bluuebunny/crossref_metadata_2025 huggingface dataset:
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 QA

Results:

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.
SU‐F‐T‐540: Comprehensive Fluence Delivery Optimization with Multileaf Collimation
Authors: Weppler S , McGeachy P , Villarreal‐Barajas J , Khan R
Published: July 2016

Purpose:

Multileaf collimator (MLC) leaf sequencing is performed via commercial black‐box implementations, on which a user has limited to no access. We have developed an explicit, generic MLC sequencing model to serve as a tool for future investigations of fluence map optimization, fluence delivery optimization, and rotational collimator delivery methods.

Methods:

We have developed a novel, comprehensive model to effectively account for a variety of transmission and penumbra effects previously treated on an ad hoc basis in the literature. As the model is capable of quantifying a variety of effects, we utilize the asymmetric leakage intensity across each leaf to deliver fluence maps with pixel size smaller than the narrowest leaf width. Developed using linear programming and mixed integer programming formulations, the model is implemented using state of the art open‐source solvers. To demonstrate the versatility of the algorithm, a graphical user interface (GUI) was developed in MATLAB capable of accepting custom leaf specifications and transmission parameters. As a preliminary proof‐ofconcept, we have sequenced the leaves of a Varian 120 Leaf Millennium MLC for five prostate cancer patient fields and one head and neck field. Predetermined fluence maps have been processed by data smoothing methods to obtain pixel sizes of 2.5 cm2. The quality of output was analyzed using computer simulations.

Results:

For the prostate fields, an average root mean squared error (RMSE) of 0.82 and gamma (0.5mm/0.5%) of 91.4% were observed compared to RMSE and gamma (0.5mm/0.5%) values of 7.04 and 34.0% when the leakage considerations were omitted. Similar results were observed for the head and neck case.

Conclusion:

A model to sequence MLC leaves to optimality has been proposed. Future work will involve extensive testing and evaluation of the method on clinical MLCs and comparison with black‐box leaf sequencing algorithms currently used by commercial treatment planning systems.
SU‐F‐T‐625: Optimal Treatment Planning Strategy Among Arc Arrangements for Prostate SBRT with VMAT Technique
Authors: Chung J , Kang S , Suh T , Lee J , Kim J , Eom K
Published: July 2016

Purpose:

The purpose of this study is to determine the optimal treatment planning strategy among the different arc arrangements for prostate stereotactic body radiotherapy (SBRT) plans with volumetric modulated arc therapy (VMAT).

Methods:

Ten patients with prostate cancer were selected. The SBRT‐VMAT plans for each patient were generated with single‐full (181° to 179°; 1FA), single‐partial (240° to 120°; 1PA), double‐full (181° to 179° and 179° to 181°; 2FA), and double‐partial (240° to 120° and 120° to 240°; 2PA) arc arrangements. The prescription dose was 42.7 Gy in 7 fractions. Dose distribution was calculated using a 10‐MV flattening‐filter‐free beam and the Acuros XB algorithm. Dosimetric parameters of target volume and organs at risk (OARs) were evaluated from cumulative dose‐volume histograms on prostate SBRT‐VMAT plans between single‐arc (1FA and 1PA) and double‐arc (2FA and 2PA) arrangements.

Results:

All plans using four arc arrangements were highly conformal with conformity index (CI)<1.05 and conformation number (CN)=0.91, and the doses to target volume were homogeneous (homogeneity index (HI)= 0.09 0.12). Pertaining to the dose to the OARs, there were significant differences in the rectum, left and right femoral head doses while having no difference in the bladder dose. The partial‐arc (1PA and 2PA) had relatively high reductions for the mean rectum dose compared to full‐arc (1FA and 2FA). The near‐to‐maximum dose (D2%) and mean dose of the left and right femoral head were always lower on prostate SBRT‐VMAT plan using the full‐arc, when compared to the partial‐arc arrangement.

Conclusion:

This study confirmed that prostate SBRT‐VMAT using 1PA was feasible fast delivery time and produced equivalent target coverage and better rectum sparing, although the D2% and mean dose of the left and right femoral head increased slightly. Therefore, the results of this study suggest that the use of 1PA is an attractive choice for delivering prostate SBRT‐VMAT.
SU‐F‐T‐630: Energy Spectral Study On Lipiodol After Trans‐Arterial Chemoembolization Using the Flattened and Unflattened Photon Beams
Authors: Kawahara D , Ozawa S , Saito A , Nishio T , Hioki K , Masuda H , Okumura T , Ochi Y , Nakashima T , Suzuki T , Tanaka S , Ohno Y , Nagata Y
Published: July 2016

Purpose:

SBRT combining transarterial chemoembolization with Lipiodol is expected to improve local control. Our showed that the dose enhancement effect in the Lipiodol with 10X flattening filter free (FFF) was inserted. This study was to investigate the energy fluence variations of electron in the Lipiodol using flattened (FF) and FFF beams.

Methods:

FF and FFF for 6X and 10X beams by TrueBeam were used in this study. The Lipiodol (3 X 3 X 3 cm3) was located at the depth of 5 cm in water, the dose enhancement factor (DEF) and energy fluence were calculated by Monte Carlo (MC) calculations (PHITS).

Results:

DEFs with FF and FFF of 6X were 17.1% and 24.3% at rebuild‐up region in the Lipiodol (5.3cm depth), 7.0% and 17.0% at the center of Lipiodol (6.5cm depth), and −13.2% and −8.2% at behind Lipiodol (8.3cm depth). DEFs with FF and FFF of 10X were 21.7% and 15.3% at rebuild‐up region, 8.2% and 10.5% at the center of Lipiodol, and −14.0% and −8.6% at behind Lipiodol. Spectral results showed that the FFF beam contained more low‐energy (0–0.3MeV) component of electrons than FF beam, and FF beam contained more high‐energy (over 0.3MeV) electrons than FFF beam in Lipiodol. Behind the Lipiodol, build‐down effect with FF beam was larger than FFF beam because FF beam contained more high energy electrons. The difference of DEFs between FFF and FF beams for 6X were larger than for 10X. This is because 10X beam contained more high‐energy electrons. Conclusion: It was found that the 6XFFF beam gives the largest change of energy fluence and the largest DEF in this study. These phenomena are mainly caused by component of low‐energy electrons, and this energy is almost correspond to the boundary of photo electronic dominant and Compton scattering dominant region for photon beams.
SU‐F‐T‐635: Lung SBRT: Dosimetric and Treatment Time Comparison of Volumetric‐Modulated Arc Therapy and Three‐Dimensional Conformal Radiotherapy in Clinically Treated Cases
Authors: Han J , Xu Z , Baker J , Hsia A , Ryu S
Published: July 2016

Purpose:

To compare three‐dimensional conformal radiotherapy (3D CRT) and volumetric‐modulated arc therapy (VMAT) in lung stereotactic body radiation therapy (SBRT)

Methods:

A retrospective study of clinically treated lung SBRT cases treated between 2010 and 2015 at our hospital was performed. All treatment modalities were included in this evaluation (VMAT, 3D CRT, static IMRT, and dynamic conformal arc therapy). However, the majority of treatment modalities were either VMAT or 3D CRT. Treatment times of patients and dosimetric plan quality metrics were compared. Treatment times were calculated based on the time the therapist opened and closed the patient's treatment plan. This treatment time closely approximates the utilization time of the treatment room. The dosimetric plan quality metrics evaluated include ICRU conformity index, the volume of 105% prescribed dose outside PTV, the ratio of volume of 50% prescribed dose to the volume of PTV, the percentage of maximum dose at 2 cm away from PTV to the prescribed dose, and the V20 (percentage of lung volume receiving 20 Gy or more).

Results:

Treatment time comparisons show that on average VMAT has shorter treatment times than 3D CRT. Dose conformity, defined by the ICRU conformity index, and high dose spillage, defined by the volume of 105% dose outside the PTV, is reduced when using VMAT compared to 3D CRT. V20 and intermediate dose spillage/fall‐off metrics of VMAT and 3D are not significantly different.

Conclusion:

Clinically treated lung SBRT cases indicate VMAT is superior to 3D with regard to shorter treatment times, plan dose conformity, and plan high dose spillage.
SU‐F‐T‐649: Dosimetric Evaluation of Non‐Coplanar Arc Therapy Using a Novel Rotating Gamma Ray System
Authors: Eldib A , Chibani O , Mora G , Jin L , Fan J , Li J , Veltchev I , Ma C
Published: July 2016

Purpose:

Stereotactic intra and extra‐cranial body radiation therapy has evolved with advances in treatment accuracy, effective radiation dose, and parameters necessary to maximize machine capabilities. Novel gamma systems with a ring type gantry were developed having the ability to perform oblique arcs. The aim of this study is to explore the dosimetric advantages of this new system.

Methods:

The rotating Gamma system is named CybeRay (Cyber Medical Corp., Xian, China). It has a treatment head of 16 cobalt‐60 sources focused to the isocenter, which can rotate 360° on the ring gantry and swing 35° in the superior direction. Treatment plans were generated utilizing our in‐house Monte Carlo treatment planning system. A cylindrical phantom was modeled with 2mm voxel size. Dose inside the cylindrical phantom was calculated for coplanar and non‐coplanar arcs. Dosimetric differences between CybeRay cobalt beams and CyberKnife 6MV beams were compared in a lung phantom and for previously treated SBRT patients.

Results:

The full width at half maxima of cross profiles in the S‐I direction for the coplanar setup matched the cone sizes, while for the non‐coplanar setup, FWHM was larger by 2mm for a 10mm cone and about 5mm for larger cones. In the coronal and sagittal view, coplanar beams showed elliptical shaped isodose lines, while non‐coplanar beams showed circular isodose lines. Thus proper selection of the oblique angle and cone size can aid optimal dose matching to the target volume. Comparing a single 5mm cone from CybeRay to that from CyberKnife showed similar penumbra in a lung phantom but CybeRay had significant lower doses beyond lung tissues. Comparable treatment plans were obtained with CybeRay as that from CyberKnife.ConclusionThe noncoplanar multiple source arrangement of CybeRay will be of great clinical benefits for stereotactic intra and extra‐cranial radiation therapy.
SU‐F‐T‐650: The Comparison of Robotic Partial Breast Stereotactic Irradiation Using MLC Vs. Iris Cone
Authors: Ding C , Timmerman R , Jiang S , Rahimi A
Published: July 2016

Purpose:

To evaluate the dosimetric impact on treatment planning for partial breast stereotactic irradiation using Cyberknife with MLC versus Iris Cone.

Methods:

Ten patients whom underwent lumpectomy for DCIS or stage I invasive non‐lobular epithelial breast cancer were included in this study. All patients were previously treated on the Cyberknife using Iris cone with the prescription dose of 37.5Gy in 5 fractions covering at least 95% of PTV on our phase I SBRT 5 fraction partial breast irradiation trial. Retrospectively, treatment planning was performed and compared using the new Cyberknife M6 MLC system for each patient. Using the same contours and critical organ constraints for both MLC and Iris cone plans, the dose on target and critical organs were analyzed accordingly.

Results:

Dose to critical organs such as ipsilateral lung, contralateral lung, heart, skin, ipsilateral breast, and rib were analyzed, as well as conformity index and high dose spillage of the target area. In 9 of 10 patients, the MLC plans had less total ipsilateral breast volume encompassing the 50% prescription isodose (mean:22.3±8.2% MLC vs. 31.6±8.0 Iris, p=0.00014) .The MLC plans mean estimated treatment delivery time was significantly less than the Iris plans (51±3.9min vs. 56.2±9min, p=0.03) Both MLC and Iris cone plans were able to meet all dose constraints and there was no statistical difference between those dose constraints.

Conclusion:

Both MLC and Iris Cone can deliver conformal dose to a partial breast target and satisfy the dose constraints of critical organs. The new Cyberknife with MLC can deliver a more conformal dose in the lower dose region and spare more ipsilateral breast tissue to the 50% prescription isodose. The treatment time for partial breast SBRT plans was also reduced using MLC.

Project receives research support from Accuray Inc.
SU‐F‐T‐655: Evaluation of Neutron Dose Equivalent Inside of Treatment Vault of Radiotherapy by Photoneutron Production in the Primary Barriers
Authors: Choi C , Kim J , Park S , Park J
Published: July 2016

Purpose:

Photon beams with energy higher than 10 MV interact with metal material in the primary barriers, where lead or steel have been widely used, neutrons can be generated. Monte Carlo simulations were performed to simulate the production of photoneutrons and the neutron shielding effect.

Methods:

For two photon beam energies, 15 MV and 18 MV, we simulated to strike metal sheets (steel and lead), and the ambient dose equivalents were calculated at the isocenter (in the patient plane) while delivering 1 Gy to the patient. For these cases, the thickness of the neutron shielding materials (Borated polyethylene (BPE) and concrete) were simulated to reduce the patient exposure by neutron doses.

Results:

When 18 MV photons interact with the metal sheets in the primary barrier, the evaluated neutron doses at the isocenter inside the treatment vault were 48.7 µSv and 7.3 µSv for lead and steel, respectively. In case of 15 MV photons, the calculated neutron doses were 18.6 µSv and 0.6 µSv for lead and steel, respectively. The neutron dose delivered to the patient can be reduced to negligible levels by including a 10 cm thick sheet of BPE or 22 cm thick sheet of concrete.

Conclusion:

When bunker shielding is designed with a primary barrier including a metal sheet inside the wall for a high energy machine, proper neutron shielding should be constructed to avoid undesirable extra dose.
SU‐F‐T‐657: In‐Room Neutron Dose From High Energy Photon Beams
Authors: Christ D , Ding G
Published: July 2016

Purpose:

To estimate neutron dose inside the treatment room from photodisintegration events in high energy photon beams using Monte Carlo simulations and experimental measurements.

Methods:

The Monte Carlo code MCNP6 was used for the simulations. An Eberline ESP‐1 Smart Portable Neutron Detector was used to measure neutron dose. A water phantom was centered at isocenter on the treatment couch, and the detector was placed near the phantom. A Varian 2100EX linear accelerator delivered an 18MV open field photon beam to the phantom at 400MU/min, and a camera captured the detector readings. The experimental setup was modeled in the Monte Carlo simulation. The source was modeled for two extreme cases: a) hemispherical photon source emitting from the target and b) cone source with an angle of the primary collimator cone. The model includes the target, primary collimator, flattening filter, secondary collimators, water phantom, detector and concrete walls. Energy deposition tallies were measured for neutrons in the detector and for photons at the center of the phantom.

Results:

For an 18MV beam with an open 10cm by 10cm field and the gantry at 180°, the Monte Carlo simulations predict the neutron dose in the detector to be 0.11% of the photon dose in the water phantom for case a) and 0.01% for case b). The measured neutron dose is 0.04% of the photon dose. Considering the range of neutron dose predicted by Monte Carlo simulations, the calculated results are in good agreement with measurements.

Conclusion:

We calculated in‐room neutron dose by using Monte Carlo techniques, and the predicted neutron dose is confirmed by experimental measurements. If we remodel the source as an electron beam hitting the target for a more accurate representation of the bremsstrahlung fluence, it is feasible that the Monte Carlo simulations can be used to help in shielding designs.
SU‐F‐T‐672: A Novel Kernel‐Based Dose Engine for KeV Photon Beams
Authors: Reinhart M , Fast M F , Nill S , Oelfke U
Published: July 2016

Purpose:

Mimicking state‐of‐the‐art patient radiotherapy with high precision irradiators for small animals allows advanced dose‐effect studies and radiobiological investigations. One example is the implementation of pre‐clinical IMRT‐like irradiations, which requires the development of inverse planning for keV photon beams. As a first step, we present a novel kernel‐based dose calculation engine for keV x‐rays with explicit consideration of energy and material dependencies.

Methods:

We follow a superposition‐convolution approach adapted to keV x‐rays, based on previously published work on micro‐beam therapy. In small animal radiotherapy, we assume local energy deposition at the photon interaction point, since the electron ranges in tissue are of the same order of magnitude as the voxel size. This allows us to use photon‐only kernel sets generated by MC simulations, which are pre‐calculated for six energy windows and ten base materials. We validate our stand‐alone dose engine against Geant4 MC simulations for various beam configurations in water, slab phantoms with bone and lung inserts, and on a mouse CT with (0.275mm)3 voxels.

Results:

We observe good agreement for all cases. For field sizes of 1mm2 to 1cm2 in water, the depth dose curves agree within 1% (mean), with the largest deviations in the first voxel (4%) and at depths>5cm (<2.5%). The out‐of‐field doses at 1cm depth agree within 8% (mean) for all but the smallest field size. In slab geometries, the mean agreement was within 3%, with maximum deviations of 8% at water‐bone interfaces. The γ‐index (1mm/1%) passing rate for a single‐field mouse irradiation is 71%.

Conclusion:

The presented dose engine yields an accurate representation of keV‐photon doses suitable for inverse treatment planning for IMRT. It has the potential to become a significantly faster yet sufficiently accurate alternative to full MC simulations. Further investigations will focus on energy sampling as well as calculation times.

Research at ICR is also supported by Cancer Research UK under Programme C33589/A19727 and NHS funding to the NIHR Biomedical Research Centre at RMH and ICR. MFF is supported by Cancer Research UK under Programme C33589/A19908.
SU‐G‐BRA‐04: Simulation of Errors in Maximal Intensity Projection (MIP)‐Based Lung Tumor Internal Target Volumes (ITV) Using Real‐Time 2D MRI and Deformable Image Registration Based Lung Tumor Tracking
Authors: Thomas D , Kishan A , Santhanam A , Min Y , O'Connell D , Lamb J , Cao M , Agazaryan N , Yang Y , Lee P , Low D
Published: July 2016

Purpose:

To evaluate the effect of inter‐ and intra‐fractional tumor motion on the error in four‐dimensional computed tomography (4DCT) maximal intensity projection (MIP)–based lung tumor internal target volumes (ITV), using deformable image registration of real‐time 2D‐sagital cine‐mode MRI acquired during lung SBRT treatments.

Methods:

Five lung tumor patients underwent free breathing SBRT treatment on the ViewRay, with dose prescribed to PTV (4DCT MIP‐based ITV+3–6mm margin). Sagittal slice cine‐MR images (3.5×3.5mm pixels) were acquired through the center of the tumor at 4 frames per second throughout the treatments (3–4 fractions of 21–32 minutes duration). Tumor GTVs were contoured on the first frame of the cine and tracked throughout the treatment using off‐line optical‐flow based deformable registration implemented on a GPU cluster. Pseudo‐4DCT MIP‐based ITVs were generated from MIPs of the deformed GTV contours limited to short segments of image data. All possible pseudo‐4DCT MIP‐based ITV volumes were generated with 1s resolution and compared to the ITV volume of the entire treatment course. Varying pseudo‐4DCT durations from 10‐50s were analyzed.

Results:

Tumors were covered in their entirety by PTV in the patients analysed here. However, pseudo‐4DCT based ITV volumes were observed that were as small as 29% of the entire treatment‐ITV, depending on breathing irregularity and the duration of pseudo‐4DCT. With an increase in duration of pseudo‐4DCT from 10–50s the minimum volume acquired from 95% of all pseudo‐4DCTs increased from 62%–81% of the treatment ITV.

Conclusion:

A 4DCT MIP‐based ITV offers a ‘snap‐shot’ of breathing motion for the brief period of time the tumor is imaged on a specific day. Real time MRI over prolonged periods of time and over multiple treatment fractions shows that the accuracy of this snap‐shot varies according to inter‐ and intra‐fractional tumor motion. Further work is required to investigate the dosimetric effect of these results.
SU‐G‐BRA‐05: Application of a Feature‐Based Tracking Algorithm to KV X‐Ray Fluoroscopic Images Toward Marker‐Less Real‐Time Tumor Tracking
Authors: Nakamura M , Nakao M , Matsuo Y , Mukumoto N , Iizuka Y , Yokota K , Mizowaki T , Hiraoka M
Published: July 2016

Purpose:

To detect target position on kV X‐ray fluoroscopic images using a feature‐based tracking algorithm, Accelerated‐KAZE (AKAZE), for markerless real‐time tumor tracking (RTTT).

Methods:

Twelve lung cancer patients treated with RTTT on the Vero4DRT (Mitsubishi Heavy Industries, Japan, and Brainlab AG, Feldkirchen, Germany) were enrolled in this study. Respiratory tumor movement was greater than 10 mm. Three to five fiducial markers were implanted around the lung tumor transbronchially for each patient. Before beam delivery, external infrared (IR) markers and the fiducial markers were monitored for 20 to 40 s with the IR camera every 16.7 ms and with an orthogonal kV x‐ray imaging subsystem every 80 or 160 ms, respectively. Target positions derived from the fiducial markers were determined on the orthogonal kV x‐ray images, which were used as the ground truth in this study. Meanwhile, tracking positions were identified by AKAZE. Among a lot of feature points, AKAZE found high‐quality feature points through sequential cross‐check and distance‐check between two consecutive images. Then, these 2D positional data were converted to the 3D positional data by a transformation matrix with a predefined calibration parameter. Root mean square error (RMSE) was calculated to evaluate the difference between 3D tracking and target positions. A total of 393 frames was analyzed. The experiment was conducted on a personal computer with 16 GB RAM, Intel Core i7‐2600, 3.4 GHz processor.

Results:

Reproducibility of the target position during the same respiratory phase was 0.6 +/− 0.6 mm (range, 0.1–3.3 mm). Mean +/− SD of the RMSEs was 0.3 +/− 0.2 mm (range, 0.0–1.0 mm). Median computation time per frame was 179 msec (range, 154–247 msec).

Conclusion:

AKAZE successfully and quickly detected the target position on kV X‐ray fluoroscopic images. Initial results indicate that the differences between 3D tracking and target position would be clinically acceptable.
SU‐G‐BRA‐06: Quantification of Tracking Performance of a Multi‐Layer Electronic Portal Imaging Device
Authors: Hu Y , Rottmann J , Myronakis M , Berbeco R
Published: July 2016

Purpose:

The purpose of this study was to quantify the improvement in tumor tracking, with and without fiducial markers, afforded by employing a multi‐layer (MLI) electronic portal imaging device (EPID) over the current state‐of‐the‐art, single‐layer, digital megavolt imager (DMI) architecture.

Methods:

An ideal observer signal‐to‐noise ratio (d’) approach was used to quantify the ability of an MLI EPID and a current, state‐of‐the‐art DMI EPID to track lung tumors from the treatment beam's‐eye‐view. Using each detector modulation transfer function (MTF) and noise power spectrum (NPS) as inputs, a detection task was employed with object functions describing simple three‐dimensional Cartesian shapes (spheres and cylinders). Marker‐less tumor tracking algorithms often use texture discrimination to differentiate benign and malignant tissue. The performance of such algorithms is simulated by employing a discrimination task for the ideal observer, which measures the ability of a system to differentiate two image quantities. These were defined as the measured textures for benign and malignant lung tissue.

Results:

The NNPS of the MLI ∼25% of that of the DMI at the expense of decreased MTF at intermediate frequencies (0.25≤<f≤<0.5 cycles/mm). Lung tissue textures were found to follow a power‐law trend in the frequency domain. It was found that for both fiducial marker tracking and lung tissue texture differentiation, the signal power of each task is retained at low frequencies. Thus, little difference may be observed in signal power when DMI and MLI are compared. In all cases, improvements in tracking were greater than a factor of 2.

Conclusion:

MLI performance in tumor tracking is greatly improved by the additional imager layers. This implies that further improvements in tracking may be gained through increasing the thickness of each MLI layer. For tracking, the MLI performance is limited by noise response. Losses in MTF result in negligible differences in d’.

The project was partially supported by a grant from Varian Medical Systems, Inc. and grant No. R01CA188446‐01 from the National Cancer Institute.
SU‐G‐BRA‐10: Marker Free Lung Tumor Motion Tracking by An Active Contour Model On Cone Beam CT Projections for Stereotactic Body Radiation Therapy of Lung Cancer
Authors: Chao M , Wei J , Yuan Y , Lo Y
Published: July 2016

Purpose:

To develop a novel strategy to extract the lung tumor motion from cone beam CT (CBCT) projections by an active contour model with interpolated respiration learned from diaphragm motion.

Methods:

Tumor tracking on CBCT projections was accomplished with the templates derived from planning CT (pCT). There are three major steps in the proposed algorithm: 1) The pCT was modified to form two CT sets: a tumor removed pCT and a tumor only pCT, the respective digitally reconstructed radiographs DRRtr and DRRto following the same geometry of the CBCT projections were generated correspondingly. 2) The DRRtr was rigidly registered with the CBCT projections on the frame‐by‐frame basis. Difference images between CBCT projections and the registered DRRtr were generated where the tumor visibility was appreciably enhanced. 3) An active contour method was applied to track the tumor motion on the tumor enhanced projections with DRRto as templates to initialize the tumor tracking while the respiratory motion was compensated for by interpolating the diaphragm motion estimated by our novel constrained linear regression approach. CBCT and pCT from five patients undergoing stereotactic body radiotherapy were included in addition to scans from a Quasar phantom programmed with known motion. Manual tumor tracking was performed on CBCT projections and was compared to the automatic tracking to evaluate the algorithm accuracy.

Results:

The phantom study showed that the error between the automatic tracking and the ground truth was within 0.2mm. For the patients the discrepancy between the calculation and the manual tracking was between 1.4 and 2.2 mm depending on the location and shape of the lung tumor. Similar patterns were observed in the frequency domain.

Conclusion:

The new algorithm demonstrated the feasibility to track the lung tumor from noisy CBCT projections, providing a potential solution to better motion management for lung radiation therapy.