a lung lesion deforming incoherently with respect to the body, which adheres to a simple respiratory trend. In both cases, coupling of incoherent motion components due to a low model DoF is clearly demonstrated.

Conclusion:

Multi‐linear decomposition can enable decoupling of distinct motion factors in high‐rank DVF measurements. This may improve motion model expressiveness and adaptability to on‐board deformation, aiding model‐based image reconstruction for target verification.

NIH Grant No. R01‐184173
SU‐F‐J‐145: MRI‐Guided Interventional Boost Radiotherapy for Rectal Cancer: Investigating the Feasibility of Adapting the Anatomy
Authors: Kleijnen J J E , Couwenberg A M , van Asselen B , Lagendijk J J W , Intven M , Raaymakers B W
Published: July 2016

Purpose:

The recent development of an MRI‐linac allows adaptation of treatments to the anatomy of the moment. This anatomy, in turn, could be altered into a more favorable situation for radiotherapy purposes. The purpose of this study is to investigate the potential dosimetric benefits of manipulating rectal anatomy in MRI‐guided interventional external‐beam radiotherapy for rectal cancer.

Methods:

For this retrospective analysis, four patients (1M/3F) diagnosed with rectal cancer were included. These underwent MR‐imaging using sonography transmission gel as endorectal contrast at time of diagnosis and standard, non‐contrast, MR‐imaging prior to radiotherapy planning. In the contrast scan, the rectum is inflated by the inserted contrast gel, thereby potentially increasing the distance between tumor and the organs‐at‐risk (OAR). Both anatomies were delineated and 7‐ beam IMRT‐plans were calculated for both situations (RT‐standard and RT‐inflated), using in‐house developed treatment planning software. Each plan was aimed to deliver 15Gy to the planning target volume (PTV; tumor+3mm margin) with a D99>95% and Dmax<120% of the planned dose. The D2cc dose to the OAR were then compared for both situations.

Results:

At equal (or better) target coverage, we found a mean reduction in D2cc of 4.1Gy/237% [range 2.6Gy–6.3Gy/70%–621%] for the bladder and of 2.0Gy/145% [range −0.7Gy–7.9Gy/−73%–442%] for the small‐bowel, for the RT‐inflated compared to the RT‐standard plans. For the three female patients, a reduction in D2cc of 5.2Gy/191% [range 3.2Gy–9.2Gy/44%–475%] for the gynecological organs was found. We found all D2cc doses to be better for the RT‐inflated plans, except for one patient for whom the bladder D2cc dose was slightly increased.

Conclusion:

Reduction of OAR dose by manipulation of anatomy is feasible. Inflation of the rectum results in more distance between OAR and PTV. This leads to a substantial reduction in dose to OAR at equal or better target coverage.