bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐492: Influence of Clipping PTV in Build‐Up Region On IMRT Plan Quality and Deliverability
Authors: Sharma S , Manigandan D , Sahai P , Biswas A , Subramani V , Chander S , Julkha P , Rath G
Published: June 2015

Purpose:

To study the influence of clipping PTV from body contour on plan quality and deliverability in build‐up region for superficial target.

Methods:

Five previously treated patients of post‐operative carcinoma of parotid were re‐planned for IMRT (6MV X‐rays, sliding window technique, five fields and 60Gy/30 fractions) using eclipse treatment planning system (TPS) by keeping dose volume constraints and all other parameters constant, only PTV was clipped from body contour by 0mm, 1mm, 2mm and 3mm respectively. Planned fluence was transferred to previously scanned solid water phantom by placing I'matriXX array at 0.5cm depth (2mm slab+3mm inherent). Fluence was delivered by Varian CL2300C/D linac at 99.5cm source to detector distance. Measured fluence was compared with TPS dose plane using 2D gamma evaluation using 3%/3mm DTA criteria. Total MU (monitor unit) required to deliver a plan was also noted. For plan quality, PTV, maximum‐dose, minimum‐dose, coverage index (CI=PTV volume covered by prescription dose/PTV) and heterogeneity index HI=D5/D95 were analyzed using dose volume histogram (DVH).

Results:

The Result of gamma function analysis for I'matriXX and TPS were 97.63±1.79%, 97.48±0.99, 98.08±0.89% and 98.01±0.78% at 0.5cm build‐up depth for 0, 1, 2 and 3mm PTV clipping, respectively. I'matriXX measured dose was higher compared to TPS. Total MU required for delivering a plan were 552±61, 503±47, 436±24 and 407±22. Maximum‐dose to PTV was 6635.80±62.01cGy, 6635.80±40.60cGy, 6608.43±51.07cGy and 6564.20±28.51cGy. Similarly, minimum‐dose to PTV was 3306.23±458.56cGy, 3546.57±721.01cGy, 4591.43±298.81cGy and 4861.90±412.40cGy. CI was 0.9347±0.020, 0.9398±0.021, 0.9448±0.022 and 0.9481±0.021. Similarly, HI was 1.089±0.015, 1.084±0.014, 1.078±0.009 and 1.074±0.008 for 0, 1, 2 and 3mm PTV clipping, respectively.

Conclusion:

Gamma function analysis resulted in almost similar results. However, I'matriXX was overestimating the dose compared to TPS. MU required to deliver a plan decreases with increase in PTV clipping. CI, PTV minimum‐dose and plan homogeneity increases with increase in PTV clipping from skin.
SU‐E‐T‐500: Initial Implementation of GPU‐Based Particle Swarm Optimization for 4D IMRT Planning in Lung SBRT
Authors: Modiri A , Hagan A , Gu X , Sawant A
Published: June 2015

Purpose

4D‐IMRT planning, combined with dynamic MLC tracking delivery, utilizes the temporal dimension as an additional degree of freedom to achieve improved OAR‐sparing. The computational complexity for such optimization increases exponentially with increase in dimensionality. In order to accomplish this task in a clinically‐feasible time frame, we present an initial implementation of GPU‐based 4D‐IMRT planning based on particle swarm optimization (PSO).

Methods

The target and normal structures were manually contoured on ten phases of a 4DCT scan of a NSCLC patient with a 54cm3 right‐lower‐lobe tumor (1.5cm motion). Corresponding ten 3D‐IMRT plans were created in the Eclipse treatment planning system (Ver‐13.6). A vendor‐provided scripting interface was used to export 3D‐dose matrices corresponding to each control point (10 phases × 9 beams × 166 control points = 14,940), which served as input to PSO. The optimization task was to iteratively adjust the weights of each control point and scale the corresponding dose matrices. In order to handle the large amount of data in GPU memory, dose matrices were sparsified and placed in contiguous memory blocks with the 14,940 weight‐variables. PSO was implemented on CPU (dual‐Xeon, 3.1GHz) and GPU (dual‐K20 Tesla, 2496 cores, 3.52Tflops, each) platforms. NiftyReg, an open‐source deformable image registration package, was used to calculate the summed dose.

Results

The 4D‐PSO plan yielded PTV coverage comparable to the clinical ITV‐based plan and significantly higher OAR‐sparing, as follows: lung Dmean=33%; lung V20=27%; spinal cord Dmax=26%; esophagus Dmax=42%; heart Dmax=0%; heart Dmean=47%. The GPU‐PSO processing time for 14940 variables and 7 PSO‐particles was 41% that of CPU‐PSO (199 vs. 488 minutes).

Conclusion

Truly 4D‐IMRT planning can yield significant OAR dose‐sparing while preserving PTV coverage. The corresponding optimization problem is large‐scale, non‐convex and computationally rigorous. Our initial results indicate that GPU‐based PSO with further software optimization can make such planning clinically feasible.

This work was supported through funding from the National Institutes of Health and Varian Medical Systems.
SU‐E‐T‐502: Initial Results of a Comparison of Treatment Plans Produced From Automated Prioritized Planning Method and a Commercial Treatment Planning System
Authors: Tiwari P , Hong L , Apte A , Yang J , Mechalakos J , Mageras G , Hunt M , Chen Y , Deasy J
Published: June 2015

Purpose

We developed an automated treatment planning system based on a hierarchical goal programming approach. To demonstrate the feasibility of our method, we report the comparison of prostate treatment plans produced from the automated treatment planning system with those produced by a commercial treatment planning system.

Methods

In our approach, we prioritized the goals of the optimization, and solved one goal at a time. The purpose of prioritization is to ensure that higher priority dose‐volume planning goals are not sacrificed to improve lower priority goals. The algorithm has four steps. The first step optimizes dose to the target structures, while sparing key sensitive organs from radiation. In the second step, the algorithm finds the best beamlet weight to reduce toxicity risks to normal tissue while holding the objective function achieved in the first step as a constraint, with a small amount of allowed slip. Likewise, the third and fourth steps introduce lower priority normal tissue goals and beam smoothing. We compared with prostate treatment plans from Memorial Sloan Kettering Cancer Center developed using Eclipse, with a prescription dose of 72 Gy. A combination of liear, quadratic, and gEUD objective functions were used with a modified open source solver code (IPOPT).

Results

Initial plan results on 3 different cases show that the automated planning system is capable of competing or improving on expert‐driven eclipse plans. Compared to the Eclipse planning system, the automated system produced up to 26% less mean dose to rectum and 24% less mean dose to bladder while having the same D95 (after matching) to the target.

Conclusion

We have demonstrated that Pareto optimal treatment plans can be generated automatically without a trial‐and‐error process. The solver finds an optimal plan for the given patient, as opposed to database‐driven approaches that set parameters based on geometry and population modeling.
SU‐E‐T‐518: Investigation of Gold Nanoparticle Radiosensitization for Carbon Ion Therapy
Authors: Lin Y , Held K , McMahon S , Paganetti H , Schuemann J
Published: June 2015

Purpose

The aim of this work is to investigate the radiosensitization effect of gold nanoparticles (GNP) in carbon ion irradiation. Nano‐scale dosimetric characteristics of GNP interaction with carbon ions as well as the secondary particles generated as a carbon beam traverses the water phantom were studied.

Methods

Monte Carlo simulations were carried out using TOPAS (Tool for Particle Simulation). First, a water phantom was irradiated by the carbon ion beam and the particle shower spectrum at several depths was recorded in phase spaces. We analyzed the number and energy spectrum of each particle type. Then, the phase spaces obtained from Step 1 were modified to nanometer scale to irradiate a single 50 nm GNP. The secondary electrons that escaped from the GNPs following interactions with each particle type were recorded as phase spaces. The number and energy spectrum of the secondary electrons were studied. The same simulations were repeated replacing the GNPs with water nanoparticles (WNPs) with the same size. The energy absorbed in either GNP or WNP was scored.

Results

There is a large amount of secondary particles generated through carbon ion beam interaction with the water phantom. Analysis of the secondary electrons generated by the primary particles which escape from the nanoparticle revealed that majority (above 80%) of these electrons were generated by the GNP interaction with Carbon beam itself, making it the biggest contributor to the enhancement. The ratio of the energy absorbed by GNP and WNP is about 8–10 for charged particles and above 3000 for gammas.

Conclusion

We showed in the study the GNPs may potentially be used to enhance carbon ion therapy, and the main mechanism of enhancement is the interaction with Carbon ion particles itself.
SU‐E‐T‐526: Irradiation of Human Cell Lines Using Carbon Ions: Real Time Dosimetry Using Gaf‐Chromic Film
Authors: Lin Y , La Tessa C , Rusek A , Held K
Published: June 2015

Purpose:

The purpose of this study is to investigate and quantify several factors affecting biological effects of carbon ions such as cell type, dose, energy and position where the cells are irradiated along the pristine Bragg curve.

Methods:

Experiments to quantify clonogenic cell survival in three human lung cancer cell lines and a fibroblast cell line were performed at the NASA Space Radiation Laboratory, BNL, Upton, USA. A system of water or media‐filled T25 flasks lined up along the beam axis was designed so that the cell‐containing surfaces of the flasks were placed at specific depths along the Bragg curve. Gaf‐chromic films were placed between the flasks to monitor the dose distribution in the sample as soon as the irradiation was finished. Additional studies were conducted at four selected depths along the Bragg curve to obtain full cell survival dose response curves for the four cell lines.

Results:

The percent depth dose of the beams was determined using an ionization chamber and showed that the physical Bragg peak is at 22.5 cm water depth. However, the clonogenic cell survival data indicated that the maximum cell killing occurred at 21.5 cm. Gaf‐chromic films revealed some inhomogeneity in the dose distribution on the flasks near the peak, presumably due to lack of scattering from the sides of the flasks, which might account for the differences. Depending on the cell line and radiation dose, the maximum cell killing (i.e., the greatest RBE) is at the 21.5 (the peak) or 24 cm (distal fall off) depth.

Conclusion:

There is a difference in biological effect along the Bragg curve of a carbon ion beam, indicating an elevated RBE at or beyond the end of the range. Gaf‐chromic films are proven to be effective in monitoring the 2D irradiation pattern to the flasks.

Research supported by NIH/NCI through grant no. R21 CA182259.
SU‐E‐T‐532: Left‐Sided Breast Cancer Irradiation Using Volumatric Modulated Arc Therapy: An Evaluation of Multiple Commercial Systems
Authors: Liu R , Liu T , Qi S
Published: June 2015

Purposes:

There has been growing interest in treating breast cancer using VMAT technique. Our goal is to compare the dosimetry and treatment delivery parameters for the left‐sided breast cancer treatment using various VMAT platforms from commercially available planning systems.

Methods:

Five consecutive left‐sided breast cancer patients initially treated with conventional 3D‐conformal radiotherapy (3DCRT) were selected. Four VMAT plans using most popular treatment planning systems, including Eclipse (Version 11, Varian), Pinnacle (Version 9.8, Philips), Monaco (Version 2.03, Elekta) and helical Tomotherapy (V4.0, Accuray). The same structure set and same planning goals were used for all VMAT plans. The dosimetric parameters including target coverage and minimum/maximum/mean, dose‐volume endpoints for the selected normal structures: the heart, ipsilateral‐/contralateral lung and breast, were evaluated. Other dosimetric indices including heterogeneity index (HI) were evaluated. The treatment delivery parameters, such as monitor unit (MUs) and delivery time were also compared.

Results:

VMAT increases dose homogeneity to the treated volume and reduces the irradiated heart and left‐lung volumes. Compared to the 3DCRT technique, all VMAT plans offer better heart and left‐lung dose sparing; the mean heart doses were 4.5±1.6(Monaco), 1.2±0.4(Pinnacle), 1.3± (Eclipse) and 5.6±4.4(Tomo), the mean left‐lung doses were 5.9±1.5(Monaco), 3.7±0.7(Pinnacle), 1.4± (Eclipse) and 5.2±1.6 (Tomo), while for the 3DCRT plan, the mean heart and left‐Lung doses were 2.9±2.0, and 6.8±4.4 (Gy) respectively. The averaged contralateral‐breast and lung mean doses were higher in VMAT plans than the 3DCRT plans but were not statistically significant. Among all the VMAT plans, the Pinnacle plans often yield the lowest right‐lung/breast mean doses, and slightly better heterogeneity indices that are similar to Tomotherapy plans. Treatment delivery time of the VMAT plans (except helical Tomotherapy IMRT) is estimated to be comparable with the conventional 3DCRT.

Conclusion:

VMAT achieves equal or better PTV coverage and comparable OARs sparing compared to the conventional 3DCRT techniques.
SU‐E‐T‐546: Modeling and Validation of the a New Proton Therapy System Using a Monte‐Carlo Environment Optimized for Protons
Authors: Grantham K , Klein E
Published: June 2015

Purpose:

Monte‐Carlo modeling is an important tool for understanding the behavior of therapeutic proton beams in a heterogeneous media such as the patient. To gain confidence that a Monte‐Carlo model is accurate in complex geometries and media, it must first be compared with measurement in simple situations. This study documents the validation of our Monte‐Carlo Model.

Methods:

A model of the MEVION s250 Proton therapy system was created in the TOPAS Monte‐Carlo environment using machine geometry and field shaping system information provided by the vendor. For each of 24 options, validation of the TOPAS model was performed by comparing the dose scored by TOPAS to the dose measurements obtained during the commissioning of the treatment planning system. The measurements compared consisted of: pristine peak depth‐dose profiles, in‐air profiles for a standard‐sized square field (20cm×20cm or 10cm×10cm depending on the maximum field size for each option) at isocenter and at 20cm upstream and downstream of isocenter, and in‐air profiles with a half‐beam blocked aperture at isocenter and at 20cm upstream and downstream of isocenter. For all Monte‐Carlo simulations, 10^8 particle histories were run.

Results:

Range measurements of the Monte‐Carlo simulations matched the measured data within 1mm. Distal fall‐off of the simulated fields matched within <1mm. Lateral penumbra and field size measurements of the standard‐sized square and half‐beam blocked fields matched within 1mm at all three planes compared. A small difference was seen in the in‐air profiles at doses <0%. The suspected cause of the difference was the aperture shape. The measured data utilized a divergent aperture. The Monte‐Carlo calculation used a non‐divergent aperture.

Conclusion:

The validation measurements indicate that we were able to accurately model the MEVION s250 Proton therapy system using Monte‐Carlo Calculations. This may reduce the commissioning time for future users.
SU‐E‐T‐547: Modeling Biological Response to Proton Irradiation and Evaluating Its Potential Clinical Consequences
Authors: Taleei R , Peeler C , Guan F , Patel D , Titt U , Mirkovic D , Grosshans D , Mohan R
Published: June 2015

Purpose:

In addition to physical uncertainties, proton therapy may also be associated with biologic uncertainties. Currently a generic RBE value of 1.1 is used for treatment planning. In this work the effects of variable RBE, in comparison to a fixed RBE, were evaluated by calculating the effective dose for proton treatments.

Methods:

The repair misrepair fixation (RMF) model was used to calculate variable proton RBEs. The RBE weighted spread‐out Bragg peak (SOBP) dose in water phantom was calculated using Monte Carlo simulation and compared to 1.1 weighted SOBP dose. A head and neck proton treatment was used to evaluate the potential effects, by comparing the head and neck treatment plan computed with a commercial treatment planning system that incorporates fixed RBE of 1.1 and a Monte Carlo treatment planning system that incorporates variable RBE.

Results:

RBE calculations along the depth of SOBP showed that the RBE at the entrance is approximately 1 and reaches 1.1 near the center of the SOBP. However, in distal regions the RBE rises to higher values (up to 3.5 depending on the cell type). Comparison of commercial treatment plans using a fixed RBE of 1.1 and Monte Carlo using variable RBE showed noticeable differences in the effective dose distributions.

Conclusion:

The comparison of the treatment planning with fixed and variable RBE shows that using commercial treatment planning systems that incorporate fixed RBE (1.1) could Result in overestimation of the effective dose to part of head and neck target volumes, while underestimating the effective dose to the normal tissue beyond the tumor. The accurate variable RBE as a function of proton beam energy in patient should be incorporated in treatment planning to improve the accuracy of effective dose calculation.
SU‐E‐T‐548: Modeling of Breast IORT Using the Xoft 50 KV Brachytherapy Source and 316L Steel Rigid Shield
Authors: Burnside W
Published: June 2015

Purpose:

Xoft provides a set of 316L Stainless Steel Rigid Shields to be used with their 50 kV X‐ray source for Breast IORT treatments. Modeling the different shield sizes in MCNP provides information to help make clinical decisions for selecting the appropriate shield size.

Methods:

The Xoft Axxent 50 kV Electronic Brachytherapy System has several applications in radiation therapy, one of which is treating cancer of the breast intraoperatively by placing the miniaturized X‐ray tube inside an applicator balloon that is expanded to fill the lumpectomy bed immediately following tumor removal. The ribs, lung, and muscular chest wall are all regions at risk to receive undesired dose during the treatment. A Xoft 316L Stainless Steel Rigid Shield can be placed between the intracostal muscles of the chest wall and the remaining breast tissue near the balloon to attenuate the beam and protect these organs. These shields are provided in 5 different sizes, and the effects on dose to the surrounding tissues vary with shield size. MCNP was used to model this environment and tally dose rate to certain regions of interest.

Results:

The average rib dose rate calculated using 0cm (i.e., no shield), 3cm, and 5cm diameter shields were 26.89, 15.43, and 8.91 Gy/hr respectively. The maximum dose rates within the rib reached 94.74 Gy/hr, 53.56 Gy/hr, and 31.44 Gy/hr for the 0cm, 3cm, and 5cm cases respectively. The shadowing effect caused by the steel shields was seen in the 3‐D meshes and line profiles.

Conclusion:

This model predicts a higher dose rate to the underlying rib region with the 3cm shield compared to the 5cm shield; it may be useful to select the largest possible diameter when choosing a shield size for a particular IORT patient. The ability to attenuate the beam to reduce rib dose was also confirmed.

Research sponsored by Xoft Inc, a subsidiary of iCAD.
SU‐E‐T‐567: Neutron Dose Equivalent Evaluation for Pencil Beam Scanning Proton Therapy with Apertures
Authors: Geng C , Schuemann J , Moteabbed M , Paganetti H
Published: June 2015

Purpose:

To determine the neutron contamination from the aperture in pencil beam scanning during proton therapy.

Methods:

A Monte Carlo based proton therapy research platform TOPAS and the UF‐series hybrid pediatric phantoms were used to perform this study. First, pencil beam scanning (PBS) treatment pediatric plans with average spot size of 10 mm at iso‐center were created and optimized for three patients with and without apertures. Then, the plans were imported into TOPAS. A scripting method was developed to automatically replace the patient CT with a whole body phantom positioned according to the original plan iso‐center. The neutron dose equivalent was calculated using organ specific quality factors for two phantoms resembling a 4‐ and 14‐years old patient.

Results:

The neutron dose equivalent generated by the apertures in PBS is 4–10% of the total neutron dose equivalent for organs near the target, while roughly 40% for organs far from the target. Compared to the neutron dose equivalent caused by PBS without aperture, the results show that the neutron dose equivalent with aperture is reduced in the organs near the target, and moderately increased for those organs located further from the target. This is due to the reduction of the proton dose around the edge of the CTV, which causes fewer neutrons generated in the patient.

Conclusion:

Clinically, for pediatric patients, one might consider adding an aperture to get a more conformal treatment plan if the spot size is too large. This work shows the somewhat surprising fact that adding an aperture for beam scanning for facilities with large spot sizes reduces instead of increases a potential neutron background in regions near target.

Changran Geng is supported by the Chinese Scholarship Council (CSC) and the National Natural Science Foundation of China (Grant No. 11475087).
SU‐E‐T‐678: Response Calibration Using Electron Depth‐Dose Data for MRI‐Based 3D Polymer Gel Dosimetry
Authors: Watanabe Y , Warmington L , Gopishankar N
Published: June 2015

Purpose:

To evaluate a calibration method using the depth‐dose data of an electron beam for MRI‐based polymer gel dosimetry.

Methods:

MAGAT was manufactured in‐house to fill two 400mL‐cylindrical phantoms and nine 22mL‐glass vials. Phantom‐A was irradiated along the cylinder axis with a 9MeV electron beam of 6 cm × 6 cm field size (FS). Phantom‐B was irradiated with a 6MV photon beam of 3 cm × 3 cm FS by a 360‐degree arc technique. Eight vials were irradiated in a water‐bath to various doses with a 20 cm × 20 cm FS 6MV photon beam. All irradiated phantoms and one un‐irradiated vial were scanned with a 3T MRI scanner to obtain the spin‐spin relaxation rate (R2) distributions. By comparing the measured R2‐to‐depth data with the known depth‐dose data for Phantom‐A, R2‐to‐dose calibration data were obtained (e‐beam method). Another calibration data were obtained from the 9 vials data (9‐vial method). We tested two regression equations, i.e., third‐order polynomial and tangent functions, and two dose normalization methods, i.e., one‐point and two‐point methods. Then, these two calibration methods were used to obtain the 3D dose distribution of Phantom‐B and evaluated by comparing the measured data with the dose distribution from a treatment planning system. The comparison was made with gamma passing rate (2%/2mm criteria).

Results:

We did not observe a clear advantage of the e‐beam method over the 9‐vial method for the 3D dose comparison with the test case. Nevertheless, we found that the e‐beam method required a smaller dose scaling for the dose comparison. Furthermore, the tangent function showed better data fitting than the polynomial function with smaller uncertainty of the estimated coefficients.

Conclusions:

Considering the overall superior performance, we recommend the e‐beam method with the tangent function as the regression equation and one‐point dose normalization for the MRI‐based polymer gel dosimetry.
SU‐E‐T‐680: Rigid Registration Image Fusion for Volumetric Dose Evaluation of Gynecological Patients Treated with EBRT and HDR Brachytherapy
Authors: Cantley J , Albani D , Ellis R , Sherertz T , Herrmann K , Podder T
Published: June 2015

Purpose:

To evaluate the effectiveness of rigid registration image fusion and dose composites in HDR brachytherapy patients who have previously undergone EBRT.

Methods:

Data was collected from five randomly selected patients with cervical cancer who were treated with both EBRT (50.4Gy) and HDR brachytherapy (30Gy in 5 fractions) using a split‐ring and tandem applicator. Planning CTs, contours, and dose profiles were exported from the Pinnacle and Oncentra treatment planning systems into the MIM 6.0 software tool for image fusion and dose composite generation. The planning CT for the third course of HDR brachytherapy was used as the primary image for each patient. Rigid registration image fusion was performed in two different ways: the first method used bony anatomy for initial matching and then fine tuned using surrounding OARs; the second method used the HDR applicator for matching. For EBRT CTs in which no applicator was present, images were fused using the uterus. Treatment doses were transferred to the primary image and then EQD2‐BED calculations were performed using the linear quadratic model in MIM software. Results from MIM calculations were compared with the hand calculations based upon the ABS EQD2 worksheet used clinically to estimate aggregated dose to the bladder, rectum, sigmoid, and bowel.

Results:

Results revealed differences in the 2cc dose between the calculation and dose composite methods for the sigmoid (mean±SD) as 7.96%±5.11% and 6.49%±3.02% for the OAR and applicator methods, respectively; bladder as 5.77%±3.28% for applicator method. No statistically significant differences (p‐value >0.05) were observed for the bladder using the OAR method, or for the rectum or bowel using either method.

Conclusion:

Early results suggest that current methods may be overestimating dose to the bladder while underestimating dose to sigmoid. However, more patient data needs to be collected to determine the significance of the findings and clinical implications.
SU‐E‐T‐688: Secondary MU Calculation for Flattening Filter Free (FFF) Photon Beams
Authors: Kim M , Zhu T
Published: June 2015

Purpose:

A secondary monitor unit (MU) checking algorithm was developed for flattening‐filter free (FFF) photon beams. Conventional algorithms are based on the equivalent‐square method to calculate the dose per MU. This is invalid because of the non‐uniform profile of the FFF beam. An empirical point‐spread kernel based algorithm that was previously developed was commissioned for a Varian TrueBeam FFF beam.

Methods:

Benchmark values at various off‐axis points are checked for dose per MU and compared to the algorithm‐calculated values for 6 and 10 MV FFF beams. Various SSD, jaw openings, and off‐axis points were measured for each energy beam. The MU calculation program is then compared to Eclipse calculations for patient plans.

Results:

It was found that the developed MU calculating algorithm can be used as a secondary MU check for FFF photon beams for the TrueBeam. The calculated dose per MU were within 2% of the measured value for various beam settings. Varian Clinac benchmark values were also compared to the calculations.

Conclusion:

This work demonstrates the successful commissioning of a secondary MU calculation algorithm for photon FFF beams at 6 and 10 MV.
SU‐E‐T‐690: Sensitivity Analysis to Machine Error: Comparisons of VMAT QA Systems
Authors: Liang B , Liu B , Yin F , Zhou F , Wu Q
Published: June 2015

Purpose:

In VMAT delivery, the gantry angles, dose rate and the MLC positions are all modulated. It is therefore necessary to perform pre‐treatment QA to detect any possible errors either in the plan or machine delivery system. Previously we developed a QA technique for VMAT using EPID in cine mode on a TrueBeam LINAC. The purpose of this study is to compare the technique with commercially available VMAT QA systems on the sensitivity to machine error.

Methods:

In our technique, the VMAT plan was delivered with EPID acquiring cine images simultaneously. The measured portal dose (PD) is derived from the acquired images. The predicted PD is calculated using the control point information in the plan and the delivery information in the EPID images. 3D γ analysis with the 3rd axis being gantry angle is performed between predicted and measured PD. The commercial VMAT QA system was Delta‐4 system from ScandiDose. The QA of the original plan is the reference. Several types of machine errors were simulated and evaluated: gantry angle, MLC position, and output. The original plan is modified by introducing intentional errors of various magnitudes. The modified plan is delivered and the measured PD is compared with the original predicted PD to determine the sensitivity to machine errors.

Results:

For the reference, in Delta‐4, the γ passrate is 99.6% for 3%/3mm criteria, and our technique has γ passrate of 98.5% for 3%/3mm/2° criteria. When errors are introduced, the passrate decreases. The sensitivity of Deltat4 (EPID) to gantry angle, MLC, and output are 1.4%/° (2.8%/°), 22%/mm(6%/mm), and 0%/% (0.1%/%), respectively. Similar results were observed under different criteria.

Conclusion:

Compared with Delta‐4 system, the EPID technique is more sensitive to gantry angle error, but less sensitive to MLC positioning error. Delta‐4 system is insensitive to the machine output error.

This work was partially supported by the National Natural Science Foundation of China (61171005) and the China Scholarship Council (CSC).
SU‐E‐T‐693: Should We Use RapidArc (VMAT) for Breast Treatments? A Dosimetric Comparison of IMRT Versus VMAT Optimization in Whole Breast Irradiation of Early Stage Breast Cancer
Authors: Sedeh N Moshiri , Pella S , Leventouri T , Littlejohn D , Costantino T
Published: June 2015

Purpose:

The purpose of this study is to compare the dose‐volumetric results of intensity modulated radiation therapy (IMRT) with RapidArc (RA Varian Medical Systems, Palo Alto, CA) for whole breast irradiation.

Methods:

25 whole left breast patient's plans (either RapidArc plan or IMRT) previously treated were the subjects of this study. Eclipse v 11.0.47 was used to create the alternative plans for each case using the same CT images, contours, energy, Linac and normalization. The prescription dose to the planning target volume was 50 Gy in 25 fractions. All plans were normalized such that 100% of the dose covered 95% of planning target volume (PTV).

Results:

V10, V20 and Dmean Gy of left lung differ significantly between the two plans (p‐value <0.0001, =0.0473 and <0.0001 respectively). However, V30 Gy does not (p‐value 0.463). V25, D33 and Dmean Gy of heart differ significantly between the two plans (p‐value =0.034, <0.0001 and 0.01 respectively). However V10 Gy does not (p‐value 0.058). V5 of both right breast and right lung differs significantly between the two plans (p‐value <0.0007 and =0.0112, respectively). Dmean of both right breast and right lung differs significantly between the two plans (p‐value <0.0001 for both). The mean conformity index did not differ significantly, p‐value 0.142. There was a significant difference between the mean MUs of the two plans as well, p‐value <0.0001.

Conclusion:

Mean doses to left lung, heart, right lung and right breast were significantly different in RapidArc than IMRT plans. IMRT treatment delivery was faster than RapidArc in terms of the total monitor units used (mean of 382 vs 707 respectively). In fact, since it was observed that both plans have the same mean of conformity index, IMRT is not only faster but also safer regarding not irradiating the organs at risk.
SU‐E‐T‐696: Similar‐Case‐Based Framework of Beam Angle Configurations Using Treatment‐Plan‐Related Features in Lung Stereotactic Body Radiation Therapy
Authors: Imai M , Arimura H , Nonaka A , Nakamura K , Shioyama Y , Honda H , Hirata H
Published: June 2015

Purpose:

Our goal of this study was to investigate a computational framework for beam angle configurations based on similar cases using treatment‐plan‐related features in lung stereotactic body radiation therapy.

Methods:

A radiation treatment planning database including 81 lung cancer cases and 10 test cases were employed for development and test of the proposed framework. A lung shape feature, which is a shape similarity of two‐dimensional (2D) lung region using a Dice's similarity coefficient (DSC), was newly introduced as a treatment‐plan‐related feature. First, ten cases with slice levels similar to a test case were selected based on a 2D lung shape similarity at an isocenter plane. Second, five similar cases were chosen using additional treatment‐plan‐related features with respect to lung and spinal cord. Finally, five beam angle configurations of the test case were determined from 5 similar cases by performing an affine linear registration of the lung region between the similar case and the test case. For evaluation of the proposed framework, dose evaluation indices with respect to planning target volume (PTV), lung, and spinal cord were computed to select a usable plan among five similar‐case‐based plans. Dose evaluation indices of usable plans produced by the proposed and conventional frameworks for 10 test cases were compared with original plans designed by radiation oncologists.

Results:

The average homogeneity index in PTVs and V10 in lung for usable plans made by the proposed framework were statistically lower than those for original plans (p<0.05), whereas there were no statistically significant differences between the conventional framework and original plans in any evaluation indices.

Conclusion:

The proposed framework with treatment‐plan‐related features had a potential to suggest usable plans, which can produce more homogeneous dose distributions in PTV and lower volumes with more than 10 Gy in lung, compared with the conventional framework.
SU‐E‐T‐698: Simplified Pencil Beam Kernel For Unfiltered Energies
Authors: Erturk M , Kocar C , Tombakoglu M , Gurdalli S
Published: June 2015

Purpose:

Aim of the study was to evaluate pencil beam kernel, with minimum kernel parameters, for unfiltered photon energies by using measured broad beam data.

Methods:

Double exponential function (A_z*exp(‐a_z*r)+B_z(‐b_z*r), which required 4 parameters for each depth, was chosen as pencil beam kernel function. When first term was assumed as primary dose kernel and the second exponential term was assumed as scattered dose kernel only Bz, which was magnitude of the scattered dose component relative to primary dose component, was leaved as a function of depth. Profile at air was used as intensity data for each depth, so depth dependency of intensity was also neglected. MATLAB optimization toolbox (“fminsearch”) was used to minimize differences between computed and measured profiles. Penalty function was created with global gamma analysis by using 1% — 1mm criteria. Interested dose point threshold was set as 5% of the maximum dose. Profiles of 10×10 field at five standard depths were used as comparison data. Work flow started with suggestion of kernel parameters, then dose distribution of five standard depths was computed and compared with measured data by using gamma analysis, this calculation was iterated until convergence.

Results:

After convergence, it was seen that Bz could be described as a first order polynomial of depth (R^2=0.985 when parameters were fitted with relevant depth). Then B_z was defined as (b0*r+b1) and kernel was reoptimized. All points on 5×5 and 10×10 field profiles at five depths were in the criteria of 1% — 1mm global gamma analysis. For 20×20 there were no any failed points when criteria was %2–2mm for threshold %20 of the macximum dose.

Conclusion:

It is possible to reduce pencil beam kernel parametres for unfiltered photon energies. Improvement required for large fields.
SU‐E‐T‐701: Single Isocenter Volumetric Modulated Arc Therapy (VMAT) With Or Without Field Overlap in the Treatment of Left Sided Breast and Regional Lymphatic Tissue: Impact On Surrounding OAR Doses
Authors: Algan O , Hossain S , Lee G , Ahmad S
Published: June 2015

Purpose:

To investigate the impact of field overlap on dosimetric outcomes for patients receiving radiation therapy to the whole breast as well as the supraclavicular and internal mammary nodal regions.

Methods:

Seven patients with left sided breast cancer were evaluated on this IRB approved study. Four 200° partial arcs were used to optimize single isocenter VMAT plans using 2 different techniques: Technique 1 utilized treatment plans with no field overlap (NFOL) and 30 or 330 degree collimation. Technique 2 utilized 2cm field overlap (FOL) and 30 degree collimation. A single physician contoured all PTV and contralateral breast volumes. The same PTV and OAR volumes were used for both treatment planning techniques. The prescription dose was 46Gy delivered in 23 fractions with a minimum of 95% of the volume receiving 95% of the dose. A two‐sided paired t‐test was used to compare evaluated dosimetric parameters.

Results:

The mean PTV volume was 923cc (range 589–1218cc). In general, use of FOL resulted in a reduction (though not statistically significant, unless otherwise stated) in OAR dosimetric parameters when compared to NFOL. For left lung, mean dose was 14.3 vs. 13.6Gy, the V20Gy was 23.4% vs. 20.8%, and V30Gy was 10.8% vs. 7.1% (p < 0.01), for NFOL and FOL, respectively. Similarly, for total lung, mean dose was 9.2 vs. 8.8Gy, V20Gy was 11.2% vs. 9.9%, and V30Gy was 5.1 vs. 3.4% (p < 0.01), for heart, mean dose was 4.9 vs. 4.6Gy, V5Gy was 29.7 vs. 27.9%, and the V10Gy was 4.7 vs. 4.0%. Right breast was least impacted with the use of FOL: mean dose 2.6Gy vs. 2.6Gy, D2% of 9.0Gy vs. 9.4Gy (p = 0.5).

Conclusion:

Use of a 2cm FOL with VMAT treatment plans resulted in reduced doses to the lung and heart with minimal increase in right breast dose.
SU‐E‐T‐702: SIR‐Spheres Dose Vial Activity Assay Cross‐Calibration with An Outside Radiopharmacy
Authors: Gress D , Erwin W
Published: June 2015

Purpose:

To perform a dose calibrator (DC) cross‐calibration for assaying SIR‐Spheres patient doses after out‐sourcing dose dispensing to an outside radiopharmacy.

Methods:

The setting for our DC (CRC‐15R, Capintec) required for our assay to match that of the outside radiopharmacy (accounting for decay) was determined independently for 20 dispensed doses (v‐vial in acrylic shield). The mean of the twenty settings, plus and minus one and two standard deviations, as well as, minimum and maximum, were computed. For the next 20 doses, the activity was measured using the computed DC settings. From those measurements, a least squares fit of % error with respect to the outside radiopharmacy's specified activity versus DC setting was generated to indicate an optimum single dose calibrator setting for measuring future doses. An ionization chamber survey meter (451B, Fluke Biomedical) was used in a fixed geometry to measure the exposure rate of each of the first 20 dispensed doses, and generate a linear correlation of meter reading versus radiopharmacy‐specified activity, to provide an independent method of verifying that activity.

Results:

Survey meter measurements demonstrated reliability of the radiopharmacy's specified activities, with R2 equal to 0.99 and a conversion factor (slope) of 0.0584 [mR/hr]/mCi. The range of DC settings yielded activity readout range of ±5.25%. The least squares fit of % error relative to the radiopharmacy's specified activity versus computed DC setting had an R2 value of 0.999 and the fit passed through 0% error very near 63×10. Each data point in the fit was the mean of 20 measurements at each setting.

Conclusion:

An outside radiopharmacy's assay of SIR‐Spheres doses was validated, and our data suggest that a single DC setting may be used for an in‐house activity assay within approximately 5% of that from the outside radiopharmacy.
SU‐E‐T‐705: Skin Dosimetry Comparisons of CyberKnife and Tomotherapy for Head‐And‐Neck Stereotatic Body Radiotherapy
Authors: Yoon J , Woo J , Park J , Cho S , Lee E , Choi W , Park K , Lee H
Published: June 2015

Purpose:

To perform a comparative evaluation of the skin dose in CyberKnife and Tomotherapy to predict an accurate dose in head‐and‐neck SBRT.

Methods:

Arbitrarily‐defined planning target volume (PTV) near the skin was drawn on planning CT acquired from an anthropomorphic head‐and‐neck phantom that is used to perform the end‐to‐end test in CyberKnife. Calculation doses were obtained from Multiplan treatment planning system (TPS) using ray‐tracing and monte‐carlo (MC) algorithms for CyberKnife. For Tomotherapy, the skin dose was estimated with convolution superposition (CS) algorithm from Volo TPS. We selected 90% coverage of PTV in 3Gy prescription dose. We compared skin doses near target and at 5 cm far from the target. Optically‐stimulated luminescent dosimeter (OSLD) measurements of radiation dose to the skin over the head‐and‐neck were made during PTV delivery in CyberKnife and Tomotherapy. Individually‐calibrated OSLDs were placed on the surface of the phantom at a number of test positions. The measurement doses were compared with surface doses calculated from ray‐tracing, MC and CS algorithms.

Results:

The calculated skin doses near target were estimated to be 78∼93% in ray‐tracing, 50∼68% in MC and 78∼97% in CS. Skin doses near target were measured to be 54∼81% of the prescription dose in CyberKnife and to be 89∼104% of the target dose in Tomotherapy. The averaging differences between calculation and measurement values at the skin near target and at 5cm far from the target were 4.7%, 3.3%, and 4.8% in ray‐tracing, MC, and CS, respectively.

Conclusion:

We verified the skin dose comparisons based on three algorithms used in Cyberknife and Tomotherapy. By the measurement values using OSLD, we found that skin dose could be minimized in CyberKnife compared to using Tomotherapy, which lead to a lower skin dose in head‐and‐neck SBRT. In the aspect of correlation between measured and calculated doses, MC was superior to ray‐tracing and CS
SU‐E‐T‐715: Subacute Effects of Pulsed Low Dose Rate Radiotherapy and Conventional Radiotherapy On Normal Mouse Tissues
Authors: Cvetkovic D , Wang B , Chen L , Ma C
Published: June 2015

Purpose:

Pulsed low‐dose‐rate radiotherapy (PLDR) can be used as a re‐irradiation technique for recurrent cancers. We hypothesized that PLDR induces less toxicity to normal mouse tissues than conventional radiotherapy (CRT) for the same dose and regimen.

Methods:

Experiment 1: 22 male BALB/c nude mice were randomly assigned into a non‐irradiated control group (n=2), a CRT group (n=10), and a PLDR group (n=10). The mice received 8Gy total body irradiation (TBI) either continuously at a dose rate of 300MU/min (CRT) or in 0.2Gyx40 pulses separated by 3min intervals (PLDR). The mice were weighed daily, sacrificed when terminally ill or by day 12, and various organs were removed, formalin‐fixed, paraffin‐embedded and stained with H&E. Morphological changes were observed under a microscope. Experiment 2: 10 male nude mice were assigned into a control group, a 7Gy CRT, a 7Gy PLDR, an 8Gy CRT, and an 8Gy PLDR group; n=2 for each group. Body weight, urine/feces output, and food and water consumption were recorded daily, mice sacrificed on day 7, and organs collected for histology.

Results:

Statistically significant differences were found in the weight and survival time (8 vs. 12 days) between the CRT and PLDR groups (Exp 1). The greatest body weight decline in Exp 2 was observed in the 8Gy CRT group. Histopathological analysis revealed atrophy in spleen, bone marrow and small intestine of all irradiated animals. The damage was mild to moderate in PLDR groups, and severe in CRT groups. Additionally, stomach atrophy was seen in all of the CRT cases, but only in 25% of PLDR cases. There was no apparent difference in the level of tissue radiation injury at 7Gy and 8Gy.

Conclusion:

Our results verified the hypothesis that PLDR reduces the normal tissue toxicity from radiotherapy. Therefore, PLDR is an effective treatment for recurrent cancers.
SU‐E‐T‐722: Technical and Clinical Experience with the 1st Single Room Proton Therapy System
Authors: Klein E , Zhao T , Sun B , Goddu S , Santanam L , Bradley J
Published: June 2015

Purpose:

In December, 2013 we treated our first patient with the Mevion S250 Proton Therapy System. This followed seven months of acceptance testing and commissioning, including; dosimetric data acquisition, safety checks, establishment of QA programs, mechanical and imaging checks, modeling validation, etc.

Methods:

The Mevion S250 possesses a compact synchrocyclotron attached to a gantry due to its small size (1.8m diameter) and light weight (22 tons). The system includes a 6D robotic couch allowing for any beam trajectory. The system provides 3D‐2D imaging via fixed x‐rays. Our TPS is Varian Eclipse, for which modeling and validation comprised most of the commissioning. The electronic medical record system is Elekta's MOSIAQ 2.5, which provides connectivity for setup, imaging and treatment.

Results:

The modeling and validation met gamma of 3%/1mm for 98% of points. The imaging quality is superior than our other existing systems. Neutron dose was <1.0mSv/Gy for most clinical fields. The isocentricity of gantry and couch was measured to be ±0.5 and ±0.6mm, respectively. Daily QA is a 30 minute procedure, including; couch isocentricity, interlocks, warning indicators, imaging, and dosimetric checks for options. Output, modulation flatness, range, field symmetry are measured with a single exposure for 3 options. We currently treat 20–24 patients per day and uptime for most months has been >95%. Over the first 14 months, for our first 150 cases, were predominantly; adult CNS, pediatrics (including CSI), lung, and liver. Thorax patients receive weekly scans for adaptive planning.

Conclusion:

The Mevion S250 has added a vital option to compliment our other modalities within our NCI Comprehensive Cancer Center.
MO‐FG‐303‐01: FEATURED PRESENTATION and BEST IN PHYSICS (THERAPY): Automating LINAC QA: Design and Testing of An Image Acquisition and Processing System Utilizing a Combination of Radioluminescent Phosphors, Embedded X‐Ray Markers and Optical Measurements
Authors: Jenkins C , Naczynski D , Yu S , Xing L
Published: June 2015

Purpose:

The recent development of phosphors to visualize radiation beams from linear accelerators (LINAC) offers a unique opportunity for evaluating radiation fields within the context of the treatment space. The purpose of this study was to establish an automated, self‐calibrating prototype system for performing quality assurance (QA) measurements.

Methods:

A thin layer of Gd₂O₂S:Tb phosphor and fiducial markers were embedded on several planar faces of a custom‐designed phantom. The phantom was arbitrarily placed near iso‐center on the couch of a LINAC equipped with on‐board megavoltage (MV) and kilovoltage (kV) imagers. A plan consisting of several beams and integrated image acquisitions was delivered. Images of the phantom were collected throughout the delivery. Salient features, such as fiducials, crosshairs and beam edges were then extracted from these images used to calibrate the system, adjust for variations in phantom placement, and perform measurements. Beam edges were visualized by imaging the light generated by the phosphor on the phantom enabling direct comparison with the light field and laser locations. Registration of MV, kV and optical image data was performed using the embedded fiducial markers, enabling comparison of imaging center locations. Measurements specified by TG‐142 were calculated and compared with those obtained from a commercially available QA system.

Results:

The system was able to automatically extract the location of the fiducials, lasers, light field and radiation field from the acquired images regardless of phantom positioning. It was also able to automatically identify the locations of fiducial markers on kV and MV images. All collected measurements were within TG‐142 guidelines. The difference between the prototype and commercially available system were less than 0.2 mm.

Conclusion:

The prototype system demonstrated the capability of accurately and autonomously evaluating various TG‐142 parameters independent of operator input and phantom setup.