Initial Experience of CT-Based Online Adaptive Radiotherapy for Nasopharyngeal Carcinoma With a Novel Integrated Platform: A Case Report.

Intensity-modulated radiation therapy (IMRT) improves tumor control and reduces long-term radiation-induced complications of patients with nasopharyngeal carcinoma (NPC), contingent upon accurate contouring and precise delivery of treatment plans. Online adaptive radiotherapy (ART) involves real-time treatment plan modification based on the variations in targets and organs at risk (OARs) to uphold treatment planning accuracy. This study describes the first reported case of fan beam computed tomography (FBCT)-guided online ART for NPC using a novel integrated platform. Online ART was performed at the 25th fraction in this case, as tumors and the patient's anatomy were observed to regress inter-fractionally, necessitating adjustments to the contours based on the anatomy of the day. Online ART plan optimized target volume coverage while reducing doses to OARs. Notably, online ART significantly improved radiotherapy efficiency. This patient achieved a clinical complete response 12 weeks post-treatment, with Epstein-Barr virus DNA levels reduced to 0 copies/ml. Currently, the patient is alive without evidence of high-grade toxicity or local recurrence at approximately 10 months post-treatment. This case confirms the feasibility and dosimetric benefit of online ART for NPC using a novel integrated platform. Further research is needed to confirm its clinical benefits.

Assessment of Volumetric Changes Using Megavoltage-Cone Beam Computed Tomography (MV-CBCT) for Adaptive Radiotherapy in Head and Neck Cancer: A Case Series.

Intensity-modulated radiation therapy (IMRT) has brought about interest in adaptive radiotherapy (ART) due to its benefit of accurately prescribing doses to tumors and sparing normal critical organs. Critical dosimetric errors and geometrical misses can occur due to anatomical changes during radiotherapy. In the present study, five patients with head and neck malignancies undergoing radiation therapy were assessed for changes in primary gross tumor volume (GTVp), nodal gross tumor volume (GTVn), and clinical target volume-high risk (CTV-HR) using weekly megavoltage-cone beam computed tomography (MV-CBCT) scans. All patients had a reduction in GTV and lateral neck diameter (LND). There were reductions in tumor volumes leading to re-planning in the 20th fraction. Daily CBCT can guide the decision on the need for adaptation in patients with tumor volume reduction and with volumes going outside the body.

CT-Guided Online Adaptive Stereotactic Body Radiotherapy (SBRT) for Retroperitoneal Sarcoma After Previous Radiotherapy: A Case Report.

CT-guided online adaptive radiotherapy (OART) is a novel and robust treatment technique in radiotherapy. Thanks to its excellent accommodation of inter-fraction variations, OART is characterized by superior accuracy compared to other contemporary treatment techniques in radiotherapy such as image-guided radiotherapy (IGRT). Planning target volume (PTV), which takes into account interfraction movements, could therefore be reduced while utilizing OART with a consequent dose reduction for adjacent healthy tissue. Herein we report our successful experience in treating a patient with retroperitoneal sarcoma after previous radiotherapy and surgery. The tumor was in close proximity to the spinal canal and abutted a large bowel segment and the last portions of the duodenum. Radiotherapy regimen consisted of 30 Gy in five fractions. Treatment implementation and delivery were feasible and the treatment was given without any interruptions. After a follow-up period of nine months so far, the patient reported no radiation-related adverse effects. Furthermore, her post-treatment magnetic resonance imaging (MRI) scans demonstrate good radiographic response.  Our case highlights the use of OART to treat a challenging case in radiotherapy as it was given in the setting of re-irradiation to a mesenchymal tumor, which is considered exquisitely radio-resistant.

Personalized Brachytherapy: Applications and Future Directions.

Brachytherapy offers a highly conformal and adaptive approach to radiation therapy for various oncologic conditions. This review explores the rationale, applications, technological advances, and future directions of personalized brachytherapy. Integration of advanced imaging techniques, 3D-printed applicators, and artificial intelligence are rapidly enhancing brachytherapy delivery and efficiency, while genomic tests and molecular biomarkers are refining patient and dose selection. Emerging research on combining brachytherapy with immunotherapy offers unique synergistic potential, and technologies such as intensity-modulated and shielded brachytherapy applicators present novel opportunities to further optimize dose distributions. Despite these promising advances, the field faces challenges including a need to train more practitioners and develop new approaches to treating a broader range of malignancies. As personalized medicine evolves, brachytherapy's ability to deliver highly targeted, individualized treatments positions it as a critical component in future cancer care.

Cone-Beam Computed Tomography (CBCT)-Based Online Adaptive Radiation Therapy (oART) for a Prostate Cancer Patient With Inflammatory Bowel Disease and Bilateral Total Hip Arthroplasty: A Case Report.

This case report addresses the complex management of a patient with concurrent prostate cancer, inflammatory bowel disease (IBD), and bilateral total hip arthroplasty, and demonstrates the efficacy of cone-beam computed tomography (CBCT)-guided daily online adaptive radiation therapy (oART) and advanced imaging techniques in overcoming significant treatment challenges. A 68-year-old male with a history of ulcerative colitis and bilateral hip prostheses was diagnosed with high-risk prostate cancer. Conventional radiation therapy modalities, including external beam radiation therapy (EBRT), proton therapy, and magnetic resonance imaging (MRI)-based oART, faced limitations because of the patient's comorbidities and metallic implants. Daily oART, using the Ethos platform (Varian Medical Systems, Palo Alto, CA, USA) with HyperSight™ metal artifact reduction (MAR) imaging, was employed to enhance treatment efficacy. The daily oART treatment on the Ethos platform facilitated the successful delivery of a therapeutic dose while sparing healthy tissues, and the treatment was successful without an IBD flare-up. Daily oART also optimized the target dose while best sparing the critical organs based on the patient's daily anatomy. The HyperSight MAR algorithm significantly reduced imaging artifacts caused by the hip prostheses, enabling accurate identification of the prostate, bladder, and surrounding organs. The oART workflow was delivered without technical challenges, with a total session time of 20 to 30 minutes, similar to our typical prostate patients without hip implants. Despite the complex anatomy and comorbid conditions, the treatment plan met all organ-at-risk constraints and delivered the prescribed dose to the target volumes. Ethos oART with HyperSight provided an effective solution for treating a patient with concurrent prostate cancer, IBD, and bilateral hip arthroplasty. The patient's case was successfully treated without complications, despite such challenging clinical and technical scenarios.

Personalizing radiotherapy with adaptive radiotherapy: Interest and challenges.

Adaptive radiotherapy (ART) is a recent development in radiotherapy technology and treatment personalization that allows treatment to be tailored to the daily anatomical changes of patients. While it was until recently only performed "offline", i.e. between two radiotherapy sessions, it is now possible during ART to perform a daily online adaptive process for a given patient. Therefore, ART allows a daily customization to ensure optimal coverage of the treatment target volumes with minimized margins, taking into account only the uncertainties related to the adaptive process itself. This optimization appears particularly relevant in case of daily variations in the positioning of the target volume or of the organs at risk (OAR) associated with a proximity of these volumes and a tenuous therapeutic index. ART aims to minimize severe acute and late toxicity and allows tumor dose escalation. These new achievements have been possible thanks to technological development, the contribution of new multimodal and onboard imaging modalities and the integration of artificial intelligence tools for the contouring, planning and delivery of radiation therapy. Online ART is currently available on two types of radiotherapy machines: MR-linear accelerators and recently CBCT-linear accelerators. We will first describe the benefits, advantages, constraints and limitations of each of these two modalities, as well as the online adaptive process itself. We will then evaluate the clinical situations for which online adaptive radiotherapy is particularly indicated on MR- and CBCT-linear accelerators. Finally, we will detail some challenges and possible solutions in the development of online ART in the coming years.

Achieving a Pathologic Complete Response for Locally Advanced Esophageal Adenocarcinoma Using Cone-Beam Computed Tomography-Based Online Adaptive Radiotherapy.

Neo-adjuvant chemoradiotherapy (CRT) and perioperative chemotherapy are different strategies for treating non-metastatic esophageal cancer (EC). The advantages of neo-adjuvant therapies are primarily seen in patients who achieve a pathologic complete response (pCR) and therefore show higher survival rates and better prognosis. In general, less than one-third of patients with EC experience pCR after neo-adjuvant therapies; however, patients with esophageal adenocarcinoma (AC) demonstrate lower rates of pCR compared to those with esophageal squamous cell carcinoma (SCC), respectively. Herein, we describe two cases of locally advanced esophageal AC treated with cone-beam computed tomography (CBCT)-based online adaptive radiotherapy (ART) on the ETHOS platform. Both patients received CRT with 50.4 Gy in 28 fractions, combined with weekly carboplatin and paclitaxel. For each fraction, we evaluated scheduled and adapted plans using dose-volume histogram (DVH) data, and patients were treated with the superior plan. We prioritized ensuring optimal coverage of the planning target volume (PTV) over limiting the dose to organs at risk (OARs) when selecting the superior treatment plan. In this instance, we present the translation of superior dosimetric data into clinical benefits, as evidenced by an excellent pathologic response.

Cone-Beam Computed Tomography-Guided Online Adaptive Radiotherapy: Promising Results for Bladder Cancer Case.

Bladder radiotherapy is challenging due to daily anatomical variations and unpredictable bladder filling, particularly affecting tumors in the cranial part. Conventional radiotherapy requires large planning target volume margins to manage these uncertainties, but this can expose healthy tissue to high radiation doses, increasing the risk of acute and late toxicity. Our aim was to study the potential to limit high-dose exposure to healthy tissue by comparing daily online adaptive radiotherapy (oART) with conventional, non-adaptive radiotherapy (non-ART). The comparison was performed on a bladder cancer patient treated with a simultaneous integrated boost while having a challenging tumor location in the cranial part of the bladder. Liquid fiducial markers aided during the localization of the tumor bed to deliver this focal boost. The dose distribution of oART fractions performed in the clinic was compared with simulated non-ART fractions on the post-treatment cone-beam computed tomography (CBCT). The results showed that while maintaining target coverage of the bladder and gross tumor volume in 100% of the fractions for both workflows, the high dose exposure to organs-at-risk was lower for oART. The small bowel received statistically significantly (p ≤ 0.05) less dose with oART compared to non-ART, with a median volume difference of 20 cm3 receiving 95% of the prescribed dose (55 Gy). The total volume of tissue outside the target receiving 95% of the prescribed dose was also smaller for oART compared to non-ART (p ≤ 0.05). The follow-up of two years showed that the patient had no long-term toxicity effects. Therefore, CBCT-guided oART has been shown to offer a conformal treatment for a challenging patient and can provide a clear advantage in the treatment of bladder cancer.

Split-Course Adaptive Radioimmunotherapy for Oligometastatic Non-Small Cell Lung Cancer (SiCARIO): A Case Report.

Current treatment paradigms for oligometastatic non-small cell lung cancer (NSCLC) utilize systemic chemotherapy alone or in combination with immune checkpoint inhibitors (ICIs). The addition of ICIs in NSCLC has led to significant improvements in survival; however, recurrence remains common. New methods are needed to enhance anti-tumor immune responses and improve patient outcomes. Here, we present the first case of utilization of the Ethos OART platform to deliver multi-site pulsed hypofractionated radiotherapy in a patient with oligometastatic disease on the single arm prospective clinical trial SiCARIO (Split-Course Adaptive Radioimmunotherapy in Oligometastatic NSCLC, NCT05501665). A 67-year-old man with stage IV NSCLC with metastases to bilateral adrenal glands, retroperitoneum, and mesentery was prescribed treatment of 40 Gy in 5 fractions on SiCARIO in combination with SOC chemoimmunotherapy. A multi-target single isocenter approach was utilized to treat nine distinct targets in five total isocenters. Treatment plans were generated using an isotopic approach prioritizing organ at risk (OAR) constraints with the goal of minimum coverage of at least 30 Gy in 5 fractions. CBCT was acquired with each fraction to generate new targets and OAR contours based on anatomic changes with the patient on the treatment table. A comparison of an adapted plan to a base plan was performed online with a selection of superior plans based on target coverage and OAR constraints. The adapted plan was deemed superior for all but 1 fraction of a single isocenter for this patient. The discussion will focus primarily on the bilateral adrenal isocenter, where bulk tumor shrinkage of greater than 80% was observed in this patient with corresponding significant dosimetric benefits. This case demonstrates a potential clinical benefit of OART in multi-metastasis RT. Further data is needed to confirm the safety and efficacy of this approach. Enrollment is ongoing.

Dose-escalated Adaptive Radiotherapy for Bladder Cancer: Results of the Phase 2 RAIDER Randomised Controlled Trial.

BACKGROUND AND OBJECTIVE: Delivering radiotherapy to the bladder is challenging as it is a mobile, deformable structure. Dose-escalated adaptive image-guided radiotherapy could improve outcomes. RAIDER aimed to demonstrate the safety of such a schedule. METHODS: RAIDER is an international phase 2 noncomparative randomised controlled trial (ISRCTN26779187). Patients with unifocal T2-T4a urothelial bladder cancer were randomised (1:1:2) to standard whole bladder radiotherapy (WBRT), standard-dose adaptive radiotherapy (SART), or dose-escalated adaptive radiotherapy (DART). Two fractionation (f) schedules recruited independently. WBRT and SART dose was 55 Gy/20f or 64 Gy/32f, and DART dose was 60 Gy/20f or 70 Gy/32f. For SART and DART, a radiotherapy plan (small, medium, or large) was chosen daily. The primary endpoint was the proportion of patients with radiotherapy-related late Common Terminology Criteria for Adverse Events grade ≥3 toxicity; the trial was designed to rule out >20% toxicity with DART. KEY FINDINGS AND LIMITATIONS: A total of 345 patients were randomised between October 2015 and April 2020: 41/46 WBRT, 41/46 SART, and 81/90 DART patients in the 20f/32f cohorts, respectively. The median age was 72/73 yr; 78%/85% had T2 tumours, 46%/52% had neoadjuvant chemotherapy, and 70%/71% had radiosensitising therapy. The median follow-up was 42.1/38.2 mo. Sixty-six of 77 (86%) 20f and 74 of 82 (90%) 32f participants planned for DART met the mandatory medium plan dose constraints. Radiotherapy-related grade ≥3 toxicity was reported in one of 58 patients (90% confidence interval [CI] 0.1, 7.9) with 20f DART and zero of 56 patients with 32f DART. Two-year overall survival was 77% (95% CI 69, 82) for WBRT + SART and 80% (95% CI 73, 85) for DART (hazard ratio = 0.84, 95% CI 0.59, 1.21, p = 0.4). Thirteen of 345 (3.8%) participants had salvage cystectomy. CONCLUSIONS AND CLINICAL IMPLICATIONS: Grade ≥3 late toxicity was low. DART was safe and feasible to deliver, meeting preset toxicity thresholds. Disease-related outcomes are promising for dose-escalated treatments, with a low salvage cystectomy rate and overall survival similar to that seen in cystectomy cohorts.

Minimizing human interference in an online fully automated daily adaptive radiotherapy workflow for bladder cancer.

PURPOSE: The aim was to study the potential for an online fully automated daily adaptive radiotherapy (RT) workflow for bladder cancer, employing a focal boost and fiducial markers. The study focused on comparing the geometric and dosimetric aspects between the simulated automated online adaptive RT (oART) workflow and the clinically performed workflow. METHODS: Seventeen patients with muscle-invasive bladder cancer were treated with daily Cone Beam CT (CBCT)-guided oART. The bladder and pelvic lymph nodes (CTVelective) received a total dose of 40 Gy in 20 fractions and the tumor bed received an additional simultaneously integrated boost (SIB) of 15 Gy (CTVboost). During the online sessions a CBCT was acquired and used as input for the AI-network to automatically delineate the bladder and rectum, i.e. influencers. These influencers were employed to guide the algorithm utilized in the delineation process of the target. Manual adjustments to the generated contours are common during this clinical workflow prior to plan reoptimization and RT delivery. To study the potential for an online fully automated workflow, the oART workflow was repeated in a simulation environment without manual adjustments. A comparison was made between the clinical and automatic contours and between the treatment plans optimized on these clinical (Dclin) and automatic contours (Dauto). RESULTS: The bladder and rectum delineated by the AI-network differed from the clinical contours with a median Dice Similarity Coefficient of 0.99 and 0.92, a Mean Distance to Agreement of 1.9 mm and 1.3 mm and a relative volume of 100% and 95%, respectively. For the CTVboost these differences were larger, namely 0.71, 7 mm and 78%. For the CTVboost the median target coverage was 0.42% lower for Dauto compared to Dclin. For CTVelective this difference was 0.03%. The target coverage of Dauto met the clinical requirement of the CTV-coverage in 65% of the sessions for CTVboost and 95% of the sessions for the CTVelective. CONCLUSIONS: While an online fully automated daily adaptive RT workflow shows promise for bladder treatment, its complexity becomes apparent when incorporating a focal boost, necessitating manual checks to prevent potential underdosage of the target.

Online Adaptive Radiotherapy for Planning Target Volume (PTV) Reduction in Gastric Mucosa-Associated Lymphoid Tissue (MALT) Lymphoma.

Online adaptive radiotherapy (oART) uses daily imaging to identify changes in the patient's anatomy and generate a new treatment plan adapted to these changes, and it can be used for treating gastric mucosa-associated lymphoid tissue (MALT) lymphomas. This study aimed to determine the intrafraction motion and planning target volume (PTV) margins required for an oART workflow on a cone beam computed tomography (CBCT)-based dedicated system (Ethos®, Varian Medical Systems, Palo Alto, California, United States) and investigate the potential benefits for patients compared with a non-adaptive workflow. Involving three patients treated for gastric MALT lymphoma with the oART under breath-hold (BH) technique, the study determined a PTV margin for adaptive treatment using CBCT scans performed at the beginning and just before treating the patients for 34 fractions. Different PTVs were made by isotropically extending the clinical target volume (CTV) contoured on the first CBCT (CTV1) at intervals of 1 mm to evaluate intrafraction gastric motion, with the expansion covering the contoured CTV on the second CBCT (CTV2) quantifying the intrafraction motion (adaptive treatment) and the expansion from the CTV delineated on the planning scanner (CTVplanning) that could cover both CTV1 and CTV2 defining the interfraction motion (non-adaptive treatment). PTV margins were then determined as the extension of the CTV allowing coverage of 95% of its volume in 90% of fractions, and the dosimetric impact on dose constraints between an adaptive plan and a non-adaptive plan based on the predetermined margins was evaluated. A total of 68 CBCTs were analyzed, revealing that the PTV margin for oART was 4 mm, while for non-adaptive treatment it was 12 mm, with an average time elapsed between CBCT1 and CBCT2 of 11.62 minutes and no correlation between inter-CBCT timing and PTV margins (Pearson R-coefficient=0.10). All dosimetric constraints were met in both adaptive and non-adaptive plans, but the adaptive plan allowed for reduced organ-at-risk (OAR) doses in each patient. The study concluded that oART could reduce PTV margins in the treatment of gastric MALT lymphoma, especially with a BH strategy, impacting OAR dosimetry, though more prospective studies are required to validate these findings and determine their clinical impact on patients.

Autodelineation methods in a simulated fully automated proton therapy workflow for esophageal cancer.

Background and purpose: Proton Online Adaptive RadioTherapy (ProtOnART) harnesses the dosimetric advantage of protons and immediately acts upon anatomical changes. Here, we simulate the clinical application of delineation and planning within a ProtOnART-workflow for esophageal cancer. We aim to identify the most appropriate technique for autodelineation and evaluate full automation by replanning on autodelineated contours. Materials and methods: We evaluated 15 patients who started treatment between 11-2022 and 01-2024, undergoing baseline and three repeat computed tomography (CT) scans in treatment position. Quantitative and qualitative evaluations compared different autodelineation methods. For Organs-at-risk (OAR) deep learning segmentation (DLS), rigid and deformable propagation from baseline to repeat CT-scans were considered. For the clinical target volume (CTV), rigid and three deformable propagation methods (default, heart as controlling structure and with focus region) were evaluated. Adaptive treatment plans with 7 mm (ATP7mm) and 3 mm (ATP3mm) setup robustness were generated using best-performing autodelineated contours. Clinical acceptance of ATPs was evaluated using goals encompassing ground-truth CTV-coverage and OAR-dose. Results: Deformation was preferred for autodelineation of heart, lungs and spinal cord. DLS was preferred for all other OARs. For CTV, deformation with focus region was the preferred method although the difference with other deformation methods was small. Nominal ATPs passed evaluation goals for 87 % of ATP7mm and 67 % of ATP3mm. This dropped to respectively 2 % and 29 % after robust evaluation. Insufficient CTV-coverage was the main reason for ATP-rejection. Conclusion: Autodelineation aids a ProtOnART-workflow for esophageal cancer. Currently available tools regularly require manual annotations to generate clinically acceptable ATPs.

Impact of contrast-enhanced CT in the dosimetry of SBRT for liver metastases treated with MR-Linac.

BACKGROUND: To investigate the impact of using contrast-enhanced computed tomography (CHCT) in the dosimetry of stereotactic body radiation therapy (SBRT) for liver metastases treated with MR-Linac. METHODS: A retrospective study was conducted on 21 liver cancer patients treated with SBRT (50 Gy in 5 fractions) using a 1.5 Tesla Unity MR-Linac. The clinical treatment plans optimised on plain computed tomography (pCT) were used as reference. The electronic density (ED) of regions of interest (ROIs) including the liver, duodenum, esophagus, spinal cord, heart, ribs, and lungs, from pCT and CHCT, was analysed. The average ED of each ROI from CHCT was used to generate synthetic CT (sCT) images by assigning the average ED value from the CHCT to the pCT. Clinical plans were recalculated on sCT images. Dosimetric comparisons between the original treatment plan (TPpCT) and the sCT plan (TPsCT) were performed using dose-volume histogram (DVH) parameters, and gamma analysis. RESULTS: Significant ED differences (p < 0.05) were observed in the liver, great vessels, heart, lungs, and spinal cord between CHCT and pCT, with the lungs showing the largest differences (average deviation of 11.73% and 12.15% for the left and right lung, respectively). The target volume covered by the prescribed dose (VDpre), and the dose received by 2% and 98% of the volume (D2%, and D98%, respectively) showed statistical differences (p < 0.05), while the gradient index (GI) and the conformity index (CI) did not. Average deviations in target volume dosimetric parameters were below 1.02%, with a maximum deviation of 5.57% for. For the organs at risk (OARs), significant differences (p < 0.05) were observed for D0.35cc and D1.2cc of the spinal cord, D10cc for the stomach, D0.5cc for the heart, and D30% for the liver-GTV, with mean deviations lower than 1.83% for all the above OARs. Gamma analysis using 2%-2 mm criteria yielded a median value of 95.64% (range 82.22-99.65%) for the target volume and 99.40% (range 58-100%) for the OARs. CONCLUSION: The findings suggest that the use of CHCT in the SBRT workflow for liver metastases may result in minor target volume overdosage, indicating its potential for adoption in clinical settings. However, its use should be further explored in a broader context and tied to personalized treatment approaches.

News and prospects on radiotherapy for bladder cancer: Is trimodal therapy becoming the gold standard?

Trimodal therapy consisting of transurethral resection of bladder tumors followed by radiotherapy and chemotherapy, has emerged as a valuable therapeutic alternative to radical cystectomy in patients with muscle invasive bladder cancer. Concomitant radiosensitising chemotherapy is a component of trimodality increasing locoregional control compared to radiotherapy alone. The combinations 5-fluorouracil with mitomycin or cisplatin are the best supported in the literature. Gemcitabine appears to be a feasible and promising alternative. There is considerable international heterogeneity in terms of dose, volumes and fractionation. The most commonly used regimens are moderately hypofractionated (55Gy in 20 fractions over 4 weeks) and normofractionated (64Gy in 32 fractions) regimens. Radiotherapy for bladder cancer is an effective and evolving treatment, with current technical developments, and studies of new combinations with systemic treatments underway.

Large Pleural Metastases With Significant Inter-fractional Volume Reduction During Online Adaptive Radiotherapy: A Case Report With Dosimetry Comparison.

Online adaptive radiotherapy (oART) dose calculation relies on synthetic computed tomography (sCT), which notably influences anatomical changes. This study elucidates how sCT may respond to significant inter-fractional tumor volume reduction and its subsequent impact on dose distribution. In this case report, we exported sCT and cone-beam CT (CBCT) images from each treatment session. We retrospectively analyzed 20 adaptive and scheduled plans of a patient receiving oART for large pleural metastases with notable inter-fractional tumor regression. By overriding the CT number of the dissipated tumor volume with that of the lungs on each sCT, we recalculated each plan. We compared the dose distribution between the adaptive and scheduled plans. Percentage dose difference and 3D gamma analysis were employed to assess dose variability. Results of the dose analysis showed that, compared to the online (non-overridden) plans, the recalculated plans using overridden sCT demonstrated right-shifted dose-volume histogram curves for the targets and right lung, with a slight but statistically significant increase of no less than 1.5% in D mean and D max for the targets and right lung. The location of hotspots shifted in alignment with tumor shrinkage and beam arrangement. Both recalculated adaptive and scheduled plans achieved ideal GTV, CTV, and PTV coverage, with adaptive plans significantly reducing the dose and irradiated volume to the right lung. In conclusion, as the pleural tumor volume decreased, online plans slightly underestimated the dose distribution and shifted the location of hotspots, though this remained clinically acceptable. Importantly, adaptive plans significantly minimized the irradiated volume of the critical OAR (right lung) while ensuring optimal dose coverage of the target volume, demonstrating the potential of sCT and adaptive oART to enhance treatment precision and efficacy in dynamically changing tumor environments.

A patient-specific auto-planning method for MRI-guided adaptive radiotherapy in prostate cancer.

BACKGROUND AND PURPOSE: Fast and automated generation of treatment plans is desirable for magnetic resonance imaging (MRI)-guided adaptive radiotherapy (MRIgART). This study proposed a novel patient-specific auto-planning method and validated its feasibility in improving the existing online planning workflow. MATERIALS AND METHODS: Data from 40 patients with prostate cancer were collected retrospectively. A patient-specific auto-planning method was proposed to generate adaptive treatment plans. First, a population dose-prediction model (M0) was trained using data from previous patients. Second, a patient-specific model (Mps) was created for each new patient by fine-tuning M0 with the patient's data. Finally, an auto plan was optimized using the parameters derived from the predicted dose distribution by Mps. The auto plans were compared with manual plans in terms of plan quality, efficiency, dosimetric verification, and clinical evaluation. RESULTS: The auto plans improved target coverage, reduced irradiation to the rectum, and provided comparable protection to other organs-at-risk. Target coverage for the planning target volume (+0.61 %, P = 0.023) and clinical target volume 4000 (+1.60 %, P < 0.001) increased. V2900cGy (-1.06 %, P = 0.004) and V1810cGy (-2.49 %, P < 0.001) to the rectal wall and V1810cGy (-2.82 %, P = 0.012) to the rectum were significantly reduced. The auto plans required less planning time (-3.92 min, P = 0.001), monitor units (-46.48, P = 0.003), and delivery time (-0.26 min, P = 0.004), and their gamma pass rates (3 %/2 mm) were higher (+0.47 %, P = 0.014). CONCLUSION: The proposed patient-specific auto-planning method demonstrated a robust level of automation and was able to generate high-quality treatment plans in less time for MRIgART in prostate cancer.

Prior-image-based low-dose CT reconstruction for adaptive radiation therapy.

Objective. The study aims to reduce the imaging radiation dose in Adaptive Radiotherapy (ART) while maintaining high-quality CT images, critical for effective treatment planning and monitoring.Approach. We developed the Prior-aware Learned Primal-Dual Network (pLPD-UNet), which uses prior CT images to enhance reconstructions from low-dose scans. The network was separately trained on thorax and abdomen datasets to accommodate the unique imaging requirements of each anatomical region.Main results. The pLPD-UNet demonstrated improved reconstruction accuracy and robustness in handling sparse data compared to traditional methods. It effectively maintained image quality essential for precise organ delineation and dose calculation, while achieving a significant reduction in radiation exposure.Significance. This method offers a significant advancement in the practice of ART by integrating prior imaging data, potentially setting a new standard for balancing radiation safety with the need for high-resolution imaging in cancer treatment planning.

Clinical implementation of real time motion management for prostate SBRT: A radiation therapist's perspective.

Background and purpose: The adoption of hypo-fractionated stereotactic body radiotherapy (SBRT) for treating prostate cancer has led to an increase in specialised techniques for monitoring prostate motion. The aim of this study was to comprehensively review a radiation therapist (RTT) led treatment process in which two such systems were utilised, and present initial findings on their use within a SBRT prostate clinical trial. Materials and Methods: 18 patients were investigated, nine were fitted with the Micropos RayPilotTM (RP) system (Micropos Medical, Gothenburg, SE) and nine were fitted with the Micropos Raypilot Hypocath TM (HC) system. 36.25 Gray (Gy) was delivered in 5 fractions over 7 days with daily pre- and post-treatment cone beam computed tomography (CBCT) images acquired. Acute toxicity was reported on completion of treatment at six- and 12-weeks post-treatment, using the Radiation Therapy Oncology Group (RTOG) grading system and vertical (Vrt), longitudinal (Lng) and lateral (Lat) transmitter displacements recorded. Results: A significant difference was found in the Lat displacement between devices (P=0.003). A more consistent bladder volume was reported in the HC group (68.03 cc to 483.7 cc RP, 196.11 cc to 313.85 cc HC). No significant difference was observed in mean dose to the bladder, rectum and bladder dose maximum between the groups. Comparison of the rectal dose maximum between the groups reported a significant result (P=0.09). Comparing displacements with toxicity endpoints identified two significant correlations: Grade 2 Genitourinary (GU) at 6 weeks, P=0.029; and no toxicity, Gastrointestinal (GI) at 12 weeks P=0.013. Conclusion: Both the directly implanted RP device and the urinary catheter-based HC device are capable of real time motion monitoring. Here, the HC system was advantageous in the SBRT prostate workflow.

Dose tracking assessment for magnetic resonance guided adaptive radiotherapy of rectal cancers.

BACKGROUND: Magnetic resonance-guided adaptive radiotherapy (MRgART) at MR-Linac allows for plan optimisation on the MR-based synthetic CT (sCT) images, adjusting the target and organs at risk according to the patient's daily anatomy. Conversely, conventional linac image-guided radiotherapy (IGRT) involves rigid realignment of regions of interest to the daily anatomy, followed by the delivery of the reference computed tomography (CT) plan. This study aims to evaluate the effectiveness of MRgART versus IGRT for rectal cancer patients undergoing short-course radiotherapy, while also assessing the dose accumulation process to support the findings and determine its usefulness in enhancing treatment accuracy. METHODS: Nineteen rectal cancer patients treated with a 1.5 Tesla MR-Linac with a prescription dose of 25 Gy (5 Gy x 5) and undergoing daily adapted radiotherapy by plan optimization based on online MR-based sCT images, were included in this retrospective study. For each adapted plan ([Formula: see text]), a second plan ([Formula: see text]) was generated by recalculating the reference CT plan on the daily MR-based sCT images after rigid registration with the reference CT images to simulate the IGRT workflow. Dosimetry of [Formula: see text] and[Formula: see text]was compared for each fraction. Cumulative doses on the first and last fractions were evaluated for both workflows. The dosimetry per single fraction and the cumulative doses were compared using dose-volume histogram parameters. RESULTS: Ninety-five fractions delivered with MRgART were compared to corresponding simulated IGRT fractions. All MRgART fractions fulfilled the target clinical requirements. IGRT treatments did not meet the expected target coverage for 63 out of 94 fractions (67.0%), with 13 fractions showing a V95 median point percentage decrease of 2.78% (range, 1.65-4.16%), and 55 fractions exceeding the V107% threshold with a median value of 15.4 cc (range, 6.0-43.8 cc). For the bladder, the median [Formula: see text] values were 18.18 Gy for the adaptive fractions and 19.60 Gy for the IGRT fractions. Similarly the median [Formula: see text] values for the small bowel were 23.40 Gy and 25.69 Gy, respectively. No statistically significant differences were observed in the doses accumulated on the first or last fraction for the adaptive workflow, with results consistent with the single adaptive fractions. In contrast, accumulated doses in the IGRT workflow showed significant variations mitigating the high dose constraint, nevertheless, more than half of the patients still did not meet clinical requirements. CONCLUSIONS: MRgART for short-course rectal cancer treatments ensures that the dose delivered matches each fraction of the planned dose and the results are confirmed by the dose accumulation process, which therefore seems redundant. In contrast, IGRT may lead to target dose discrepancies and non-compliance with organs at risk constraints and dose accumulation can still highlight notable dosimetric differences.