bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐F‐J‐99: Dose Accumulation and Evaluation in Lung SBRT Among All Phases of Respiration
Authors: Azcona JD , Burguete J , Barbes B , Aristu J , Moreno M , Zubiria A , Arce P , Lagares JI
Published: July 2016

Purpose:

To calculate the total planning dose on lung tumors (GTV) by accumulating the dose received in all respiration phases.

Methods:

A patient 4D planning CT (phase‐binned, from a Siemens Somatom CT) was used to locate the GTV of a lung tumor in all respiratory phases with Pinnacle (v9.10). GTV contours defined in all phases were projected to the reference phase, where the ITV was defined. Centroids were calculated for all the GTV projections. No deformation or rotation was taken into account. The only GTV contour as defined in the reference phase was voxelized to track each voxel individually. We accumulated the absorbed dose in different phases on each voxel. A 3DCRT and a VMAT plan were designed on the reference phase fulfilling the ITV dosimetric requirements, using the 10MV FFF photon model from an Elekta Versa linac. ITV‐to‐PTV margins were set to 5mm. In‐house developed MATLAB code was used for tumor voxeling and dose accumulation, assuming that the dose distribution planned in the reference phase behaved as a “dose‐cloud” during patient breathing.

Results:

We tested the method on a patient 4DCT set of images exhibiting limited tumor motion (<5mm). For the 3DCRT plan, D95 was calculated for the GTV with motion and for the ITV, showing an agreement of 0.04%. For the VMAT plan, we calculated the D95 for every phase as if the GTV in that phase had received the whole treatment. Differences in D95 for all phases are within 1%, and estimate the potential interplay effect during delivery.

Conclusion:

A method for dose accumulation and assessment was developed that can compare GTV motion with ITV dosage, and estimate the potential interplay effect for VMAT plans. Work in progress includes the incorporation of deformable image registration and 4D CBCT dose calculation for dose reconstruction and assessment during treatment.
SU‐F‐J‐104: Weekly MRI for Dose Assessment of Organs at Risk During Treatment of HN Cancer of the Oropharynx
Authors: Ludwig K , Li J , Venigalla P , Zhang J , Tang X , Tyagi N , Fontenla S , Lee N , Saleh Z
Published: July 2016

Purpose:

Investigate the feasibility of using weekly MRI to assess dose to organs at risk utilizing deformable image registration.

Methods:

Sixteen H&N patients with oropharyngeal cancer were imaged on a 3T MR scanner using T2W and mDIXON sequence. Patients were imaged on a weekly basis in treatment position. Parotids (LP & RP), submandibular glands (LS, RS), and oral cavity (OC) were delineated on the weekly MR and reviewed by a board certified radiation oncologist. The original planning CT (pCT), RT‐Dose, and RT‐Structures were deformed and registered to each weekly MRIs. The deformed CTs and RT‐Structures were imported to the treatment planning system (TPS) and rigidly registered to the pCT. Forward dose calculation of the original RT‐Plan was used to estimate the delivered dose on the deformed CT. The dose volume histograms (DVH) statistics were performed to compare planned dose, deformed dose, and forward calculated dose. In addition, Dice similarity metric (DSM) was used to compare deformed and reference structures.

Results:

The average (min,max) DSM between deformed and reference structures was 0.71 (0.69,0.93); 0.70 (0.64,0.89); 0.65 (0.48,0.86); 0.63 (0.37,0.89); and 0.63 (0.58,0.87); for LP, RP, LS, RS, and OC respectively. The respective average relative structures volumes changed at a weekly rate of −4.99%; −4.40%; +3.45%; +1.46%; −1.39%, respectively. The percentage difference %(min,max) between estimated delivered dose and planned dose was +3.94 (−51.3,+30.5); +6.33 (−58.6,+82.7); +2.46 (−38.9,+37.6,); +2.38(−49.0,+28.9); +3.55(−17.0,+43.1).

Conclusion:

The recalculated dose based on weekly MRI deviated from planned dose for all OARs. Meanwhile, the deformed dose did not reflect the subtle changes in OARs as compared to the recalculated dose. This study demonstrates the feasibility of using weekly MRI to monitor volumetric changes which has important implications on actual delivered dose.
SU‐F‐J‐110: MRI‐Guided Single‐Session Simulation, Online Adaptation, and Treatment
Authors: Hill P , Geurts M , Mittauer K , Bayouth J
Published: July 2016

Purpose:

To develop a combined simulation and treatment workflow for MRI‐guided radiation therapy using the ViewRay treatment planning and delivery system.

Methods:

Several features of the ViewRay MRIdian planning and treatment workflows are used to simulate and treat patients that require emergent radiotherapy. A simple “pre‐plan” is created on diagnostic imaging retrieved from radiology PACS, where conformal fields are created to target a volume defined by a physician based on review of the diagnostic images and chart notes. After initial consult in radiation oncology, the patient is brought to the treatment room, immobilized, and imaged in treatment position with a volumetric MR. While the patient rests on the table, the pre‐plan is applied to the treatment planning MR and dose is calculated in the treatment geometry. After physician review, modification of the plan may include updating the target definition, redefining fields, or re‐balancing beam weights. Once an acceptable treatment plan is finalized and approved, the patient is treated.

Results:

Careful preparation and judicious choices in the online planning process allow conformal treatment plans to be created and delivered in a single, thirty‐minute session. Several advantages have been identified using this process as compared to conventional urgent CT simulation and delivery. Efficiency gains are notable, as physicians appreciate the predictable time commitment and patient waiting time for treatment is decreased. MR guidance in a treatment position offers both enhanced contrast for target delineation and reduction of setup uncertainties. The MRIdian system tools designed for adaptive radiotherapy are particularly useful, enabling plan changes to be made in minutes. Finally, the resulting plans, typically 6 conformal beams, are delivered as quickly as more conventional AP/PA beam arrangements with comparatively superior dose distributions.

Conclusion:

The ViewRay treatment planning software and delivery system can accommodate a fast simulation and treatment workflow.
SU‐F‐J‐121: Dosimetric Evaluation of Active Breathing Coordinator‐Response Gating System Linked to Linear Accelerator in Volumetric Modulated Arc Therapy
Authors: Lee S , Zheng Y , Albani D , Colussi V , Dorth J , Sohn J
Published: July 2016

Purpose:

To reduce internal target volume (ITV), respiratory management is a must in imaging and treatment for lung, liver, and breast cancers. We investigated the dosimetric accuracy of VMAT treatment delivery with a Response™ gating system linked to linear accelerator.

Methods:

The Response™ gating module designed to directly control radiation beam by breath‐holding with a ABC system (Elekta AB, Stockholm, Sweden) was tested for VMAT treatments. Seven VMAT plans including three conventional and four stereotactic body radiotherapy (SBRT) cases were evaluated. Each plan was composed of two or four arcs of 6MV radiation beam with prescribed dose ranged from 1.8 to 9 Gy per fraction. Each plan was delivered continuously without gating and delivered with multiple interruptions by the ResponseTM gating module with a 20 or 30 second breath‐holding period. MapCheck2 and Gafchromic EBT3 films sandwiched in MapPHAN were used to measure the delivered dose with and without gating. Films were scanned on a flatbed color scanner, and red channel was extracted for film dosimetry. Gamma analysis was performed to analyze the dosimetrical accuracy of the radiation delivery with gating.

Results:

The measured doses with gating remarkably agree with the planned dose distributions in the results of gamma index passing rate (within 20% isodose; >98% for 3%/3mm and >92% for 2%/2mm in MapCheck2, and >91% for 3%/3mm criteria in EBT3 film except one case which was for large target and highly modulated). No significant difference (student t‐test: p‐value < 0.0005) was shown between the doses delivered with and without gating. There was no indication of radiation gap or overlapping during deliver interruption in film dosimetry.

Conclusion:

The Response™ gating system can be safely used during VMAT treatment. The accurate performance of the gating system linked to ABC can contribute to ITV reduction for SBRT using VMAT.
SU‐F‐J‐123: CT‐Based Determination of DIBH Variability and Its Dosimetric Impact On Post‐Mastectomy Plus Regional Nodal Radiation Therapy
Authors: Malin M , Kang H , Tatebe K , Hasan Y , Chmura S , Al‐Hallaq H
Published: July 2016

Purpose:

Breast cancer radiotherapy delivered using voluntary deep inspiration breath‐hold (DIBH) requires reproducible breath holds, particularly when matching supraclavicular fields to tangential fields. We studied the impact of variation in DIBHs on CTV and OAR dose metrics by comparing the dose distribution computed on two DIBH CT scans taken at the time of simulation.

Methods:

Ten patients receiving 50Gy in 25 fractions to the left chestwall and regional lymph nodes were studied. Two simulation CT scans were taken during separate DIBHs along with a free‐breathing (FB) scan. The treatment was planned using one DIBH CT. The dose was recomputed on the other two scans using adaptive planning (Pinnacle 9.10) in which the scans are registered using a cross‐correlation algorithm. The chestwall, lymph nodes and OARs were contoured on the scans following the RTOG consensus guidelines. The overall translational and rotational variation between the DIBH scans was used to estimate positional variation between breath‐holds. Dose metrics between plans were compared using paired t‐tests (p < 0.05) and means and standard deviations were reported.

Results:

The registration parameters were sub‐millimeter and sub‐degree. Although DIBH significantly reduced mean heart dose by 2.4Gy compared to FB (p < 0.01), no significant changes in dose were observed for targets or OARs between the two DIBH scans. Nodal coverage as assessed by V90% was 90%±8% and 89%±8% for supraclavicular and 99%±2% and 97%±22% for IM nodes. Though a significant decrease (10.5%±12.4%) in lung volume in the second DIBH CT was observed, the lung V20Gy was unchanged (14±2% and 14±3%) between the two DIBH scans.

Conclusion:

While the lung volume often varied between DIBHs, the CTV and OAR dose metrics were largely unchanged. This indicates that manual DIBH has the potential to provide consistent dose delivery to the chestwall and regional nodes targets when using matched fields.
SU‐F‐J‐129: Verification of Geometric and Dosimetric Accuracy of Respiratory Management Systems Using Homemade Phantom
Authors: Goksel E , Kucucuk H , Senkesen O , Tezcanli E
Published: July 2016

Purpose:

Different placements of Infrared Cameras (IRC) in CT and treatment rooms can cause gating window level (GWL) variations leading to differences between GWL used for planning and treatments. Although, Varian Clinac DHX‐OBI sytem and CT are equipped with the same kind of IRC, Truebeam STx (TB) has a different type of IRC known as banana type. In this study; geometric and dosimetric accuracy of respiratory management system (RPM) for different machines were investigated with a special homemade phantom.

Methods:

Special phantom was placed on the respiratory simulator machine and a CT data set was obtained at the end of the expirium phase (EOE). Conformal and IMRT plans were generated on the EOE CT image series for both DHX‐OBI and TB LINACs while a VMAT plan was generated only for TB.The acquired respiratory graphs in the CT were directly sent to DHX‐OBI system, and they were converted with software before sending to TB. EBT3 films were placed inside the phantom and were irradiated using RPM system with two machines for different plans. Planar dose distributions were compared with gamma analysis (GA) method (3mm, %3) to evaluate planned‐measured dose differences. In addition, radio‐opac marker was placed in the center of the phantom to evaluate the geometric accuracy of treatment field with gated flouroscopy (GF).

Results:

There were no shifts detected between planning and treeatment GWL for both DHX‐OBI and TB. Difference on the GF image between digital graticule and radio‐opac marker was <1mm for TB and 1mm for DHX‐OBI. Although, GA agreement was 97% for conformal and IMRT techniques in TB, it was 96% for VMAT technique. While GA agreement was 98% for conformal technique in DHX‐OBI, IMRT was 95%.ConclusionThis study showed that RPM can be used accurately in spite of different IRC placements or different types of ICR used.
SU‐F‐J‐135: Tumor Displacement‐Based Binning for Respiratory‐Gated Time‐Independent 5DCT Treatment Planning
Authors: Yang L , O'Connell D , Lee P , Shaverdian N , Kishan A , Lewis J , Dou T , Thomas D , Qi X , Low D
Published: July 2016

Purpose:

A published 5DCT breathing motion model enables image reconstruction at any user‐selected breathing phase, defined by the model as a specific amplitude (v) and rate (f). Generation of reconstructed phase‐specific CT scans will be required for time‐independent radiation dose distribution simulations. This work answers the question: how many amplitude and rate bins are required to describe the tumor motion with a specific spatial resolution?

Methods:

19 lung‐cancer patients with 21 tumors were scanned using a free‐breathing 5DCT protocol, employing an abdominally positioned pneumatic‐bellows breathing surrogate and yielding voxel‐specific motion model parameters α and β corresponding to motion as a function of amplitude and rate, respectively. Tumor GTVs were contoured on the first (reference) of 25 successive free‐breathing fast helical CT image sets. The tumor displacements were binned into widths of 1mm to 5mm in 1mm steps and the total required number of bins recorded. The simulation evaluated the number of bins needed to encompass 100% of the breathing‐amplitude and between the 5th and 95th percentile amplitudes to exclude breathing outliers.

Results:

The mean respiration‐induced tumor motion was 9.90mm ± 7.86mm with a maximum of 25mm. The number of bins required was a strong function of the spatial resolution and varied widely between patients. For example, for 2mm bins, between 1–13 amplitude bins and 1–9 rate bins were required to encompass 100% of the breathing amplitude, while 1–6 amplitude bins and 1–3 rate bins were required to encompass 90% of the breathing amplitude.

Conclusion:

The strong relationship between number of bins and spatial resolution as well as the large variation between patients implies that time‐independent radiation dose distribution simulations should be conducted using patient‐specific data and that the breathing conditions will have to be carefully considered. This work will lead to the assessment of the dosimetric impact of binning resolution.

This study is supported by Siemens Healthcare
SU‐F‐J‐136: Impact of Audiovisual Biofeedback On Interfraction Motion Over a Course of Liver Cancer Stereotactic Body Radiotherapy
Authors: Pollock S , Tse R , Martin D , McLean L , Pham M , Tait D , Estoesta R , Whittington G , Turley J , Kearney C , Cho G , Hill R , Pickard S , Aston P , Makhija K , O'Brien R , Keall P
Published: July 2016

Purpose:

In abdominal radiotherapy inconsistent interfraction respiratory motion can result in deviations during treatment from what was planned in terms of target position and motion. Audiovisual biofeedback (AVB) is an interactive respiratory guide that produces a guiding interface that the patient follows over a course of radiotherapy to facilitate regular respiratory motion. This study assessed the impact of AVB on interfraction motion consistency over a course of liver cancer SBRT.

Methods:

Five liver cancer patients have been recruited into this study, 3 followed AVB over their course of SBRT and 2 were free breathing (FB). Respiratory signals from the Varian RPM were obtained during 4DCT and each treatment fraction. Respiratory signals were organized into 10 respiratory bins, and interfraction consistency was quantified by the difference between each treatment fraction respiratory bin and each respiratory bin from 4DCT. Interfraction consistency was considered as both the relative difference (as a percentage) and absolute difference (in centimeters) between treatment respiratory bins and 4DCT respiratory bins.

Results:

The relative difference between 4DCT and treatment respiratory bins was 22 ± 16% for FB, and 15 ± 10% for AVB, an improvement of 32% (p < 0.001) with AVB. The absolute difference between 4DCT and treatment respiratory bins was 0.15 ± 0.10 cm for FB, and 0.14 ± 0.13 cm for AVB, an improvement of 4% (p = 0.6) with AVB.

Conclusion:

This was the first study to compare the impact of AVB breathing guidance on interfraction motion consistency over a course of radiotherapy. AVB demonstrated to significantly reduce the relative difference between 4DCT and treatment respiratory motion, but the absolute differences were comparable, largely due to one AVB patient exhibiting a larger amplitude than the other patients. This study demonstrates the potential benefit of AVB in reducing motion variations during treatment from what was planned.

Paul Keall, Sean Pollock, Ricky OBrien and Kuldeep Makhija are shareholders of Respiratory Innovations, an Australian company that is developing a device to improve breathing stability. No funding or support was provided by Respiratory Innovations. Paul Keall is one of the inventors of US patent # 7955270.
SU‐F‐J‐142: Proposed Method to Broaden Inclusion Potential of Patients Able to Use the Calypso Tracking System in Prostate Radiotherapy
Authors: Fiedler D , Kuo H , Bodner W , Tome W
Published: July 2016

Purpose:

To introduce a non‐standard method of patient setup, using BellyBoard immobilization, to better utilize the localization and tracking potential of an RF‐beacon system with EBRT for prostate cancer.

Methods:

An RF‐beacon phantom was imaged using a wide bore CT scanner, both in a standard level position and with a known rotation (4° pitch and 7.5° yaw). A commercial treatment planning system (TPS) was used to determine positional coordinates of each beacon, and the centroid of the three beacons for both setups. For each setup at the Linac, kV AP and Rt Lateral images were obtained. A full characterization of the RF‐beacon system in clinical mode was completed for various beacons’ array‐to‐centroid distances, which includes vertical, lateral, and longitudinal offset data, as well as pitch and yaw offset measurements for the tilted phantom. For the single patient who has been setup using the proposed BellyBoard method, a supine simulation was first obtained. When abdominal protrusion was found to be exceeding the limits of the RF‐Beacon system through distance‐based analysis in the TPS, the patient is re‐simulated prone with the BellyBoard. Array to centroid distance is measured again in the TPS, and if found to be within the localization or tracking region it is applied.

Results:

Characterization of limitations for the RF‐beacon system in clinical mode showed acceptable consistency of offset determination for phantom setup accuracy. The nonstandard patient setup method reduced the beacons’ centroid‐to‐array distance by 8.32cm, from 25.13cm to 16.81cm; completely out of tracking range (greater than 20cm) to within setup tracking range (less than 20cm).

Conclusion:

Using the RF‐beacon system in combination with this novel patient setup can allow patients who would otherwise not be candidates for beacon enhanced EBRT to now be able to benefit from the reduced PTV margins of this treatment method.
SU‐F‐J‐149: Beam and Cryostat Scatter Characteristics of the Elekta MR‐Linac
Authors: Duglio M , Towe S , Roberts D
Published: July 2016

Purpose:

The Elekta MR‐Linac combines a digital linear accelerator system with a 1.5T Philips MRI machine. This study aimed to determine key characteristic information regarding the MR‐Linac beam and in particular it evaluated the effect of the MR cryostat on the out of field scatter dose.

Methods:

Tissue phantom ratios, profiles and depth doses were acquired in plastic water with an IC‐profiler or with an MR compatible water tank using multiple system configurations (Full (B0= 1.5T), Full (B0=0T) and No cryostat). Additionally, an in‐house CAD based Monte Carlo code based on Penelope was used to provide comparative data.

Results:

With the cryostat in place and B0=0T, the measured TPR for the MR Linac system was 0.702, indicating an energy of around 7MV. Without the cryostat, the measured TPR was 0.669. For the Full (B0=0T) case, out of field dose at a depth of 10 cm in the isocentric plane, 5 cm from the field edge was 0.8%, 3.1% and 5.4% for 3×3 cm2, 10×10 cm2 and 20×20 cm2 fields respectively.The out of field dose (averaged between 5 cm and 10 cm beyond the field edges) in the “with cryostat” case is 0.78% (absolute difference) higher than without the cryostat for clinically relevant field sizes (i.e. 10×10 cm2) and comparable to measured conventional 6MV treatment beams at a depth of 10 cm (within 0.1% between 5 cm and 6 cm from field edge). At dose maximum and at 5 cm from the field edge, the “with cryostat” out of field scatter for a 10×10 cm2 field is 1.5% higher than “without cryostat”, with a modest increase (0.9%) compared to Agility 6MV in the same conditions.

Conclusion:

The study has presented typical characteristics of the MR‐Linac beam and determined that out of field dose is comparable to conventional treatment beams.

All authors are employed by Elekta Ltd., who are developing an MR‐Linac.
SU‐F‐J‐157: Effect of Contouring Uncertainty in Post Implant Dosimetry of Low‐Dose‐Rate Prostate Permanent Seed Brachytherapy
Authors: Mashouf S , Safigholi H , Merino T , Soliman A , Ravi A , Morton G , Song W
Published: July 2016

Purpose:

There is strong evidence relating post‐implant dosimetry for low‐dose‐rate (LDR) prostate seed brachytherapy to local control rates. The delineation of the prostate on CT images, however, represents a challenge due to the lack of soft tissue contrast in order to identify the prostate borders. This study aims at quantifying the sensitivity of clinically relevant dosimetric parameters to uncertainty in the contouring of prostate.

Methods:

CT images, post‐op plans and contours of a cohort of patients (n=43) (low risk=55.8%, intermediate risk=39.5%, high risk=4.7%), who had received prostate seed brachytherapy, were imported into MIM Symphony treatment planning system. The prostate contours in post‐implant CT images were expanded/contracted uniformly for margins of ±1.00 mm, ±2.00 mm, ±3.00 mm, ±4.00 mm and ±5.00 mm. The values for V100 and D90 were extracted from Dose Volume Histograms for each contour and compared.

Results:

Significant changes were observed in the values of D90 and V100 as well as the number of suboptimal plans for expansion or contraction margins of only few millimeters. Evaluation of coverage based on D90 was found to be less sensitive to expansion errors compared to V100. D90 led to a lower number of implants incorrectly identified with insufficient coverage for expanded contours which increases the accuracy of post‐implant QA using CT images compared to V100.

Conclusion:

In order to establish a successful post implant QA for LDR prostate seed brachytherapy, it is necessary to identify the low and high thresholds of important dose metrics of the target volume such as D90 and V100. Since these parameters are sensitive to target volume definition, accurate identification of prostate borders would help to improve accuracy and predictive value of the post‐implant QA process. In this respect, use of imaging modalities such as MRI where prostate is well delineated should prove useful.
SU‐F‐J‐162: Is Bulky Electron Density Assignment Appropriatefor MRI‐Only Based Treatment Planning for Lung Cancer?
Authors: Prior P , Chen X , Johnstone C , Gore E , Li X
Published: July 2016

Purpose:

To assess the appropriateness of bulky electron density assisment for MRI‐only treatment planning for lung cancer via comparing dosimetric difference between MRI‐ and CT‐based plans.

Methods:

Planning 4DCTs acquired for six representative lung cancer patients were used to generate CT‐based IMRT plans. To avoid the effect of anatomic difference between CT and MRI, MRI‐based plans were generated using CTs by forcing the relative electron density (rED) of organ specific values from ICRU report 46 and using the mean rED value of the internal target volume (ITV) of the patient for the ITV. Both CT and “MRI” plans were generated using a research planning system (Monaco, Elekta) employing Monte Carlo dose calculation the following dose‐volume‐parameters (DVPs): D99 – dose delivered to 99% of the ITV/PTV volume; D95; D5; D1; Vpd –volume receiving the prescription dose; V5 – volume of normal lung irradiated > 5 Gy; and V20. The percent point difference and dose difference was used for comparison for Vpd‐V5‐V20 and D99‐D1, respectively. Four additional plans per patient were calculated with rEDITV = 0.6 and 1.0 and rEDlung = 0.1 and 0.5.

Results:

Noticeable differences in the ITV and PTV point doses and DVPs were observed. Variations in Vpd ranged from 0.0–6.4% and 0.32–18.3% for the ITV and PTV, respectively. The ITV and PTV variations in D99, D95, D5 and D1 were 0.15–3.2 Gy. The normal lung V5 & V20 variations were no larger than 1.9%. In some instances, varying the rEDITV between rEDmean, 0.6 and 1.0 resulted in D95 increases ranging from 3.9–6.3%. Uniform rED assignment on normal lung affected DVPs of ITV and PTV by 4.0–9.8% and 0.3–19.6%, respectively.

Conclusion:

The commonly‐used uniform rED assignment in MRI‐only based planning may not be appropriate for lung‐cancer. A voxel based method, e.g. synthetic CT generated from MRI data, is required.

This work was partially funded by Elekta, Inc.
SU‐F‐J‐164: A Simulation Study On Anovel 4D MRI Reconstruction Method Based On Probability‐Driven Sorting
Authors: Liang X , Yin F , Liu Y , Cai J
Published: July 2016

Purpose:

To evaluate a novel probability‐driven sorting based 4D MRI reconstruction method by comparing with the conventional 4D MRI reconstruction methods.

Methods:

We have proposed a novel probability‐driven sorting based 4D MRI reconstruction method capable of retaining breathing variation information in breathing signals by generating multiple breathing cycles instead of a single cycle as the case with conventional 4D MRI reconstruction methods. It is expected that our proposed method can reduce motion artifacts caused by breathing variations, and can generate more accurate Average Intensity Projections (AIP). To evaluate the performance of the novel method, the probability‐driven sorting based method, along with two conventional phase‐based methods, for cine acquisition mode, and sequential acquisition mode, was applied on six patient breathing curves to simulate the 4D MRI reconstruction process using eXtended CArdiac Torso (XCAT) phantom. In the 4D images, a spherical target of 3 cm in diameter was generated in the liver and set to move with the liver. AIPs were generated for all three sets of 4D images. Ground‐truth AIP was generated by averaging all the 3D volumes of the phantom. Motion artifacts were evaluated by the tumor volume consistency in 4D images and volume difference from the tumor volumes measured in 3D images. AIPs from the three sorting methods were evaluated and compared to the reference AIP in terms of intensity difference.

Results:

Probability‐driven sorting has higher target volume consistency between phases for all the six patients, indicating the less motion artifacts. AIP from probability‐driven sorting has the best agreement with the ground‐truth AIP among the three reconstruction methods.

Conclusion:

Based on the cases in this study, it has been shown that probability‐driven sorting method is capable of generating multi‐cycle 4D MRI images with reduced motion artifacts and improved AIP accuracy. 1R21CA165384
SU‐F‐J‐167: Use of MR for Permanent Prostate Implant Preplanning
Authors: Narayana V , Yao B , McLaughlin P
Published: July 2016

Purpose:

To study the feasibility using MR imaging to improve target definition on ultrasound during permanent prostate implants and aid in source strength determination for treatment planning in the OR.

Methods:

Patients who receive permanent prostate implants undergo MR and CT imaging prior to the implant procedure to determine the volume of the prostate, bony restriction to the procedure, bladder extension, external sphincter length and neurovascular bundle. The volume of the prostate is generally used to order seeds for the procedure. In 10 patients, the MR was used as the preplanning study with the PTV defined as a 2 mm expansion of the MR prostate in all directions except the posterior. Various dose volume parameters for the MR prostate and the PTV were compared to the actual preplan developed and executed in the OR. In addition, there parameters were compared to the post implant dosimetry performed 3 weeks after the implant procedure.

Results:

The results show that the number of seeds used using MR and US (ultrasound) planning was generally with 2 seeds and the maximum difference was 7 seeds. There is no significant difference between any of the dose index parameters of V100, V150, V200, D99 and D90 parameters between MR planning, US planning and postimplant evaluation There was a significant difference between planned D99 (avg of 105%) and achieved D99 (avg 91%).

Conclusion:

MR imaging is an invaluable tool to improve target definition for permanent prostate implants. Use of MR images for preplanning improves the confidence with which source can be ordered for the procedure that is OR planned. Ordering a maximum of 10 seeds more than planned would be sufficient to deliver a plan in the OR using US. Moving ahead to non‐rigid registration between MR ad US images could further increase the confidence level of MR planning.
SU‐F‐J‐175: Evaluation of Metal Artifact Reduction Algorithms in Computed Tomography and Their Application to Radiation Therapy Treatment Planning
Authors: Norris H , Rangaraj D , Kim S
Published: July 2016

Purpose:

High‐Z (metal) implants in CT scans cause significant streak‐like artifacts in the reconstructed dataset. This results in both inaccurate CT Hounsfield units for the tissue as well as obscuration of the target and organs at risk (OARs) for radiation therapy planning. Herein we analyze two metal artifact reduction algorithms: GE's Smart MAR and a Metal Deletion Technique (MDT) for geometric and Hounsfield Unit (HU) accuracy.

Methods:

A CT‐to‐electron density phantom, with multiple inserts of various densities and a custom Cerrobend insert (Zeff=76.8), is utilized in this continuing study. The phantom is scanned without metal (baseline) and again with the metal insert. Using one set of projection data, reconstructed CT volumes are created with filtered‐back‐projection (FBP) and the MAR and the MDT algorithms. Regions‐of‐Interest (ROIs) are evaluated for each insert for HU accuracy; the metal insert's Full‐Width‐Half‐Maximum (FWHM) is used to evaluate the geometric accuracy. Streak severity is quantified with an HU error metric over the phantom volume.

Results:

The original FBP reconstruction has a Root‐Mean‐Square‐Error (RMSE) of 57.55 HU (STD=29.19, range=−145.8 to +79.2) compared to baseline. The MAR reconstruction has a RMSE of 20.98 HU (STD=13.92, range=−18.3 to +61.7). The MDT reconstruction has a RMSE of 10.05 HU (STD=10.5, range=−14.8 to +18.6). FWHM for baseline=162.05; FBP=161.84 (−0.13%); MAR=162.36 (+0.19%); MDT=162.99 (+0.58%). Streak severity metric for FBP=19.73 (22.659% bad pixels); MAR=8.743 (9.538% bad); MDT=4.899 (5.303% bad).

Conclusion:

Image quality, in terms of HU accuracy, in the presence of high‐Z metal objects in CT scans is improved by metal artifact reduction reconstruction algorithms. The MDT algorithm had the highest HU value accuracy (RMSE=10.05 HU) and best streak severity metric, but scored the worst in terms of geometric accuracy. Qualitatively, the MAR and MDT algorithms increased detectability of inserts, although there is a loss of in‐plane resolution near the metallic insert.
SU‐F‐J‐182: Investigation of Systems for Improved Accuracy in Clinical Y‐90 Percent Delivered Calculations
Authors: McBeth R , Elder D , Kesner A
Published: July 2016

Purpose:

Y‐90 Selective Internal Radiation Therapy (SIRT) is used to treat liver tumors, and by nature has variability in the percent of the intended dose that is actually delivered. To determine the quality of the administration, pre and post activity measurements are taken, and used to infer percent delivered. Vendor specifications indicate the use of an ion chamber to take these measurements. In our work, we investigated the accuracy of ion chambers, and compared them to other detector systems.

Methods:

We have built phantoms, phantom holders, and protocols, which allow us to measure our Y90 doses with varying apparatuses: a dose calibrator, a Geiger‐counter, an ion chamber, a crystal based thyroid probe, and a gamma camera. We have set up a system that has enabled us to gather data by measuring clinical Y90 doses as they are used in the clinic using all of the instrumental methods. Five initial doses (25 measurements/acquisitions) have been taken at the time of this abstract submission.

Results:

Our initial results show that measurements acquired using scintillation based detectors (thyroid probe and gamma camera) correlate better with the gold standard (i.e. the dose calibrator). Pearson correlations between the dose calibrator measurements and the GM counter, Ion chamber, thyroid probe, and gamma camera were found to be 0.88, 0.83, 0.98, 0.99, respectively. More acquisitions and analysis are planned to determine the precision of the systems, as well as optimal energy window settings.

Conclusion:

It is likely that current standard practice can be improved using scintillation crystal based detectors. Such systems are more sensitive, can integrate signal, and can use energy discrimination. Furthermore, phantoms can be built to integrate with probe and gamma camera systems that are robust and provide reproducibility. Future work will include expanded acquisition and analysis.
SU‐F‐J‐187: The Statistical NTCP and TCP Models in the Proton Therapy
Authors: Jang S , Frometa T , Pyakuryal A , Sio T , Piseaux R , Acosta S , Ocana K
Published: July 2016

Purpose:

The statistical models (SM) are typically used as a subjective description of a population for which there is only limited sample data, and especially in cases where the relationship between variables is known. The normal tissue complications and tumor control are frequently stochastic effects in the Radiotherapy (RT). Based on probabilistic treatments, it recently has been formulated new NTCP and TCP models for the RT. Investigating the particular requirements for their clinical use in the proton therapy (PT) is the goal of this work.

Methods:

The SM can be used as phenomenological or mechanistic models. The former way allows fitting real data and getting theirparameters. In the latter one, we should do efforts for determining the parameters through the acceptable estimations, measurements, and/or simulation experiments. Experimental methodologies for determination of the parameters have been developed from the fraction cells surviving the proton irradiation curves in tumor and OAR, and precise RBE models are used for calculating the variable of effective dose. As the executions of these methodologies have a high costs, so we have developed computer tools enable to perform simulation experiments as complement to limitations of the real ones.

Results:

The requirements for the use of the SM in the PT, such as validation and improvement of the elaborated and existent methodologies for determining the SM parameters and effective dose respectively, were determined.

Conclusion:

The SM realistically simulates the main processes in the PT, and for this reason these can be implemented in this therapy, which are simples, computable and they have other advantages over some current models. It has been determined some negative aspects for some currently used probabilistic models in the RT, like the LKB NTCP and others derived from logistic functions; which can be improved with the proposed methods in this study.
SU‐F‐J‐191: Dosimetric Evaluation of a Left Chestwall Patient Treated with a Compact Proton Pencil Beam Gantry Utilizing Daily Setup CBCT
Authors: Maynard M , Chen K , Rosen L , Wu H
Published: July 2016

Purpose:

To evaluate the robustness of the gradient technique for treating a multi‐isocenter left chest wall patient with a compact proton pencil beam gantry. Both CBCT and stereoscopic imaging are used to facilitate daily treatment setup.

Methods:

To treat the elongated chest wall planning target volume (PTV) with the compact PBS system, a 28 fraction (5040 CcGE) treatment plan was created using two fields with gradient matching technique. Daily table shifts between treatment field isocenters were obtained from the record and verify system for each treatment fraction. Copies of the initial treatment plan were made for each fraction and the field isocenter coordinates for each plan copy were adjusted to reflect daily table shifts. Doses were re‐calculated for each fraction, summed, and compared against the initial plan.

Results:

The table shifts (average and range) were 2.2 (−5.1–+3.9), 3.0 (−6.0–+4.0) and 3.0 (−10.1–+1.9) millimeters in the anterior‐posterior, superior‐inferior and right‐left directions, respectively. Dose difference to the PTV, heart and ipsilateral lung were evaluated. The percentage of the PTV receiving the prescription dose decreased from 94.6% to 89.1%. The D95 of the PTV increased from 99.6% to 99.9%. The maximum dose in PTV increased from 106.6% to 109.2% and V105 increased from 1.0% to 16.5%. The V20 of the ipsilateral lung increased from 18.5% to 21.0%. The mean heart dose difference was negligible.

Conclusion:

Observed dose differences to lung and heart tissues due to daily setup variations remained acceptably low while maintaining sufficient dose coverage to the PTV. This initial case study demonstrates the robustness of the gradient technique to treat a large target, multi‐isocenter plan with a compact proton pencil beam gantry equipped with CBCT and stereoscopic imaging modalities.
SU‐F‐J‐198: A Cross‐Platform Adaptation of An a Priori Scatter Correction Algorithm for Cone‐Beam Projections to Enable Image‐ and Dose‐Guided Proton Therapy
Authors: Andersen A , Park Y , Casares‐Magaz O , Elstroem U , Petersen J , Winey B , Muren L
Published: July 2016

Purpose:

Cone‐beam CT (CBCT) imaging may enable image‐ and dose‐guided proton therapy, but is challenged by image artefacts. The aim of this study was to demonstrate the general applicability of a previously developed a priori scatter correction algorithm to allow CBCT‐based proton dose calculations.

Methods:

The a priori scatter correction algorithm used a plan CT (pCT) and raw cone‐beam projections acquired with the Varian On‐Board Imager. The projections were initially corrected for bow‐tie filtering and beam hardening and subsequently reconstructed using the Feldkamp‐Davis‐Kress algorithm (rawCBCT). The rawCBCTs were intensity normalised before a rigid and deformable registration were applied on the pCTs to the rawCBCTs. The resulting images were forward projected onto the same angles as the raw CB projections. The two projections were subtracted from each other, Gaussian and median filtered, and then subtracted from the raw projections and finally reconstructed to the scatter‐corrected CBCTs. For evaluation, water equivalent path length (WEPL) maps (from anterior to posterior) were calculated on different reconstructions of three data sets (CB projections and pCT) of three parts of an Alderson phantom. Finally, single beam spot scanning proton plans (0–360 deg gantry angle in steps of 5 deg; using PyTRiP) treating a 5 cm central spherical target in the pCT were re‐calculated on scatter‐corrected CBCTs with identical targets.

Results:

The scatter‐corrected CBCTs resulted in sub‐mm mean WEPL differences relative to the rigid registration of the pCT for all three data sets. These differences were considerably smaller than what was achieved with the regular Varian CBCT reconstruction algorithm (1–9 mm mean WEPL differences). Target coverage in the re‐calculated plans was generally improved using the scatter‐corrected CBCTs compared to the Varian CBCT reconstruction.

Conclusion:

We have demonstrated the general applicability of a priori CBCT scatter correction, potentially opening for CBCT‐based image/dose‐guided proton therapy, including adaptive strategies.

Research agreement with Varian Medical Systems, not connected to the present project.
SU‐F‐J‐201: Validation Study of Proton Radiography Against CT Data for Quantitative Imaging of Anatomical Changes in Head and Neck Patients
Authors: Hammi A , Weber D , Lomax A
Published: July 2016

Purpose:

In clinical pencil‐beam‐scanned (PBS) proton therapy, the advantage of the characteristic sharp dose fall‐off after the Bragg Peak (BP) becomes a disadvantage if the BP positions of a plan's constituent pencil beams are shifted, eg.due to anatomical changes. Thus, for fractionated PBS proton therapy, accurate knowledge of the water equivalent path length (WEPL) of the traversed anatomy is critical. In this work we investigate the feasibility of using 2D proton range maps (proton radiography, PR) with the active‐scanning gantry at PSI.

Methods:

We simulated our approach using Monte Carlo methods (MC) to simulate proton beam interactions in patients using clinical imaging data. We selected six head and neck cases having significant anatomical changes detected in per‐treatment CTs.PRs (two at 0°/90°) were generated from MC simulations of low‐dose pencil beams at 230MeV. Each beam's residual depth‐dose was propagated through the patient geometry (from CT) and detected on exiting the patient anatomy in an ideal depth‐resolved detector (eg. range telescope). Firstly, to validate the technique, proton radiographs were compared to the ground truth, which was the WEPL from ray‐tracing in the patient CT at the pencil beam location. Secondly, WEPL difference maps (per‐treatment – planning imaging timepoints) were then generated to locate the anatomical changes, both in the CT (ground truth) and in the PRs. Binomial classification was performed to evaluate the efficacy of the technique relative to CT.

Results:

Over the projections simulated over all six patients, 70%, 79% and 95% of the grid points agreed with the ground truth proton range to within ±0.5%, ±1%, and ±3% respectively. The sensitivity, specificity, precision and accuracy were high (mean±1σ, 83±8%, 87±13%, 95±10%, 83±7% respectively).

Conclusion:

We show that proton‐based radiographic images can accurately monitor patient positioning and in vivo range verification, while providing equivalent WEPL information to a CT scan, with the advantage of a much lower imaging dose.
SU‐F‐T‐54: Determination of the AAPM TG‐43 Brachytherapy Dosimetry Parameters for A New Titanium‐Encapsulated Yb‐169 Source by Monte Carlo Calculations
Authors: Reynoso F , Munro J , Cho S
Published: July 2016

Purpose:

To determine the AAPM TG‐43 brachytherapy dosimetry parameters of a new titanium‐encapsulated Yb‐169 source designed to maximize the dose enhancement during gold nanoparticle‐aided radiation therapy (GNRT).

Methods:

An existing Monte Carlo (MC) model of the titanium‐encapsulated Yb‐169 source, which was described in the current investigators’ published MC optimization study, was modified based on the source manufacturer's detailed specifications, resulting in an accurate model of the titanium‐encapsulated Yb‐169 source that was actually manufactured. MC calculations were then performed using the MCNP5 code system and the modified source model, in order to obtain a complete set of the AAPM TG‐43 parameters for the new Yb‐169 source.

Results:

The MC‐calculated dose rate constant for the new titanium‐encapsulated Yb‐169 source was 1.05 ± 0.03 cGy per hr U, indicating about 10% decrease from the values reported for the conventional stainless steel‐encapsulated Yb‐169 sources. The source anisotropy and radial dose function for the new source were found similar to those reported for the conventional Yb‐169 sources.

Conclusion:

In this study, the AAPM TG‐43 brachytherapy dosimetry parameters of a new titanium‐encapsulated Yb‐169 source were determined by MC calculations. The current results suggested that the use of titanium, instead of stainless steel, to encapsulate the Yb‐169 core would not lead to any major change in the dosimetric characteristics of the Yb‐169 source, while it would allow more low energy photons being transmitted through the source filter thereby leading to an increased dose enhancement during GNRT. Supported by DOD/PCRP grant W81XWH‐12‐1‐0198

This investigation was supported by DOD/PCRP grant W81XWH‐12‐1‐ 0198.
SU‐F‐T‐57: Delivered Activity Accuracy of Radium 223 Dichloride Injections, When Being Administrated for Castration Resistant Prostate Cancer, Symptomatic Bone Metastases. The Impact of Residual Activity in the Spent Syringe and Dispensing Accuracy of Ra 223
Authors: Jennings G
Published: July 2016

Purpose:

To quantify the delivered activity accuracy of Radium 223 dichloride injections, when being administrated for castration – resistant prostate cancer, symptomatic bone metastases. The impact of residual activity in the spent syringe and dispensing accuracy of Ra 223.

Methods:

The administration is by slow intravenous injection over 1 minute followed by double flushing of the 10 mL syringe and IV with saline. Eighty (80) procedures was used to investigate variations in the activity from the amount prescribed (µCi) = 1.35 × Patient weight Kg. The Activity dispensed into a 10mL syringe using a NIST traceable Capintec CRC‐25R Chamber and a cross calibrated capintec CRC‐15R to measure activity in the syringe immediately before and after administration

Results:

The patients weight range from 121Ib to 235lb and doses ranging 74.25 µCi to 144.2 µCi. The deviation of dispensed dose vs Prescribed dose average +2.1% with a range of −1.1% to +5.7%. The Dose measured before administration ranges 79.3 µCi to 154.9 µCi. Deviation from the dispensed dose was show to average +2.9% with a range of −0.8% to +7.3%. The average residual dose post injection was 2.5 µCi or 2.2% of the pre injection activity. Ranging from 0.9 µCi to 6.2 µCi, 0.7% to 5.4% respectively. Subtracting the residual activity from that measured activity before injection and comparing it to prescription dose was shown to have an average variation of +2.7% with a range of −0.8% to 7.4%.

Conclusion:

The case resulted in the 6.2 µCi maximum residual dose had two syringes. A small, 82.8 µCi activity, case resulted in the 7.4% maximum variation in measures less residual verses prescription dose. The average +2.1 % dispenses activity of Ra 223 over the prescription dosage was seen to counteract the average 2.2% residual dosage found to remain in the syringe