bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐F‐T‐421: Dosimetry Change During Radiotherapy and Dosimetry Difference for Rigid and Deformed Registration in the Mid‐Thoracic Esophageal Carcinoma
Authors: Tao C , Liu T , Chen J , Zhu J , Yin Y 
Published: July 2016

Purpose:This study aimed to analyze dosimetry changes during radiotherapy for the mid‐thoracic esophageal carcinoma, and investigate dosimetry difference between rigid and deformed registration.Methods:Twelve patients with primary middle thoracic esophageal carcinoma were selected randomly. Based on first CT scanning of each patient, plans‐o were generated by experience physicists. After 20 fractions treatment, the corresponding plans‐re were created with second CT scanning. And then, these two CT images were rigid and deformed registration respectively, and the dose was accumulated plan‐o with plan‐re. The dosimetry variation of these plans (plan‐o: with 30 fractions, plan‐rig: the accumulated dose with rigid registration and plan‐def: the accumulated dose with deformed registration) were evaluated by paired T‐test.Results:The V20 value of total lung were 32.68%, 30.3% and 29.71% for plan‐o, plan‐rig and plan‐def respectively. The mean dose of total lung was 17.19 Gy, 16.67 Gy and 16.51 Gy for plan‐o plan‐rig and plan‐def respectively. There were significant differences between plan‐o and plan‐rig or plan‐def for both V20 and mean dose of total lung (with p= 0.003, p= 0.000 for V20 and p=0.008, p= 0.000 for mean dose respectively). There was no significant difference between plan‐rig and plan‐def (with p=0.118 for V20 and p=0.384 for mean dose). The max dose of spinal‐cord was 41.95 Gy, 41.48 Gy and 41.4 Gy for plan‐o, plan‐rig and plan‐def respectively. There were no significant differences for the max dose of spinal‐cord between these plans.Conclusion:The target volume changes and anatomic position displacement of mid‐thoracic esophageal carcinoma should not be neglected in clinics. These changes would cause overdose in normal tissue. Therefore, it is necessary to have another CT scanning and re‐plan during the mid‐thoracic esophageal carcinoma radiotherapy. And the dosimetry difference between rigid and deformed fusions was not found in this study.
SU‐F‐T‐431: Dosimetric Validation of Acuros XB Algorithm for Photon Dose Calculation in Water
Authors: Kumar L , Yadav G , Kishore V , Bhushan M , Samuvel K , Suhail M 
Published: July 2016

Purpose:To validate the Acuros XB algorithm implemented in Eclipse Treatment planning system version 11 (Varian Medical System, Inc., Palo Alto, CA, USA) for photon dose calculation.Methods:Acuros XB is a Linear Boltzmann transport equation (LBTE) solver that solves LBTE equation explicitly and gives result equivalent to Monte Carlo. 6MV photon beam from Varian Clinac‐iX (2300CD) was used for dosimetric validation of Acuros XB. Percentage depth dose (PDD) and profiles (at dmax, 5, 10, 20 and 30 cm) measurements were performed in water for field size ranging from 2×2,4×4, 6×6, 10×10, 20×20, 30×30 and 40×40 cm2. Acuros XB results were compared against measurements and anisotropic analytical algorithm (AAA) algorithm.Results:Acuros XB result shows good agreement with measurements, and were comparable to AAA algorithm. Result for PDD and profiles shows less than one percent difference from measurements, and from calculated PDD and profiles by AAA algorithm for all field size. TPS calculated Gamma error histogram values, average gamma errors in PDD curves before dmax and after dmax were 0.28, 0.15 for Acuros XB and 0.24, 0.17 for AAA respectively, average gamma error in profile curves in central region, penumbra region and outside field region were 0.17, 0.21, 0.42 for Acuros XB and 0.10, 0.22, 0.35 for AAA respectively.Conclusion:The dosimetric validation of Acuros XB algorithms in water medium was satisfactory. Acuros XB algorithm has potential to perform photon dose calculation with high accuracy, which is more desirable for modern radiotherapy environment.
SU‐F‐T‐432: Magnetic Field Dose Effects for Various Radiation Beam Geometries for Patients Treated with Hypofractionated Partial Breast Irradiation
Authors: Lim‐Reinders S , Keller B , McCann C , Sahgal A , Lee J , Kim A 
Published: July 2016

Purpose:Hypofractionated partial breast irradiation (HPBI) is being used at our clinic to treat inoperable breast cancer patients who have advanced disease. We are investigating how these patients could benefit from being treated in an MRI‐linac, where real‐time daily MRI tumor imaging and plan adaptation would be possible. As a first step, this study evaluates the dosimetric impact of the magnetic field for different radiation beam geometries on relevant OARs.Methods:Five patients previously treated using HPBI were selected. Six treatment plans were generated for each patient, evaluating three beam geometries (VMAT, IMRT, 3DCRT) with and without B0=1.5 T. The Monaco TPS was used with the Elekta MRI‐Linac beam model, where the magnetic field is orthogonal to the radiation beam. All plans were re‐scaled to the same isocoverage with a prescription of 40Gy/5 to the PTV. Plans were evaluated for the effect of the magnetic field and beam modality on skin V3 0, lung V2 0 and mean heart dose.Results:Averaged over all patients, skin V3 0for 3DCRT was higher than VMAT and IMRT (by +22% and +21%, with B0‐ON). The magnetic field caused larger increases in skin V3 0for 3DCRT (+8%) than VMAT (+3%) and IMRT (+4%) compared with B0‐OFF. With B0‐ON, 3DCRT had a markedly lower mean heart dose than VMAT (by 538cGy) and IMRT (by 562cGy); for lung V2 0, 3DCRT had a marginally lower dose than VMAT (by −2.2%) and IMRT (also −2.2%). The magnetic field had minimal effect on the mean heart dose and lung V2 0 for all geometries.Conclusion:The decreased skin dose in VMAT and IMRT can potentially mitigate the effects of skin reactions for HPBI in an MRI‐linac. This study illustrated that more beam angles may result in lower skin toxicity and better tumor conformality, with the trade‐off of elevated heart and lung doses.We are receiving funding support from Elekta
SU‐F‐T‐441: Dose Calculation Accuracy in CT Images Reconstructed with Artifact Reduction Algorithm
Authors: Ng C , Lee V , Chan S , Lee F , Ngan R 
Published: July 2016

Purpose:Accuracy of radiotherapy dose calculation in patients with surgical implants is complicated by two factors. First is the accuracy of CT number, second is the dose calculation accuracy. We compared measured dose with dose calculated on CT images reconstructed with FBP and an artifact reduction algorithm (OMAR, Philips) for a phantom with high density inserts. Dose calculation were done with Varian AAA and AcurosXB.Methods:A phantom was constructed with solid water in which 2 titanium or stainless steel rods could be inserted. The phantom was scanned with the Philips Brillance Big Bore CT. Image reconstruction was done with FBP and OMAR. Two 6 MV single field photon plans were constructed for each phantom. Radiochromic films were placed at different locations to measure the dose deposited. One plan has normal incidence on the titanium/steel rods. In the second plan, the beam is at almost glancing incidence on the metal rods. Measurements were then compared with dose calculated with AAA and AcurosXB.Results:The use of OMAR images slightly improved the dose calculation accuracy. The agreement between measured and calculated dose was best with AXB and image reconstructed with OMAR. Dose calculated on titanium phantom has better agreement with measurement. Large discrepancies were seen at points directly above and below the high density inserts. Both AAA and AXB underestimated the dose directly above the metal surface, while overestimated the dose below the metal surface. Doses measured downstream of metal were all within 3% of calculated values.Conclusion:When doing treatment planning for patients with metal implants, care must be taken to acquire correct CT images to improve dose calculation accuracy. Moreover, great discrepancies in measured and calculated dose were observed at metal/tissue interface. Care must be taken in estimating the dose in critical structures that come into contact with metals.
SU‐F‐T‐522: Dosimetric Study of Junction Dose in Double Isocenter Flatten and Flatten Filter Free IMRT and VMAT Plan Delivery
Authors: Samuvel K , Yadav G , Bhushan M , Tamilarasu S , Kumar L , Suhail M 
Published: July 2016

Purpose:To quantify the dosimetric accuracy of junction dose in double isocenter flattened and flatten filter free(FFF) intensity modulated radiation therapy(IMRT) and volumetric modulated arc therapy(VMAT) plan delivery using pelvis phantom.Methods:Five large field pelvis patients were selected for this study. Double isocenter IMRT and VMAT treatment plans were generated in Eclipse Treatment planning System (V.11.0) using 6MV FB and FFF beams. For all the plans same distance 17.0cm was kept between one isocenter to another isocenter. IMRT Plans were made with 7 coplanar fields and VMAT plans were made with full double arcs. Dose calculation was performed using AAA algorithms with dose grid size of 0.25 cm. Verification plans were calculated on Scanditronix Wellhofer pelvis slab phantom. Measurement point was selected and calculated, where two isocenter plan fields are overlapping, this measurement point was kept at distance 8.5cm from both isocenter. The plans were delivered using Varian TrueBeamTM machine on pelvis slab phantom. Point dose measurements was carried out using CC13 ion chamber volume of 0.13cm3.Results:The measured junction point dose are compared with TPS calculated dose. The mean difference observed was 4.5%, 6.0%, 4.0% and 7.0% for IMRT‐FB,IMRT‐FFF, VMAT‐FB and VMAT‐FFF respectively. The measured dose results shows closer agreement with calculated dose in Flatten beam planning in both IMRT and VMAT, whereas in FFF beam plan dose difference are more compared with flatten beam plan.Conclusion:Dosimetry accuracy of Large Field junction dose difference was found less in Flatten beam compared with FFF beam plan delivery. Even though more dosimetric studies are required to analyse junction dose for FFF beam planning using multiple point dose measurements and fluence map verification in field junction area.
SU‐F‐T‐535: An Android App and Windows Executable with GUI for the Monitor Unit Calculation in KV X‐Ray Therapy
Authors: Pearse J , Chow J 
Published: July 2016

Purpose:We created two applications, one for use on Android and one for use on Windows, to carry out monitor unit (MU) calculations. These applications carried out these long calculations quickly, while avoiding the potential for human error.Methods:A general formula for calculating MU for an orthovoltage x‐ray machine was used and implemented in two programs created for Android and Windows. The formula relies on the prescribed dose and fractionation. Other values the formula relies upon are relative exposure factor (REF) and backscatter factor (BSF). These factors are specific to each unit and head in use, and are measured and tabulated prior to use. In the case of a BSF not falling on already known values, the programs were made to automatically use linear interpolation to find an appropriate BSF. The programs also allow for a stand‐off correction, calculated using the inverse‐square law, and an attenuator value that can be arbitrarily input by the user.Results:The two programs were built using C#, and use essentially the same types of backends to do their calculations. Differences in the programs are mainly in the graphical user interfaces. The backend was made to mimic the way a human does the same calculations. Previously measured REF and BSF tables for three different x‐ray energies and field size types were loaded into the program beforehand for testing. Both applications were easy to use, and produced the exact same results in all situations. These results matched the same calculations done by hand. Differences were only found when hand calculations use shortcuts to find BSF values that lie outside of the pre‐measured values.Conclusion:Our programs can efficiently and effectively calculate MU as well as or better than by hand. The Android version can be useful in the future for emergency situations.
SU‐F‐T‐544: Development of a Clinically Feasible Workflow of 4D MRI‐Based Treatment Planning for Liver SBRT
Authors: Han S , Yin F , Czito B , Palta M , Cai J 
Published: July 2016

Purpose:To develop a clinically feasible workflow of 4D MRI‐based treatment planning for liver SBRT.Methods:A clinical workflow based on 4D MRI for liver SBRT was designed to largely simulate the same procedure as 4D CT for lung SBRT. Key features of the workflow include: (1) contouring tumor volume at each phases (2) contouring more structures, (3) assigning CT numbers to structures for dose calculation. Uncertainties (bone delineation, MRI distortion, CT number assignment, etc.) were investigated using five clinical treatment plans of liver SBRT by simulating the following scenarios: homogeneous calculation, calculation with CT number assignment (for each structure separately and for all combined), calculation with and without distortion (mimicked by shirking body structure by 1mm to 5 mm). Dose‐histogram volume (DVF) parameters were collected from the simulated cases and compared to those in the original plan. Lastly, a patient example case of 4D MRI‐based treatment plan was performed to demonstrate the feasibility of the proposed workflow.Results:In homogeneous calculation, the average percentage volume error (ΔV30) of liver was 0.40% and maximum average dose error (GTV ΔD95) was 1.08Gy. Between MRI‐based and original plans, liver ΔV30 was 0.28% and maximum average dose error (GTV ΔD95) was 0.75Gy. Basically dose errors and percentage volume error increased as distortion increased. In some special cases, in original plans, the minimum spinal cord max dose error appeared when distortion was 4mm; in MRI‐based plans, the minimum liver ΔV30 appeared when distortion was 3mm. In the example case, mean liver dose was 20.7Gy in 4D MRI‐based plan and 34.2Gy in 4D CT‐based plan.Conclusion:A clinically feasible workflow of 4D MRI‐based treatment planning for liver SBRT has been established. Dose uncertainties of the workflow were generally small, except for large MR geometric distortions (> 3 mm).NIH (1R21CA165384)
SU‐F‐T‐548: An Extraction Method for Correction of Detector Volume Effect in Small Field Profile Measurement
Authors: Chiu T , Yang B , Law M , Lam W , Kong C , Geng H , Cheung K , Yu S 
Published: July 2016

Purpose:To investigate the appropriateness of Gaussian detector response function in SRS profile measurement.Methods:In‐air profile data for a 6MV beam were collected by using ionization chambers and radiochromic film. Two ionization chambers (FC65‐G(IBA) and PinPoint(PTWTW31009)) were used to scan the beam profile. Film was used to measure the beam penumbra. A half‐blocked beam was acquired with stepping size of 0.2mm and gradient of the measured profile represents the detector response function. The field widths of 2cm and 3cm were measured at SAD. Two detector response functions were evaluated, i.e. a traditional single Gaussian and a three‐Gaussian symmetric function. Two corresponding models were used to fit measured data. One was error functions with one shaping parameter. The other model was a symmetrical superposition of three sets of error functions with fixed separation and two different shaping parameters. In both fitting, resultant Gaussian kernels and corresponding σs could be calculated analytically. SNR of the fitted curves were obtained and compared.Results:Our measured data indicated that the ionization chambers had a three‐peak response function. From the first modeling, SNR for FC65‐G were 36.0dB and 38.3dB for 2cm and 3cm field respectively. The corresponding SNR for the PinPoint were 43.6dB and 42.5dB. From the second modeling, SNR for FC65‐G were 42.5dB and 47.4dB for 2cm and 3cm field respectively. The corresponding SNR for the PinPoint were 44.0dB and 44.5 dB. Three‐gaussian model had an observable improvement for FC65‐G chamber. Film measured penumbra was 3–5 times smaller than that of ionization‐chambers.Conclusion:Superposition of three Gaussian kernels resembles the detector response due to central electrode and chamber wall and results in a better fitting to the measurement data than a single Gaussian kernel. Our study indicated that the Three‐Gaussian model was more suitable for the detector with sigma comparable to penumbra width.
SU‐F‐T‐553: Sector Output Uniformity of the Perfexion Gamma Knife
Authors: Volotskova O , Jozsef G , Osterman K , Han K , Xu A 
Published: July 2016

Purpose:To study the uniformity of single‐sector outputs from the 3 collimators of the Perfexion Gamma Knife (PGK) unit and investigate the potential impact on Gamma Knife treatment planning.Methods:An A16 ion chamber and a SFD diode detector were used to measure both the output factors and the single‐sector outputs from a PGK unit. The detectors were placed in custom inserts in the center of a spherical solid water phantom and connected to a Max 4000 electrometer during the measurements. For single‐sector outputs, a treatment plan with a prescription dose of 1 Gy at the focal point was generated for each sector of the 16 mm, 8 mm, and 4 mm collimators and was exported to the console computer for dose delivery. The procedure was repeated 3 times for each sector and an average value was taken as the sector output.Results:The differences between the output factors from the diode measurements and the clinical values for the 8 mm and 4 mm collimators were −0.4% and −2.1% respectively. The corresponding values for the A16 ion chamber were −3.5% and −17.1%. The maximum differences among the 8 single‐sector outputs for the 16 mm, 8 mm, and 4 mm collimators were 4%, 3.7%, and 4.6% respectively. Variations of the sector outputs (defined as the standard deviation‐to‐mean ratio) among the 8 single‐sector outputs for the 16 mm, 8 mm, and 4 mm collimators were measured at 1.16%, 1.32%, and 1.81%. Measurements using the ion chamber were similar to those acquired with the diode for the 16 mm and 8 mm collimators.Conclusion:Single‐sector outputs for the 8 sectors of the 16 mm, 8 mm, and 4 mm collimators of the PGK differed by less than 5% and are within the specified range of planning accuracy.
SU‐F‐T‐629: Effect of Multi‐Leaf Collimator (MLC) Width On Plan Quality of Single‐Isocenter VMAT Intracranial Stereotactic Radiosurgery for Multiple Metastases
Authors: Kraus J , Thomas E , Wu X , Fiveash J , Popple R 
Published: July 2016

Purpose:Single‐isocenter VMAT has been shown able to create high quality plans for complex intracranial multiple metastasis SRS cases. Linacs capable of the technique are typically outfitted with an MLC that consists of a combination of 5 mm and 10 mm leaves (standard) or 2.5 mm and 5 mm leaves (high‐definition). In this study, we test the hypothesis that thinner collimator leaves are associated with improved plan quality.Methods:Ten multiple metastasis cases were identified and planned for VMAT SRS using a 10 MV flattening filter free beam. Plans were created for a standard (std) and a high‐definition (HD) MLC. Published values for leaf transmission factor and dosimetric leaf gap were utilized. All other parameters were invariant. Conformity (plan and individual target), moderate isodose spill (V50%), and low isodose spill (mean brain dose) were selected for analysis.Results:Compared to standard MLC, HD‐MLC improved overall plan conformity (median: Paddick CI_HD = 0.83, Paddick CI_std = 0.79; p = 0.004 and median: RTOG CI_HD =1.18, RTOG CI_std =1.24; p = 0.01), improved individual lesion conformity (median: Paddick CI_HD,i =0.77, Paddick CI_std,i =0.72; p < 0.001 and median: RTOG CI_HD,i = 1.28, RTOG CI_std,i =1.35; p < 0.001), improved moderate isodose spill (median: V50%_HD = 37.0 cc, V50%_std = 45.7 cc; p = 0.002), and improved low dose spill (median: dmean_HD = 2.90 Gy, dmean_std = 3.19 Gy; p = 0.002).Conclusion:For the single‐isocenter VMAT SRS of multiple metastasis plans examined, use of HD‐MLC modestly improved conformity, moderate isodose, and low isodose spill compared to standard MLC. However, in all cases we were able to generate clinically acceptable plans with the standard MLC. More work is need to further quantify the difference in cases with higher numbers of small targets and to better understand any potential clinical significance.This research was supported in part by Varian Medical Systems.
SU‐F‐T‐634: Feasibility Study of Respiratory Gated RapidArc SBRT Using a 6MV FFF Photon Beam
Authors: Dou K , Jacobs M , Laser B , Safaraz M , Rodgers J 
Published: July 2016

Purpose:To conduct a feasibility study on retrospective respiratory gating and marker tracking for lung stereotactic body radiotherapy (SBRT) with a gated RapidArc delivery using a 6MV flattened filter free photon mode.Methods:A CIRS dynamic thorax phantom Model 008A with different inserts was used for treatment planning and respiratory gating. 4D CT had a free breathing simulation followed by a respiration gated, ten phased CT using a Philips Brilliance CT with a Varian RPM respiratory gating system. The internal target volume was created from the ten phase gated CT images, followed by exporting to a Varian Eclipse TPS v11 for treatment planning on the free breath images. Both MIP and AIP were also generated for comparison of planning and target motion tracking. The planned dose was delivered with a 6MV FFF photon beam from a Varian TrueBeam accelerator. Gated target motion was also verified by tracking the implanted makers during delivery using continuous kV imaging in addition to CBCT, kV and MV localization and verification.Results:Gating was studied in three situations of lower, normal, and faster breathing at a respiratory cycle of 5, 15 and 25 breaths per minute, respectively. 4D treatment planning was performed at a normal breathing of 15 breaths per minute. The gated patterns obtained using the TrueBeam IR camera were compared with the planned ones while gating operation was added prior to delivery . Gating was realized only when the measured respiratory patterns matched to the planned ones. The gated target motion was verified within the tolerance by kV and MV imaging. Either free breathing CT or averaged CT images were studied to be good for image guidance to align the target.Conclusion:Gated RapidArc SBRT delivered with a 6MV FFF photon beam is realized using a dynamic lung phantom.