Elekta Versa HD Research Articles

In-Depth Exploration of Advanced Settings in Personalized Automation of Radiotherapy Treatment Planning Using Reference Datasets

Introduction: The personalized planning engine in Pinnacle Evolution (version 16.4.3) for automated treatment planning incorporates the feasibility of DVH using several advanced optimization parameters that are generally empirically determined. Materials and Methods: Using the head and neck (HNCa) and prostate cancer (PCa) cases available from the AAPM TG-244 and the VMAT technique using an Elekta Versa HD LINAC, the role of the advanced optimization parameters has been investigated after identifying clinical goals. Plan complexity indexes were calculated using LINAC WATCH software v. 3.6 (Qualiformed, La Roche-sur-Yon, FRA) and correlated to dose distributions and dosimetric evaluations. Moreover, the plan deliverability was assessed using gamma (γ)-index analysis. Results: One hundred sixty plans were optimized (eighty per district). Out of the calculated ones, 88% and 100% were deliverable for HNCa and PCa, respectively, and 68% resulted in a γ-index ≥ 95% for both districts. Conclusions: Ad hoc measurements allowed us to identify a robust subset of acceptable input parameters based on γ-index passing rate criteria. Our approach identified advanced parameters to exploit the capability of the personalized planning engine of Pinnacle Evolution to be incorporated into the planning templates for HNCa and PCa radiotherapy planning.

Five‐year evaluation of linear accelerator‐based SRS platform isocentricity

AbstractLinear accelerator (LINAC)‐based stereotactic radiosurgery (SRS) has become a mainstay in the management of intracranial tumors. However, the high fractional doses and sharp gradients used in SRS place heavy demands on geometric accuracy. Image guidance systems such as ExacTrac (ETX, Brainlab AG, Munich, Germany) have been developed to facilitate position verification at nonzero table angles. Though convenient, potential loss of mechanical rigidity between the imaging and treatment systems can be cause for concern, as the ETX system is not mounted to the rotating gantry. In this retrospective study, we analyzed 518 Winston‐Lutz (WL) tests performed in the last 5 years with ETX alignment on our Elekta Versa HD (Elekta AB, Stockholm, Sweden) linear accelerator to determine the achievable limits of precision and stability over time for our LINAC‐based SRS platform. Results demonstrated remarkable stability over time. 3D and directional misalignments never exceeded 1.0 mm over the study period; however, table rotation was shown to be the most significant source of positional uncertainty. Gantry sag, as measured by gun‐to‐target misalignments at the gantry‐0 and gantry‐180‐degree positions, was consistent, measuring 1.23 ± 0.18 mm over the study period. Measured accuracy was well within acceptable tolerances for cranial SRS treatment delivery. Notably, the use of the ETX system for intrafraction repositioning effectively eliminates couch walkout, the most significant source of uncertainty identified in this study. Our results thus corroborate safe SRS treatment delivery on our Versa HD with ExacTrac image guidance.

Design and performance of a novel multi-leaf collimator composed of leaves with fixed and movable layers.

The multi-leaf collimator (MLC) is an advanced device utilized for beam shaping and intensity modulation in radiotherapy. With the framework of the contemporary single-layer MLC featuring a rounded leaf tip, the leaf tip transmission and leakage exert a considerable influence on radiotherapy. To scale down the leakage and transmission from the leaf gap when the opposite leaves are closed. This study proposes a new design of MLC, named dynamic leaf machine (DLM), specifically engineered to diminish the transmission and leakage from the MLC leaf tip. The DLM incorporates an innovative leaf configuration that involves a combination of fixed and movable layers in a single MLC leaf named fixed and movable (FM) layers leaf, which is advantageous in dealing with transmission and leakage from the leaf tip by employing a staggered arrangement of the fixed and movable layer when the opposite leaves are closed. Subsequently, the DLM is assembled on the Elekta VERSA HD accelerator to assess its performance, focusing on aspects of mechanical characters, transmission, leakage, and penumbra. In comparison to conventional MLC leaves, the FM leaf design in the DLM has achieved a remarkable reduction in the leakage between opposed closed leaves, decreasing it from 48.41% to 0.41%. Additionally, the transmission between the adjacent leaves has been measured at 0.59%, and the penumbra in 16mm × 32mm field is 2.82mm, aligning with the performance of conventional MLC. The DLM with FM leaf performs a significant reduction in transmission from the opposite leaf tip in comparison to conventional MLC while maintaining minimal penumbra, effectively mitigating the transmission and leakage problem between opposing leaves, thereby enhancing the effect of radiotherapy.

Commissioning and validation of a single photon beam model in RayStation for multiple matched Elekta Linacs.

A single treatment planning system (TPS) model for matched linacs provides flexible clinical workflows from patient treatment to intensity-modulated radiation therapy (IMRT) quality assurance (QA) measurement. Since general guidelines for building a single TPS model and its validation for matched linacs are not well established, we present our RayStation photon TPS modeling strategy for matched Elekta VersaHD linacs. The four linacs installed from 2013 to 2020 were matched in terms of Percent Depth Dose (PDD), profile, output factor and wedge factors for 6-MV, 10-MV, 15-MV, and 6-MV-FFF, and maintained following TG-142 recommendations until RayStation commissioning. The RayStation single model was built to represent all four linacs within the tolerance limits recommended by MPPG-5.a. The comprehensive validation tests were performed for one linac following MPPG-5.a and TG-119 guidelines, and spot checks for the other three. Our TPS modeling/validation method was evaluated by re-analyzing the previous 103 patient-specific IMRT/volumetric modulated arc therapy (VMAT) QA measurements with the calculated planar doses by the single model in comparison with the analysis results using four individual Pinnacle TPS models. For all energies, our single model PDDs were within 1% agreement of the four-linac commissioning measurements. The MPPG-5.a validation tests from 5.1 through 7.5 and all TG-119 measurements passed within the recommended tolerance limits. The IMRT QA results (mean±standard deviation) for RayStation single model versus Pinnacle individual models were 98.9%±1.3% and 98.0%±1.4% for 6-MV, 99.9%±0.1% and 99.1%±1.9% for 10-MV, and 98.2%±1.3% and 97.9%±1.8% for 6-MV-FFF, respectively. We successfully built and validated a single photon beam model in RayStation for four Elekta Linacs. The proposed new validation methods were proven to be both efficient and effective.

HDR brachytherapy versus robotic-based and linac-based stereotactic ablative body radiotherapy in the treatment of liver metastases – A dosimetric comparison study of three radioablative techniques

PurposeThe aim of our study was to compare dosimetric aspects of three radioablation modalities – direct high-dose-rate brachytherapy (HDR-BT) and virtually planned stereotactic body radiation therapy performed on CyberKnife (SBRTck) and Elekta Versa HD LINAC (SBRTe) applied in patients with liver metastases. Material and methodsWe selected 30 patients with liver metastases, who received liver interstitial HDR-BT and virtually prepared plans for SBRTck and SBRTe. In all the cases, the prescribed dose was a single fraction of 25 Gy. Treatment delivery time, doses delivered to PTV and organs at risk, as well as conformity indices, were calculated and compared. ResultsThe longest median treatment delivery time was observed in SBRTck in contrast to HDR-BT and SBRTe which were significantly shorter and comparable. HDR-BT plans achieved better coverage of PTV (except for D98%) in contrast to SBRT modalities. Between both SBRT modalities, SBRTck plans resulted in better dose coverage in Dmean, D50%, and D90% values compared to SBRTe without difference in D98%. The SBRTe was the most advantageous considering the PCI and R100%. SBRTck plans achieved the best HI, while R50% value was comparable between SBRTe and SBRTck. The lowest median doses delivered to uninvolved liver volume (V5Gy, V9.1Gy) were achieved with HDR-BT, while the difference between SBRT modalities was insignificant. SBRT plans were better regarding more favourable dose distribution in the duodenum and right kidney, while HDR-BT achieved lower doses in the stomach, heart, great vessels, ribs, skin and spinal cord. There were no significant differences in bowel and biliary tract dose distribution between all selected modalities. ConclusionsHDR-BT resulted in more favourable dose distribution within PTVs and lower doses in organs at risk, which suggests that this treatment modality could be regarded as an alternative to other local ablative therapies in carefully selected patients’ with liver malignancies. Future studies should further address the issue of comparing treatment modalities in different liver locations and clinical scenarios.

Design and characterisation of a minibeam collimator utilising Monte Carlo simulation and a clinical linear accelerator

Objective. Spatially fractionated radiotherapy is showing promise as a treatment modality. Initial focus was on beams of photons at low energy produced from a synchrotron but more recently research has expanded to include applications in proton therapy. Interest in photon beams remains and this is the focus of this paper Approach. This study presents a 3D printed tungsten minibeam collimator intended to produce peak-to-valley dose ratios (PVDR) of between seven and ten with a 1 MV, bremsstrahlung generated, photon beam. The design of the collimator is motivated by a Monte Carlo study estimating the PVDR for different collimator designs at different energies. This collimator was characterised on a clinical linear accelerator (Elekta VersaHD) as well as an orthovoltage unit. Main results. The performance of the fabricated collimator was measured on Elekta VersaHD running in unflattened mode with a 6 MV beam. On the Elekta VersaHD units the PVDR was measured to be between approximately 1.5 and 2.0 at 3 cm deep. For measurements with the orthovoltage unit PVDRs of greater than 10 were observed at a depth of 4 cm. Significance. The results confirmed that the predictions from simulation could be reproduced on linear accelerators currently in clinical usage, producing PVDRs between 2–2.5. Using the model to predict PVDRs using 1 MV photon beams, the threshold considered to produce enhanced normal tissue dose tolerance ( > 7) was surpassed. This suggests the possibility of using such techniques with versions of existing Linac technology which have been modified to operate at low energy and high beam currents.

An automation of Monte Carlo workflow for dosimetry study of an Elekta LINAC delivery system in radiotherapy

PurposeThis study aims to automate the Monte Carlo (MC) workflow utilized for radiotherapy dosimetry, focusing on an Elekta LINAC delivery system. It addresses the challenge of integrating MC simulations into routine clinical practice, making this accurate yet complex method more accessible and efficient for radiotherapy dosimetry. Methods and MaterialsWe developed a user-friendly software featuring a graphical user interface (GUI) that integrates EGSnrc for MC simulations. The software streamlines the process from retrieving Digital Imaging and Communications in Medicine (DICOM) data to executing dose calculations and comparing dose distributions. To validate our proposed tool, we compared its computed doses for IMRT and VMAT plans from the Pinnacle TPS for an Elekta Versa HD linear accelerator against MC simulation results. This comparison utilized our in-house software and GUI as the tool, covering various treatment sites and prescriptions. ResultsThe automated MC workflow demonstrated high accuracy in dose calculations and streamlined integration with clinical workflows. The comparison between the MC-simulated and TPS-calculated doses revealed excellent agreement, highlighting the reliability of MC for independent dose verification in complex treatment scenarios. ConclusionsThe automated MC workflow developed represents a substantial improvement in the practicality and efficiency of MC simulations in radiotherapy. This advancement not only simplifies the dosimetry process but also ensures high accuracy, establishing it as a valuable tool for routine patient-specific quality assurance and the development of specialized treatment procedures.

Surface dose measurement and comparison between TLD and OSLD during modified re constructive mastectomy irradiation

Radiotherapy (RT) is one of the major treatment modalities among surgery and chemotherapy for carcinoma breast. The surface dose study of modified reconstructive constructive Mastectomy (MRM) breast is important due to the heterogeneity in the body contour and the conventional treatment angle to save the lungs and heart from the radiation. These angular entries of radiation beam cause an unpredictable dose deposition on the body surface, which has to be monitored. Thermoluminescent dosimeter (TLD) or optically stimulated luminescent dosimeter (nano OSLD) are commonly preferable dosimeters for this purpose. The surface dose response of TLD and nano OSLD during MRM irradiation has been compared with the predicted dose from the treatment planning system (TPS). The study monitored 100 MRM patients by employing a total 500 dosimeters consisting of TLD (n = 250) and nano OSLD (n = 250), during irradiation from an Elekta Versa HD 6 MV Linear accelerator. The study observed a variance of 3.9% in the dose measurements for TLD and 3.2% for nano OSLD from the planned surface dose, with a median percentage dose of 44.02 for nano OSLD and 40.30 for TLD (p value 0.01). There was no discernible evidence of variation in dose measurements attributable to differences in field size or from patient to patient. Additionally, no variation was observed in dose measurements when comparing the placement of the dosimeter from central to off-centre positions. In comparison, a minor difference in dose measurements were noted between TLD and nano OSLD, The study’s outcomes support the applicability of both TLD and nano OSLD as effective dosimeters during MRM breast irradiation for surface dose evaluation.

Comparison between Volumetric Modulated arc Therapy based Coplanar and Noncoplanar Planning for Stereotactic Body Radiation Therapy of Liver

The study aims to investigate potential dosimetric benefits between non-coplanar and coplanar beam arrangements of Volumetric-Modulated Arc Therapy (VMAT) plans for liver stereotactic body radiotherapy (SBRT). Thirteen patients who had undergone liver SBRT treatment in our department were chosen retrospectively for the study. Two sets of SBRT-VMAT plans namely, non-coplanar (NC-VMAT) and Coplanar (C-VMAT) were generated in Monaco(v5.11) planning system for Elekta Versa HD Linac using unflatten 6MV photon. The NC-VMAT plans were created by two/three non-coplanar partial arcs with couch rotation of ±150 and had an arc span of 1300 to 1600 whereas the C-VMAT plans consisted of a full arc. Both plans were compared by statistically analyzing various dosimetric and technical parameters. There is no statistically significant difference observed between the C-VMAT and NC-VMAT plans for planning target volume (PTV) coverage. However, the spine dose (D1cc) was much less in the NC-VMAT plan compared to the C-VMAT plan, with mean values of 6.127 ± 3.08Gy and 9.058 ± 4.76Gy, respectively (p-value=0.002). The low dose spillage to the healthy tissue was compared by the volume receiving 5Gy (V5Gy) and 10Gy (V10Gy). V5Gy of the NC-VMAT plan was 2399.23±1870.76cc while that of C-VMAT plans was 2835.36±1930.20cc with the p-value <0.001. Moreover, the monitor units(MU) were less with NC-VMAT than with C-VMAT SBRT plans (p=0.015). The plan quality of NC-VMAT plans was favorable compared to C-VMAT plans for liver SBRT especially in reducing spine dose, low dose spillage to healthy tissue, and MU.

Effect of prescription isodose line on tissue sparing in linear accelerator-based stereotactic radiosurgery treating multiple brain metastases using dynamic conformal arcs.

Linear accelerator-based stereotactic radiosurgery (SRS) has become a mainstay for simultaneous management of multiple intracranial targets. Recent improvements in treatment planning systems (TPS) have enabled treatment of multiple brain metastases using dynamic conformal arcs (DCA) and a single treatment isocenter. However, as the volume of healthy tissue receiving at least 12Gy (V12) is linked to the probability of developing radionecrosis, balancing target coverage while minimizing V12 is a critical factor affecting SRS plan quality. Current TPS allow users to adjust various parameters influencing plan optimization. The purpose of this work is to quantify the effect of negative margins on V12 for cranial SRS plans managing multiple brain metastases. Using the Brainlab Elements v3.0 TPS (Brainlab, Munich, Germany), we calculated V10, V12, V15, monitor units, and conformity index for seventeen SRS plans treating 2-10 metastases on our Elekta Versa HD (Elekta, Stockholm, Sweden) linear accelerator. We compared plans optimized using 70%-90% prescription isodose lines (IDL) in 5% increments. Irrespective of the number of treated metastases, optimization at a lower prescription IDL reduced V10, V12, and V15 and increased MU compared to the 90% IDL (p<0.01). However, comparing the 70% and 75% IDL optimizations, there was little difference in tissue sparing. The conformity index showed no consistent trends at different IDLs due to a significant spread in case data. For our plans treating up to 10 metastases, diminishing returns for tissue sparing at IDLs below 80% paired with increasing treatment MU and dosimetric hot spot made optimization at lower IDLs less favorable. In our clinic, after consulting with a physician, it was determined that optimization at the 80% IDL achieved the best balance of V12, treatment MU, and maximum dose. Clinics implementing LINAC-based SRS programs may consider using similar evaluations to develop their own clinical protocols.

ПРИМЕНЕНИЕ НОВЫХ МЕТОДИК ЛУЧЕВОЙ ТЕРАПИИ В ЛЕЧЕНИИ РАКА МОЛОЧНОЙ ЖЕЛЕЗЫ И РАКА ПРЕДСТАТЕЛЬНОЙ ЖЕЛЕЗЫ В РАМКАХ РЕАЛИЗАЦИИ НАЦИОНАЛЬНОГО ПРОЕКТА «ЗДРАВООХРАНЕНИЕ» В НОВОСИБИРСКОЙ ОБЛАСТИ

In 2023, within the framework of the national project “Healthcare”, two state of the art linear accelerators for radiation therapy were put into operation at the State Budgetary Healthcare Institution of the Novosibirsk Region “Novosibirsk Regional Clinical Oncology Dispensary”: Elekta Versa HD and Elekta Infinity. Thanks to the new equipment and the new dosimetric planning system, it became possible to use modern radiation therapy technologies in the Novosibirsk Region. The use of the new equipment is becoming especially relevant for the treatment of leading tumor diseases – breast cancer in women and prostate cancer in men.

Effect of glass compression plate on EBT-XD film dosimetry for pretreatment quality assurance of stereotactic body radiotherapy.

EBT-XD film specially designed for high dose verifications such as stereotactic treatments. The dose response of the film can be affected by several factors, the curly nature of the film being one of them. In this study this curly nature of the film was investigated for stereotactic body radiotherapy (SBRT) plan verifications. For this study, 18 SBRT (11 prostate, 3 spines, and 4 lungs) cases were enrolled. For all the cases, VMAT plans were created in the Monaco treatment planning system and plan was delivered in Elekta Versa HD linear accelerator and delivered fluence was captured by EBT-XD films. All films were scanned with and without a compression plate. All the films were analyzed using the single-channel film method using the red channel. A significant difference in the gamma passing rates (GPR) for the films scanned with and without the compression plate was observed. The maximum percentage differences in GPR between using and not using a compression plate were 12.7% for 1% 1 mm, 8.1% for 2% 2 mm, 7.5% for 3% 2 mm, and 5% for 3% 3mm criteria. Similarly, the mean %difference in GPR was 5.8% for 1% 1 mm, 2.4% for 2% 2 mm, 1.6% for 3% 2 mm and 0.96% for 3% 3 mm criteria. The results suggest that placing a compression plate over the film during scanning provided a great advantage in achieving a more accurate gamma passing rate irrespective of gamma criteria.

Evaluation of Daily Patient Position Accuracy and Calculation of Setup Errors with Skin Markers and Surface-Guided Radiotherapy (SGRT) in Breast Cancer

This study aims to compare the inter-fractional patient positioning errors between the use of skin markers and SGRT in patients receiving breast radiotherapy. It also includes calculating the inter- and intra-fractional PTV margins required for free breathing (FB) and deep inspiration breath-hold (DIBH) techniques due to setup uncertainties. The treatment data of a total of 2209 fractions from 80 patients who received whole breast or chest wall radiotherapy at an institution between March 2021 and December 2022 were retrospectively analyzed. In the first group of patients, the skin markers placed in the Computed Tomography (CT) scan with the FB technique were aligned and positioned with the room lasers in the Elekta Versa HD, and plan-specific shifts were made. The optical surface scanning procedure was applied to the second group of patients with the Sentinel™ system for FB or DIBH techniques in simulation. Patients were positioned for treatment by matching reference surface images with real-time images from the Catalyst™ HD surface imaging system. Positions of all patients were verified with kilovoltage or cone-beam CT imaging systems, and 3D shift vectors were recorded daily. To compare both setup methods, PTV margins including mean positioning shifts (MPS), the vector length of the shifts and setup errors were calculated from van Herk's formulas. The MPS of all patients using skin markers were 0.20±0.85 cm, 0.32±1.55 cm, and 0.18±0.44 cm in the vertical, longitudinal and lateral directions, respectively. Then, these values given above were found to be 0.12±0.15 cm, 0.06±0.17 cm, 0.07±0.23 cm for FB using Catalyst™ HD, and 0.34±0.30 cm, 0.29±0.26 cm, 0.23±0.30 cm for DIBH. In different setup techniques, no statistically significant difference was found between the 3D shift vectors in any direction with Wilcoxon signed-rank test (p>0.05). The mean standard deviation values in all directions were calculated as 1.22 cm and 0.61 cm, respectively, in patients using skin markers and SGRT. This study indicates a significant difference between the positioning shifts of patients positioned with skin markers and SGRT. The surface imaging system is an advantageous non-invasive method that increases setup accuracy and reproducibility in breast radiotherapy.

Commissioning of Aktina SRS cones and dosimetric validation of the RayStation photon Monte Carlo dose calculation algorithm

Clinical implementation of SRS cones demands particular experimental care and dosimetric considerations in order to deliver precise and safe radiotherapy to patients. The purpose of this work was to present the commissioning data of recent Aktina cones combined with a 6MV flattened beam produced by an Elekta VersaHD linear accelerator. Additionally, the modelling process, and an assessment of dosimetric accuracy of the RayStation Monte Carlo dose calculation algorithm for cone based SRS was performed. There are currently no studies presenting beam data for this equipment and none that outlines the modelling parameters and validation of dose calculation using RayStation’s photon Monte Carlo dose engine with cones. Beam data was measured using an SFD and a microDiamond and benchmarked against EBT3 film for cones of diameter 5–39 mm. Modelling was completed and validated within homogeneous and heterogeneous phantoms. End-to-end image-guided validation was performed using a StereoPHAN™ housing, an SRS MapCHECK and EBT3 film, and calculation time was investigated as a function of statistical uncertainty and field diameter. The TPS calculations agreed with measured data within their estimated uncertainties and clinical treatment plans could be calculated in under a minute. The data presented serves as a reference for others commissioning Aktina stereotactic cones and the modelling parameters serve similarly, while providing a starting point for those commissioning the same TPS algorithm for use with cones. It has been shown in this work that RayStation’s Monte Carlo photon dose algorithm performs satisfactorily in the presence of SRS cones.

Small field output correction factors at 18MV.

The response of various detectors in the radiotherapy energy range has been investigated, especially for 6 and 10MV energies for small fields, and is summarized in TRS-483. However, data for accelerator energies above 10MV are sparse or unavailable for many detectors, especially for the energy of 18MV. Small variations in field output factors for the commissioning of a treatment planning system can have a high impact on calculation of dosedistributions. Many studies describe an energy dependence of the response for a large number of detectors. We wanted to close the gap for the 18MV energy regime and determined field output correction factors for different detectors at18MV. An ELEKTA Versa HD accelerator at 18MV was used together with a PTW MP3 water phantom at an SSD of 90cm. The following detectors were examined: PTW Semiflex 31021, PinPoint 3D 31022, diode 60012, diode 60008 and microDiamond 60019, Sun Nuclear EDGE detector, IBA PFD, SFD, Razor Chamber, Razor Nano Chamber and Razor Diode, Standard Imaging Scintillator Exradin W2 1x3, W2 1x1 and Gafchromic EBT3 film. The dose response was determined at a depth of 10cm for square fields between 0.5 and 10cm side length. As reference data a composure of radiochromic film data for small fields ( cm) and data of all compatible chambers for larger fields ( cm) was used. The effective field sizes of small fields were determined from profiles obtained on radiochromic film. The obtained field output correction factors obey the rules of the TRS-483protocol. The W2 1x1 scintillator and the Razor Chamber showed the smallest deviations from the reference curve. The shielded diodes (diode 60008, EDGE detector) showed the highest over-response at small fields, followed by PFD, microDiamond and the unshielded diodes (diode 60012, SFD). The ionization chambers exhibited the well-known volume effect, that is, strong under-response at small fields of up to 9% for the PinPoint 3D, 7% for the Razor Chamber and up to 30% for the Semiflex detector for the smallest studied field size. The small chambers showed a polarity effect in axial orientation, especially the Razor Nano Chamber. Corrections at 18 MV are generally larger than those provided by TRS-483, continuing the trend of increasing corrections between 6 and 10 MV also at a higher accelerator energy. Only the PinPoint 3D Chamber showed a slightly smallercorrection. Field output correction factors were determined for square field sizes between 0.5 and 10cm at 18MV. Most detectors needed a larger correction than at 6 and 10MV. Thus, the use of correction factors will improve beam data for18MV.

Comparison of Different Dosimetric Indices for Volumetric Arc Modulated Treatment Planning Using 2 Different Treatment Planning Systems: A Feasibility Study for Total Body Irradiation

Objective: To compare two different treatment planning systems (TPSs) for plan quality and to check the feasibility of VMAT TBI on the Elekta linear accelerator ‘Versa HD’. Methods: Ten clinical VMAT TBI plans were replanned in Monaco TPS version 5 for retrospective dosimetric analysis and to check the feasibility of treatment delivery in Elekta Versa HD. A dose of 12 Gy in 6 fractions was prescribed to cover 95% PTV. The OARs were the lungs, kidneys, heart, liver, and brain. Dosimetric optimization and calculation were performed in Monaco TPS with a statistical uncertainty of 1%, 2 mm grid. The chosen criterion for plan evaluation and comparison was based on plan quality, dosimetric indices like conformity and homogeneity index, and OAR doses. The comparison of time for optimization, monitor units, and beam on time was also analyzed. Pre-treatment verification using Octavious phantom and gamma analysis using Low’s method with a dose difference of 3% and distance to agreement 3mm criteria was done. The dosimetry of 2 VMAT TBI plans were compared using Wilcoxon signed rank test. Result: The calculated average maximum and mean doses of the PTV were 14.3321Gy and 12.235Gy for eclipse; and 14.428Gy and 12.198Gy for the Monaco system, respectively. The planning time in Monaco was approx. 4.5–6hrs compared to 14–18hrs for Eclipse TPS. Statistically significant difference was observed between the results of 2 TPSs in terms of monitor units, mean doses to lungs, kidneys, heart, and liver and planning time (P &lt; 0.05). However, calculated p values for HI, CI, and brain for both VMAT TBI plans were not statistically different. Conclusion: The study showed the feasibility of VMAT TBI for VERSA HD as it offers faster, better optimization in a single target compared to the Eclipse.

Benchmarking Tests of Contemporary SRS Platforms: Have Technological Developments Resulted in Improved Treatment Plan Quality?

Stereotactic radiosurgery treatment delivery can be performed with a range of devices, each of which have evolved over recent years. We sought to evaluate the differences in performance of contemporary stereotactic radiosurgery platforms and also to compare them with earlier platform iterations from a previous benchmarking study. The following platforms were selected as "state of the art" in 2022: Gamma Knife Icon (GK), CyberKnife S7 (CK), Brainlab Elements (Elekta VersaHD and Varian TrueBeam), Varian Edge with HyperArc (HA), and Zap-X. Six benchmarking cases were used from a 2016 study. To reflect the evolution of increasing numbers of metastases treated per patient, a 14-target case was added. The 28 targets among the 7 patients ranged from 0.02 to 7.2 cc in volume. Participating centers were sent images and contours for each patient and asked to plan them to the best of their ability. Although some variation in local practice was allowed (eg, margins), groups were asked to prescribe a specified dose to each target and tolerance doses to organs at risk were agreed upon. Parameters compared included coverage, selectivity, Paddick conformity index, gradient index (GI), R50%, efficiency index, doses to organs at risk, and planning and treatment times. Mean coverage for all targets ranged from 98.2% (Brainlab/Elekta) to 99.7% (HA-6X). Paddick conformity index values ranged from 0.722 (Zap-X) to 0.894 (CK). GI ranged from a mean of 3.52 (GK), representing the steepest dose gradient, to 5.08 (HA-10X). The GI appeared to follow a trend with beam energy, with the lowest values from the lower energy platforms (GK, 1.25 MeV; Zap-X, 3 MV) and the highest value from the highest energy (HA-10X). Mean R50% values ranged from 4.48 (GK) to 5.98 (HA-10X). Treatment times were lowest for C-arm linear accelerators. Compared with earlier studies, newer equipment appears to deliver higher quality treatments. CyberKnife and linear accelerator platforms appear to give higher conformity whereas lower energy platforms yield a steeper dose gradient.

Quantification of the role of lead foil in flattening filter free beam reference dosimetry

To quantify the potential error in outputs for flattening filter free (FFF) beams associated with use of a lead foil in beam quality determination per the addendum protocol for TG-51, we examined differences in measurements of the beam quality conversion factor kQ when using or not using lead foil. Two FFF beams, a 6 MV FFF and a 10 MV FFF, were calibrated on eight Varian TrueBeams and two Elekta Versa HD linear accelerators (linacs) according to the TG-51 addendum protocol by using Farmer ionization chambers [TN 30013 (PTW) and SNC600c (Sun Nuclear)] with traceable absorbed dose-to-water calibrations. In determining kQ , the percentage depth-dose at 10cm [PDD(10)] was measured with 10×10 cm2 field size at 100cm source-to-surface distance (SSD). PDD(10) values were measured either with a 1 mm lead foil positioned in the path of the beam [%dd(10)Pb ] or with omission of a lead foil [%dd(10)]. The %dd(10)x values were then calculated and the kQ factors determined by using the empirical fit equation in the TG-51 addendum for the PTW 30013 chambers. A similar equation was used to calculate kQ for the SNC600c chamber, with the fitting parameters taken from a very recent Monte Carlo study. The differences in kQ factors were compared for with lead foil vs. without lead foil. Differences in %dd(10)x with lead foil and with omission of lead foil were 0.9±0.2% for the 6 MV FFF beam and 0.6±0.1% for the 10 MV FFF beam. Differences in kQ values with lead foil and with omission of lead foil were -0.1±0.02% for the 6 MV FFF and -0.1±0.01% for the 10 MV FFF beams. With evaluation of the lead foil role in determination of the kQ factor for FFF beams. Our results suggest that the omission of lead foil introduces approximately 0.1% of error for reference dosimetry of FFF beams on both TrueBeam and Versa platforms.

Precise dosimetric comparison between GAMOS and the collapsed cone convolution algorithm of 4D DOSE accumulated in lung SBRT treatments

BackgroundIt is widely accepted that Monte Carlo dose calculations offers a higher precision that the commercially available dose calculation algorithms. This advantage may be especially relevant for lung Stereotactic Body Radiation Therapy (SBRT), as this is a precise technique applied to an area of big inhomogeneity. PurposeWe conducted a comparative study to reveal the differences between the doses calculated using the Collapsed Cone Convolution algorithm and the GAMOS/Geant4 Monte Carlo calculation for lung cancer patients treated with Stereotactic Body Radiation Therapy on an Elekta Versa HD linac. MethodsFor this study a set of ten patient treatments carried out at the Clínica Universidad de Navarra was selected. Theanalysis is based on the comparison of several dosimetric quantities for the Gross Tumor Volume (GTV) and several OrgansAt Risk (OARs), and also a gamma index calculation with distance-to-agreement set to 2 mm and dose difference to 3%, as recommended by ICRU to assess clinical impact. In order to guarantee a small uncertainty in the Monte Carlo calculation of the dosimetric quantities, we studied in detail the validity of different methods that may be used to determine this uncertainty.To compensate for lung movements, a 4D-Cone-beam Computed Tomography (CBCT) was acquired before treatment, whichallowed us to identify eight respiratory phases using a temporal binning. Using commercial MIM software®, we performed a deformable image registration between the eight CT respiration phases to construct the 4D doses. The same procedure was applied for the Treatment Planning System (TPS) dose files and for the Monte Carlo dose files. ResultsThe differences between the two algorithms reveal the known weaknesses of the Collapsed Cone Convolution (CCC) algorithm for the calculation of lateral doses and in regions of large density change. The comparison between the two algorithms for individual phase doses shows differences up to 5% of the GTV D95 or 3–4 Gy in some OARs, which may have a clinical impact. Nevertheless these differences are reduced for the 4D dose in most quantities under study. ConclusionsComparing the dose calculated with a Collapsed Cone Convolution algorithm with GAMOS/Geant4 for ten patients and eight respiratory phases, we found some differences that could have a clinical impact. When combining the eight temporal phases into a 4D dose using the MIM Deformable Image Registration software, the differences diminished substantially.Our statistical analysis concludes that dose uncertainty in the voxels with a maximum dose below a given percentage guarantees uncertainty in the dosimetric quantities below that figure.

Photoneutrons and Gamma Capture Dose Rates at the Maze Entrance of Varian TrueBeam and Elekta Versa HD Medical Linear Accelerators

Herein, we evaluated the neutron and gamma capture dose equivalent rates at the maze entrance of Varian TrueBeam and Elekta Versa HD™ medical linear accelerators (linacs) using experimental measurements as well as empirical calculations. Dose rates were measured using calibrated neutron and gamma area survey meters placed side-by-side at the measurement point of interest. Measurements were performed at a source-to-detector distance of 100 cm, with a 10 × 10 cm2 field size therapeutic X-ray beam, and a 30 × 30 × 15 cm3 solid water patient equivalent phantom, with a linac operating at 15, 10 MV, and 10 MV flattened filter-free (FFF). Dose rates were also measured at different points at the centerline along the maze towards the maze entrance. The measured dose equivalent rates at the maze entrance were comparable to those reported in the literature. The dose rates along the maze decreased exponentially towards the maze entrance and were significant for short maze lengths. The evaluated empirical methods for estimating neutron dose rates at the maze entrance of a linac proposed by Kersey, the modified Kersey method and Falcão method, agree by a factor of two from the experimental measurements. The results revealed vital radiation protection considerations owing to neutron contamination in external beam therapy.