bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐T‐417: A Method for Predicting and Correcting the Dosimetric Effect of a Radiotherapy Treatment Couch in Actual Treatment Position
Authors: Duan J , Shen S , Wu X , Huang M , Benhabib S , Cardan R , Popple R , Brezovich I 
Published: July 2014

Purpose:Although radiation attenuation by the treatment couch can be included in the calculation of radiotherapy dose, difference between planned and actual treatment couch positions can generate significant dose discrepancies. We propose a method to predict and correct the dosimetric effect of the couch in actual treatment position.Methods:The couch transmission factor, T, varies with beam angle, G, couch lateral position, x, and vertical position, y, i.e., T=T(x,y,G). If T(x,y,G) is known for a fixed couch vertical position y=h, the transmission of central‐axis beam (CAX) T(x,y,G) can be obtained by T(x,y,G)=T(x+,h,G), where x+=x‐(y‐h)tan(G) and G is the angle between the beam and the vertical axis. Similarly, the transmission of any off‐CAX point can be obtained using a similar formula. We measured CAX couch transmission at a fixed couch vertical position over the couch lateral motion range for all gantry angles by continuously scanning rotating arc beams. A 2D couch transmission correction matrix can thus be generated from T(x,h,G) for each treatment field for the actual couch position. By applying the transmission correction matrix to the planned field dose, the couch effect can be predicted and corrected. To verify this method, we measured couch transmission T(x, y=10cm, G=225°)(225°=IEC 135°) and compared to that obtained from equivalent T(x+, y=3cm, G=225°) over the range of lateral motion with a step size of 2 cm .Results:The measured couch transmission factors T(x, y=10cm, G=225°) are in excellent agreement with those obtained from the equivalent T(x+, y=3cm, G=225°). The mean difference is 0.00406±0.00135.Conclusion:The couch transmission correction matrix for any couch position and beam angle can be obtained from one set of scanning measurements at a fixed couch vertical position. The dosimetric effect of the treatment couch can be predicted and corrected by applying the couch transmission correction to the planned dose.
SU‐E‐T‐417: The Impact of Normal Tissue Constraints On PTV Dose Homogeneity for Intensity Modulated Radiotherapy (IMRT), Volume Modulated Arc Therapy (VMAT) and Tomotherapy
Authors: Peng J , McDonald D , Ashenafi M , Ellis A , Vanek K 
Published: July 2014

Purpose:Complex intensity modulated arc therapy tends to spread low dose to normal tissue(NT)regions to obtain improved target conformity and homogeneity and OAR sparing. This work evaluates the trade‐offs between PTV homogeneity and reduction of the maximum dose(Dmax)spread to NT while planning of IMRT,VMAT and Tomotherapy.Methods:Ten prostate patients,previously planned with step‐and‐shoot IMRT,were selected. To fairly evaluate how PTV homogeneity was affected by NT Dmax constraints,original IMRT DVH objectives for PTV and OARs(femoral heads,and rectal and bladder wall)applied to 2 VMAT plans in Pinnacle(V9.0), and Tomotherapy(V4.2). The only constraint difference was the NT which was defined as body contours excluding targets,OARs and dose rings.NT Dmax constraint for 1st VMAT was set to the prescription dose(Dp).For 2nd VMAT(VMAT_NT)and Tomotherapy,it was set to the Dmax achieved in IMRT(~70‐80% of Dp).All NT constraints were set to the lowest priority. Three common homogeneity indices(HI),RTOG_HI=Dmax/Dp,moderated_HI=D95%/D5% and complex_HI=(D2%‐D98%)/Dp*100 were calculated.Results:All modalities with similar dosimetric endpoints for PTV and OARs. The complex_HI shows the most variability of indices,with average values of 5.9,4.9,9.3 and 6.1 for IMRT,VMAT,VMAT_NT and Tomotherapy,respectively.VMAT provided the best PTV homogeneity without compromising any OAR/NT sparing.Both VMAT_NT and Tomotherapy,planned with more restrictive NT constraints,showed reduced homogeneity,with VMAT_NT showing the worst homogeneity(P<0.0001)for all HI. Tomotherapy gave the lowest NT Dmax,with slightly decreased homogeneity compared to VMAT. Finally, there was no significant difference in NT Dmax or Dmean between VMAT and VMAT_NT.Conclusion:PTV HI is highly dependent on permitted NT constraints. Results demonstrated that VMAT_NT with more restrictive NT constraints does not reduce Dmax NT,but significantly receives higher Dmax and worse target homogeneity. Therefore, it is critical that planners do not use too restrictive NT constraints during VMAT optimization. Tomotherapy plan was not as sensitive to NT constraints,however,care shall be taken to ensure NT is not pushed too hard. These results are relevant for clinical practice. The biological effect of higher Dmax and increased target heterogeneity needs further study.
SU‐E‐T‐419: Workflow and FMEA in a New Proton Therapy (PT) Facility
Authors: Cheng C , Wessels B , Hamilton H , Difranco T , Mansur D 
Published: July 2014

Purpose:Workflow is an important component in the operational planning of a new proton facility. By integrating the concept of failure mode and effect analysis (FMEA) and traditional QA requirements, a workflow for a proton therapy treatment course is set up. This workflow serves as the blue print for the planning of computer hardware/software requirements and network flow. A slight modification of the workflow generates a process map(PM) for FMEA and the planning of QA program in PT.Methods:A flowchart is first developed outlining the sequence of processes involved in a PT treatment course. Each process consists of a number of sub‐processes to encompass a broad scope of treatment and QA procedures. For each subprocess, the personnel involved, the equipment needed and the computer hardware/software as well as network requirements are defined by a team of clinical staff, administrators and IT personnel.Results:Eleven intermediate processes with a total of 70 sub‐processes involved in a PT treatment course are identified. The number of sub‐processes varies, ranging from 2‐12. The sub‐processes within each process are used for the operational planning. For example, in the CT‐Sim process, there are 12 sub‐processes: three involve data entry/retrieval from a record‐and‐verify system, two controlled by the CT computer, two require department/hospital network, and the other five are setup procedures. IT then decides the number of computers needed and the software and network requirement. By removing the traditional QA procedures from the workflow, a PM is generated for FMEA analysis to design a QA program for PT.Conclusion:Significant efforts are involved in the development of the workflow in a PT treatment course. Our hybrid model of combining FMEA and traditional QA program serves a duo purpose of efficient operational planning and designing of a QA program in PT.
SU‐E‐T‐420: Impact of Different Prescription Isodose Lines On Plan Quality for Brain Metastases Using Multiplan System
Authors: Zhang Y , Li X , Li T , Ozhasoglu C , Burton S , Flickinger J , clump d , heron d , Huq M 
Published: July 2014

Purpose:With the sequential optimization algorithm in MultiPlan system, clinical objectives (homogeneity, PTV coverage, conformity, normal tissue protection) can be optimized in sequence. However, the prescription isodose line (RxIDL) varies widely among institutions, which can influence the optimized dose distribution. The aim of this study is to investigate the impact of different prescription isodose lines on plan quality for the treatment of brain metastases using CyberKnife Multiplan system.Methods:Ten patients with multiple metastases were selected for this study. Four plans were generated for each patient such that 100% of the target volume receives the prescribed dose of 18 Gy, which was 50%, 60%, 70%, and 80% prescription Isodose line, separately. The prescription isodose was calculated as the ratio of the prescription dose and the maximum dose in target volume. The dosimetric parameters, including PTV coverage, conformity index (CI), gradient index (GI) and the volume covered by 12 Gy (V12Gy) were analyzed. The plan Monitor Units (MU) and treatment time were also compared.Results:All plans can provide the same target coverage (100%) and similar conformity index (1.26, 1.30, 1.32, and 1.29 on average for 80%, 70%, 60%, and 50% RxIDL plans, separately); there was no difference in critical structure dose. The 50% RxIDL plans have much lower GI (4.21±1.79 for 50% and 5.56±2.92 for 80% RxIDL plans) and V12Gy (13.36±10.31cc for 50% and 15.87±11.85cc for 80% RxIDL plans). The variation in estimated treatment delivery time was insignificant.Conclusion:The dose falloff is much faster for the lower RxIDL plans in terms of GI and V12Gy. For 50% RxIDL plans, the average V12Gy decreases by 16% compared to 80% RxIDL plans, which indicates that the normal tissue can be better protected by decreasing the prescription Isodose line.
SU‐E‐T‐421: Feasibility Study of Volumetric Modulated Arc Therapy with Constant Dose Rate for Endometrial Cancer
Authors: Yang R , Wang J 
Published: July 2014

Purpose:To investigate the feasibility, efficiency, and delivery accuracy of volumetric modulated arc therapy with constant dose rate (VMAT‐CDR) for whole‐pelvic radiotherapy (WPRT) of endometrial cancer.Methods:The nine‐Field intensity‐modulated radiotherapy (IMRT), VMAT with variable dose‐rate (VMAT‐VDR), and VMAT‐CDR plans were created for 9 patients with endometrial cancer undergoing WPRT. The dose distribution of planning target volume (PTV), organs at risk (OARs), and normal tissue (NT) were compared. The monitor units (MUs) and treatment delivery time were also evaluated. For each VMAT‐CDR plan, a dry Run was performed to assess the dosimetric accuracy with MatriXX from IBA.Results:Compared with IMRT, the VMAT‐CDR plans delivered a slightly greater V20 of the bowel, bladder, pelvis bone, and NT, but significantly decreased the dose to the high‐dose region of the rectum and pelvis bone. The MUs Decreased from 1105 with IMRT to 628 with VMAT‐CDR. The delivery time also decreased from 9.5 to 3.2 minutes. The average gamma pass rate was 95.6% at the 3%/3 mm criteria with MatriXX pretreatment verification for 9 patients.Conclusion:VMAT‐CDR can achieve comparable plan quality with significant shorter delivery time and smaller number of MUs compared with IMRT for patients with endometrial cancer undergoing WPRT. It can be accurately delivered and be an alternative to IMRT on the linear accelerator without VDR capability.This work is supported by the grant project, National Natural; Science Foundation of China (No. 81071237).
SU‐E‐T‐422: Correlation Between 2D Passing Rates and 3D Dose Differences for Pretreatment VMAT QA
Authors: Jin X , Xie C 
Published: July 2014

Purpose:Volumetric modulated arc therapy (VMAT) quality assurance (QA) is typically using QA methods and action levels taken from fixedbeam intensity‐modulated radiotherapy (IMRT) QA methods. However, recent studies demonstrated that there is no correlation between the percent gamma passing rate (%GP) and the magnitude of dose discrepancy between the planned dose and the actual delivered dose for IMRT. The purpose of this study is to investigate whether %GP is correlated with clinical dosimetric difference for VMAT.Methods:Twenty nasopharyngeal cancer (NPC) patients treated with dual‐arc simultaneous integrated boost VMAT and 20 esophageal cancer patients treated with one‐arc VMAT were enrolled in this study. Pretreatment VMAT QA was performed by a 3D diode array ArcCheck. Acceptance criteria of 2%/2mm, 3%/3mm, and 4%/4mm were applied for 2D %GP. Dose values below 10% of the per‐measured normalization maximum dose were ignored.Mean DVH values obtained from 3DVH software and TPS were calculated and percentage dose differences were calculated. Statistical correlation between %GP and percent dose difference was studied by using Pearson correlation.Results:The %GP for criteria 2%/2mm, 3%/3mm, and 4%/4mm were 82.33±4.45, 93.47±2.31, 97.13±2.41, respectively. Dose differences calculated from 3DVH and TPS for beam isocenter, mean dose of PTV, maximum dose of PTV, D2 of PTV and D98 of PTV were ‐1.04±3.24, ‐0.74±1.71, 2.92±3.62, 0.89±3.29, ‐1.46±1.97, respectively. No correction were found between %GP and dose differences.Conclusion:There are weak correlations between the 2D %GP and dose differences calculated from 3DVH. The %GP acceptance criteria of 3%/3mm usually applied for pretreatment QA of IMRT and VMAT is not indicating strong clinical correlation with 3D dose difference. 3D dose reconstructions on patient anatomy may be necessary for physicist to predict the accuracy of delivered dose for VMAT QA.
SU‐E‐T‐423: TrueBeam Small Field Dosimetry Using Commercial Plastic Scintillation and Other Stereotactic Detectors
Authors: Pino R , Therriault‐Proulx F , Wang X , Yang J , Beddar S 
Published: July 2014

Purpose:To perform dose profile and output factor (OF) measurements with the Exradin W1 plastic scintillation detector (PSD) for small fields made by the high‐definition multi‐leaf collimator (MLC) on the TrueBeam STx system and to compare them to values measured with an IBA CC01 ionization chamber and a Sun Nuclear Edge detector diode for 6 MV photon beams.Methods:The Exradin W1 is a new small volume near‐water equivalent and energy independent PSD manufactured by Standard Imaging, Inc. All measurements were performed in an IBA Blue Phantom water tank. Square MLC‐shaped fields with sides ranging from 0.5 cm to 2 cm and jawshaped fields with sides ranging from 1 cm to 40 cm were measured using an SAD setup at 10 cm depth. Dose profile and percent depth dose (PDD) measurements were also taken under the same conditions for MLC fields 0.5×0.5 and 1×1 cm2 in size with jaws at 2×2cm2. The CC01 and W1 were vertically mounted.Results:OFs measured with the W1 for jaw only square fields were consistent with the ones measured with a Farmers PTW TN33013 ion chamber (1.8% maximum deviation). OF and penumbra measurement results are presented below. PDDs measured for all detectors are within 1.5% for the 0.5×0.5 cm2 and within 1% for the 1×1 cm2 MLC fields.Output factors:MLC size W1 CC01 EDGE0.5cm 0.555 0.541 0.5851.0cm 0.716 0.702 0.7331.5cm 0.779 0.761 0.7772.0cm 0.804 0.785 0.796Penumbras (mm):MLC size W1 CC01 EDGE0.5cm 2.7 2.9 2.51.0cm 3.0 3.4 2.Conclusion:OFs measured for small MLC fields were consistent with the ones measured with the other stereotactic detectors. Measured penumbras are consistent with detector size. The Exradin W1 PSD is an excellent choice for characterizing MLC‐shaped small beam dosimetry used for stereotactic radiosurgery and body radiation therapy.Sam Beddar would like to disclose a NIH/NCI SBIR Phase II grant (2R44CA153824‐02A1) with Standard Imaging, Title: “Water‐Equivalent Plastic Scintillation Detectors for Small Field Radiotherapy”
SU‐E‐T‐424: Dosimetric Verification of Modulated Electron Radiation Therapy Delivered Using An Electron Specific Multileaf Collimator for Treatment of Scalp Cases
Authors: Eldib A , Jin L , Martin J , Li J , Chibani O , Mora G , Galloway T , Ma C 
Published: July 2014

Purpose:Modulated electron radiotherapy (MERT) has the potential to achieve better treatment outcome for shallow tumors such as those of breast and scalp. In a separate study with scalp lesions, MERT was compared to volumetric modulated arc therapy. Our results showed a reduction in the dose reaching the brain with MERT. However dose calculation accuracy and delivery efficiency challenges remain. Thus in the current study we proceed to add more cases to demonstrate MERT beneficial outcome and its delivery accuracy using an electron specific multileaf collimator (eMLC).Methods:We have used the MCBEAM code for treatment head simulation and for generating phase space files to be used as radiation source input for our Monte Carlo based treatment planning system (MC TPS). MCPLAN code is used for calculation of patient specific dose deposition coefficient and for final MERT plan dose calculation. An in‐house developed optimization code is used for the optimization process. MERT plans were generated for real patients and head and neck phantom. Film was used for dosimetric verification. The film was cut following the contour of the curved phantom surface and then sealed with black masking tape. In the measurement, the sealed film packet was sandwiched between two adjacent slabs of the head and neck phantom. The measured 2D dose distribution was then compared with calculations.Results:The eMLC allows effective treatment of scalps with multi‐lesions spreading around the patient head, which was usually difficult to plan or very time consuming with conventional applicators. MERT continues to show better reduction in the brain dose. The dosimetric measurements showed slight discrepancy, which was attributed to the film setup.Conclusion:MERT can improve treatment plan quality for patients with scalp cancers. Our in‐house MC TPS is capable of performing treatment planning and accurate dose calculation for MERT using the eMLC.
SU‐E‐T‐425: Spherical Dose Distributions for Radiosurgery Using a Standardized MLC Plan
Authors: Popple R , Brezovich I , Wu X , Fiveash J 
Published: July 2014

Purpose:To investigate a standardized MLC treatment plan to generate small spherical dose distributions.Methods:The static virtual cone plan comprised six table positions with clockwise and counterclockwise arcs having collimator angles 45 and 135 degrees, respectively, at each position. The central two leaves of a 2.5 mm leaf width MLC were set to a constant gap. Control points were weighted proportional to the sine of the gantry angle. Plans were created for the 10 MV flattening‐filter‐free beam of a TrueBeam STx (Varian Medical Systems) with gaps of 1, 1.5, 2, and 3 mm and were delivered to a phantom containing radiochromic film. Dose was calculated using the Eclipse AAA (Varian Medical Systems). A dynamic plan in which the table and gantry moved simultaneously with 1.5 mm gap was also created and delivered using the TrueBeam developer mode.Results:The full‐width‐half‐max (FWHM) varied with leaf gap, ranging from 5.2 to 6.2 mm. Calculated FWHM was smaller than measured by 0.7 mm for the 1 mm gap and ≤ 0.4 mm for the larger gaps. The measured‐to‐calculated dose ratio was 0.93, 0.96, 1.01, and 0.99 for 1 mm, 1.5 mm, 2 mm, and 3 mm gaps, respectively. The dynamic results were the same as the static. The position deviations between the phantom target position and the center of the dose distribution were < 0.4 mm.Conclusion:The virtual cone can deliver spherical dose distributions suitable for radio surgery of small targets such as the trigeminal nerve. The Eclipse AAA accurately calculates the expected dose, particularly for leaf gap ≥ 1.5 mm. The measured dose distribution is slightly larger than the calculation, which is likely due to systematic leaf position error, isocenter variation due to gantry sag and table eccentricity, and inaccuracy in MLC leaf end modeling.
SU‐E‐T‐426: Dose Delivery Accuracy in Breast Field Junction for Free Breath and Deep Inspiration Breath Hold Techniques
Authors: Epstein D , Shekel E , Levin D 
Published: July 2014

Purpose:The purpose of this work was to verify the accuracy of the dose distribution along the field junction in a half beam irradiation technique for breast cancer patients receiving radiation to the breast or chest wall (CW) and the supraclavicular LN region for both free breathing and deep inspiration breath hold (DIBH) technique.Methods:We performed in vivo measurements for nine breast cancer patients receiving radiation to the breast/CW and to the supraclavicular LN region. Six patients were treated to the left breast/CW using DIBH technique and three patients were treated to the right breast/CW in free breath. We used five microMOSFET dosimeters: three located along the field junction, one located 1 cm above the junction and the fifth microMOSFET located 1 cm below the junction. We performed consecutive measurements over several days for each patient and compared the measurements to the TPS calculation (Eclipse, Varian™).Results:The calculated and measured doses along the junction were 0.97±0.08 Gy and 1.02±0.14 Gy, respectively. Above the junction calculated and measured doses were 0.91±0.08 Gy and 0.98±0.09 Gy respectively, and below the junction calculated and measured doses were 1.70±0.15 Gy and 1.61±0.09 Gy, respectively. All differences were not statistically significant. When comparing calculated and measured doses for DIBH patients only, there was still no statistically significant difference between values for all dosimeter locations. Analysis was done using the Mann‐Whitney Rank‐Sum Test.Conclusion:We found excellent correlation between calculated doses from the TPS and measured skin doses at the junction of several half beam fields. Even for the DIBH technique, where there is more potential for variance due to depth of breath, there is no over or underdose along the field junction. This correlation validates the TPS, as well an accurate, reproducible patient setup.
SU‐E‐T‐427: Cell Surviving Fractions Derived From Tumor‐Volume Variation During Radiotherapy for Non‐Small Cell Lung Cancer: Comparison with Predictive Assays
Authors: Chvetsov A , Yartsev S , Schwartz J , Mayr N 
Published: July 2014

Purpose:To show that a distribution of cell surviving fractions S2 in a heterogeneous group of patients can be derived from tumor‐volume variation curves during radiotherapy for non‐small cell lung cancer.Methods:Our analysis was based on two data sets of tumor‐volume variation curves for heterogeneous groups of 17 patients treated for nonsmall cell lung cancer with conventional dose fractionation. The data sets were obtained previously at two independent institutions by using megavoltage (MV) computed tomography (CT). Statistical distributions of cell surviving fractions S2 and cell clearance half‐lives of lethally damaged cells T1/2 have been reconstructed in each patient group by using a version of the two‐level cell population tumor response model and a simulated annealing algorithm. The reconstructed statistical distributions of the cell surviving fractions have been compared to the distributions measured using predictive assays in vitro.Results:Non‐small cell lung cancer presents certain difficulties for modeling surviving fractions using tumor‐volume variation curves because of relatively large fractional hypoxic volume, low gradient of tumor‐volume response, and possible uncertainties due to breathing motion. Despite these difficulties, cell surviving fractions S2 for non‐small cell lung cancer derived from tumor‐volume variation measured at different institutions have similar probability density functions (PDFs) with mean values of 0.30 and 0.43 and standard deviations of 0.13 and 0.18, respectively. The PDFs for cell surviving fractions S2 reconstructed from tumor volume variation agree with the PDF measured in vitro. Comparison of the reconstructed cell surviving fractions with patient survival data shows that the patient survival time decreases as the cell surviving fraction increases.Conclusion:The data obtained in this work suggests that the cell surviving fractions S2 can be reconstructed from the tumor volume variation curves measured during radiotherapy with conventional fractionation. The proposed method can be used for treatment evaluation and adaptation.