Static Plans Research Articles

Customized Travel Planner using MapReduce and Approximation Algorithm

It is fun to travel but painful to arrange the trip. When travelers start off planning they need flights, accommodation and attractions. Which scattered across multiple websites on the internet? Traveler spends time scouting each of them for the best deals, and gets the attraction reviews from established planners in the market. It will be always good if traveler gives specified designations and time he wants to spend for the trip and some platform will automatically did everything for traveler with added bonus of optimal and customized itineraries. This system is designed for such travelers to design customized itineraries which will be optimal and consist of Point-Of-Interest (POI) selected by traveler, rather than go and visit the traditional and static trip plans by many travel agencies. This system is two-stage processing system for cost effective and optimal results. First is preprocessing stage works offline uses parallel processing engine as MapReduce to precompute Single-Day Itineraries. In further stage which is online the precomputed itineraries are combined to give multiday itineraries. These itineraries produced are optimal as per travelers selected Point-OfInterest (POI).Here Greedy Approximation Algorithm is used to combine the single day itineraries. In this way TeamOrienteering-Problem (TOP) is transferred to Set-Packing Problem another NP-complete problem.

Evaluation and Study on the Bearing Capacity of Deck Type Concrete Arch Bridge

As more and more arch bridges built with the construction method of cantilever erection, the strength and entirety of the bridge shall worry the designers. This paper studies an arch bridge with a 65-meter span, gives the static loading test plan and the dynamic test plan, analyzes the testing data of the displacement and strain, explains the methods of static and dynamic load test in detail, and gives a conclusion about the bearing capacity and dynamic properties of bridge. This can be referred by the similar bridge.

SU-C-210-02: Impact of Intrafractional Motion On TomoTherapy Stereotactic Body Radiotherapy (SBRT) 4D Dosimetry

Purpose: TomoTherapy treatment has unique challenges in handling intrafractional motion compared to conventional LINAC. This study is aimed to gain a realistic and quantitative understanding of motion impact on TomoTherapy SBRT treatment of lung and prostate cancer patients. Methods: A 4D dose engine utilizing GPUs and including motion during treatment was developed for the efficient simulation of TomoTherapy delivered dosimetry. Two clinical CyberKnife lung cases with respiratory motion tracking and two prostate cases with a slower non-periodical organ motion treated by LINAC plus Calypso tracking were used in the study. For each disease site, one selected case has an average motion (6mm); the other has a large motion (10mm for lung and 15mm for prostate). SBRT of lung and prostate cases were re-planned on TomoTherapy with 12 Gyx4 fractions and 7Gyx5 fractions, respectively, all with 95% PTV coverage. Each case was planned with 4 jaw settings: 1) conventional 1cm static, 2) 2.5cm static, 3) 2.5cm dynamic, and 4) 5cm dynamic. The intrafractional rigid motion of the target was applied in the dose calculation of individual fractions of each plan and total dose was accumulated from multiple fractions. Results: For 1cm static jaw plans with motions applied, PTV coverage is related to motion type and amplitude. For SBRT patients with average motion (6mm), the PTV coverage remains > 95% for lung case and 74% for prostate case. For cases with large motion, PTV coverage drops to 61% for lung SBRT and 49% for prostate SBRT. Plans with other jaws improve uniformity of moving target, but still suffer from poor PTV coverage (< 70%). Conclusion: TomoTherapy lung SBRT is less motion-impacted when average amplitude of respiratory-induced intrafractional motion is present (6mm). When motion is large and/or non-periodic (prostate), all studied plans lead to significantly decreased target coverage in actual delivered dosimetry.

SU‐E‐T‐367: Evaluate the Dosimetric Impacts On Patient Specific Treatment Plans Due to Set Up Uncertainties During LINAC Annual QA and Commission

Purpose:To quantify the dosimetric impact on patient's specific treatment plans due to set up uncertainties during LINAC commission and annual QA and to determine the maximum set up uncertainty allowance range.Methods:A 60×60×60 cm3 solid water cube was created in Varian Eclipse TPS. Beam data profiles (crossline and diagonal) and PDDs for field sizes ranging from 2×2 cm2 to 40×40 cm2 were simulated. Three main uncertainty scenarios were purposely introduced for gantry position tilts (0–5°), source axis distance changes (100–105 cm), and iso‐center position shifts (0–5 mm) during the simulation. A gamma analysis was used to compare the correct simulated profiles with the profiles for each scenario. Two static IMRT treatment plans (H&amp;N and GYN) with tumors at 5 cm and 15 cm depths were compared using similar set up uncertainties.Results:A gamma analysis using ±3%/±3mm with 90% passing rate criteria is included to show the passing rate for each scenario. Crossline and diagonal profiles showed a gamma passing rating of ≥ 90% at depth ≤10 cm for these scenarios: gantry tilted from 0–5°, SAD changed from 100–105 cm, and iso‐center shifted ≤ 4 mm. From 10 to 20 cm depths, all three scenarios failed with gamma passing ≤ 90% excepted for diagonal profiles at Gantry =2°, SAD =1 cm, and iso‐center =1 mm off center. Diagonal profiles showed a higher gamma passing rating compared to crossline profiles for all three scenarios. PDD differences also increased as depth increased. For patient's specific treatment plans, maximum uncertainties allowed to obtain a ≥90% gamma passing rating are: gantry tilts ±1 degree, SAD shifts ±2 cm, and iso‐center moves ±3 mm.Conclusion:This study validated AAPM TG 142 recommendations on the mechanical and dosimetry uncertainties and provided proofs on maximum acceptance tolerances for LINAC annual QA and commission.

TU-AB-303-12: Towards Inter and Intra Fraction Plan Adaptation for the MR-Linac

Purpose: To develop a new sequencer for IMRT that during treatment can account for anatomy changes provided by online and real-time MRI. This sequencer employs a novel inter and intra fraction scheme that converges to the prescribed dose without a final segment weight optimization (SWO) and enables immediate optimization and delivery of radiation adapted to the deformed anatomy. Methods: The sequencer is initially supplied with a voxel-based dose prescription and during the optimization iteratively generates segments that provide this prescribed dose. Every iteration selects the best segment for the current anatomy state, calculates the dose it will deliver, warps it back to the reference prescription grid and subtracts it from the remaining prescribed dose. This process continues until a certain percentage of dose or a number of segments has been delivered. The anatomy changes that occur during treatment require that convergence is achieved without a final SWO. This is resolved by adding the difference between the prescribed and delivered dose up to this fraction to the prescription of the subsequent fraction. This process is repeated for all fractions of the treatment. Results: Two breast cases were selected to stress test the pipeline by producing artificial inter and intra fraction anatomy deformations using a combination of incrementally applied rigid transformations. The dose convergence of the adaptive scheme over the entire treatment, relative to the prescribed dose, was on average 8.6% higher than the static plans delivered to the respective deformed anatomies and only 1.6% less than the static segment weighted plans on the static anatomy. Conclusion: This new adaptive sequencing strategy enables dose convergence without the need of SWO while adapting the plan to intermediate anatomies, which is a prerequisite for online plan adaptation. We are now testing our pipeline on prostate cases using clinical anatomy deformation data from our department. This work is financially supported by Elekta AB, Stockholm, Sweden.

WE‐EF‐303‐02: BEST IN PHYSICS (JOINT IMAGING‐ THERAPY): A Comprehensive Simulation of Image Guided Beam Gating for Liver Tumor Treatments Using Scanned Proton Therapy

Purpose:To evaluate the effectiveness of image guided beam gating for PBS liver treatments under realistic breathing conditions.Methods:We have previously proposed a Beams’ Eye View (BEV) X‐ray image system as an online motion monitoring device for deriving a gating signal for PBS proton therapy. Using dedicated 4D dose calculations (4DDC), in this work we have simulated gated liver treatments using three amplitude‐based gating windows (10/5/3mm) based on motion extracted from BEV imaging of fiducial markers or the diaphragm. In order to improve motion mitigation, BEV guided gating has also been combined with either volumetric (VS) or layered (LS) rescanning. Nine 4DCT(MRI) liver data‐sets have been used for the investigation, which not only consider realistic patient geometries but also motion variations between different breathing cycles. All 4D plans have been quantified in terms of plan homogeneity in the PTV (D5‐D95), the total estimated treatment time and the beam‐on duty cycle.Results:Neither gating nor rescanning can fully retrieve a comparable plan homogeneity to the static case, and considerable reductions of the duty cycle (&lt;10%) were observed as a Result motion variations when small gating windows are used. However, once combined with rescanning, dose homogeneity within 1% of the static plan could be achieved with reasonable prolongation of the treatment time for all 9 subjects. No differences were observed between the efficacy of layered or volumetric re‐scanning, or of gating signals extracted from fiducial or diaphragm motions. However, layered rescanning may be preferred over volumetric rescanning when performed in combination with gating as it is generally more time‐efficient and dosimetrically robust to patient and motion variationsConclusionCombining BEV beam gating with rescanning is an efficient and effective approach to treating mobile liver tumours, and is equally effective if either the diaphragm or fiducial markers are used as motion surrogates.

Construction of indoor floor plan and localization

Indoor positioning and tracking services are garnering more attention. Recently, several state-of-the-art localization techniques have been proposed that use radio maps or the sensors readily available on smartphones. This paper presents a localization system called construction of indoor floor plan and localization (CALL), which is based on a floor plan, access points (APs), and smartphone sensors. The public access points provide a number of reference points that can be used to build the floor plan automatically, and acquire the user initial position. Moreover, The APs are used to calibrate and adjust the user's position, distance, and direction in real time. Smartphone sensors are used to detect the number of steps and the direction. The proposed method is implemented on a smartphone and tested in real indoor environments. Our experiment with CALL demonstrates that using a static floor plan instead of radio map will avoid the costly database updates and searches that are usually required in other approaches due to signal attenuation. It shows that CALL outperforms the existing works in terms of accuracy and effectiveness in indoor localization.

Planning for mARC treatments with the Eclipse treatment planning system.

While modulated arc (mARC) capabilities have been available on Siemens linear accelerators for almost two years now, there was, until recently, only one treatment planning system capable of planning these treatments. The Eclipse treatment planning system now offers a module that can plan for mARC treatments. The purpose of this work was to test the module to determine whether it is capable of creating clinically acceptable plans. A total of 23 plans were created for various clinical sites and all plans delivered without anomaly. The average 3%/3 mm gamma pass rate for the plans was 98.0%, with a standard deviation of 1.7%. For a total of 14 plans, an equivalent static gantry IMRT plan was also created to compare delivery time. In all but two cases, the mARC plans delivered significantly faster than the static gantry plan. We have confirmed the successful creation of mARC plans that are deliverable with high fidelity on an ARTISTE linear accelerator, thus demonstrating the successful implementation of the Eclipse mARC module.PACS numbers: 87.55.D‐, 87.55.ne, 87.57.uq,

An analysis of load reduction and load shifting techniques in commercial and industrial buildings under dynamic electricity pricing schedules

Due to fluctuations in the supply and demand for electricity throughout the day, the wholesale cost to an electric utility to produce and provide electricity to customers varies continuously throughout the day. Presently, certain utilities are devising alternative electricity pricing structures that vary cost based upon the time in which electricity is used. Energy efficiency retrofits are typically conducted with consideration to static pricing plans for electricity and are indifferent to dynamic pricing policies. To be most effective, energy efficiency measures should be considered with regard to the time energy is used. This study investigates potential cost conservation measures that focus on reducing energy at times of higher energy costs to maximize energy savings. It is shown that shifting work schedules of office buildings with one shift 1h early can slightly reduce monthly electricity rates by 1–3% and that thermal energy storage systems can be cost effective for retrofits with dynamic pricing schedules and areas that need full replacement of air conditioning.

Multigating, a 4D Optimized Beam Tracking in Scanned Ion Beam Therapy

The treatment of moving tumors with a scanned ion beam is challenging due to interplay effects and changing beam range. We propose multigating, as a method for 4D-treatment optimization and delivery. In 3D beam tracking, tracking vectors are added during delivery to beam spot positions based on the detected motion phase. This has the disadvantage of dose errors in case of complex motion patterns and an uncertain out-of-target dose distribution. In multigating, the motion phase for each beam spot is predefined, which allows to add the tracking vector prior to beam weight optimization on all motion phases. The synchronization of delivery and target motion is assured by fast gating. The feasibility of the delivery was shown in a film experiment and required only minor software modification to the treatment planning system. In a treatment planning study in 4 lung cancer patients, target coverage could be restored to the level of a static reference plan by multigating (V95 > 99%) but not by standard beam tracking (V95 < 95%). The conformity of the multigating plans was only slightly lower than those of the static plan, with a conformity number of 72.0% (median, range 64.6–76.6%) compared to 75.8% (70.8–81.5%) in spite of target motion of up to 22 mm. In conclusion, we showed the technical feasibility of multigating, a 4D-optimization and delivery method using scanned beams that allows for conformal and homogeneous dose delivery to moving targets also in case of complex motion.

Efficacy of the Dynamic Jaw Mode in Helical Tomotherapy With Static Ports for Breast Cancer.

The recently developed dynamic jaw technology of tomotherapy can reduce craniocaudal dose spread without much prolonging the treatment time. This study aimed to investigate the efficacy of the dynamic jaw mode for tomotherapy of breast cancer. Static tomotherapy plans of the whole breast and supraclavicular regional lymph nodes, and plans for the whole breast only were generated in 25 patients with left-sided breast cancer. Plans with a field width of 2.5 or 5 cm with the dynamic or fixed jaw modes were made for each patient. The prescribed dose was 50 Gy in 25 fractions. In whole breast and supraclavicular nodal radiotherapy, dose distributions and homogeneity of the planning target volume (PTV) with the dynamic jaw mode were slightly inferior to those with the fixed jaw mode with a 5-cm field width (P < .05). However, lung low-dose volumes and mean doses of the larynx, thyroid, skin, and all the healthy tissues combined were smaller with the dynamic jaw mode than with the fixed jaw mode with a 5-cm field width (P < .001). In whole breast radiotherapy, mean doses of the skin and healthy tissues were lower with the dynamic jaw mode than with the fixed jaw mode with a 5-cm field width (P < .001) without significant differences in PTV dose distributions, homogeneity, and conformity. The dynamic jaw mode provided better sparing of organs at risks with minimal disturbance of dose–volume indices of PTV. Considering the treatment time, the 5-cm-field dynamic jaw mode is more efficient than the 2.5-cm fixed jaw mode.

When is respiratory management necessary for partial breast intensity modulated radiotherapy: A respiratory amplitude escalation treatment planning study

PurposeThe impact of typical respiratory motion amplitudes (∼2mm) on partial breast irradiation (PBI) is minimal; however, some patients have larger respiratory amplitudes that may negatively affect dose homogeneity. Here we determine at what amplitude respiratory management may be required to maintain plan quality. Methods and MaterialsTen patients were planned with PBI IMRT. Respiratory motion (2–20mm amplitude) probability density functions were convolved with static plan fluence to estimate the delivered dose. Evaluation metrics included target coverage, ipsilateral breast hotspot, homogeneity, and uniformity indices. ResultsDegradation of dose homogeneity was the limiting factor in reduction of plan quality due to respiratory motion, not loss of coverage. Hotspot increases were observed even at typical motion amplitudes. At 2 and 5mm, 2/10 plans had a hotspot greater than 107% and at 10mm this increased to 5/10 plans. Target coverage was only compromised at larger amplitudes: 5/10 plans did not meet coverage criteria at 15mm amplitude and no plans met minimum coverage at 20mm. ConclusionsWe recommend that if respiratory amplitude is greater than 10mm, respiratory management or alternative radiotherapy should be considered due to an increase in the hotspot in the ipsilateral breast and a decrease in dose homogeneity.

SU-E-T-185: Feasibility Study of Dose Rate Modulated Arc Therapy (DrMAT) for Lung SBRT

Purpose: To show the feasibility of clinical application of DrMAT for SBRT in lung cancer patients. DrMAT is a form of dynamic conformal arc therapy where MLC segments and dose rates are controlled through simple field weight optimization. Methods: To show feasibility a new treatment plan was created based on the CT of SBRT lung cancer patients. Static plans with 33 fields are made, which have 11deg in between each field and are acquired rotating gantry angle from 180deg to 188deg in CCW direction, total 352deg is rotated. MLC maintained static aperture for each field. To optimize 33 individual fields, field weight was adjusted accordingly using weight optimization algorithm. Keeping weights and MU of static plan, static MLC aperture was converted to multiple arc segments. Arc plan could be created with the fields in the intervals of 11deg. Static MLC should be converted to arc segment MLC. Dynamic conformal arc therapy plan consists of 33 arc fields, is converted to one dose rate modulated arc therapy (DrMAT) plan. DrMAT plan consists of 166 control points which becomes a single arc plan that changes the shape of MLC for every 2.2deg. The resulting DrMAT plan is not an inverse plan it is a simple form of dynamic conformal arc plan using field weight obtained from static plan. This is compared and evaluated with the VMAT plan. Results: DrMAT and VMAT plans have been compared based on the RTOG1021. Both DrMAT and VMAT plans satisfy 100% irradiation to 95% of PTV and critical organs did not exceed dose limit suggested in RTOG1021. DrMAT plan is almost similar with VMAT plan in Result. Conclusion: Field weight optimization method did not show better Resultcompared to VMAT optimization. However, considering simplicity, DrMAT satisfies the condition in RTOG1021. Therefore clinical application of DrMAT is feasible.

SU-E-T-203: Improvement of Dosimetric Quality and Delivery Efficiency with TomoEdge Dynamic Jaws

Purpose: The TomoEdge Dynamic jaws is the newest evolution to the TomoTherapy system. It opens the jaws dynamically as they sweep across the target. We report our initial experience with the TomoEdge by quantifying the dosimetric and plan efficiency as compared to the static jaw. Methods: A total of 15 cases, including five Head and neck, five localized prostrate and five prostrate with nodal involvement were selected in this study. For each case, four TomoHelical plans were generated using Tomotherapy planning system. The pitch and modulation factor were held constant for all plans, while jaw settings were changed, 2.5 cm static vs. dynamic and 5 cm static vs. dynamic jaws were used for each plan. Plan quality was evaluated using the conformity index for 95% isodose, homogeneity index, dose-volume histogram (DVHs), integral dose to the non-treatment volume (NTV), and dose profiles (defined at the center of the treatment volume in the longitudinal direction). To characterize the plan delivery efficiency, the treatment time and monitor units (MUs) of the four treatment plans were collected and analyzed. Results: Both dynamic and static jaw techniques yielded clinical acceptable plans with comparable dosimetric indices. The Homogeneity index and CI95 do not show a significant difference with regards to static versus swept jaws plans. Additionally, the CI50 index indicates that 5 cm dynamic setting is comparable to a 2.5 cm jaw. Most dramatically, the dose penumbra in the longitudinal direction is greatly reduced. This reduction of dose build up is apparent in the reduced mean dose to the non-treatment volume (NTV) with the dynamic jaw technique. Conclusion: TomoEdge dynamic jaw plans greatly improve the longitudinal conformity. Similar treatment time was achieved for dynamic and static jaw plans using the same jaw sizes, however, ≈ 50% of reduction of the delivery time is possible for 5 cm dynamic jaw plans.

SU-E-T-109: Development of An End-To-End Test for the Varian TrueBeamtm with a Novel Multiple-Dosimetric Modality H&amp;N Phantom

Purpose: To develop a comprehensive end-to-end test for Varian's TrueBeam linear accelerator for head and neck IMRT using a custom phantom designed to utilize multiple dosimetry devices. Methods: The initial end-to-end test and custom H&N phantom were designed to yield maximum information in anatomical regions significant to H&N plans with respect to: i) geometric accuracy, ii) dosimetric accuracy, and iii) treatment reproducibility. The phantom was designed in collaboration with Integrated Medical Technologies. A CT image was taken with a 1mm slice thickness. The CT was imported into Varian's Eclipse treatment planning system, where OARs and the PTV were contoured. A clinical template was used to create an eight field static gantry angle IMRT plan. After optimization, dose was calculated using the Analytic Anisotropic Algorithm with inhomogeneity correction. Plans were delivered with a TrueBeam equipped with a high definition MLC. Preliminary end-to-end results were measured using film and ion chambers. Ion chamber dose measurements were compared to the TPS. Films were analyzed with FilmQAPro using composite gamma index. Results: Film analysis for the initial end-to-end plan with a geometrically simple PTV showed average gamma pass rates >99% with a passing criterion of 3% / 3mm. Film analysis of a plan with a more realistic, ie. complex, PTV yielded pass rates >99% in clinically important regions containing the PTV, spinal cord and parotid glands. Ion chamber measurements were on average within 1.21% of calculated dose for both plans. Conclusion: trials have demonstrated that our end-to-end testing methods provide baseline values for the dosimetric and geometric accuracy of Varian's TrueBeam system.

SU‐E‐T‐425: Spherical Dose Distributions for Radiosurgery Using a Standardized MLC Plan

Purpose:To investigate a standardized MLC treatment plan to generate small spherical dose distributions.Methods:The static virtual cone plan comprised six table positions with clockwise and counterclockwise arcs having collimator angles 45 and 135 degrees, respectively, at each position. The central two leaves of a 2.5 mm leaf width MLC were set to a constant gap. Control points were weighted proportional to the sine of the gantry angle. Plans were created for the 10 MV flattening‐filter‐free beam of a TrueBeam STx (Varian Medical Systems) with gaps of 1, 1.5, 2, and 3 mm and were delivered to a phantom containing radiochromic film. Dose was calculated using the Eclipse AAA (Varian Medical Systems). A dynamic plan in which the table and gantry moved simultaneously with 1.5 mm gap was also created and delivered using the TrueBeam developer mode.Results:The full‐width‐half‐max (FWHM) varied with leaf gap, ranging from 5.2 to 6.2 mm. Calculated FWHM was smaller than measured by 0.7 mm for the 1 mm gap and ≤ 0.4 mm for the larger gaps. The measured‐to‐calculated dose ratio was 0.93, 0.96, 1.01, and 0.99 for 1 mm, 1.5 mm, 2 mm, and 3 mm gaps, respectively. The dynamic results were the same as the static. The position deviations between the phantom target position and the center of the dose distribution were &lt; 0.4 mm.Conclusion:The virtual cone can deliver spherical dose distributions suitable for radio surgery of small targets such as the trigeminal nerve. The Eclipse AAA accurately calculates the expected dose, particularly for leaf gap ≥ 1.5 mm. The measured dose distribution is slightly larger than the calculation, which is likely due to systematic leaf position error, isocenter variation due to gantry sag and table eccentricity, and inaccuracy in MLC leaf end modeling.

MO‐F‐16A‐01: Implementation of MPPG TPS Verification Tests On Various Accelerators

Purpose:To demonstrate the implementation of the Medical Physics Practice Guideline (MPPG) for dose calculation and beam parameters verification of treatment planning systems (TPS).Methods:We implemented the draft TPS MPPG for three linacs: Varian Trilogy, TomoHDA and Elekta Infinity. Static and modulated test plans were created. The static fields are different than used in commissioning. Data was collected using ion chambers and diodes in a scanning water tank, Delta4 phantom and a custom phantom. MatLab and Microsoft Excel were used to create analysis tools to compare reference DICOM dose with scan data. This custom code allowed for the interpolation, registration and gamma analysis of arbitrary dose profiles. It will be provided as open source code. IMRT fields were validated with Delta4 registration and comparison tools. The time for each task was recorded.Results:The tests confirmed the strengths, and revealed some limitations, of our TPS. The agreement between calculated and measured dose was reported for all beams. For static fields, percent depth dose and profiles were analyzed with criteria in the draft MPPG. The results reveal areas of slight mismatch with the model (MLC leaf penumbra, buildup region.) For TomoTherapy, the IMRT plan 2%/2 mm gamma analysis revealed poorest agreement in the low dose regions. For one static test plan for all 10MV Trilogy photon beams, the plan generation, scan queue creation, data collection, data analysis and report took 2 hours, excluding tank setup.Conclusions:We have demonstrated the implementation feasibility of the TPS MPPG. This exercise generated an open source tool for dose comparisons between scan data and DICOM dose data. An easily reproducible and efficient infrastructure with streamlined data collection was created for repeatable robust testing of the TPS. The tests revealed minor discrepancies in our models and areas for improvement that are being investigated.

SU-E-T-400: Optimized 2D Motion Tracking Using Dynamic Multi-Leaf Collimator (DMLC) for a Clinical Volumetric Modulated Arc Therapy (VMAT) Plan

Purpose: This study is to develop a 2D motion tracking algorithm combined with controlled shallow breathing and collimator angle optimization to improve MLC tracking accuracy. Method and Materials: One SBRT VMAT plan for lung cancer (2 Arcs; 8 Gy/fx in 4 fx) was selected. A non-motion 3D VMAT plan was generated based on GTV from one single selected phase of the 4DCT. A motion tracking algorithm using MATLAB was developed to modify MLC positions of the 3D VMAT DICOM file based on an ideal breathing motion model. We derived the correlations between gantry angle, collimator angle and motion amplitudes in SI and AP directions that projected onto MLC aperture. All delivery constraints followed mechanical limits of Varian TrueBeam. To avoid large time interval between adjacent control points, motion amplitudes restriction and collimator angle optimization were incorporated into the algorithm. Each arc was then divided into 6 sub-arcs corresponding to the 6 breathing phases. Sub-arc doses were individually calculated and merged to acquire the 4D dose distribution. DVH comparison and 3D gamma were used for dosimetric evaluation. Results: Total delivery time of static 3D VMAT plan (collimator=45°), plan with MLC tracking under free breathing (collimator=45°, SI=10mm and AP=8mm), plan with collimator angle optimized only (collimator=77.8°, SI=10mm and AP=8mm) and collimator angle optimized under shallow breathing (collimator=80.1°, SI=8.3mm, AP=6.6mm) were 135.7s, 235.3s, 213.9s and 188.5s, respectively. Compared with the non-motion 3D VMAT, optimized MLC tracking demonstrated small changes in target dose (%ΔD90=1%, 3D gamma passing rate=97.5%). Conclusions: Total delivery time of VMAT with tracking tends to decrease as collimator angle approaches to 90°. At selected angle, plan with shorter breathing cycle period has longer delivery time when using MLC for motion compensation. MLC tracking combined with shallow breathing and optimized collimator angle cannot only reduce delivery time but increase the tracking accuracy.

SU-E-T-106: Development of a Collision Prediction Algorithm for Determining Problematic Geometry for SBRT Treatments Using a Stereotactic Body Frame

Purpose: Collision between the gantry and the couch or patient during Radiotherapy is not a common concern for conventional RT (static fields or arc). With the increase in the application of stereotactic planning techniques to the body, collisions have become a greater concern. Non-coplanar beam geometry is desirable in stereotatic treatments in order to achieve sharp gradients and a high conformality. Non-coplanar geometry is less intuitive in the body and often requires an iterative process of planning and dry runs to guarantee deliverability. Methods: Purpose written software was developed in order to predict the likelihood of collision between the head of the gantry and the couch, patient or stereotatic body frame. Using the DICOM plan and structures set, exported by the treatment planning system, this software is able to predict the possibility of a collision. Given the plan's isocenter, treatment geometry and exterior contours, the software is able to determine if a particular beam/arc is clinically deliverable or if collision is imminent. Results: The software was tested on real world treatment plans with untreatable beam geometry. Both static non-coplanar and VMAT plans were tested. Of these, the collision prediction software could identify all as having potentially problematic geometry. Re-plans ofmore » the same cases were also tested and validated as deliverable. Conclusion: This software is capable of giving good initial indication of deliverability for treatment plans that utilize complex geometry (SBRT) or have lateral isocenters. This software is not intended to replace the standard pre-treatment QA dry run. The effectiveness is limited to those portions of the patient and immobilization devices that have been included in the simulation CT and contoured in the planning system. It will however aid the planner in reducing the iterations required to create complex treatment geometries necessary to achieve ideal conformality and organ sparing.« less

Accounting for respiratory motion in partial breast intensity modulated radiotherapy during treatment planning: A new patient selection metric

PurposeExternal beam partial breast irradiation intensity modulated radiotherapy (PBI IMRT) plans experience degradation in coverage and dose homogeneity when delivered during respiration. We examine which characteristics of the breast and seroma result in unacceptable plan degradation due to respiration. MethodsThirty-six patient datasets were planned with inverse-optimised PBI IMRT. Population respiratory data were used to create a probability density function. This probability density function (PDF) was convolved with the static plan fluences to calculate the delivered dose with respiration. To quantify the difference between static and respiratory plan quality, we analysed the mean dose shift of the target dose volume histogram (DVH), the dose shift at 95% of the volume and the dose shift at the hotspot to 2cm3of the volume. We explore which patient characteristics indicate a clinically significant degradation in delivered plan quality due to respiration. ResultsDose homogeneity constraints, rather than dosimetric coverage, were the limiting factors for all patient plans. We propose the dose evaluation volume-to-planning target volume (DEV-to-PTV) ratio as a delineating metric for identifying patient plans that will be more degraded by respiratory motion. The DEV-to-PTV ratio may be a more robust metric than ipsilateral breast volume because the seroma volume is contoured more consistently between physicians and clinics. ConclusionsFor patients with a DEV-to-PTV ratio less than 55% we recommend either not using PBI IMRT or employing motion management. Small DEV-to-PTV ratios occur when the seroma is close to inhomogeneities (i.e. air/lung), which exacerbates the dosimetric effect of respiratory motion. For small breast sizes it is unlikely that the DEV-to-PTV ratio will meet these criteria.