Routine Patient-specific Quality Assurance Research Articles

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.

VALIDATION OF COMPASS FOR PRE-TREATMENT PATIENT-SPECIFIC QUALITY ASSURANCE

Aim: Purpose of study is to validate COMPASS 3D patient specific quality-assurance software with Monaco treatment planning system (TPS) for routine quality assurance. Materials & methods: Purpose is to test the MLC modelling in COMPASS software, using Elekta Express QA package contains eight QA fields as follows (i) 10x10 (ii) 20x20 (iii) 3ABUT (iv) DMLC1 (v) HIMRT (vi) HDMLC(vii) 7SegA (viii) Four L were measured with COMPASS and compared with Monaco TPS. For clinical validation of COMPASS, VMAT plans were created for downloadable contoured structure set of AAPM TG119 cases for energy 6MV using Monaco (5.11) TPS for Versa-HD linear-accelerator and verified by COMPASS (calculated and measured). Results: For express QA check, all beams showed gamma pass-rate above 95% except for FourL field. FourL field Monaco versus COMPASS reconstructed gamma pass-rate was 98.4% but Monaco versus COMPASS computed gamma pass rate was 93.4%. COMPASS computed and measured, TG119 test cases showed good agreement with Monaco TPS, except some higher variation in low dose region. Conclusion: COMPASS measured (reconstructed) and computed results are in good agreement with Monaco TPS, therefore can be used for routine patient-specific quality-assurance. Special consideration has to be taken for superficially located targets.

Commissioning and clinical implementation of the first commercial independent Monte Carlo 3D dose calculation to replace CyberKnife M6™ patient-specific QA measurements.

PurposeTo report on the commissioning and clinical validation of the first commercially available independent Monte Carlo (MC) three‐dimensional (3D) dose calculation for CyberKnife robotic radiosurgery system® (Accuray, Sunnyvale, CA).MethodsThe independent dose calculation (IDC) by SciMoCa® (Scientific RT, Munich, Germany) was validated based on water measurements of output factors and dose profiles (unshielded diode, field‐size dependent corrections). A set of 84 patient‐specific quality assurance (QA) measurements for multi‐leaf collimator (MLC) plans, using an Octavius two‐dimensional SRS1000 array (PTW, Freiburg, Germany), was compared to results of respective calculations. Statistical process control (SPC) was used to detect plans outside action levels.ResultsOf all output factors for the three collimator systems of the CyberKnife, 99% agreed within 2% and 81% within 1%, with a maximum deviation of 3.2% for a 5‐mm fixed cone. The profiles were compared using a one‐dimensional gamma evaluation with 2% dose difference and 0.5 mm distance‐to‐agreement (Γ(2,0.5)). The off‐centre ratios showed an average pass rate >99% (92–100%). The agreement of the depth dose profiles depended on field size, with lowest pass rates for the smallest MLC field sizes. The average depth dose pass rate was 88% (35–99%). The IDCs showed a Γ(2,1) pass rate of 98%. Statistical process control detected six plans outside tolerance levels in the measurements, all of which could be attributed the measurement setup. Independent dose calculations showed problems in five plans, all due to differences in the algorithm between TPS and IDC. Based on these results changes were made in the class solution for treatment plans.ConclusionThe first commercially available MC 3D dose IDC was successfully commissioned and validated for the CyberKnife and replaced all routine patient‐specific QA measurements in our clinic.

4089 Clinical Implementation of Monte Carlo Dose Calculation for Patient-Specific Radiotherapy Quality Assurance

OBJECTIVES/GOALS: The Monte Carlo dose calculation method is often considered the “gold standard” for patient dose calculations and can be as radiation dose measurements. Our study aims to develop a true Monte Carlo model that can be implemented in our clinic as part of our routine patient-specific quality assurance. METHODS/STUDY POPULATION: We have configured and validated a model of one of our linear accelerators used for radiation therapy treatments using the EGSnrc Monte Carlo simulation software. Measured dosimetric data was obtained from the linear accelerator and was used as the standard to compare the doses calculated with our model in EGSnrc. We will compare dose calculations between commercial treatment planning systems, the EGSnrc Monte Carlo model, and patient-specific measurements. We will implement the Monte Carlo model in our clinic for routine second-checks of patient plans, and to recalculate plans delivered to patients using machine log files. RESULTS/ANTICIPATED RESULTS: Our Monte Carlo model is within 1% agreement with our measured dosimetric data, and is an accurate representation of our linear accelerators used for patient treatments. With this high level of accuracy, we have begun simulating more complex patient treatment geometries, and expect the level of accuracy to be within 1% of measured data. We believe the Monte Carlo calculation based on machine log files will correlate with patient-specific QA analysis and results. The Monte Carlo model will be a useful tool in improving our patient-specific quality assurance protocol and can be utilized in further research. DISCUSSION/SIGNIFICANCE OF IMPACT: This work can be implemented directly in clinical practice to ensure patient doses are calculated as accurately as possible. These methods can be used by clinics who do not have access to more advanced dose calculation software, ensuring accuracy for all patients undergoing radiotherapy treatments.

POD-DOSI: A dedicated dosimetry system for GammaPod commissioning and quality assurance.

GammaPod, a stereotactic partial breast irradiator allowing highly conformal radiation dose delivery, has its unique mechanical design and treatment planning system (TPS). However, the uniqueness of the system poses challenges regarding initial GammaPod system commissioning and routine quality assurance (QA). In this study, we report POD-DOSI, a dedicated dosimetry system for accurate and efficient commissioning and QA of GammaPod. The POD-DOSI system consists of two subsystems, POD-Scanner and POD-Calculator. The POD-Scanner is an automatic ion-chamber positioning system driven by two translational stepper motors for anterior-posterior, longitudinal, and lateral beam scanning. The stepper motors are controlled by a microcomputer through an in-house-developed graphical user interface, which can be remotely accessed by a laptop via wireless connection. The POD-Calculator is a commissioned GPU-based Monte Carlo dose calculation engine, which calculates dose by transporting particles from phase space constructed for GammaPod. In our institution, the POD-DOSI system was used for GammaPod TPS commissioning and dose verification. The POD-Calculator was further developed as a secondary dose calculation tool performing patient-specific plan QA before each treatment. The POD-DOSI system has been fully evaluated and tested, both mechanically and dosimetrically, and applied successfully to drive the commissioning of our GammaPod system. The POD-Scanner achieved 0.1mm accuracy in ion-chamber positioning tests. The POD-Calculator generated dose profiles matched well with water phantom measurements and TPS calculations to <0.5mm accuracy. For end-to-end test on 56 different treatment plans, in-water point dose measurements by POD-Scanner were within ±2.20% of the doses calculated by POD-Calculator (range: -2.01% to 2.20%, mean: 0.04%, std_dev: 1.10%). Correspondingly, when switching the calculation medium from water to breast tissue, the point doses calculated by the POD-Calculator were within ±1.60% of the point doses calculated by the GammaPOD TPS (range: -1.59% to 1.51%, mean: -0.02%, std_dev: 0.73%). The average three-dimensional gamma passing rate between the GammaPod TPS doses and the POD-Calculator doses was 97.10% under the 2%/1mm gamma criteria. The POD-DOSI system substantially shortened the GammaPod dosimetry commissioning time from weeks to days. The developed POD-DOSI system resolves the challenges and streamlines the process of GammaPod commissioning and QA. It improves the efficiency and accuracy for both GammaPod commissioning and routine patient-specific QA.

Point Dose Measurement for Verification of Treatment Planning System using an Indigenous Heterogeneous Pelvis Phantom for Clarkson, Convolution, Superposition, and Fast Superposition Algorithms

Background: Nowadays, advanced radiotherapy equipment includes algorithms to calculate dose. The verification of the calculated doses is important to achieve accurate results. Mostly homogeneous dosimetric phantoms are available commercially which do not mimic the actual patient anatomy; therefore, an indigenous heterogeneous pelvic phantom mimicking actual human pelvic region has been used to verify the doses calculated by different algorithms. Objective: This study aims to compare the planed dose using different algorithms with measured dose using an indigenous heterogeneous pelvic phantom.Material and Methods: In this experimental study, various three dimensional conformal radiotherapy (3D-CRT) plans were made using different doses calculated by algorithms. The plans were delivered by medical linear accelerator and doses were measured by ion chamber placed in the indigenous pelvic phantom. Planned and measured doses were compared with together and analyzed. Results: The relative electron densities of different parts in the pelvic phantom were found to be in good agreement with that of actual pelvic parts, including bladder, rectum, fats and bones. The highest percentage deviations between planned and measured dose were calculated in the single field for Superposition algorithm (3.09%) and single field with 45˚wedge for Superposition (3.04%). The least percentage deviation was calculated in the opposite field for Convolution which was - 0.08%. The results were within the range of ±5% as recommended by International Commission on Radiation Units and Measurement. Conclusion: The cost-effective indigenous heterogeneous pelvic phantom has the density pattern similar to the actual pelvic region; thus, it can be used for routine patient-specific quality assurance.

GafChromic® EBT3 films for patient specific IMRT QA using a multichannel approach

PurposeTo evaluate EBT3 for pre-treatment patient specific quality assurance (QA). The method we propose combines the experience gained in our center with the guidelines of the protocol proposed by Lewis et al. in 2012. To compare the multichannel approach with the single channel dosimetry. MethodsGafchromic® EBT3 films were irradiated both at linac and TomoTherapy and calibration curves were obtained. A series of irradiations with simple fields (uniform dose distributions on regular shaped targets) was performed. In a second stage, films were exposed to full clinical plans at linac (step and shoot IMRT and VMAT). At TomoTherapy dose maps were obtained for a clinical plan in three different coronal planes. Films were digitized using an Epson 10000XL scanner and FilmQA™ Pro software was employed for the analysis. ResultsThe measured calibration curves suggest that, at least for the two beams taken into account (6 MV linac and TomoTherapy), a single calibration can be successfully adopted for each film lot. The application of the multichannel optimization method strongly improves the results in terms of gamma passing rates of the comparison between measured and calculated maps. ConclusionsUp to now EBT films, although attractive, were not preferred for routine patient specific QA due to their complex and time consuming processing and to the challenging work of characterization. The application of the mentioned protocol, together with some additional precautions, and the adoption of the multichannel optimization dosimetry, make this detector a handy and reliable tool for patient specific QA.

Evaluation of 3D Gamma index calculation implemented in two commercial dosimetry systems

3D Gamma index is one of the metrics which have been widely used for clinical routine patient specific quality assurance for IMRT, Tomotherapy and VMAT. The algorithms for calculating the 3D Gamma index using global and local methods implemented in two software tools: PTW- VeriSoft® as a part of OCTIVIUS 4D dosimeter systems and 3DVHTM from Sun Nuclear were assessed. The Gamma index calculated by the two systems was compared with manual calculated for one data set. The Gamma pass rate calculated by the two systems was compared using 3%/3mm, 2%/2mm, 3%/2mm and 2%/3mm for two additional data sets. The Gamma indexes calculated by the two systems were accurate, but Gamma pass rates calculated by the two software tools for same data set with the same dose threshold were different due to the different interpolation of raw dose data by the two systems and different implementation of Gamma index calculation and other modules in the two software tools. The mean difference was -1.3%±3.38 (1SD) with a maximum difference of 11.7%.

Evaluation of Portal Dosimetry for VMAT Treatments

Evaluation of Portal Dosimetry for VMAT Treatments

A patient-specific quality assurance study on absolute dose verification using ionization chambers of different volumes in RapidArc treatments

The recalculation of 1 fraction from a patient treatment plan on a phantom and subsequent measurements have become the norms for measurement-based verification, which combines the quality assurance recommendations that deal with the treatment planning system and the beam delivery system. This type of evaluation has prompted attention to measurement equipment and techniques. Ionization chambers are considered the gold standard because of their precision, availability, and relative ease of use. This study evaluates and compares 5 different ionization chambers: phantom combinations for verification in routine patient-specific quality assurance of RapidArc treatments. Fifteen different RapidArc plans conforming to the clinical standards were selected for the study. Verification plans were then created for each treatment plan with different chamber-phantom combinations scanned by computed tomography. This includes Medtec intensity modulated radiation therapy (IMRT) phantom with micro-ionization chamber (0.007 cm3) and pinpoint chamber (0.015 cm3), PTW-Octavius phantom with semiflex chamber (0.125 cm3) and 2D array (0.125 cm3), and indigenously made Circular wax phantom with 0.6 cm3 chamber. The measured isocenter absolute dose was compared with the treatment planning system (TPS) plan. The micro-ionization chamber shows more deviations when compared with semiflex and 0.6 cm3 with a maximum variation of −4.76%, −1.49%, and 2.23% for micro-ionization, semiflex, and farmer chambers, respectively. The positive variations indicate that the chamber with larger volume overestimates. Farmer chamber shows higher deviation when compared with 0.125 cm3. In general the deviation was found to be <1% with the semiflex and farmer chambers. A maximum variation of 2% was observed for the 0.007 cm3 ionization chamber, except in a few cases. Pinpoint chamber underestimates the calculated isocenter dose by a maximum of 4.8%. Absolute dose measurements using the semiflex ionization chamber with intermediate volume (0.125 cm3) shows good agreement with the TPS calculated among the detectors used in this study. Positioning is very important when using smaller volume chambers because they are more sensitive to geometrical errors within the treatment fields. It is also suggested to average the dose over the sensitive volume for larger-volume chambers. The ionization chamber-phantom combinations used in this study can be used interchangeably for routine RapidArc patient-specific quality assurance with a satisfactory accuracy for clinical practice.

SU‐E‐T‐464: A Patient Specific Quality Assurance Study on Absolute Dose Verification Using Ionization Chambers of Different Volumes in RapidArc Treatments

Purpose: To evaluate and compare five different ionization chamber ‐ phantom combinations for verification in routine patient specific quality assurance of RapidArc treatments. Methods: Fifteen different RapidArc plans conforming to the clinical standards were selected for the study. Verification plan was subsequently created for each treatment plans with different chamber‐phantom combinations CT scanned. This includes Medtec‐ IMRT phantom with micro ionization chamber (0.007cm3) and pinpoint chamber (0.015cm3), PTW‐Octavius phantom with semiflex chamber (0.125cm3) and 2D array (0.125cm3) and indigenously made Circular wax phantom with 0.6 cm3 chamber. The measured isocentre absolute dose was compared with the TPS planned. Results: Micro ionization chamber shows more deviations when compared to semiflex and 0.6 cm3 with a maximum variation of −4.76%,−1.49% and 2.23% for micro ionization, semiflex and farmer chambers respectively. The positive variations indicate that the chamber with larger volume slightly overestimates. Farmer chamber shows higher deviation when compared to 0.125cm3. In general the deviation was found to be less than 1% with semiflex and farmer chamber. A maximum variation of 2% between the plans was observed for 0.007cm3 ionization chamber, except for few cases. Pinpoint chamber underestimates the calculated isocentre dose by maximum 4%. Conclusions: Absolute dose measurements using semiflex ionization chamber with intermediate volume (0.125cm3) shows good agreement with the TPS calculated among the detectors used in this study. Positioning is very important when using smaller volume chambers as they are more sensitive to geometrical errors within the treatment fields. Also it is suggested to average the dose over the sensitive volume for larger volume chambers. The ionization chamber‐phantom combinations used in this study can be used interchangeably for routine RapidArc patient specific quality assurance with a satisfactory accuracy for clinical practices.

SU-E-T-214: Volumetric Particle Beam Quality Assurance

Purpose: Quality assurance (QA) and dose output measurements for particle therapy, where the range varies across the field is a challenge. Our goal was to devise a system that was both accurate and efficient. Methods: We have utilized a MatriXX(IBA) device in a protective sleeve within water to measure absolute dose and profiles. The MatriXXcan be positioned remotely to various depths in water. For high energy electrons (using a custom compensator‐CC) and protons (range compensator) depths may be chosen according to the therapeutic ranges across the field. Measured data was compared to phantom calculated profiles using the I'mRTsoftware (IBA). Two CC were constructed, CT scanned, and calculated, on top of a test phantom. The CC in front of a water phantom was irradiated with 20 MeV electrons. One CC was intentionally altered (added plastic narrow ring) to ensure a deviation could be detected. Setup and measurement times were recorded. Results: We found good agreement between measured absolute dose/profiles and calculations for two CCs at three depths (6.17, 8.17 and 10.17 cm). The Gamma index (3 mm, 3%) was calculated to be met over the majority of irradiated field. The MatriXX accurately detected the intentionally altered CC by for the measurement vs. the calculated plan. Setup and measurement times were reasonable for routine patient specific QA (∼5 min. per CC tested) excluding setup. Conclusions: The results indicate our measurement system using the MatriXX device in water was sufficient for measuring dose and profiles for electrons. We plan on performing dose output and profile measurements for proton patients when we go clinical in 2012. We anticipate performing QA for as many as 6 proton fields in <1hour. We have devised a measurement system that is accurate, efficient and sensitive to deviations.