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• Total Body Irradiation in-vivo dosimetry data over 10 years were analyzed. • Monitor Units' median percentage difference from planned was limited. • Median percentage dose difference at six anatomical locations was inside 10 % range. • The neck region showed the highest dosimetric differences from planned. • In-vivo dosimetry omission impact was evaluated, leading to interesting results. Myeloablative Total Body Irradiation (TBI) used in our Institution, as part of the conditioning scheme for haematopoietic stem cell transplantation, is an extended-distance supine technique that has been implemented using a 15 MV LINAC beam, lead lung compensators, PMMA, and water bolus to improve homogeneity. This study reviews in-vivo dosimetry (IVD) over 10 years of treatments, assessing the technique's robustness, accuracy, and efficiency. A 2-lateral opposite fields plan was calculated from planning CT with validated Oncentra TPS (Elekta AB, Sweden). Monitor units (MUs), lung compensators shape and thickness were calculated to deliver the prescription dose (12 Gy in 6 bi-daily fractions or 9.9 Gy in 3 daily fractions) to the patient's abdomen midline at the umbilical level, maintaining lung dose within ±5 % range of prescription. Data from 103 patients, of which more than 87 % were pediatric, were retrieved and analyzed for a total of 537 treatment fractions. The impact of IVD omission was evaluated, supposing doing it only once or in the first two fractions, if necessary. Median ΔMU from planned was −1.2 %. Median percentage dose deviation from prescription in 6 anatomical regions was below 2 %. IVD omission could have resulted in an increase of 7 patients registering at least one anatomical region outside the ±5 % dose range at the end of treatment. It is possible to confirm the implemented technique's robustness and accuracy in delivering the prescribed dose under IVD monitoring. Nevertheless, this technique and associated IVD are time-consuming and IVD omission could be assessed with limited drawbacks. [ABSTRACT FROM AUTHOR]

• Pelvis auto-segmentation tools were compared, from atlas-techniques to deep learning. • Deep learning showed better and faster segmentation results. • Differences found in cervical cancer tapered off in prostate cancer contouring. • Expert radiation oncologists qualitatively preferred deep learning. • Automated tools allow for faster radiotherapy workflow and high-quality treatments. Artificial intelligence can standardize and automatize highly demanding procedures, such as manual segmentation, especially in an anatomical site as common as the pelvis. This study investigated four automated segmentation tools on computed tomography (CT) images in female and male pelvic radiotherapy (RT) starting from simpler and well-known atlas-based methods to the most recent neural networks-based algorithms. The evaluation included quantitative, qualitative and time efficiency assessments. A mono-institutional consecutive series of 40 cervical cancer and 40 prostate cancer structure sets were retrospectively selected. After a preparatory phase, the remaining 20 testing sets per each site were auto-segmented by the atlas-based model STAPLE, a Random Forest-based model, and two Deep Learning-based tools (DL), MVision and LimbusAI. Setting manual segmentation as the Ground Truth, 200 structure sets were compared in terms of Dice Similarity Coefficient (DSC), Hausdorff Distance (HD), and Distance-to-Agreement Portion (DAP). Automated segmentation and manual correction durations were recorded. Expert clinicians performed a qualitative evaluation. In cervical cancer CTs, DL outperformed the other tools with higher quantitative metrics, qualitative scores, and shorter correction times. On the other hand, in prostate cancer CTs, the performance across all the analyzed tools was comparable in terms of both quantitative and qualitative metrics. Such discrepancy in performance outcome could be explained by the wide range of anatomical variability in cervical cancer with respect to the strict bladder and rectum filling preparation in prostate Stereotactic Body Radiation Therapy (SBRT). Decreasing segmentation times can reduce the burden of pelvic radiation therapy routine in an automated workflow. [ABSTRACT FROM AUTHOR]

In stereotactic radiosurgery (SRS) and fractionated stereotactic radiosurgery (fSRS) of brain metastases (BM) using single-isocenter VMAT, intra-fraction positioning errors may affect target coverage. This study aims to investigate geometric and dosimetric accuracy in single and multiple BM treatments. Seventy patients with single (n = 38) and multiple (n = 32) BM treated with 15-21 Gy in 1 (n = 59) or 27 Gy in 3 (n = 11) fractions using coplanar FFF-VMAT technique were analyzed. PTV was defined by a 2 mm isotropic GTV expansion. Pre-treatment setup errors were evaluated with CBCT and corrected with a robotic six degrees-of-freedom couch. For each fraction, intra-fractional errors were measured by post-treatment CBCT and applied to the planning CT. Plans involving translations and rotations (Fx-plan) were recalculated with Monte Carlo TPS. Original and Fx-plans were compared in terms of target and brain dose parameters, performing the Wilcoxon-Mann-Whitney test (alpha = 0.05). The relationships of the BM volume, maximum dimension, distance-to-isocenter (for multiple BM cases only) and barycenter shift with the difference in target coverage between the two plans were investigated. The median post-treatment 3D error and maximum rotational error over all 129 BM were 0.5 mm [0.1–2.7] and 0.3° [0.0–1.3], respectively. The resulting median BM barycenter shift was 0.5 mm [0.1–2.7]. The percentage of fractions in which at least one BM barycenter shifted by more than 2 mm from the planned position was 4% and 1% for single and multiple BM cases, respectively. The median single GTV volume was 0.27 cc [0.01–10.48], while the PTV had a median volume of 1.05 cc [0.12–17.05]. The median BM maximum dimension was 10.7 mm [2.9–34.1] and for multiple BM the median distance-to-isocenter was 5.15 cm [0.89–7.52]. For single BM patients, the GTV D95% was never reduced by > 5%, while PTV D95% reductions > 1% occurred in only 11 (29%) PTV. For multiple BM patients, the target statistics were slightly worse, with dose deficits larger than 5% and 1% occurring respectively in 2 BM and 34 (37%) PTV. Anyway, the majority of single and multiple BM had a loss of coverage for both GTV and PTV below 1% in Fx-plans. Larger than 5% brain V12 Gy (SRS) and V20 Gy (fSRS) increases were observed for only one single BM patient. None of the two dosimetric comparisons resulted statistically significant (p>0.05). The differences in target coverage showed a moderate-to-strong correlation only with the BM barycenter shift in both cases (R2 = 0.70-0.73 for single and R2 = 0.44-0.50 for multiple BM). Due to the optimal patient setup, as well as the full six degrees-of-freedom corrections, the safety PTV margin, and the fast beam delivery, the dosimetric effects of residual setup and patient motion errors for both single and multiple BM cases were negligible. These findings warrant a potential reduction in the PTV margin with this treatment technique. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the impact of intrafraction prostate motion and interfraction anatomical changes on dose metrics and the effect of beam gating and motion correction in dose-escalated Linac-based SBRT. Thirteen patients (56 fractions) with organ-confined prostate cancer underwent dose-escalated FFF-VMAT SBRT. Accurate patient setup was ensured by CBCT, and real-time 3D prostate motion data were obtained using a novel electromagnetic tracking device. Treatment was interrupted when the signals exceeded a 2 mm threshold in any of the three spatial directions and couch position was corrected unless the offset was transient. Prostate trajectories with and without beam gating and motion correction events were reconstructed and analyzed. Rectum and bladder volumes on each daily CBCT were recorded and compared with volumes at simulation. The prostate motion observed for each fraction was incorporated into the patient original treatment plan with an isocenter shift method. Actually, delivered treatments were then obtained by recalculating the reconstructed motion-encoded plan on deformed CTs reflecting the patient CBCT-anatomy of the day. Non-gated treatments were also simulated using the prostate motion data assuming that no treatment interruptions have occurred. Treatment interruptions because of target motion trespassing the predefined threshold occurred in 25 fractions (45%). Rectum and bladder volume changes were relevant in most patients. The mean relative dose differences between actually delivered and planned treatments were -3.0% [-18.5 – 2.8] for CTV D99% and -2.6% [-17.8 – 1.0] for PTV D95% over all 56 fractions. However, the median cumulative CTV coverage with 93% of the prescribed dose turned out to be satisfactory. Urethra sparing was slightly degraded and a mean reduction of rectum and bladder dose was seen in all but two dose metrics: the maximum dose to rectum mucosa and the bladder D40%. Nevertheless, only 2 major deviations in rectum mucosa D0.035cc were observed at the end of the treatment. The greatest contribution to target missing and OARs doses came from the interfraction anatomical variations, while intrafraction prostate motion marginally contributed in gated treatments. In non-gated treatments, further deteriorations by 2.4 – 2.8% in minimum target coverage metrics and by 3.1 – 11.6% in bladder dose parameters would have occurred on average. The implemented motion management strategy and the strict patient preparation regimen, along with current PTV margins, robustness of original treatment plans, and fast FFF beam delivery, ensured no significant degradations of dose metrics due to both intrafraction motion and interfraction anatomical changes. Non-gated treatments would have more widely deteriorated the dosimetry of some individual fractions. Thus, continuous monitoring, beam gating and motion correction are recommended to safely deliver dose-escalated prostate SBRT. [ABSTRACT FROM AUTHOR]

This study reports the first clinical experience worldwide using a novel electromagnetic (EM) tracking device for intrafraction prostate motion management during dose-escalated Linac-based stereotactic body radiation therapy (SBRT). Thirteen patients with organ-confined prostate cancer underwent dose-escalated SBRT using flattening filter-free (FFF) volumetric modulated arc therapy (VMAT). The prescribed dose was 40 Gy in 5 fractions or 38 Gy in 4 fractions. The EM tracking device consisted of an integrated Foley catheter with a transmitter. Patients were simulated and treated with a filled bladder and an empty rectum. Setup accuracy was achieved by ConeBeam-CT (CBCT) matching and the prostate motion was tracked during all the procedure. Treatment was interrupted when the signals exceeded a 2 mm threshold in any of the three spatial directions and, unless the offset was transient, target position was re-defined by repeating CBCT. Moreover, the displacements that would have occurred without any intrafraction organ motion management (i.e., no interruptions and repositionings) were simulated and analyzed. In 31 out of 56 monitored fractions (55%), no intervention was required to correct the target position as a result of an excessive displacement. In 25 (45%) a correction was mandated, but only in 10 (18%), the beam delivery was interrupted. Total treatment time lasted on average 10.2 minutes, 6.7 minutes for setup, and 3.5 minutes for beam delivery. The prostate was found inside the 2 mm threshold from its initial position in 96% of the treatment time, i.e., in 94% of the time during the setup, and in 98% during the delivery (beam on + interruptions). Without any intrafraction motion management, the overall mean treatment time and the mean delivery time would have been 6.9 minutes and 3.2 minutes, respectively. The prostate would have been found outside the tolerance in 8% of the total session time, in 4% of the time during the setup, and in 14% during the beam-on phase. The probability of motion > 2 mm in the lateral, longitudinal, and vertical direction after 5 minutes was 3.6% (2/56), 8.9% (5/56), and 14.3% (8/56), respectively. The predominant motion pattern was posterior with a mean motion ≤ 2 mm occurring within 10 minutes. Moreover, the analysis of the rotation angles from all patients showed a systematic rotation in the pitch axis which is absent in the yaw axis. Concurrently, the range and standard deviation of rotation angles were larger in the pitch axis. EM real-time tracking was successfully implemented for intrafraction motion management during dose-escalated prostate SBRT. Results showed that most of the observed displacements were < 2 mm in any direction; however, there were a non-insignificant number of fractions with motion exceeding the predefined threshold, which would have otherwise gone undetected without intrafraction motion management. [ABSTRACT FROM AUTHOR]