Treatment Planning System Commissioning Research Articles

The influence of basic plan parameters on calculated small field output factors – A multicenter study

The influence of basic plan parameters such as slice thickness, grid resolution, algorithm type and field size on calculated small field output factors (OFs) was evaluated in a multicentric study. Three computational homogeneous water phantoms with slice thicknesses (ST) 1, 2 and 3mm were shared among twenty-one centers to calculate OFs for 1x1, 2x2 and 3x3 cm2 field sizes (FSs) (normalized to 10x10 cm2 FS), with their own treatment planning system (TPS) and the energy clinically used for stereotactic body radiation therapy delivery. OFs were calculated for each combination of grid resolution (GR) (1, 2 and 3mm) and ST and finally compared with the OFs measured for the TPS commissioning. A multivariate analysis was performed to test the effect of basic plan parameters on calculated OFs. A total of 509 data points were collected. Calculated OFs are slightly higher than measured ones. The multivariate analysis showed that Center, GR, algorithm type, and FS are predictive variables of the difference between calculated and measured OFs (p<0.001). As FS decreases, the spread in the difference between calculated and measured OFs became larger when increasing the GR. Monte Carlo and Analytical Anisotropic Algorithms, presented a dependence on GR (p<0.01), while Collapsed Cone Convolution and Acuros did not. The effect of the ST was found to be negligible. Modern TPSs slightly overestimate the calculated small field OFs compared with measured ones. Grid resolution, algorithm, center number and field size influence the calculation of small field OFs.

Integrating X-ray kV millimetric field dosimetry with a synthetic diamond detector into the treatment planning system commissioning of a preclinical irradiator.

Small animal irradiators are equipped with x-ray beams and cone collimators with millimeter dimensions to be used in preclinical research. The use of small fields in the kV energy range may require the application of energy-dependent, field size-dependent, or depth-dependent correction factors to the dosimetric data acquired for treatment planning system (TPS) commissioning purposes to obtain accurate dose values. Considering that these corrections are also detector dependent, the suitability of a synthetic single-crystal diamond detector for small-field relative dosimetry in a preclinical irradiator (220-kVp) was evaluated to avoid the necessity of applying correction factors during TPS commissioning. The detector response was assessed during the transition for field sizes ranging from 20×20mm2 to 3×3mm2 , using the small animal radiation research platform (SARRP). The percentage depth dose distributions (PDDs), lateral profiles and output factors (OFs) were measured. The PDDs for the synthetic diamond detector were compared to the distributions acquired using a small-volume microchamber (0.016cm3 ) and with Monte Carlo calculations using the MC3D in-house software package. The profiles and OFs were compared to the data from a silicon solid-state detector and to radiochromic film data provided by the manufacturer; for the OF determination, measurements made using a microchamber were added for comparison. The performance of several detectors used as references was previously validated for relative dosimetry in preclinical irradiators. A commercial TPS was commissioned for the factor-based algorithm, using the data acquired with the diamond detector, and no additional correction factors were applied. To verify the performance of the TPS and the accuracy of the dosimetric methodology, radiochromic film irradiation in water was conducted, and two-dimensional (2D) dose distributions in the coronal and axial planes were compared under different gamma criteria. Compared with the microchamber and MC3D distributions, the agreement of the PDDs using the synthetic diamond detector was better than 2%. The profile data exhibited very good agreement compared with the data from the silicon detector, with an average and a maximum difference of 0.31 and 0.39mm in the penumbras, respectively. Compared with the data from the radiochromic film, the average and maximum differences were equal to 0.77 and 0.89mm, respectively. Very good agreement, within 1%, was obtained between the OFs measured with the synthetic diamond detector and the radiochromic film, compared only for the cone collimators. The validation of the TPS commissioning using gamma criteria compared to film showed an average passing rate of 100% and 93.2% with a global gamma criterion of 1mm/3% for the coronal and axial planes, respectively, including the 3×3mm2 field size and penumbra regions. Synthetic diamond is a suitable detector for the complete relative dosimetry of small x-ray fields. The commissioning of the TPS with its own beam dosimetric data exhibited encouraging results even in a 3×3mm2 field and penumbra region. This methodology allows for the prediction of 2D dose distributions with an accuracy in water ranging from 3 to 5% compared to the 2D distribution from film dosimetry.

Dose calculation accuracy in proximity of a pacemaker: A multicenter study with threecommercial treatment planning systems.

This study compares Treatment Planning System (TPS) out of field dose calculation on a pacemaker (PMK) during external beam radiotherapy treatment. We consider four TPSs (Elekta-Monaco, Oncentra- Masterplan and two Philips-Pinnacle3) commissioned for two linacs (Elekta Sinergy and Varian Clinac) delivering two test beams (a highly modulated one and a square field) and two clinical breast plans. To calculate and measure dose to a PMK we built a Real Water3 phantom with a PMK embedded in it. Measures are performed with thermo-luminescent dosimeters and Mosfet dosimeters. We evaluate differences between TPS calculated values for the dose to the PMK (both point dose and dose-volume histogram parameters) when the PMK is positioned in the first 10cm outside the radiation fields. TPS calculation accuracy is evaluated comparing such values with measures. Differences in TPS calculations are on average 3.5cGyGy-1 for the modulated beam, and always lower than 2cGyGy-1 for the square beam. TPS dose calculation depends mostly on the TPS algorithm and model rather than the linac commissioned. TPSs considered show different degrees of calculation accuracy. In the first 4cm to the field edge three out of four TPSs are in good agreement with measurements in the square beam, but only one keeps the agreement in the modulated beam: the others show over and underestimations up to +20% -40%. The same accuracy is found considering a homogeneous phantom. Our results confirm what reported in previous studies and highlight the impact of TPS commissioning.

Migration of treatment planning system using existing commissioned planning system

AbstractIntroduction:Commissioning of a new planning system involves extensive data acquisition which can be onerous involving significant clinic downtime. This could be circumvented by extracting data from existing treatment planning system (TPS) to speed up the process.Material and methods:In this study, commissioning beam data was obtained from a clinically commissioned TPS (Pinnacle™) using Matlab™ generated Pinnacle™ executable scripts to commission an independent 3D dose verification TPS (Eclipse™). Profiles and output factors for commissioning as required by Eclipse™ were computed on a 50 × 50 × 50 cm3 water phantom at a dose grid resolution of 2 mm3. Verification doses were computed and compared to clinical TPS dose profiles based on TG-106 guidelines. Standard patient plans from Pinnacle™ including intensity modulated radiation therapy and volumetric modulated arc therapy were re-computed on Eclipse™ TPS while maintaining the same monitor units. Computed dose was exported back to Pinnacle for comparison with the original plans. This methodology enabled us to alleviate all ambiguities that arise in such studies.Results:Profile analysis using in-house software showed that for all field sizes including small multi-leaf collimator-generated fields, &gt;95% of infield and penumbra data points of Eclipse™ match Pinnacle™ generated and measured profiles with 2%/2 mm gamma criteria. Excellent agreement was observed in the penumbra regions, with &gt;95% of the data points passing distance to agreement criteria for complex C-shaped and S-shaped profiles. Dose volume histograms and isodose lines of patient plans agreed well to within a 0·5% for target coverage.Findings:Migration of TPS is possible without compromising accuracy or enduring the cumbersome measurement of commissioning data. Economising time for commissioning such a verification system or for migration of TPS can add great QA value and minimise downtime.

40. Design of a national survey to assess the technology applied to SBRT

Purpose Stereotactic body radiation therapy (SBRT) approach for treating early stage solid tumor and metastases is increasing worldwide. In 2013 the Italian Association of Medical Physicists (AIFM) constituted a working group in order to standardize SBRT dosimetric aspects. A survey was designed aiming to delineate the status of the technology applied in SBRT on a national level. Clinical evaluation of SBRT was out of the present study. Methods A questionnaire was designed by three medical physicists expert of SBRT using Google Forms containing questions regarding image-guidance solutions, respiratory management, delivery mode, treatment planning system (TPS) commissioning, and QA approach. A large number of medical physicists from 54 centers with heterogeneous technology was invited to participate and 45 of them completed the survey. Experts were asked to provide suggestions based on personal experience and specificity. Results After two webcall and two versions, the final questionnaire was developed. Results showed great heterogeneity in terms of technologies, image-guidance solutions, respiratory management, delivery mode, TPS commissioning and QA approach. The most available delivery system was conventional linacs with VMAT modality; the most common energies used were 6 MV and 6 MV-FFF; for the 56% of centers robotic couch was available, CBCT was the most used IGRT technique (78% of centers) and 40% of centers did not use respiratory management during treatment delivery. The smallest measured field size for lateral beam profiles was lower than 1 × 1 cm2, while only the 62% of centers used the same field size for the TPS commissioning (from 1 × 1 cm2 to 4 × 4 cm2). A large number of centers (51%) feel the necessity to upgrade their dosimetric devices dedicated to SBRT QA. Conclusions This survey on SBRT could allow to improve the QA procedure and to define minimum requirements for SBRT dosimetric verification. Stereotactic body radiation therapy (SBRT) approach for treating early stage solid tumor and metastases is increasing worldwide. In 2013 the Italian Association of Medical Physicists (AIFM) constituted a working group in order to standardize SBRT dosimetric aspects. A survey was designed aiming to delineate the status of the technology applied in SBRT on a national level. Clinical evaluation of SBRT was out of the present study. A questionnaire was designed by three medical physicists expert of SBRT using Google Forms containing questions regarding image-guidance solutions, respiratory management, delivery mode, treatment planning system (TPS) commissioning, and QA approach. A large number of medical physicists from 54 centers with heterogeneous technology was invited to participate and 45 of them completed the survey. Experts were asked to provide suggestions based on personal experience and specificity. After two webcall and two versions, the final questionnaire was developed. Results showed great heterogeneity in terms of technologies, image-guidance solutions, respiratory management, delivery mode, TPS commissioning and QA approach. The most available delivery system was conventional linacs with VMAT modality; the most common energies used were 6 MV and 6 MV-FFF; for the 56% of centers robotic couch was available, CBCT was the most used IGRT technique (78% of centers) and 40% of centers did not use respiratory management during treatment delivery. The smallest measured field size for lateral beam profiles was lower than 1 × 1 cm2, while only the 62% of centers used the same field size for the TPS commissioning (from 1 × 1 cm2 to 4 × 4 cm2). A large number of centers (51%) feel the necessity to upgrade their dosimetric devices dedicated to SBRT QA. This survey on SBRT could allow to improve the QA procedure and to define minimum requirements for SBRT dosimetric verification.

A simple method for determining dosimetric leaf gap with cross-field dose width for rounded leaf-end multileaf collimator systems

PurposeThe dosimetric leaf gap (DLG) and multileaf collimator (MLC) transmission are two important systematic parameters used to model the rounded MLC leaf ends effect when commissioning an Eclipse treatment planning system (TPS). Determining the optimal DLG is a time consuming process. This study develops a simple and reliable method for determining the DLG using the cross-field dose width.Methods and materialsA Varian TrueBeam linac with 6 MV, 10 MV, 6 MV flattening filter free (FFF) and 10 MV FFF photon beams and equipped with the 120 Millennium MLC and the Eclipse™ TPS was used in this study. Integral sliding fields and static slit MLC field doses with different gap widths were measured with an ionization chamber and GAFCHROMIC EBT3 films, respectively. Measurements were performed for different beam energies and at depths of 5 and 10 cm. DLGs were derived from a linear extrapolation to zero dose and intercepting at the gap width axis. In the ion chamber measurements method, the average MLC leaf transmission to the gap reading for each gap (RgT) were calculated with nominal and cross-field dose widths, respectively. The cross-field dose widths were determined according to the dose profile measured with EBT3 films. Additionally, the optimal DLG values were determined using plan dose measurements, as the value that produced the closest agreement between the planned and measured doses. DLGs derived from the nominal and cross-field dose width, the film measurements, and the optimal process, were obtained and compared.ResultsThe DLG values are insensitive to the variations in depth (within 0.07 mm). DLGs derived from nominal gap widths showed a significantly lower values (with difference about 0.5 mm) than that from cross-field dose widths and from film measurements and from plan optimal values. The method in deriving DLGs by correcting the nominal gap widths to the cross-field dose widths has shown good agreements to the plan optimal values (with difference within 0.21 mm).ConclusionsThe DLG values derived from the cross-field dose width method were consistent with the values derived from film measurements and from the plan optimal process. A simple and reliable method to determine DLG for rounded leaf-end MLC systems was established. This method provides a referable DLG value required during TPS commissioning.

P151] Implementation of advanced techniques in radiotherapy and comparison to standard 3DCRT plans- initial institutional experience

Purpose The transition from three-dimensional conformal therapy (3DCRT) to intensity modulated (IMRT) or volumetric modulated arc therapy (VMAT) requires implementation of complex advanced dosimetry, fully commissioned treatment planning system (TPS), machine and other equipment and skills of employees. IMRT/VMAT is implemented in our clinic one year ago. Methods Twenty-one gynecological patient treated in our clinic was selected for the study. Patients were planned for 3D CRT, but due to unacceptable doses to organs at risk (QUANTEC), treatment plans for IMRT or VMAT were generated, and dosimetrically verified before treatment delivery. The TPS used was Monaco 5.11 (Elekta) with Monte Carlo (VMAT) and Collapsed Cone (3DCRT) algorithm.The treatments were delivered by Versa HD (Elekta, Crawley, UK) using 10 MV (VMAT) and 15MV (3DCRT). The patients were prescribed 50.4 Gy/28 fractions (4) and 45 Gy/25 fractions (17 patients). The coverage of PTV and doses to organs at risk were recorded, both for VMAT/IMRT treatment and 3DCRT. Results Coverage PTV: The ICRU 83 criteria for PTV coverage were fulfilled in all 3DCRT/VMAT/IMRT plans. Doses to OARS: in average, the V45 in small bowel in IMRT/VMAT plans was approximately 6 times smaller than the same of 3DCRT plans. The V45 of small bowels was in average 45cm3 in IMRT/VMAT plans, while in 3DCRT plans it was 233 cm3. In case of femoral head, significant reduction in V30 (9.8 % vs. 33.1%) and mean dose in case of IMRT/VMAT plans. Rectum was planned with significantly less dose in terms of V30 (79.5% vs 95.2%) in IMRT/VMAT plans. Bladder was better spared in VMAT plans in terms of V40 (51% vs. 91%), but maximum dose was higher in VMAT plans than in 3DCRT (50.1 Gy to 48.1 Gy in average). Homogeneity index was in average 0.11 for VMAT plans and 0.09 for 3DCRT plans. Conclusion Both 3DCRT and IMRT/VMAT provided good coverage of PTV, but analysis of dosimetric data revealed significant differences in normal tissue doses. The advanced treatment planning, evaluation, dosimetric evaluation and delivery is far more complex than the same for 3DCRT,but patient benefit (OAR sparing) confirms necessity for implementation of advanced techniques.

OA036] Clinical implementation and evaluation of the Mobius3D system for independent dose calculation

Purpose The complexity of dose planning and treatment delivery systems has increased and necessitates a more comprehensive physics quality assurance (QA). These QA checks can, however, be quite time consuming. Therefore, there is a need for automation of QA which usually rely on empirically established tolerance levels. Mobius3D is a commercial fully automated QA system that uses a collapsed cone convolution/superposition algorithm for verification of treatment plans. The purpose of this study was to investigate the level of deviation between this system and the clinical commissioned treatment planning system (Eclipse v.13.5) using the Anisotropic Analytical Algorithm when the MLC modeling was optimized. Methods The Mobius3D system comes with golden beam data and calculates the dose on the patient CT data set. For MLC optimization, 8 IMRT/VMAT plans from various anatomical regions were included and recalculated in a cylindrical plastic phantom containing two planar diode arrays (Delta4 phantom, ScandiDos). The plans were then verified experimentally at the accelerator and all passed a local 3%/2 mm gamma criteria (passing rate > 90%). The dosimetric leaf gap (DLG) used to model the MLC in Mobius3D was optimized to keep the PTV mean dose of the 8 plans within 2% in the Delta4 geometry resulting in a +0.6 mm adjustment of the DLG from the default value. To establish the level of dose deviation and establish acceptance criteria, 34 treatment plans in different geometries, such us lung (10), head and neck (HN, 10), and pelvis (14) were evaluated for both IMRT and VMAT. Results The absolute mean and max PTV dose deviation for (lung/HN/pelvis) were: 0.8/2.2/2.1% and 1.4/2.9/2.8%. All max deviations were positive, i.e. a higher dose estimate by Mobius3D. 5 HN IMRT plans before DLG adjustment all showed negative deviations of −3.12/−3.8% (PTV mean/max). Conclusions A random sample of treatment plans were within 2.5% in absolute mean dose of the PTV between Mobius3D and the TPS. MLC parameter optimization plays an important role in establishing an acceptance criterion.

Validation of MLC-based linac radiosurgery for trigeminal neuralgia.

This study details a validation process for linear accelerator‐based treatment of trigeminal neuralgia using HD‐MLC field collimation. Nine trigeminal neuralgia treatment plans utilizing HD‐MLC were selected for absolute dose measurement at isocenter using a commercial scintillating detector in an anthropomorphic phantom. Four plans were chosen for film dosimetry measurements in each of the three principal planes to assess spatial dose distribution agreement with the treatment planning system. Additionally, trajectory log analysis for each treatment field in the nine cases was performed to assess mechanical positioning accuracy of the MLC system during delivery. Scintillator and film measurements both revealed mean dose agreement at isocenter of better than 3% while FWHM of the 2D dose distribution in each plane showed agreement between plan and measurement within 0.2 mm. Analysis of log files revealed a maximum MLC leaf positioning error of 0.04 mm across 178 treatment fields. In conjunction with a quality‐controlled treatment delivery methodology, an appropriately commissioned treatment planning system can be used for accurate and clinically appropriate design of trigeminal neuralgia treatment plans utilizing HD‐MLC.

Proton range verification in inhomogeneous tissue: Treatment planning system vs. measurement vs. Monte Carlo simulation.

In particle radiotherapy, range uncertainty is an important issue that needs to be overcome. Because high-dose conformality can be achieved using a particle beam, a small uncertainty can affect tumor control or cause normal-tissue complications. From this perspective, the treatment planning system (TPS) must be accurate. However, there is a well-known inaccuracy regarding dose computation in heterogeneous media. This means that verifying the uncertainty level is one of the prerequisites for TPS commissioning. We evaluated the range accuracy of the dose computation algorithm implemented in a commercial TPS, and Monte Carlo (MC) simulation against measurement using a CT calibration phantom. A treatment plan was produced for eight different materials plugged into a phantom, and two-dimensional doses were measured using a chamber array. The measurement setup and beam delivery were simulated by MC code. For an infinite solid water phantom, the gamma passing rate between the measurement and TPS was 97.7%, and that between the measurement and MC was 96.5%. However, gamma passing rates between the measurement and TPS were 49.4% for the lung and 67.8% for bone, and between the measurement and MC were 85.6% for the lung and 100.0% for bone tissue. For adipose, breast, brain, liver, and bone mineral, the gamma passing rates computed by TPS were 91.7%, 90.6%, 81.7%, 85.6%, and 85.6%, respectively. The gamma passing rates for MC for adipose, breast, brain, liver, and bone mineral were 100.0%, 97.2%, 95.0%, 98.9%, and 97.8%, respectively. In conclusion, the described procedure successfully evaluated the allowable range uncertainty for TPS commissioning. The TPS dose calculation is inefficient in heterogeneous media with large differences in density, such as lung or bone tissue. Therefore, the limitations of TPS in heterogeneous media should be understood and applied in clinical practice.

Supplemental computational phantoms to estimate out-of-field absorbed dose in photon radiotherapy

The purpose of this study was to develop a straightforward method of supplementing patient anatomy and estimating out-of-field absorbed dose for a cohort of pediatric radiotherapy patients with limited recorded anatomy. A cohort of nine children, aged 2–14 years, who received 3D conformal radiotherapy for low-grade localized brain tumors (LBTs), were randomly selected for this study. The extent of these patients’ computed tomography simulation image sets were cranial only. To approximate their missing anatomy, we supplemented the LBT patients’ image sets with computed tomography images of patients in a previous study with larger extents of matched sex, height, and mass and for whom contours of organs at risk for radiogenic cancer had already been delineated. Rigid fusion was performed between the LBT patients’ data and that of the supplemental computational phantoms using commercial software and in-house codes. In-field dose was calculated with a clinically commissioned treatment planning system, and out-of-field dose was estimated with a previously developed analytical model that was re-fit with parameters based on new measurements for intracranial radiotherapy. Mean doses greater than 1 Gy were found in the red bone marrow, remainder, thyroid, and skin of the patients in this study. Mean organ doses between 150 mGy and 1 Gy were observed in the breast tissue of the girls and lungs of all patients. Distant organs, i.e. prostate, bladder, uterus, and colon, received mean organ doses less than 150 mGy. The mean organ doses of the younger, smaller LBT patients (0–4 years old) were a factor of 2.4 greater than those of the older, larger patients (8–12 years old). Our findings demonstrated the feasibility of a straightforward method of applying supplemental computational phantoms and dose-calculation models to estimate absorbed dose for a set of children of various ages who received radiotherapy and for whom anatomies were largely missing in their original computed tomography simulations.

Characterization and clinical evaluation of a novel 2D detector array for conventional and flattening filter free (FFF) IMRT pre-treatment verification

Background and purposeThe novel MatriXXFFF (IBA Dosimetry, Germany) detector is a new 2D ionization chamber detector array designed for patient specific IMRT-plan verification including flattening-filter-free (FFF) beams. This study provides a detailed analysis of the characterization and clinical evaluation of the new detector array. Material and methodsThe verification of the MatriXXFFF was subdivided into (i) physical dosimetric tests including dose linearity, dose rate dependency and output factor measurements and (ii) patient specific IMRT pre-treatment plan verifications. The MatriXXFFF measurements were compared to the calculated dose distribution of a commissioned treatment planning system by gamma index and dose difference evaluations for 18 IMRT-sequences. All IMRT-sequences were measured with original gantry angles and with collapsing all beams to 0° gantry angle to exclude the influence of the detector's angle dependency. ResultsThe MatriXXFFF was found to be linear and dose rate independent for all investigated modalities (deviations ≤0.6%). Furthermore, the output measurements of the MatriXXFFF were in very good agreement to reference measurements (deviations ≤1.8%). For the clinical evaluation an average pixel passing rate for γ(3%,3mm) of (98.5±1.5)% was achieved when applying a gantry angle correction. Also, with collapsing all beams to 0° gantry angle an excellent agreement to the calculated dose distribution was observed (γ(3%,3mm)=(99.1±1.1)%). ConclusionsThe MatriXXFFF fulfills all physical requirements in terms of dosimetric accuracy. Furthermore, the evaluation of the IMRT-plan measurements showed that the detector particularly together with the gantry angle correction is a reliable device for IMRT-plan verification including FFF.

O13. A comparison of TPS commissioning dosimeters

Introduction The quality of treatment planning system (TPS) commissioning data largely determines the quality of the derived TPS beam model. Modern treatment techniques require a very high degree of competence from the dosimetrist, as well as the dosimetry equipment used for TPS commissioning. Once derived, the beam model should be verified with a range of tests other than commissioning procedures to test the beam model against linac output. Generally, dosimeters used for TPS beam data collection differ largely from those used for post-modelling verification measurements; therefore their correlation needs to be investigated. Materials and Methods Reference beam profile commissioning data were acquired with a Diamond detector (PTW-60019) for field sizes 2 × 2, 3 × 3 and 5 × 5 cm2 at depths 5 and 10 cm in water. Measurements were repeated with a 2D diode array (SunNuclear Mapcheck2) and compared to reference data. Default array spatial resolution of 1 cm was optimized to 1 mm by manual stepping of the device; therefore only measured (non-interpolated) data was gathered and collated using Excel VBA. A 2D gamma analysis with criteria 1%/1 mm was used for quantitative comparisons. Results Comparison of datasets revealed γ 1 in the open and penumbra regions for all scans evaluated. Mapcheck generally yielded a sharper penumbra (0.5 mm) while the largest differences were seen outside the field with Mapcheck demonstrating a 1.5% larger relative dose. Such small deviations can be attributed to differences in the detector sensitive volumes and dosimeter setup. Further, reducing the amount of steps per array profile by two-thirds (from 10 step increments to 3) did not influence the results significantly. Conclusion Results showed with increased resolution the sensitivity of the array are comparable to a diamond detector for small field profiles. Excellent overall agreement was found between these. However, the dosimetric accomplishment may be weakened by acquisition and processing workload therefore optimization thereof was demonstrated.

A robustness analysis method with fast estimation of dose uncertainty distributions for carbon-ion therapy treatment planning

A simple and efficient approach is needed for robustness evaluation and optimization of treatment planning in routine clinical particle therapy. Here we propose a robustness analysis method using dose standard deviation (SD) in possible scenarios such as the robustness indicator and a fast dose warping method, i.e. deformation of dose distributions, taking into account the setup and range errors in carbon-ion therapy. The dose warping method is based on the nominal dose distribution and the water-equivalent path length obtained from planning computed tomography data with a clinically commissioned treatment planning system (TPS). We compared, in a limited number of scenarios at the extreme boundaries of the assumed error, the dose SD distributions obtained by the warping method with those obtained using the TPS dose recalculations. The accuracy of the warping method was examined by the standard-deviation-volume histograms (SDVHs) for varying degrees of setup and range errors for three different tumor sites. Furthermore, the influence of dose fractionation on the combined dose uncertainty, taking into consideration the correlation of setup and range errors between fractions, was evaluated with simple equations using the SDVHs and the mean value of SDs in the defined volume of interest. The results of the proposed method agreed well with those obtained with the dose recalculations in these comparisons, and the effectiveness of dose SD evaluations at the extreme boundaries of given errors was confirmed from the responsivity and DVH analysis of relative SD values for each error. The combined dose uncertainties depended heavily on the number of fractions, assumed errors and tumor sites. The typical computation time of the warping method is approximately 60 times less than that of the full dose calculation method using the TPS. The dose SD distributions and SDVHs with the fractionation effect will be useful indicators for robustness analysis in treatment planning, and the results of our comparative study show that the proposed analysis method would be beneficial in routine clinical use.

TU‐D‐BRA‐00: Treatment Planning System Commissioning and QA

IntroductionTreatment planning systems (TPS) are a cornerstone of modern radiation therapy. Errors in their commissioning or use can have a devastating impact on many patients. To support safe and high quality care, medical physicists must conduct efficient and proper commissioning, good clinical integration, and ongoing quality assurance (QA) of the TPS. AAPM Task Group 53 and related publications have served as seminal benchmarks for TPS commissioning and QA over the past two decades. Over the same time, continuing innovations have made the TPS even more complex and more central to the clinical process. Medical goals are now expressed in terms of the dose and margins around organs and tissues that are delineated from multiple imaging modalities (CT, MR and PET); and even temporally resolved (i.e., 4D) imaging. This information is passed on to optimization algorithms to establish accelerator movements that are programmed directly for IMRT, VMAT and stereotactic treatments. These advances have made commissioning and QA of the TPS much more challenging.This education session reviews up‐to‐date experience and guidance on this subject; including the recently published AAPM Medical Physics Practice Guideline (MPPG) #5 “Commissioning and QA of Treatment Planning Dose Calculations: Megavoltage Photon and Electron Beams”.TPS Commissioning and QA: Planning and Monitoring ‐ (Salomons) This session will review publications and other resources relating to TPS commissioning and QA. A knowledge‐based framework for selecting and commissioning a TPS will be presented, focusing on: Plan requirements, Algorithm capabilities, Software design and connectivity, Process integration, and Training. The spatial and dosimetric accuracies demanded of the modern TPS have exceeded the capabilities of our measurement tools. As a result, important information can sometimes be hidden in in the measurement noise. Control charts allow one to distinguish between systematic trends and random noise for commonly repeated measurements such as individual plan measurements for IMRT and VMAT treatments. The application of control charts to such measurements will be presented.Recommendations of MPPG #5 and practical implementation strategies ‐ (Smilowitz)The recently published recommendations from Task Group No. 244, Medical Physics Practice Guideline on Commissioning and QA of Treatment Planning Dose Calculations: Megavoltage Photon and Electron Beams will be presented. The recommendations focus on the validation of commissioning data and dose calculations. Tolerance values for non‐IMRT beam configurations are summarized based on established criteria and data collected by the IROC. More stringent evaluation criteria for IMRT dose calculations are suggested to test the limitations of the TPS dose algorithms for advanced delivery conditions. The MPPG encourages users to create a suite of validation tests for dose calculation for various conditions for static photon beams, heterogeneities, IMRT/VMAT and electron beams. This test suite is intended to be used for subsequent testing, including TPS software upgrades. In the past, the recommendations of some reports have not been widely implemented due to practical limitations. Implementation strategies, tools and processes developed by multiple centers for efficient and “doable” MPPG #5 testing will be presented, as well as a discussion on the overall validation experience. Gamma analysis as a metric for reporting TPS Commissioning and QA results will be discussed.TPS commissioning and QA: Incorporating the entire planning process (Mutic)The TPS and its features do not perform in isolation. Instead, the features and modules are key components in a complex process that begins with CT Simulation and extends to treatment delivery, along with image guidance and verification. Most importantly, the TPS is used by people working in a multi‐disciplinary environment. It is very difficult to predict the outcomes of human interactions with software. Therefore, an interdisciplinary approach to training, commissioning and QA will be presented, along with an approach to the physics chart check and end‐to‐end testing as a tool for TPS QA. The role of standardization and automation in QA will also be discussed. A number of actual TPS defects will be presented along with heuristics for identifying similar defects in the future. Learning Objectives: Identify some of the key documents relevant for TPS commissioning and QA Increase familiarity with the process of commissioning a TPS Learn about the use of Control Charts for TPS QA Understand the new recommendations from MPPG #5 on TPS Dose Algorithm Commissioning and QC/QA Learn practical implementation processes and tools for MPPG #5 validation recommendations Increase awareness of the link between TPS QA and chart checking Review the role of the TPS in the overall planning processFunding Support, Disclosures, and Conflict of Interest: Sasa Mutic: ViewRay Inc.: Grant, Travel Expenses &amp; Honoraria Varian Medical Systems: Grant, Travel Expenses &amp; Honoraria Philips Healthcare: Travel Expenses Siemens: Travel Expenses TreatSafely LLC.: Ownership Radialogica LLC.: Ownership

Optical-CT 3D Dosimetry Using Fresnel Lenses with Minimal Refractive-Index Matching Fluid.

Telecentric optical computed tomography (optical-CT) is a state-of-the-art method for visualizing and quantifying 3-dimensional dose distributions in radiochromic dosimeters. In this work a prototype telecentric system (DFOS—Duke Fresnel Optical-CT Scanner) is evaluated which incorporates two substantial design changes: the use of Fresnel lenses (reducing lens costs from $10-30K t0 $1-3K) and the use of a ‘solid tank’ (which reduces noise, and the volume of refractively matched fluid from 1ltr to 10cc). The efficacy of DFOS was evaluated by direct comparison against commissioned scanners in our lab. Measured dose distributions from all systems were compared against the predicted dose distributions from a commissioned treatment planning system (TPS). Three treatment plans were investigated including a simple four-field box treatment, a multiple small field delivery, and a complex IMRT treatment. Dosimeters were imaged within 2h post irradiation, using consistent scanning techniques (360 projections acquired at 1 degree intervals, reconstruction at 2mm). DFOS efficacy was evaluated through inspection of dose line-profiles, and 2D and 3D dose and gamma maps. DFOS/TPS gamma pass rates with 3%/3mm dose difference/distance-to-agreement criteria ranged from 89.3% to 92.2%, compared to from 95.6% to 99.0% obtained with the commissioned system. The 3D gamma pass rate between the commissioned system and DFOS was 98.2%. The typical noise rates in DFOS reconstructions were up to 3%, compared to under 2% for the commissioned system. In conclusion, while the introduction of a solid tank proved advantageous with regards to cost and convenience, further work is required to improve the image quality and dose reconstruction accuracy of the new DFOS optical-CT system.

Determination of boundaries between ranges of high and low gradient of beam profile

AimThis work addresses the problem of treatment planning system commissioning by introducing a new method of determination of boundaries between high and low gradient in beam profile. BackgroundThe commissioning of a treatment planning system is a very important task in the radiation therapy. One of the main goals of this task is to compare two field profiles: measured and calculated. Applying points of 80% and 120% of nominal field size can lead to the incorrect determination of boundaries, especially for small field sizes. Materials and methodsThe method that is based on the beam profile gradient allows for proper assignment of boundaries between high and low gradient regions even for small fields. TRS 430 recommendations for commissioning were used. ResultsThe described method allows a separation between high and low gradient, because it directly uses the value of the gradient of a profile. For small fields, the boundaries determined by the new method allow a commissioning of a treatment planning system according to the TRS 430, while the point of 80% of nominal field size is already in the high gradient region. ConclusionsThe method of determining the boundaries by using the beam profile gradient can be extremely helpful during the commissioning of the treatment planning system for Intensity Modulated Radiation Therapy or for other techniques which require very small field sizes.

WE-AB-201-00: Treatment Planning System Commissioning and QA

WE-AB-201-00: Treatment Planning System Commissioning and QA

WE-AB-201-02: TPS Commissioning and QA: A Process Orientation and Application of Control Charts

WE-AB-201-02: TPS Commissioning and QA: A Process Orientation and Application of Control Charts

WE-AB-201-01: Treatment Planning System Commissioning and QA: Challenges and Opportunities

WE-AB-201-01: Treatment Planning System Commissioning and QA: Challenges and Opportunities