Planning Target Volume Research Articles

The impact of setup errors on dose distribution in cervical cancer radiotherapy and the margin from CTV to PTV

PurposeThis study calculates the needed margin from clinical target volume (CTV) to planning target volume (PTV) in IMRT for cervical cancer. It also assesses the impact of setup errors on target and organ at risk (OAR) dose distribution.MethodsWe retrospectively analyzed 50 cervical cancer patients who underwent IMRT, with 210 CBCT scans. We calculated the CTV-to-PTV margin and simulated setup errors in the TPS to reassess dose distribution impacts on targets and OAR.ResultsSetup errors in X(anterior–posterior,AP), Y(cranial–caudal,CC), and Z(left–right,LR) directions were (1.4 ± 1.0) mm, (2.3 ± 1.5) mm, and (1.9 ± 1.2) mm, respectively, leading to CTV-to-PTV margins of 4.4 mm, 6.4 mm, and 5.8 mm. X-axis errors did not significantly affect target dosimetry (P > 0.05), but Y and Z errors did (P < 0.05). X-axis errors impacted the small intestine and rectum (P < 0.05), Y-axis errors mainly affected the colon (P < 0.05), and Z-axis errors affected the colon, small intestine, and rectum (P < 0.05).ConclusionOur study underscores the need to account for setup errors in radiotherapy for cervical cancer. Customizing the CTV-to-PTV margin based on institutional error data is key to maintaining target dose coverage and optimizing treatment outcomes.

CBCT-Based Online Adaptive Radiotherapy: A Promising Approach for Gastric Mucosa-Associated Lymphoid Tissue (MALT) Lymphoma?

PurposeDaily online adaptive radiotherapy (oART) opens the opportunity to treat gastric mucosa-associated lymphoid tissue (MALT) lymphoma with a reduced margin. This study reports our early experience of cone-beam computed tomography (CBCT)-based daily oART treating gastric MALT lymphoma with breath-hold (BH) and reduced margins. MethodsTen patients were treated on a CBCT-based oART system. Organs at risk (OARs) and the clinical target volume (CTV) were adjusted based on the daily CBCT. Planning target volume (PTV) was derived from the CTV with a 0.5-0.7 cm margin with BH. Multiple beam arrangements were compared during the preplanning phase to ensure minimal Monitor Unit (MU) for patient comfort and breath-hold reproducibility. For 108 fractions from the ten patients, the PTV, CTV coverage, Paddick Conformity Index (CI) were compared between the adapted and scheduled plans. The MU, Paddick CI, and gradient index (GI) were compared using relative percentage differences between the adapted plans and preplans. The OAR doses from 106 fractions across nine patients were reported for the preplans, adapted plans, and scheduled plans. The time statistics for each step of the clinical workflow were recorded and reported for 93 treatment fractions from nine patients. ResultsThe PTV volume varied from -37.1% to 90.5% (11.7% ± 18.5%) throughout treatments across all patients. The adapted plan was chosen as the treatment plan for each fraction due to superior PTV and CTV coverage while maintaining a similar OAR dose. The PTV and CTV coverage for the adapted and scheduled plans was VRx=95.0 ± 0.3% vs. 64.1 ± 19.6% and VRx=99.9 ± 0.1% vs. 74.0 ± 22.2%, respectively. The adapted plans' MU, Paddick CI, and GI were, on average, 4.1%, 0.4%, and -4.2% of the preplan values, respectively. The console's adaptive workflow and physician time were 25±7 and 19±6 minutes, respectively. ConclusionA CBCT-based oART system with the proposed workflow is feasible for treating gastric MALT lymphoma patients using a reduced PTV margin while maintaining excellent target coverage within a reasonable time, resulting in consistent adapted plan quality. This approach can be expanded to a larger cohort of gastrointestinal patients.

Efficacy of a thermoplastic mask and pneumatic abdominal compression device for immobilization in stereotactic ablative radiotherapy of spine metastases.

Stereotactic ablative radiotherapy (SABR) has become a key technique in management of spine metastases. With improved control over treatment plan dosimetry, there is a greater need for accurate patient positioning to guarantee agreement between the treatment plan and delivered dose. With serious potential complications such as fracture and myelopathy, the margins of error in SABR of the spine are minimal. In this study, we assessed the performance of two patient immobilization setups in SABR for spinal metastases. First, a Type-S head and shoulders mask (CQ Medical, Avondale, PA), and second, the BPL1 setup, which includes a wing board, vacuum bag, and the Respiratory Belt for the Body Pro-Lok ONE (CQ Medical, Avondale, PA). Immobilization was assessed using image-guided intrafraction repositioning shifts. Required planning target volume (PTV) margins were calculated based on repositioning data for 172 treated fractions using 2 standard deviation (2SD) and analytic approaches. Overall, 91.7% and 74.1% of fractions treated had total 3D repositioning shifts ≤3.0mm using the Type-S and BPL1 setups, respectively. In the thoracic spine, 43.2% and 46.5% of fractions had shifts ≤1.5mm for the respective setups. Suggested margins were under 3.5mm in all directions and use cases. In the posterior-anterior direction, the BPL1 setup had a 0.6mm smaller suggested margin for the thoracic spine compared to the Type-S setup, at 1.4mm, calculated using the analytic approach. Both the Type-S and BPL1 setups are effective for immobilization in spine SABR. The Type-S demonstrated superior immobilization in the upper spine and remains the clinical standard for cervical and upper thoracic spine positioning. The BPL1 setup showed effective immobilization in use cases treating the mid-to lower thoracic spine and lumbar spine and remains our clinical standard for those use cases. Results additionally demonstrate feasibility of potential PTV margin reduction.

Impact of Treatment Technique on Testicular Dose and Sexual Activity in Rectal Cancer Patients

Abstract Objective To estimate the incidental radiation dose delivered to the testicles in three-dimensional conformal radiotherapy (3DCRT), intensity-modulated radiotherapy (IMRT), and volumetric-modulated arc therapy (VMAT) in rectal cancer patients and its impact on sexual activity using a quality-of-life questionnaire. Materials and Methods The present study included 40 male patients, aged between 25 and 50 years. with locally-advanced rectal cancer, who would undergo neoadjuvant radiotherapy at a dose of 45 Gray (Gy) in 25 fractions (fr) in the supine position. Planning was performed for three techniques: 3DCRT, IMRT, and VMAT. The testicular dose, testicular volume, planning target volume (PTV), the distance of the tumor from the anal verge, and tumor thickness and length in each plan were recorded. A quality-of-life questionnaire pertaining only to sexual activity by the European Organization for Research and Treatment of Cancer–Quality of Life in Colorectal (EORTC QLQ-CR29) and the Functional Assessment of Cancer Therapy–Colorectal (FACT-C) were used to assess the posttreatment effect on sexual life. Results The mean values for tumor length, thickness, and PTV were of 8.9 cm, 1.77 cm and 1,352 cm3 respectively. The mean dose to the right and left testicles (in centigray, cGy) were as follows: 3DCRT – 336.23 and 206.65; IMRT – 165.15 and 140.25; and VMAT – 209.2 and 229.2 respectively. A significant correlation was observed involving the PTV and testicular volume and the incidental testicular dose received. The questionnaire-based analysis of sexual activity included 31 patients who were alive, of whom 27 had resumed their normal sexual life 3 months after the treatment without difficulty (score 4). Conclusion The IMRT showed a significant reduction in the testicular dose when compared to 3DCRT and VMAT. The PTV and testicular volume presented a statistically significant impact on the testicular dose, and the main reason for abstinence was nervousness about disease recurrence.

The conversion of electroanatomic maps for compatibility with treatment planning systems in cardiac radioablation target volume definition.

Cardiac radioablation (CRA) is a new and promising treatment modality for patients with ventricular tachycardia refractory to standard-of-care treatment. Electroanatomic maps are used to define radiation target volumes; however, there is currently no native method to import electroanatomic maps into the treatment planning system (TPS). To develop Edico, a semi-automated tool to enable electroanatomic map import into a TPS, by converting electroanatomic maps to a Digital Imaging and COmmunications in Medicine (DICOM) standard. The overall aim is to facilitate target volume delineation and improve workflow efficiency in treating patients. Edico imports voltage and spatial data from electroanatomic maps and sorts these into voxels to be exported in a DICOM format, with each voxel containing the average voltage value of the data that falls within it. Three different rectangular electroanatomic maps were created and processed using Edico to ensure that expected features are maintained through processing. A sensitivity analysis of voxel size was completed using 19 different electroanatomic maps processed at five different sets of voxel dimensions, for a total of 95 resulting voxelized datasets. The coefficient of variation in each populated voxel in the datasets was analyzed to determine which voxel sizes are necessary to ensure that data loss is kept to a minimum throughout processing, despite averaging. Five electroanatomic maps were used to re-contour clinical target volumes and planning target volumes for previously-treated patients with their electroanatomic maps now directly registered to their planning computed tomography (CT) scans. All three rectangular test electroanatomic maps were processed as expected. All tested voxel sizes resulted in low coefficients of variation overall, with the exception of the largest voxel size of 1.8×1.8×8mm. When using Edico, a user should choose voxel dimensions similar to or smaller than those of a planning CT. Of five pairs of clinical and planning target volumes from previously treated patients, adjustments were made to four (80%), retrospectively, using the electroanatomic maps generated using Edico, registered to the patients' planning CTs. Edico provides a reliable solution for electroanatomic map import into a TPS and facilitates clinical and planning target volume identification in CRA.

Impact of belly board immobilization devices and body mass factor on setup displacement using daily cone-beam CT in rectal cancer radiotherapy.

The objective of this study is to evaluate the impact of different belly board and daily changes in patient's body-mass factor (BMF) on setup displacement in radiotherapy for rectal cancer. Twenty-five patients were immobilized using the thermoplastic mask with belly board (TM-BB), and 30 used the vacuum bag cushion with belly board (VBC-BB), performing daily cone-beam computed tomography (CBCT) scans 625 times and 750 times, respectively. Daily pretreatment CBCT scans were registered to the planned CT images for BMF change determination and setup displacement measurement. Independent t-tests compared setup displacement between the two groups in left-right (LR), superior-inferior (SI), and anterior-posterior (AP) directions, as well as the BMF changes. The impact of daily BMF changes on setup displacement was evaluated using multivariate logistic regression and 10-fold cross-validation. The setup displacement for TM-BB in the LR, SI, and AP directions were 0.31±0.25, 0.58±0.40, and 0.19±0.18cm, respectively, while VBC-BB showed 0.19±0.15, 0.26±0.22, and 0.36±0.29cm in the corresponding directions, respectively. Margins of planning target volume (PTV) for TM-BB were 8, 10, and 6mm in LR, SI, and AP directions, while VBC-BB showed margins of 5,7, and 8mm, respectively. The daily BMF changes for both groups were ranked in descending order as follows: sacral rotation angle (RS), hip lateral diameter (HLD), and hip anterior-posterior diameter (HAPD). HAPD was the main factor affecting setup displacement in both the AP and SI directions in TM-BB, while RS was the primary factor for setup displacement in the AP direction in VBC-BB. Compared with TM-BB, VBC-BB had a larger AP displacement but smaller in LR and SI displacement. Daily changes in BMF have distinct effects on setup displacement in different immobilization devices. Image-guided radiation therapy (IGRT) is highly recommended and BMF changes should be given consideration during radiotherapy.

Fluence smoothing evaluation for whole-breast automatically generated treatment plans.

This study aimed to identify the fluence smoothing threshold that preserves the dosimetric quality of planning for breast cancer intensity-modulated radiation therapy (IMRT). We conducted automated treatment planning for 60 breast cancer patients using the Eclipse Scripting Application Programming Interface. The plans included four-field IMRT, emphasizing smoothing weight combinations while maintaining a 4:3 aspect ratio between the X and Y directions. Four weight sets (40×30, 100×75, 150×115.2, and 200×150) were tested, resulting in four plans per patient. A total dose of 40.05Gy over 15 fractions was prescribed. Optimization weigths were dynamically adjusted based on dosimetric evaluations, with the maximum coverage priority set at 200. Statistical analyses were used to assess the dosimetric data. The median planning target volume (PTV) coverage varied across smoothing levels, with default smoothing (40×30) providing superior median PTV coverage. Lung constraints showed significant differences mainly at higher smoothing levels. Heart constraints exhibited less variation between smoothing levels, with significant differences primarily in the maximum and mean doses for right-sided patients and between default and higher smoothing levels for left-sided patients. No significant differences were observed in contralateral breast constraints among all smoothing levels, except at the maximum level for right-sided patients. Monitor units decreased with increasing smoothing weight, showing significant differences between default and other settings. For right-sided patients, the median number of monitor units varied from 1346 (40×30) to 754 (200×150), and for left-sided patients, from 1333 (40×30) to 804 (200×150). Chi-square tests revealed differences in dose constraint adherence between default and maximum smoothing levels, particularly in target coverage. Our findings suggest that using a ratio of smoothing weights to target priorities between 1:1.5 and 1:1.6 leads to a favorable balance between complexity and dosimetric plan quality, with no significant impacts on dose constraint adherence.

Dose compensation for decreased biological effective dose due to intrafractional interruption during radiotherapy: integration with a commercial treatment planning system

Objective.While the biological effective dose (BED) has been used to estimate the damage to tumor cells in radiotherapy, BED does not consider intrafractional interruption (IFI) occurring during irradiation. We aim to develop a framework to evaluate the decrease in BED [ΔBED] and to create a plan compensating for the decrease by IFI.Approach.ΔBEDwas calculated using a model based on the microdosimetric kinetic model (MKM) for four brain tumor cases treated using a volumetric-modulated arc therapy. Four biologically compensated plans (BCPs) were created in the treatment planning system by a single-time optimization using a base plan consideringΔBEDcreated in in-house software and optimization objectives for the original clinically delivered plan to achieve a homogeneous BED distribution within the planning target volume (PTV). The BED-volume histogram was evaluated for non-compensated plan and BCP with different timepoint of interruption, a percentage of gantry rotation angle (GRA) before interruption in planned GRA,ηand duration of interruptionτ. Characteristics of the dose accumulation were analyzed for different collimator angle sets, Plan A (10°, 85°) and Plan B (45° and 315°), for the first case.Main Results.Hot spots in theΔBEDdistribution forη= 25%, 50%, and 75% were observed at superior-and-interior ends, central region, and peripheral region in PTV, respectively. These behaviors could be understood by characteristics of the MKM-based model producing maximumΔBEDat 50% of the dose accumulation.ΔBED50%ranged 4.5%-6.6%, 5.0%-7.3%, and 5.3%-7.7% forτ= 60, 90, and 120 min, respectively. Plan A showed fast dose accumulation at superior and inferior edges while slow on peripheries in the lateral dose profile. Plan B showed more homogeneous PD distributions than Plan A during irradiation.Significance.The developed framework successfully evaluated and compensated for the decreased BED distribution.

Thyroid avoidance in treatment planning for breast cancer patients irradiated to the supraclavicular nodes.

Hypothyroidism affects up to 21% of women with breast cancer after supraclavicular node irradiation. The PENTEC (pediatric normal tissue effects in the clinic) initiative highlighted the need to minimize the thyroid dose, albeit without giving aspecific constraint. This study aimed to define areasonable target thyroid mean dose (Dmean) between 10 and 15 Gy using intensity-modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) and examine its impact on the hypothyroidism risk. Forty-three breast cancer patients with supraclavicular irradiation neglecting the thyroid in terms of dose protection were included from 01/2020 to 04/2021. An IMRT or VMAT technique was used in23 and 20patients, respectively. Replanning aimed for athyroid Dmean of 10 Gy. IMRT plans still exceeding 10 Gy were converted into VMAT plans. Fisher's sign test compared original and revised plans and the hypothyroidism risk was calculated. Initial radiotherapy plans had athyroid Dmean of 18.4 ± 7.9 Gy (IMRT: 20.4 ± 8.8 Gy, VMAT: 16.2 ± 6.2 Gy). Replanning significantly reduced Dmean to 10.3 ± 4.5 Gy (-44%) overall (IMRT: -50%, VMAT: -35%), with 56% achieving ≤ 10 Gy (IMRT: 33.3%, VMAT: 61%). Furthermore, an IMRT to VMAT conversion yielded athyroid Dmean of 9.2 ± 3.5 Gy, with 74.4% of patients ≤ 10 Gy, albeit at the cost of higher doses to the contralateral breast. Clinical and planning target volume (CTV/PTV) coverage remained uncompromised. The calculated hypothyroidism risk significantly decreased from 24.5% to 13.3% (Dmean = 10 Gy) or 16.3% (Dmean = 13.5 Gy). Implementing athyroid organ at risk (OAR) constraint Dmean of 13.5 Gy was feasible in 88% of patients without compromising other OARs and CTV/PTV coverage, and resulted in a33-46% reduction of the hypothyroidism risk. Retrospectively registered.

Assessment of Setup-errors in 3Dd-Conformal Radiotherapy for Head and Neck Cancer Patients Using an Electronic Portal Imaging Device

Patient setup is crucial in radiotherapy since treatment is delivered as fractionated treatment over a period of time. Using own institutional margins by considering the setup errors will provide better radiotherapy outcome. Therefore, this study aims to assess set up errors for head and neck cancer patients using an electronic portal imaging device at Apeksha Hospital, Maharagama, Sri Lanka. A total of 101 head and neck cancer patients who were immobilized with thermoplastic mask were selected in this study. Stored data from July 2021 to July 2022 were obtained from ARIA patient management system in the Varian 2300CD Unit at Apeksha Hospital. In order to calculate systematic and random errors, translational errors in all directions were collected utilizing 303 pairs of orthogonal portal images. Moreover, three different algorithms were used to obtain the margin of clinical target volume (CTV) to planning target volume (PTV). The estimated systematic and random errors in the directions of antero-posterior, superior-inferior and medio-lateral are 0.13 cm, 0.10 cm and 0.08 cm, and 0.22 cm, 0.21 cm, and 0.19 cm respectively. Less than 0.5 cm margin were obtained by applying three different algorithms. This study indicates that using a 0.5 cm margin for head and neck cancer patients treating in 2300CD Varian Unit at Apeksha Hospital is safe. Further, this study recommends to developing institutional CTV to PTV margin for all sites of cancer to reduce unnecessary radiation to the surrounding normal healthy tissues.

Pneumonitis after normofractionated radioimmunotherapy: a method for dosimetric evaluation

BackgroundPost-Therapy-Pneumonitis (PTP) is a critical side effect of both, thoracic radio(chemo)therapy (R(C)T) and immune checkpoint inhibition (ICI). However, disease characteristics and patient-specific risk factors of PTP after combined R(C)T + ICI are less understood. Given that RT-triggered PTP is strongly dependent on the volume and dose of RT [1], driven by inflammatory mechanisms, we hypothesize that combination therapy of R(C)T with ICI influences the dose-volume-effect correlation for PTP. This study focuses on the development of a method for evaluation of alterations of dosimetric parameters for PTP after R(C)T with and without ICI.Methods and materialsPTP volumes were delineated on the follow-up diagnostic Computed Tomography (CT) and deformably matched to the planning CT for patients with PTP after thoracic R(C)T + ICI or R(C)T. Dose data was converted to 2-Gy equivalent doses (EQD2) and dosimetrically analyzed. Dosimetric and volumetric parameters of the segmented PTP volumes were analyzed. The method was exemplarily tested on an internal patient cohort including 90 patients having received thoracic R(C)T + ICI (39) and R(C)T (51). Thirtytwo patients with PTP were identified for further analysis. Additional data on previous chemotherapy, RT, smoking status and pulmonary co-morbidity were conducted. A matched pair analysis with regard to planning target volumes (PTV) was conducted for curative intended (definitive) and palliative patient cohorts individually.ResultsThe presented method was able to quantify and compare the dosimetric parameters of PTP for the different therapies. For our study group, no significant differences between R(C)T + ICI and R(C)T only was observed. However, the dosimetric analysis revealed large volumetric fractions (55%) of the PTP volumes to be located outside of high dose (EQD2 < 40 Gy) regions for R(C)T + ICI. There was a non-significant trend towards increased area under the curve of the dose volume histogram (AUC) values for R(C)T + ICI compared to R(C)T only (3743.6 Gy∙% vs. 2848.8 Gy∙%; p-value = 0.171). In contrast to the data for the palliative intended treatment group, for definitive R(C)T + ICI, data tended towards increased volumes with higher doses.ConclusionsThe proposed method was capable to quantify dosimetric differences in the dose-volume-effect relationship of PTP for patients with R(C)T + ICI and patients with R(C)T only. In this exploratory analysis, no significant dosimetric differences within PTP volumes for the different groups could be observed. However, our observations suggest, that for safe application of thoracic R(C)T + ICI, further careful investigation of dosimetric prescription and analysis concepts with larger and conformer study groups is recommendable.

Analysis of linear accelerator-based fractionated stereotactic radiotherapy in brain metastases: efficacy, safety, and dose tolerances

ObjectiveTo assess the efficacy and safety of linear accelerator-based fractionated stereotactic radiotherapy (LINAC-FSRT) in patients with brain metastases (BM).MethodsWe retrospectively analyzed 214 patients treated with LINAC-FSRT, categorized based on biologically effective dose (BED10, α/β = 10) into two groups (≤55 Gy, &amp;gt;55 Gy). Stratified analyses were conducted based on targeted therapy to compare survival outcomes. To examine brain tissue dose-tolerance volume, patients were divided into two groups: the standard Hypofractionated Treatment Effects in the Clinic (HyTEC) protocol group and an adjusted HyTEC protocol group where dose-volume restrictions exclude the planning target volume (PTV).ResultsResults as of December 2023 showed median intracranial progression-free survival (iPFS) at 12.4 months, with median overall survival (OS) not reached and a one-year local control (LC) rate of 68.7%. Mild to moderate toxicity affected 17.3% of patients, while severe toxicity occurred in 2.8%. Multivariate Cox analysis indicated that uncontrolled extracranial disease significantly reduced iPFS (HR = 2.692, 95%CI:1.880–3.853, P &amp;lt; 0.001) and OS (HR = 3.063, 95%CI:1.987–4.722, P &amp;lt; 0.001). BED10 &amp;gt;55 Gy (HR = 0.656, 95%CI:0.431–0.998, P = 0.049) improved OS, showing statistical significance (P = 0.037) without affecting iPFS or CNS toxicity (P = 0.127, P = 0.091). Stratified analysis highlighted nearly significant OS improvements with high-dose FSRT and targeted therapy (P = 0.054), while concurrent therapy markedly enhanced iPFS (P = 0.027). No significant differences were observed in intracranial local failure (ILF—which represents progression in previously treated areas during follow-up), one-year LC rates, iPFS, or OS between dose-volume groups. Adjusting HyTEC volume restrictions did not significantly increase CNS adverse reactions (P = 0.889).ConclusionsLINAC-FSRT is safe and effective in BM. BED10&amp;gt;55 Gy notably enhances OS post-LINAC-FSRT and may benefit LC. High BED10 FSRT with targeted therapy likely boosts synergy, and concurrent targeted therapy significantly improves iPFS. Diminishing dose volume constraints at different fractions based on the HyTEC guidelines is feasible.

Primary Results of NRG-RTOG1106/ECOG-ACRIN 6697: A Randomized Phase II Trial of Individualized Adaptive (chemo)Radiotherapy Using Midtreatment 18F-Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography in Stage III Non-Small Cell Lung Cancer.

NRG-RTOG0617 demonstrated a detrimental effect of uniform high-dose radiation in stage III non-small cell lung cancer. NRG-RTOG1106/ECOG-ACRIN6697 (ClinicalTrials.gov identifier: NCT01507428), a randomized phase II trial, studied whether midtreatment 18F-fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT) can guide individualized/adaptive dose-intensified radiotherapy (RT) to improve and predict outcomes in patients with this disease. Patients fit for concurrent chemoradiation were randomly assigned (1:2) to standard (60 Gy/30 fractions) or FDG-PET-guided adaptive treatment, stratified by substage, primary tumor size, and histology. All patients had midtreatment FDG-PET/CT; adaptive arm patients had an individualized, intensified boost RT dose to residual metabolically active areas. The primary therapeutic end point was 2-year centrally reviewed freedom from local-regional progression (FFLP), defined as no progression in or near the planning target volume and/or regional nodes. FFLP was analyzed on a modified intent-to-treat population at a one-sided Z-test significance level of 0.15. The primary imaging end point was centrally reviewed change in SUVpeak from baseline to midtreatment; its association with FFLP was assessed using the two-sided Wald test on the basis of Cox regression. Of 138 patients enrolled, 127 were eligible. Adaptive-arm patients received a mean 71 Gy in 30 fractions, with mean lung dose 17.9 Gy. There was no significant difference in centrally reviewed 2-year FFLP (59.5% and 54.6% in standard and adaptive arms; P = .66). There were no significant differences in protocol-specified grade 3 toxicities, survival, or progression-free survival (P > .4). Median SUVpeak and metabolic tumor volume (MTV) in the adaptive arm decreased 49% and 54%, from pre-RT to mid-RT PET. However, ΔSUVpeak and ΔMTV were not associated with FFLP (hazard ratios, 0.997; P = .395 and .461). Midtreatment PET-adapted RT dose escalation as given in this study was safe and feasible but did not improve efficacy outcomes.

Understanding and modeling human-AI interaction of artificial intelligence tool in radiation oncology clinic using deep neural network: a feasibility study using three year prospective data

Objective.Artificial intelligence (AI) based treatment planning tools are being implemented in clinic. However, human interactions with such AI tools are rarely analyzed. This study aims to comprehend human planner's interaction with the AI planning tool and incorporate the analysis to improve the existing AI tool.Approach.An in-house AI tool for whole breast radiation therapy planning was deployed in our institution since 2019, among which 522 patients were included in this study. The AI tool automatically generates fluence maps of the tangential beams to create anAI plan. Human planner makes fluence edits deemed necessary and after attending physician approval for treatment, it is recorded asfinal plan. Manual modification value maps were collected, which is the difference between theAI-planand thefinal plan. Subsequently, a human-AI interaction (HAI) model using full scale connected U-Net was trained to learn such interactions and perform plan enhancements. The trained HAI model automatically modifies theAI planto generate AI-modified plans (AI-m plan), simulating human editing. Its performance was evaluated against originalAI-planandfinal plan. Main results. AI-m planshowed statistically significant improvement in hotspot control over theAI plan, with an average of 25.2cc volume reduction in breast V105% (p= 0.011) and 0.805% decrease in Dmax (p< .001). It also maintained the same planning target volume (PTV) coverage as thefinal plan, demonstrating the model has captured the clinic focus of improving PTV hot spots without degrading coverage.Significance.The proposed HAI model has demonstrated capability of further enhancing theAI planvia modeling human-AI tool interactions. This study shows analysis of human interaction with the AI planning tool is a significant step to improve the AI tool.

Assessing the correlation between Gamma passing rate and clinical dosimetric variations in breast cancer IMRT plans with multi-leaf collimator errors: perspectives from the ArcCHECK QA system.

This study aimed to comprehensively investigate the influence of multi-leaf collimator (MLC) position errors on both the clinical absolute dose distribution and Gamma passing rate (%GP) in intensity-modulated radiation therapy (IMRT) plans for breast cancer. Additionally, the correlation between %GP and the clinical absolute dose relative difference (%DE) caused by MLC position errors was analysed. Ten IMRT plans for breast cancer were randomly selected. Systematic and random MLC position errors were introduced into DICOM files representing the investigated treatment plans by modifying the plan files and adjusting the MLC positions. Systematic errors were categorized as MLC opening errors, closing errors, and shift errors. The %DE in the tumour planning target volume (PTV) and organs at risk (OARs) caused by MLC errors were statistically analyzed using dose-volume histogram (DVH) analysis. The ArcCHECK quality assurance (QA) system was used to detect the %GP differences between baseline plans and plans with MLC errors. The correlation between %GP and %DE was obtained using linear regression methods. The results of this study indicate that MLC opening and closing errors have a significant impact on %DE and %GP in IMRT plans for breast cancer. Opening and closing errors can be detected at a gamma level of 3%/2mm, if error values are greater than or equal to 0.5mm, and %GP can predict DVH dosimetric changes caused by MLC opening and closing errors. It is concluded that DVH-based verification of IMRT plans can serve as an adjunct method to Gamma analysis to improve QA accuracy for breast cancer cases. Additionally, it is concluded that greater attention should be given to MLC leaf opening and closing errors in clinical practice.

Spatially Fractionated Radiotherapy with Very High Energy Electron Pencil Beam Scanning.

&#xD;To evaluate spatially fractionated radiation therapy (SFRT) for very-high-energy electrons (VHEEs) delivered with pencil beam scanning. Radiochromic film was irradiated at the CERN Linear Electron Accelerator for Research (CLEAR) using 194 MeV electrons with a step-and-shoot technique, moving films within a water tank. Peak-to-valley dose ratios (PVDRs), depths of convergence (PVDR≤1.1), peak doses, and valley doses assessed SFRT dose distribution quality. A Monte Carlo (MI) model of the pencil beams was developed using TOPAS and applied to a five-beam VHEE SFRT treatment for a canine glioma patient, compared to a clinical 6 MV VMAT plan. The plans were evaluated based on dose-volume histograms, mean dose, and maximum dose to the planning target volume (PTV) and organs at risk (OARs).&#xD;Main Results:&#xD;Experimental PVDR values were maximized at 15.5 ± 0.1 at 12 mm depth for 5 mm spot spacing. A depth of convergence of 76.5 mm, 70.7 mm, and 56.6 mm was found for 5 mm, 4 mm, and 3 mm beamlet spacings, respectively. MC simulations and experiments showed good agreement, with maximum relative dose differences of 2% in percentage depth dose curves and less than 3% in beam profiles. Simulated PVDR values reached 180 ± 4, potentially achievable with reduced leakage dose. VHEE SFRT plans for the canine glioma patient showed a decrease in mean dose (>16%) to OARs while increasing the PTV mean dose by up to 15%. Lowering beam energy enhanced PTV dose homogeneity and reduced OAR maximum doses. The presented work demonstrates that pencil beam scanning SFRT with VHEEs could treat deep-seated tumors such as head and neck cancer or lung lesions, though small beam size and leakage dose may limit the achievable PVDR.&#xD.

Simulated study relating dose-volume histogram metrics to three-dimensional gamma analysis results

This study aims to investigate the relationship between the three-dimensional gamma index (3DGI) results and its clinical significance, proposing a correlation between changes in dose values in the dose-volume histogram (DVH) of the evaluated structures and 3DGI percentages of approval. In this study, we created 30 plans by including 1 mm displacement errors in the lateral, vertical, and longitudinal axes of each table, and compared them to a simulated, error-free treatment plan for prostate cancer. The plans were made in a commercial treatment planning system, using 6MV Varian 120-leaf multileaf collimators (MLC) linear accelerators and intensity modulated radiation therapy sliding window technique. We used a calculation algorithm-based MATLAB programming to evaluate the 3DGI analysis of fluence maps. The acceptance criteria were 3%/2 mm, 10% dose threshold, and 95% gamma passing rate. We compared 3DGI results with differences in structures DVH. DVH metrics versus 3DGI analysis showed a correlation between the percentage of point&amp;rsquo;s approval and planning target volume (PTV) coverage, presenting a degree of agreement of 0.85%, 0.96%, and 0.94% in the longitudinal, lateral, and vertical axes, respectively. In summary, it was possible to establish a linear relationship between the percentage of points approved in the 3DGI analysis and the PTV dose. A similar behavior was also observed in bladder and rectum DVH, but for these structures, the relationship was not the same in the three displaced axes.

Efficacy of palliative hemostatic radiotherapy for tumor bleeding and pain relief in locally advanced pelvic gynecological malignancies.

The appearance of symptomatic tumor-related vaginal bleeding and pain in advanced incurable cancer patients with pelvic gynecological malignancies remains atherapeutic challenge in oncological treatment. The aim of our analysis was to evaluate the efficacy and safety of palliative hemostatic radiotherapy. We retrospectively identified patients who had received palliative hemostatic radiotherapy (RT) at our institution between 2011 and 2023 and evaluated acute toxicity, local control, cessation of bleeding, and pain relief. In total, 40patients with amedian planning target volume of 804 cm3 were treated with amedian total dose of 39 Gy in 13fractions, resulting in 6‑month and 1‑year local control rates of 66.9 and 60.8%, respectively. No higher-grade (>gradeIII) acute RT-induced toxicity appeared. Complete cessation of bleeding was achieved in 80.0% of all patients after amedian of 16days and pain relief was documented in 60.9% at first follow-up. 37.5% of the women required ablood transfusion and 25% an additional tamponade with local hemostatic agents. Successful stopping of bleeding was significantly less frequent in patients receiving anticoagulation concurrently with radiation and in the case of infield re-irradiation. Patients with ahigher total RT dose had cessation of bleeding significantly more often, with acut-off value of at least EQD2 (α/β = 10) = 36 Gy. The applied RT technique and planning target volume had no significant influence on the occurrence of bleeding cessation. Palliative hemostatic radiotherapy for locally advanced pelvic gynecological malignancies is safe and effective in achieving high control rates of hemostasis in tumor bleeding and pain relief.

RADT-36. FUNCTION-ADAPTED RADIOTHERAPY PLANNING IN THE MANAGEMENT OF HIGH-GRADE GLIOMAS: A COMPARING STUDY FOR DOSE SPARING OF SPEECH-ELOQUENT BRAIN AREAS

Abstract BACKGROUND Radiotherapy (RT) for brain tumors can induce injury of functional white matter tracts. In neurosurgery navigated transcranial magnetic stimulation (nTMS)- and diffusion tensor imaging (DTI)-based fiber tracts (FT) is an established tool to protect functional FT during tumor resection. We investigated it´s applicability in RT planning with the aim of dose reduction of language-associated fiber tracts. METHODS Preoperative, nTMS-generated and DTI-based FT of the functional left hemispheric language network of patients with language-eloquent malignant gliomas (WHO III/IV) were imported into the planning software (ARIA®) according to the DICOM standard and contoured as a risk structure. Brain shift after tumor resection was compensated using elastic fusion (Brainlab®). The treatment plans were optimized or recalculated with the aim of reducing the dose to the fiber tracts outside the planning target volume (PTV). The dosimetric evaluation was performed according to dose volume histogram parameters. RESULTS RT plans of 27 patients were retrospectively evaluated in the study. The mean dose (Dmean) to the fiber tracts was 37.3+/-11.8 Gy, with plan optimization dose was 33.6 +/- 12.2 Gy (-10.9% p&amp;lt;0.01), within the 20 Gy isodose the dose reduction to be achieved was on average - 25.0% (range 0-48.5%). The V54Gy and V20Gy were on average 40.2 +/- 23.7% and 72.3 +/- 21.1% compared to 38.2 +/- 23.5% and 58.1 +/- 23.7% (both p&amp;lt;0.01) with optimization. The Dmean of the PTV did not change (59.8 Gy vs. 59.8 Gy (p=0.5)), nor did the dose homogeneity (HI, (D5-D95)/Dp)(p=0.63)). The dose exposure of the organs at risk was within the specified dose constraints. CONCLUSION This study showed that (nTMS)- and diffusion tensor imaging (DTI)-based fiber tractography could be used in radiotherapy planning to spare language-eloquent brain areas without having to accept dose reductions within the PTV. Whether the concept of tract-based sparing of language function brings clinical benefits to patients needs to be further investigated in prospective studies.

Feasibility of creating a daily adaptive plan using automatic DIR-created target and OARs contours in patients with prostate cancer magnetic-resonance-guided adaptive radiotherapy.

The purpose of this study was to evaluate the feasibility of treatment plans for prostate cancer with magnetic resonance (MR)-guided online adaptive radiotherapy, which are generated using deformable image registration (DIR)-created contours of the targets and organs. Totally, 150 fractions from 30 prostate cancer patients implanted with a hydrogel spacer and treated with the MR-Linac were studied. Reference treatment plans that satisfied all institutional dose constraints were initially created on planning MRI. The adaptive treatment plans were created on daily MRI based on the reference plan using the DIR-created contours, ensuring all dose constraints were met. Subsequently, a clinician manually created reference contours for each daily MRI. Finally, the dose volume histogram indices of the plan generated with DIR-created contours were re-evaluated with clinician created contours. The evaluated contours included the bladder wall, rectum wall, sigmoid, small bowel and planning target volume (PTV) for dose prescription. The PTV for dose prescription met the dose constraints in all fractions. The bladder and rectum walls met the dose constraint of maximum dose (D0.03 cc) in all fractions. Five patients failed to meet the sigmoid and small bowel dose constraints, with the largest deviation being 13.3% exceedance at D2 cc in the small bowel added 3mm margin. This study suggests that most treatment plans created without modifying the DIR-created contours are clinically viable. However, dislodgements of the small bowel and sigmoid may exceed the extent of DIR propagation from the reference plan contours, and it is recommended that these contours be verified.