bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐09: A Dosimetric Analysis of Various Clinically Used Bolus Materials
Authors: Stowe M , Yeager C , Zhou F , Hand C
Published: July 2014

Purpose:

To evaluate the dosimetric effect of various clinically used bolus materials.

Methods:

Materials investigated include solid water, superflab, wet gauze, wet sheets, Play‐Doh™, and gauze embedded with petroleum jelly. Each bolusing material was scanned in a Philips CT to determine the Hounsfield unit (HU) and to verify uniformity throughout the material. Using the corresponding HU, boluses of 0.5 cm and 1.0 cm thicknesses were created in the Eclipse treatment planning system (TPS) on a solid water phantom. Dose was calculated at various depths for beam energies 6 MV, 6 MeV, 9 MeV, and 12 MeV to determine the effects of each material on deposition of dose. In addition, linac‐based measurements at these energies were made using a farmer chamber in solid water. Wet sheets and wet gauze were measured with various water content to quantify the effects on dose.

Results:

Preliminary CT scans find a range in HU of bolus materials from −120 to almost 300. There is a trend in the dose at depth based on the HU of the material; however inconsistencies are found when the bolus materials have a negative HU value. The measured data indicates that there is a linear relationship between the mass of water in a material and the dose reading, the slope of which is material dependent.

Conclusion:

Due to the variation in HU of the bolus materials studied, it is recommended that any new bolus be evaluated before clinical use to determine physical and dosimetric properties. If possible, patients should have bolus included in their CT scans; or if the bolus is created in the TPS, the HU should correspond to the material used. For water‐soaked materials, once the bolus material is selected (gauze or sheet), the bolusing effect is only dependent on the amount of water applied to the material.
SU‐E‐T‐12: A Feasibility Study of Patient Specific QA Using Gafchromic Film of Dynamic Feathering in Junctions of Craniospinal Irradiation
Authors: Stanford J , Duggar W , Yang C
Published: July 2014

Purpose:

Cranio‐spinal irradiation is the most complicated format of the conventional external beam radiation therapy because it involves matches of non‐coplanar beams which are susceptible to daily setup errors. This study explores the efficacy of Gafchromic film dosimetry to quantitatively verify the junctions for cranio‐spinal radiation feathered with field in field technique.

Methods:

15cm in thickness of solid water phantom was scanned vertically and exported to the Pinnacle TPS as primary phantom data set. A patient cranio‐spinal plan, consisted of two bilateral whole brain beams dynamically matched with a posterior spinal beam using field in field technique, was transferred to the phantom and recalculated for one fraction with set monitor units identical to the original plan. Next, planar dose distribution on the phantom was exported to the FilmQA Pro 2013 software (Ashland, Inc.) in binary format for comparison with the measured dose distribution. An EBT2 film was sandwiched in the middle of the phantom and the phantom was set up according to the QA plan based on the room laser system. The shifts instructions associated with the patient original plan were made and the beams from the patient original plan delivered to the solid water phantom via the record and verify system in QA mode. The dose distribution from the measured film was compared with the planned reference distribution using gamma analysis and profile comparison.

Results:

Gamma passing rate of 91 % with DTA 3mm and 5% dose difference was obtained within the junction region, significantly greater passing rate above 95 % was obtained in the homogeneous region of the brain field.

Conclusion:

This study confirms that Gafchromic film dosimetry can be used to validate the efficacy of FIF feathering technique for cranio‐spinal treatment. FIF technique with Gafchromic dosimetry may now be the new standard for delivering efficient and accurate cranio‐spinal radiation with confidence.
SU‐E‐T‐21: A Novel Sampling Algorithm to Reduce Intensity‐Modulated Radiation Therapy (IMRT) Optimization Time
Authors: Tiwari P , Xie Y , Chen Y , Deasy J
Published: July 2014

Purpose:

The IMRT optimization problem requires substantial computer time to find optimal dose distributions because of the large number of variables and constraints. Voxel sampling reduces the number of constraints and accelerates the optimization process, but usually deteriorates the quality of the dose distributions to the organs. We propose a novel sampling algorithm that accelerates the IMRT optimization process without significantly deteriorating the quality of the dose distribution.

Methods:

We included all boundary voxels, as well as a sampled fraction of interior voxels of organs in the optimization. We selected a fraction of interior voxels using a clustering algorithm, that creates clusters of voxels that have similar influence matrix signatures. A few voxels are selected from each cluster based on the pre‐set sampling rate.

Results:

We ran sampling and no‐sampling IMRT plans for de‐identified head and neck treatment plans. Testing with the different sampling rates, we found that including 10% of inner voxels produced the good dose distributions. For this optimal sampling rate, the algorithm accelerated IMRT optimization by a factor of 2–3 times with a negligible loss of accuracy that was, on average, 0.3% for common dosimetric planning criteria.

Conclusion:

We demonstrated that a sampling could be developed that reduces optimization time by more than a factor of 2, without significantly degrading the dose quality.
SU‐E‐T‐25: A Study of the Optimal PTV Margin for Patients Receiving CBCT‐Guided Prostate IMRT Based On CBCT Dose Calculation
Authors: Gill S , Pearson D , Dalhart A , Reddy K , Chen C
Published: July 2014

Purpose:

Variation in daily setup and rectum/bladder filling leads to uncertainties in the delivery of prostate IMRT. To determine the optimal PTV margin for CBCT‐guided prostate IMRT, daily CBCTs were used to estimate prostate and OAR doses, compared to those expected from planning.

Methods:

Patients diagnosed with prostate cancer were treated with prostate IMRT to 70Gy in 28 fractions. Daily CBCT was utilized for image guidance. The prostate CTV and OARs were contoured on all CBCTs. IMRT plans were created using 1 mm, 3 mm, 5 mm and 7 mm CTV to PTV margins. Dosimetric analysis of the plans following daily CBCT translational shifts was performed.

Results:

28 CBCT sessions were evaluated for preliminary results. Planned prostate CTV V100% was 100% for all PTV margins. Based on CBCT analysis, the actual cumulative V100% was 96.65±4.73%, 98.82±2.72%, 99.86±0.53% and 99.96±0.11% for 1‐, 3‐, 5‐ and 7 mm margins, respectively. The planned rectum V70Gy was 0.88%, 2.67%, 6.02% and 13.42%, for 1‐mm, 3‐mm, 5‐mm and 7‐mm PTV margins. The actual cumulative V70Gy for the rectum was 5.47±2.7%, 9.64±3.12%, 13.68±3.39% and 20.82±3% for 1‐, 3‐, 5‐ and 7 mm margins, respectively. The planned vs. delivered rectum V60 Gy was 6.99 vs. 14.73±3.63% (1 mm), 9.83 vs. 18.43±3.73% (3), 13.61 vs. 22.5±3.86% (5) and 23.20 vs. 30.82±4 % (7). The planned vs. delivered bladder V70Gy was 0.01%, 0.24%, 0.98% and 1.75% vs. 0.24±0.25%, 0.93±0.69%, 2.46±1.36% and 4.07±2% for 1‐, 3‐, 5‐ and 7 mm margins, respectively.

Conclusion:

Daily setup variation during prostate IMRT yields differences in the actual vs. expected doses received by the prostate CTV, rectum and bladder. The magnitude of these differences is significantly affected by the PTV margin utilized. A 3–5 mm PTV margin appears to be optimal for prostate IMRT when daily CBCT is used for image guidance.
SU‐E‐T‐29: A Web Application for GPU‐Based Monte Carlo IMRT/VMAT QA with Delivered Dose Verification
Authors: Folkerts M , Graves Y , Tian Z , Gu X , Jia X , Jiang S
Published: July 2014

Purpose:

To enable an existing web application for GPU‐based Monte Carlo (MC) 3D dosimetry quality assurance (QA) to compute “delivered dose” from linac logfile data.

Methods:

We added significant features to an IMRT/VMAT QA web application which is based on existing technologies (HTML5, Python, and Django). This tool interfaces with python, c‐code libraries, and command line‐based GPU applications to perform a MC‐based IMRT/VMAT QA. The web app automates many complicated aspects of interfacing clinical DICOM and logfile data with cutting‐edge GPU software to run a MC dose calculation. The resultant web app is powerful, easy to use, and is able to re‐compute both plan dose (from DICOM data) and delivered dose (from logfile data). Both dynalog and trajectorylog file formats are supported. Users upload zipped DICOM RP, CT, and RD data and set the expected statistic uncertainty for the MC dose calculation. A 3D gamma index map, 3D dose distribution, gamma histogram, dosimetric statistics, and DVH curves are displayed to the user. Additional the user may upload the delivery logfile data from the linac to compute a “delivered dose” calculation and corresponding gamma tests. A comprehensive PDF QA report summarizing the results can also be downloaded.

Results:

We successfully improved a web app for a GPU‐based QA tool that consists of logfile parcing, fluence map generation, CT image processing, GPU based MC dose calculation, gamma index calculation, and DVH calculation. The result is an IMRT and VMAT QA tool that conducts an independent dose calculation for a given treatment plan and delivery log file. The system takes both DICOM data and logfile data to compute plan dose and delivered dose respectively.

Conclusion:

We sucessfully improved a GPU‐based MC QA tool to allow for logfile dose calculation. The high efficiency and accessibility will greatly facilitate IMRT and VMAT QA.
SU‐E‐T‐33: An EPID‐Based Method for Testing Absolute Leaf Position for MLC Without Backup Jaws
Authors: Hancock S , Whitaker M
Published: July 2014

Purpose:

Methods in common use for MLC leaf position QA are limited to measurements relative to an arbitrary reference position. The authors previously presented an EPID‐based method for efficiently testing accuracy of leaf position relative to the mechanical isocenter for MLC with backup jaws. The purpose of this work is to extend that method to the general case of MLC without backup jaws.

Methods:

A pair of collimator walkout images is used to determine the location of the mechanical isocenter relative to the center of one field using a parameter called X‐offset. The method allows for shift of the imager panel to cover subsets of MLC leaves within the limited field of view of the imager. For a shifted panel position, an image of three beam strips defined by a subset of MLC leaves allows determination of the position of each leaf relative to the isocenter. The location of the isocenter is determined by applying X‐offset to an image of a single rectangular field obtained at that panel position. The method can also be used to test backup jaws instead of MLC leaves. A software tool was developed to efficiently analyze the images.

Results:

The software tool reports leaf position and deviation from nominal position, and provides visual displays to facilitate rapid qualitative interpretation. Test results using this method agree well with results using the previous method requiring backup jaws. Test results have been successfully used to recalibrate one model MLC (Elekta MLCi2™). Work in progress includes extension of the software tool to other MLC models, and quantification of reproducibility of the measurements.

Conclusion:

This work successfully demonstrates a method to efficiently and accurately measure MLC leaf position, or backup jaw position, relative to the mechanical isocenter of the collimator.
SU‐E‐T‐34: An in Vivo Study On Pulsed Low Dose‐Rate Radiotherapy for Prostate Cancer
Authors: Wang B , Cvetkovic D , Chen X , Zhang P , Zhang C , Chen L , Ma C
Published: July 2014

Purpose:

Re‐irradiation with conventional radiotherapy techniques (CRT) may pose significant risks due to high accumulative radiation doses. Pulsed low dose‐rate radiotherapy (PLDR) has been used in clinical trials for recurrent cancer treatment. In our previous studies, PLDR irradiation showed significantly lower toxicity than CRT, resulting in much longer survival of mice after PLDR total body irradiation (TBI) than conventional TBI. The purpose of this study was to investigate tumor control efficacy of PLDR treatment for prostate cancer with an animal model of prostate cancer LNCaP.

Methods:

We used an orthotopic murine model of LNCaP cell line for this study. LNCaP cells were implanted into immune‐suppressed male nude mice via surgery. We monitored the tumor growth with MRI. The tumor‐bearing mice were allocated into a PLDR(n=9), CRT(n=7), and control group(n=7) randomly. The mice in the PLDR and CRT groups were irradiated with 2Gy dose for one time. For the CRT treatment, the mice received 2Gy at a dose‐rate of 300 MU/minute. For the PLDR treatment, the 2Gy dose was further divided into ten pulses of 0.2Gy at the same dose‐rate with an interval of 3 minutes between the pulses.

Results:

Sizable tumor growth delays were observed for the PLDR and CRT groups through weekly MRI scans. The mean values of the normalized tumor volumes (± standard deviation of the mean) were 1.53±0.07, 1.53±0.14, and 1.81±0.09 at one week after treatment, 2.28±0.13, 2.19±0.16, and 3.04±0.25 at two weeks after treatment, and 3.31±0.23, 3.14±0.24 and 4.62±0.49 at three weeks after treatment, for the PLDR, CRT, and control groups, respectively.

Conclusion:

The PLDR and CRT treatments showed comparable tumor control rates in this study. Our in vivo results indicate that PLDR may be a viable option for treating recurrent prostate cancer due to its equivalent tumor control but low normal tissue toxocities.
SU‐E‐T‐35: An Investigation of the Accuracy of Cervical IMRT Dose Distribution Using 2D/3D Ionization Chamber Arrays System and Monte Carlo Simulation
Authors: Zhang Y , Liu D , Yang J , Liu H
Published: July 2014

Purpose:

The purpose of this work is to compare the verification results of three solutions (2D/3D ionization chamber arrays measurement and Monte Carlo simulation), the results will help make a clinical decision as how to do our cervical IMRT verification.

Methods:

Seven cervical cases were planned with Pinnacle 8.0m to meet the clinical acceptance criteria. The plans were recalculated in the Matrixx and Delta4 phantom with the accurate plans parameters. The plans were also recalculated by Monte Carlo using leaf sequences and MUs for individual plans of every patient, Matrixx and Delta4 phantom. All plans of Matrixx and Delta4 phantom were delivered and measured. The dose distribution of iso slice, dose profiles, gamma maps of every beam were used to evaluate the agreement. Dose‐volume histograms were also compared.

Results:

The dose distribution of iso slice and dose profiles from Pinnacle calculation were in agreement with the Monte Carlo simulation, Matrixx and Delta4 measurement. A 95.2%/91.3% gamma pass ratio was obtained between the Matrixx/Delta4 measurement and Pinnacle distributions within 3mm/3% gamma criteria. A 96.4%/95.6% gamma pass ratio was obtained between the Matrixx/Delta4 measurement and Monte Carlo simulation within 2mm/2% gamma criteria, almost 100% gamma pass ratio within 3mm/3% gamma criteria. The DVH plot have slightly differences between Pinnacle and Delta4 measurement as well as Pinnacle and Monte Carlo simulation, but have excellent agreement between Delta4 measurement and Monte Carlo simulation.

Conclusion:

It was shown that Matrixx/Delta4 and Monte Carlo simulation can be used very efficiently to verify cervical IMRT delivery. In terms of Gamma value the pass ratio of Matrixx was little higher, however, Delta4 showed more problem fields. The primary advantage of Delta4 is the fact it can measure true 3D dosimetry while Monte Carlo can simulate in patients CT images but not in phantom.
SU‐E‐T‐39: Analyses of Plan Quality Using Different Gantry Rotation Time On Volumetric Modulated Arc Therapy in Rectal Carcinoma
Authors: Chi Z , Li R , qiu r , cao y , Han C
Published: July 2014

Purpose:

To compare plan quality of volumetric modulated arc radiotherapy (VMAT) using different gantry rotation times.

Methods:

In ten rectal carcinoma patients, plans with different gantry rotation times were designed by Oncentra4.3 planning system, each of them was optimized by experienced planners using almost similar parameters and dose constraints except the different gantry rotation time. The gantry rotation time was increased from 30s to 150s by step of 30(30s, 60s, 90s, 120s, and 150s). Plans (VMAT30s, VMAT60s, VMAT90s, VMAT120s and VMAT150s) were normalized so that at least 95% of PTV would receive the prescription dose 50 Gray in 25 fractions. Dose‐volume histograms and isodose distributions were evaluated. Conformity indices (CI), homogeneous indices (HI), monitor units (MUs), delivery time were also compared.

Results:

As the increasing of gantry rotation time, VMAT150s provided comparable organs at risk sparing and better target coverage and conformity than VMAT30s. In the normal tissue such as bladder and femurs, the VMAT plans show almost the same V30 and Dmean for them compared with IMRT plans, meanwhile the conformity indices (CI) was better than IMRT plans(p=0.021). However, there was no significant different among the VMAT60s, VMAT90s, VMAT120s and VMAT150s (p=0.054). VMAT150s increased delivery time and monitor units in plans without improving plan quality compared to VMAT60s, VMAT90s and VMAT120s.

Conclusion:

VMAT60s, VMAT90s, VMAT120s and VMAT150s achieved comparable treatment plans in rectal carcinoma. Slower gantry movement in VMAT150s only improves slight improvement than the others.
SU‐E‐T‐43: Analytical Model for Photon Peripheral Dose in Radiotherapy Treatments
Authors: Nieto B Sanchez , El far R , Romero‐Exposito M , Lagares J , Mateo JC , Terron JA , Irazola L , Sanchez‐Doblado F
Published: July 2014

Purpose:

The higher survival rate of radiotherapy patients entails a growing concern on second cancers associated to peripheral doses. Currently, dosimetry of out‐of field doses is still under development. Our group has developed a methodology to estimate neutron equivalent dose in organs (1,2). We aimed to propose a model to estimate out‐of‐field photon doses in isocentric treatments from basic clinical data.

Methods:

The proposed function models the dose as the sum of leakage and scatter terms. The latter is modeled as a virtual source at the collimator, which suffers from attenuation in air and tissue, corrected by the inverse‐square‐law. The model was parameterized using experimental measurements with TLD700 chips placed inside an anthropomorphic phantom (6–18MV) irradiated with conformal and modulated techniques in Elekta, Siemens and Varian linacs. This model provides photon dose at a point as a function of clinical parameters as prescription dose/UM, PTV volume, distance to the field edge, height of the MLC leaves and distance from the the MLC to the isocenter. Model was tested against independent measurements (TLD100) for a VMAT treatment on a Elekta. Dose to organs is modeled from dose to points along the head‐to‐feet axis of the organ of a “standard man” escalated by patient height.

Results:

Our semi‐empirical model depends on 3 given parameters (leakage parameter can be individualized). A novelty of our model, over other models (e.g., PERIDOSE), arises from its applicability to any technique (independently of the number of MU needed to deliver a dose). Differences between predictions and measurements were < 0.005mSv/UM.

Conclusion:

We have proposed a unique model which successfully account for photon peripheral organ dose. This model can be applied in the day‐to‐day clinic as it only needs a few basic parameters which are readily accessible.1. Radiother. Oncol. 107:234–243, 2013. 2. Phys. Med. Biol. 57:6167–6191, 2012.
SU‐E‐T‐45: Antibody Mean Residence Time in Blood and Its Correlation with Protein Molecular Weight
Authors: Kwok C , Williams L
Published: July 2014

Purpose:

Animal biodistribution data are required prior to introducing a new radiopharmaceutical into clinical trials. Protein engineering, using recombinant DNA techniques can produce a large number of related (cognate) antibodies to a given molecular target. Thus, it is important that these constructs be numerically related to one another via a single criterion. In the following, we use the mean residence time (MRT) in murine blood as this criterion.

Methods:

Five cognate anti‐CEA (Carcinoembryonic Antigen) antibodies were compared with regard to their MRT in whole blood of CEA‐positive tumor‐bearing (LS174T) mice. MRT was defined by blood AUC (area under the curve) divided by the initial blood uptake value; all in units of percent injected dose per gram (%ID/g). Cognates included single chain scFv (25 kDa), diabody (50 kDa), minibody (80 kDa), F(ab')2 (120 kDa), and intact (155 kDa) forms of the murine cT84.66 antibody against CEA. All were labeled with radioactive iodine.

Results:

The agents, in the sequence listed, exhibited MRT values of 1.16 +/‐ 0.01 h, 0.99 h, 5.06 +/‐ 0.70 h, 6.61 +/‐ 0.36 h, and 59.3 +/‐ 2.4 h respectively. Because of the monotonic nature of the sequence, a linear correlation analysis was performed between molecular weight (MW) and MRT or ln(MRT) of the 5 proteins. Probability of random correlation was 0.10 for MRT and 0.01 for ln(MRT).

Conclusion:

MRT values of cognate anti‐CEA antibodies were found to be a monotonically increasing sequence with respect to MW. Cognate MW values correlated best to ln(MRT) of the protein species. Thus MRT was proportional to an exponential function of molecular weight. The extended intact antibody circulation time presumably reflected its relatively maximal MW. Presence of an intact FC segment on this native antibody may also have influenced these results.
SU‐E‐T‐46: Application of a Twin‐Detector Method for the Determination of the Mean Photon Energy Em at Points of Measurement in a Water Phantom Surrounding a GammaMed HDR 192Ir Brachytherapy Source
Authors: Chofor N , Nebah F , Harder D , Poppe B
Published: July 2014

Purpose:

In a brachytherapy photon field in water the fluence‐averaged mean photon energy Em at the point of measurement correlates with the radiation quality correction factor kQ of a non water‐equivalent detector. To support the experimental assessment of Em, we show that the normalized signal ratio NSR of a pair of radiation detectors, an unshielded silicon diode and a diamond detector can serve to measure quantity Em in a water phantom at a Ir‐192 unit.

Methods:

Photon fluence spectra were computed in EGSnrc based on a detailed model of the GammaMed source. Factor kQ was calculated as the ratio of the detector's spectrum‐weighted responses under calibration conditions at a 60Co unit and under brachytherapy conditions at various radial distances from the source. The NSR was investigated for a pair of a p‐type unshielded silicon diode 60012 and a synthetic single crystal diamond detector 60019 (both PTW Freiburg). Each detector was positioned according to its effective point of measurement, with its axis facing the source. Lateral signal profiles were scanned under complete scatter conditions, and the NSR was determined as the quotient of the signal ratio under application conditions x and that at position r_ref = 1 cm.

Results:

The radiation quality correction factor kQ shows a close correlation with the mean photon energy Em. The NSR of the diode/diamond pair changes by a factor of two from 0–18 cm from the source, while Em drops from 350 to 150 keV. Theoretical and measured NSR profiles agree by ± 2 % for points within 5 cm from the source.

Conclusion:

In the presence of the close correlation between radiation quality correction factor kQ and photon mean energy Em, the NSR provides a practical means of assessing Em under clinical conditions. Precise detector positioning is the major challenge.
SU‐E‐T‐50: Automatic Validation of Megavoltage Beams Modeled for Clinical Use in Radiation Therapy
Authors: Melchior M , Aranda F Salinas , Sciutto S , Dodat D , Larragueta N
Published: July 2014

Purpose:

To automatically validate megavoltage beams modeled in XiO™ 4.50 (Elekta, Stockholm, Sweden) and Varian Eclipse™ Treatment Planning Systems (TPS) (Varian Associates, Palo Alto, CA, USA), reducing validation time before beam‐on for clinical use.

Methods:

A software application that can automatically read and analyze DICOM RT Dose and W2CAD files was developed using MatLab integrated development environment. TPS calculated dose distributions, in DICOM RT Dose format, and dose values measured in different Varian Clinac beams, in W2CAD format, were compared. Experimental beam data used were those acquired for beam commissioning, collected on a water phantom with a 2D automatic beam scanning system. Two methods were chosen to evaluate dose distributions fitting: gamma analysis and point tests described in Appendix E of IAEA TECDOC‐1583. Depth dose curves and beam profiles were evaluated for both open and wedged beams. Tolerance parameters chosen for gamma analysis are 3% and 3 mm dose and distance, respectively.Absolute dose was measured independently at points proposed in Appendix E of TECDOC‐1583 to validate software results.

Results:

TPS calculated depth dose distributions agree with measured beam data under fixed precision values at all depths analyzed. Measured beam dose profiles match TPS calculated doses with high accuracy in both open and wedged beams. Depth and profile dose distributions fitting analysis show gamma values < 1. Relative errors at points proposed in Appendix E of TECDOC‐1583 meet therein recommended tolerances.Independent absolute dose measurements at points proposed in Appendix E of TECDOC‐1583 confirm software results.

Conclusion:

Automatic validation of megavoltage beams modeled for their use in the clinic was accomplished. The software tool developed proved efficient, giving users a convenient and reliable environment to decide whether to accept or not a beam model for clinical use. Validation time before beam‐on for clinical use was reduced to a few hours.
SU‐E‐T‐55: Biological Equivalent Dose (BED) Comparison Between Permanent Interstitial Brachytherapy and Conventional External Beam Radiotherapy for Prostate Cancer
Authors: Liu X , Rahimian J , Cosmatos H , Goy B , Heywood C , Qian Y
Published: July 2014

Purpose:

The goal of this research is to calculate and compare the Biological Equivalent Dose (BED) between permanent prostate Iodine‐125 implant brachytherapy as monotherapy with the BED of conventional external beam radiation therapy (EBRT).

Methods:

A retrospective study of 605 patients treated with Iodine‐125 seed implant was performed in which physician A treated 274 patients and physician B treated 331 patients. All the Brachytherapy treatment plans were created using VariSeed 8 planning system. The Iodine‐125 seed source activities and loading patterns varied slightly between the two physicians. The prescription dose is 145 Gy to PTV for each patient. The BED and Tumor Control Probability (TCP) were calculated based on the TG 137 formulas. The BED for conventional EBRT of the prostate given in our institution in 2Gy per fraction for 38 fractions was calculated and compared.

Results:

Physician A treated 274 patients with an average BED of 123.92±0.87 Gy and an average TCP of 99.20%; Physician B treated 331 patients with an average BED of 124.87±1.12 Gy and an average TCP of 99.30%. There are no statistically significant differences (T‐Test) between the BED and TCP values calculated for these two group patients. The BED of the patients undergoing conventional EBRT is calculated to be 126.92Gy. The BED of the patients treated with permanent implant brachytherapy and EBRT are comparable. Our BED and TCP values are higher than the reported values by TG 137 due to higher Iodine‐125 seed activity used in our institution.

Conclusion:

We calculated the BED,a surrogate of the biological response to a permanent prostate brachytherapy using TG 137 formulas and recommendation. The TCP of better than 99% is calculated for these patients. A clinical outcome study of these patients correlating the BED and TCP values with PSA and Gleason Levels as well as patient survival is warranted.
SU‐E‐T‐56: Brain Metastasis Treatment Plans for Contrast‐Enhanced Synchrotron Radiation Therapy
Authors: Obeid L , Tessier A , Vautrin M , Sihanath R , Benkebil M , Adam J
Published: July 2014

Purpose:

Iodine‐enhanced radiotherapy is an innovative treatment combining the selective accumulation of an iodinated contrast agent in brain tumors with irradiations using monochromatic medium energy x‐rays. The aim of this study is to compare dynamic stereotactic arc‐therapy and iodineenhanced SSRT.

Methods:

Five patients bearing brain metastasis received a standard helical 3D‐scan without iodine. A second scan was acquired 13 min after an 80 g iodine infusion. Two SSRT treatment plans (with/without iodine) were performed for each patient using a dedicated Monte Carlo (MC) treatment planning system (TPS) based on the ISOgray TPS. Ten coplanar beams (6×6 cm2, shaped with collimator) were simulated. MC statistical error objective was less than 5% in the 50% isodose. The dynamic arc‐therapy plan was achieved on the Iplan Brainlab TPS. The treatment plan validation criteria were fixed such that 100% of the prescribed dose is delivered at the beam isocentre and the 70% isodose contains the whole target volume. The comparison elements were the 70% isodose volume, the average and maximum doses delivered to organs at risk (OAR): brainstem, optical nerves, chiasma, eyes, skull bone and healthy brain parenchyma.

Results:

The stereotactic dynamic arc‐therapy remains the best technique in terms of dose conformation. Iodine‐enhanced SSRT presents similar performances to dynamic arc‐therapy with increased brainstem and brain parenchyma sparing. One disadvantage of SSRT is the high dose to the skull bone. Iodine accumulation in metastasis may increase the dose by 20–30%, allowing a normal tissue sparing effect at constant prescribed dose. Treatment without any iodine enhancement (medium‐energy stereotactic radiotherapy) is not relevant with degraded HDVs (brain, parenchyma and skull bone) comparing to stereotactic dynamic arc‐therapy.

Conclusion:

Iodine‐enhanced SSRT exhibits a good potential for brain metastasis treatment regarding the dose distribution and OAR criteria.
SU‐E‐T‐236: Monte Carlo Calculations for Radiosurgery of the Clivus
Authors: Ho A , Gibbs I , Chang S , Soltys S
Published: July 2014

Purpose:

We sought to determine if dosimetric differences exist between Ray‐Trace (RT) and Monte‐Carlo (MC) calculation algorithms for radiosurgery for tumors of the clivus, given their proximity to air‐tissue inhomogeneity.

Methods:

We retrospectively identified 10 patients with a tumor of the clivus where the target was located near an air‐tissue interface. CyberKnife treatment was delivered in 1 to 5 fractions. Plans originally calculated with the RT algorithm were re‐calculated with the same monitor units (MU) with the MC algorithm. Similarly, plans originally calculated with MC were recalculated with RT. MC calculations were performed using High Resolution with 2% uncertainty on the MultiPlan 4.6 planning system. If the RT plans were originally calculated using water‐air density model, they were re‐calculated with Body standard density model, and then compared with MC plans computed with Body standard density model. The maximum dose (Dmax) to the planning target volumes (PTV) and critical structures, minimum dose (Dmin) and coverage percentage for the PTV were calculated.

Results:

For 8 cases, MC PTV Dmin was a median 5% (range 0–10%) and Dmax a median 6% (range 3–9%) higher than for RT. For 2 cases, MC PTV Dmin was 6 and 2% and Dmax was 1 and 3% lower than for RT. MC PTV Dmin and Dmax maybe higher or lower than for RT even though the target coverage for MC was less than for RT (median 4%, range 0–13%) with the same MU used. The degree of differences depends on the location of the target relative to the air‐tissue inhomogeneity. Examples are shown that the targets are underdosed near the air‐tissue inhomogenity.

Conclusion:

Monte Carlo dose calculations are recommended for targets near tissue homogeneity such as the clivus. Assuming that Monte Carlo more closely approximates the true dosimetry, the use of Ray Trace could overestimate target coverage.
SU‐E‐T‐245: MR Guided Focused Ultrasound Increased PARP Related Apoptosis On Prostate Cancer in Vivo
Authors: Chen L , Chen X , Cvetkovic D , Gupta R , Yang D , Ma C
Published: July 2014

Purpose:

Our previous study demonstrated that significant tumor growth delay was observed in the mice treated with pulsed high intensity focused ultrasound (pHIFU). The purpose of this study is to understand the cell killing mechanisms of pHIFU.

Methods:

Prostate cancer cells (LNCaP), were grown orthotopically in 17 nude mice. Tumor‐bearing mice were treated using pHIFU with an acoustic power of 25W, pulse width 100msec and 300 pulses in one sonication under MR guidance. Mutiple sonications were used to cover the whole tumor volume. Temperature (less than 40 degree centigrade in the focal spot) was monitored using MR thermometry. Animals were euthanized at pre‐determined time points (n=2) after treatment: 0 hours; 6 hrs; 24 hrs; 48 hrs; 4 days and 7 days. Two tumorbearing mice were used as control. Three tumor‐bearing mice were treated with radiation (RT, 2 Gy) using 6 MV photon beams. RT treated mice were euthanized at 0 hr, 6 hrs and 24 hrs. The tumors were processed for immunohistochemical (IHC) staining for PARP (a surrogate of apoptosis). A multispectral imaging analysis system was used to quantify the expression of PARP staining. Cell apoptosis was calculated based on the PARP expression level, which is the intensity of the DAB reaction.

Results:

Our data showed that PARP related apoptosis peaked at 48 hrs and 7 days in pHIFU treated mice, which is comparable to that for the RT group at 24 hrs. The preliminary results from this study were consistent with our previous study on tumor growth delay using pHIFU.

Conclusion:

Our results demonstrated that non‐thermal pHIFU increased apoptotic tumor cell death through the PARP related pathway. MR guided pHIFU may have a great potential as a safe, noninvasive treatment modality for cancer therapy. This treatment modality might be able to synergize with PARP inhibitors to achieve better result.
SU‐E‐T‐246: MU Model Implementation for a Passively Scattered Proton Beam: Inclusion of the Bolus Gap and Nozzle Extension Factors
Authors: Simpson R , Ghebremedhin A , Gordon I , Patyal B , Piskulich F. , LeMaster Brett
Published: July 2014

Purpose:

To develop and implement an MU model for a passively scattered proton beam, and eliminate the need for patient specific calibrations for field sizes from 3cm to 15cm. This would enable consistent and timely calibrations for a wide variety of patient portals, streamlining the treatment process.

Methods:

Measurements were initially made using a Standard Imaging A‐16 ion chamber and a modified water tank to determine the bolus gap factors (BGF) for multiple combinations of aperture size, bolus thickness, and air gap. The BGF was then separated into two component factors: the bolus thickness factor (BTF) and the nozzle extension factor (NEF). Polynomial curves were generated using the measured data to produce BTF tables for air gaps from 0cm to 30cm and for bolus thicknesses from 0cm to 10cm, and NEF tables for the full range of clinically used nozzle extensions. Additionally, data tables were created for every factor that affects beam output in the MU model. The MUs were then modeled for 487 patient portals and retrospectively compared to the MUs generated from the physical calibrations previously performed.

Results:

Of the 487 patient portals tested, 100% of the portals used for the comparison were within 2.5% from the MUs generated using a physical calibration, and 95.9% of the MU model portals tested were within 2%. The patient portals tested had field sizes ranging from 2.1cm to 10.1cm, with air gaps from 2cm to 25cm. Output factors for field sizes below 3cm with irregularly shaped fields demonstrated inconsistent results and will be further studied.

Conclusion:

The most problematic output factor, the BGF, was modeled accurately and consistently using the lowest order polynomial curve fits and interpolation between measured data. The study results demonstrate the robustness of the MU model and the potential for saving valuable personnel and beam time.
SU‐E‐T‐248: Near Real‐Time Analysis of Radiation Delivery and Imaging, Accuracy to Ensure Patient Safety
Authors: Wijesooriya K , Seitter K , Desai V , Read P , Larner J
Published: July 2014

Purpose:

To develop and optimize an effective software method for comparing planned to delivered control point machine parameters for all VARIAN TrueBeam treatments so as to permit (1) assessment of a large patient pool throughout their treatment course to quantify treatment technique specific systematic and random uncertainty of observables, (2) quantify the site specific daily imaging shifts required for target alignment, and (3) define tolerance levels for mechanical parameters and imaging parameters based on statistical analysis data gathered, and the dosimetric impact of variations.

Methods:

Treatment and imaging log files were directly compared to plan parameters for Eclipse and Pinnacle planned treatments via 3D, IMRT, control point, RapidArc, and electrons. Each control point from all beams/arcs (7984) for all fractions (1940) of all patients treated over six months were analyzed. At each control point gantry angle, collimator angle, couch angle, jaw positions, MLC positions, MU were compared. Additionally per‐treatment isocenter shifts were calculated.

Results were analyzed as a whole in treatment type subsets:

IMRT, 3D, RapidArc; and in treatment site subsets: brain, chest/mediastinum, esophagus, H&N, lung, pelvis, prostate. Results: Daily imaging isocenter shifts from initial external tattoo alignment were dependent on the treatment site with < 0.5 cm translational shifts for H&N, Brain, and lung SBRT, while pelvis, esophagus shifts were ∼1 cm. Mechanical delivery parameters were within tolerance levels for all sub‐beams. The largest variations were for RapidArc plans: gantry angle 0.11±0.12,collimator angle 0.00±0.00, jaw positions 0.48±0.26, MLC leaf positions 0.66±0.08, MU 0.14±0.34.

Conclusion:

Per‐control point validation reveals deviations between planned and delivered parameters. If used in a near real‐time error checking system, patient safety can be improved by equipping the treatment delivery system with additional forcing functions which by‐pass human error avenues.
SU‐E‐T‐252: On the Evaluation of Patient Specific IMRT QA Using EPID, Dynalog Files and Patient Anatomy
Authors: Defoor D , Vazquez Quino L , Stathakis S , Mavroidis P , Papanikolaou N
Published: July 2014

Purpose:

This research, investigates the viability of using the Electronic portal imaging device (EPID) coupled with the treatment planning system (TPS), to calculate the doses delivered and verify agreement with the treatment plan. The results of QA analysis using the EPID, Delta4 and fluence calculations using the multi‐leaf collimator (MLC) dynalog files on 10 IMRT patients are presented in this study.

Methods:

EPID Fluence Images in integrated mode and Dynalog files for each field were acquired for 10 IMRT (6MV) patients and processed through an in house MatLab program to create an opening density matrix (ODM) which was used as the input fluence for dose calculation with the TPS (Pinnacle3, Philips). The EPID used in this study was the aSi1000 Varian on a Novalis TX linac equipped with high definition MLC. The resulting dose distributions were then exported to VeriSoft (PTW) where a 3D gamma was calculated using 3mm‐3% criteria. The Scandidos Delta4 phantom was also used to measure a 2D dose distribution for all 10 patients and a 2D gamma was calculated for each patient using the Delta4 software.

Results:

The average 3D gamma for all 10 patients using the EPID images was 98.2% ± 2.6%. The average 3D gamma using the dynalog files was 94.6% ± 4.9%. The average 2D gamma from the Delta4 was 98.1% ± 2.5%. The minimum 3D gamma for the EPID and dynalog reconstructed dose distributions was found on the same patient which had a very large PTV, requiring the jaws to open to the maximum field size.

Conclusion:

Use of the EPID, combined with a TPS is a viable method for QA of IMRT plans. A larger ODM size can be implemented to accommodate larger field sizes. An adaptation of this process to Volumetric Arc Therapy (VMAT) is currently under way.
SU‐E‐T‐256: Optimizing the Combination of Targeted Radionuclide Therapy Agents Using a Multi‐Scale Patient‐Specific Monte Carlo Dosimetry Platform
Authors: Besemer A , Titz B , Grudzinski J , Weichert J , Hall L , Bednarz B
Published: July 2014

Purpose:

Combination targeted radionuclide therapy (TRT) is appealing because it can potentially exploit different mechanisms of action from multiple radionuclides as well as the variable dose rates due to the different radionuclide half‐lives. The work describes the development of a multiobjective optimization algorithm to calculate the optimal ratio of radionuclide injection activities for delivery of combination TRT.

Methods:

The ‘diapeutic’ (diagnostic and therapeutic) agent, CLR1404, was used as a proof‐of‐principle compound in this work. Isosteric iodine substitution in CLR1404 creates a molecular imaging agent when labeled with I‐124 or a targeted radiotherapeutic agent when labeled with I‐125 or I‐131. PET/CT images of high grade glioma patients were acquired at 4.5, 24, and 48 hours post injection of 124I‐CLR1404. The therapeutic 131I‐CLR1404 and 125ICLR1404 absorbed dose (AD) and biological effective dose (BED) were calculated for each patient using a patient‐specific Monte Carlo dosimetry platform. The optimal ratio of injection activities for each radionuclide was calculated with a multi‐objective optimization algorithm using the weighted sum method. Objective functions such as the tumor dose heterogeneity and the ratio of the normal tissue to tumor doses were minimized and the relative importance weights of each optimization function were varied.

Results:

For each optimization function, the program outputs a Pareto surface map representing all possible combinations of radionuclide injection activities so that values that minimize the objective function can be visualized. A Pareto surface map of the weighted sum given a set of user‐specified importance weights is also displayed. Additionally, the ratio of optimal injection activities as a function of the all possible importance weights is generated so that the user can select the optimal ratio based on the desired weights.

Conclusion:

Multi‐objective optimization of radionuclide injection activities can provide an invaluable tool for maximizing the dosimetric benefits in multi‐radionuclide combination TRT.

BT, JG, and JW are affiliated with Cellectar Biosciences which owns the licensing rights to CLR1404 and related compounds.
SU‐E‐T‐258: Parallel Optimization of Beam Configurations for CyberKnife Treatments
Authors: Viulet T , Blanck O , Schlaefer A
Published: July 2014

Purpose:

The CyberKnife delivers a large number of beams originating at different non‐planar positions and with different orientation. We study how much the quality of treatment plans depends on the beams considered during plan optimization. Particularly, we evaluate a new approach to search for optimal treatment plans in parallel by running optimization steps concurrently.

Methods:

So far, no deterministic, complete and efficient method to select the optimal beam configuration for robotic SRS/SBRT is known. Considering a large candidate beam set increases the likelihood to achieve a good plan, but the optimization problem becomes large and impractical to solve. We have implemented an approach that parallelizes the search by solving multiple linear programming problems concurrently while iteratively resampling zero weighted beams. Each optimization problem contains the same set of constraints but different variables representing candidate beams. The search is synchronized by sharing the resulting basis variables among the parallel optimizations. We demonstrate the utility of the approach based on an actual spinal case with the objective to improve the coverage.

Results:

The objective function is falling and reaches a value of 5000 after 49, 31, 25 and 15 iterations for 1, 2, 4, and 8 parallel processes. This corresponds to approximately 97% coverage in 77%, 59%, and 36% of the mean number of iterations with one process for 2, 4, and 8 parallel processes, respectively. Overall, coverage increases from approximately 91.5% to approximately 98.5%.

Conclusion:

While on our current computer with uniform memory access the reduced number of iterations does not translate into a similar speedup, the approach illustrates how to effectively parallelize the search for the optimal beam configuration. The experimental results also indicate that for complex geometries the beam selection is critical for further plan optimization.
SU‐E‐T‐259: Particle Swarm Optimization in Radial Dose Function Fitting for a Novel Iodine‐125 Seed
Authors: Wu X , Duan J , Popple R , Cardan R , Huang M , Benhabib S , Shen S , Brezovich I
Published: July 2014

Purpose:

To determine the coefficients of bi‐ and tri‐exponential functions for the best fit of radial dose functions of the new iodine brachytherapy source: Iodine‐125 Seed AgX‐100.

Methods:

The particle swarm optimization (PSO) method was used to search for the coefficients of the biand tri‐exponential functions that yield the best fit to data published for a few selected radial distances from the source. The coefficients were encoded into particles, and these particles move through the search space by following their local and global best‐known positions. In each generation, particles were evaluated through their fitness function and their positions were changed through their velocities. This procedure was repeated until the convergence criterion was met or the maximum generation was reached. All best particles were found in less than 1,500 generations.

Results:

For the I‐125 seed AgX‐100 considered as a point source, the maximum deviation from the published data is less than 2.9% for bi‐exponential fitting function and 0.2% for tri‐exponential fitting function. For its line source, the maximum deviation is less than 1.1% for bi‐exponential fitting function and 0.08% for tri‐exponential fitting function.

Conclusion:

PSO is a powerful method in searching coefficients for bi‐exponential and tri‐exponential fitting functions. The bi‐ and tri‐exponential models of Iodine‐125 seed AgX‐100 point and line sources obtained with PSO optimization provide accurate analytical forms of the radial dose function. The tri‐exponential fitting function is more accurate than the bi‐exponential function.