bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐F‐T‐483: An Investigation into the Effect of Varying Temperature On PTP Corrections in TG‐51
Authors: Neba N , Mensah‐Brown N , Howlin T , Howard S , Saleh H 
Published: July 2016

Purpose:To determine the effect on machine output calibration, following the TG‐51 protocol, as the water temperature increasingly deviates from Standard temperature (22°C)Methods:A water tank was set up according to TG‐51 protocol. Two sets of measurements were taken and the pressure recorded. The measurements consisted of readings at different temperatures. In the first set, P(ion), P(pol), and P(elec) were assumed constant while they were accounted for in the second. The outputs were normalized to that at 22°C. The first readings were taken after the chamber had equilibrated to the water temperature. The water temperature was then raised at intervals of approximately 1–2°C and measurements taken after 5–10 minutes (as per TG‐51).Results:In both measurements, P(TP) was corrected for using equation 10 in TG‐51. The normalized output is expected to be 1.0 with all corrections accounted for. However as the water temperature was gradually increased, the normalized output also varied. The largest discrepancy observed while not accounting for the factors, P(ion), P(pol), and P(elec) was 1.1%, and while accounting for these factors, the largest discrepancy was 1.0%.Conclusion:Our results show discrepancies in output measured at different temperatures. Although a lack of equilibrium may explain these discrepancies, it is not as easy to ensure true equilibrium. It is also possible that these discrepancies are real and related to the inherent venting mechanism of the chamber. However, more work would need to be done to investigate this further and to determine if this effect is true across all Exradin and/or other manufacturer chambers. Most importantly, the physicist should perform TG‐51 at room temperature and pressure to better ensure thermal equilibrium. If this is not currently being done, and not enough time is given, especially when the water temperature is “significantly” different from 22°C, the calibration will be less accurate.
SU‐F‐T‐485: Independent Remote Audits for TG51 NonCompliant Photon Beams Performed by the IROC Houston QA Center
Authors: Alvarez P , Molineu A , Lowenstein J , Taylor P , Kry S , Followill D 
Published: July 2016

Purpose:IROC_H conducts external audits for output check verification of photon and electron beams. Many of these beams can meet the geometric requirements of the TG 51 calibration protocol. For those photon beams that are non TG 51 compliant like Elekta GammaKnife, Accuray CyberKnife and TomoTherapy, IROC_H has specific audit tools to monitor the reference calibration.Methods:IROC_H used its TLD and OSLD remote monitoring systems to verify the output of machines with TG 51 non compliant beams. Acrylic OSLD miniphantoms are used for the CyberKnife. Special TLD phantoms are used for TomoTherapy and GammaKnife machines to accommodate the specific geometry of each machine. These remote audit tools are sent to institutions to be irradiated and returned to IROC_H for analysis.Results:The average IROC_H/institution ratios for 480 GammaKnife, 660 CyberKnife and 907 rotational TomoTherapy beams are 1.000±0.021, 1.008±0.019, 0.974±0.023, respectively. In the particular case of TomoTherapy, the overall ratio is 0.977±0.022 for HD units. The standard deviations of all results are consistent with values determined for TG 51 compliant photon beams. These ratios have shown some changes compared to values presented in 2008. The GammaKnife results were corrected by an experimentally determined scatter factor of 1.025 in 2013. The TomoTherapy helical beam results are now from a rotational beam whereas in 2008 the results were from a static beam. The decision to change modality was based on recommendations from the users.Conclusion:External audits of beam outputs is a valuable tool to confirm the calibrations of photon beams regardless of whether the machine is TG 51 or TG 51 non compliant.The difference found for TomoTherapy units is under investigation. This investigation was supported by IROC grant CA180803 awarded by the NCI
SU‐F‐T‐489: 4‐Years Experience of QA in TomoTherapy MVCT: What Do We Look Out For?
Authors: Lee F , Chan K 
Published: July 2016

Purpose:To evaluate the QA results of TomoTherapy MVCT from March 2012 to February 2016, and to identify issues that may affect consistency in HU numbers and reconstructed treatment dose in MVCT.Methods:Monthly QA was performed on our TomoHD system. Phantom with rod inserts of various mass densities was imaged in MVCT and compared to baseline to evaluate HU number consistency. To evaluate treatment dose reconstructed by delivered sinogram and MVCT, a treatment plan was designed on a humanoid skull phantom. The phantom was imaged with MVCT and treatment plan was delivered to obtain the sinogram. The dose reconstructed with the Planned Adaptive software was compared to the dose in the original plan. The QA tolerance for HU numbers was ±30 HU, and ±2% for discrepancy between original plan dose and reconstructed dose. Tolerances were referenced to AAPM TG148.Results:Several technical modifications or maintenance activities to the system have been identified which affected QAResults:1) Upgrade in console system software which added a weekly HU calibration procedure; 2) Linac or MLC replacement leading to change in Accelerator Output Machine (AOM) parameters; 3) Upgrade in planning system algorithm affecting MVCT dose reconstruction. These events caused abrupt changes in QA results especially for the reconstructed dose. In the past 9 months, when no such modifications were done to the system, reconstructed dose was consistent with maximum deviation from baseline less than 0.6%. The HU number deviated less than 5HU.Conclusion:Routine QA is essential for MVCT, especially if the MVCT is used for daily dose reconstruction to monitor delivered dose to patients. Several technical events which may affect consistency of this are software changes, linac or MLC replacement. QA results reflected changes which justify re‐calibration or system adjustment. In normal circumstances, the system should be relatively stable and quarterly QA may be sufficient.
SU‐F‐T‐500: The Effectiveness of a Patient Specific Bolus Made by Using Three‐Dimensional Printing Technique in Photon Radiotherapy
Authors: Fujimoto K , Shiinoki T , Yuasa Y , Hanazawa H , Shibuya K 
Published: July 2016

Purpose:A commercially available bolus (commercial‐bolus) would not completely contact with the irregular shape of a patient's skin. The purposes of this study were to customize a patient specific three‐dimensional (3D) bolus using a 3D printer (3D‐bolus) and to evaluate its clinical feasibility for photon radiotherapy.Methods:The 3D‐bolus was designed using a treatment planning system (TPS) in DICOM‐RT format. To print the 3D bolus, the file was converted into stereolithography format. To evaluate its physical characteristics, plans were created for water equivalent phantoms without the bolus, with the 3D‐bolus printed in a flat form, and with the virtual bolus which supposed a commercial‐bolus. These plans were compared with the percent depth dose (PDD) measured from the TPS. Furthermore, to evaluate its clinical feasibility, the treatment plans were created for RANDO phantoms without the bolus and with the 3D‐bolus which was customized for contacting with the surface of the phantom. Both plans were compared with the dose volume histogram (DVH) of the target volume.Results:In the physical evaluation, dmax of the plan without the bolus, with the 3D‐bolus, and with the virtual bolus were 2.2 cm, 1.6 cm, and 1.7 cm, respectively. In the evaluation of clinical feasibility, for the plan without the bolus, Dmax, Dmin, Dmean, D90%, and V90% of the target volume were 102.6 %, 1.6 %, 88.8 %, 57.2 %, and 69.3 %, respectively. By using the 3D‐bolus, the prescription dose could be delivered to at least 90 % of the target volume, Dmax, Dmin, Dmean, D90%, and V90% of the target volume were 104.3 %, 91.6 %, 92.1 %, 91.7 %, and 98.0 %, respectively. The 3D‐bolus has the potential to be useful for providing effective dose coverage in the buildup region.Conclusion:A 3D‐bolus produced using 3D printing technique is comparable to a commercially available bolus.
SU‐F‐T‐504: Non‐Divergent Planning Method for Craniospinal Irradiation
Authors: Sperling N , Bogue J , Parsai E 
Published: July 2016

Purpose:Traditional Craniospinal Irradiation (CSI) planning techniques require careful field placement to allow optimal divergence and field overlap at depth, and measurement of skin gap. The result of this is a necessary field overlap resulting in dose heterogeneity in the spinal canal. A novel, nondivergent field matching method has been developed to allow simple treatment planning and delivery without the need to measure skin gap.Methods:The CSI patient was simulated in the prone, and a plan was developed. Bilateral cranial fields were designed with couch and collimator rotation to eliminate divergence with the upper spine field and minimize anterior divergence into the lenses. Spinal posterior‐to‐anterior fields were designed with the couch rotated to 90 degrees to allow gantry rotation to eliminate divergence at the match line, and the collimator rotated to 90 degrees to allow appropriate field blocking with the MLCs. A match line for the two spinal fields was placed and the gantry rotated to equal angles in opposite directions about the match line. Jaw positions were then defined to allow 1mm overlap at the match line to avoid cold spots. A traditional CSI plan was generated using diverging spinal fields, and a comparison between the two techniques was generated.Results:The non‐divergent treatment plan was able to deliver a highly uniform dose to the spinal cord with a cold spot of only 95% and maximum point dose of 115.8%, as compared to traditional plan cold spots of 87% and hot spots of 132% of the prescription dose.Conclusion:A non‐divergent method for planning CSI patients has been developed and clinically implemented. Planning requires some geometric manipulation in order to achieve an adequate dose distribution, however, it can help to manage cold spots and simplify the shifts needed between spinal fields.
SU‐F‐T‐508: A Collimator‐Based 3‐Dimensional Grid Therapy Technique in a Small Animal Radiation Research Platform
Authors: Jin J , Kong V , Zhang H 
Published: July 2016

Purpose:Three dimensional (3D) Grid Therapy using MLC‐based inverse‐planning has been proposed to achieve the features of both conformal radiotherapy and spatially fractionated radiotherapy, which may deliver very high dose in a single fraction to portions of a large tumor with relatively low normal tissue dose. However, the technique requires relatively long delivery time. This study aims to develop a collimator‐based 3D grid therapy technique. Here we report the development of the technique in a small animal radiation research platform.Methods:Similar as in the MLC‐based technique, 9 non‐coplanar beams in special channeling directions were used for the 3D grid therapy technique. Two specially designed grid collimators were fabricated, and one of them was selectively used to match the corresponding gantry/couch angles so that the grid opening of all 9 beams are met in the 3D space in the target. A stack of EBT3 films were used as 3D dosimetry to demonstrate the 3D grid‐like dose distribution in the target. Three 1‐mm beams were delivered to the stack of films in the area outside the target for alignment when all the films were scanned to reconstruct the 3D dosimtric image.Results:3D film dosimetry showed a lattice‐like dose distribution in the 3D target as well as in the axial, sagittal and coronal planes. The dose outside the target also showed a grid like dose distribution, and the average dose gradually decreased with the distance to the target. The peak to valley ratio was approximately 5:1. The delivery time was 7 minutes for 18 Gy peak dose, comparing to 6 minutes to deliver a 18‐Gy 3D conformal plan.Conclusion:We have demonstrated the feasibility of the collimator‐based 3D grid therapy technique which can significantly reduce delivery time comparing to MLC‐based inverse planning technique.
SU‐F‐T‐511: Feasibility Study of Using Flattening‐Filter‐Free Photon Beams to Deliver Conventional Flat Beam
Authors: Potter N , Lebron S , Yan G , Li J , Liu C , Lu B 
Published: July 2016

Purpose:Various dosimetric benefits such as increased dose rate, and reduced leakage and out of field dose has led to the growth of FFF technology in the clinic. In this study, we concentrate on investigating the feasibility of using flattening‐filter‐free (FFF) beams to deliver conventional flat beams (CFB), since completely getting rid of the flattening‐filter module from the gantry head can not only simplify the gantry design but also decrease the workload on machine maintain and quality assurance.Methods:The sliding window based IMRT technique was utilized to generate the CFB from the FFF beam for various beam configurations on the Elekta Versa HD. The flat beam reproducibility and MU efficiency were compared for each beam configuration among FFF planning, delivery and CFB planning.Results:Compared to the CFB plan, the 3%3mm passing rates of the FFF beams from both measurement and plan are 100% and 95%(or better) for 15×15 cm2 or smaller field size and for any field size greater than 15×15 cm2at 10 cm depth, respectively. The largest discrepancy is about 5% and typically appears at the field shoulder area. The MU increase average was 80% for FFF compared to CFB, however has a minimal impact on treatment delivery time.Conclusion:The ability to deliver conventional flat treatments is not absent when operating in FFF mode. With proper TPS manipulation and beam modulation, FFF mode can achieve reasonable flat profiles and comparable dose coverage as CFB does for various conventional treatment techniques, such as four field box, or long spine treatment techniques. The ability to deliver most clinical treatments from the same treatment unit, will allow for less quality assurance as well as maintenance, and completely eliminate the need for the flattening filter on modern linacs.
SU‐F‐T‐512: A Dosimetric Comparison for Palliative Spine Metastasis Treatments: 3‐D Vs. Conformal Arc
Authors: Ulizio V , Taylor M 
Published: July 2016

Purpose:Spine metastases have traditionally been treated using a parallel opposed 3‐D technique: an anterior field and a posterior field (AP/PA). This has proven to give the lesions adequate coverage. The downside to this type of treatment is that the full prescription dose covers a large area of the patient and can go through critical organs such as the heart, spine, lungs, bowel, and others depending on the vertebrae being treated. Conformal arc therapy can also be used for this type of treatment. These two techniques will be compared for target coverage and doses to organs at risk (OARs).Methods:20 multi‐vertebra metastases patients were chosen for this study, with a range of vertebrae being treated amongst each case. The original AP/PA treatments were re‐planned with 1–3 conformal arcs placed depending on the location of nearby OARs. The GTV coverage was normalized so that both techniques had equal coverage. The OAR doses and the volume of the 50% prescription dose value were then compared between the two planning techniques.Results:Initial results on average show lower doses for the heart maximum, heart mean, lung V20, spinal cord maximum, and bowel maximum for the conformal arc plans. The AP/PA plans however on average showed lower kidney mean dose, liver mean dose, and parotid mean dose. The 50% prescription dose volume was smaller in all the conformal arc plans except for one.Conclusion:From the preliminary results the conformal arc plans spare critical OARs better than the two field technique, except when treating the vertebrae near the kidneys, liver, and parotids. The conformal arc plans also have a lower volume of the 50% prescription dose value. The data suggests that conformal arcs can be used for certain palliative spine treatments and that this technique should be considered when beginning planning.
SU‐F‐T‐513: Dosimetric Validation of Spatially Fractionated Radiotherapy Using Gel Dosimetry
Authors: Papanikolaou P , Watts L , Pappas E , Kalaitzakis G , Maris T , Kirby N , Rasmussen K , Gutierrez A , Stathakis S , Pappas E 
Published: July 2016

Purpose:Spatially fractionated radiation therapy, also known as GRID therapy, is used to treat large solid tumors by irradiating the target to a single dose of 10–20Gy through spatially distributed beamlets. We have investigated the use of a 3D gel for dosimetric characterization of GRID therapy.Methods:GRID therapy is an external beam analog of volumetric brachytherapy, whereby we produce a distribution of hot and cold dose columns inside the tumor volume. Such distribution can be produced with a block or by using a checker‐like pattern with MLC. We have studied both types of GRID delivery. A cube shaped acrylic phantom was filled with polymer gel and served as a 3D dosimeter. The phantom was scanned and the CT images were used to produce two plans in Pinnacle, one with the grid block and one with the MLC defined grid. A 6MV beam was used for the plan with a prescription of 1500cGy at dmax. The irradiated phantom was scanned in a 3T MRI scanner.Results:3D dose maps were derived from the MR scans of the gel dosimeter and were found to be in good agreement with the predicted dose distribution from the RTP system. Gamma analysis showed a passing rate of 93% for 5% dose and 2mm DTA scoring criteria. Both relative and absolute dose profiles are in good agreement, except in the peripheral beamlets where the gel measured slightly higher dose, possibly because of the changing head scatter conditions that the RTP is not fully accounting for. Our results have also been benchmarked against ionization chamber measurements.Conclusion:We have investigated the use of a polymer gel for the 3D dosimetric characterization and evaluation of GRID therapy. Our results demonstrated that the planning system can predict fairly accurately the dose distribution for GRID type therapy.
SU‐F‐T‐521: Flattening‐Filter‐Free Beam Parameters Comparison From Different Linac Machine Types
Authors: Hussain A 
Published: July 2016

Purpose:Novel linac machines, TrueBeam (TB) and Elekta Versa have updated head designing and software control system, include flattening‐filter‐free (FFF) photon and electron beams. Later on FFF beams were also introduced on C‐Series machines. In this work FFF beams for same energy 6MV but from different machine versions were studied with reference to beam data parameters.Methods:The 6MV‐FFF percent depth doses, profile symmetry and flatness, dose rate tables, and multi‐leaf collimator (MLC) transmission factors were measured during commissioning process of both C‐series and Truebeam machines. The scanning and dosimetric data for 6MV‐FFF beam from Truebeam and C‐Series linacs was compared. A correlation of 6MV‐FFF beam from Elekta Versa with that of Varian linacs was also found.Results:The scanning files were plotted for both qualitative and quantitative analysis. The dosimetric leaf gap (DLG) for C‐Series 6MV‐FFF beam is 1.1 mm. Published values for Truebeam dosimetric leaf gap is 1.16 mm. 6MV MLC transmission factor varies between 1.3 % and 1.4 % in two separate measurements and measured DLG values vary between 1.32 mm and 1.33 mm on C‐Series machine. MLC transmission factor from C‐Series machine varies between 1.5 % and 1.6 %. Some of the measured data values from C‐Series FFF beam are compared with Truebeam representative data. 6MV‐FFF beam parameter values like dmax, OP factors, beam symmetry and flatness and additional parameters for C‐Series and Truebeam liancs will be presented and compared in graphical form and tabular data form if selected.Conclusion:The 6MV flattening filter (FF) beam data from C‐Series & Truebeam and 6MV‐FFF beam data from Truebeam has already presented. This particular analysis to compare 6MV‐FFF beam from C‐Series and Truebeam provides opportunity to better elaborate FFF mode on novel machines. It was found that C‐Series and Truebeam 6MV‐FFF dosimetric and beam data was quite similar.
SU‐F‐T‐526: A Comparative Study On Gating Efficiency of Varian RPM Device and Calypso System
Authors: Ravindran P , WuiAnn W , LIM Y 
Published: July 2016

Purpose:In general, the linear accelerator is gated using respiratory signal obtained by way of external sensors to account for the breathing motion during radiotherapy. One of the commonly used gating devices is the Varian RPM device. Calypso system that uses electromagnetic tracking of implanted or surface transponders could also be used for gating. The aim of this study is to compare the gating efficiency of RPM device and the calypso system by phantom studies.Methods:An ArcCheck insert was used as the phantom with a Gafchromic film placed in its holder. The ArcCheck insert was placed on a Motion Sim platform and moved in the longitudinal direction simulating a respiratory motion with a period of 5 seconds and amplitude of ±6mm. The Gafchromic film was exposed to a 2 × 2cm2 field, i) with the phantom static, ii) phantom moving but ungated iii) gated with gating window of 2mm and 3mm. This was repeated with Calypso system using surface transponders with the same gating window. The Gafchromic films were read with an EPSON 11000 flatbed scanner and analysed with ߢMedphysto’ software.Results:The full width at half maximum (FWHM) as measured with film at the level of the film holder was 1.65cm when the phantom was static. FWHM measured with phantom moving and without gating was 1.16 cm and penumbra was 7 mm (80–20%) on both sides. When the beam was gated with 2 mm gating window the FWHM was 1.8 cm with RPM device and 1.9 cm with Calypso. Similarly, when the beam was gated with 3 mm window, the FWHM was 1.9cm with RPM device and 2cm with Calypso.Conclusion:This work suggests that the gating efficiency of RPM device is better than that of the Calypso with surface transponder, with reference to the latency in gating.