bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐J‐182: Reproducibility of Tumor Motion Probability Distribution Function in Stereotactic Body Radiation Therapy of Lung Using Real‐Time Tumor‐Tracking Radiotherapy System
Authors: Shiinoki T , Kawamura S , Hanazawa H , Park S , Uehara T , Yuasa Y , Koike M , Takahashi T , Shibuya K
Published: June 2015

Purpose:

We aim to achieve new four‐dimensional radiotherapy (4DRT) using the next generation real‐time tumor‐tracking (RTRT) system and flattening‐filter‐free techniques. To achieve new 4DRT, it is necessary to understand the respiratory motion of tumor. The purposes of this study were: 1.To develop the respiratory motion analysis tool using log files. 2.To evaluate the reproducibility of tumor motion probability distribution function (PDF) during stereotactic body RT (SBRT) of lung tumor.

Methods:

Seven patients having fiducial markers closely implanted to the lung tumor were enrolled in this study. The positions of fiducial markers were measured using the RTRT system (Mitsubishi Electronics Co., JP) and recorded as two types of log files during the course of SBRT. For each patients, tumor motion range and tumor motion PDFs in left‐right (LR), anterior‐posterior (AP) and superior‐inferior (SI) directions were calculated using log files of all beams per fraction (PDFn). Fractional PDF reproducibility (Rn) was calculated as Kullback‐Leibler (KL) divergence between PDF1 and PDFn of tumor motion. The mean of Rn (Rm) was calculated for each patient and correlated to the patient's mean tumor motion range (Am). The change of Rm during the course of SBRT was also evluated. These analyses were performed using in‐house developed software.

Results:

The Rm were 0.19 (0.07–0.30), 0.14 (0.07–0.32) and 0.16 (0.09–0.28) in LR, AP and SI directions, respectively. The Am were 5.11 mm (2.58–9.99 mm), 7.81 mm (2.87–15.57 mm) and 11.26 mm (3.80–21.27 mm) in LR, AP and SI directions, respectively. The PDF reproducibility decreased as the tumor motion range increased in AP and SI direction. That decreased slightly through the course of RT in SI direction.

Conclusion:

We developed the respiratory motion analysis tool for 4DRT using log files and quantified the range and reproducibility of respiratory motion for lung tumors.
SU‐E‐J‐191: Motion Prediction Using Extreme Learning Machine in Image Guided Radiotherapy
Authors: Jia J , Cao R , Pei X , Wang H , Hu L
Published: June 2015

Purpose:

Real‐time motion tracking is a critical issue in image guided radiotherapy due to the time latency caused by image processing and system response. It is of great necessity to fast and accurately predict the future position of the respiratory motion and the tumor location.

Methods:

The prediction of respiratory position was done based on the positioning and tracking module in ARTS‐IGRT system which was developed by FDS Team (www.fds.org.cn). An approach involving with the extreme learning machine (ELM) was adopted to predict the future respiratory position as well as the tumor's location by training the past trajectories. For the training process, a feed‐forward neural network with one single hidden layer was used for the learning. First, the number of hidden nodes was figured out for the single layered feed forward network (SLFN). Then the input weights and hidden layer biases of the SLFN were randomly assigned to calculate the hidden neuron output matrix. Finally, the predicted movement were obtained by applying the output weights and compared with the actual movement. Breathing movement acquired from the external infrared markers was used to test the prediction accuracy. And the implanted marker movement for the prostate cancer was used to test the implementation of the tumor motion prediction.

Results:

The accuracy of the predicted motion and the actual motion was tested. Five volunteers with different breathing patterns were tested. The average prediction time was 0.281s. And the standard deviation of prediction accuracy was 0.002 for the respiratory motion and 0.001 for the tumor motion.

Conclusion:

The extreme learning machine method can provide an accurate and fast prediction of the respiratory motion and the tumor location and therefore can meet the requirements of real‐time tumor‐tracking in image guided radiotherapy.
SU‐E‐J‐193: Application of Surface Mapping in Detecting Swallowing for Head‐&‐Neck Cancer
Authors: Cao D , Xie X , Mehta V , Shepard D
Published: June 2015

Purpose:

Recent evidence is emerging that long term swallowing function may be improved after radiotherapy for head‐&‐neck cancer if doses are limited to certain swallowing structures. Immobilization of patients with head‐&‐neck cancer is typically done with a mask. This mask, however, doesn't limit patient swallowing. Patient voluntary or involuntary swallowing may introduce significant tumor motion, which can lead to suboptimal delivery. In this study, we have examined the feasibility of using surface mapping technology to detect patient swallowing during treatment and evaluated its magnitude.

Methods:

The C‐RAD Catalyst system was used to detect the patient surface map. A volunteer lying on the couch was used to simulate the patient under treatment. A virtual marker was placed near the throat and was used to monitor the swallowing action. The target motion calculated by the Catalyst system through deformable registration was also collected. Two treatment isocenters, one placed close to the throat and the other placed posterior to the base‐of‐tongue, were used to check the sensitivity of surface mapping technique.

Results:

When the patient's throat is not in the shadow of the patient's chest, the Catalyst system can clearly identify the swallowing motion. In our tests, the vertical motion of the skin can reach to about 5mm. The calculated target motion can reach up to 1 cm. The magnitude of this calculated target motion is more dramatic when the plan isocenter is closer to the skin surface, which suggests that the Catalyst motion tracking technique is more sensitive to the swallowing motion with a shallower isocenter.

Conclusion:

Surface mapping can clearly identify patient swallowing during radiation treatment. This information can be used to evaluate the dosimetric impact of the involuntary swallowing. It may also be used to potentially gate head‐&‐neck radiation treatments. A prospective IRB approved study is currently enrolling patients in our institution.

Research was funded through an Elekta grant
SU‐E‐J‐208: Feasibility Study On Using Small Plastic Phantoms for Auditing Radiation Output of MR‐Linac Systems
Authors: Wen Z , Alvarez P , Ibbott G
Published: June 2015

Purpose:

To study feasibility of using small plastic phantoms designed for conventional linac output auditing to measure the output of MR‐Linac systems.

Methods:

For simulations, the CT scan of an IROC(formerly RPC) acrylic block phantom designed for 8 MV beams was imported in a research version of the treatment planning system (Monaco). Dose delivered to three TLDs in the block was calculated with a Monte Carlo algorithm and a beam model based on an MR‐linac prototype with and without a magnetic field (B=1.5T). In a large mathematical water phantom, the same beam was used to calculate dose in full scatter conditions. The block factor (F) was calculated as the ratio of the average dose to the block TLDs to the dose at the reference point in the mathematical phantom. For experimental measurement, four IROC blocks were irradiated with the MR‐linac prototype, and data were analyzed by IROC.

Results:

The F factor without a B field was 1.053. When a B field was applied, it changed the dose distribution in the block, especially on the edges. With a B field parallel to the long axes of the TLD, F was 1.038. However, with a perpendicular B field, F factor increased slightly to 1.075. In the IROC report, the output determined with two blocks parallel to the B field was 2.3% higher than the output by the two blocks perpendicular to the B field. The average of all four blocks was within 2% of machine output measured with an ion chamber.

Conclusion:

It may be feasible to expand the utility of the acrylic block phantoms for radiation output auditing from conventional linacs to MR‐linacs. However, the scatter correction factor can change due to the B field and its orientation to the block. More symmetric phantom designs may be less prone to mistakes.

We acknowledge research support from Elekta
SU‐E‐J‐228: MRI‐Based Planning: Dosimetric Feasibility of Dose Painting for ADCDefined Intra‐Prostatic Tumor
Authors: Chen X , Dalah E , Prior P , Lawton C , Li X
Published: June 2015

Purpose:

Apparent diffusion coefficient (ADC) map may help to delineate the gross tumor volume (GTV) in prostate gland. Dose painting with external beam radiotherapy for GTV might increase the local tumor control. The purpose of this study is to explore the maximum boosting dose on GTV using VMAT without sacrificing sparing of organs at risk (OARs) in MRI based planning.

Methods:

VMAT plans for 5 prostate patients were generated following the commonly used dose volume (DV) criteria based on structures contoured on T2 weighted MRI with bulk electron density assignment using electron densities derived from ICRU46. GTV for each patient was manually delineated based on ADC maps and fused to T2‐weighted image set for planning study. A research planning system with Monte Carlo dose engine (Monaco, Elekta) was used to generate the VMAT plans with boosting dose on GTV gradually increased from 85Gy to 100Gy. DV parameters, including V(boosting‐dose) (volume covered by boosting dose) for GTV, V75.6Gy for PTV, V45Gy, V70Gy, V72Gy and D1cc (Maximum dose to 1cc volume) for rectum and bladder, were used to measure plan quality.

Results:

All cases achieve at least 99.0% coverage of V(boosting‐dose) on GTV and 95% coverage of V75.6Gy to the PTV. All the DV criteria, V45Gy≤50% and V70Gy≤15% for bladder and rectum, D1cc ≤77Gy (Rectum) and ≤80Gy (Bladder), V72Gy≤5% (rectum and bladder) were maintained when boosting GTV to 95Gy for all cases studied. Except for two patients, all the criteria were also met when the boosting dose goes to 100Gy. Conclusion: It is dosimetrically feasible safe to boost the dose to at least 95Gy to ADC defined GTV in prostate cancer using MRI guided VMAT delivery.

Conclusion:

It is dosimetrically feasible safe to boost the dose to at least 95Gy to ADC defined GTV in prostate cancer using MRI guided VMAT delivery.

This research is partially supported by Elekta Inc.
SU‐E‐J‐242: Volume‐Dependence of Quantitative Imaging Features From CT and CE‐CT Images of NSCLC
Authors: Fave X , Fried D , Zhang L , Yang J , Balter P , Followill D , Gomez D , Jones A , Stingo F , Court L
Published: June 2015

Purpose:

To determine whether tumor volume plays a significant role in the values obtained for texture features when they are extracted from computed tomography (CT) images of non‐small cell lung cancer (NSCLC). We also sought to identify whether features can be reliably measured at all volumes or if a minimum volume threshold should be recommended.

Methods:

Eleven features were measured on 40 CT and 32 contrast‐enhanced CT (CECT) patient images for this study. Features were selected for their prognostic/diagnostic value in previous publications. Direct correlations between these textures and volume were evaluated using the Spearman correlation coefficient. Any texture that the Wilcoxon rank‐sum test was used to compare the variation above and below a volume cutoff. Four different volume thresholds (5, 10, 15, and 20 cm3) were tested.

Results:

Four textures were found to be significantly correlated with volume in both the CT and CE‐CT images. These were busyness, coarseness, gray‐level nonuniformity, and run‐length nonuniformity with correlation coefficients of 0.92, −0.96, 0.94, and 0.98 for the CT images and 0.95, −0.97, 0.98, and 0.98 for the CE‐CT images. After volume normalization, the correlation coefficients decreased substantially. For the data obtained from the CT images, the results of the Wilcoxon rank‐sum test were significant when volume thresholds of 5–15 cm3 were used. No volume threshold was shown to be significant for the CE‐CT data.

Conclusion:

Equations for four features that have been used in several published studies were found to be volume‐dependent. Future studies should consider implementing normalization factors or removing these features entirely to prevent this potential source of redundancy or bias.

This work was supported in part by National Cancer Institute grant R03CA178495‐01. Xenia Fave is a recipient of the American Association of Physicists in Medicine Graduate Fellowship.
SU‐E‐J‐247: Time Evolution of Radiation‐Induced Lung Injury After Stereotactic Proton Therapy
Authors: Grassberger C , Sharp G , Fintelmann F , Paganetti H , Willers H
Published: June 2015

Purpose:

Quantitative metrics to assess patient‐specific radiation‐induced lung injury have the potential to guide individualization of therapy and be early indicators of recurrence. Here we investigate computed tomography (CT) density changes in normal lung after stereotactic Proton Therapy.

Methods:

Participants in a phase‐I clinical trial for stereotactic body radiation therapy (SBRT) with protons are analyzed on a rolling basis. The dataset includes 9 patients with 34 CT images to date. Follow‐up images are registered to the planning CT using deformable image registration and the change in CT density is correlated to the dose to examine the time‐evolution of Hounsfield Unit (HU) changes after large doses of proton radiation.

Results:

The lung density observed on the follow‐up images increases significantly with dose for all dose levels above 5 Gy(RBE) (p<0.001) for 8/9 patients. The change per unit dose [HU/Gy] varies significantly among the patients, from 0.1 (for the one patient without significant correlation) to 5.7 ΔHU/Gy(RBE). The current population average of ΔHU/Gy(RBE) is 2.1, i.e. a 1 Gy(RBE) increase in dose leads on average to a 2.1 HU increase in CT density. The slope of the dose‐response curve is constant for all timepoints investigated (from 3–24+ months). Additionally a pronounced non‐linearity in the dose response curve is noted for long follow‐up times (>18 months).

Conclusion:

CT density changes have a robust correlation with proton dose, quantitatively similar to photon dose, and may allow estimation of a patient's intrinsic radiosensitivity after proton therapy. The stability of the correlation with time however diverges from what is known about CT response after photon irradiation. This could have important implications for clinical decision‐making during proton therapy for lung cancer, especially for scheduling of follow‐up CT/PET imaging and diagnosis of recurrence.
SU‐E‐J‐253: The Radiomics Toolbox in the Computational Environment for Radiological Research (CERR)
Authors: Apte A , Veeraraghavan H , Oh J , Kijewski P , Deasy J
Published: June 2015

Purpose:

To present an open source and free platform to facilitate radiomics research — The “Radiomics toolbox” in CERR.

Method:

There is scarcity of open source tools that support end‐to‐end modeling of image features to predict patient outcomes. The “Radiomics toolbox” strives to fill the need for such a software platform. The platform supports (1) import of various kinds of image modalities like CT, PET, MR, SPECT, US. (2) Contouring tools to delineate structures of interest. (3) Extraction and storage of image based features like 1st order statistics, gray‐scale co‐occurrence and zonesize matrix based texture features and shape features and (4) Statistical Analysis. Statistical analysis of the extracted features is supported with basic functionality that includes univariate correlations, Kaplan‐Meir curves and advanced functionality that includes feature reduction and multivariate modeling. The graphical user interface and the data management are performed with Matlab for the ease of development and readability of code and features for wide audience. Open‐source software developed with other programming languages is integrated to enhance various components of this toolbox. For example: Java‐based DCM4CHE for import of DICOM, R for statistical analysis.

Results:

The Radiomics toolbox will be distributed as an open source, GNU copyrighted software. The toolbox was prototyped for modeling Oropharyngeal PET dataset at MSKCC. The analysis will be presented in a separate paper.

Conclusion:

The Radiomics Toolbox provides an extensible platform for extracting and modeling image features. To emphasize new uses of CERR for radiomics and image‐based research, we have changed the name from the “Computational Environment for Radiotherapy Research” to the “Computational Environment for Radiological Research”.
SU‐E‐J‐261: The Importance of Appropriate Image Preprocessing to Augment the Information of Radiomics Image Features
Authors: Zhang L , Fried D , Fave X , Mackin D , Yang J , Court L
Published: June 2015

Purpose:

To investigate how different image preprocessing techniques, their parameters, and the different boundary handling techniques can augment the information of features and improve feature's differentiating capability.

Methods:

Twenty‐seven NSCLC patients with a solid tumor volume and no visually obvious necrotic regions in the simulation CT images were identified. Fourteen of these patients had a necrotic region visible in their pre‐treatment PET images (necrosis group), and thirteen had no visible necrotic region in the pre‐treatment PET images (non‐necrosis group). We investigated how image preprocessing can impact the ability of radiomics image features extracted from the CT to differentiate between two groups. It is expected the histogram in the necrosis group is more negatively skewed, and the uniformity from the necrosis group is less. Therefore, we analyzed two first order features, skewness and uniformity, on the image inside the GTV in the intensity range [−20HU, 180HU] under the combination of several image preprocessing techniques: (1) applying the isotropic Gaussian or anisotropic diffusion smoothing filter with a range of parameter(Gaussian smoothing: size=11, sigma=0:0.1:2.3; anisotropic smoothing: iteration=4, kappa=0:10:110); (2) applying the boundaryadapted Laplacian filter; and (3) applying the adaptive upper threshold for the intensity range. A 2‐tailed T‐test was used to evaluate the differentiating capability of CT features on pre‐treatment PT necrosis.

Result:

Without any preprocessing, no differences in either skewness or uniformity were observed between two groups. After applying appropriate Gaussian filters (sigma>=1.3) or anisotropic filters(kappa >=60) with the adaptive upper threshold, skewness was significantly more negative in the necrosis group(p<0.05). By applying the boundary‐adapted Laplacian filtering after the appropriate Gaussian filters (0.5 <=sigma<=1.1) or anisotropic filters(20<=kappa <=50), the uniformity was significantly lower in the necrosis group (p<0.05).

Conclusion:

Appropriate selection of image preprocessing techniques allows radiomics features to extract more useful information and thereby improve prediction models based on these features.
SU‐E‐J‐266: Cone Beam Computed Tomography (CBCT) Inter‐Scan and Inter‐Observer Tumor Volume Variability Assessment in Patients Treated with Stereotactic Body Radiation Therapy (SBRT) for Early Stage Non‐Small Cell Lung Cancer (NSCLC)
Authors: Hou Y , Aileen C , Kozono D , Killoran J , Wagar M , Lee S , Hacker F , Aerts H , Lewis J , Mak R
Published: June 2015

Purpose:

Quantification of volume changes on CBCT during SBRT for NSCLC may provide a useful radiological marker for radiation response and adaptive treatment planning, but the reproducibility of CBCT volume delineation is a concern. This study is to quantify inter‐scan/inter‐observer variability in tumor volume delineation on CBCT.

Methods:

Twenty earlystage (stage I and II) NSCLC patients were included in this analysis. All patients were treated with SBRT with a median dose of 54 Gy in 3 to 5 fractions. Two physicians independently manually contoured the primary gross tumor volume on CBCTs taken immediately before SBRT treatment (Pre) and after the same SBRT treatment (Post). Absolute volume differences (AVD) were calculated between the Pre and Post CBCTs for a given treatment to quantify inter‐scan variability, and then between the two observers for a given CBCT to quantify inter‐observer variability. AVD was also normalized with respect to average volume to obtain relative volume differences (RVD). Bland‐Altman approach was used to evaluate variability. All statistics were calculated with SAS version 9.4.

Results:

The 95% limit of agreement (mean ± 2SD) on AVD and RVD measurements between Pre and Post scans were −0.32cc to 0.32cc and −0.5% to 0.5% versus −1.9 cc to 1.8 cc and −15.9% to 15.3% for the two observers respectively. The 95% limit of agreement of AVD and RVD between the two observers were −3.3 cc to 2.3 cc and −42.4% to 28.2% respectively. The greatest variability in inter‐scan RVD was observed with very small tumors (< 5 cc).

Conclusion:

Inter‐scan variability in RVD is greatest with small tumors. Inter‐observer variability was larger than inter‐scan variability. The 95% limit of agreement for inter‐observer and inter‐scan variability (∼15–30%) helps define a threshold for clinically meaningful change in tumor volume to assess SBRT response, with larger thresholds needed for very small tumors.

Part of the work was funded by a Kaye award; Disclosure/Conflict of interest: Raymond H. Mak: Stock ownership: Celgene, Inc. Consulting: Boehringer‐Ingelheim, Inc.
SU‐E‐J‐268: Change of CT Number During the Course of Chemoradiation Therapy for Pancreatic Cancer
Authors: Chen X , Zhang J , Dalah E , Liu F , Li X
Published: June 2015

Purpose:

It has been observed radiation can induce changes in CT number (CTN) inside tumor during the course of radiation therapy (RT) for several tumor sites including lung and head and neck, suggesting that the CTN change may be potentially used to assess RT response. In this study, we investigate the CTN changes inside tumor during the course of chemoradiation therapy (CRT) for pancreatic cancer.

Methods:

Daily diagnostic‐quality CT data acquired during IGRT for 17 pancreatic head cancer patients using an in‐room CT (CTVision, Siemens) were analyzed. All patients were treated with a radiation dose of 50.4 in 1.8 Gy per fraction. On each daily CT set, The contour of the pancreatic head, included in the treatment target, was generated by populating the pancreatic head contour from the planning CT or MRI using an auto‐segmentation tool based on deformable registration (ABAS, Elekta) with manual editing if necessary. The CTN at each voxel in the pancreatic head contour was extracted and the 3D distribution of the CTNs was processed using MATLAB. The mean value of CTN distribution was used to quantify the daily CTN change in the pancreatic head.

Results:

Reduction of CTN in pancreatic head was observed during the CRT delivery in 14 out the 17 (82%) patients studied. Although the average reduction is only 3.5 Houncefield Unit (HU), this change is significant (p<0.01). Among them, there are 7 patients who had a CTN drop larger than 5 HU, ranging from 6.0 to 11.8 HU. In contrast to this trend, CTN was increased in 3 patients.

Conclusion:

Measurable changes in the CT number in tumor target were observed during the course of chemoradiation therapy for the pancreas cancer patients, indicating this radiation‐induced CTN change may be used to assess treatment response.
SU‐E‐J‐272: Auto‐Segmentation of Regions with Differentiating CT Numbers for Treatment Response Assessment
Authors: Yang C , Gilat‐Schmidt T , Noid G , Dalah E , Paulson E , Li X
Published: June 2015

Purpose:

It has been reported recently that the change of CT number (CTN) during and after radiation therapy (RT) may be used to assess RT response. The purpose of this work is to develop a tool to automatically segment the regions with differentiating CTN and/or with change of CTN in a series of CTs.

Methods:

A software tool was developed to identify regions with differentiating CTN using K‐mean Cluster of CT numbers and to automatically delineate these regions using convex hull enclosing method. Pre‐ and Post‐RT CT, PET, or MRI images acquired for sample lung and pancreatic cancer cases were used to test the software tool. K‐mean cluster of CT numbers within the gross tumor volumes (GTVs) delineated based on PET SUV (standard uptake value of fludeoxyglucose) and/or MRI ADC (apparent diffusion coefficient) map was analyzed. The cluster centers with higher value were considered as active tumor volumes (ATV). The convex hull contours enclosing preset clusters were used to delineate these ATVs with color washed displays. The CTN defined ATVs were compared with the SUV‐ or ADC‐defined ATVs.

Results:

CTN stability of the CT scanner used to acquire the CTs in this work is less than 1.5 Hounsfield Unit (HU) variation annually. K‐mean cluster centers in the GTV have difference of ∼20 HU, much larger than variation due to CTN stability, for the lung cancer cases studied. The dice coefficient between the ATVs delineated based on convex hull enclosure of high CTN centers and the PET defined GTVs based on SUV cutoff value of 2.5 was 90(±5)%.

Conclusion:

A software tool was developed using K‐mean cluster and convex hull contour to automatically segment high CTN regions which may not be identifiable using a simple threshold method. These CTN regions were reasonably overlapped with the PET or MRI defined GTVs.
SU‐E‐J‐274: Responses of Medulloblastoma Cells to Radiation Dosimetric Parameters in Intensity‐Modulated Radiation Therapy
Authors: Park J , Park J , Rogalla S , Woo D , Lee D , Park H , Contag C , Suh T
Published: June 2015

Purpose:

To evaluate radiation responses of the medulloblastoma cell line Daoy in intensity‐modulated radiation therapy (IMRT), quantitative variations to variable radiation dosimetic parameters were tracked by bioluminescent images (BLIs).

Methods:

The luciferase and green fluorescent protein positive Daoy cells were cultured on dishes. The medulloblastoma cells irradiated to different dose rate, interval of fractionated doses, field margin and misalignment, and dose uniformity in IMRT were monitored using bioluminescent images. The cultured cells were placed into a dedicated acrylic phantom to deliver intensity‐modulated fluences and calculate accurate predicted dose distribution. The radiation with dose rate from 0.5 Gy/min to 15 Gy/min was irradiated by adjusting monitor unit per minute and source‐to‐surface distances. The intervals of fractionated dose delivery were changed considering the repair time of double strand breaks (DSB) revealed by straining of gamma‐H2AX.The effect of non‐uniform doses on the cells were visualized by registering dose distributions and BLIs. The viability according to dosimetric parameters was correlated with bioluminescent intensities for cross‐check of radiation responses.

Results:

The DSB and cell responses due to the first fractionated dose delivery significantly affected final tumor control rather than other parameters. The missing tumor volumes due to the smaller field margin than the tumor periphery or field misalignment caused relapse of cell responses on BLIs. The dose rate and gradient had effect on initial responses but could not bring out the distinguishable killing effect on cancer cells.

Conclusion:

Visualized and quantified bioluminescent images were useful to correlate the dose distributions with spatial radiation effects on cells. This would derive the effective combination of dose delivery parameters and fractionation. Radiation responses in particular IMRT configuration could be reflected to image based‐dose re‐optimization.
SU‐E‐T‐03: 3 Year Clinical Experience with the IBA Proton Eyeline
Authors: Kryck E , Mamalui‐Hunter M , Li Z , Slopsema R
Published: June 2015

Purpose:

Over the past 3 years, more than 50 patients with ocular disease have been treated with a prototype commercial eyeline developed by Ion Beam Applications (IBA). It is particularly crucial for the dosimetry of the machine to be accurate, precise, and reproducible because of the small treatment volumes and several surrounding critical structures. A quality assurance (QA) program has been developed in order to regularly check and record the machine's dosimetry over time. In this study we have summarized and evaluated three years of patient and system QA data for the eyeline prototype.

Methods:

In order to accurately deliver the prescribed dose to the patient's treatment site, an output model was created based on several machine parameters. This output model, along with the requested system parameters, are regularly checked and recorded by a QA program. 10 standard proton fields have been created which have regular QA performed monthly with a water tank and parallel‐plate chamber, and recorded in a database. QA has additionally been performed for each patient‐specific treatment field. This is to verify and evaluate the patient output model as well as the system parameters for range&modulation combinations different than the standard QA fields.

Results:

140 beam measurements have been analyzed for range, modulation, and output. The range is typically within tolerance, although there are about 6 cases where the system did not perform as expected. The modulation appears to be very stable, always being within tolerance. Output for the standard QA fields are typically within 2.5% from the baseline value. The patient output measurements agree within 2.5% from the model.

Conclusion:

Overall the eyeline performs well within the tolerances set, and the patient output measurements agree within 2% of the model.
SU‐E‐T‐06: 4D Particle Swarm Optimization to Enable Lung SBRT in Patients with Central And/or Large Tumors
Authors: Modiri A , Gu X , Hagan A , Sawant A
Published: June 2015

Purpose:

Patients presenting with large and/or centrally‐located lung tumors are currently considered ineligible for highly potent regimens such as SBRT due to concerns of toxicity to normal tissues and organs‐at‐risk (OARs). We present a particle swarm optimization (PSO)‐based 4D planning technique, designed for MLC tracking delivery, that exploits the temporal dimension as an additional degree of freedom to significantly improve OAR‐sparing and reduce toxicity to levels clinically considered as acceptable for SBRT administration.

Methods:

Two early‐stage SBRT‐ineligible NSCLC patients were considered, presenting with tumors of maximum dimensions of 7.4cm (central‐right lobe; 1.5cm motion) and 11.9cm (upper‐right lobe; 1cm motion). In each case, the target and normal structures were manually contoured on each of the ten 4DCT phases. Corresponding ten initial 3D‐conformal plans (Pt#1: 7‐beams; Pt#2: 9‐beams) were generated using the Eclipse planning system. Using 4D‐PSO, fluence weights were optimized over all beams and all phases (70 and 90 apertures for Pt1&2, respectively). Doses to normal tissues and OARs were compared with clinicallyestablished lung SBRT guidelines based on RTOG‐0236.

Results:

The PSO‐based 4D SBRT plan yielded tumor coverage and dose—sparing for parallel and serial OARs within the SBRT guidelines for both patients. The dose‐sparing compared to the clinically‐delivered conventionallyfractionated plan for Patient 1 (Patient 2) was: heart Dmean = 11% (33%); lung V20 = 16% (21%); lung Dmean = 7% (20%); spinal cord Dmax = 5% (16%); spinal cord Dmean = 7% (33%); esophagus Dmax = 0% (18%).

Conclusion:

Truly 4D planning can significantly reduce dose to normal tissues and OARs. Such sparing opens up the possibility of using highly potent and effective regimens such as lung SBRT for patients who were conventionally considered SBRT non‐eligible. Given the large, non‐convex solution space, PSO represents an attractive, parallelizable tool to successfully achieve a globally optimal solution for this problem.

This work was supported through funding from the National Institutes of Health and Varian Medical Systems.
SU‐E‐T‐13: A Comparative Dosimetric Study On Radio‐Dynamic Therapy for Pelvic Cancer Treatment: Strategies for Bone Marrow Dose and Volume Reduction
Authors: Li C , Wang B , Dong Z , Ge W , Xu L , Ma C
Published: June 2015

Purpose:

Radio‐dynamic therapy (RDT) is a potentially effective modality for local and systemic cancer treatment. Using RDT, the administration of a radio‐sensitizer enhances the biological effect of high‐energy photons. Although the sensitizer uptake ratio of tumor to normal tissue is normally high, one cannot simply neglect its effect on critical structures. In this study, we aim to explore planning strategies to improve bone marrow sparing without compromising the plan quality for RDT treatment of pelvic cancers.

Methods:

Ten cervical and ten prostate cancer patients who previously received radiotherapy at our institution were selected for this study. For each patient, nine plans were created using the Varian Eclipse treatmentplanning‐system (TPS) with 3D‐CRT, IMRT, and VMAT delivery techniques containing various gantry angle combinations and optimization parameters (dose constraints to the bone marrow). To evaluate the plans for bone marrow sparing, the dose‐volume parameters V5, V10, V15, V20, V30, and V40 for bone marrow were examined. Effective doseenhancement factors for the sensitizer were used to weigh the dose‐volume histograms for various tissues from individual fractions.

Results:

The planning strategies had different impacts on bone marrow sparing for the cervical and prostate cases. For the cervical cases, provided the bone marrow constraints were properly set during optimization, the dose to bone marrow sparing was found to be comparable between different IMRT and VMAT plans regardless of the gantry angle selection. For the prostate cases, however, careful selection of gantry angles could dramatically improve the bone marrow sparing, although the dose distribution in bone marrow was clinically acceptable for all prostate plans that we created.

Conclusion:

For intensity‐modulated RDT planning for cervical cancer, planners should set bone marrow constraints properly to avoid any adverse damage, while for prostate cancer one can carefully select gantry angles to improve bone marrow sparing when necessary.
SU‐E‐T‐25: A Dosimetric Comparison of Three‐Dimension Conformal and Intensity‐Modulated Radiation Therapy in Esophageal Cancer
Authors: Gallardo N , Maneru F , Fuentemilla N , Olasolo J , Gracia M , Pellejero S , Bragado L , Lozares S , Miquelez S , Martin M
Published: June 2015

Purpose:

dosimetric comparison of 3DCRT and IMRT in 9 esophageal cancer. The aim of this paper is to know which of these two techniques is dosimetrically more favorable dosimetrically at both the CTV coverage and dose obtained in the relevant organs at risk, in this case, lungs and heart, as the spinal cord received in all cases below 45 Gy.

Methods:

we chose 9 patients from our center (CHN) with the same type of esophageal cancer and in which the prescribed dose was the same, 54 Gy. For these treatments we have used the same fields and the same angles (AP (0 °), OPD (225°–240°) and OPI (125°–135°)).All plans have been implemented using Eclipse (version 11.0) with AAA( Analytical Anisotropic Algorithm )(Version 11.0.31).

Results:

To analyze the coverage of the CTV, we have evaluated the D99% and found that the average dose received by 99% of CTV with IMRT is 53.8 ± 0.4 Gy (99.6% of the prescribed dose) and the mean value obtained with 3DCRT is 52.3 ± 0.6 Gy (96.8% of the prescribed dose).The last data analyzed was the D2% of PTV, a fact that gives us information on the maximum dose received by our PTV. D2% of the PTV for IMRT planning is 55.4 ± 0.4 Gy (102.6% of the prescribed dose) and with 3DCRT is 56.8 ± 0.7 Gy (105.2% of the prescribed dose).All parameters analyzed at risk organs (V30, V40, V45 and V50 for the case of heart and V5, V10, V15 and V20 for the case of the lungs) provide us irradiated volume percentages lower in IMRT than 3DCRT.

Conclusion:

IMRT provides a considerable improvement in the coverage of the CTV and the doses to organs at risk.
SU‐E‐T‐31: A Fast Finite Size Pencil Beam (FSPB) Convolution Algorithm for a New Co‐60 Arc Therapy Machine
Authors: Chibani O , Eldib A , Ma C
Published: June 2015

Purpose:

Present a fast Finite Size Pencil Beam (FSPB) convolution algorithm for a new Co‐60 arc therapy machine. The FSPB algorithm accounts for (i) strong angular divergence (short SAD), (ii) heterogeneity effect for primary attenuation, and (iii) source energy spectrum.

Methods:

The FSPB algorithm is based on a 0.5×0.5‐cm2 dose kernel calculated using the GEPTS (Gamma Electron and Positron Transport System) Monte Carlo code. The dose kernel is tabulated using a thin XYZ mesh (0.1 mm steps in lateral directions) for radius less than 1 cm and using an RZ mesh (with varying steps) for larger radial distance. To account for SSD effect, 11 dose kernels with SSDs varying between 30 cm to 80 cm are calculated. Maynord factor and “lateral stretching” are applied to account for differences between closest and actual SSD. Appropriate rotations and second order interpolation are used to calculate the dose from a given beamlet to a point.

Results:

Accuracy: Dose distributions in water with 80 cm SSD are calculated using the new FSPB convolution algorithm and full Monte Carlo simulation (gold standard). Figs 1–4 show excellent agreements between FSPB and Monte Carlo calculations for different field sizes and at different depths. The dose distribution for a prostate case is calculated using FSPB (Fig.5). Sixty conformal beams with rectum blocking are assumed. Figs 6–8 show the comparison with Monte Carlo simulation based on the same beam apertures. The excellent agreement demonstrates the accuracy of the new algorithm in handling SSD variation, oblique incidence, and scatter contribution.Speed: The FSPB convolution algorithm calculates 28 million dose points per second using a single 2.2‐GHz CPU. The present algorithm is seven times faster than a similar algorithm from Gu et al. (Phys. Med. Biol. 54, 2009, 6287–6297).

Conclusion:

A fast and accurate FSPB convolution algorithm was developed and benchmarked.
SU‐E‐T‐38: A Head to Head Comparison of Two Commercial Phantoms Used for SRS QA
Authors: Sarkar V , Huang L , Huang Y , Szegedi M , Rassiah‐Szegedi P , Zhao H , Salter B
Published: June 2015

Purpose:

To compare and contrast two commercial SRS QA phantoms.

Methods:

Both phantoms were evaluated in terms of their ease of setup as well as the time required to switch inserts for different tests. They were both used to evaluate the coincidence of the radiation and laser isocenters of a linear accelerator. End‐to‐end dosimetric tests were also performed using both ion chambers and films along two planes through the center of the phantoms. Since one phantom allows for multiple ion chamber orientations, a test was also performed to determine the effect of having the chamber oriented along the radiation beam axis’.

Results:

Changing inserts took 2 minutes on average for one phantom compared to 5 minutes for the other. The laser/radiation isocenter coincidence as determined from each phantom showed a maximum difference of 0.2mm. Ion chamber results were within 0.5% of the expected values when the chamber was perpendicular to the beams but measured a 3% underdose when the chamber was along the beam direction. Gamma (2%,2mm) pass rates of corresponding films were within 1% between phantoms.

Conclusion:

The results of the corresponding tests run on both phantoms were comparable, showing that the phantoms were equivalent for the subset of SRS QA tests run here. However, the under dose observed when the chamber was parallel to the beam direction suggests that this configuration should be avoided.
SU‐E‐T‐43: A Methodology for Quality Control of IMPT Treatment Plan Based On VMAT Plan
Authors: Jiang S , Yang Y , Liao L , Wang X , Li H , Zhu X , Zhang X
Published: June 2015

Purpose:

IMPT plan design is highly dependent on planner's experiences. VMAT plan design is relatively mature and can even be automated. The quality of IMPT plan designed by in‐experienced planner could be inferior to that of VMAT plan designed by experienced planner or automatic planning software. Here we introduce a method for designing IMPT plan based on VMAT plan to ensure the IMPT plan be superior to IMRT/VMAT plan for majority clinical scenario.

Methods:

To design a new IMPT plan, a VMAT plan is first generated either by experienced planner or by in‐house developed automatic planning system. An in‐house developed tool is used to generate the dose volume constrains for the IMPT plan as plan template to Eclipse TPS. The beam angles for IMPT plan are selected based on the preferred angles in the VMAT plan. IMPT plan is designed by importing the plan objectives generated from VMAT plan. Majority thoracic IMPT plans are designed using this plan approach in our center. In this work, a thoracic IMPT plan under RTOG 1308 protocol is selected to demonstrate the effectiveness and efficiency of this approach. The dosimetric indices of IMPT are compared with VMAT plan.

Results:

The PTV D95, lung V20, MLD, mean heart dose, esophagus D1, cord D1 are 70Gy, 31%, 17.8Gy, 25.5Gy, 73Gy, 45Gy for IMPT plan and 65.3Gy, 34%, 21.6Gy, 35Gy, 74Gy, 48Gy for VMAT plan. For majority cases, the high dose region of the normal tissue which is in proximity of PTV is comparable between IMPT and VMAT plan. The low dose region of the IMPT plan is significantly better than VMAT plan.

Conclusion:

Using the knowledge gained in VMAT plan design can help efficiently and effectively design high quality IMPT plan. The quality of IMPT plan can be controlled to ensure the superiority of IMPT plan compared to VMAT/IMRT plan.
SU‐E‐T‐45: A Modified Winston‐Lutz Test for Single Isocenter Multiple Targets SRS QA
Authors: Song C , Xue K , Li R , Xue T
Published: June 2015

Purpose:

When treating multiple targets with a single isocenter, the distances between some targets and the isocenter may be large. The gantry, couch and collimator angle errors, as well as the isocenter errors, are important for this kind of SRS treatment. We developed a Modified Winston‐Lutz (MWL) test to check the combined errors of the isocenter, the aforementioned angles, and MLC position and alignment.

Methods:

We use a phantom cube (VisionRt SRS QA phantom) containing 5 ceramic spheres with diameters of 7.5 mm. The maximum distance between two spheres is 8.0 cm, with the central sphere at the center of the phantom. The treatment machine is a TrueBeam STx with HD‐MLC. The spheres are contoured on CT images using the Varian Eclipse planning system. We generated eight fields with combinations of gantry angles of 0, 90, 180 and 270, couch angles of 0, 90 and 270, and collimator angles of 0, 45, 90, 270 and 315. The MLC apertures of four fields are fitted to spheres 1, 3 and 5 with 2 mm margins, and the other four fields are fitted to spheres 2 and 4. After CBCT alignment of the phantom, the eight fields are imaged with the MV port imager.

Results:

The MLC aperture off‐center errors of the central sphere and the maximum off‐center errors of the other four spheres are measured on the port images for each field. After eight tests, the errors of the central sphere on each field range from 0.0 mm to 0.6 mm. The maximum errors of the other spheres on each field range from 0.5 mm to 1.0 mm.

Conclusion:

We have developed an MWL test for single isocenter multiple target SRS treatments. On the TrueBeam, the errors of targets within 4 cm of the isocenter are 1 mm or less.
SU‐E‐T‐46: A Monte Carlo Investigation of Radiation Interactions with Gold Nanoparticles in Water for 6 MV, 85 KeV and 40 KeV Photon Beams
Authors: Flint D B , O'Brien D J , McFadden C H , Hallacy T M , Wolfe T , Krishnan S , Sawakuchi G O
Published: June 2015

Purpose:

To determine the effect of gold‐nanoparticles (AuNPs) on energy deposition in water for different irradiation conditions.

Methods:

TOPAS version B12 Monte Carlo code was used to simulate energy deposition in water from monoenergetic 40 keV and 85 keV photon beams and a 6 MV Varian Clinac photon beam (IAEA phase space file, 10x10 cm2, SSD 100 cm). For the 40 and 85 keV beams, monoenergetic 2x2 mm2 parallel beams were used to irradiate a 30x30x10 µm 3 water mini‐phantom located at 1.5 cm depth in a 30x30x50 cm3 water phantom. 5000 AuNPs of 50 nm diameter were randomly distributed inside the mini‐phantom. Energy deposition was scored in the mini‐phantom with the AuNPs’ material set to gold and then water. For the 6 MV beam, we created another phase space (PHSP) file on the surface of a 2 mm diameter sphere located at 1.5 cm depth in the water phantom. The PHSP file consisted of all particles entering the sphere including backscattered particles. Simulations were then performed using the new PHSP as the source with the mini‐phantom centered in a 2 mm diameter water sphere in vacuum. The g4em‐livermore reference list was used with “EMRangeMin/EMRangeMax = 100 eV/7 MeV” and “SetProductionCutLowerEdge = 990 eV” to create the new PHSP, and “SetProductionCutLowerEdge = 100 eV” for the mini‐phantom simulations. All other parameters were set as defaults (“finalRange = 100 µm”).

Results:

The addition of AuNPs resulted in an increase in the mini‐phantom energy deposition of (7.5 ± 8.7)%, (1.6 ± 8.2)%, and (−0.6 ± 1.1)% for 40 keV, 85 keV and 6 MV beams respectively.

Conclusion:

Enhanced energy deposition was seen at low photon energies, but decreased with increasing energy. No enhancement was observed for the 6 MV beam. Future work is required to decrease the statistical uncertainties in the simulations.

This research is partially supported from institutional funds from the Center for Radiation Oncology Research, The University of Texas MD Anderson Cancer Center.
SU‐E‐T‐48: A Multi‐Institutional Study of Independent Dose Verification for Conventional, SRS and SBRT
Authors: Takahashi R , Tachibana H , Kamima T , Itano M , Yamazaki T , Ishibashi S , Higuchi Y , Shimizu H , Yamamoto T , Yamashita M , Baba H , Sugawara Y , Sato A , Nishiyama S , Kawai D , Miyaoka S
Published: June 2015

Purpose:

To show the results of a multi‐institutional study of the independent dose verification for conventional, Stereotactic radiosurgery and body radiotherapy (SRS and SBRT) plans based on the action level of AAPM TG‐114.

Methods:

This study was performed at 12 institutions in Japan. To eliminate the bias of independent dose verification program (Indp), all of the institutions used the same CT‐based independent dose verification software (Simple MU Analysis, Triangle Products, JP) with the Clarkson‐based algorithm. Eclipse (AAA, PBC), Pinnacle3 (Adaptive Convolve) and Xio (Superposition) were used as treatment planning system (TPS). The confidence limits (CL, Mean±2SD) for 18 sites (head, breast, lung, pelvis, etc.) were evaluated in comparison in dose between the TPS and the Indp.

Results:

A retrospective analysis of 6352 treatment fields was conducted. The CLs for conventional, SRS and SBRT were 1.0±3.7 %, 2.0±2.5 % and 6.2±4.4 %, respectively. In conventional plans, most of the sites showed within 5 % of TG‐114 action level. However, there were the systematic difference (4.0±4.0 % and 2.5±5.8 % for breast and lung, respectively). In SRS plans, our results showed good agreement compared to the action level. In SBRT plans, the discrepancy between the Indp was variable depending on dose calculation algorithms of TPS.

Conclusion:

The impact of dose calculation algorithms for the TPS and the Indp affects the action level. It is effective to set the site‐specific tolerances, especially for the site where inhomogeneous correction can affect dose distribution strongly.