Treatment Planning System Dose Research Articles

Dosimetric Validation of Treatment Planning System for Volumetric Modulated Arc Therapy Using AAPM Medical Physics Practice Guideline 5.b.

To assess the precision of dose calculations for Volumetric Modulated Arc Therapy (VMAT) using megavoltage (MV) photon beams, we validated the accuracy of two algorithms: AUROS XB and Analytical Anisotropic Algorithm (AAA). This validation will encompass both flattening filter (FF) and flattening filter-free beam (FFF) modes, using AAPM Medical Physics Practice Guideline (MPPG 5b). VMAT validation tests were generated for 6 MV FF and 6 MV FFF beams using the AAA and AXB algorithms in the Eclipse V.15.1 treatment planning system (TPS). Corresponding measurements were performed on a linear accelerator using a diode detector and a radiation field analyzer. Point dose (PD) and in-vivo measurements were conducted using an A1SL ion chamber and (TLD) from Thermofisher, respectively. The Rando Phantom was employed for end-to-end (E2E) tests. The mean difference (MD) between the TPS-calculated values and the measured values for the PDD and output factors were within 1% and 0.5%, respectively, for both 6 MV FF and 6 MV FFF. In the TG 119 sets, the MD for PD with both AAA and AXB was <0.9%. For the TG 244 sets, the minimum, maximum, and mean deviations in PD for both 6 MV FF and 6 MV FFF beams were 0.3%, 1.4% and 0.8% respectively. In the E2E test, using the Rando Phantom, the MD between the TLD dose and the TPS dose was within 0.08% for both 6 MV FF (p=1.0) and 6 MV FFF (0.018) beams. The accuracy of the TPS and its algorithms (AAA and AXB) has been successfully validated. The recommended tests included in the VMAT/IMRT validation section proved invaluable for verifying the PDD, output factors, and the feasibility of complex clinical cases. E2E tests were instrumental in validating the entire workflow from CT simulation to treatment delivery.

Time-gated single-pixel imaging of Cherenkov emission from a medical linear accelerator

Cherenkov imaging is an ideal tool for real-time in vivo verification of a radiation therapy dose. Given that radiation is pulsed from a medical linear accelerator (LINAC) together with weak Cherenkov emissions, time-gated high-sensitivity imaging is required for robust measurements. Instead of using an expensive camera system with limited efficiency of detection in each pixel, a single-pixel imaging (SPI) approach that maintains promising sensitivity over the entire spectral band could be used to provide a low-cost and viable alternative. A prototype SPI system was developed and demonstrated here in Cherenkov imaging of LINAC dose delivery to a water tank. Validation experiments were performed using four regular fields and an intensity-modulated radiotherapy (IMRT) delivery plan. The Cherenkov image-based projection percent depth dose curves (pPDDs) were compared to pPDDs simulated by the treatment planning system (TPS), with an overall average error of 0.48, 0.42, 0.65, and 1.08% for the 3, 5, 7, and 9 cm square beams, respectively. The composite image of the IMRT plan achieved a 85.9% pass rate using 3%/3 mm gamma index criteria, in comparing Cherenkov intensity and TPS dose. This study validates the feasibility of applying SPI to the Cherenkov imaging of radiotherapy dose for the first time to our knowledge.

Radiation Doses Received by Major Organs at Risk in Children and Young Adolescents Treated for Cancer with External Beam Radiation Therapy: A Large-scale Study from 12 European Countries

BackgroundChildhood cancer survivors are at high risk of long-term iatrogenic events, in particular those treated with radiotherapy. The prediction of risk of such events is mainly based on the knowledge of the radiation dose received to healthy organs and tissues during treatment of childhood cancer diagnosed decades ago. PurposeWe aimed to set up a standardised organ dose table in order to help former patients and clinician in charge of long term follow-up clinics. Material and methodsWe performed whole body dosimetric reconstruction for 2646 patients from 12 European Countries treated between 1941 and 2006 (median: 1976). Most planning were 2D or 3D, 46% of patients were treated using Cobalt 60 and 41% using linear accelerator, the median prescribed dose being 27.2 Gy (IQ1-IQ3: 17.6-40.0 Gy), A patient specific voxel-based anthropomorphic phantom with more than 200 anatomical structures or sub-structures delineated as a surrogate of each subject's anatomy was used. The radiation therapy was simulated with a treatment planning system (TPS) based on available treatment information. The radiation dose received by any organ of the body was estimated by extending the TPS dose calculation to the whole-body, by type and localisation of childhood cancer. ResultsThe integral dose and normal-tissue doses to most of the 23 considered organs increased between the 1950’s and the 1970’s and decreased or plateaued thereafter. Whatever the organ considered, the type of childhood cancer explained most of the variability in organ dose. The country of treatment explained only a small part of the variability. ConclusionThe detailed dose estimates provide very useful information for former patients or clinicians who have only limited knowledge about radiation therapy protocols or techniques, but who know the type and site of childhood cancer, gender, age and year of treatment. This will allow better prediction of the long-term risk of iatrogenic events and better referral to long-term follow-up clinics.

Investigation of skin dose of post-mastectomy radiation therapy for the halcyon and tomotherapy treatment machine: Comparison of calculation and in vivo measurements

In treatments such as post-mastectomy radiation therapy (PMRT) for breast cancer patients, skin doses are of great importance in terms of tumor control and side effects. This dosimetric study aimed to measure the skin dose on the chest wall surface for post-mastectomy radiotherapy with Tomotherapy and Halcyon devices using thermoluminescence dosimetry (TLD) and to evaluate the accuracy of the skin dose calculated by treatment planning systems (TPS). Computed tomography (CT) images of the Alderson Rando phantom were obtained. Treatment plans were created with Tomotherapy and Halycon devices for a total of 50 Gy with a fraction dose of 2 Gy to the target volume. The left chest wall was divided into 9 regions for detailed surface dose assessment. 88 dose measurement points were determined on the left chest wall. The phantom was irradiated separately in Halycon and Tomotherapy devices. In vivo, dose measurements were performed with TLD in both devices. TPS and TLD doses were compared for the left chest wall surface. For skin dose, TLD measurements were lower than the dose estimate by Tomotherapy TPS and higher than the dose estimate by Halycon TPS. In addition, the skin dose measurements showed that the skin dose of the Tomotherapy device was higher than that of the Halycon. It is recommended to consider the distance of the treatment device and the accuracy of the TPS dose calculation in skin dose assessment in PMRT.

TLD measurement to investigate the bolus effect on skin dose in total body irradiation with helical tomotherapy

The aim of this study is to investigate the skin dose of total body irradiation (TBI) with Helical Tomotherapy and the need to use a bolus to achieve an adequate skin dose. To simulate the RANDO phantom geometrically, arms and legs created from rice were added to the RANDO phantom and it was immobilized in a vacuum bed. Computed tomography (CT) images of the lower and upper parts of the phantom with a slice thickness of 3 mm were acquired with and without bolus. Fifteen thermoluminescent dosimeters (TLDs) were placed on the skin line of the RANDO phantom. Treatment plans were prepared, and the phantom was irradiated both with and without bolus by the Helical Tomotherapy technique. Results of the measurements and treatment planning system (TPS) doses were compared by the non-parametric Wilcoxon signed-rank test. All procedures were repeated three times and results were evaluated. At the end of the study, it was proven that even when no bolus is used, the skin receives an adequate dose in TBI with Helical Tomotherapy while achieving homogeneous dose distribution and saving critical organs at the same time.

Investigation of the effect of bolus on skin dose in breast cancer treatment with tomotherapy and LINAC radiotherapy devices

In postmastectomy radiation therapy (PMRT), it is important that the chest wall skin is included in the target volume and receives an adequate dose. This study aims to investigate the effect of bolus on skin dose in breast cancer treatment with Tomotherapy and LINAC radiotherapy devices and to examine the accuracy of the surface dose calculated by treatment planning system (TPS) with thermoluminescence dosimetry (TLD). Female Alderson Rando Phantom's chest wall is virtually divided into 9 regions. Computed tomography (CT) images of the phantom were obtained with a section thickness of 3 mm. Two plans, with and without bolus, were created for each of the helical tomotherapy (HT), intensity-modulated radiotherapy (IMRT) and field-in-field (FiF) techniques. A bolus thickness of 0.5 cm was used for all bolus plans. Doses calculated from TPSs were obtained for 88 predetermined points on the chest wall. After irradiation, doses measured with TLDs were obtained. The effect of bolus use on the chest wall surface was examined. The increase in surface dose due to bolus use was 50.35%, 55.35% and 68.56% for HT, IMRT and FiF techniques in TPS, respectively. This increase in TLD measurements was 58.18%, 30.90% and 46.31% for HT, IMRT and FiF techniques, respectively. The best agreement between TPS and TLD doses for bolus and non-bolus plans was found in the HT technique. The difference between TPS and TLD doses decreased within the three treatment techniques due to bolus use. Since the chest wall skin cannot receive the required dose in IMRT and FiF techniques, bolus use is recommended until acute skin reactions occur. There is no need to use a bolus for the HT technique.

Dose measurement of optic chiasm and parotid organs using OCTAVIUS 4D phantom: a dynamic IMRT method for nasopharyngeal cancer treatment

IntroductionIn intensity-modulated radiation therapy (IMRT) techniques, although the dose conformity increases, the out-of-field doses would not decrease. This study aimed to assess the dose error calculated by the treatment planning system (TPS) in the out-of-field regions using the dynamic IMRT (D-IMRT) method in nasopharyngeal cancer (NPC) patients. MethodsThe out-of-field doses were measured for the chiasm and parotid organs using the D-IMRT technique (6 MV energy) with Monaco TPS. Computed tomography (CT) images of 10 NPC patients (54–77 years, mean: 61.6 ± 12.2 years) were considered and countered using 7-field and 11-field methods. The OCTAVIUS 4D phantom was utilized for dose assessment. ResultsAccording to the OCTAVIUS measurements, the Monaco TPS dose errors ranged from −58.8 to 105.5%. The average dose error for optic chiasm and parotid organs was −25% and 8.5%, respectively, with several cases falling within tolerance (±5%). ConclusionThere were considerable dose calculation errors by Monaco TPS for organs located in out-of-field regions (optic chiasm and parotid) during IMRT for NPC patients. Therefore, accurate dose estimation in the out-of-field regions should be considered in clinical practices.

Performance characterization of a novel hybrid dosimetry insert for simultaneous spatial, temporal, and motion-included dosimetry for MR-linac.

Several (online) adaptive radiotherapy procedures are available to maximize healthy tissue sparing in the presence of inter/intrafractional motion during stereotactic body radiotherapy (SBRT) on an MR-linac. The increased treatment complexity and the motion-delivery interplay during these treatments require MR-compatible motion phantoms with time-resolved dosimeters to validate end-to-end workflows. This is not possible with currently available phantoms. Here, we demonstrate a new commercial hybrid film-scintillator cassette, combining high spatial resolution radiochromic film with four time-resolved plastic scintillator dosimeters (PSDs) in an MRI-compatible motion phantom. First, the PSD's performance for consistency, dose linearity, and pulse repetition frequency (PRF) dependence was evaluated using an RW3 solid water slab phantom. We then demonstrated the MRI4D scintillator cassette's suitability for time-resolved and motion-included quality assurance for adapt-to-shape (ATS), trailing, gating, and multileaf collimator (MLC) tracking adaptations on a 1.5 T MR-linac. To do this, the cassette was inserted into the Quasar MRI4D phantom, which we used statically or programmed with artificial and patient-derived motion. Simultaneously with dose measurements, the beam-gating latency was estimated from the time difference between the target entering/leaving the gating window and the beam-on/off times derived from the time-resolved dose measurements. Experiments revealed excellent detector consistency (standard deviation 0.6%), dose linearity (R2 = 1), and only very low PRF dependence ( 0.4%). The dosimetry cassette demonstrated a near-perfect agreement during an ATS workflow between the time-resolved PSD and treatment planning system (TPS) dose (0%-2%). The high spatial resolution film measurements confirmed this with a 1%/1-mm local gamma pass-rate of 90%. When trailing patient-derived prostate motion for a prostate SBRT delivery, the time-resolved cassette measurements demonstrated how trailing mitigated the motion-induced dose reductions from 1%-17% to 1%-2% compared to TPS dose. The cassette's simultaneously measured spatial dose distribution highlighted the dosimetric gain of trailing by improving the 3%/3-mm local gamma pass-rates from 80% to 97% compared to the static dose. Similarly, the cassette demonstrated the benefit of real-time adaptations when compensating patient-derived respiratory motion by showing how the TPS dose was restored from 2%-56% to 0%-12% (gating) and 1%-26% to 1%-7% (MLC tracking) differences. Larger differences are explainable by TPS-PSD coregistration uncertainty combined with a steep dose gradient outside the PTV. The cassette also demonstrated how the spatial dose distributions were drastically improved by the real-time adaptations with 1%/1-mm local gamma pass-rates that were increased from 8 to 79% (gating) and from 35 to 89% (MLC tracking). The cassette-determined beam-gating latency agreed within 12 ms with the ground truth latency measurement. Film and PSD dose agreed well for most cases (differences relative to TPS dose 4%), while film-PSD coregistration uncertainty caused relative differences of 5%-8%. This study demonstrates the excellent suitability of a new commercial hybrid film-scintillator cassette for simultaneous spatial, temporal, and motion-includeddosimetry.

Patient specific quality assurance of volumetric modulated arc therapy of synchronous bilateral breast cancer

Synchronous bilateral breast cancers (SBBC) present a considerable issue in external beam radiotherapy because of large fields size and large target volumes. Mono-isocentric volumetric modulated arc therapy (VMAT) appears as an appropriate irradiation technique for these types of tumors. The aim of this study was to demonstrate the utility of a 3D DVH pretreatment quality assurance program in VMAT of SBBC cases. Twenty SBBC patients who underwent radiation therapy in our department were retrospectively enrolled in this study. Fifteen patients were treated exclusively to the mammary glands. Five patients benefited from a dose boost on the tumor bed (60Gy). Nine patients were irradiated on the supraclavicular nodes (50Gy). This dose was delivered in 25 fractions and integrated boost was used when appropriate. Depending on the complexity of the treatment plans; 2 or 4 arcs VMAT plans were used in a mono-isocentric technique. The patient specific quality assurance (PSQA) was evaluated using COMPASS measured data, COMPASS reconstructed (CR) and COMPASS computed (CC) dose compared to treatment planning system (TPS) dose. Clinical evaluation was based on DVH metrics for target volumes and organ at risks.The maximum average dose deviation between TPS, CC, and CR was below 3%. The paired t-test between TPS, CC, and CR shows a strong agreement (p < 0.001). The 3DVH dose distribution comparison between TPS and COMPASS were also performed with good gamma score for global analysis.COMPASS was successfully evaluated as a 3DVH pretreatment system for SBBC despite the large fields size and complex target volumes. It allows the verification of the plan in 3D patient anatomy and the evaluation of dose discrepancies.

Enhancing Precision in L-band Electron Paramagnetic Resonance Tooth Dosimetry: Incorporating Digital Image Processing and Radiation Therapy Plans for Geometric Correction.

Following unforeseen exposure to radiation, quick dose determination is essential to prioritize potential patients that require immediate medical care. L-band electron paramagnetic resonance tooth dosimetry can be efficiently used for rapid triage as this poses no harm to the human incisor, although geometric variations among human teeth may hinder accurate dose estimation. Consequently, we propose a practical geometric correction method using a mobile phone camera. Donated human incisors were irradiated with calibrated 6-MV photon beam irradiation, and dose-response curves were developed by irradiation with a predetermined dose using custom-made poly(methyl methacrylate) slab phantoms. Three radiation treatment plans for incisors were selected and altered to suit the head phantom. The mean doses on tooth structures were calculated using a commercial treatment planning system, and the electron paramagnetic resonance signals of the incisors were measured. The enamel area was computed from camera-acquired tooth images. The relative standard uncertainty was rigorously estimated both with and without geometric correction. The effects on the electron paramagnetic resonance signal caused by axial and rotational movements of tooth samples were evaluated through finite element analysis. The mean absolute deviations of mean doses both with and without geometric correction showed marginal improvement. The average relative differences without and with geometric correction significantly decreased from 21.0% to 16.8% (p = 0.01). The geometric correction method shows potential in improving dose precision measurement with minimal delay. Furthermore, our findings demonstrated the viability of using treatment planning system doses in dose estimation for L-band electron paramagnetic resonance tooth dosimetry.

Shaping success: clinical implementation of a 3D-printed electron cutout program in external beam radiation therapy.

The integration of 3D-printing technology into radiation therapy (RT) has allowed for a novel method to develop personalized electron field-shaping blocks with improved accuracy. By obviating the need for handling highly toxic Cerrobend molds, the clinical workflow is significantly streamlined. This study aims to expound upon the clinical workflow of 3D-printed electron cutouts in RT and furnish one year of in-vivo dosimetry data. 3D-printed electron cutouts for 6x6 cm, 10x10 cm, and 15x15 cm electron applicators were designed and implemented into the clinical workflow after dosimetric commissioning to ensure congruence with the Cerrobend cutouts. The clinical workflow consisted of four parts: i) the cutout aperture was extracted from the treatment planning system (TPS). A 3D printable cutout was then generated automatically through custom scripts; ii) the cutout was 3D-printed with PLA filament, filled with tungsten ball bearings, and underwent quality assurance (QA) to verify density and dosimetry; iii) in-vivo dosimetry was performed with optically stimulated luminescence dosimeters (OSLDs) for a patient's first treatment and compared to the calculated dose in the TPS; iv) after treatment completion, the 3D-printed cutout was recycled. QA and in-vivo OSLD measurements were conducted (n=40). The electron cutouts produced were 6x6 cm (n=3), 10x10 cm (n=30), and 15x15 cm (n=7). The expected weight of the cutouts differed from the measured weight by 0.4 + 1.1%. The skin dose measured with the OSLDs was compared to the skin dose in the TPS on the central axis. The difference between the measured and TPS doses was 4.0 + 5.2%. The successful clinical implementation of 3D-printed cutouts reduced labor, costs, and removed the use of toxic materials in the workplace while meeting clinical dosimetric standards.

IMRT QA result prediction via MLC transmission decomposition.

Quality assurance measurement of IMRT/VMAT treatment plans is resource intensive, and other more efficient methods to achieve the same confidence are desirable. We aimed to analyze treatment plans in the context of the treatment planning systems that created them, in order to predict which ones will fail a standard quality assurance measurement. To do so, we sought to create a tool external to the treatment planning system that could analyze a set of MLC positions and provide information that could be used to calculate various evaluation metrics. The tool was created in Python to read in DICOM plan files and determine the beam fluence fraction incident on each of seven different zones, each classified based on the RayStation MLC model. The fractions, termed grid point fractions, were validated by analyzing simple test plans. The average grid point fractions, over all control points for 46 plans were then computed. These values were then compared with gamma analysis pass percentages and median dose differences to determine if any significant correlations existed. Significant correlation was found between the grid point fraction metrics and median dose differences, but not with gamma analysis pass percentages. Correlations were positive or negative, suggesting differing model parameter value sensitivities, as well as potential insight into the treatment planning system dose model. By decomposing MLC control points into different transmission zones, it is possible to create a metric that predicts whether the analyzed plan will pass a quality assurance measurement from a dose calculation accuracy standpoint. The tool and metrics developed in this work have potential applications in comparing clinical beam models or identifying their weak points. Implementing the tool within a treatment planning system would also provide more potential plan optimization parameters.

Correction factors for commissioning and patient specific quality assurance of stereotactic fields in a Monte Carlo based treatment planning system

Validation of small field dosimetry is crucial for stereotactic radiosurgery (SRS) and stereotactic body radiotherapy (SBRT). Accurate and considered measurement of linear accelerator dose must be compared to precise and accurate calculation by the treatment planning system (TPS). Monte Carlo calculated distributions contain statistical noise, reducing the reliance that should be given to single voxel doses. The average dose to a small volume of interest (VOI) can minimise the influence of noise, but for small fields introduces significant volume averaging. Similar challenges present during measurement of composite dose from clinical plans when a small volume ionisation chamber is used. This study derived correction factors for VOI averaged TPS doses calculated for small fields, allowing correction to an isocentre dose following account for statistical noise. These factors were used to determine an optimal VOI to represent small volume ionisation chambers during patient specific quality assurance (PSQA). A retrospective comparison of 82 SRS and 28 SBRT PSQA measurements to TPS calculated doses from varying VOI was completed to evaluate the determined volumes. Small field commissioning correction factors of under 5% were obtained for field sizes of 8 mm and larger. Optimal spherical VOI with radius between 1.5 and 1.8 mm and 2.5 to 2.9 mm were determined for IBA CC01 and CC04 ionisation chambers respectively. Review of PSQA confirmed an optimal agreement between CC01 measured doses and a volume of 1.5 to 1.8 mm while CC04 measured doses showed no variation with VOI.

High-resolution entry and exit surface dosimetry in a 1.5 T MR-linac

The magnetic field of a transverse MR-linac alters electron trajectories as the photon beam transits through materials, causing lower doses at flat entry surfaces and increased doses at flat beam-exiting surfaces. This study investigated the response of a MOSFET detector, known as the MOSkin™, for high-resolution surface and near-surface percentage depth dose measurements on an Elekta Unity. Simulations with Geant4 and the Monaco treatment planning system (TPS), and EBT-3 film measurements, were also performed for comparison. Measured MOSkin™ entry surface doses, relative to Dmax, were (9.9 ± 0.2)%, (10.1 ± 0.3)%, (11.3 ± 0.6)%, (12.9 ± 1.0)%, and (13.4 ± 1.0)% for 1 × 1 cm2, 3 × 3 cm2, 5 × 5 cm2, 10 × 10 cm2, and 22 × 22 cm2 fields, respectively. For the investigated fields, the maximum percent differences of Geant4, TPS, and film doses extrapolated and interpolated to a depth suitable for skin dose assessment at the beam entry, relative to MOSkin™ measurements at an equivalent depth were 1.0%, 2.8%, and 14.3%, respectively, and at a WED of 199.67 mm at the beam exit, 3.2%, 3.7% and 5.7%, respectively. The largest measured increase in exit dose, due to the electron return effect, was 15.4% for the 10 × 10 cm2 field size using the MOSkin™ and 17.9% for the 22 × 22 cm2 field size, using Geant4 calculations. The results presented in the study validate the suitability of the MOSkin™ detector for transverse MR-linac surface dosimetry.

Contralateral breast radiation doses in breast cancer patients treated with helical tomotherapy.

We aimed to evaluate contralateral breast doses calculated with a Treatment Planning System (TPS) and verified with metal oxide semiconductor field effect transistor (MOSFET) detectors in patients with early-stage breast cancer (BC) who received helical tomotherapy (HT) after breast-conserving surgery. The dosimetric data of 30 patients (15 left-sided and 15 right-sided) with BC treated with 50.4 Gy to the whole breast and 64.4 Gy to the tumor bed in 28 fractions were analyzed. TPS doses were calculated and MOSFET doses were measured in the contralateral breast (CB) at cranial, caudal, and midpoint and 2 cm lateral to the central point. TPS and MOSFET doses were compared in the entire cohort as well as by tumor location (inner vs outer quadrant) and planning target volume of the breast (<1200 cc vs ≥1200 cc). The average doses at superior, inferior, central, and lateral points calculated with the TPS were 0.26 ± 0.15 cGy, 0.21 ± 0.09 cGy, 0.65 ± 0.14 cGy, and 0.50 ± 0.11 cGy, respectively, and were 0.37 ± 0.16 cGy, 0.34 ± 0.12 cGy, 0.60 ± 0.18 cGy, and 0.34 ± 0.15 cGy, respectively in MOSFET readings. Except for the central point, TPS-calculated doses and MOSFET readings were differed. The doses to the CB in patients with inner and outer quadrant tumors were not significantly different. In patients with large breasts, MOSFET doses were higher at superior and lateral points than TPS doses, but TPS doses were greater at inferior points. MOSFET readings were higher than TPS calculated doses in patients with inner or outer quadrant tumors in small or large breast volumes. The dose calculated by the TPS and that measured by MOSFET differed by a very small amount. The maximum dose to the CB administered at the midpoint was 1.8 Gy, as calculated using the TPS and confirmed using MOSFET detectors, in patients with early-stage BC undergoing breast-only radiotherapy with HT.

Pretreatment Spinal Column Dose Estimation for Spinal SBRT Using Octavius Four-dimensional Phantom and Dose-volume Histograms Four-dimensional Feature: A Dosimetric Analysis.

The aim of this study was to estimate the spinal column dose for spinal Stereotactic body radiation therapy (SBRT) before patient treatment using the PTW dosimetry Octavius dose-volume histograms (DVH) four-dimensional (4D) feature. Twenty-three patients were included in the study, and a volumetric modulated arc therapy plan with 6MV flattening filter-free (6FFF) was generated for each patient in the Eclipse planning system using the Anisotropic Analytical Algorithm (AAA) algorithm (Varian Medical Systems, Palo Alto, CA) for the TrueBeam STx LINAC machine. The Octavius 4D system was used to estimate the spinal cord dose by delivering the plans to the 4D phantom. The measured dose was compared with the Eclipse treatment planning system (TPS) (Varian Medical Systems, Palo Alto, CA) dose. The spinal cord max and mean doses estimated using Varisoft DVH 4D are in close agreement with the TPS calculated max and mean doses. The deviation between measured dose and TPS dose is ±5% for the spinal max dose, and the deviation between measured dose and TPS dose is ± 3% for the spinal mean dose. The study demonstrates that the PTW Octavius 4D phantom and DVH 4D feature can be used as a tool to estimate spinal cord dose before the treatment in spinal SBRT plans. The system provides an independent dose measurement that is comparable to the TPS dose. The close agreement between measured and calculated doses validates the use of this system as a critical organ dose verification tool.

In Vivo Dosimetry for Superficial High Dose Rate Brachytherapy with Optically Stimulated Luminescence Dosimeters: A Comparison Study with Metal-Oxide-Semiconductor Field-Effect Transistors

The purpose of the study was to calibrate and commission optically-stimulated luminescence dosimeters (OSLDs) for in vivo measurements in contact-based 192Ir treatments for superficial high dose rate (HDR) brachytherapy in place of metal-oxide-semiconductor field-effect transistors (MOSFETs). Dose linearity and dose rate dependence were tested by varying source-to-OSLD distance and dwell time. Angular dependence was measured using a solid water phantom setup for OSLD rotation. A group of OSLDs were readout 34 consecutive times to test readout depletion while OSLDs were optically annealed using a mercury lamp for 34.7 h. End-to-end tests were performed using a Freiburg flap and Valencia applicator. OSLD measurements were compared to MOSFETs and treatment planning system (TPS) doses. OSLD response was supralinear for doses above 275 cGy. They were found to be independent of dose rate and dependent on the incident angle in edge-on scenarios. OSLDs exhibited minimal readout depletion and were successfully annealed after 24 h of illumination. Freiburg flap measurements agreed well with the TPS. For the Valencia, OSLDs showed to be the more accurate system over MOSFETs, with a maximum disagreement with the TPS being 0.09%. As such, OSLDs can successfully be used in place of MOSFETs for in vivo dosimetry for superficial HDR brachytherapy.

Impact through versatility: Patterns of in vivo dosimetry utilization with TLD across a large multi-site radiotherapy department.

The complexity of modern radiotherapy treatment pathways necessitate input from different professions to ensure treatment is delivered safely and as planned. In vivo dosimetry is one method of treatment verification providing the opportunity for both in-field verification or out-of-field measurements. It was the aim of this work to review the impact of an in vivo dosimetry programme with t.he view to justify resources and assist in developing a plan for equipment acquisition. Results of 310 (approximately 2 per 1000 treatment fractions) in vivo measurements were reviewed over a two-year time span. The in vivo dosimetry programme using thermoluminescence (TLD) chips was able to detect three significant treatment errors, amongst some 13 000 patients treated. These errors would likely to have been undetected through other quality assurance measures. Increasing demands in workload were found to be associated with commissioning of new equipment and techniques. A skilled operator with knowledge of TLD physics, treatment planning system (TPS) dose calculation algorithms and radiation transport proved to be essential for appropriate interpretation of TLD results particularly in complex radiation delivery scenarios. TLD continues to play a large role in patient safety and quality assurance at our institution.

Efficient dose-volume histogram-based pretreatment patient-specific quality assurance methodology with combined deep learning and machine learning models for volumetric modulated arc radiotherapy.

Weak correlation between gamma passing rates and dose differences in target volumes and organs at risk (OARs) has been reported in several studies. Evaluation on the differences between planned dose-volume histogram (DVH) and reconstructed DVH from measurement was adopted and incorporated into patient-specific quality assurance (PSQA). However, it is difficult to develop a methodology allowing the evaluation of errors on DVHs accurately and quickly. To develop a DVH-based pretreatment PSQA for volumetric modulated arc therapy (VMAT) with combined deep learning (DL) and machine learning models to overcome the limitation of conventional gamma index (GI) and improve the efficiency of DVH-based PSQA. A DL model with a three-dimensional squeeze-and-excitation residual blocks incorporated into a modified U-net was developed to predict the measured PSQA DVHs of 208 head-and-neck (H&N) cancer patients underwent VMAT between 2018 and 2021 from two hospitals, in which 162 cases was randomly selected for training, 18 for validation, and 28 for testing. After evaluating the differences between treatment planning system (TPS) and PSQA DVHs predicted by DL model with multiple metrics, a pass or fail (PoF) classification model was developed using XGBoost algorithm. Evaluation of domain experts on dose errors between TPS and reconstructed PSQA DVHs was taken as ground truth for PoF classification model training. The prediction model was able to achieve a good agreement between predicted, measured, and TPS doses. Quantitative evaluation demonstrated no significant difference between predicted PSQA dose and measured dose for target and OARs, except for Dmean of PTV6900 (p=0.001), D50 of PTV6000 (p=0.014), D2 of PTV5400 (p=0.009), D50 of left parotid (p=0.015), and Dmax of left inner ear (p=0.007). The XGBoost model achieved an area under curves, accuracy, sensitivity, and specificity of 0.89 versus 0.88, 0.89 versus 0.86, 0. 71 versus 0.71, and 0.95 versus 0.91 with measured and predicted PSQA doses, respectively. The agreement between domain experts and the classification model was 86% for 28 test cases. The successful prediction of PSQA doses and classification of PoF for H&N VMAT PSQA indicating that this DVH-based PSQA method is promising to overcome the limitations of GI and to improve the efficiency and accuracy of VMAT delivery.

Clinical pilot study for EPID-based in vivo dosimetry using EPIgray™ for head and neck VMAT.

This work details the clinical pilot study methodology used at Wellington Blood and Cancer Centre (WBCC) before the clinical release of in vivo dosimetry (IVD) system EPIgray™ for head and neck (H&N) volumetric modulated arc therapy (VMAT) treatments. Clinical pilot studies make it possible to select appropriate, department-specific tolerance ranges for the treatment type and site under investigation. An IVD clinical pilot study of H&N VMAT treatments was conducted over 3months at WBCC using EPIgray™ dose reconstruction software and included 12 patients and 32 individual treatment fractions. Statistical analysis of the dose deviations between the treatment planning system (TPS) dose and EPIgray™ reconstructed dose confirmed that a deviation tolerance range of ± 7.0% was an appropriate choice for H&N VMAT at WBCC.