bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐597: Parameterization of the Photon Beam Dosimetry for a Commercial Linear Accelerator
Authors: Lebron S , Lu B , Yan G , Kahler D , Li J , Barraclough B , Liu C
Published: June 2015

Purpose:

In radiation therapy, accurate data acquisition of photon beam dosimetric quantities is important for (1) beam modeling data input into a treatment planning system (TPS), (2) comparing measured and TPS modelled data, (3) a linear accelerator's (linac) beam characteristics quality assurance process, and (4) establishing a standard data set for data comparison, etcetera. Parameterization of the photon beam dosimetry creates a portable data set that is easy to implement for different applications such as those previously mentioned. The aim of this study is to develop methods to parameterize photon percentage depth doses(PDD), profiles, and total scatter output factors(Scp).

Methods:

Scp, PDDs and profiles for different field sizes (from 2×2 to 40×40cm2), depths and energies were measured in a linac using a three‐dimensional water tank. All data were smoothed and profile data were also centered, symmetrized and geometrically scaled. The Scp and PDD data were analyzed using exponential functions. For modelling of open and wedge field profiles, each side was divided into three regions described by exponential, sigmoid and Gaussian equations. The model's equations were chosen based on the physical principles described by these dosimetric quantities. The equations’ parameters were determined using a least square optimization method with the minimal amount of measured data necessary. The model's accuracy was then evaluated via the calculation of absolute differences and distance–to–agreement analysis in low gradient and high gradient regions, respectively.

Results:

All differences in the PDDs’ buildup and the profiles’ penumbra regions were less than 2 mm and 0.5 mm, respectively. Differences in the low gradient regions were 0.20 ± 0.20% and 0.50 ± 0.35% for PDDs and profiles, respectively. For Scp data, all differences were less than 0.5%.

Conclusion:

This novel analytical model with minimum measurement requirements proved to accurately calculate PDDs, profiles, and Scp for different field sizes, depths and energies.
SU‐E‐T‐601: Patient Specific QA Check for Radiotherapy with Carbon Beam at SAGA HIMAT
Authors: Himukai T , Tsunashima Y , Kanazawa M , Mizota M , Shioyama Y , Endo M
Published: June 2015

Purpose:

To verify a patient specific QA for a prescribed dose per monitor unit (MU) and range check of carbon ion radiotherapy with a beam wobbling method at SAGA HIMAT.

Methods:

The dose distribution in a water phantom was recalculated with a treatment plan made by XiO‐N (Mitsubishi Electric Corporation, Tokyo). The depth dose distributions at central axis were compared with measurements using pinpoint ionization chamber (PTW31014). Measured data were analyzed for dose and distance difference with criteria of 3% and 2mm. To check for the MU and range, analysis data were used at center and distal end of a spread out bragg peak (SOBP) depth, respectively.

Results:

Treatment plan of 1400 beams in 500 patients were used for analysis. The pass rate of the MU and range was about 98% and 74%, respectively. The rate of both was 73%. The plan data passed only the MU check were verified depth dose profile. The data passed only the range and failed of both were compared depth dose distributions at off axis. If it was failed, we discussed with physicians.

Conclusion:

Most of patient specific QA check for a prescribed MU and range check at SAGA HIMAT were passed.
SU‐E‐T‐604: Penumbra Characteristics of a New InCiseâ„¢ Multileaf Collimator of CyberKnife M6â„¢ System
Authors: Hwang M , Jang S , Ozhasoglu C , Lalonde R , Heron D , Huq M
Published: June 2015

Purpose:

The InCise™ Multileaf Collimator (MLC) of CyberKnife M6™ System has been released recently. The purpose of this study was to explore the dosimetric characteristics of the new MLC. In particular, the penumbra characteristics of MLC fields at varying locations are evaluated.

Methods:

EBT3‐based film measurements were performed with varying MLC fields ranging from 7.5 mm to 27.5 mm. Seventeen regions of interests (ROIs) were identified for irradiation. These are regions located at the central area (denoted as reference field), at the left/right edge areas of reference open field, at an intermediate location between central and edge area. Single beam treatment plans were designed by using the MultiPlan and was delivered using the Blue Phantom. Gafchromic films were irradiated at 1.5 cm depth in the Blue Phantom and analyzed using the Film Pro software. Variation of maximum dose, penumbra of MLC‐defined fields, and symmetry/flatness were calculated as a function of locations of MLC fields.

Results:

The InCise™ MLC System showed relatively consistent dose distribution and penumbra size with varying locations of MLC fields. The measured maximum dose varied within 5 % at different locations compared to that at the central location and agreed with the calculated data well within 2%. The measured penumbrae were in the range of 2.9 mm and 3.7 mm and were relatively consistent regardless of locations. However, dose profiles in the out‐of‐field and in‐field regions varied with locations and field sizes. Strong variation was seen for all fields located at 55 mm away from the central field. The MLC leakage map showed that the leakage is dependent on position.

Conclusion:

The size of penumbra and normalized maximum dose for MLC‐defined fields were consistent in different regions of MLC. However, dose profiles in the out‐field region varied with locations and field sizes.
SU‐E‐T‐615: Plan Comparison Between Photon IMRT and Proton Plans Incorporating Uncertainty Analysis
Authors: Cheng C , Wessels B , Jesseph F , Mattson D , Mansur D
Published: June 2015

Purpose:

In this study, we investigate the effect of setup uncertainty on DVH calculations which may impact plan comparison.

Methods:

Treatment plans (6 MV VMAT calculated on Pinnacle TPS) were chosen for different disease sites: brain, prostate, H&N and spine in this retrospective study. A proton plan (PP) using double scattering beams was generated for each selected VMAT plan subject to the same set of dose‐volume constraints as in VMAT. An uncertainty analysis was incorporated on the DVH calculations in which isocenter shifts from 1 to 5 mm in each of the ±x, ±y and ±z directions were used to simulate the setup uncertainty and residual positioning errors. A total of 40 different combinations of isocenter shifts were used in the re‐calculation of DVH of the PTV and the various OARs for both the VMAT and the corresponding PT.

Results:

For the brain case, both VMAT and PP are comparable in PTV coverage and OAR sparing, and VMAT is a clear choice for treatment due to its ease of delivery. However, when incorporating isoshifts in DVH calculations, a significant change in dose‐volume relationship emerges. For example, both VMAT and PT provide adequate coverage, even with ±3mm isoshift. However, +3mm isoshift results in increase of V40(Lcochlea, VMAT) from 7.2% in the original plan to 45% and V40(R cochlea, VMAT) from 75% to 92%. For protons, V40(Lcochlea, PT) increases from 62% in the initial plan to 75%, while V40(Rcochea, PT) increases from 7% to 26%.

Conclusion:

DVH alone may not be sufficient to allow an unequivocal decision in plan comparison, especially when two rival plans are very similar in both PTV coverage and OAR sparing. It is a good practice to incorporate uncertainty analysis on photon and proton plan comparison studies to test the plan robustness in plan evaluation.
SU‐E‐T‐616: Plan Quality Assessment of Both Treatment Planning System Dose and Measurement‐Based 3D Reconstructed Dose in the Patient
Authors: Olch A
Published: June 2015

Purpose:

Systematic radiotherapy plan quality assessment promotes quality improvement. Software tools can perform this analysis by applying site‐specific structure dose metrics. The next step is to similarly evaluate the quality of the dose delivery. This study defines metrics for acceptable doses to targets and normal organs for a particular treatment site and scores each plan accordingly. The input can be the TPS or the measurement‐based 3D patient dose. From this analysis, one can determine whether the delivered dose distribution to the patient receives a score which is comparable to the TPS plan score, otherwise replanning may be indicated.

Methods:

Eleven neuroblastoma patient plans were exported from Eclipse to the Quality Reports program. A scoring algorithm defined a score for each normal and target structure based on dose‐volume parameters. Each plan was scored by this algorithm and the percentage of total possible points was obtained. Each plan also underwent IMRT QA measurements with a Mapcheck2 or ArcCheck. These measurements were input into the 3DVH program to compute the patient 3D dose distribution which was analyzed using the same scoring algorithm as the TPS plan.

Results:

The mean quality score for the TPS plans was 75.37% (std dev=14.15%) compared to 71.95% (std dev=13.45%) for the 3DVH dose distribution. For 3/11 plans, the 3DVH‐based quality score was higher than the TPS score, by between 0.5 to 8.4 percentage points. Eight/11 plans scores decreased based on IMRT QA measurements by 1.2 to 18.6 points.

Conclusion:

Software was used to determine the degree to which the plan quality score differed between the TPS and measurement‐based dose. Although the delivery score was generally in good agreement with the planned dose score, there were some that improved while there was one plan whose delivered dose quality was significantly less than planned. This methodology helps evaluate both planned and delivered dose quality.

Sun Nuclear Corporation has provded a license for the software described.
SU‐E‐T‐619: Planning 131I Thyroid Treatments for Patients Requiring Hemodialysis
Authors: Stroud D
Published: June 2015

Purpose:

Treatment of 131I thyroid cancer patients who also require regular hemodialysis (HD) treatments requires consideration of the administered activity and the HD schedule. In this work the red bone marrow is considered the dose limiting organ and the treatment plan optimized the HD schedule with the amount of radioactivity administered.

Methods:

The ‘Safe’ dose was considered to be 2 Gy (200 rad) to the red bone marrow.1 131Iodine doses of 50 mCi to 100 mCi were modeled and found to require a range of HD schedules. In order to achieve the safe dose to the red marrow, more aggressive HD schedules are required. 100 mCi required an aggressive HD treatment of every 24 hours for at least one week to achieve the ‘safe’ dose and an exposure appropriate for release from the hospital. A more normal schedule of HD beginning at 18 hours then every 48 hours allowed for up to 60 mCi administered dose allowed for a safe dose and expected release after less than one week.2In addition room was equipped with video cameras cameras for monitoring the patient and their vital signs from an adjacent room during HD. In this way the dialysis nurses were able to monitor the patient closely from an adjoining room.

Results:

Two HD patients were administered adjusted doses of about 50 mCi. The medical and nursing staff were exposed to no more than 4 mR for the entire treatment. The residual Iodine in the patient appeared to be normal after 4 to 6 days when the patient was released.

Conclusion:

With careful treatment planning 131Iodine treatments can be performed safely for patients needing HD and treatments appear to be as effective as those for patients with normal renal function.
SU‐E‐T‐620: Planning and Dosimetry for Pulsed Low Dose Rate RT for Recurrent Lung, Spine, GYN and Head and Neck Cancers
Authors: Tong X , Luo F , Liu Y , Zhang W , Xu Q , Zhang T , Li J , Chen L , Ma C
Published: June 2015

Purpose:

Extensive in vitro and in vivo studies have shown that pulsed low dose rate (PLDR) radiotherapy has potential to provide significant local tumor control and to reduce normal tissue toxicities. This work investigated the planning and dosimetry of PLDR re‐irradiation for recurrent cancers.

Methods:

We analyzed the treatment plans and dosimetry for 13 recurrent patients who were treated with the PLDR technique in this study. All cases were planned with the 3DCRT technique with optimal beam angle selection. The treatment was performed on a Siemens accelerator using 6MV beams. The target volume ranged between 161 and 703cc. The previous RT dose was 40–60Gy while the re‐irradiation dose was 16–60Gy. The interval between previous RT and re‐irradiation was 13–336 months, and the follow‐up time was up to 27months. The total prescription dose was administered in 2Gy/day fractions with the daily dose delivered in 10 sub‐fractions (pulses) of 20cGy with a 3min interval between the pulses to achieve an effective dose rate of 6.7cGy/min.

Results:

The clinical outcome was analyzed based on the treatment plans. All pulses were kept with Dmax<40cGy. The PLDR treatments were effective (CR: 3 patients, PR: 10 patients). The acute and late toxicities were all acceptable (generally grade II or under). Two patients died three months after the PLDR re‐irradiation, one due to massive cerebral infarction and the other due to acute cardiac failure. All others survived more than 8 months. Five patients showed good conditions at the last follow‐up. Among them two recurrent lung cancer patients had survived 23 months and one nasopharyngeal cancer patient had survived 27 months.

Conclusion:

The PLDR technique was effective for the palliative treatment of head and neck, lung, spine and GYN cancers. Further phase II and III studies are warranted to quantify the efficacy of PLDR for recurrent cancers.
SU‐E‐T‐621: Planning Methodologies for Cancer of the Anal Canal: Comparing IMRT, Rapid Arc, and Pencil Beam Scanning Proton Beam
Authors: McGlade J , Kassaee A
Published: June 2015

Purpose:

To evaluate planning methods for anal canal cancer and compare the results of 9‐field Intensity Modulated Radiotherapy (IMRT), Volumetric Modulated Arc Therapy (Varian, RapidArc), and Proton Pencil Beam Scanning (PBS).

Methods:

We generated plans with IMRT, RapidArc (RA) and PBS for twenty patients for both initial phase including nodes and cone down phase of treatment using Eclipe (Varian). We evaluated the advantage of each technique for each phase. RA plans used 2 to 4 arcs and various collimator orientations. PBS used two posterior oblique fields. We evaluated the plans comparing dose volume histogram (DVH), locations of hot spots, and PTV dose conformity.

Results:

Due to complex shape of target, for RA plans, multiple arcs (>2) are required to achieve optimal PTV conformity. When the PTV exceeds 15 cm in the superior‐inferior direction, limitations of deliverability start to dominate. The PTV should be divided into a superior and an inferior structure. The optimization is performed with fixed jaws for each structure and collimator set to 90 degrees for the inferior PTV. Proton PBS plans show little advantage in small bowel sparing when treating the nodes. However, PBS plan reduces volumetric dose to the bladder at the cost of higher doses to the perineal skin. IMRT plans provide good target conformity, but they generate hot spots outside of the target volume.

Conclusion:

When using one planning technique for entire course of treatment, Multiple arc (>2) RA plans are better as compared to IMRT and PBS plans. When combining techniques, RA for the initial phase in combination with PBS for the cone down phase results in the most optimal plans.
SU‐E‐T‐622: Planning Technique for Passively‐Scattered Involved‐Node Proton Therapy of Mediastinal Lymphoma with Consideration of Cardiac Motion
Authors: Flampouri S , Li Z , Hoppe B
Published: June 2015

Purpose:

To develop a treatment planning method for passively‐scattered involved‐node proton therapy of mediastinal lymphoma robust to breathing and cardiac motions.

Methods:

Beam‐specific planning treatment volumes (bsPTV) are calculated for each proton field to incorporate pertinent uncertainties. Geometric margins are added laterally to each beam while margins for range uncertainty due to setup errors, breathing, and calibration curve uncertainties are added along each beam. The calculation of breathing motion and deformation effects on proton range includes all 4DCT phases. The anisotropic water equivalent margins are translated to distances on average 4DCT. Treatment plans are designed so each beam adequately covers the corresponding bsPTV. For targets close to the heart, cardiac motion effects on dosemaps are estimated by using a library of anonymous ECG‐gated cardiac CTs (cCT). The cCT, originally contrast‐enhanced, are partially overridden to allow meaningful proton dose calculations. Targets similar to the treatment targets are drawn on one or more cCT sets matching the anatomy of the patient. Plans based on the average cCT are calculated on individual phases, then deformed to the average and accumulated. When clinically significant dose discrepancies occur between planned and accumulated doses, the patient plan is modified to reduce the cardiac motion effects.

Results:

We found that bsPTVs as planning targets create dose distributions similar to the conventional proton planning distributions, while they are a valuable tool for visualization of the uncertainties. For large targets with variability in motion and depth, integral dose was reduced because of the anisotropic margins. In most cases, heart motion has a clinically insignificant effect on target coverage.

Conclusion:

A treatment planning method was developed and used for proton therapy of mediastinal lymphoma. The technique incorporates bsPTVs compensating for all common sources of uncertainties and estimation of the effects of cardiac motion not commonly performed.
SU‐E‐T‐624: Portal Dosimetry Commissioning of Multiple (6) Varian TrueBeam Linacs Equipped with PortalVision DMI MV Imager
Authors: Weldon M , DiCostanzo D , Grzetic S , Hessler J
Published: June 2015

Purpose:

To show that a single model for Portal Domisetry (PD) can be established for beam‐matched TrueBeam™ linacs that are equipped with the DMI imager (43×43cm effective area).

Methods:

Our department acquired 6 new TrueBeam™s, 4 “Slim” and 2 “Edge” models. The Slims were equipped with 6 and 10MV photons, and the Edges with 6MV. MLCs differed between the Slims and Edges (Millennium 120 vs HD‐MLC respectively). PD model was created from data acquired using a single linac (Slim). This includes maximum field size profile, as well as output factors and acquired measured fluence using the DMI imager. All identical linacs were beam‐matched, profiles were within 1% at maximum field size at a variety of depths. The profile correction file was generated from 40×40 profile acquired at 5cm depth, 95cm SSD, and was adjusted for deviation at the field edges and corners. The PD model and profile correction was applied to all six TrueBeam™s and imagers. A variety of jaw only and sliding window (SW) MLC test fields, as well as TG‐119 and clinical SW and VMAT plans were run on each linac to validate the model.

Results:

For 6X and 10X, field by field comparison using 3mm/3% absolute gamma criteria passed 90% or better for all cases. This was also true for composite comparisons of TG‐199 and clinical plans, matching our current department criteria.

Conclusion:

Using a single model per photon energy for PD for the TrueBeam™ equipped with a DMI imager can produce clinically acceptable results across multiple identical and matched linacs. It is also possible to use the same PD model despite different MLCs. This can save time during commissioning and software updates.
SU‐E‐T‐628: Predicted Risk of Post‐Irradiation Cerebral Necrosis in Pediatric Brain Cancer Patients: A Treatment Planning Comparison of Proton Vs. Photon Therapy
Authors: Freund D , Zhang R , Newhauser W , Sanders M
Published: June 2015

Purpose:

Post‐irradiation cerebral necrosis (PICN) is a severe late effect that can Result from brain cancers treatment using radiation therapy. The purpose of this study was to compare the treatment plans and predicted risk of PICN after volumetric modulated arc therapy (VMAT) to the risk after passively scattered proton therapy (PSPT) and intensity modulated proton therapy (IMPT) in a cohort of pediatric patients.

Methods:

Thirteen pediatric patients with varying age and sex were selected for this study. A clinical treatment volume (CTV) was constructed for 8 glioma patients and 5 ependymoma patients. Prescribed dose was 54 Gy over 30 fractions to the planning volume. Dosimetric endpoints were compared between VMAT and proton plans. The normal tissue complication probability (NTCP) following VMAT and proton therapy planning was also calculated using PICN as the biological endpoint. Sensitivity tests were performed to determine if predicted risk of PICN was sensitive to positional errors, proton range errors and selection of risk models.

Results:

Both PSPT and IMPT plans resulted in a significant increase in the maximum dose and reduction in the total brain volume irradiated to low doses compared with the VMAT plans. The average ratios of NTCP between PSPT and VMAT were 0.56 and 0.38 for glioma and ependymoma patients respectively and the average ratios of NTCP between IMPT and VMAT were 0.67 and 0.68 for glioma and ependymoma plans respectively. Sensitivity test revealed that predicted ratios of risk were insensitive to range and positional errors but varied with risk model selection.

Conclusion:

Both PSPT and IMPT plans resulted in a decrease in the predictive risk of necrosis for the pediatric plans studied in this work. Sensitivity analysis upheld the qualitative findings of the risk models used in this study, however more accurate models that take into account dose and volume are needed.
SU‐E‐T‐629: Prediction of the ViewRay Radiotherapy Treatment Time for Clinical Logistics
Authors: Liu S , Wooten H , Wu Y , Yang D
Published: June 2015

Purpose:

An algorithm is developed in our clinic, given a new treatment plan, to predict treatment delivery time for radiation therapy (RT) treatments of patients on ViewRay magnetic resonance‐image guided radiation therapy (MR‐IGRT) delivery system. This algorithm is necessary for managing patient treatment appointments, and is useful as an indicator to assess the treatment plan complexity.

Methods:

A patient's total treatment delivery time, not including time required for localization, may be described as the sum of four components: (1) the treatment initialization time; (2) the total beam‐on time; (3) the gantry rotation time; and (4) the multileaf collimator (MLC) motion time. Each of the four components is predicted separately. The total beam‐on time can be calculated using both the planned beam‐on time and the decay‐corrected delivery dose rate. To predict the remaining components, we quantitatively analyze the patient treatment delivery record files. The initialization time is demonstrated to be random since it depends on the final gantry angle and MLC leaf positions of the previous treatment. Based on modeling the relationships between the gantry rotation angles and the corresponding rotation time, and between the furthest MLC leaf moving distance and the corresponding MLC motion time, the total delivery time is predicted using linear regression.

Results:

The proposed algorithm has demonstrated the feasibility of predicting the ViewRay treatment delivery time for any treatment plan of any patient. The average prediction error is 0.89 minutes or 5.34%, and the maximal prediction error is 2.09 minutes or 13.87%.

Conclusion:

We have developed a treatment delivery time prediction algorithm based on the analysis of previous patients’ treatment delivery records. The accuracy of our prediction is sufficient for guiding and arranging patient treatment appointments on a daily basis. The predicted delivery time could also be used as an indicator to assess the treatment plan complexity.

This work was supported by a research grant from Viewray Inc.
SU‐E‐T‐646: Quality Assurance of Truebeam Multi‐Leaf Collimator Using a MLC QA Phantom
Authors: Zhang J , Hong D , Lu J
Published: June 2015

Purpose:

To perform a routine quality assurance procedure for Truebeam multi‐leaf collimator (MLC) using MLC QA phantom, verify the stability and reliability of MLC during the treatment.

Methods:

MLC QA phantom is a specialized phantom for MLC quality assurance (QA), and contains five radio‐opaque spheres that are embedded in an “L” shape. The phantom was placed isocentrically on the Truebeam treatment couch for the tests. A quality assurance plan was setted up in the Eclipse v10.0, the fields that need to be delivered in order to acquire the necessary images, the MLC shapes can then be obtained by the images. The images acquired by the electronic portal imaging device (EPID), and imported into the PIPSpro software for the analysis. The tests were delivered twelve weeks (once a week) to verify consistency of the delivery, and the images are acquired in the same manner each time.

Results:

For the Leaf position test, the average position error was 0.23mm±0.02mm (range: 0.18mm∼0.25mm). The Leaf width was measured at the isocenter, the average error was 0.06mm±0.02mm (range: 0.02mm∼0.08mm) for the Leaf width test. Multi‐Port test showed the dynamic leaf shift error, the average error was 0.28mm±0.03mm (range: 0.2mm∼0.35mm). For the leaf transmission test, the average inter‐leaf leakage value was 1.0%±0.17% (range: 0.8%∼1.3%) and the average inter‐bank leakage value was 32.6%±2.1% (range: 30.2%∼36.1%).

Conclusion:

By the test of 12 weeks, the MLC system of the Truebeam is running in a good condition and the MLC system can be steadily and reliably carried out during the treatment. The MLC QA phantom is a useful test tool for the MLC QA.
SU‐E‐T‐648: Quality Assurance Using the RADPOS System for 4D Radiotherapy with CyberKnife
Authors: Marants R , Vandervoort E , Cygler J E
Published: June 2015

Purpose:

The CyberKnife robotic radiosurgery system uses Synchrony respiratory motion compensation, which requires independent performance verification. In this work, the RADPOS 4D dosimetry system's motion measurements are compared with internal fiducial position measurements. In addition, RADPOS measurements are compared with Synchrony's predictive correlation model, which is based on internal fiducial and external LED marker position measurements.

Methods:

A treatment plan was created for a lung insert containing fiducials, RADPOS detector, and Solid Water tumor phantom. Two Quasar Respiratory Motion Phantoms (Q1 and Q2) and two RADPOS detectors (R1 and R2) were used: Q1 simulated lung motion with a lung insert moving in the superior/inferior direction, while Q2 simulated chest motion with a chest platform moving in the anterior/posterior direction. Before treatment, R1 was secured inside of the tumor phantom within Q1, while LED markers and R2 were positioned on the chest platform of Q2. Two treatment delivery cases were studied: isocentric plan (I) and non‐isocentric patient plan (P). Four motion cases were studied: no motion (0), sinusoidal and in‐phase (1), sinusoidal and out‐of‐phase (2), patient waveform and out‐of‐phase (3). A coordinate alignment algorithm was implemented, allowing RADPOS and model position data to be compared within the fiducial coordinate system.

Results:

The standard deviation of the differences between RADPOS and fiducial position measurements was below 0.6 mm for all experimental cases. The standard deviation of the differences between RADPOS and model position data was 1.0, 1.5, and 1.6 mm along the primary direction of motion for case I1, I2, and P3, respectively.

Conclusion:

Our work demonstrates that RADPOS is a useful tool for independent quality assurance of CyberKnife treatment with Synchrony respiratory compensation. RADPOS and fiducial position measurement closely match, and RADPOS confirms the effectiveness of CyberKnife's Synchrony motion tracking.

This work was supported by OCAIRO (Ontario Consortium for Adaptive Interventions in Radiation Oncology) grant.
SU‐E‐T‐650: Quantification and Modeling of the Dosimetric Impact of the IBEAM Evo Treatment Couchtop EP (Elekta) in VMAT
Authors: Zhang R , Bai W , Fleckenstein J
Published: June 2015

Purpose:

quantification and modelling of the dosimetric impact of the treatment couch in Monaco Treatment Planning System.

Methods:

The attenuation characteristics of couchtop EP was evaluated for two different photon acceleration potentials (6MV and 10MV) for a field size of (10×10) cm2. Phantom positions in A‐B direction: on the left half, in the center and on the right half of the couch. Dose measurements of couch attenuation were performed at gantry angles from 180° to 122°, using a 0.125cc semiflex ionization chamber isocentrically placed in the center of a homogeneous cylindric sliced RW3 phantom. Each experimental setup was first measured on the LINAC and then reproduced in the TPS. By adjusting the relative‐to‐water electron density (ED) values of the couch, the measured attenuation was replicated. The simulated results were evaluated by comparing the measurements and simulations.

Results:

Without the couch model included the maximum difference between measured and calculated dose was 5.5% (5.1%) and 6.6% (6.1%) for 2 mm and 5 mm voxel size, when the phantom was positioned on the left (center). The couch model was included in the TPS with a uniform ED of 0.18 or a 2 component model with a fiber ED= 0.6 and foam core ED= 0.1. After including the treatment couch, the mean dose attenuation was reduced from 2.8% without couch included to (0.0, 0.8, −0.2, 0.6)%. The 4 different values represent the 1 and 2 components model and 2 and 5 mm voxel grid size.

Conclusion:

For a uniform relative‐to‐water couch electron density of 0.18 a good agreement between measured and calculated dose distributions was obtained for all different energies, voxel grid spacings and gantry angles. Therefore, we conclude that the Monaco couch model accurately describes the dose perturbations due to the presence of the patient couch and should therefore be used during treatment planning.

This project is supported by Technology Foundation for Selected Overseas Chinese Scholar, Ministry of Hebei Personnel of China
SU‐E‐T‐651: Quantification of Dosimetric Accuracy of Respiratory Gated Stereotactic Body Radiation Therapy
Authors: Thiyagarajan Rajesh , Nambiraj N Arunai , Sinha Sujit Nath , Sigamani Ashokkumar , Yadav Girigesh , Raman Kothanda , Vikraman S , Maragathaveni S , Dhivya N , Kataria Tejinder
Published: June 2015

Purpose:

To quantify the dosimetric accuracy of respiratory gated stereotactic body radiation therapy delivery using dynamic thorax phantom.

Methods:

Three patients with mobile target (2 lung, 1liver) were chosen. Retrospective 4DCT image sets were acquired for using Varian RPM system. An in‐house MATLAB program was designed for MIP, MinIP and AvgIP generation. ITV was contoured on MIP image set for lung patients and on MinIP for liver patient. Dynamic IMRT plans were generated on selected phase bin image set in Eclipse (v10.0) planning system. CIRS dynamic thorax phantom was used to perform the dosimetric quality assurance. Patient breathing pattern file from RPM system was converted to phantom compatible file by an in‐house MATLAB program. This respiratory pattern fed to the CIRS dynamic thorax phantom. 4DCT image set was acquired for this phantom using patient breathing pattern. Verification plans were generated using patient gating window and delivered on the phantom. Measurements were carried out using with ion chamber and EBT2 film. Exposed films were analyzed and evaluated in FilmQA software.

Results:

The stability of gated output in comparison with un‐gated output was within 0.5%. The Ion chamber measured and TPS calculated dose compared for all the patients. The difference observed was 0.45%, −0.52% and −0.54 for Patient 1, Patient2 and Patient 3 respectively.Gamma value evaluated from EBT film shows pass rates from 92.41% to 99.93% for 3% dose difference and 3mm distance to agreement criteria.

Conclusion:

Dosimetric accuracy of respiratory gated SBRT delivery for lung and liver was dosimetrically acceptable. The Ion chamber measured dose was within 0.203±0.5659% of the expected dose. Gamma pass rates were within 96.63±3.84% of the expected dose.
SU‐E‐T‐655: Quantifying the Dosimetric Characteristics of a Calypso Compatible Radiotherapy Treatment Couch with Angular Transmission Functions
Authors: Duan J , Shen S , Wu X , Popple R , Cardan R , Huang M , Tannazi F , Brezovich I
Published: June 2015

Purpose:

To quantified the dosimetric characteristics of a Calypso compatible radiotherapy couch using continuously scanned transmission factor as a function of gantry angle.

Methods:

Radiation dose as a function of gantry angle was measured with an ionization chamber at the center of a 30 cm diameter cylindrical phantom placed on Qfix kVue Calypso compatible couch. A 3‐D scanner was employed to continuously scan the dose during an arc rotation delivery. Nearly continuous transmission curves of 0.03° step size were obtained from IEC gantry angle 90° to180° for 6 MV and 15 MV photon beams at three couch longitudinal positions (due to longitudinally non‐uniform shape of the couch rails) with rails both at the center and on sides. The transmission curves were evaluated to assess the attenuation by the couch. They were also compared to those of a carbon fiber couch top.

Results:

The scanned transmission curves of the Calypso comptible couch showed fine details of the couch transmission as a function of gantry angle. The attenuation by the couch varied from 2.4% to 12.9% for the 6 MV photo beam and from 1.8% to 8.9% for the 15 MV photon beam depending on the gantry angle. The attenuation by the flat couch top is only approximately 2 to 3%, but by the rail is much more significant. Because the rails are not uniformly shaped in the longitudinal direction, attenuation by the rail for the same gantry angle varied with the rail longitudinal position. The transmission curves of the carbon fiber couch top are nearly identical to those of the Calypso compatible couch top.

Conclusion:

The Calypso compatible couch attenuates radiation by 2.4%–12.9% and 1.8%–8.9% for 6 MV and 15 MV photon beams, respectively. The attenuation by the rails is much more significant than the flat couch top.
SU‐E‐T‐657: Quantitative Assessment of Plan Robustness for Helical Tomotherapy for Head and Neck Cancer Radiotherapy
Authors: Matney J , Lian J , Chao E , Chera B , Marks L , Das S
Published: June 2015

Introduction:

Geometric uncertainties in daily patient setup can lead to variations in the planned dose, especially when using highly conformal techniques such as helical Tomotherapy. To account for the potential effect of geometric uncertainty, our clinical practice is to expand critical structures by 3mm expansion into planning risk volumes (PRV). The PRV concept assumes the spatial dose cloud is insensitive to patient positioning. However, no tools currently exist to determine if a Tomotherapy plan is robust to the effects of daily setup variation. We objectively quantified the impact of geometric uncertainties on the 3D doses to critical normal tissues during helical Tomotherapy.

Methods:

Using a Matlab‐based program created and validated by Accuray (Madison, WI), the planned Tomotherapy delivery sinogram recalculated dose on shifted CT datasets. Ten head and neck patients were selected for analysis. To simulate setup uncertainty, the patient anatomy was shifted ±3mm in the longitudinal, lateral and vertical axes. For each potential shift, the recalculated doses to various critical normal tissues were compared to the doses delivered to the PRV in the original plan

Results:

18 shifted scenarios created from Tomotherapy plans for three patients with head and neck cancers were analyzed. For all simulated setup errors, the maximum doses to the brainstem, spinal cord, parotids and cochlea were no greater than 0.6Gy of the respective original PRV maximum. Despite 3mm setup shifts, the minimum dose delivered to 95% of the CTVs and PTVs were always within 0.4Gy of the original plan.

Conclusions:

For head and neck sites treated with Tomotherapy, the use of a 3mm PRV expansion provide a reasonable estimate of the dosimetric effects of 3mm setup uncertainties. Similarly, target coverage appears minimally effected by a 3mm setup uncertainty. Data from a larger number of patients will be presented. Future work will include other anatomical sites.
SU‐E‐T‐661: Quantitative MRI Assessment of a Novel Direction‐Modulated Brachytherapy Tandem Applicator for Cervical Cancer
Authors: Soliman A , Elzibak A , Fatemi A , Safigholi H , Han D , Leung E , Ravi A , Song W
Published: June 2015

Purpose:

To quantitatively evaluate the MR image quality of a novel direction modulated brachytherapy (DMBT) tandem applicator for cervical cancer, using the clinical MRI scanning protocol for image guided brachytherapy.

Methods:

The tungsten alloy‐based applicator was placed in a water phantom and clinical imaging protocol was performed. Axial images were acquired using 2D turbo‐spin echo (TSE) T2‐weighted sequence on a 1.5T GE 450w MR scanner and an 8‐channel body coil. As multi‐channel receiver coil was used, inhomogeneities in the B1 receive field must be considered before performing the quantification process. Therefore the applicator was removed from the phantom and the whole imaging session was performed again for the water phantom with the same parameters. Images from the two scans were then subtracted, resulting in a difference image that only shows the applicator with its surrounding magnetic susceptibility dipole artifact. Line profiles were drawn and plotted on the difference image at various angles and locations along the tandem. Full width at half maximum (FWHM) was measured at all the line profiles to quantify the extent of the artifact. Additionally, the extent of the artifact along the diameter of the tandem was measured at various angles and locations.

Results:

After removing the background inhomogeneities of the receiver coil, FWHM of the tandem measured 5.75 ± 0.35 mm (the physical tandem diameter is 5.4 mm). The average extent of the artifacts along the diameter of the tandem measured is 2.14 ± 0.56 mm. In contrast to CT imaging of the same applicator (not shown here), the tandem can be easily identified without additional correction algorithms.

Conclusion:

This work demonstrated that the novel DMBT tandem applicator has minimal susceptibility artifact in T2‐weighted images employed in clinical practice for MRI‐guided brachytherapy of cervical cancer.
SU‐E‐T‐665: Radiochromic Film Quenching Effect Reduction for Proton Beam Dosimetry
Authors: Aldelaijan S , Alzorkany F , Moftah B , Alrumayan F , Seuntjens J , Lewis D , Devic S
Published: June 2015

Purpose:

Depending on the useful dose range in which radiochromic films operate, number of different radiochromic film models have been designed. The impact of different film models on quenching effect for percent depth dose (PDD) measurements in proton beams has been investigated.

Methods:

Calibrated PTW Markus ionization chamber was used to measure PDD and beam output for 26.5 MeV protons produced by CS30 cyclotron. An aluminum cylinder was added in front of the beam exit serving as a radiation shutter. The measured signal was normalized to a monitor chamber reading and subsequently scaled by ratio of water‐to‐air stopping powers at given depth, while the effective depth of measurements was scaled by ratios of material‐to‐water physical densities and CSDA ranges. Output was measured in water at 2.1 mm reference‐depth in the plateau upstream from the Bragg peak. Following the TRS‐398 reference dosimetry protocol for proton beams, the output was calibrated in water. Three radiochromic film models (EBT, EBT3 and HD‐V2) were calibrated within Lexan phantom positioned at the same water‐equivalent depth. Thicknesses of films sensitive layers were 34 µm, 30 µm and 8 µm, respectively. Small film pieces (1 × 2 cm2) were positioned within polyethylene phantom along the beam central axis with an angulation of 5° for PDD measurements.

Results:

While the output of the proton beam was found to be around 7 Gy/sec, the actual value of the output per monitor chamber reading (2.32 Gy/nC) was used for reference‐dose irradiations during film calibration. Dose ratios at the Bragg peak relative to the reference‐depth were 3.88, 2.52, 2.19, and 2.02 for the Markus chamber, HD‐V2, EBT3, and EBT film models, respectively.

Conclusion:

Results at hand suggest that quenching effect is reduced when a radiochromic film model with smaller sensitive layer thickness is used for PDD measurements in proton beams.

David Lewis is the owner of RCF Consulting, LLC
SU‐E‐T‐667: Radiosensitization Due to Gold Nanoparticles: A Monte Carlo Cellular Dosimetry Investigation of An Expansive Parameter Space
Authors: Martinov M , Thomson R
Published: June 2015

Purpose:

To investigate dose enhancement to cellular compartments following gold nanoparticle (GNP) uptake in tissue, varying cell and tissue morphology, intra and extracellular GNP distribution, and source energy using Monte Carlo (MC) simulations.

Methods:

Models of single and multiple cells are developed for normal and cancerous tissues; cells (outer radii 5–10 µm) are modeled as concentric spheres comprising the nucleus (radii 2.5–7.5 µm) and cytoplasm. GNP distributions modeled include homogeneous distributions throughout the cytoplasm, variable numbers of GNP‐containing endosomes within the cytoplasm, or distributed in a spherical shell about the nucleus. Gold concentrations range from 1 to 30 mg/g. Dose to nucleus and to cytoplasm for simulations including GNPs are compared to simulations without GNPs to compute Nuclear and Cytoplasm Dose Enhancement Factors (NDEF, CDEF). Photon source energies are between 20 keV and 1.25 MeV.

Results:

DEFs are highly sensitive to GNP intracellular distribution; for a 2.5 µm radius nucleus irradiated by a 30 keV source, NDEF varies from 1.2 for a single endosome containing all GNPs to 8.2 for GNPs distributed about the nucleus (7 mg/g). DEFs vary with cell dimensions and source energy: NDEFs vary from 2.5 (90 keV) to 8.2 (30 keV) for a 2.5 µm radius nucleus and from 1.1 (90 keV) to 1.3 (30 keV) for a 7.5 µm radius nucleus, both with GNPs in a spherical shell about the nucleus (7 mg/g). NDEF and CDEF are generally different within a single cell. For multicell models, the presence of gold within intervening tissues between source and target perturbs the fluence reaching cellular targets, resulting in DEF inhomogeneities within a population of irradiated cells.

Conclusion:

DEFs vary by an order of magnitude for different cell models, GNP distributions, and source energies, demonstrating the importance of detailed modelling for advancing GNP development for radiotherapy.

Funding provided by the Natural Sciences and Engineering Council of Canada (NSERC), and the Canada Research Chairs Program (CRC)
SU‐E‐T‐673: Recent Developments and Comprehensive Validations of a GPU‐Based Proton Monte Carlo Simulation Package, GPMC
Authors: Qin N , Giantsoudi D , Tian Z , Schuemann J , Pompos A , Paganetti H , Jiang S , Jia X
Published: June 2015

Purpose:

A GPU‐based Monte Carlo (MC) simulation package gPMC has been previously developed and high computational efficiency was achieved. This abstract reports our recent improvements on this package in terms of accuracy, functionality, and code portability.

Methods:

In the latest version of gPMC, nuclear interaction cross section database was updated to include data from TOPAS/Geant4. Inelastic interaction model, particularly the proton scattering angle distribution, was updated to improve overall simulation accuracy. Calculation of dose averaged LET (LETd) was implemented. gPMC was ported onto an OpenCL environment to enable portability across different computing devices (GPUs from different vendors and CPUs). We also performed comprehensive tests of the code accuracy. Dose from electro‐magnetic (EM) interaction channel, primary and secondary proton doses and fluences were scored and compared with those computed by TOPAS.

Results:

In a homogeneous water phantom with 100 and 200 MeV beams, mean dose differences in EM channel computed by gPMC and by TOPAS were 0.28% and 0.65% of the corresponding maximum dose, respectively. With the Geant4 nuclear interaction cross section data, mean difference of primary proton dose was 0.84% for the 200 MeV case and 0.78% for the 100 MeV case. After updating inelastic interaction model, maximum difference of secondary proton fluence and dose were 0.08% and 0.5% for the 200 MeV beam, and 0.04% and 0.2% for the 100 MeV beam. In a test case with a 150MeV proton beam, the mean difference between LETd computed by gPMC and TOPAS was 0.96% within the proton range. With the OpenCL implementation, gPMC is executable on AMD and Nvidia GPUs, as well as on Intel CPU in single or multiple threads. Results on different platforms agreed within statistical uncertainty.

Conclusion:

Several improvements have been implemented in the latest version of gPMC, which enhanced its accuracy, functionality, and code portability.
SU‐E‐T‐675: Remote Dosimetry with a Novel PRESAGE Formulation
Authors: Mein S , Juang T , Malcolm J , Adamovics J , Oldham M
Published: June 2015

Purpose:

3D‐gel dosimetry provides high‐resolution treatment validation; however, scanners aren't widely available. In remote dosimetry, dosimeters are shipped out from a central base institution to a remote site for irradiation, then shipped back for scanning and analysis, affording a convenient service for treatment validation to institutions lacking the necessary equipment and resources. Previous works demonstrated the high‐resolution performance and temporal stability of PRESAGE. Here the newest formulation is investigated for remote dosimetry use.

Methods:

A new formulation of PRESAGE was created with the aim of improved color stability post irradiation. Dose sensitivity was determined by irradiating cuvettes on a Varian Linac (6MV) from 0–15Gy and measuring change in optical density at 633nm. Sensitivity readings were tracked over time in a temperature control study to determine long‐term stability. A large volume study was performed to evaluate the accuracy for remote dosimetry. A 1kg dosimeter was pre‐scanned, irradiated on‐site with an 8Gy 4field box treatment, post‐scanned and shipped to Princess Margaret Hospital for remote reading on an identical scanner.

Results:

Dose sensitivities ranged from 0.0194–0.0295 ΔOD/(Gy*cm)—similar to previous formulations. Post‐irradiated cuvettes stored at 10°C retained 100% initial sensitivity over 5 days and 98.6% over 10 weeks while cuvettes stored at room temperature fell to 95.8% after 5 days and 37.4% after 10 weeks. The immediate and 5‐day scans of the 4field box dosimeter data was reconstructed, registered to the corresponding eclipse dose‐distribution, and compared with analytical tools in CERR. Immediate and 5‐day scans looked visually similar. Line profiles revealed close agreement aside from a slight elevation in dose at the edge in the 5‐day readout.

Conclusion:

The remote dosimetry formulation exhibits excellent temporal stability in small volumes. While immediate and 5‐day readout scans of large volume dosimeters show promising agreement, further development is required to reduce an apparent time dependent edge elevation.