bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐J‐156: Preclinical Inverstigation of Dynamic Tumor Tracking Using Vero SBRT Linear Accelerator: Motion Phantom Dosimetry Study
Authors: Mamalui‐Hunter M , Wu J , Li Z , Su Z
Published: July 2014

Purpose:

Following the ‘end‐to‐end testing’ paradigm of Dynamic Target Tracking option in our Image‐Guided dedicated SBRT VeroTM linac, we verify the capability of the system to deliver planned dose to moving targets in the heterogeneous thorax phantom (CIRSTM). The system includes gimbaled C‐band linac head, robotic 6 degree of freedom couch and a tumor tracking method based on predictive modeling of target position using fluoroscopically tracked implanted markers and optically tracked infrared reflecting external markers.

Methods:

4DCT scan of the motion phantom with the VisicoilTM implanted marker in the close vicinity of the target was acquired, the ‘exhale’=most prevalent phase was used for planning (iPlan by BrainLabTM). Typical 3D conformal SBRT treatment plans aimed to deliver 6‐8Gy/fx to two types of targets: a)solid water‐equivalent target 3cm in diameter; b)single VisicoilTM marker inserted within lung equivalent material. The planning GTV/CTV‐to‐PTV margins were 2mm, the block margins were 3 mm. The dose calculated by MonteCarlo algorithm with 1% variance using option Dose‐to‐water was compared to the ion chamber (CC01 by IBA Dosimetry) measurements in case (a) and GafchromicTM EBT3 film measurements in case (b). During delivery, the target 6 motion patterns available as a standard on CIRSTM motion phantom were investigated: in case (a), the target was moving along the designated sine or cosine4 3D trajectory; in case (b), the inserted marker was moving sinusoidally in 1D.

Results:

The ion chamber measurements have shown the agreement with the planned dose within 1% under all the studied motion conditions. The film measurements show 98.1% agreement with the planar calculated dose (gamma criteria: 3%/3mm).

Conclusion:

We successfully verified the capability of the SBRT VeroTM linac to perform real‐time tumor tracking and accurate dose delivery to the target, based on predictive modeling of the correlation between implanted marker motion and external surrogate of breathing motion.
SU‐E‐J‐160: Comparing the Setup Accuracy of Non‐Ionizing Patient Localization Systems with CBCT to Reduce Imaging Dose in Prone Breast Treatments
Authors: Chung E , Yamamoto T , Mayadev J , Dieterich S
Published: July 2014

Purpose:

CBCT is the current gold standard to verify prone breast patient setup. We investigated in a phantom if non‐ionizing localization systems can replace ionizing localization systems for prone breast treatments.

Methods:

An anthropomorphic phantom was positioned on a prone breast board. Electromagnetic transponders were attached on the left chest surface. The CT images of the phantom were imported to the treatment planning system. The isocenter was set to the center of the transponders. The positions of the isocenter and transponders transferred to the transponder tracking system. The posterior phantom surface was contoured and exported to the optical surface tracking system. A CBCT was taken for the initial setup alignment on the treatment machine. Using the electromagnetic and optical localization systems, the deviation of the phantom setup from the original CT images was measured. This was compared with the difference between the original CT and kV‐CBCT images.

Results:

For the electromagnetic localization system, the phantom position deviated from the original CT in 1.5 mm, 0.0 mm and 0.5 mm in the anterior‐posterior (AP), superior‐inferior (SI) and left‐right (LR) directions. For the optical localization system, the phantom position deviated from the original CT in 2.0 mm, −2.0 mm and 0.1 mm in the AP, SI and LR directions. For the CBCT, the phantom position deviated from the original CT in 4.0 mm, 1.0 mm and −1.0 mm in the AP, SI and LR directions. The measured values from the non‐ionizing localization systems differed from those with the CBCT less than 3.0 mm in all directions.

Conclusions:

This phantom study showed the feasibility of using a combination of non‐ionizing localization systems to achieve a similar setup accuracy as CBCT for prone breast patients. This could potentially eliminate imaging dose. As a next step, we are expanding this study to actual patients.

This work has been in part supported by Departmental Research Award RODEPT1‐JS001, Department of Radiation Oncology, UC Davis Medical Center.
SU‐E‐J‐162: Quality Assurance Procedures for MR Guided Focused Ultrasound Treatment of Bone Metastasis
Authors: Chen L , Chen X , Wang B , Gupta R , Ma C
Published: July 2014

Purpose:

The purpose of this work is to develop and verify our quality assurance (QA) procedures to ensure the safety and efficacy of MR‐guided focused ultrasound (MRgFUS) treatment of bone metastases.

Methods:

A practical QA program was developed. Monthly and daily QA (DQA) procedures were performed. The major QA items included the checks of the machine hardware, software and patient safety features. Briefly, these checks/tests include: 1) the cooling system reservoir and treatment table; 2) power to the treatment table; 3) the MR coil; 4) the transducer position with MRI; 5) image display on the treatment work station; 6) the effective focal spot in 3 directions using MR thermometry; and 7) all the safety devices including a sonication lamp, and the emergency stop‐sonication switches. In order to avoid patient skin burn, it is important to remove gas bubbles in the interfaces between the treatment table and the gel pad, and the gel pad and patients skin during the patient setup. Our QA procedures have been verified and evaluated through patient treatments. Seven patients with scapula, humeral head, sacrum, ilium, pubic ramus and acetabular bone metastases were treated using MRgFUS.

Results:

Our study showed that all seven patients tolerated the MRgFUS treatment well. No skin toxicity or other complications were observed. The pain score (0–10) using the visual analog scale (VAS) was significantly reduced from 8.0 ± 1.1 before treatment to 4.7 ± 3.0, 3.0 ± 1.5, 3.2 ± 2.8 and 3.4 ± 1.5 at one day, one month, two months and three months after the MRgFUS treatment, respectively.

Conclusion:

We demonstrated that with the appropriate QA procedures, MRgFUS is a safe, effective and noninvasive treatment modality for palliation of bone metastases.
SU‐E‐J‐182: A Feasibility Study Evaluating Automatic Identification of Gross Tumor Volume for Breast Cancer Radiotherapy Using Dynamic Contrast‐Enhanced MR Imaging
Authors: Wang C , Horton J , Yin F , Blitzblau R , Palta M , Chang Z
Published: July 2014

Purpose:

To develop a computerized pharmacokinetic model‐free Gross Tumor Volume (GTV) segmentation method based on dynamic contrastenhanced MRI (DCE‐MRI) data that can improve physician GTV contouring efficiency.

Methods:

12 patients with biopsy‐proven early stage breast cancer with post‐contrast enhanced DCE‐MRI images were analyzed in this study. A fuzzy c‐means (FCM) clustering‐based method was applied to segment 3D GTV from pre‐operative DCE‐MRI data. A region of interest (ROI) is selected by a clinician/physicist, and the normalized signal evolution curves were calculated by dividing the signal intensity enhancement value at each voxel by the pre‐contrast signal intensity value at the corresponding voxel. Three semi‐quantitative metrics were analyzed based on normalized signal evolution curves: initial Area Under signal evolution Curve (iAUC), Immediate Enhancement Ratio (IER), and Variance of Enhancement Slope (VES). The FCM algorithm wass applied to partition ROI voxels into GTV voxels and non‐GTV voxels by using three analyzed metrics. The partition map for the smaller cluster is then generated and binarized with an automatically calculated threshold. To reduce spurious structures resulting from background, a labeling operation was performed to keep the largest three‐dimensional connected component as the identified target. Basic morphological operations including hole‐filling and spur removal were useutilized to improve the target smoothness. Each segmented GTV was compared to that drawn by experienced radiation oncologists. An agreement index was proposed to quantify the overlap between the GTVs identified using two approaches and a thershold value of 0.4 is regarded as acceptable.

Results:

The GTVs identified by the proposed method were overlapped with the ones drawn by radiation oncologists in all cases, and in 10 out of 12 cases, the agreement indices were above the threshold of 0.4.

Conclusion:

The proposed automatic segmentation method was shown to be promising and might be used to improve physician contouring efficiency.

J Horton receives grant from NIH and Varian Medical Systems; F‐F Yin receives grant from Varian Medical Systems
SU‐E‐J‐183: Quantifying the Image Quality and Dose Reduction of Respiratory Triggered 4D Cone‐Beam Computed Tomography with Patient‐ Measured Breathing
Authors: Cooper B , OBrien R , Kipritidis J , Keall P
Published: July 2014

Purpose:

Respiratory triggered four dimensional cone‐beam computed tomography (RT 4D CBCT) is a novel technique that uses a patient's respiratory signal to drive the image acquisition with the goal of imaging dose reduction without degrading image quality. This work investigates image quality and dose using patient‐measured respiratory signals for RT 4D CBCT simulations instead of synthetic sinusoidal signals used in previous work.

Methods:

Studies were performed that simulate a 4D CBCT image acquisition using both the novel RT 4D CBCT technique and a conventional 4D CBCT technique from a database of oversampled Rando phantom CBCT projections. A database containing 111 free breathing lung cancer patient respiratory signal files was used to create 111 RT 4D CBCT and 111 conventional 4D CBCT image datasets from realistic simulations of a 4D RT CBCT system. Each of these image datasets were compared to a ground truth dataset from which a root mean square error (RMSE) metric was calculated to quantify the degradation of image quality. The number of projections used in each simulation is counted and was assumed as a surrogate for imaging dose.

Results:

Based on 111 breathing traces, when comparing RT 4D CBCT with conventional 4D CBCT the average image quality was reduced by 7.6%. However, the average imaging dose reduction was 53% based on needing fewer projections (617 on average) than conventional 4D CBCT (1320 projections).

Conclusion:

The simulation studies using a wide range of patient breathing traces have demonstrated that the RT 4D CBCT method can potentially offer a substantial saving of imaging dose of 53% on average compared to conventional 4D CBCT in simulation studies with a minimal impact on image quality.

A patent application (PCT/US2012/048693) has been filed which is related to this work.
SU‐E‐J‐194: Dynamic Tumor Tracking End‐To‐End Testing Using a 4D Thorax Phantom and EBT3 Films
Authors: Su Z , Wu J , Li Z , Mamalui‐Hunter M
Published: July 2014

Purpose:

To quantify the Vero linac dosimetric accuracy of the tumor dynamic tracking treatment using EBT3 film embedded in a 4D thorax phantom.

Methods:

A dynamic thorax phantom with tissue equivalent materials and a film insert were used in this study. The thorax phantom was scanned in 4DCT mode with a viscoil embedded in its film insert composed of lung equivalent material. Dynamic tracking planning was performed using the 50% phase CT set with 5 conformal beams at gantry angles of 330, 15, 60, 105 and 150 degrees. Each field is a 3cm by 3cm square centered at viscoil since there was no solid mass target. Total 3 different 1–2cos4 motion profiles were used with varied motion magnitude and cycle frequency. Before treatment plan irradiation, a 4D motion model of the target was established using a series of acquired fluoroscopic images and infrared markers motion positions. During irradiation, fluoroscopic image monitoring viscoil motion was performed to verify model validity. The irradiated films were scanned and the dose maps were compared to the planned Monte Carlo dose distributions. Gamma analyses using 3%–3mm, 2%–3mm, 3%–2mm, 2%–2mm criteria were performed and presented.

Results:

For each motion pattern, a 4D motion model was built successfully and the target tracking performance was verified with fluoroscopic monitoring of the viscoil motion and its model predicted locations. The film gamma analysis showed the average pass rates among the 3 motion profiles are 98.14%, 96.2%, 91.3% and 85.61% for 3%–3mm, 2%–3mm, 3%–2mm, 2%–2mm criteria.

Conclusion:

Target dynamic tracking was performed using patient‐like breathing patterns in a 4D thorax phantom with EBT3 film insert and a viscoil. There was excellent agreement between acquired and planned dose distributions for all three target motion patterns. This study performed end‐to‐end testing and verified the treatment accuracy of tumor dynamic tracking.
SU‐E‐J‐203: Reconstruction of the Treatment Area by Use of Sinogram in Helical Tomotherapy
Authors: Haga A , Nakagawa K , Maurer C , Ruchala K , Chao E , Casey D , Ida S , Sakata D , Magome T , Nakano M , Masutani Y
Published: July 2014

Purpose:

TomoTherapy (Accuray Co.) has an image‐guided radiotherapy system with megavoltage (MV) X‐ray source and the on‐board imaging device. With the MV computed tomography (MVCT), it became feasible to perform the efficient daily‐3D registration of the patient position before each treatment delivery. This system also allows one to acquire the delivery sinogram during the actual treatment, which partly includes the information of the irradiated object. In this study, we try to develop the image reconstruction during treatment in helical Tomotherapy.

Methods:

Sinogram data were acquired during helical Tomotherapy delivery using an arc‐shaped detector array that consists of 738 xenon‐gas filled detector cells. In preprocessing, these were normalized by full air‐scan data. A software program was developed that reconstructs 3D images during treatment with corrections as; (1) the regions outside the field were masked not to be added in the backprojection (a masking correction), and (2) each voxel of the reconstructed image was divided by the number of the X‐ray passing through its voxel (a ray‐passing correction).

Results:

Without masking and ray‐passing corrections, the image reconstruction was failed. The masking correction made the image clear, however, the streak artifact was accompanied. The ray‐passing correction reduced this artifact. Although the SNR (the ratio of mean to standard deviation in homogeneous region) and the contrast of the reconstructed image were slightly improved with the ray‐passing correction, the masking correction only is enough for the visualization purpose.

Conclusion:

The visualization of the treatment area was feasible by use of the sinogram in helical Tomotherapy. This proposed method can be utilized in the treatment verification.

This work was partly supported by JSPS KAKENHI 24234567. No COI, but the data in this paper were prepared by collaborators in Accuray.
SU‐E‐J‐207: Assessing the Validity of 4D‐CT Based Target Volumes and Free Breathing CBCT Localization in Lung Stereotactic Ablative Radiation Therapy (SABR)
Authors: Badkul R , Pokhrel D , Jiang H , Park J , Wang F , Kumar P
Published: July 2014

Purpose:

Four‐dimensional‐computed‐tomography(4D‐CT) imaging for target‐volume delineation and cone‐beam‐tomography(CBCT) for treatment localization are widely utilized in lung‐SABR.Aim of this study was to perform a quantitative‐assessment and inter‐comparison of Internal‐targetvolumes(ITV) drawn on various phases of breathing‐cycle 4D‐CT‐scans, Maximum‐intensity‐projection(MIP), average‐intensity‐projection(AIP)and static CT‐scans of lung‐motion‐phantom to simulate lung‐SABR patient geometry. We also analyzed and compared the ITVs drawn on freebreathing‐ CBCT.

Materials & Methods:

4D‐CT‐scans were acquired on Philips big‐bore 16slice CT and Bellows‐respiratory monitoring‐system using retrospective phase‐binning method. Each respiratory cycle divided into 10‐phases. Quasar‐Phantom with lung‐inserts and 3cm‐diameter nylonball to simulate tumor and was placed on respiratory‐motion‐platform for 4D‐CT and CBCT‐acquisition. Amplitudes of motions: 0.5,1.0,2.0,3.0cm in superior‐inferior direction with breathing‐cycle time of 6,5,4,6sec, respectively used.4D‐CTs with 10‐phases(0%to90%)for each excursion‐set and 3D‐CT for static‐phantom exported to iPlan treatment‐planningsystem(TPS). Tumor‐volumes delineated in all phases of 4D‐CT, MIP,AIP,CBCT scans using fixed‐HU‐threshold(−500to1000)values automatically.For each 4D‐dataset ITV obtained by unifying the tumorcontours on all phases.CBCT‐ITV‐volumes were drawn in Eclipse‐TPS.

Results:

Mean volume of tumor contours for all phases compared with static 3D‐CT were 0.62±0.08%, 1.67±0.26%, 4.77±0.54% and 9.27±1.23% for 0.5cm,1cm,2cm,3cm excursions respectively. Differences of mean Union‐ITV with MIP‐ITV were close(≤2.4%).Mean Union‐ITV from expected‐theoretical values differed from −4.9% to 3.8%.Union‐ITV and MIP‐ITV were closer within 2.3%. AIP‐ITVs were underestimated from 14 to 32% compared to union‐ITV for all motion datasets. Differences of −5.9% to −44% and −5% to 6.7% for CBCT‐ITV from MIP‐ITV and AIP‐ITV respectively.Motion excursions and centroid positions were within 2mm for 4D‐CT and CBCT‐ITVs to that of expected values.

Conclusion:

4D‐CT MIP‐ITV and Union‐ITV showed very good agreement that validates that ITV can be fast contoured on MIP.Contouring ITV in AIP must be avoided as it significantly underestimates the volume with all excursions. Free breathing CBCT‐ITV showed good agreement with AIP‐ITV but underestimated the MIP‐ITV. Estimation of excursions and centroid values for 4D‐CT and CBCT were in good agreement with expected values.
SU‐E‐T‐01: 2‐D Characterization of DLG Among All MLC Leaf Pairs
Authors: Kumaraswamy L , Schmitt J , Bailey D , Xu Z , Podgorsak M
Published: July 2014

Purpose:

The aim of this study is to evaluate the variation of dosimetric leaf‐gap (DLG) along the travel path of each MLC leaf pair. This study evaluates whether the spatial variations in DLG could cause dose differences between TPS‐calculated and measured dose.

Methods:

The 6MV DLG values were measured for all leaf pairs in the direction of leaf motion using a 2‐D diode array and 0.6cc ion chamber. These measurements were performed on two Varian Linacs, employing the Millennium 120‐leaf MLC and a 2‐D‐DLG variation map was created via in‐house software. Several test plans were created with sweeping MLC fields using constant gaps from 2mm to 10mm and corrected for 2‐D variation utilizing in‐house software. Measurements were performed utilizing the MapCHECK at 5.0cm depth for plans with and without the 2‐D DLG correction and compared to the TPS calculated dose via gamma analysis (3%/3mm).

Results:

The measured DLGs for the middle 40 MLC leaf pairs (0.5cm width) were very similar along the central superior‐inferior axis, with maximum variation of 0.2mm. The outer 20 MLC leaf pairs (1.0cm width) have DLG values from 0.32mm (mean) to 0.65mm (maximum) lower than the central leaf‐pair, depending on off‐axis distance. Gamma pass rates for the 2mm, 4mm, and 6mm sweep plans increased by 23.2%, 28.7%, and 26.0% respectively using the 2‐D‐DLG correction. The most improved dose points occur in areas modulated by the 1.0cm leaf‐pairs. The gamma pass rate for the 10mm sweep plan increased by only 7.7%, indicating that the 2D variation becomes less significant for dynamic plans with larger MLC gaps.

Conclusion:

Fluences residing significantly off‐axis with narrow sweeping gaps may exhibit significant variations from planned dose due to large differences between the true DLG exhibited by the 1.0cm leaf‐pairs versus the constant DLG value utilized by the TPS for dose calculation.
SU‐E‐T‐02: 3D Dose Reconstruction of Volumetric Modulated Arc Therapy From Delivered EPID Dose Image
Authors: Yoon J , Jung J , Kim J , Yeo I
Published: July 2014

Purpose:

To evaluate dose reconstruction of volumetric modulated arc therapy (VMAT) from EPID image prediction.

Methods:

A test VMAT plan with dynamic MLCs was developed on a water equivalent cubic phantom with dimension of 31.4×34×34 cm3. From the initial MLC opening of 5×5 cm2 at gantry 0°, they moved with a constant speed as the gantry rotates, until they reached X1 at −2.5 cm and X2 at = −2.237 cm at gantry 90°. The plan was delivered while cine EPID images were acquired. For the 84 gantry angle segments, doses to the phantom were calculated by XVMC and reconstructed from EPID based on fast density‐scaled model and non‐iterative dose reconstruction method we have previously developed. The reconstructed dose was compared with the forwardly calculated dose individually over 84 gantry angle segments and cumulatively in terms of gamma evaluation and dose volume histogram for PTV (3×3×3 cm3) positioned at the center of the phantom.

Results:

3D‐gamma pass rate was 97.0 % cumulatively with 3 %/3 mm criteria and maximum 100% individually. The DVHs of PTV were indistinguishable except in the region of high dose (>95% of prescribed dose) where the difference of a few percent in volume was found.

Conclusion:

Showing good agreement with the forwardly calculated dose, we have extended our model of dose reconstruction successfully to the verification of VMAT. Although more clinical demonstration is to be followed, our study presents a promising tool for time‐resolved and cumulative VMAT validation.
SU‐E‐T‐04: 3D Printed Patient‐Specific Surface Mould Applicators for Brachytherapy Treatment of Superficial Lesions
Authors: Cumming I , Joshi C P , Lasso A , Rankin A , Falkson C , Schreiner L John , Fichtinger G
Published: July 2014

Purpose:

Evaluate the feasibility of constructing 3D‐printed patient‐specific surface mould applicators for HDR brachytherapy treatment of superficial lesions.

Methods:

We propose using computer‐aided design software to create 3D printed surface mould applicators for brachytherapy. A mould generation module was developed in the open‐source 3D Slicer (www.slicer.org) medical image analysis platform. The system extracts the skin surface from CT images, and generates smooth catheter paths over the region of interest based on user‐defined start and end points at a specified stand‐off distance from the skin surface. The catheter paths are radially extended to create catheter channels that are sufficiently wide to ensure smooth insertion of catheters for a safe source travel. An outer mould surface is generated to encompass the channels. The mould is also equipped with fiducial markers to ensure its reproducible placement. A surface mould applicator with eight parallel catheter channels of 4mm diameters was fabricated for the nose region of a head phantom; flexible plastic catheters of 2mm diameter were threaded through these channels maintaining 10mm catheter separations and a 5mm stand‐off distance from the skin surface. The apparatus yielded 3mm thickness of mould material between channels and the skin. The mould design was exported as a stereolithography file to a Dimension SST1200es 3D printer and printed using ABS Plus plastic material.

Results:

The applicator closely matched its design and was found to be sufficiently rigid without deformation during repeated application on the head phantom. Catheters were easily threaded into channels carved along catheter paths. Further tests are required to evaluate feasibility of channel diameters smaller than 4mm.

Conclusion:

Construction of 3D‐printed mould applicators show promise for use in patient specific brachytherapy of superficial lesions. Further evaluation of 3D printing techniques and materials is required for constructing sufficiently thin, rigid and durable surface moulds suitable for clinical deployment.
SU‐E‐T‐07: A Comparison of SSD and Field Size Dependence of Output for Megavoltage Electron Beams for Different Manufacturers
Authors: Dimofte A , Zhu T
Published: July 2014

Purpose:

The purpose of this study was to compare the electron beam in‐air output factor (H) for Varian and Siemens accelerators.

Methods:

Measurements were performed among four accelerators: Varian CL2300ix, Varian TrueBeam, Siemens Oncor, and Siemens Primus. The nominal electron energy measured ranges from 6 to 21 MeV. Measurements were made in air using a diode detector for different square cone sizes (6 – 25cm) with circular field inserts with radius r between 1 cm and 8 cm and for different SSD (100 – 120 cm). H is defined asH(r,SSD)= X(r,SSD)/X(open,SSD), where X is the charge measured by the diode detector without buildup cap in air.

Results:

For the same nominal energy, cone size, radius of circular cutout, and SSD, H agreed within a maximum deviation of 2.3% and standard deviation of 1% among Varian accelerators but can be as much as 8.7% different between the Varian and the Siemens accelerators. H is a function of electron energy and cutout radius only when the field radius for H measured at different SSD is renormalized as r = r0*5/(SSD‐95), where r0 is the physical field radius at the end of the cone. The radius dependence of H for five cone sizes (6×6, 10×10, 15×15, 20×20 and 25×25cm2) and three SSD(100, 110 and 120cm) for three energies was measured.

Conclusion:

The in air output factor (H) measured for the same manufacturer can be treated as identical to within 1.1% for Varian machines and to within 1.6% for Siemens machines, but the difference in H measured for the different manufacturers is large enough (>2%) to require machine specific data set.
SU‐E‐T‐15: A Home Grown Process Improvement Tracking Tool
Authors: Sansourekidou P , Pavord D
Published: July 2014

Purpose:

To evaluate the use of a web based error tracking system.

Methods:

A web based error tracking system called the PIT (Process Improvement Tracking Tool) was used by all staff members to enter errors found at all parts of the treatment process in four satellite facilities. An error is defined as an action that did not fully comply with policy and procedure. Entries were made in real time by all staff members and require that the user enters the date of the incident, the patient medical record number, the physical location of the site, the process during which the error was found and categorize the incident type.

Results:

Number of errors is approximately proportional to the number of patient treatments. Errors: VBMC 45%, UROC 25%, FROC 13%, PHC 17%. Treatments: VBMC 38%, UROC 32%, FROC 16%, PHC 14%. Staff members making the most mistakes are therapists (36%), dosimetrists (23%) and physicists (15%). Processes where errors were found: physics weekly 25%, therapist weekly 18%, physics second check 15%, physics peer review 6%, therapists check 5%, treatment 5% and various other steps 26%.

Conclusion:

Proportionality of the number of patients treated to the number of errors implies homogeneity across four satellites. Differences between staff member error percentages need to be investigated more thoroughly, but possible explanations are workload and staffing levels. Step in the process where errors are found implies the need for improved processes upstream. Specifically, 5% errors discovered during treatment is considered very high and a specific attempt to reduce it will be undertaken. The vast majority of the errors discovered during treatment were found before the treatment was delivered. Only four were discovered after delivery and none involved significant dose errors. Further work is required to identify the exact procedures within the department that will achieve this goal.
SU‐E‐T‐16: A Hybrid VMAT/IMRT Technique for the Treatment of Nasopharyngeal Carcinoma
Authors: Zhao N , Yang R , Wang J
Published: July 2014

Purpose:

To investigate a Hybrid VMAT/IMRT technique which combines volumetric modulated arc therapy (VMAT) and intensity modulated radiation therapy (IMRT) for nasopharyngeal carcinoma (NPC).

Methods:

2 full arcs VMAT, 9‐field IMRT and Hybrid VMAT/IMRT plans were created for 10 patients with NPC. The Hybrid VMAT/IMRT technique consisted of 1 full VMAT arc and 7 IMRT fields. The dose distribution of planning target volume (PTV) and organs at risk (OARs) for Hybrid VMAT/IMRT was compared with IMRT and VMAT. The monitor units (MUs) were also evaluated.

Results:

The Hybrid VMAT/IMRT technique significantly improved target dose homogeneity compared with IMRT and VMAT for PTV70 and PTV54. For PTV70 and PTV60, the Hybrid VMAT/IMRT technique significantly improved target dose conformity compared with IMRT (0.62 vs 0.47; p<0.05 and 0.64 vs 0.58; p<0.05, respectively) and VMAT (0.62 vs 0.43; p<0.05 and 0.64 vs 0.6; p<0.05, respectively). The near maximum dose (D2%) of temporomandibular joint (TMJ), temporal lobe and mandible for Hybrid plans were 5.5%, 7.9% and 5.2% lower than IMRT plans (p<0.05). The mean dose of TMJ, temporal lobe, mandible and unspecified tissue for Hybrid plans were 12.8%, 11.4%, 4.2% and 4.1% lower than IMRT plans (p<0.05). The mean dose of right parotid, mandible and unspecified tissue for Hybrid plans were 3.3%, 2.4% and 3.1% lower than VMAT plans (p<0.05). The mean MUs needed for IMRT, VMAT and Hybrid plans were 2256, 507 and 1394, respectively.

Conclusion:

Hybrid VMAT/IMRT technique significantly improved the target dose homogeneity and conformity compared with IMRT and VMAT and reduced the dose of OARs and unspecified tissue compared with IMRT with fewer MUs. Compared with VMAT, Hybrid VMAT/IMRT technique can better protect parotid gland, mandible and unspecified tissue. Ruijie Yang was funded by the grant project: National Natural Science Foundation of China (No. 81071237). Other authors have no competing interest for this work.
SU‐E‐T‐17: A Mathematical Model for PinPoint Chamber Correction in Measuring Small Fields
Authors: Li T , Zhang Y , Li X , Heron D.E. , Huq M.Saiful
Published: July 2014

Purpose:

For small field dosimetry, such as measuring the cone output factor for stereotactic radiosurgery, ion chambers often result in underestimation of the dose, due to both the volume averaging effect and the lack of electron equilibrium. The purpose of this work is to develop a mathematical model, specifically for the pinpoint chamber, to calculate the correction factors corresponding to different type of small fields, including single cone‐based circular field and non‐standard composite fields.

Methods:

A PTW 0.015cc PinPoint chamber was used in the study. Its response in a certain field was modeled as the total contribution of many small beamlets, each with different response factor depending on the relative strength, radial distance to the chamber axis, and the beam angle. To get these factors, 12 cone‐shaped circular fields (5mm,7.5mm, 10mm, 12.5mm, 15mm, 20mm, 25mm, 30mm, 35mm, 40mm, 50mm, 60mm) were irradiated and measured with the PinPoint chamber. For each field size, hundreds of readings were recorded for every 2mm chamber shift in the horizontal plane. These readings were then compared with the theoretical doses as obtained with Monte Carlo calculation. A penalized‐least‐square optimization algorithm was developed to find out the beamlet response factors. After the parameter fitting, the established mathematical model was validated with the same MC code for other non‐circular fields.

Results:

The optimization algorithm used for parameter fitting was stable and the resulted response factors were smooth in spatial domain. After correction with the mathematical model, the chamber reading matched with the Monte Carlo calculation for all the tested fields to within 2%.

Conclusion:

A novel mathematical model has been developed for the PinPoint chamber for dosimetric measurement of small fields. The current model is applicable only when the beam axis is perpendicular to the chamber axis. It can be applied to non‐standard composite fields. Further validation with other type of detectors is being conducted.
SU‐E‐T‐18: A New Approach To Cancer Treatment
Authors: Akber S
Published: July 2014

Purpose:

To assess the correlation between mean lethal radiation doses (Do) with NMR water proton spin lattice relaxation time (T1) in different phases of Hela cells.

Methods:

Analysis of T1 with Do was assessed in M, G1, G2 and S‐phase at energies of 220 kVp, 280 kVp and 1.25 MeV (Co‐60).

Results:

T1 against Do in M, G1, G2, and S phase at 220 kVp yield a correlation of 0.80. At 280 kVp and 1.25 MeV the correlation is 0.77 and 0.82 respectively.

Conclusion:

It appears that T1 value decreases from M phase (1020 ± 84 ms) to S phase (534 ± 43 ms). The Do values increases from M phase to S phase. The variation in T1 and Do in different phases of the cell cycles provide a clue to time the mitotic phase at the radiation treatment time. It appears that T1 value decreases from M phase (1020 ± 84 ms) to S phase (534 ± 43 ms). The Do values increases from M phase to S phase. The variation in T1 and Do in different phases of the cell cycles provide a clue to time the mitotic phase at the radiation treatment time.
SU‐E‐T‐19: A New End‐To‐End Test Method for ExacTrac for Radiation and Plan Isocenter Congruence
Authors: Lee S , Nguyen N , Liu F , Huang Y , Sio T , Jung J , Pyakuryal A , Jang S
Published: July 2014

Purpose:

To combine and integrate quality assurance (QA) of target localization and radiation isocenter End to End (E2E) test of BrainLAB ExacTrac system, a new QA approach was devised using anthropomorphic head and neck phantom. This test insures the target localization as well as radiation isocenter congruence which is one step ahead the current ExacTrac QA procedures.

Methods:

The head and neck phantom typically used for CyberKnife E2E test was irradiated to the sphere target that was visible in CT‐sim images. The CT‐sim was performed using 1 mm thickness slice with helical scanning technique. The size of the sphere was 3‐cm diameter and contoured as a target volume using iPlan V.4.5.2. A conformal arc plan was generated using MLC‐based with 7 fields, and five of them were include couch rotations. The prescription dose was 5 Gy and 95% coverage to the target volume. For the irradiation, two Gafchromic films were perpendicularly inserted into the cube that hold sphere inside. The linac used for the irradiation was TrueBeam STx equipped with HD120 MLC. In order to use ExacTrac, infra‐red head–array was used to correlate orthogonal X‐ray images.

Results:

Using orthogonal X‐rays of ExacTrac the phantom was positioned. For each field, phantom was check again with X‐rays and re‐positioned if necessary. After each setup using ExacTrac, the target was irradiated. The films were analyzed to determine the deviation of the radiation isocenter in all three dimensions: superior‐inferior, left‐right and anterior‐posterior. The total combining error was found to be 0.76 mm ± 0.05 mm which was within sub‐millimeter accuracy.

Conclusion:

Until now, E2E test for ExacTrac was separately implemented to test image localization and radiation isocenter. This new method can be used for periodic QA procedures.
SU‐E‐T‐24: A Simple Correction‐Based Method for Independent Monitor Unit (MU) Verification in Monte Carlo (MC) Lung SBRT Plans
Authors: Pokhrel D , Badkul R , Jiang H , Estes C , Kumar P , Wang F
Published: July 2014

Purpose:

Lung‐SBRT uses hypo‐fractionated dose in small non‐IMRT fields with tissue‐heterogeneity corrected plans. An independent MU verification is mandatory for safe and effective delivery of the treatment plan. This report compares planned MU obtained from iPlan‐XVM‐Calgorithm against spreadsheet‐based hand‐calculation using most commonly used simple TMR‐based method.

Methods:

Treatment plans of 15 patients who underwent for MC‐based lung‐SBRT to 50Gy in 5 fractions for PTV V100%=95% were studied. ITV was delineated on MIP images based on 4D‐CT scans. PTVs(ITV+5mm margins) ranged from 10.1‐ 106.5cc(average=48.6cc). MC‐SBRT plans were generated using a combination of non‐coplanar conformal arcs/beams using iPlan XVM‐Calgorithm (BrainLAB iPlan ver.4.1.2) for Novalis‐TX consisting of micro‐MLCs and 6MV‐SRS (1000MU/min) beam. These plans were re‐computed using heterogeneity‐corrected Pencil‐Beam (PB‐hete) algorithm without changing any beam parameters, such as MLCs/MUs. Dose‐ratio: PB‐hete/MC gave beam‐by‐beam inhomogeneity‐correction‐factors (ICFs):Individual Correction. For independent‐2nd‐check, MC‐MUs were verified using TMR‐based hand‐calculation and obtained an average ICF:Average Correction, whereas TMR‐based hand‐calculation systematically underestimated MC‐MUs by ∼5%. Also, first 10 MC‐plans were verified with an ion‐chamber measurement using homogenous phantom.

Results:

For both beams/arcs, mean PB‐hete dose was systematically overestimated by 5.5±2.6% and mean hand‐calculated MU systematic underestimated by 5.5±2.5% compared to XVMC. With individual correction, mean hand‐calculated MUs matched with XVMC by – 0.3±1.4%/0.4±1.4 for beams/arcs, respectively. After average 5% correction, hand‐calculated MUs matched with XVMC by 0.5±2.5%/0.6±2.0% for beams/arcs, respectively. Smaller dependence on tumor volume(TV)/field size(FS) was also observed. Ion‐chamber measurement was within ±3.0%.

Conclusion:

PB‐hete overestimates dose to lung tumor relative to XVMC. XVMC‐algorithm is much more‐complex and accurate with tissues‐heterogeneities. Measurement at machine is time consuming and need extra resources; also direct measurement of dose for heterogeneous treatment plans is not clinically practiced, yet. This simple correction‐based method was very helpful for independent‐2nd‐check of MC‐lung‐SBRT plans and routinely used in our clinic. A look‐up table can be generated to include TV/FS dependence in ICFs.
SU‐E‐T‐27: A Tool for Routine Quality Assurance of Radiotherapy Dose Calculation Software
Authors: Popple R , Cardan R , Duan J , Wu X , Shen S , Brezovich I
Published: July 2014

Purpose:

Dose calculation software is thoroughly evaluated when it is commissioned; however, evaluation of periodic software updates is typically limited in scope due to staffing constraints and the need to quickly return the treatment planning system to clinical service. We developed a tool for quickly and comprehensively testing and documenting dose calculation software against measured data.

Methods:

A tool was developed using MatLab (The MathWorks, Natick, MA) for evaluation of dose calculation algorithms against measured data. Inputs to the tool are measured data, reference DICOM RT PLAN files describing the measurements, and dose calculations in DICOM format. The tool consists of a collection of extensible modules that can perform analysis of point dose, depth dose curves, and profiles using dose difference, distance‐to‐agreement, and the gamma‐index. Each module generates a report subsection that is incorporated into a master template, which is converted to final form in portable document format (PDF).

Results:

After each change to the treatment planning system, a report can be generated in approximately 90 minutes. The tool has been in use for more than 5 years, spanning 5 versions of the eMC and 4 versions of the AAA. We have detected changes to the algorithms that affected clinical practice once during this period.

Conclusion:

Our tool provides an efficient method for quality assurance of dose calculation software, providing a complete set of tests for an update. Future work includes the addition of plan level tests, allowing incorporation of, for example, the TG‐119 test suite for IMRT, and integration with the treatment planning system via an application programming interface. Integration with the planning system will permit fully‐automated testing and reporting at scheduled intervals.
SU‐E‐T‐30: Absorbed Doses Determined by Texture Analysis of Gafchromic EBT3 Films Using Scanning Electron Microscopy: A Feasibility Study
Authors: Park S , Kim H , Ye S
Published: July 2014

Purpose:

The texture analysis method is useful to estimate structural features of images as color, size, and shape. The study aims to determine a dose‐response curve by texture analysis of Gafchromic EBT3 film images using scanning electron microscopy (SEM).

Methods:

The uncoated Gafchromic EBT3 films were prepared to directly scan over the active surface layer of EBT3 film using SEM. The EBT3 films were exposed at a dose range of 0 to 10 Gy using a 6 MV photon beam. The exposed film samples were SEM‐scanned at 100X, 1000X, and 3000X magnifications. The four texture features (Homogeneity, Correlation, Contrast, and Energy) were calculated based on the gray level co‐occurrence matrix (GLCM) derived from the SEM images at each dose. To validate a correlation between delivered doses and texture features, an R‐squared value in linear regression was tested.

Results:

The results showed that the Correlation index was more suitable as dose indices than the other three texture features due to higher linearity and sensitivity of the dose response curves. Further the Correlation index of 3000X magnified SEM images with 9 pixel offsets had an R‐squared value of 0.964. The differences between the delivered doses and the doses measured by this method were 0.9, 1.2, 0.2, and 0.2 Gy at 5, 10, 15, and 20 Gy, respectively.

Conclusion:

It seems to be feasible to convert micro‐scale structural features of χtχχχhe EBT3 films to absorbed doses using the texture analysis method.
SU‐E‐T‐38: An Overlap‐Wall‐Histogram Plan Quality Classifier for Automatic Prostate Cancer IMRT Treatment Plan Quality Control
Authors: Song T , Tian Z , Jia X , Zhou L , Jiang S , Gu X
Published: July 2014

Purpose:

A new patient geometry descriptor, PTV and a hollow organ overlapping wall histogram (OWH), is proposed to combine with dose to wall histogram (DWH) to develop a plan quality classification model for automatic prostate IMRT plan quality assessment and improvement.

Methods:

In this study, we define a geometric metric named COP (closeness of an OAR to PTV) to quantify the difficulty of patient geometry for planning and a dosimetric metric named DSO (dose spillage over an OAR) to evaluate treatment plan quality in terms of OAR dose sparing. COP and DSO are defined as the weighted sum of OWH and DWH respectively. Fifteen clinically acceptable prostate treatment plans were selected to study the correlation between COP and DSO. After plotting COP as X axis and DSO as Y axis, a linear correlation was established and the entire space is classified into high and poor plan quality regions by a linear fitting with these COP‐DSO pairs. This proposed classifier is evaluated with other 25 prostate plans. Any evaluation plan falling into the poor plan quality region will be re‐planned, and the re‐planning can be guided by a selected reference plan having similar COP but lower DSO values. Re‐planned high‐quality plans will be added to database, affording more options during reference plan selection.

Results:

Using our classification model, 8 out of 25 plans are identified as poor quality plans. After re‐planning, the dose volume for bladder wall W7 5(wall receiving more than 75Gy),W7 0,W6 5 and W6 0 can be reduced by 3.34%, 3%, 6.99%, 6.54% for the worst quality plan and 1.11%, 0.95%, 1.45% and 1.81% averaged over 8 plans, without sacrificing PTV coverage and rectum dose sparing.

Conclusion:

Our proposed model is capable to identify poor quality plans and find a specific reference plan to guide re‐planning, thus improve plan quality.
SU‐E‐T‐40: Analysis of Composite MVCT Planning Dosimetry with SBRT of Upper Peripheral Lung Cancer
Authors: Yang C , Doxsee K , Chen Y
Published: July 2014

Purpose:

Quantitatively evaluate and compare the final adaptive planning doses of upper peripherally located lung SBRT treated with Tomotherapy using 3rd party software tool.

Methods:

With tumor located in the upper quadrant of lung, a 3rd party software tool was implemented to evaluate the Tomotherapy composite dosimetry created by adaptive fan beam MVCT images described by RTOG 0915 dose criteria (48 Gy / 4 fractions). The composite doses was then summarized with deformable registration in this package with corresponding target and critical structures. The final dosimetry variation, both for target and critical structures, were evaluated in a tabular format and isodose distribution comparisons.

Results:

Composite SBRT treatment doses were evaluated with adaptive planning. The PTV and several critical structures were mapped/deformed into the package via DICOM from Tomotherapy after the final composite doses were created. Initial plan versus the final composite plan calculated from verification images were compared. The ITV defined by 4D CT and contoured on MVCT images were correlated in patient repositioning. Final composite dose calculated for PTV coverage has shown 0.1–0.17 cGy coverage (0.2–0.4% of prescription dose) variation. Total lung and cord were both less than 0.17 Gy which represented <0.4% difference. All other critical structure were within statistical significance. The adaptive plans justified/included the breathing and motion during the treatment process. Final 95% isotope line coverage from prescription has been met without issues.

Conclusions:

With lung tumor location in the upper peripheral area, breathing control was not necessary required during SBRT treatment using Tomotherapy technique. Slow fan beam CT provides definitive ITV information and the adaptive composite plan for all fractions were suitable for final dose delivery. The final composite dose calculated with Tomotherapy adaptive tool indicated that the composite dosimetry justified the target location with SBRT delivery, safe with minimum margin of errors.
SU‐E‐T‐51: Bayesian Network Models for Radiotherapy Error Detection
Authors: Kalet A , Phillips M , Gennari J
Published: July 2014

Purpose:

To develop a probabilistic model of radiotherapy plans using Bayesian networks that will detect potential errors in radiation delivery.

Methods:

Semi‐structured interviews with medical physicists and other domain experts were employed to generate a set of layered nodes and arcs forming a Bayesian Network (BN) which encapsulates relevant radiotherapy concepts and their associated interdependencies. Concepts in the final network were limited to those whose parameters are represented in the institutional database at a level significant enough to develop mathematical distributions. The concept‐relation knowledge base was constructed using the Web Ontology Language (OWL) and translated into Hugin Expert Bayes Network files via the the RHugin package in the R statistical programming language. A subset of de‐identified data derived from a Mosaiq relational database representing 1937 unique prescription cases was processed and pre‐screened for errors and then used by the Hugin implementation of the Estimation‐Maximization (EM) algorithm for machine learning all parameter distributions. Individual networks were generated for each of several commonly treated anatomic regions identified by ICD‐9 neoplasm categories including lung, brain, lymphoma, and female breast.

Results:

The resulting Bayesian networks represent a large part of the probabilistic knowledge inherent in treatment planning. By populating the networks entirely with data captured from a clinical oncology information management system over the course of several years of normal practice, we were able to create accurate probability tables with no additional time spent by experts or clinicians. These probabilistic descriptions of the treatment planning allow one to check if a treatment plan is within the normal scope of practice, given some initial set of clinical evidence and thereby detect for potential outliers to be flagged for further investigation.

Conclusion:

The networks developed here support the use of probabilistic models into clinical chart checking for improved detection of potential errors in RT plans.