Impact of data transfer between treatment planning systems on dosimetric parameters.

PURPOSE: In radiotherapy it is often necessary to transfer a patient's DICOM (Digital Imaging and COmmunications in Medicine) dataset from one system to another for re-treatment, plan-summation or registration purposes. The aim of the study is to evaluate effects of dataset transfer between treatment planning systems. MATERIALS AND METHODS: Twenty-five patients treated in a 0.35T MR-Linac (MRidian, ViewRay) for locally-advanced pancreatic cancer were enrolled. For each patient, a nominal dose distribution was optimized on the planning MRI. Each plan was daily re-optimized if needed to match the anatomy and exported from MRIdian-TPS (ViewRay Inc.) to Eclipse-TPS (Siemens-Varian). A comparison between the two TPSs was performed considering the PTV and OARs volumes (cc), as well as dose coverages and clinical constraints. RESULTS: From the twenty-five enrolled patients, 139 plans were included in the data comparison. The median values of percentage PTV volume variation are 10.8 % for each fraction, while percentage differences of PTV coverage have a mean value of -1.4 %. The median values of the percentage OARs volume variation are 16.0 %, 7.0 %, 10.4 % and 8.5 % for duodenum, stomach, small and large bowel, respectively. The percentage variations of the dose constraints are 41.0 %, 52.7 % and 49.8 % for duodenum, stomach and small bowel, respectively. CONCLUSIONS: This study has demonstrated a non-negligible variation in size and dosimetric parameters when datasets are transferred between TPSs. Such variations should be clinically considered. Investigations are focused on DICOM structure algorithm employed by the TPSs during the transfer to understand the cause of such variations.

Inter-institutional variability of knowledge-based plan prediction of left whole breast irradiation.

PURPOSE: Within a multi-institutional project, we aimed to assess the transferability of knowledge-based (KB) plan prediction models in the case of whole breast irradiation (WBI) for left-side breast irradiation with tangential fields (TF). METHODS: Eight institutions set KB models, following previously shared common criteria. Plan prediction performance was tested on 16 new patients (2 pts per centre) extracting dose-volume-histogram (DVH) prediction bands of heart, ipsilateral lung, contralateral lung and breast. The inter-institutional variability was quantified by the standard deviations (SDint) of predicted DVHs and mean-dose (Dmean). The transferability of models, for the heart and the ipsilateral lung, was evaluated by the range of geometric Principal Component (PC1) applicability of a model to test patients of the other 7 institutions. RESULTS: SDint of the DVH was 1.8 % and 1.6 % for the ipsilateral lung and the heart, respectively (20 %-80 % dose range); concerning Dmean, SDint was 0.9 Gy and 0.6 Gy for the ipsilateral lung and the heart, respectively (<0.2 Gy for contralateral organs). Mean predicted doses ranged between 4.3 and 5.9 Gy for the ipsilateral lung and 1.1-2.3 Gy for the heart. PC1 analysis suggested no relevant differences among models, except for one centre showing a systematic larger sparing of the heart, concomitant to a worse PTV coverage, due to high priority in sparing the left anterior descending coronary artery. CONCLUSIONS: Results showed high transferability among models and low inter-institutional variability of 2% for plan prediction. These findings encourage the building of benchmark models in the case of TF-WBI.

Evaluation of clinical parallel workflow in online adaptive MR-guided Radiotherapy: A detailed assessment of treatment session times.

Introduction: Advancements in MRI-guided radiotherapy (MRgRT) enable clinical parallel workflows (CPW) for online adaptive planning (oART), allowing medical physicists (MPs), physicians (MDs), and radiation therapists (RTTs) to perform their tasks simultaneously. This study evaluates the impact of this upgrade on the total treatment time by analyzing each step of the current 0.35T-MRgRT workflow. Methods: The time process of the workflow steps for 254 treatment fractions in 0.35 MRgRT was examined. Patients have been grouped based on disease site, breathing modality (BM) (BHI or FB), and fractionation (stereotactic body RT [SBRT] or standard fractionated long course [LC]). The time spent for the following workflow steps in Adaptive Treatment (ADP) was analyzed: Patient Setup Time (PSt), MRI Acquisition and Matching (MRt), MR Re-contouring Time (RCt), Re-Planning Time (RPt), Treatment Delivery Time (TDt). Also analyzed was the timing of treatments that followed a Simple workflow (SMP), without the online re-planning (PSt + MRt + TDt.). Results: The time analysis revealed that the ADP workflow (median: 34 min) is significantly (p < 0.05) longer than the SMP workflow (19 min). The time required for ADP treatments is significantly influenced by TDt, constituting 40 % of the total time. The oART steps (RCt + RPt) took 11 min (median), representing 27 % of the entire procedure. Overall, 79.2 % of oART fractions were completed in less than 45 min, and 30.6 % were completed in less than 30 min. Conclusion: This preliminary analysis, along with the comparative assessment against existing literature, underscores the potential of CPW to diminish the overall treatment duration in MRgRT-oART. Additionally, it suggests the potential for CPW to promote a more integrated multidisciplinary approach in the execution of oART.

Motion and dosimetric criteria for selecting gating technique for apical lung lesions in magnetic resonance guided radiotherapy.

Introduction: Patients treatment compliance increases during free-breathing (FB) treatment, taking generally less time and fatigue with respect to deep inspiration breath-hold (DIBH). This study quantifies the gross target volume (GTV) motion on cine-MRI of apical lung lesions undergoing a SBRT in a MR-Linac and supports the patient specific treatment gating pre-selection. Material and methods: A total of 12 patients were retrospectively enrolled in this study. During simulation and treatment fractions, sagittal 0.35 T cine-MRI allows real-time GTV motion tracking. Cine-MRI has been exported, and an in-house developed MATLAB script performed image segmentation for measuring GTV centroid position on cine-MRI frames. Motion measurements were performed during the deep inspiration phase of DIBH patient and during all the session for FB patient. Treatment plans of FB patients were reoptimized using the same cost function, choosing the 3 mm GTV-PTV margin used for DIBH patients instead of the original 5 mm margin, comparing GTV and OARs DVH for the different TP. Results: GTV centroid motion is <2.2 mm in the antero-posterior and cranio-caudal direction in DIBH. For FB patients, GTV motion is lower than 1.7 mm, and motion during the treatment was always in agreement with the one measured during the simulation. No differences have been observed in GTV coverage between the TP with 3-mm and 5-mm margins. Using a 3-mm margin, the mean reduction in the chest wall and trachea-bronchus Dmax was 2.5 Gy and 3.0 Gy, respectively, and a reduction of 1.0 Gy, 0.6 Gy, and 2.3% in Dmax, Dmean, and V5Gy, respectively, of the homolateral lung and 1.7 Gy in the contralateral lung Dmax. Discussions: Cine-MRI allows to select FB lung patients when GTV motion is <2 mm. The use of narrower PTV margins reduces OARs dose and maintains target coverage.

Why we should care about gas pockets in online adaptive MRgRT: a dosimetric evaluation.

Introduction: Contouring of gas pockets is a time consuming step in the workflow of adaptive radiotherapy. We would like to better understand which gas pockets electronic densitiy should be used and the dosimetric impact on adaptive MRgRT treatment. Materials and methods: 21 CT scans of patients undergoing SBRT were retrospectively evaluated. Anatomical structures were contoured: Gross Tumour Volume (GTV), stomach (ST), small bowel (SB), large bowel (LB), gas pockets (GAS) and gas in each organ respectively STG, SBG, LBG. Average HU in GAS was converted in RED, the obtained value has been named as Gastrointestinal Gas RED (GIGED). Differences of average HU in GAS, STG, SBG and LBG were computed. Three treatment plans were calculated editing the GAS volume RED that was overwritten with: air RED (0.0012), water RED (1.000), GIGED, generating respectively APLAN, WPLAN and the GPLAN. 2-D dose distributions were analyzed by gamma analysis. Parameter called active gas volume (AGV) was calculated as the intersection of GAS with the isodose of 5% of prescription dose. Results: Average HU value contained in GAS results to be equal to -620. No significative difference was noted between the average HU of gas in different organ at risk. Value of Gamma Passing Rate (GPR) anticorrelates with the AGV for each plan comparison and the threshold value for GPR to fall below 90% is 41, 60 and 139 cc for WPLANvsAPLAN, GPLANvsAPLAN and WPLANvsGPLAN respectively. Discussions: GIGED is the right RED for Gastrointestinal Gas. Novel AGV is a useful parameter to evaluate the effect of gas pocket on dose distribution.

THeragnostic utilities for neoplastic DisEases of the rectum by MRI guided radiotherapy (THUNDER 2) phase II trial: interim safety analysis.

BACKGROUND: The THUNDER-2 phase II single institutional trial investigates the benefits of MRI-guided radiotherapy (MRIgRT) in treating locally advanced rectal cancer (LARC). This study focuses on evaluating the impact of escalating radiation therapy dose in non-responder patients using the Early Tumour Regression Index (ERI) for predicting complete response (CR). The trial's primary endpoint is to increase the CR rate in non-responders by 10% and assess the feasibility of the delta radiomics-based MRIgRT predictive model. This interim analysis assesses the feasibility and safety of the proposed MRIgRT dose escalation strategy in terms of acute toxicity (gastrointestinal, genitourinary and haematological) and treatment adherence. METHODS: Stage cT2-3, N0-2, or cT4 patients with anal sphincter involvement, N0-2a, M0, but without high-risk features were enrolled. MRIgRT treatment consisted of a standard dose of 55 Gy to the Gross Tumor Volume (GTV) and mesorectum, and 45 Gy to the mesorectum and drainage nodes in 25 fractions with concomitant chemotherapy. 0.35 T MRI was used for simulation imaging and daily alignment. ERI was calculated at the 10th fraction. Non-responders with an ERI above 13.1 received intensified dose escalation from the 11th fraction, resulting in a total dose of 60.1 Gy. Acute toxicity was assessed using the CTCAE v.5 scale. RESULTS: From March 2021 to November 2022, 33 out of the total number of 63 patients to be enrolled (52.4%) were included, with one withdrawal unrelated to treatment. Sixteen patients (50%) underwent dose escalation. Treatment was well tolerated, with only one patient (3.1%) in the standard treatment group experiencing acute Grade 3 diarrhea, proctitis, and cystitis. No significant differences in toxicity were observed between the two groups (p = 0.5463). CONCLUSIONS: MRIgRT treatment with dose escalation up to 60.1 Gy is well tolerated in LARC patients predicted as non-responders by ERI, confirming the feasibility and safety of this approach. The THUNDER-2 trial's primary and secondary endpoints will be fully analyzed when all planned patients will be enrolled.

Innovations in imaging modalities: a comparative review of MRI, long-axial field-of-view PET, and full-ring CZT-SPECT in detecting bone metastases.

The accurate diagnosis of bone metastasis, a condition in which cancer cells have spread to the bone, is essential for optimal patient care and outcome. This review provides a detailed overview of the current medical imaging techniques used to detect and diagnose this critical condition focusing on three cardinal imaging modalities: positron emission tomography (PET), single photon emission computed tomography (SPECT) and magnetic resonance imaging (MRI). Each of these techniques has unique advantages: PET/CT combines functional imaging with anatomical imaging, allowing precise localization of metabolic abnormalities; the SPECT/CT offers a wider range of radiopharmaceuticals for visualizing specific receptors and metabolic pathways; MRI stands out for its unparalleled ability to produce high-resolution images of bone marrow structures. However, as this paper shows, each modality has its own limitations. The comprehensive analysis does not stop at the technical aspects, but ventures into the wider implications of these techniques in a clinical setting. By understanding the synergies and shortcomings of these modalities, healthcare professionals can make diagnostic and therapeutic decisions. Furthermore, at a time when medical technology is evolving at a breakneck pace, this review casts a speculative eye towards future advances in the field of bone metastasis imaging, bridging the current state with future possibilities. Such insights are essential for both clinicians and researchers navigating the complex landscape of bone metastasis diagnosis.

Dose-response Analysis in Hepatic Tumors Treated with 90Y-TARE According to a Personalized Dosimetric Workflow: Preliminary Results.

BACKGROUND: Transarterial Radioembolization (TARE) is a widespread radiation therapy for unresectable hepatic lesions, but a clear understanding of the dose-response link is still missing. The aim of this preliminary study is to investigate the role of both dosimetric and clinical parameters as classifiers or predictors of response and survival for TARE in hepatic tumors and to present possible response cut-off. METHODS: 20 patients treated with glass or resin microspheres according to a personalized workflow were included. Dosimetric parameters were extracted from personalized absorbed dose maps obtained from the convolution of 90Y PET images with 90Y voxel S-values. RESULTS: D95 ≥ 104 Gy and tumor mean absorbed dose MADt ≥ 229 Gy were found to be optimal cut-off values for complete response, while D30 ≥ 180 Gy and MADt ≥ 117 Gy were selected as cut-off values for at least partial response and predicted better survival. Clinical parameters Alanine Transaminase (ALT) and Model for End-Stage Liver Disease (MELD) didn't show sufficient classification capability for response or survival. CONCUSION: These preliminary results highlight the importance of an accurate dosimetric evaluation and suggest a cautious approach when considering clinical indicators. Dosimetric cut-off values could be a support tool in both planning and post-treatment phases. Larger multi-centric randomized trials, with standardized methods regarding patient selection, response criteria, Regions of Interest definition, dosimetric approach and activity planning are needed to confirm these promising results.

Use of secondary air kerma from dose area product and fluoroscopy time for preventive effective dose estimation in interventional radiology procedures for staff.

INTRODUCTION: interventional radiology workers are potentially exposed to high levels of ionizing radiation, therefore preventive dose estimation is mandatory for the correct risk classification of staff. Effective dose (ED) is a radiation protection quantity strictly related to the secondary air kerma (KS), using appropriate multiplicative conversion factors (ICRP 106). The aim of this work is to evaluate the accuracy ofKSestimated from physically measurable quantities such as dose-area product (DAP) or fluoroscopy time (FT). METHODS: radiological units (n= 4) were characterized in terms of primary beam air kerma and DAP-meter response, consequently defining a DAP-meter correction factor (CF) for each unit.KS, scattered from an anthropomorphic phantom and measured by a digital multimeter, was then compared with the value estimated from DAP and FT. Different combinations of tube voltages, field sizes, current and scattering angles were used to simulate the variation of working conditions. Further measurements were performed to estimate the couch transmission factor for different phantom placements on the operational couch, defining a CF as the mean transmission factor. RESULTS: when no CFs were applied, the measuredKSshowed a median percentage difference of between 33.8% and 115.7% with respect toKSevaluated from DAP, and between -46.3% and 101.8% forKSevaluated from FT. By contrast, when previously defined CFs were applied to the evaluatedKS, the median percentage difference between the measuredKSand the value evaluated from DAP ranged from between -7.94% and 15.0%, and between -66.2% and 17.2% for that evaluated from FT. CONCLUSION: when appropriate CF are applied, the preventive ED estimation from the median DAP value seems to be more conservative and easier to obtain with respect to the one obtained from the FT value. Further measurements should be performed with a personal dosimeter during routine activities to assess the properKSto ED conversion factor.