bluuebunny/crossref_metadata_2025 huggingface dataset:
TH‐C‐12A‐02: Comparison of Two RapidArc Delivery Strategies in Stereotactic Body Radiotherapy of Stage I and II Peripheral Lung Tumors with Unflattened Beams
Authors: Huang B , Lu J , Lin P , Chen J , Kuang Y , Chen C
Published: July 2014

Purpose:

The full arcs strategy used in SBRT with RapidArc and unflattened (FFF) beams in large and heterogeneous peripheral non‐smallcell lung cancer (NSCLC) appears to be suboptimal as it increases the disadvantageous dose to the contralateral lung, which potentially increases the toxicity to surrounding tissues. In this study, we investigated, for the first time, the dose delivery strategies using partial arcs (PA) and the fully rotational arcs with avoidance sectors (FAAS) for SBRT with FFF beams in peripheral NSCLC patients.

Methods:

Eighteen patients with NSCLC (stage I and II) were selected for this study. Nine patients with a GTV <= 10cc were designated as the small tumor group. The remaining nine patients with a GTV between 10 cc and 44 cc were assigned to the large tumor group. The treatment plans were generated in eighteen patients using PA and FAAS, respectively, and delivered with a Varian TrueBeam Linac. Dosimetry of the target and organs at risk (OAR), total MU, out‐of‐field dose, and delivery time were analyzed. Delta4 and Portal dosimetry were employed to evaluate the delivery accuracy.

Results:

or the small tumor group, the FAAS plans significantly achieved a better conformity index, the lower total MU and out‐of‐field dose, a shorter treatment time, and the reduced doses to cord, heart, and lung (p < 0.05). But the target doses were slightly higher than that delivered by PA plans. For the large tumor group, the PA plans significantly attained a better conformity index and a shorter treatment time (p < 0.05). Furthermore, all plans achieved a high pass rate, with all the gamma indices greater than 97% at the Г3mm, 3% threshold.

Conclusion:

This study suggests that FAAS strategy is more beneficial for small tumor patients undergoing lung SBRT with FFF beams. However, for large tumor patients, PA strategy is recommended.

NIH/NIGMS grant U54 GM104944, Lincy Endowed Assistant Professorship
TH‐C‐12A‐04: Dosimetric Evaluation of a Modulated Arc Technique for Total Body Irradiation
Authors: Tsiamas P , Czerminska M , Makrigiorgos G , Karen M , Zygmanski P
Published: July 2014

Purpose:

A simplified Total Body Irradiation (TBI) was developed to work with minimal requirements in a compact linac room without custom motorized TBI couch. Results were compared to our existing fixed‐gantry double 4 MV linac TBI system with prone patient and simultaneous AP/PA irradiation.

Methods:

Modulated arc irradiates patient positioned in prone/supine positions along the craniocaudal axis. A simplified inverse planning method developed to optimize dose rate as a function of gantry angle for various patient sizes without the need of graphical 3D treatment planning system. This method can be easily adapted and used with minimal resources. Fixed maximum field size (40×40 cm2) is used to decrease radiation delivery time. Dose rate as a function of gantry angle is optimized to result in uniform dose inside rectangular phantoms of various sizes and a custom VMAT DICOM plans were generated using a DICOM editor tool. Monte Carlo simulations, film and ionization chamber dosimetry for various setups were used to derive and test an extended SSD beam model based on PDD/OAR profiles for Varian 6EX/ TX. Measurements were obtained using solid water phantoms. Dose rate modulation function was determined for various size patients (100cm − 200cm). Depending on the size of the patient arc range varied from 100° to 120°.

Results:

A PDD/OAR based beam model for modulated arc TBI therapy was developed. Lateral dose profiles produced were similar to profiles of our existing TBI facility. Calculated delivery time and full arc depended on the size of the patient (∼8min/ 100° − 10min/ 120°, 100 cGy). Dose heterogeneity varied by about ±5% − ±10% depending on the patient size and distance to the surface (buildup region).

Conclusion:

TBI using simplified modulated arc along craniocaudal axis of different size patients positioned on the floor can be achieved without graphical / inverse 3D planning.
TH‐C‐12A‐05: Dynamic Couch Motion for Improvement of Radiation Therapy Trajectories in DCA and VMAT
Authors: MacDonald L , Thomas Christopher
Published: July 2014

Purpose:

To investigate the potential improvement in dosimetric external beam radiation therapy plan quality using an optimized dynamic gantry and couch motion trajectory which minimizes exposure to the organs at risk.

Methods:

Patient‐specific anatomical information of head‐and‐neck and cranial cancer patients was used to quantify the geometric overlap between target volumes and organs‐at‐risk (OARs) based on their two‐dimensional projection from source to a plane at isocentre as a function of gantry and couch angle. QUANTEC dose constraints were then used as weighting factors for the OARs to generate a map of couch‐gantry coordinate space indicating degree of overlap at each point in space. A couch‐gantry collision space was generated by direct measurement on a Varian Truebeam linac using an anthropomorphic solid‐water phantom. A dynamic, fully customizable algorithm was written to generate a navigable ideal trajectory for the patient specific couch‐gantry space. The advanced algorithm includes weighting factors which can be used to balance the implementation of absolute minimum values of overlap, with the clinical practicality of largescale couch motion and delivery time. Optimized trajectories were calculated for cranial DCA treatments and for head‐and‐neck VMAT treatments and compared to conventional DCA and VMAT treatment trajectories.

Results:

Comparison of optimized treatment trajectories with conventional treatment trajectories indicates a decrease in dose to the organs‐at‐risk between 4.64% and 6.82% (2.39 and 3.52 Gy) of the prescription dose per patient per organ at risk.

Conclusion:

Using simultaneous couch and gantry motion during radiation therapy to minimize the geometrical overlap in the beams‐eye‐view target volumes and the organs‐at‐risk can have an appreciable dose reduction to organs‐at‐risk.
TH‐C‐12A‐07: Implementation of a Pulsed Low Dose Date Radiotherapy (PLRT) Protocol for Recurrent Cancers Using Advanced Beam Delivery
Authors: Ma C , Lin M , Chen L , Price R , Li J , Kang S , Wang P , Lang J
Published: July 2014

Purpose:

Recent in vitro and in vivo experimental findings provided strong evidence that pulsed low‐dose‐rate radiotherapy (PLDR) produced equivalent tumor control as conventional radiotherapy with significantly reduced normal tissue toxicities. This work aimed to implement a PLDR clinical protocol for the management of recurrent cancers utilizing IMRT and VMAT.

Methods:

Our PLDR protocol requires that the daily 2Gy dose be delivered in 0.2Gy×10 pulses with a 3min interval between the pulses. To take advantage of low‐dose hyper‐radiosensitivity the mean dose to the target is set at 0.2Gy and the maximum dose is limited to 0.4Gy per pulse. Practical planning strategies were developed for IMRT and VMAT: (1) set 10 ports for IMRT and 10 arcs for VMAT with each angle/arc as a pulse; (2) set the mean dose (0.2Gy) and maximum dose (0.4Gy) to the target per pulse as hard constraints (no constraints to OARs); (3) select optimal port/arc angles to avoid OARs; and (4) use reference structures in or around target/OARs to reduce maximum dose to the target/OARs. IMRT, VMAT and 3DCRT plans were generated for 60 H&N, breast, lung, pancreas and prostate patients and compared.

Results:

All PLDR treatment plans using IMRT and VMAT met the dosimetry requirements of the PLDR protocol (mean target dose: 0.20Gy±0.01Gy; maximum target dose < 0.4Gy). In comparison with 3DCRT, IMRT and VMAT exhibited improved target dose conformity and OAR dose sparing. A single arc can minimize the difference in the target dose due to multi‐angle incidence although the delivery time is longer than 3DCRT and IMRT.

Conclusion:

IMRT and VMAT are better modalities for PLDR treatment of recurrent cancers with superior target dose conformity and critical structure sparing. The planning strategies/guidelines developed in this work are practical for IMRT/VMAT treatment planning to meet the dosimetry requirements of the PLDR protocol.
TH‐C‐12A‐09: Planning and Delivery of the Fully Dynamic Trajectory Modulated Arc Therapy: Application to Accelerated Partial Breast Irradiation
Authors: Liang J , Atwood T , Fahimian B , Chin E , Otto K , Hristov D
Published: July 2014

Purpose:

A novel trajectory modulated arc therapy (TMAT) system was developed that uses source motion trajectory involving synchronized gantry rotation with translational and rotational couch movement. MLC motion and dose rate were fully optimized for dynamic beam delivery. This work presents a platform for planning deliverable TMAT on a collision free coronal trajectory and evaluates its benefit for accelerated partial breast irradiation (APBI) in a prone position.

Methods:

The TMAT algorithm was built on VMAT with modifications (physical properties on couch movement were defined) and enhancements (pencil beam dose calculation engine to support extended SSDs) to make it feasible for TMAT delivery. A Matlab software environment for TMAT optimization and dose calculation was created to allow any user specified motion axis. TMAT delivery was implemented on Varian TrueBeamTM STx via XML scripts. 10 prone breast irradiation cases were evaluated in VMAT and compared with a 6‐ field non‐coplanar IMRT plan. Patient selection/exclusion criteria and structure contouring followed the guidelines of NSABP B‐39/RTOG 0413 protocol.

Results:

TMAT delivery time was ∼4.5 minutes. 251.5°±7.88° of non‐isocentric couch arc was achieved by the optimized trajectory with 180– 210 control points at 1°–2° couch increments. The improved dose distribution by TMAT was most clearly observed by the marked reduction in the volume of irradiated normal breast tissue in the high dose region. The ratios of the normal breast tissue volume receiving more than 50%, 80% and 100% of the prescription dose for TMAT versus IMRT were: V50%(TMAT/IMRT) = 78.38%±13.03%, V80%(TMAT/IMRT) = 44.19%±9.04% and V100% (TMAT/IMRT) = 9.96%±7.55%, all p≤0.01.

Conclusion:

The study is the first demonstration of planning and delivery implementation of a fully dynamic APBI TMAT system with continuous couch motion. TMAT achieved significantly improved dosimetry over noncoplanar IMRT on dose volume parameters correlated with toxicity and cosmetic outcome of APBI.

This project was supported by Varian Research Grant.
TH‐C‐12A‐10: Surface Dose Enhancement Using Novel Hybrid Electron and Photon Low‐Z Therapy Beams: Monte Carlo Simulation
Authors: Parsons C , Parsons D , Robar J , Kelly R
Published: July 2014

Purpose:

The introduction of the TrueBeam linac platform provides access to an in‐air target assembly making it possible to apply novel treatments using multiple target designs. One such novel treatment uses multiple low‐Z targets to enhance surface dose replacing the use of synthetic tissue equivalent material (bolus). This treatment technique will decrease the common dosimetric and set up errors prevalent in using physical treatment accessories like bolus. The groundwork for a novel treatment beam used to enhance surface dose to within 80‐100% of the dose at dmax by utilizing low‐Z (Carbon) targets of various percent CSDA range thickness operated at 2.5–4 MeV used in conjunction with a clinical 6 MV beam is presented herein.

Methods:

A standard Monte Carlo model of a Varian Clinac accelerator was developed to manufacturers specifications. Simulations were performed using Be, C, AL, and C, as potential low‐Z targets, placed in the secondary target position. The results determined C to be the target material of choice. Simulations of 15, 30 and 60% CSDA range C beams were propagated through slab phantoms. The resulting PDDs were weighted and combined with a standard 6 MV treatment beam. Versions of the experimental targets were installed into a 2100C Clinac and the models were validated.

Results:

Carbon was shown to be the low‐Z material of choice for this project. Using combinations of 15, 30, 60% CSDA beams operated at 2.5 and 4 MeV in combination with a standard 6 MV treatment beam the surface dose was shown to be enhanced to within 80–100% the dose at dmax.

Conclusion:

The modeled low‐Z beams were successfully validated using machined versions of the targets. Water phantom measurements and slab phantom simulations show excellent correlation. Patient simulations are now underway to compare the use of bolus with the proposed novel beams.

NSERC
TH‐E‐BRE‐02: A Forward Scattering Approximation to Dose Calculation Using the Linear Boltzmann Transport Equation
Authors: Catt B , Snyder M
Published: July 2014

Purpose:

To investigate the use of the linear Boltzmann transport equation as a dose calculation tool which can account for interface effects, while still having faster computation times than Monte Carlo methods. In particular, we introduce a forward scattering approximation, in hopes of improving calculation time without a significant hindrance to accuracy.

Methods:

Two coupled Boltzmann transport equations were constructed, one representing the fluence of photons within the medium, and the other, the fluence of electrons. We neglect the scattering term within the electron transport equation, resulting in an extreme forward scattering approximation to reduce computational complexity. These equations were then solved using a numerical technique for solving partial differential equations, known as a finite difference scheme, where the fluence at each discrete point in space is calculated based on the fluence at the previous point in the particle's path. Using this scheme, it is possible to develop a solution to the Boltzmann transport equations by beginning with boundary conditions and iterating across the entire medium. The fluence of electrons can then be used to find the dose at any point within the medium.

Results:

Comparisons with Monte Carlo simulations indicate that even simplistic techniques for solving the linear Boltzmann transport equation yield expected interface effects, which many popular dose calculation algorithms are not capable of predicting. Implementation of a forward scattering approximation does not appear to drastically reduce the accuracy of this algorithm.

Conclusion:

Optimized implementations of this algorithm have been shown to be very accurate when compared with Monte Carlo simulations, even in build up regions where many models fail. Use of a forward scattering approximation could potentially give a reasonably accurate dose distribution in a shorter amount of time for situations where a completely accurate dose distribution is not required, such as in certain optimization algorithms.
TH‐E‐BRE‐03: A Novel Method to Account for Ion Chamber Volume Averaging Effect in a Commercial Treatment Planning System Through Convolution
Authors: Barraclough B , Li J , Liu C , Yan G
Published: July 2014

Purpose:

Fourier‐based deconvolution approaches used to eliminate ion chamber volume averaging effect (VAE) suffer from measurement noise. This work aims to investigate a novel method to account for ion chamber VAE through convolution in a commercial treatment planning system (TPS).

Methods:

Beam profiles of various field sizes and depths of an Elekta Synergy were collected with a finite size ion chamber (CC13) to derive a clinically acceptable beam model for a commercial TPS (Pinnacle3), following the vendor‐recommended modeling process. The TPS‐calculated profiles were then externally convolved with a Gaussian function representing the chamber (σ = chamber radius). The agreement between the convolved profiles and measured profiles was evaluated with a one dimensional Gamma analysis (1%/1mm) as an objective function for optimization. TPS beam model parameters for focal and extra‐focal sources were optimized and loaded back into the TPS for new calculation. This process was repeated until the objective function converged using a Simplex optimization method. Planar dose of 30 IMRT beams were calculated with both the clinical and the re‐optimized beam models and compared with MapCHEC™ measurements to evaluate the new beam model.

Results:

After re‐optimization, the two orthogonal source sizes for the focal source reduced from 0.20/0.16 cm to 0.01/0.01 cm, which were the minimal allowed values in Pinnacle. No significant change in the parameters for the extra‐focal source was observed. With the re‐optimized beam model, average Gamma passing rate for the 30 IMRT beams increased from 92.1% to 99.5% with a 3%/3mm criterion and from 82.6% to 97.2% with a 2%/2mm criterion.

Conclusion:

We proposed a novel method to account for ion chamber VAE in a commercial TPS through convolution. The reoptimized beam model, with VAE accounted for through a reliable and easy‐to‐implement convolution and optimization approach, outperforms the original beam model in standard IMRT QA verification.
TH‐E‐BRE‐04: An Online Replanning Algorithm for VMAT
Authors: Ahunbay E , Moreau M , Li X
Published: July 2014

Purpose:

To develop a fast replanning algorithm based on segment aperture morphing (SAM) for online replanning of volumetric modulated arc therapy (VMAT) with flattening filtered (FF) and flattening filter free (FFF) beams.

Methods:

A software tool was developed to interface with a VMAT planning system ((Monaco, Elekta), enabling the output of detailed beam/machine parameters of original VMAT plans generated based on planning CTs for FF or FFF beams. A SAM algorithm, previously developed for fixed‐beam IMRT, was modified to allow the algorithm to correct for interfractional variations (e.g., setup error, organ motion and deformation) by morphing apertures based on the geometric relationship between the beam's eye view of the anatomy from the planning CT and that from the daily CT for each control point. The algorithm was tested using daily CTs acquired using an in‐room CT during daily IGRT for representative prostate cancer cases along with their planning CTs. The algorithm allows for restricted MLC leaf travel distance between control points of the VMAT delivery to prevent SAM from increasing leaf travel, and therefore treatment delivery time.

Results:

The VMAT plans adapted to the daily CT by SAM were found to improve the dosimetry relative to the IGRT repositioning plans for both FF and FFF beams. For the adaptive plans, the changes in leaf travel distance between control points were < 1cm for 80% of the control points with no restriction. When restricted to the original plans' maximum travel distance, the dosimetric effect was minimal. The adaptive plans were delivered successfully with similar delivery times as the original plans. The execution of the SAM algorithm was < 10 seconds.

Conclusion:

The SAM algorithm can quickly generate deliverable online‐adaptive VMAT plans based on the anatomy of the day for both FF and FFF beams.
TH‐E‐BRE‐07: Development of Dose Calculation Error Predictors for a Widely Implemented Clinical Algorithm
Authors: Egan A , Laub W
Published: July 2014

Purpose:

Several shortcomings of the current implementation of the analytic anisotropic algorithm (AAA) may lead to dose calculation errors in highly modulated treatments delivered to highly heterogeneous geometries. Here we introduce a set of dosimetric error predictors that can be applied to a clinical treatment plan and patient geometry in order to identify high risk plans. Once a problematic plan is identified, the treatment can be recalculated with more accurate algorithm in order to better assess its viability.

Methods:

Here we focus on three distinct sources dosimetric error in the AAA algorithm. First, due to a combination of discrepancies in smallfield beam modeling as well as volume averaging effects, dose calculated through small MLC apertures can be underestimated, while that behind small MLC blocks can overestimated. Second, due the rectilinear scaling of the Monte Carlo generated pencil beam kernel, energy is not properly transported through heterogeneities near, but not impeding, the central axis of the beamlet. And third, AAA overestimates dose in regions very low density (< 0.2 g/cm3). We have developed an algorithm to detect the location and magnitude of each scenario within the patient geometry, namely the field‐size index (FSI), the heterogeneous scatter index (HSI), and the lowdensity index (LDI) respectively.

Results:

Error indices successfully identify deviations between AAA and Monte Carlo dose distributions in simple phantom geometries. Algorithms are currently implemented in the MATLAB computing environment and are able to run on a typical RapidArc head & neck geometry in less than an hour.

Conclusion:

Because these error indices successfully identify each type of error in contrived cases, with sufficient benchmarking, this method can be developed into a clinical tool that may be able to help estimate AAA dose calculation errors and when it might be advisable to use Monte Carlo calculations.
TH‐E‐BRE‐09: TrueBeam Monte Carlo Absolute Dose Calculations Using Monitor Chamber Backscatter Simulations and Linac‐Logged Target Current
Authors: A Popescu I , Lobo J , Sawkey D , Svatos M
Published: July 2014

Purpose:

To simulate and measure radiation backscattered into the monitor chamber of a TrueBeam linac; establish a rigorous framework for absolute dose calculations for TrueBeam Monte Carlo (MC) simulations through a novel approach, taking into account the backscattered radiation and the actual machine output during beam delivery; improve agreement between measured and simulated relative output factors.

Methods:

The ‘monitor backscatter factor’ is an essential ingredient of a well‐established MC absolute dose formalism (the MC equivalent of the TG‐51 protocol). This quantity was determined for the 6 MV, 6X FFF, and 10X FFF beams by two independent Methods: (1) MC simulations in the monitor chamber of the TrueBeam linac; (2) linac‐generated beam record data for target current, logged for each beam delivery. Upper head MC simulations used a freelyavailable manufacturer‐provided interface to a cloud‐based platform, allowing use of the same head model as that used to generate the publicly‐available TrueBeam phase spaces, without revealing the upper head design. The MC absolute dose formalism was expanded to allow direct use of target current data.

Results:

The relation between backscatter, number of electrons incident on the target for one monitor unit, and MC absolute dose was analyzed for open fields, as well as a jaw‐tracking VMAT plan. The agreement between the two methods was better than 0.15%. It was demonstrated that the agreement between measured and simulated relative output factors improves across all field sizes when backscatter is taken into account.

Conclusion:

For the first time, simulated monitor chamber dose and measured target current for an actual TrueBeam linac were incorporated in the MC absolute dose formalism. In conjunction with the use of MC inputs generated from post‐delivery trajectory‐log files, the present method allows accurate MC dose calculations, without resorting to any of the simplifying assumptions previously made in the TrueBeam MC literature. This work has been partially funded by Varian Medical Systems.
TH‐E‐BRF‐02: 4D‐CT Ventilation Image‐Based IMRT Plans Are Dosimetrically Comparable to SPECT Ventilation Image‐Based Plans
Authors: Kida S , Bal M , Kabus S , Loo B , Keall P , Yamamoto T
Published: July 2014

Purpose:

An emerging lung ventilation imaging method based on 4D‐CT can be used in radiotherapy to selectively avoid irradiating highly‐functional lung regions, which may reduce pulmonary toxicity. Efforts to validate 4DCT ventilation imaging have been focused on comparison with other imaging modalities including SPECT and xenon CT. The purpose of this study was to compare 4D‐CT ventilation image‐based functional IMRT plans with SPECT ventilation image‐based plans as reference.

Methods:

4D‐CT and SPECT ventilation scans were acquired for five thoracic cancer patients in an IRB‐approved prospective clinical trial. The ventilation images were created by quantitative analysis of regional volume changes (a surrogate for ventilation) using deformable image registration of the 4D‐CT images. A pair of 4D‐CT ventilation and SPECT ventilation image‐based IMRT plans was created for each patient. Regional ventilation information was incorporated into lung dose‐volume objectives for IMRT optimization by assigning different weights on a voxel‐by‐voxel basis. The objectives and constraints of the other structures in the plan were kept identical. The differences in the dose‐volume metrics have been evaluated and tested by a paired t‐test. SPECT ventilation was used to calculate the lung functional dose‐volume metrics (i.e., mean dose, V20 and effective dose) for both 4D‐CT ventilation image‐based and SPECT ventilation image‐based plans.

Results:

Overall there were no statistically significant differences in any dose‐volume metrics between the 4D‐CT and SPECT ventilation imagebased plans. For example, the average functional mean lung dose of the 4D‐CT plans was 26.1±9.15 (Gy), which was comparable to 25.2±8.60 (Gy) of the SPECT plans (p = 0.89). For other critical organs and PTV, nonsignificant differences were found as well.

Conclusion:

This study has demonstrated that 4D‐CT ventilation image‐based functional IMRT plans are dosimetrically comparable to SPECT ventilation image‐based plans, providing evidence to use 4D‐CT ventilation imaging for clinical applications.

Supported in part by Free to Breathe Young Investigator Research Grant and NIH/NCI R01 CA 093626. The authors thank Philips Radiation Oncology Systems for the Pinnacle3 treatment planning systems
TH‐E‐BRF‐04: Characterizing the Response of Texture‐Based CT Image Features for Quantification of Radiation‐Induced Normal Lung Damage
Authors: Krafft S , Court L , Briere T , Martel M
Published: July 2014

Purpose:

Radiation induced lung damage (RILD) is an important dose‐limiting toxicity for patients treated with radiation therapy. Scoring systems for RILD are subjective and limit our ability to find robust predictors of toxicity. We investigate the dose and time‐related response for texture‐based lung CT image features that serve as potential quantitative measures of RILD.

Methods:

Pre‐ and post‐RT diagnostic imaging studies were collected for retrospective analysis of 21 patients treated with photon or proton radiotherapy for NSCLC. Total lung and selected isodose contours (0–5, 5–15, 15–25Gy, etc.) were deformably registered from the treatment planning scan to the pre‐RT and available follow‐up CT studies for each patient. A CT image analysis framework was utilized to extract 3698 unique texture‐based features (including co‐occurrence and run length matrices) for each region of interest defined by the isodose contours and the total lung volume. Linear mixed models were fit to determine the relationship between feature change (relative to pre‐RT), planned dose and time post‐RT.

Results:

Seventy‐three follow‐up CT scans from 21 patients (median: 3 scans/patient) were analyzed to describe CT image feature change. At the p=0.05 level, dose affected feature change in 2706 (73.1%) of the available features. Similarly, time affected feature change in 408 (11.0%) of the available features. Both dose and time were significant predictors of feature change in a total of 231 (6.2%) of the extracted image features.

Conclusion:

Characterizing the dose and time‐related response of a large number of texture‐based CT image features is the first step toward identifying objective measures of lung toxicity necessary for assessment and prediction of RILD. There is evidence that numerous features are sensitive to both the radiation dose and time after RT. Beyond characterizing feature response, further investigation is warranted to determine the utility of these features as surrogates of clinically significant lung injury.
TH‐E‐BRF‐05: Comparison of Survival‐Time Prediction Models After Radiotherapy for High‐Grade Glioma Patients Based On Clinical and DVH Features
Authors: Magome T , Haga A , Igaki H , Sekiya N , Masutani Y , Sakumi A , Mukasa A , Nakagawa K
Published: July 2014

Purpose:

Although many outcome prediction models based on dose‐volume information have been proposed, it is well known that the prognosis may be affected also by multiple clinical factors. The purpose of this study is to predict the survival time after radiotherapy for high‐grade glioma patients based on features including clinical and dose‐volume histogram (DVH) information.

Methods:

A total of 35 patients with high‐grade glioma (oligodendroglioma: 2, anaplastic astrocytoma: 3, glioblastoma: 30) were selected in this study. All patients were treated with prescribed dose of 30–80 Gy after surgical resection or biopsy from 2006 to 2013 at The University of Tokyo Hospital. All cases were randomly separated into training dataset (30 cases) and test dataset (5 cases). The survival time after radiotherapy was predicted based on a multiple linear regression analysis and artificial neural network (ANN) by using 204 candidate features. The candidate features included the 12 clinical features (tumor location, extent of surgical resection, treatment duration of radiotherapy, etc.), and the 192 DVH features (maximum dose, minimum dose, D95, V60, etc.). The effective features for the prediction were selected according to a step‐wise method by using 30 training cases. The prediction accuracy was evaluated by a coefficient of determination (R2) between the predicted and actual survival time for the training and test dataset.

Results:

In the multiple regression analysis, the value of R2 between the predicted and actual survival time was 0.460 for the training dataset and 0.375 for the test dataset. On the other hand, in the ANN analysis, the value of R2 was 0.806 for the training dataset and 0.811 for the test dataset.

Conclusion:

Although a large number of patients would be needed for more accurate and robust prediction, our preliminary Result showed the potential to predict the outcome in the patients with high‐grade glioma.

This work was partly supported by the JSPS Core‐to‐Core Program(No. 23003) and Grant‐in‐aid from the JSPS Fellows.
TH‐E‐BRF‐07: Raman Spectroscopy for Radiation Treatment Response Assessment in a Lung Metastases Mouse Model
Authors: Devpura S , Barton K , Brown S , Sethi S , Klein M , Siddiqui F , Chetty I
Published: July 2014

Purpose:

Raman spectroscopy is an optical spectroscopic method used to probe chemical information about a target tissue. Our goal was to investigate whether Raman spectroscopy is able to distinguish lung tumors from normal lung tissue and whether this technique can identify the molecular changes induced by radiation.

Methods:

4T1 mouse breast cancer cells were implanted subcutaneously into the flanks of 6 Balb/C female mice. Four additional mice were used as “normal lung” controls. After 14 days, 3 mice bearing tumors received 6Gy to the left lung with 6MV photons and the other three were treated as “unirradiated tumor” controls. At a 24‐hour time point, lungs were excised and the specimens were sectioned using a cryostat; alternating sections were either stained with hematoxylin and eosin (H&E) for evaluation by a pathologist or unstained for Raman measurements. 240 total Raman spectra were collected; 84 from normal lung controls; 63 from unirradiated tumors and 64 from tumors irradiated with 6Gy in a single fraction. Raman spectra were also collected from normal lung tissues of mice with unirradiated tumors. Principal component analysis (PCA) and discriminant function analysis (DFA) were performed to analyze the data.

Results:

Raman bands assignable to DNA/RNA showed prominent contributions in tumor tissues while Raman bands associated with hemoglobin showed strong contributions in normal lung tissue. PCA/DFA analysis identified normal lung tissue and tumor with 100% and 98.4% accuracy, respectively, relative to pathologic scoring. Additionally, normal lung tissues from unirradiated mice bearing tumors were classified as normal with 100% accuracy. In a model consisting of unirradiated and irradiated tumors identification accuracy was 79.4% and 93.8% respectively, relative to pathologic assessment.

Conclusion:

Initial results demonstrate the promise for Raman spectroscopy in the diagnosis normal vs. lung metastases as well as the assessment of radiation therapy response. Further investigations are needed to validate these results.

This study was supported in part by a research grant from Varian Medical Systems, Palo Alto, CA
TH‐E‐BRF‐08: Subpopulations of Similarly‐Responding Lesions in Metastatic Prostate Cancer
Authors: Lin C , Harmon S , Perk T , Jeraj R
Published: July 2014

Purpose:

In patients with multiple lesions, resistance to cancer treatments and subsequent disease recurrence may be due to heterogeneity of response across lesions. This study aims to identify subpopulations of similarly‐responding metastatic prostate cancer lesions in bone using quantitative PET metrics.

Methods:

Seven metastatic prostate cancer patients treated with AR‐directed therapy received pre‐treatment and mid‐treatment [F‐18]NaF PET/CT scans. Images were registered using an articulated CT registration algorithm and transformations were applied to PET segmentations. Midtreatment response was calculated on PET‐based texture features. Hierarchical agglomerative clustering was used to form groups of similarly‐responding lesions, with the number of natural clusters (K) determined by the inconsistency coefficient. Lesion clustering was performed within each patient, and for the pooled population. The cophenetic coefficient (C) quantified how well the data was clustered. The Jaccard Index (JI) assessed similarity of cluster assignments from patient clustering and from population clustering.

Results:

188 lesions in seven patients were identified for analysis (between 6 to 53 lesions per patient). Lesion response was defined as percent change relative to pre‐treatment for 23 uncorrelated PET‐based feature identifiers. . High response heterogeneity was found across all lesions (i.e. range ΔSUVmax =−95.98% to 775.00%). For intra‐patient clustering, K ranged from 1–20. Population‐based clustering resulted in 75 clusters, of 1‐6 lesions each. Intra‐patient clustering resulted in higher quality clusters than population clustering (mean C=0.95, range=0.89 to 1.00). For all patients, cluster assignments from population clustering showed good agreement to intra‐patient clustering (mean JI=0.87, range=0.68 to 1.00).

Conclusion:

Subpopulations of similarly‐responding lesions were identified in patients with multiple metastatic lesions. Good agreement was found between population‐ and patient‐level clustering, indicating that PET‐based response features may be used to quantify disease heterogeneity in advanced metastatic disease. This method for categorizing lesion response could help in identifying lesions with similar phenotypic‐ or genetic‐based resistances to therapy.

Research Supported by the Prostate Cancer Foundation.
TH‐E‐BRF‐10: Interim Esophageal Cancer Response Assessment Via 18FDG‐PET Scanning During Radiation Therapy
Authors: Higgins K , Wu Q , Perez B , Czito B , Palta M , Willett C , Das S
Published: July 2014

Purpose:

Local failure occurs in a large proportion of esophageal cancer patients treated with chemoradiation. The treatment strategy for non‐responders could potentially be modified if they are identified during therapy. This work investigates the utility of an interim 18FDG‐PET scan acquired during the course of therapy as a predictor of pathological response post‐therapy.

Methods:

Fifteen patients underwent 18FDG‐PET scanning prior to radiation therapy (RT) and once during RT, after delivery of ∼32 Gy. The physician‐contoured GTV on the planning CT scan was used to automatically segment a PET‐based GTV on the pre‐RT PET (GTV‐pre‐PET) as the volume with >40% of the maximum GTV PET SUV value. The pre‐ and intra‐RT CTs were deformably registered to each other to transfer the GTV‐pre‐PET to the intra‐RT PET (GTV‐intra‐PET). The fractional decrease in the maximum SUV, mean SUV and the SUV to the highest intensity 10% – 90% volumes from GTV‐pre‐PET to GTV‐intra‐PET were compared to pathological response assessed at the time of post‐RT surgery.

Results:

Based on post‐treatment pathology of 15 patients, 7 were classified as achieving favorable response (treatment effect grade ≤ 1) and 8 as unfavorable response (treatment effect grade > 1). Neither fractional decrease in maximum SUV nor mean SUV were significant between the favorable and unfavorable groups. However, the fractional decrease in SUV20% (SUV to the highest 20% volume) was significant (p = 0.02), with an area under the Receiver Operating Characteristics (ROC) curve of 0.84. An optimal cutoff value of 0.46 for this metric was able to distinguish between the two groups with 71% sensitivity (favorable) and 88% specificity (unfavorable).

Conclusion:

The fractional decrease in SUV to the volume with highest 20% intensity from pre‐ to intra‐RT 18FDG‐PET imaging may be used to distinguish between favorable and unfavorable responders with high sensitivity and specificity.
TH‐E‐BRF‐11: Dynamic Treatment of Clinical Margins Beyond the PET‐Avid Target in Emission Guided Radiation Therapy: A Retrospective Patient Study
Authors: Nanduri A , Fan Q , Yang J , Yamamoto T , Graves E , Loo B , Mazin S
Published: July 2014

Purpose:

Emission guided radiation therapy (EGRT) is a new modality that uses PET emissions for direct real‐time tumor tracking. Radiation beamlets are delivered along PET lines of response (LOR' s) by a fast rotating PET‐Linac closed ring gantry. In this work, we develop a scheme to treat clinical margins defined proximal to the moving PET‐avid tumor, while maintaining EGRT's inherent real‐time tracking ability.

Methods:

The principle of EGRT is to deliver radiation along PET emission paths to concentrate dose in the PET‐avid gross tumor volume (GTV). To account for adjacent non‐ PET avid regions in the clinical volume (CTV) a method was developed that expands the set of radiation beamlet responses to include the effective margin extension from the GTV to the CTV. An LOR detection may now Result in multiple beamlet responses: one along the original LOR, and others that are adjacent to it in the direction of margin extension. Evaluation studies were performed on a 4D digital patient as well as a clinical breast cancer patient with moving lung tumors. Emission data were obtained using GATE and a commercial PET scanner. Dose delivery was simulated using VMC++. For the patient study, Philips Pinnacle was used for planning and Mirada RTx was used for deformable dose registration across multiple breathing phases.

Results:

Compared with IMRT, the EGRT margin extension method achieved a 25.3% and 9.0% relative increase in dose to 95% of the CTV for the digital and clinical patients, respectively. The corresponding CTV dose increases without margin extension were 9.7% and 1.4%. The organs at risk doses were kept similar or lower for EGRT in both cases, with tumor tracking preserved.

Conclusions:

With the capability of accurate treatment of the moving CTV, EGRT has the potential to enable a practical and effective implementation of 4D biologically guided radiation therapy.

Authors SRM and AN are stockholders of RefleXion Medical
TH‐E‐17A‐01: Internal Respiratory Surrogate for 4D CT Using Fourier Transform and Anatomical Features
Authors: Hui C , Suh Y , Robertson D , Pan T , Das P , Crane C , Beddar S
Published: July 2014

Purpose:

To develop a novel algorithm to generate internal respiratory signals for sorting of four‐dimensional (4D) computed tomography (CT) images.

Methods:

The proposed algorithm extracted multiple time resolved features as potential respiratory signals. These features were taken from the 4D CT images and its Fourier transformed space. Several low‐frequency locations in the Fourier space and selected anatomical features from the images were used as potential respiratory signals. A clustering algorithm was then used to search for the group of appropriate potential respiratory signals. The chosen signals were then normalized and averaged to form the final internal respiratory signal. Performance of the algorithm was tested in 50 4D CT data sets and results were compared with external signals from the real‐time position management (RPM) system.

Results:

In almost all cases, the proposed algorithm generated internal respiratory signals that visibly matched the external respiratory signals from the RPM system. On average, the end inspiration times calculated by the proposed algorithm were within 0.1 s of those given by the RPM system. Less than 3% of the calculated end inspiration times were more than one time frame away from those given by the RPM system. In 3 out of the 50 cases, the proposed algorithm generated internal respiratory signals that were significantly smoother than the RPM signals. In these cases, images sorted using the internal respiratory signals showed fewer artifacts in locations corresponding to the discrepancy in the internal and external respiratory signals.

Conclusion:

We developed a robust algorithm that generates internal respiratory signals from 4D CT images. In some cases, it even showed the potential to outperform the RPM system. The proposed algorithm is completely automatic and generally takes less than 2 min to process. It can be easily implemented into the clinic and can potentially replace the use of external surrogates.
TH‐E‐17A‐04: Geometric Validation of K‐Space Self‐Gated 4D‐MRI Vs. 4D‐CT Using A Respiratory Motion Phantom
Authors: Yue Y , Fan Z , Yang W , Pang J , McKenzie E , Deng Z , Tuli R , Sandler H , Li D , Fraass B
Published: July 2014

Purpose:

4D‐CT is often limited by motion artifacts, low temporal resolution, and poor phase‐based target definition. We recently developed a novel k‐space self‐gated 4D‐MRI technique with high spatial and temporal resolution. The goal here is to geometrically validate 4D‐MRI using a MRI‐CT compatible respiratory motion phantom and comparison to 4D‐CT.

Methods:

4D‐MRI was acquired using 3T spoiled gradient echo‐based 3D projection sequences. Respiratory phases were resolved using self‐gated k‐space lines as the motion surrogate. Images were reconstructed into 10 temporal bins with 1.56×1.56×1.56mm3. A MRI‐CT compatible phantom was designed with a 23mm diameter ball target filled with highconcentration gadolinium(Gd) gel embedded in a 35×40×63mm3 plastic box stabilized with low‐concentration Gd gel. The whole phantom was driven by an air pump. Human respiratory motion was mimicked using the controller from a commercial dynamic phantom (RSD). Four breathing settings (rates/depths: 10s/20mm, 6s/15mm, 4s/10mm, 3s/7mm) were scanned with 4D‐MRI and 4D‐CT (slice thickness 1.25mm). Motion ground‐truth was obtained from input signals and real‐time video recordings. Reconstructed images were imported into Eclipse(Varian) for target contouring. Volumes and target positions were compared with ground‐truth. Initial human study was investigated on a liver patient.

Results:

4D‐MRI and 4D‐CT scans for the different breathing cycles were reconstructed with 10 phases. Target volume in each phase was measured for both 4D‐CT and 4D‐MRI. Volume percentage difference for the 6.37ml target ranged from 6.67±5.33 to 11.63±5.57 for 4D‐CT and from 1.47±0.52 to 2.12±1.60 for 4D‐MRI. The Mann‐Whitney U‐test shows the 4D‐MRI is significantly superior to 4D‐CT (p=0.021) for phase‐based target definition. Centroid motion error ranges were 1.35–1.25mm (4D‐CT), and 0.31–0.12mm (4D‐MRI).

Conclusion:

The k‐space self‐gated 4D‐MRI we recently developed can accurately determine phase‐based target volume while avoiding typical motion artifacts found in 4D‐CT, and is being further studied for use in GI targeting and motion management.

This work supported in part by grant 1R03CA173273‐01
TH‐E‐17A‐05: Optimizing Four Dimensional Cone Beam Computed Tomography Projection Allocation to Respiratory Bins
Authors: OBrien R , Shieh C , Kipritidis J , Keall P
Published: July 2014

Purpose:

Four dimensional cone beam computed tomography (4DCBCT) is an emerging image guidance strategy but it can suffer from poor image quality. To avoid repeating scans it is beneficial to make the best use of the imaging data obtained. For conventional 4DCBCT the location and size of respiratory bins is fixed and projections are allocated to the respiratory bin within which it falls. Strictly adhering to this rule is unnecessary and can compromise image quality. In this study we optimize the size and location of respiratory bins and allow projections to be sourced from adjacent phases of the respiratory cycle.

Methods:

A mathematical optimization framework using mixed integer quadratic programming has been developed that determines when to source projections from adjacent respiratory bins and optimizes the size and location of the bins. The method, which we will call projection sharing, runs in under 2 seconds of CPU time. Five 4DCBCT datasets of stage III‐IV lung cancer patients were used to test the algorithm. The standard deviation of the angular separation between projections (SD‐A) and the standard deviation in the volume of the reconstructed fiducial gold coil (SD‐V) were used as proxies to measure streaking artefacts and motion blur respectively.

Results:

The SD‐A using displacement binning and projection sharing was 30%–50% smaller than conventional phase based binning and 59%–76% smaller than conventional displacement binning indicating more uniformly spaced projections and fewer streaking artefacts. The SD‐V was 20–90% smaller when using projection sharing than using conventional phase based binning suggesting more uniform marker segmentation and less motion blur.

Conclusion:

Image quality was visibly and significantly improved with projection sharing. Projection sharing does not require any modifications to existing hardware and offers a more robust replacement to phase based binning, or, an option if phase based reconstruction is not of a suitable quality.

This project is supported by an NHMRC Australia Fellowship and NHMRC project grant number 1034060