HyperArc multiple brain metastases report

This report presents the initial clinical experience with HyperArc, a novel modality that incorporates a non-coplanar, arc-based multileaf collimator (MLC) and automated treatment optimization and dose delivery. The study focuses on a patient who had previously received whole-brain radiotherapy. The effectiveness and challenges of HyperArc were assessed by evaluating various quality indices for stereotactic radiosurgery within the RTOG protocol, as well as an additional measure of toxicity in the form of the V12Gy volume. The HyperArc plan achieved quality indices of 1.13, 4.58, and 0.88 for CI, GI, and CIPaddick, respectively. The mean ICRU83 value was 0.17±0.01, and it remained consistent across all six lesions. The V12Gy value was equal to 8.76 cc. The HyperArc plan successfully met the constraints for organs-at-risk (OAR). These results suggest that HyperArc is a suitable modality for treating multiple brain metastases, as indicated by the quality indices and metrics. Additionally, V12Gy is a valuable indicator for assessing low-dose spillage

Gamma Putty shielding effect in megavoltage photon beam

Purpose: Traditionally, lead and Cerrobend have been employed for field shaping in radiation therapy. Lately, another shielding material called Gamma Putty has emerged. The objective of this report is to examine its dosimetric and shielding characteristics in megavoltage photon beam.Methods: All measurements were carried out in a dual energy linac. Data were collected using a calibrated ionization chamber. Percent transmission, linear attenuation, and field size dependence were evaluated for open square fields (4 × 4 cm2 to 10 × 10 cm2) defined by collimator jaws and for different Gamma Putty thicknesses (t = 0, 0.3, 0.5, 1.0, 1.5, 2.0, and 2.5 cm) at 6 and 18 MV photon beams. The measurements were performed both in air using appropriate acrylic buildup cap and in solid water.Results: The Gamma Putty tray factor (GPTF) increased steadily with field size for both 6 and 18 MV. It was characterized by a half value thickness (HVT) of 2.513 ± 0.101 and 2.855 ± 0.024 cm for 6 and 18 MV, respectively. The reduction in surface dose was about 6%, 14.5%, 22%, 36.37%, and 54% for 6 MV and 2.75 %, 9.36 %, 16.25 %, 28.95 %, and 44.47 % for 18 MV for Gamma Putty thicknesses of 0.3, 0.5, 1.0, 1.5, 2.0, and 2.5 cm.Conclusion: The result of Gamma Putty shielding on the photon beam output increases with thickness, beam energy, and field size. Therefore, clinical use of Gamma Putty tray factors should be tailored for all thicknesses, beam energies, and field sizes.

Forecasting machine performance check output using Holt-Winters approach

Background: Machine Performance Check (MPC) is an automated TrueBeam quality control (QC) tool used to verify beam output, isocenter, and uniformity. The aim of this study was to build an MPC output variation time series modeled on the Holt-Winters method over thirty days. Methods: After AAPM TG-51 and baseline data were established for the Edge TrueBeam, daily MPC output data were gathered and analyzed through a Holt-Winters (additive and multiplicative) method. The model's performance was assessed via three standard error measures: the mean squared error (MSE), the mean absolute percentage error (MAPE), and the mean absolute deviation (MAE). The aim was achieved using a nonlinear multistart solver on the Excel platform. Results: The results showed that MPC output variation forecasting is energy and model dependent. Both additive and multiplicative Holt-Winters methods were suitable for the analysis. The performance metrics MSE, MAPE, and MAD were found to be well within acceptable limits. Conclusions: A Holt-Winters model was able to accurately forecast the MPC output variation

Statistical process control: machine performance check output variation

Background: The aim of this study was to illustrate and evaluate the use of different statistical process control (SPC) aspects to examine linear accelerator daily output variation through machine performance check (MPC) over a month. Methods: MPC daily output data were obtained over a month after AAPM TG-51 were performed. Baseline data were set, and subsequent data were conducted through SPC. The Shewhart chart was used to determine the upper and lower control limits, whereas CUSUM for subtle changes. Results: The upper and lower control limits obtained via SPC analysis of the MPC data were found to fall within AAPM Task Group 142 guidelines. MPC output variation data were within ±3% of their action limits values and were within 1% over thirty days of data. The process capability ratio and process acceptability ratio, Cp and Cpk values were ≥2 for all energies. Potential undetected deviations were captured by the CUSUM chart for photons and electrons beam energy. Conclusions: Control charts were found to be useful in terms of detecting changes in MPC output

Lung SBRT through Radiobiology

Abstract Purpose: Stereotactic body radiation therapy (SBRT) has emerged as a standard treatment modality for medically inoperable early-stage lung cancer patients. The aim of this paper is to calculate radiobiological parameters for a sample of 39 patients who underwent lung SBRT. Materials and Methods: For SBRT, a typical regimen of 50 Gy in 4 -5 fractions results in local tumor control rates around 99.9%. We calculate dose volume histograms (DVHs) of targeted tumors and organs at risk for 39 patients. All patients received 4D imaging, and their internal treatment volumes (ITVs) were created by phase-based sorting of multiple CT datasets. Planning target volume (PTV) diameters ranged from 2.0 to 5.7 cm. The DVHs for the PTV and organs at risk were analyzed using a Biosuite algorithm to calculate the equivalent uniform dose (EUD), tumor control probability (TCP) via a Poisson model, and normal tissue complication probability (NTCP) via an LKB model. The radiobiological effects were analyzed by correlating EUD and TCP with PTV volumes. Results: The mean PTV volume was 31.60 ± 25.55 cc. The mean EUDs were 5.19 ± 2.84, 5.66 ± 4.95, 61.45 ± 29.18, 3.31 ± 5.92, 6.45 ± 5.18, and 12.22 ± 5.94 Gy for lungs, spinal cord, chest/ribs, heart, esophagus, and skin, respectively. On average, the heart had the lowest EUD and the chest/ribs had the highest (61.45 ± 29.18 Gy). The mean NTCPs were estimated at 3.75% ± 2.61%, 36.25% ± 36.42%, and 0.59% ± 1.48%, for the lungs, chest and esophagus, respectively. The NTCPs of spinal cord, heart, and skin were 0.00%. The mean TCP value was 99.72% ± 0.44%. The mean BED value for our study was 109.49 Gy. Conclusions: We have calculated radiobiological predictors based on DVHs for early-stage non-small cell lung cancer via SBRT. Our calculated predictors are compatible with previously published SBRT reports

Gamma Putty dosimetric studies in electron beam

Traditionally, lead has been used for field shaping in megavoltage electron beams in radiation therapy. In this study, we analyze the dosimetric parameters of a nontoxic, high atomic number (Z = 83), bismuth-loaded material called Gamma Putty that is malleable and can be easily molded to any desired shape. First, we placed an ionization chamber at different depths in a solid water phantom under a Gamma Putty shield of thickness (t = 0, 3, 5, 10, 15, 20, and 25 mm, respectively) and measured the ionizing radiation on the central axis (CAX) for electron beam ranging in energies from 6 to 20 MeV. Next, we investigated the relationship between the relative ionization (RI) measured at a fixed depth for several Gamma Putty shield at different cutout diameters ranging from 2 to 5 cm for various beam energies and derived an exponential fitting equation for clinical purposes. The dose profiles along the CAX show that bremsstrahlung dominates for Gamma Putty thickness >15 mm. For high-energy beams (12-20 MeV) and all Gamma Putty thicknesses up to 25 mm, RI below 5% could not be achieved due to the strong bremsstrahlung component. However, Gamma Putty is a very suitable material for reducing the transmission factor below 5% and protecting underlying normal tissues for low-energy electron beams (6-9 MeV)