Background and purpose: This study aimed to evaluate the dosimetric performance and robustness of volumetric modulated arc therapy (VMAT) planning techniques-planning target volume with internal margin (INT), auto flash (AF), and virtual bolus (VB)-under simulated geometric changes during whole-breast radiotherapy.
Methods: Nine patients with left-sided breast cancer were included. Three planning techniques were compared: INT with a 5-mm skin-sparing internal margin, AF with a 1-cm automatic skin flash margin, and VB with a 5-mm optimization bolus applied only during the planning. Respiratory motion was simulated by shifting the plan center (± 3 mm and ± 5 mm) and recalculating the dose distributions.
Results: Under static conditions, all plans provided adequate target coverage, with planning target volume (PTV) V95% values of 96.45% (INT), 97.35% (AF), and 98.19% (VB). Under breast swelling of up to 5 mm, AF maintained the most stable coverage (PTV V95% = 99.10%), outperforming VB (95.02%) and INT (92.31%) (p < 0.001). In simulated incomplete inspiration (5 mm), VB showed superior robustness, achieving a PTV V95% of 90.46% compared with AF (85.30%) and INT (85.08%) (p = 0.008). AF met the ideal criteria in all cases under swelling conditions, whereas the VB was more effective against suboptimal respiration.
Conclusions: In VMAT breast radiation therapy (RT), the conventional INT approach was the least robust against variations, and additional techniques are required. AF effectively compensates for breast swelling, whereas VB preserves the target coverage under insufficient breath-hold conditions. Surface-guided radiation therapy (SGRT) and visual guidance are recommended to ensure accurate treatment.
Background: Frameless linear accelerator (linac)-based image-guided stereotactic radiosurgery (SRS) or fractionated stereotactic radiotherapy (FSRT) are a widely used treatment option for intracranial lesions. Given the high radiation doses involved, it is crucial to maintain precise patient positioning throughout treatment. This requires that geometric inaccuracies arising from patient motion or setup errors are identified and corrected. With frameless immobilization, image-guidance has a greater impact, especially in non-coplanar settings that can lead to patient motion and discrepancies between couch and radiation isocenters.
Purpose: Both patient and phantom studies were conducted to assess and quantify the magnitude of geometric uncertainties after couch rotations, aiming at evaluating the clinical need for their correction to warrant a precise treatment delivery.
Methods: Intrafraction X-ray data, performed by ExacTrac Dynamic (ETD) to monitor and correct patients' position throughout treatment delivery, were collected from 50 patients treated for brain metastases in stereotactic non-coplanar schemes and immobilized by stereotactic double-layered thermoplastic mask systems: 26 patients treated in 40 single-fraction SRS (168 stereoscopic X-ray images); 24 treated with FSRT in 128 fractions (278 stereoscopic X-ray images). Additionally, a head phantom was utilized and 350 measurements under two different couch loads were carried out to distinguish true patient motion from deviations caused by couch rotations or system-related effects. For both studies, ETD stereoscopic X-rays were acquired after each couch rotation and the first measured positioning deviation was calculated by comparing X-ray images to the treatment plan's digitally reconstructed radiographs.
Results: Clinically relevant deviations were observed, exceeding clinical tolerance (≥ 0.5 mm/0.5°) mostly in the lateral and yaw directions and requiring repositioning in nearly half of the couch rotations. These deviations measuring up to 2 mm, revealed to be emerging mainly from patient motion rather than linac setup, as the phantom study showed maximum deviations of up to 0.6 mm and 0.4° when simulating a patient treatment and an interquartile range that did not exceed 0.2 mm and 0.2°.
Conclusions: These findings demonstrate the importance of a continuous intrafraction motion monitoring and repositioning in cranial stereotactic treatments, especially in non-coplanar settings.
Background: Multiparametric MRI is useful for early detection of clinically significant prostate cancer (csPCa), but its standard apparent diffusion coefficient (ADC) has limited utility as a quantitative metric for automated, patient-level detection of csPCa. Restriction spectrum imaging (RSI), an advanced diffusion technique, yields a quantitative biomarker (RSIrs) that improves csPCa detection. RSIrs is typically calculated from a dedicated multi-b-value acquisition. RSIrs estimated from conventional MRI has not been studied.
Purpose: To evaluate the accuracy and validity of RSI metrics estimated post hoc from conventional diffusion-weighted imaging (DWI) to serve as a viable surrogate for a dedicated RSI acquisition.
Materials and methods: We conducted a retrospective, multicenter study of patients with both a dedicated RSI acquisition and conventional DWI. We compared three different RSI restriction score (RSIrs) calculation methods: from the dedicated acquisition (RSIrsdedicated), from conventional DWI alone (RSIrspost-hoc), and from a combination of conventional DWI with only the high b-values from the RSI acquisition (RSIrscombo). We compared these methods for quantitative agreement and csPCa detection performance (area under the receiver operating characteristic [AUC, 95% confidence interval]) of maximum RSIrs (RSIrsmax) in the prostate compared to that of minimum ADC (ADC).
Results: Data from n = 1095 patients (16 centers) were analyzed. Post hoc RSIrsmax differed systematically from RSIrsdedicated by a median of +156 (RSIrspost-hoc) and -59 (RSIrscombo), respectively. AUCs for csPCa detection were 0.51 [0.47,0.54], 0.60 [0.57,0.64], 0.70 [0.67,0.74], and 0.77 [0.74,0.80] for ADC, RSIrspost-hoc, RSIrscombo, and RSIrsdedicated, respectively.
Conclusion: Even when estimated using conventional DWI, RSIrs is a superior quantitative biomarker to ADC for automated, patient-level detection of csPCa. A dedicated RSI acquisition gives the best performance. A compromise would be to acquire high b-values (1500 and 2500 s/mm2) to complement low b-values (<1000 s/mm2) from conventional DWI.
Purpose: Intrafraction motion management is recognized as a critical component of radiotherapy. While clinical trials often recommend its use, they rarely define motion management tolerances. Consequently, institutions set tolerance levels independently, often without considering patient specific anatomy, dose distributions or direction of motion. This study introduces an automated method that can be used to derive patient specific, asymmetric intrafraction motion monitoring tolerances based on individualized treatment plans.
Methods: Treatment plans for 20 prostate cancer patients receiving a simultaneous integrated boost to dominant intraprostatic lesions (DIL) were retrospectively analyzed. Referred to as the isocentre translation method, patient movement was simulated by recalculating plans with the isocentre shifted by 2, 4 and 5 mm in six different directions. The magnitude and direction that resulted in violations of dose constraints for organ at risk (OAR) rectum, bladder and urethra was determined assuming a systematic shift for all fractions. A second automated approach, the contour translation method, used Eclipse Scripting API to estimate directional tolerances via contour translation and Boolean operations, avoiding dose recalculation. Results for this method were validated against the isocentre translation method and compared for efficiency by assessing processing time.
Results: The magnitude and direction of motion to cause OAR constraint violations were organ and patient specific. Urethral violations were most sensitive to shifts toward the DIL, whereas bladder and rectum constraints were primarily affected by anterior/superior and posterior shifts, respectively. The contour translation method was demonstrated to be equivalent to the isocentre translation method within an equivalence margin of 0.5 mm. The contour translation method significantly reduced processing time (4 min 40s vs. 47 min 52s per patient).
Conclusion: The direction and extent of motion impacting OAR constraints vary by patient and organ, supporting the need for personalized intrafraction motion monitoring tolerances. The proposed contour translation method provides a practical, efficient process that is able to facilitate individualized motion management in clinical workflows.
Background: Recently, deep learning (DL)-based noise reduction (DLNR) has been introduced in clinically used digital radiography (DR) systems, reporting superior performance over conventional algorithms. However, DLNR algorithms often operate as "black boxes" with nonlinear behavior, making it essential to understand the impact of such processing on image quality under different imaging conditions.
Purpose: This study aimed to quantitatively evaluate the image quality of a commercial DLNR algorithm for DR referred to as intelligent noise reduction (INR). Specifically, we compared its noise reduction performance with that of a conventional rule-based algorithm (conventional noise reduction, Con-NR) using frequency-domain metrics with detailed noise power spectrum (NPS) analysis.
Methods: The NPS was used to assess the spatial-frequency-dependent behavior of both INR and Con-NR across varying dose levels and different objects. In this work, we introduced a supplementary metric-the NPS improvement factor (NPSIF)-to quantify noise suppression across frequency ranges and facilitate direct comparison between methods.
Results: The DL-based algorithm achieved substantial noise reduction at low-dose settings compared with the conventional method, although its advantages were less pronounced at higher dose levels. The NPSIF effectively captured frequency-specific differences, thereby offering insights into the strengths and limitations of each technique.
Conclusions: The dose-dependent performance of the DL-based algorithm suggests sensitivity to the characteristics of the training data used to develop the DL model. The findings demonstrate distinct differences in the noise suppression behavior between DL-based and conventional methods in DR and underscore the importance of detailed frequency-domain evaluation for understanding advanced image processing. Further research is warranted to integrate noise analysis with diagnostic performance metrics to comprehensively assess clinical utility.
Purpose: To assess the clinical utility of Smartfuse (Therapanacea, France), a deformable image registration (DIR) algorithm for automatic propagation of target volumes in the context of offline adaptive head-and-neck radiotherapy.
Materials and methods: Ten patients underwent offline re-planning during head-and-neck radiotherapy. Target volumes (GTV and CTV) were manually delineated by radiation oncologists (ROs) on both the initial CT (CTi) and one re-planning CT (CTR). These manual contours were compared to those propagated by Smartfuse from CTi to CTR. The geometric agreement between DIR-propagated and RO-delineated contours was assessed using Dice similarity coefficient (DSC), 95th percentile Hausdorff distance (HD95), and surface Dice similarity coefficient (sDSC) with 0 and 2 mm thresholds. Dosimetric evaluation was conducted by comparing dose distributions from generated plans using automatically propagated target volumes (PTVDIR) with reference plans based on RO-delineated targets (PTVRO). Coverage of RO-delineated targets (GTVRO + CTVRO and PTVRO) was assessed using D95%, D50%, Dmax, and V95% ≥ 95%. Spatial dose differences were analyzed using dose difference (DD) metrics at 5% and 2% thresholds.
Results: Median DSC, HD95, sDSC0 mm and sDSC2 mm were 0.86, 4.0 mm, 0.29 and 0.73, respectively. For D95%, median relative differences between DIR and RO plans were -0.6% for GTVRO + CTVRO and -2.1% for PTVRO for D95%. All GTVRO + CTVRO reached V95% ≥ 95% with DIR plans, but only 61% of PTVRO did. Spatial DD analysis showed median pass rates of 99.2% (DD5%) and 74.5% (DD2%) for GTVRO + CTVRO, and 85.5% (DD5%) and 54.9% (DD2%) for PTVRO.
Conclusion: Smartfuse may facilitate efficient propagation of target volumes in this study. However, medical review of auto-propagated volumes remains essential, as dosimetric discrepancies may arise when relying solely on automatically generated PTV.
Purpose: Total body irradiation (TBI) is an important part of conditioning regimens prior to hematopoietic stem cell transplantation (HSCT). At our institution, a conventional TBI technique employing bilateral fields at extended source-to-axis distance (eSAD) and a solid three-dimensional (3D) compensator has been standard practice since the 80s. However, its ability to minimize lung dose remains limited.
Aims: This study aims to modernize the existing TBI technique using the capabilities of our treatment planning system (TPS). The proposed hybrid method replaces solid compensators with virtual compensation by combining bilateral intensity-modulated radiotherapy (IMRT) fields at eSAD of 500 cm with volumetric modulated arc therapy (VMAT) fields at standard SAD 100 cm for the thoracic region.
Methods: At first, the Anisotropic Analytical Algorithm (AAA) V16 and AcurosXB (AXB) V16 dose calculation algorithms of the Eclipse TPS (Varian) were commissioned for use at eSAD. Dosimetric measurements were performed in water, solid water, and inhomogeneous phantoms. Subsequently, a treatment planning strategy was developed to minimize the influence of positioning uncertainties on lung dose. Anonymized computed tomography (CT) datasets representing diverse patient anatomies were utilized for treatment planning evaluation. Final validation was conducted through an end-to-end test using an anthropomorphic phantom. SAD VMAT and eSAD IMRT fields were verified using a two-dimensional (2D) dosimetry chamber array positioned at both caudal and cranial thoracic levels under SAD and eSAD setups. The resulting cumulative dose was then compared with the AXB-calculated dose.
Results: At eSAD, mean measured-calculated dose deviations were < 2% for AXB and < 4% for AAA, with confidence limits of 3.5% and 5%, respectively. These results affirmed the clinical viability of both algorithms, with AXB providing superior dose calculation accuracy. Planning studies showed consistent PTV coverage with lung dose reduction across diverse anatomies, and end-to-end phantom validation confirmed the workflow practicability. Verification of summed dose using the 2D array, with 95% of evaluated points meeting a gamma criterion of 5 mm and 5%, provided additional confidence in the dosimetric robustness of the treatment concept.
Conclusion: This study showed the feasibility of a novel hybrid eSAD IMRT/VMAT TBI technique providing a clinically viable approach enabling effective lung dose sparing while maintaining the robustness of large-field irradiation.
Purpose: This study aimed to evaluate a novel technological platform, Taichi Pro-which integrates a 6 MV flattening filterfree linear accelerator with a 18 source Rotating Gamma System (RGS) to generate steep dose gradients via multisource focused γ-rays and noncoplanar arcs-for precision radiotherapy in prostate cancer. The work provides evidence to support the clinical adoption of hybridmodality radiotherapy devices.
Methods: Fifteen prostate cancer patients were enrolled. For each patient, a dual-modality Taichi Pro plan (RGS focused on the planning gross tumor volume (PGTV) + Linac covering the planning target volume (PTV)) and a Halcyon photon plan (three-arc VMAT) were designed while maintaining clinically tolerable dose to organs at risk (OAR). Comparative assessments included planning target volume (PTV and PGTV) metrics (D95%, Dmean, homogeneity index HI, conformity index CI), OAR doses (rectum V40/V60/D2cc, bladder V40, testis D2cc, etc.) and delivery efficiency to evaluate the ability to escalate target dose while sparing adjacent OARs.
Results: All plans met institutional clinical constraints. Taichi Pro significantly increased PGTV Dmean (79.48 Gy ± 1.75 Gy) compared to Halcyon (73.25 Gy ± 0.55 24 Gy, P < 0.001) and Dmax (122.74 Gy ± 8.69 Gy) compared to Halcyon (76.15 Gy ± 0.79 Gy, P < 0.001), albeit poorer homogeneity (HI: 0.50 ± 0.09 for Taichi Pro vs. 0.06 ± 0.01 for Halcyon, though within clinically acceptable limits). Taichi Pro significantly reduced rectum V60 (3.97% ± 3.25% vs. Halcyon 7.46% ± 4.78%, P = 0.016), and D2cc (61.61 Gy ± 5.01 Gy vs. Halcyon 65.29 Gy ± 4.52 Gy, P = 0.040). Taichi Pro also significantly reduced testis D2cc (2.39 ± 1.99 Gy) compared to (3.17 Gy ± 1.40 Gy, P = 0.006). Halcyon demonstrated significantly shorter beam-on time (1.81 ± 0.23 minutes vs. 5.05 ± 1.59 minutes for Taichi Pro, P < 0.001).
Conclusion: Utilizing the steep dose gradient characteristic of the RGS, the Taichi Pro dual-modality system effectively achieved target dose escalation while simultaneously improving sparing of adjacent OARs. This approach holds the potential for enhancing patient treatment outcomes and quality of life.
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