Background: Hypo-fractionation can be an effective strategy to lower costs and save time, increasing patient access to advanced radiation therapy. To demonstrate this potential in practice within the context of temporal evolution, a twenty-year analysis of a representative radiation therapy facility from 2003 to 2022 was conducted. This analysis utilized comprehensive data to quantitatively evaluate the connections between advanced clinical protocols and technological improvements. The findings provide valuable insights to the management team, helping them ensure the delivery of high-quality treatments in a sustainable manner. Methods: Several parameters related to treatment technique, patient positioning, dose prescription, fractionation, equipment technology content, machine workload and throughput, therapy times and patients access counts were extracted from departmental database and analyzed on a yearly basis by means of linear regression. Results: Patients increased by 121 ± 6 new per year (NPY). Since 2010, the incidence of hypo-fractionation protocols grew thanks to increasing Linac technology. In seven years, both the average number of fractions and daily machine workload decreased by −0.84 ± 0.12 fractions/year and −1.61 ± 0.35 patients/year, respectively. The implementation of advanced dose delivery techniques, image guidance and high dose rate beams for high fraction doses, currently systematically used, has increased the complexity and reduced daily treatment throughput since 2010 from 40 to 32 patients per 8 h work shift (WS8). Thanks to hypo-fractionation, such an efficiency drop did not affect NPY, estimating 693 ± 28 NPY/WS8, regardless of the evaluation time. Each newly installed machine was shown to add 540 NPY, while absorbing 0.78 ± 0.04 WS8. The COVID-19 pandemic brought an overall reduction of 3.7% of patients and a reduction of 0.8 fractions/patient, to mitigate patient crowding in the department. Conclusions: The evolution of therapy protocols towards hypo-fractionation was supported by the use of proper technology. The characteristics of this process were quantified considering time progression and organizational aspects. This strategy optimized resources while enabling broader access to advanced radiation therapy. To truly value the benefit of hypo-fractionation, a reimbursement policy should focus on the patient rather than individual treatment fractionation.

Patient-specific quality assurance (PSQA) procedures ensure the safe delivery of volumetric modulated arc therapy (VMAT) plans. PSQA requires extensive time and resources and may cause treatment delays if replanning is needed due to failures. Recently, our group developed a machine learning (ML) model predicting gamma passing rate (GPR) for VMAT arcs. This study explores automatable replanning strategies for plans identified at risk of failure, aiming to improve deliverability while maintaining dosimetric quality. Between 2022 and 2023, our ML model analyzed 1252 VMAT plans. Ten patients having a predicted GPR (pGPR) <95% were selected. Replanning strategies consisted of limiting monitor units (MUlimit) and employing the aperture shape controller (ASC) tool. Re-optimized plans were compared with the originals in terms of dose volume constraints (DVCs) for the target and organs-at-risk (OARs), and deliverability using the modulation complexity score (MCS), pGPR, and measured GPR (mGPR). Forty-five re-optimizations were performed. Replanning led to an increase in DVCs for OARs and a reduction for the target. Complexity decreased, reflected by the increase in the MCS from 0.17 to 0.21 (MUlimit) and 0.20 (ASC). The deliverability improved, with the pGPR increasing from 93.3% to 94.4% (MUlimit) and 95.1% (ASC), and the mGPR from 99.3% to 99.7% (MUlimit) and 99.8% (ASC). Limiting the MUs or utilizing the ASC reduced the complexity of plans and improved the GPR without compromising the dosimetric quality. These strategies can be used to automate replanning procedures, reduce the workload related to PSQA, and improve patient safety.

Background and Purpose: Small field dosimetry plays a critical role in stereotactic radiotherapy, particularly for elongated fields shaped by multileaf collimators (MLCs). This study aims to optimize the Effective Spot Size (ESS) parameters in the Acuros dose calculation algorithm (Eclipse v18.0, with the enhanced leaf modelling ELM for MLC modelling) for accurate dose calculations of small, rectangular MLC‐shaped fields. Measurements were based on the TRS‐483 protocol and a recently proposed equivalent square field size determination method. Methods: Field output factors (FOFs) were measured using a Varian TrueBeam linear accelerator with HD‐MLC for 6 MV and 10 MV beams (both flattened and unflattened). Symmetric square and rectangular fields (0.5–4 cm sides) were shaped by the MLC, with jaws fixed at 4.4 × 4.4 cm ² to minimize scatter variation. Measurements were performed at isocenter, 10 cm depth using three detectors: microDiamond, PinPoint3D, and DiodeE. The microDiamond detector results were used for ESS optimization due to its complete output correction factor availability. FOFs were calculated in Eclipse v18.0 using Acuros with varying ESS values (0–1.5 mm). The optimal ESS was determined by minimizing FOF differences between calculated and measured values for extreme elongated field sizes in the studied range (0.5 × 4 cm ² and 4 × 0.5 cm ² ). Results: The optimized ESS parameters minimized FOF discrepancies between calculated and measured doses for elongated fields, improving calculation accuracy compared to vendor‐recommended settings (ESSx = 0.5 mm, ESSy = 0.7 mm). Profiles and penumbra analyses supported these findings. Conclusions: ELM in Eclipse v.18 improves MLC modelling by representing rounded leaf ends. Only ESS parameters remain user‐tunable. A method to determine the ESS for the Acuros algorithm is presented, resulting in accurate algorithm configuration for elongated small fields shaped by an HD‐MLC. Results are presented using 6 MV and 10 MV beams, both flattened and unflattened for an HD‐MLC Varian. ESS affects output factors and penumbra, with dose calculations matching measurements within 0.2% ± 0.4% and a maximum difference of 1.1%.

Stereotactic radiosurgery (SRS) for multiple brain metastases can be delivered with a single isocenter and non-coplanar arcs, achieving highly conformal dose distributions at the cost of extreme modulation of treatment machine parameters. As a result, SRS plans are at a higher risk of patient-specific quality assurance (PSQA) failure compared to standard treatments. This study aimed to develop a machine-learning (ML) model to predict the PSQA outcome (gamma passing rate, GPR) of SRS plans. Five hundred and ninety-two consecutive patients treated between 2020 and 2024 were selected. GPR analyses were performed using a 3%/1 mm criterion and a 95% action limit for each arc. Fifteen plan complexity metrics were used as input features to predict the GPR of an arc. A stratified and a time-series approach were employed to split the data into training (1555 arcs), validation (389 arcs), and test (486 arcs) sets. The ML model achieved a mean absolute error of 2.6% on the test set, with a 0.83% median residual value (measured/predicted). Lower values of the measured GPR tended to be overestimated. Sensitivity and specificity were 93% and 56%, respectively. ML models for virtual QA of SRS can be integrated into clinical practice, facilitating more efficient PSQA approaches.

Purpose: To investigate the effect of ion recombination () and polarity () correction factors on percentage depth dose (PDD) curves for three ion chambers, using flat and flattening filter free (FFF) beams, across different broad field sizes. A method to assess these effects and their corresponding corrections is proposed.Methods: and were evaluated following the IAEA TRS‐398 protocol for three ion chambers: PTW Semiflex‐3D‐31021, PinPoint‐3D‐31022, and Semiflex‐31010. PDD measurements were acquired from d_max to 32 cm depth at four voltages (± 400 V or ± 300 V, and ± 100 V) for field sizes 4 × 4, 10 × 10, 20 × 20, and 40 × 40 cm². The values were computed after the correction at each applied voltage. This study aimed to assess the variation of the factors along scanning depths for different field sizes, to evaluate the need for correcting the scanning data.Results: was independent of depth and field size for Semiflex‐3D, while it presented an increasing value with depth for the PinPoint‐3D. increased with dose rate, i.e., decreased with depth. The variation of this perturbation effect over the PDD range was about 0.1% for flat beams with all three ion chambers. With FFF beams, it was around 0.3% with PinPoint‐3D, and 0.8% for 10FFF with Semiflex‐3D. A second‐order polynomial fit can be determined to directly correct the raw data scanned along the beam axis for both and .Conclusion: can significantly affect the PDD scanning measurements in FFF beams acquired with Semiflex‐3D. An error close to 1% at large depths could be present, meaning an error of less than 0.3% relative to the dose at the depth of d_max.

In this paper, we aim to evaluate the entity of inter-fraction organ motion and deformation in stereotactic body radiotherapy (SBRT) treatments for nodal oligometastatic prostate cancer (PCa). Thirty-three patients with lymph nodes showing oligometastatic PCa treated with SBRT were included. Organs at risk (OARs) were delineated using both simulation computer tomography (s-CT) and daily cone beam CTs (CBCTs) using the Raystation planning system. For each OAR, the union volume (UV) between all the CBCTs and s-CT was computed. An expanded volume (EV) of the s-CT OARs was applied using six different margins (3, 5, 8, 10, 15, and 20 mm). A percentage volume (V%) was computed to assess the intersection between each EV and UV. The OAR deformation and motion were further evaluated using the dice similarity coefficient (DSC) and mean distance to agreement (Mean_DA). The percentage maximum dose variations for all the OARs were estimated. A recalculation with higher dose prescriptions was performed by prescribing 36 Gy/3 fx, as well as 45 Gy/3 fx. The cauda showed the highest matching (DSC = 0.72; Mean_DA = 0.14 cm), and the colon showed the lowest one (DSC = 0.37; Mean_DA = 0.44 cm). The minimum margin, which ensured a V% > 95%, was 3 mm (97.5%) for the cauda and 15 mm (96.6%) for the colon. All the OARs reached the compliance of the constraints in each session. Regarding 36 Gy-plans, the ileum punctual compliance Dmax failed in 58.8% of patients, and it failed in 70.6% of the patients for the ileum, 7.14% for the colon, and 12.5% for the bladder in the case of 45 Gy-plans. This study is an ancillary study of the RADIOSA clinical trial (AIRC IG-22159) and can be used as a benchmark for dose escalation.