QA Plan Research Articles

2621: MR-compatible Octavius detector and phantom systems are suitable for plan QA in a 1.5 T MRI-linac.

2621: MR-compatible Octavius detector and phantom systems are suitable for plan QA in a 1.5 T MRI-linac.

Assessing focal spot alignment in clinical linear accelerators: a comprehensive evaluation with triplet phantoms.

A fundamental parameter to evaluate the beam delivery precision and stability on a clinical linear accelerator (linac) is the focal spot position (FSP) measured relative to the collimator axis of the radiation head. The aims of this work were to evaluate comprehensive data on FSP acquired on linacs in clinical use and to establish the ability of alternative phantoms to detect effects on patient plan delivery related to FSP. FSP measurements were conducted using a rigid phantom holding two ball-bearings at two different distances from the radiation source. Images of these ball-bearings were acquired using the electronic portal imaging device (EPID) integrated with each linac. Machine QA was assessed using a radiation head-mounted PTW STARCHECK phantom. Patient plan QA was investigated using the SNC ArcCHECK phantom positioned on the treatment couch, irradiated with VMAT plans across a complete 360° gantry rotation and three X-ray energies. This study covered eight Elekta linacs, including those with 6 MV, 18 MV, and 6 MV flattening-filter-free (FFF) beams. The largest range in the FSP was found for 6 MV FFF. The FSP of one linac, retrofitted with 6 MV FFF, displayed substantial differences in FSP compared to 6 MV FFF beams on other linacs, which all had FSP ranges less than 0.50mm and 0.25mm in the lateral and longitudinal directions, respectively. The PTW STARCHECK phantom proved effective in characterising the FSP, while the SNC ArcCHECK measurements could not discern FSP-related features. Minor variations in FSP may be attributed to adjustments in linac parameters, component replacements necessary for beam delivery, and the wear and tear of various linac components, including the magnetron and gun filament. Consideration should be given to the ability of any particular phantom to detect a subsequent impact on the accuracy of patient plan delivery.

Technical note: Patient-specific quality assurance for multi-target single-isocenter SRS-A target-specific approach.

As radiotherapy techniques advance, so do planning methods for multi-target intracranial SRS cases. Multi-target-single-isocenter (MTSI) planning offers high-precision beam delivery with shortened duration. However, accommodating all targets in a single Patient-Specific-Quality-Assurance (PSQA) with QA devices like SRS MapCHECK (SRS MC) is generally impractical. Consequently, we conducted PSQA, using a custom script, by relocating each Target or Neighboring-Target-Group (T-NTG) relative to the beam isocenter on the PSQA device, ensuring each target's dose coverage at high precision. SRS treatment plans use 6MV-FFF beams, consisting of four Volumetric Modulated ARC Therapy (VMAT) arcs, including one full-arc and three half arcs with couch-kicks. A custom script calculated T-NTG coordinates relative to the beam isocenter. QA verification plans were created for each T-NTG, redefining the beam isocenter for precise alignment with the center of the SRS MC. CBCT images were acquired during PSQA for SRS MC alignment, and gamma-index analysis (GIA) was performed. A single-tail paired t-test assessed the passing rate (PR) for 75 QA verification plans. GIA with l.0mm/2.0% criteria for each QA plan yielded a PR>95.5%, with an average of 98.9%. Plans achieving PR>99.0% and>97.0% constituted 63% and 92% of studied plans, respectively. Statistical significance was observed in a t-test with an ideal PR value of 100%, while insignificance was found with a PR value of 99%, suggesting that PSQA for individual targets consistently approaches 99% PR. In MTSI cases using 6MV-FFF beams, targets within the lateral dose-fall-off region require careful verification for acceptability. Our clinical study on individual T-NTG relocation demonstrates that the presented PSQA methods are generally acceptable, supported by a statistically insignificant PR against a 99% PR value. Presented statistical analysis results indicate that the proposed PSQA approach can serve as a reliable tool in clinical settings.

Clinical Workflow of Cone Beam Computer Tomography-Based Daily Online Adaptive Radiotherapy with Offline Magnetic Resonance Guidance: The Modular Adaptive Radiotherapy System (MARS).

The Ethos (Varian Medical Systems) radiotherapy device combines semi-automated anatomy detection and plan generation for cone beam computer tomography (CBCT)-based daily online adaptive radiotherapy (oART). However, CBCT offers less soft tissue contrast than magnetic resonance imaging (MRI). This work aims to present the clinical workflow of CBCT-based oART with shuttle-based offline MR guidance. From February to November 2023, 31 patients underwent radiotherapy on the Ethos (Varian, Palo Alto, CA, USA) system with machine learning (ML)-supported daily oART. Moreover, patients received weekly MRI in treatment position, which was utilized for daily plan adaptation, via a shuttle-based system. Initial and adapted treatment plans were generated using the Ethos treatment planning system. Patient clinical data, fractional session times (MRI + shuttle transport + positioning, adaptation, QA, RT delivery) and plan selection were assessed for all fractions in all patients. In total, 737 oART fractions were applied and 118 MRIs for offline MR guidance were acquired. Primary sites of tumors were prostate (n = 16), lung (n = 7), cervix (n = 5), bladder (n = 1) and endometrium (n = 2). The treatment was completed in all patients. The median MRI acquisition time including shuttle transport and positioning to initiation of the Ethos adaptive session was 53.6 min (IQR 46.5-63.4). The median total treatment time without MRI was 30.7 min (IQR 24.7-39.2). Separately, median adaptation, plan QA and RT times were 24.3 min (IQR 18.6-32.2), 0.4 min (IQR 0.3-1,0) and 5.3 min (IQR 4.5-6.7), respectively. The adapted plan was chosen over the scheduled plan in 97.7% of cases. This study describes the first workflow to date of a CBCT-based oART combined with a shuttle-based offline approach for MR guidance. The oART duration times reported resemble the range shown by previous publications for first clinical experiences with the Ethos system.

Technical note: A simple method for patient-specific quality assurance for lateral targets on a 1.5 T MR-Linac.

The Elekta Unity magnetic resonance (MR) linac is limited to longitudinal couch motion and a sagittal-only laser, which restricts the ability to perform patient-specific quality assurance (PSQA) intensity-modulated radiotherapy (IMRT) measurements for very lateral targets. This work introduces a simple method to perform PSQA using the Sun Nuclear ArcCheck-MR phantom at left and right lateral positions without additional equipment or in-house construction. The proposed setup places the center of the phantom 1.3cm vertical and 12.9cm lateral to isocenter in either the left or right direction. Computed tomography (CT) scans are used to simulate the setup and create a QA plan template in the Monaco treatment planning system (TPS). The workflow is demonstrated for four patients, with an average axial distance from the center of the bore to the planning target volume (PTV) of 12.4cm. Gamma pass rates were above 94% for all plans using global 3%/2mm gamma criterion with a 10% threshold. Setup uncertainties are slightly larger for the proposed lateral setup compared to the centered setup on the Elekta platform (∼1mm compared to ∼0.5mm), but acceptable pass rates are achievable without optimizing shifts in the gamma analysis software. In general, adding the left and right lateral positions increases the axial area in the bore encompassed by the cylindrical measurement array by 147%, substantially increasing the flexibility of measurements for offset targets. Based on this work, we propose using the lateral QA setup if the closest distance to the PTV edge from isocenter is larger than the array radius (10.5cm) or the percent of the PTV encompassed by the diode array would be increased with the lateral setup compared to the centered setup.

Is noncoplanar plan more robust to inter-fractional variations than coplanar plan in treating bilateral HN tumors with pencil-beam scanning proton beams?

Noncoplanar plans (NCPs) are commonly used for proton treatment of bilateral head and neck (HN) malignancies. NCP requires additional verification setup imaging between beams to correct residual errors of robotic couch motion, which increases imaging dose and total treatment time. This study compared the quality and robustness of NCPs with those of coplanar plans (CPs). Under an IRB-approved study, CPs were created retrospectively for 10 bilateral HN patients previously treated with NCPs maintaining identical beam geometry of the original plan but excluding couch rotations. Plan robustness to the inter-fractional variation (IV) of both plans was evaluated through the Dose Volume Histograms (DVH) of weekly quality assurance CT (QACT) sets (39 total). In addition, delivery efficiency for both plans was compared using total treatment time (TTT) and beam-on time (BOT). No significant differences in plan quality were observed in terms of clinical target volume (CTV) coverage (D95) or organ-at-risk (OAR) doses (p>0.4 for all CTVs and OARs). No significant advantage of NCPs in the robustness to IV was found over CP, either. Changes in D95 of QA plans showed a linear correlation (slope=1.006, R2 >0.99) between NCP and CP for three CTV data points (CTV1, CTV2, and CTV3) in each QA plan (117 data points for 39 QA plans). NCPs showed significantly higher beam delivery time than CPs for TTT (539±50vs. 897±142s; p<0.001); however, no significant differences were observed for BOT. NCPs are not more robust to IV than CPs when treating bilateral HN tumors with pencil-beam scanning proton beams. CPs showed plan quality and robustness similar to NCPs while reduced treatment time (∼6min). This suggests that CPs may be a more efficient planning technique for bilateral HN cancer proton therapy.

Rapid Reinstatement of Cancer Care after Hurricane Ian

Category 4 Hurricane Ian brought significant destruction and challenges to western Florida's healthcare facilities. A Radiation Oncology practice network serving the area minimized interruptions in care by implementing planned and improvised solutions. Examining actions that allowed rapid recovery of care could assist others in disaster response. The National Hurricane Center issued a hurricane warning 36 hours prior to Ian's landfall. Center closures were based on evacuations and scheduled take down of the power grid. Computers were unplugged, elevated and wrapped in plastic. The LINAC was isolated from the power grid at the main breaker. Staff and patient contacts were printed. Communication techniques were agreed upon for post-storm scenarios with or without cellular service and internet. Hurricane Ian made landfall on September 28 with 150 mph sustained winds and gusts of 216 mph. Unsafe conditions prevented action on September 28. Facility assessment began on September 29. The majority of facilities were inaccessible due to impassible roads and entry hazards, or could not be safely occupied. Based on location and condition, one center from the network of facilities was selected for immediate operational restoration. After confirmation that the site's restored power would remain stable, the LINAC was powered on. An onsite engineering evaluation was done to assess machine functionality and vacuum integrity. Medical Physics then performed monthly QA and isocenter verification due to concern for building vibrations from extreme winds. Interfacing with patient charts in the Aria database was more complex than anticipated. Aria is a hub that uses relative paths to refer to plans, structure sets, images, and radiotherapy treatment records stored in remote servers. These Aria servers could not be accessed because the remote sites had no power. As the Aria servers could not be moved, teams went to retrieve the related Adaptivo servers to allow re-import of patient plans. When booted these servers had no common network and no graphical user interface. Using command line tools, the servers were added to the hub network and IP addresses were assigned. MS-DOS command Robocopy allowed a large-scale resumable transfer from Adaptivo patient folders to the Eclipse import directory. Plan validation and QA followed. Records could not be updated with delivered treatments, necessitating reconciliation of total dose when normal operations resumed. Within 72 hours of Ian passing, treatment resumed for all patients within the cancer center network who were able to access the restored site. Within days, seven of the eight regional centers were operational and patients were redistributed. The unexpected challenges posed by data and network access suggest that improving data location and back-up networks could facilitate center response and resiliency in future disasters.

P03.07.B DOSIMETRIC ACCURACY OF CYBERKNIFE STEREOTACTIC RADIOSURGERY FOR BENIGN PERIOPTIC TUMOR

Abstract BACKGROUND The Cyberknife (CK) SRS delivers a highly focused ablative radiation dose to tumors to effectively control tumors with minimized radiation toxicity to surrounding normal tissues. This study aimed to evaluate the dosimetric accuracy of Cyberknife (CK) for benign perioptic tumor using patient specific head phantom. METHODS Patient specific head phantoms was fabricated using a 3D-printer to be dosimetrically equivalent to actual target regions of benign perioptic tumor case treated via Cyberknife radiosurgery. Head phantom QA plan was produced using the original CK contour set (target and optic nerve). The head phantom containing the Gafchromic EBT3 film was irradiated using Cyberknife 6D skull tracking method. The dose distributions calculated by MultiPlan Treatment Planning System (version 5.6) was compared with those measured by film dose using gamma analysis method. After moved rotating (1 degree) and translating (1-5mm) the couch table prior to beam delivery, we checked the 6D skull tracking accuracy according to the beam irradiation. RESULTS Gamma passing rates for the 2%/1 mm and 2%/2 mm criteria was found to be 84.11 ± 2.12% and 93.61±1.39% greater than the acceptance criteria 80% and 90%. The difference between measured and calculated dose to the optic nerve in contact with the tumor was less than 3%. CONCLUSION Dosimetric verification with patient-specific head phantoms could be successfully implemented as the evaluation method for CK perioptic tumor radiosurgery delivery with 6D skull tracking system.

Validation of a 2D dose verification systemfor intensity-modulated arc therapy

ObjectiveThe measured dose was shown to be dependent on the angle of beam incidence and influenced by couch absorption when a 2D detector was used in a stationary phantom. The use of a 2D array (MatriXX) in combination with a solid water phantom (RW3) dose verification system was explored, which could take into account the couch absorption influences, generate correction factors (CFs) for each detector element, and also calibrate the measured dose for accurate validation of intensity-modulated arc therapy (IMAT) treatment plans. MethodsBased on the introduction of a homogeneous treatment bed model in the Monaco treatment planning system, CFs(θ) were constructed for all incidence angles using 6 MV photon lines in a 28 cm × 28 cm field for MatriXX at different field incidence angles (0°–360°) as a relative ratio of simulated and measured values. The accuracy of the 2D array in combination with the solid water phantom (MatriXX/RW3) was systematically investigated by verifying 12 IMAT plans with and without CFs. In addition, the resulting assessments were evaluated by 40 additional IMAT plans of different tumor sites, using the COMPASS three-dimensional (3D) dose validation device measurements as a benchmark. ResultsAfter correction based on CFs(θ), the effect of the mean pass rates (3%/3 mm) of the MatriXX 2D array for 12 IMAT plan QA can be seenan explicit improvement of 6.1% was observed with the CFs(θ). The average pass rate increased from 92.0% to 98.1%, and the additional 40 IMAT plans QA γ(3mm/3%) matched well between COMPASS and the measurements for MatriXX/RW3, with CFs(θ)'s of 98.4 ± 1.5 vs. 99.1 ± 0.9 for the phantom plans. For different tumor sites, the cervical, thoracic, and abdominal cases for the 3D COMPASS validation devices were 97.9 ± 1.5 vs. 99.4 ± 0.3, 99.1 ± 0.9 vs. 98.6 ± 1.6, and 98.7 ± 0.9 vs. 99.3 ± 0.7, respectively, with P = 0.051, 0.420, and 0.175. For head tumors, the 2D MatriXX validation pass rate was slightly lower than 3D COMPASS (97.7 ± 2.0 vs. 99.2 ± 0.5, P = 0.048). ConclusionsThe combination of MatriXX with the solid water RW3 phantom and CFs(θ)'s incorporation of the main couch model (iBEAM evo Couchtop EP) proved to be a fast and reliable method for pre-treatment verification of arc therapy with sufficient accuracy. Slight deviations were found for patients with head tumors treated with the treatment bed extension plate assembly iBEAM® evo Extension 415. These could be minimized by constructing the extension plate couch model and then reconstructing the MatriXX/RW3 calibration factor.

Challenges and Lessons Learned From Fabrication, Testing, and Analysis of Eight MQXFA Low Beta Quadrupole Magnets for HL-LHC

By the end of October 2022, the US HL-LHC Accelerator Upgrade Project (AUP) had completed fabrication of ten MQXFA magnets and tested eight of them. The MQXFA magnets are the low-beta quadrupole magnets to be used in the Q1 and Q3 Inner Triplet elements of the High Luminosity LHC. This AUP effort is shared by BNL, Fermilab, and LBNL, with strand verification tests at NHMFL. An important step of the AUP QA plan is the testing of MQXFA magnets in a vertical cryostat at BNL. The acceptance criteria that could be tested at BNL were all met by the first four production magnets (MQXFA03-MQXFA06). Subsequently, two magnets (MQXFA07 and MQXFA08) did not meet some of the criteria and were disassembled. Lessons learned during the disassembly of MQXFA07 caused a revision to the assembly specifications that were used for MQXFA10 and subsequent magnets. In this paper, we present a summary of: 1) the fabrication and test data for all the MQXFA magnets; 2) the analysis of MQXFA07/A08 test results with characterization of the limiting mechanism; 3) the outcome of the investigation, including the lessons learned during MQXFA07 disassembly; and 4) the finite element analysis correlating observations with test performance.

Clinical experience on patient-specific quality assurance for CBCT-based online adaptive treatment plan.

Ethos CBCT-based adaptive radiotherapy (ART) system can generate an online adaptive plan by re-optimizing the initial reference plan based on the patient anatomy at the treatment. The optimization process is fully automated without any room for human intervention. Due to the change in anatomy, the ART plan can be significantly different from the initial plan in terms of plan parameters such as the aperture shapes and number of monitor units (MUs). In this study, we investigated the feasibility of using calculation-based patient specific QA for ART plans in conjunction with measurement-based and calculation-based QA for initial plans to establish an action level for the online ART patient-specific QA. A cohort of 98 cases treated on CBCT-based ART system were collected for this study. We performed measurement-based QA using ArcCheck and calculation-based QA using Mobius for both the initial plan and the ART plan for analysis. For online the ART plan, Mobius calculation was conducted prior to the delivery, while ArcCheck measurement was delivered on the same day after the treatment. We first investigated the modulation factors (MFs) and MU numbers of the initial plans and ART plans, respectively. The γ passing rates of initial and ART plan QA were analyzed. Then action limits were derived for QA calculation and measurement for both initial and online ART plans, respectively, from 30 randomly selected patient cases, and were evaluated using the other 68 patient cases. The difference in MF between initial plan and ART-plan was 12.9% ± 12.7% which demonstrates their significant difference in plan parameters. Based on the patient QA results, pre-treatment calculation and measurement results are generally well aligned with ArcCheck measurement results for online ART plans, illustrating their feasibility as an indicator of failure in online ART QA measurements. Furthermore, using 30 randomly selected patient cases, the γ analysis action limit derived for initial plans and ART plans are 89.6% and 90.4% in ArcCheck QA (2%/2mm)andare 92.4% and 93.6% in Mobius QA(3%/2mm),respectively.According to the calculated action limits, the ArcCheck measurements for all the initial and ART plans passed QA successfully while the Mobius calculation action limits flagged seven and four failure cases respectively for initial plans and ART plans, respectively. An ART plan can be substantially different from the initial plan, and therefore a separate session of ART plan QA is needed to ensure treatment safety and quality. The pre-treatment QA calculation via Mobius can serve as a reliable indicator of failure in online ART plan QA. However, given that Ethos ART system is still relatively new, ArcCheck measurement of initial plan is still in practice. It may be skipped as we gain more experience and have better understanding of the system.

Patient Specific Quality Assurance Automation with Scripting on HID Devices

<h3>Purpose/Objective(s)</h3> Many quality assurance procedures in radiotherapy are tedious and time-consuming but can be automated to improve the efficient and minimum human-errors. In this study we focused on the patient specific quality assurance (PSQA) procedure. The purpose was to develop a robust and quick software interface for Human Interactive Device (HID) operations and significantly accelerate the workflow. <h3>Materials/Methods</h3> The clinical PSQA system of our clinics consists of s treatment planning system (TPS), an oncology information system (OIS) and a measurement and analysis software. The complete PSQA process includes three main parts: (1) QA verification plan creation, (2) treatment plan loading to treatment machine and (3) measurement, data analysis and report. A homemade software tool, AUTOFLOW was developed as a general interface and installed on multiple workstations to automate the operations of local HID devices. The workflow of HID operations in these components was modularized for maximum efficiency and reliability. The required patient information for each computer was stored in a QA task file created from patient database and synchronized by the AUTOFLOW interface in individual workstations. All human operations on HID devices and communication between multiple computers were automated by the AUTOFLOW interface sequentially or parallelly during the entire PSQA process. <h3>Results</h3> We tested the developed automation workflow on 20 clinical QA plans in our current clinical environments. Overall, around 175 (±12) human HID operations on various workstations were removed from the PSQA procedure. On average, 8(±0.8) minutes was needed to complete a PSQA case with the AUTOFLOW software tool, compared to 13(±3.1) minutes for complete manual operations. These results represent a 38% saving in time. No errors were found for all operations performed with this interface. <h3>Conclusion</h3> The AUTOFLOW software interface was successfully developed and used to perform PSQA in our current clinical environment. This interface has substantially reduced the time, and eliminated user stress and input errors for our PSQA procedure. It can potentially work with other TPS, QA, R&V systems of our department to improve the efficiency and reduce human errors for other QA procedures. For future works we plan to improve the system flexibility/stability and implement this application to other QA procedures

Online adaptive radiotherapy of anal cancer: Normal tissue sparing, target propagation methods, and first clinical experience

Background and purposeOnline adaptive radiotherapy (oART) potentially spares OARs as PTV margins are reduced. This study evaluates dosimetric benefits, compared to standard non-adaptive radiotherapy (non-ART), target propagation methods, and first clinical treatments of CBCT-guided oART of anal cancer. Materials and methodsTreatment plans with standard non-ART and reduced oART PTV margins were retrospectively generated for 23 consecutive patients with anal cancer. For five patients randomly selected among the 23 patients, weekly CBCT-guided oART sessions were simulated, where the targets were either deformed or rigidly propagated. Preferred target propagation method and dose to OARs were evaluated. Ten consecutive patients with anal cancer were treated with CBCT-guided oART. Target propagation methods and oART procedure time were evaluated. ResultsFor the retrospective treatment plans, oART resulted in median reductions in bowel bag V45Gy of 11.4 % and bladder V35Gy of 16.1%. Corresponding values for the simulated sessions were 7.5% and 27.1%. In the simulated sessions, 35% of all targets were deformed while 65% were rigidly propagated. Manual editing and rigid propagation were necessary to obtain acceptable target coverage. In the clinical treatments, the primary and some elective targets were rigidly propagated, while other targets were deformed. The median oART procedure time, measured from CBCT acquisition to completion of plan review and QA, was 23 min. ConclusionsSimulated oART reduced the dose to OARs, indicating potential reduction in toxicity. Rigid propagation of targets was necessary to reduce the need for manual edit. Clinical treatments demonstrated that oART of anal cancer is feasible but time-consuming.

Static MLC transmission simulation using two-dimensional ray tracing.

PurposeWe investigated the hypothesis that the transmission function of rounded end linearly traveling multileaf collimators (MLCs) is constant with position. This assumption is made by some MLC models used in clinical treatment planning systems (TPSs) and in the Varian MLC calibration convention. If not constant, this would have implications for treatment plan QA results.MethodsA two‐dimensional ray‐tracing tool to generate transmission curves as a function of leaf position was created and validated. The curves for clinically available leaf tip positions (−20 to 20 cm) were analyzed to determine the location of the beam edge (half‐attenuation X‐ray [XR]) location, the beam edge broadening (BEB, 80%–20% width), as well as the leaf tip zone width. More generalized scenarios were then simulated to elucidate trends as a function of leaf tip radius.ResultsIn the analysis of the Varian high‐definition MLC, two regions were identified: a quasi‐static inner region centered about central axis (CAX), and an outer one, in which large deviations were observed. A phenomenon was identified where the half‐attenuation ray position, relative to that of the tip or tangential ray, increases dramatically at definitive points from CAX. Similar behavior is seen for BEB. An analysis shows that as the leaf radius parameter value is made smaller, the size of the quasi‐static region is greater (and vice versa).ConclusionThe MLC transmission curve properties determined by this study have implications both for MLC position calibrations and modeling within TPSs. Two‐dimensional ray tracing can be utilized to identify where simple behaviors hold, and where they deviate. These results can help clinical physicists engage with vendors to improve MLC models, subsequent fluence calculations, and hence dose calculation accuracy.

Comparison of pre-treatment and in-vivo dosimetry for advanced radiotherapy of prostate cancer.

BackgroundThe usage of advanced radiotherapy techniques requires validation of a previously calculated dose with the precise delivery with a linear accelerator. This study aimed to review and evaluate new verification methods of dose distribution. Moreover, our purpose was to define an internal protocol of acceptance for in-vivo measurements of dose distribution.Materials and methodsThis study included 43 treatment plans of prostate cancer calculated using the Monte Carlo algorithm. All plans were delivered using the Volumetric Modulated Arc Therapy (VMAT) technique of advanced radiotherapy by the linear accelerator Elekta VersaHD. The dose distribution was verified using: MatriXX, iViewDose, and in-vivo measurements. The verification also included recalculation of fluence maps of quality assurance plans in another independent algorithm.ResultsThe acceptance criterion of 95% points of dose in agreement was found for pre-treatment verification using MatriXX; the average γ value was 99.09 ± 0.93 (SD) and 99.64 ± 0.35 (SD) for recalculation in the Collapse Cone algorithm. Moreover, using the second algorithm in the verification process showed a positive correlation ρ = 0.58, p < 0.001. However, verification using iViewDose in a phantom and in-vivo did not meet this γ-pass rate.ConclusionsEvaluation of gamma values for in-vivo measurements utilizing iViewDose software was helpful to establish an internal dosimetry protocol for prostate cancer treatments. We assumed value at a minimum of 50% points of the dose in agreement with the 3%/3 mm criterion as an acceptable compliance level. The recalculated dose distribution of QA plans in regard to the Collapse Cone algorithm in the other treatment planning system can be used as a pre-treatment verification method used by a medical physicist in their daily work. The effectiveness of use in iViewDose software, as a pre-treatment tool, is still debatable, unlike the MatriXX device.

Comparison between different Dosimetric Tools based on Intensity-modulated Radiotherapy (IMRT): A Phantom Study

This study examined the gamma passing rate (GPR) consistency during applying different kinds of gamma analyses and dosimeters to IMRT. Methods: Import treatment protocols for QA phantom irradiation have been recalculated. A gamma analysis was used for comparing the measured and calculated dose distribution of IMRT for different gamma criteria (2%/2mm, 3%/3mm, 4%/4mm, 3%/5mm, 3%/5mm). These criteria are evaluated when 5%, 10%, or 15% of the dose distribution is suppressed. Measured and calculated dose distribution was evaluated with gamma analysis to dose difference (DD) with DTA criteria (distance to agreement). IMRT QA plans to 25 patients from various sites were formed with the Varian Eclipse treatment planning system. Results: Results indicate different diverse hardware and software combinations show varied levels of agreement with expected analysis for the same pass-rate criterion. For a dosimetry audit of the IMRT technique, an EPID detector is superior to conventional methods comparable to Gafchromic EPT3 film and 2D array due to cost, time-consuming, and set up error to get result analysis. The gamma passing rate (GPR) average is increased by increasing the low-dose threshold for different dosimetric tools. For EPID, regardless of the gamma criterion employed, the %GP does not appear to be dependent on the low-dose threshold values (5%-15%) because it indicates that fulfilment the low-dose threshold to global normalization has little effect on patient-specific QA outcomes. Conclusions: It is concluded that GPRs differ depending on gamma, dosimetric tools, and the suppressing dose ratio. To get the best results of quality assurance, each institution should thus carefully develop its procedure for gamma analysis by defining the gamma index analysis and gamma criterion using its dosimetric tools.

Beam modeling and commissioning for Monte Carlo photon beam on an Elekta Versa HD LINAC

PurposeThis study aims at analyzing beam data commissioning along with verifying Monte Carlo-based treatment planning system on the basis of the manufacturer guidelines for Elekta Versa HD Linear Accelerator. Moreover, evaluating the beam match process in terms of quality index, photon profile and multi leaf collimator (MLC) offset is aimed as well. Materials and methodsThe process of collecting beam data for Monaco 5.51 Treatment Planning System commissioning was done based on the instructions provided by the manufacturer as well as AAPM TG-106. Monte Carlo analysis was done for output factors in water, percent depth dose and beam profiles. A set of eight static and intensity modulated radiation therapy fields were used to verify the MLC parameters. ResultsThe difference between the measured and modeled penetrative quality (D10) was achieved to be 0.54%. The output factors for 6 MV photon energy were measured and the difference between the measured and Monte Carlo output results was smaller than 1% for all the fields. The average percentage of passing the gamma criteria for commissioning test fields was (95+-4)%, however, the minimum agreement was 87.5% belonging to “7SEGA”. Additionally, the agreement between both LINAC is 96%, however, the second LINAC reveals a positive offset in the point of approximately −4 cm on the x-axis at the crossplane. ConclusionTest commissioning was successfully verified using a homogeneous phantom for point dose measurements, post modelling MLC parameters and patient QA plans. All plan parameters pass the gamma criteria. 6 MV photon beam was successfully commissioned for Elekta VersaHD LINAC and is ready for clinical implementation.

Dosimetric Feasibility of HA-WBRT With an MRI-Guided Linear Accelerator

Whole brain radiotherapy with hippocampal avoidance (HA-WBRT) is a technique utilized to treat extensive metastatic brain disease while preserving memory and neurocognitive function. We hypothesized that the treatment planning and delivery of HA-WBRT plans is feasible with an MRI-guided linear accelerator (Linac) and compared plan results with clinical non-MRI-guided C-Arm Linac plans.Twelve patients treated with HA-WBRT plans on a non-MRI-guided C-Arm Linac were selected for retrospective analysis. Treatment plans were developed for comparison using a 0.35T MRI-guided Linac. Hippocampi were contoured by the physician on a T1 MRI image fused to a planning CT image with a 5mm expansion to the hippocampi for the avoidance structure. The PTV was expanded from the CTV excluding the hippocampal avoidance structure. Treatment planning goals were defined as provided in the Phase II Trial NRG CC001. MRI-guided treatment (MRgRT) plans were developed by a dosimetrist and compared with clinical plans. QA plans were developed and a subset were delivered on the MRI-guided Linac and measured with a cylindrical diode detector array. PTV coverage was normalized to ∼95% to provide a control point for comparison of dose to the organs at risk.MRgRT plans were deliverable and met all clinical goals. Mean values demonstrated that the clinical plans were cooler than MRgRT plans with mean V37.5 of 0.00% and 0.66%, respectively. Average hippocampi maximum doses were 14.20 ± 2.04 Gy and 14.33 ± 1.19 Gy for clinical vs MRgRT plans, respectively. Average hippocampi D100% were 8.63 ± 0.52 Gy and 7.87 ± 0.23 Gy, respectively. Average maximum doses to 0.03 cc of optic structures were 30.93 ± 1.10 Gy and 31.78 ± 0.66 Gy, respectively. The gamma analysis comparing planned and measured doses resulted in a mean of 99.9% ± 0.14% of passing points (3%/2mm criteria). MRgRT plans had an average of 38.33 beams with total delivery time ranging from 10.7-15.7 minutes and 4.03 minutes for total beam on time. Clinical plans had average delivery times of 3-7 minutes depending on the number of coplanar arcs.This study demonstrates that HA-WBRT can be treated using an MRI-guided linear accelerator with comparable treatment plan quality and delivery accuracy. Given the equitable dosimetric outcomes to traditional CT based plans, the use of MRgRT for hippocampal sparing whole brain radiotherapy opens the possibility of radiomic analysis and potential adaptive treatments (i.e., boost) to lesions based on disease response.

Verifying Plan QA for Online Adaptive Treatment in MR Linac

In addition to real-time tracking, a major advantage of the MR Linac is the ability to perform online plan adaptation in accordance with the patient anatomy of the day. This allows delivery of adequate tumor doses while ensuring surrounding organ at risk sparing. Treatment sites include pancreas prostate, lung and liver, among others. Typically, daily plan adaption leads to a change in monitor units (MU) from the original plan. This change can be over 100% at times. The vendor provides an online QA tool which is a secondary MU check. The purpose of this work is to evaluate the quality of plan QA in online adaptive IMRT treatments compared to physical, post-treatment measurements.We evaluated 32 online adapted plans (26 patients) which passed vendor-supplied secondary MU plan checks with a gamma criterion of 2mm/2%, and were treated clinically. We used both a diode array and an ion chamber for absolute dose measurement at isocenter. MU changes were evaluated in four groups: 0-25%, 26-50%, 51-75% and above 75% difference between adapted and original plans. Overall, MU changes ranged from 0%-102% between original and adapted fractions.The pass rates of the adapted plans were statistically significantly different from those of the original plans by up to 5% (2-tailed t-test). In 6 cases (19%) the relative dose passed and the absolute dose did not. In 4 cases (12%), the QA did not pass even using a 3mm/3% criteria. In 22 of 27 plans (82%) the ion chamber measurements were within 3% of the predicted dose. The other 5 plans had a larger than 3% difference between planned and measured dose at isocenter. In 5 plans the isocenter was too lateral to measure with an ion chamber.Our results show the vendor-supplied QA tool is in good correspondence with post treatment QA measurement. We did not find any correlation between the magnitude of MU changes between the original and adapted plans and the QA pass rates, which is reassuring given the large differences in some of the plans. Treatment site was not correlated to either the magnitude of MU changes or the QA passing rates. The vendor-supplied QA tool cannot be used when treating a patient with the original plan, and thus could not be assessed on these plans. As the optimization algorithm is identical in the treatment planning system and in the adaptive planning process in the treatment delivery computer, the underlying cause for the differences observed in passing rates is unclear. Overall, our results prove the reliability of the vendor-supplied MU secondary check as adequate real-time QA for confidently treating adapted plans.

Initial Evaluation of Biology-Guided Radiotherapy (BgRT) Plans Generated Using PET Acquired on the First Installation of New System

To evaluate Biology-guided Radiotherapy (BgRT) plans generated using PET data acquired on the first installation of the Reflexion™ X1 system. BgRT treatment planning optimizes for fluence indirectly by calculating firing filters that best translate the X1 acquired PET image to the fluences that deliver the prescribed radiation dose. During a treatment session, the firing filters are applied to limited time sampled (LTS) PET images to calculate delivery fluences.An FDG fillable phantom insert that consists of a 22 mm diameter spherical target (PTV1, ball) and a C-shape object (PTV2 with 26mm axial length, 255° partial annulus with major and minor radii of 27 mm and 12 mm) was imaged using a CT Simulator to create planning contours. The water filled insert surrounding these objects was filled with FDG to simulate a warm background. Both targets were filled with FDG, simulating a target to background ratio of 8:1. Two different BgRT treatment plans were generated for PTV1 simulating homogenous uptake, and PTV2 with an inhomogeneous FDG uptake due to necrosis (a cylinder encompassing the C shape PET avid object). A structure that is 12.5 mm away from these targets was used to simulate OAR. Two PET/CT imaging acquisitions were performed on the RefleXion X1 masking the signal outside of each target plus 10 mm margin. Two different BgRT plans were generated prescribing 50 Gy delivered in 5 fractions to each target, separately. The quality of each treatment plan was evaluated based on PTV coverage, Conformity Index at 50% and 80% isodose lines (CI50, CI80) and OAR sparing. Both BgRT plans then delivered to the independent quality assurance tool for patient specific QA verification where the 3%/3 mm gamma criteria was used.BgRT plans for both homogenous and heterogenous FDG uptake targets were created successfully. Prescription dose coverages were 94.2% and 96.3% for PTV1 and PTV2, respectively. The maximum OAR doses were 30.9 and 33.0 Gy and average OAR doses were 14.4 and 20.1 Gy for PTV1 and PTV2 plans, respectively. CI50 were 7.7 and 6.8 where CI80 were 2.5 and 2.6 for PTV1 and PTV2 plans. The patient specific QA passed with 100 % for both plans.This is the first report of the BgRT plan creation and QA delivery using a clinical installation of the Reflexion X1 system, opening the potential towards BgRT dose delivery using the real time FDG uptake measurements to biologically guide active radiation beam delivery. The X1 system was able to optimize and deliver the BgRT plans for both homogenous and heterogenous FDG uptake scenarios. BgRT is a new paradigm of dose optimization, where a new set of optimization and evaluation approaches will be needed.