Neck Plans Research Articles

Automatic Treatment Planning for Radiation Therapy: A Cross-Modality and Protocol Study

PurposeThis study investigates the applicability of 3D dose predictions from a model trained on one modality to a cross-modality automated planning workflow. Additionally, we explore the impact of integrating a multi-criteria optimizer (MCO) on adapting predictions to different clinical preferences. Methods and MaterialsUsing a previously created three-stage UNet in-house model trained on the 2020 AAPM OpenKBP challenge dataset (340 head and neck plans, all planned using 9-field static IMRT), we retrospectively generated dose predictions for 20 patients. These dose predictions were in turn used to generate deliverable IMRT, VMAT, and Tomotherapy plans using the fallback plan functionality in Raystation. The deliverable plans were evaluated against the dose predictions based on primary clinical goals. A new set of plans was also generated using MCO-based optimization with predicted dose values as constraints. Delivery QA was performed on a subset of the plans to assure clinical deliverability. ResultsThe mimicking approach accurately replicated the predicted dose distributions across different modalities, with slight deviations in spinal cord and external contour maximum doses. MCO optimization significantly reduced doses to OARs prioritized by our institution while maintaining target coverage. All tested plans met clinical deliverability standards, evidenced by a gamma analysis passing rate above 98%. ConclusionsOur findings show that a model trained only on IMRT plans can effectively contribute to planning across various modalities. Additionally, integrating predictions as constraints in an MCO-based workflow, rather than direct dose mimicking, enables a flexible, warm-start approach for treatment planning, though the benefit is reduced when the training set differs significantly from an institution's preference. Together, these approaches have the potential to significantly decrease plan turnaround time and quality variance, both at high resource medical centers that can train in-house models, and smaller centers that can adapt a model from another institution with minimal effort.

Feasibility of dose calculation for treatment plans using electron density maps from a novel dual-layer detector spectral CT simulator

BackgroundConventional single-energy CT can only provide a raw estimation of electron density (ED) for dose calculation by developing a calibration curve that simply maps the HU values to ED values through their correlations. Spectral CT, also known as dual-energy CT (DECT) or multi-energy CT, can generate a series of quantitative maps, such as ED maps. Using spectral CT for radiotherapy simulations can directly acquire ED information without developing specific calibration curves. The purpose of this study is to assess the feasibility of utilizing electron density (ED) maps generated by a novel dual-layer detector spectral CT simulator for dose calculation in radiotherapy treatment plans.Methods30 patients from head&neck, chest, and pelvic treatment sites were selected retrospectively, and all of them underwent spectral CT simulation. Treatment plans based on conventional CT images were transplanted to ED maps with the same structure set, including planning target volume (PTV) and organs at risk (OARs), and the dose distributions were then recalculated. The differences in dose and volume histogram (DVH) parameters of the PTV and OARs between the two types of plans were analyzed and compared. Besides, gamma analysis between these plans was performed by using MEPHYSTO Navigator software.ResultsIn terms of PTV, the homogeneity index (HI), gradient index (GI), D2%, D98%, and Dmean showed no significant difference between conventional plans and ED plans. For OARs, statistically significant differences were observed in parotids D50%, brainstem in head&neck plans, spinal cord in chest plans and rectum D50% in pelvic plans, whereas the variance remained minor. For the rest, the DVH parameters exhibited no significant difference between conventional plans and ED plans. All of the mean gamma passing rates (GPRs) of gamma analysis were higher than 90%.ConclusionCompared to conventional treatment plans relying on CT images, plans utilizing ED maps demonstrated similar dosimetric quality. However, the latter approach enables direct utilization in dose calculation without the requirements of establishing and selecting a specific Hounsfield unit (HU) to ED calibration curve, providing an advantage in clinical applications.

Impact of delivery variations on 3D dose distributions for volumetric modulated arc therapy plans of various complexity.

Delivery variations during radiotherapy can cause discrepancies between planned and delivered dose distribution. These variations could arise from random and systematic offsets in certain machine parameters or systematic offsets related to the calibration process of the treatment unit. The aim of this study was to present a novel simulation-based methodology to evaluate realistic delivery variations in three dimensions (3D). Additionally, we investigated the dosimetric impact of delivery variations for volumetric modulated arc therapy (VMAT) plans for different treatment sites and complexities. Twelve VMAT plans for different treatment sites (prostate-, head & neck-, lung-, and gynecological cancer) were selected. The clinical plan used for the treatment of each patient was reoptimized to create one plan with reduced complexity (i.e., simple plan) and one of higher complexity (i.e., complex plan). This resulted in a total of 36 plans. Delivery variations were simulated by randomly introducing offsets in multi-leaf collimator position, jaw position, gantry angle and collimator angle simultaneously. Twenty simulations were carried out for each of the 36 plans, yielding 720 simulated deliveries. To explore the impact of individual offsets, additional simulations were conducted for each type of offset separately. A 3D dose calculation was performed for each simulation using the same calculation engine as for the clinical plan. Two standard deviations (2SD) of dose were determined for every voxel for 3D-spatial evaluations. The dose variation in certain DVH metrics, that is, D2% and D98% for the clinical target volume and five different DVH metrics for selected organs at risk, was calculated for the twenty simulated deliveries of each plan. For comparison, the effect of delivery variations was assessed by conducting measurements with the Delta4 phantom. The volume of voxels with 2SD above 1% of the prescribed dose was consistently larger for the complex plans in comparison to their corresponding simple and clinical plans. 2SDs larger than 1% were in many cases, found to accumulate outside the planning target volume. For complex plans, regions with 2SDs larger than 1% were detected also inside the high dose region, exhibiting, on average, a size six times larger volume, than those observed in simple plans. Similar results were found for all treatment sites. Variation in the selected DVH metrics for the simulated deliveries was generally largest for the complex plans with few exceptions. When comparing the 2SD distribution of the measurements with the 2SD distribution from the simulations, the spatial information showed deviations outside the PTV in both simulations and measurements. However, the measured values were, on average, 35% higher for the prostate plans and 10% higher for the head & neck plans compared to the simulated values. The presented methodology effectively quantified and localized dose deviations due to delivery offsets. The 3D analysis provided information that was undetectable using the analysis based on DVH metrics. Dosimetric uncertainties due to delivery variations were prominent at the edge of the high-dose region irrespective of treatment site and plan complexity. Dosimetric uncertainties inside the high-dose region was more profound for plans of higher complexity.

Plan complexity metrics for head and neck VMAT competition plans

Previous plan competitions have largely focused on dose metric assessments. However, whether the submitted plans were realistic and reasonable from a quality assurance (QA) perspective remains unclear. This study aimed to investigate the relationship between aperture-based plan complexity metrics (PCM) in volumetric modulated arc therapy (VMAT) competition plans and clinical treatment plans verified through patient-specific QA (PSQA). In addition, the association of PCMs with plan quality was examined. A head and neck (HN) plan competition was held for Japanese institutions from June 2019 to July 2019, in which 210 competition plans were submitted. Dose distribution quality was quantified based on dose-volume histogram (DVH) metrics by calculating the dose distribution plan score (DDPS). Differences in PCMs between the two VMAT treatment plan groups (HN plan competitions held in Japan and clinically accepted HN VMAT plans through PSQA) were investigated. The mean (± standard deviation) DDPS for the 98 HN competition plans was 158.5 ± 20.6 (maximum DDPS: 200). DDPS showed a weak correlation with PCMs with a maximum r of 0.45 for monitor unit (MU); its correlation with some PCMs was "very weak." Significant differences were found in some PCMs between plans with the highest 20% DDPSs and the remaining plans. The clinical VMAT and competition plans revealed similar distributions for some PCMs. Deviations in PCMs for the two groups were comparable, indicating considerable variability among planners regarding planning skills. The plan complexity for HN VMAT competition plans increased for high-quality plans, as shown by the dose distribution. Direct comparison of PCMs between competition plans and clinically accepted plans showed that the submitted HN VMAT competition plans were realistic and reasonable from the QA perspective. This evaluation may provide a set of criteria for evaluating plan quality in plan competitions.

Pencil Beam Scanning Proton Therapy for Pregnant Patients With Brain and Head and Neck Cancers

When radiation therapy is medically necessary for pregnant patients, photon-based treatments (XRT) have traditionally been used, whereas proton radiation therapy (PRT) is avoided due to concerns about neutron dose. This retrospective study analyzes pregnant patients treated with XRT and models the equivalent dose that would have been delivered to the fetus with proton radiation compared with XRT. The purpose of this work is to provide a comprehensive analysis of pencil beam scanning proton therapy (PBS-PRT) for pregnant patients and to evaluate whether PBS-PRT should be the new standard of practice for treating pregnant patients with brain and head and neck cancers. PBS-PRT plans were made for seven pregnant patients who received XRT: four treated for brain tumors and three for head and neck tumors. Measurements were performed with the patient plans using an anthropomorphic phantom and Wendi-2 meter placed at the phantom's abdomen. Patient-specific measurements were used to determine the total fetal equivalent dose from PBS-PRT compared with XRT. Imaging dose was also evaluated with a Fluke 451 dose meter. The average measured fetal equivalent dose, accounting for photons and neutrons, for the brain plans was 0.4 mSv for PBS-PRT and 7 mSv for XRT. For the head and neck plans, it was 6 mSv and 90 mSv for PBS-PRT and XRT, respectively. The PBS-PRT plans were preferred by the physicians for both tumor coverage and normal-tissue sparing. Daily imaging added between 0.05 and 1.5 mSv to the total dose. This retrospective study showed that when treating brain or head and neck cancers in pregnant patients, fetal equivalent dose is reduced by approximately a factor of 10 with PBS-PRT compared with XRT without making any compromises in treatment planning objectives. These results support a change of practice to using PBS-PRT as the new standard for treating pregnant patients with brain or head and neck tumors compared with XRT.

Characterization of Cherenkov imaging parameters and positional constraints on an O-ring linear accelerator

Objective. With the introduction of Cherenkov imaging technology on the Halcyon O-ring linear accelerator platform, we seek to demonstrate the imaging feasibility and optimize camera placement. Approach. Imaging parameters were probed by acquiring triggering data Cherenkov image frames for simplistic beams on the Halcyon and comparing the analyzed metrics with those from the TrueBeam platform. Camera position was analyzed by performing 3D rendering of patient treatment plans for various sites and iterating over camera positions to assess treatment area visibility. Main results. Commercial Cherenkov imaging systems are compatible with the pulse timing of the Halcyon, and this platform design favorably impacts signal to noise in Cherenkov image frames. Additionally, ideal camera placement is treatment site dependent and is always within a biconical zone of visibility centered on the isocenter. Visibility data is provided for four treatment sites, with suggestions for camera placement based on room dimensions. Median visibility values were highest for right breast plans, with values of 80.33% and 68.49% for the front and rear views respectively. Head and neck plans presented with the lowest values at 26.44% and 38.18% respectively. Significance. This work presents the first formal camera positional analysis for Cherenkov imaging on any platform and serves as a template for performing similar work for other irradiation platforms. Additionally, this study confirms the Cherenkov imaging parameters do not need to be changed for optimal imaging on the Halcyon. Lastly, the presented methodology provides a framework which could be further expanded to other optical imaging systems which rely on line of sight visibility to the patient.

Multicenter Multivendor Evaluation of Dose Volume Histogram Creation Consistencies for 8 Commercial Radiation Therapy Dosimetric Systems

PurposeTo evaluate dose volume histogram (DVH) construction differences across eight major commercial treatment planning systems (TPSs) and dose reporting systems (DRSs) for clinically treated plans of various anatomical sites and target sizes. Materials and MethodsDose files from ten selected clinically treated plans with a hypo-fractionation, stereotactic radiotherapy prescription or sharp dose gradients such as head and neck plans ranging from prescription doses of 18 Gy in 1 fraction to 70 Gy in 35 fractions, each calculated at 0.25 cm and 0.125 cm grid size, were created and anonymized in Eclipse TPS, and exported to seven other major TPS (Pinnacle, RayStation, Elements) and DRS (MIM, Mobius, ProKnow, and Velocity) systems for comparison. Dose-volume constraint points of clinical importance for each plan were collected from each evaluated system (D0.03cc[Gy], volume, and the mean dose were used for structures without specified constraints). Each reported constraint type and structure volume was normalized to the value from Eclipse for a pairwise comparison. A Wilcoxon Rank Sum test was used for statistical significance and a multivariable regression model was evaluated adjusting for plan, grid size, and distance to target center. ResultsFor all DVH points relative to Eclipse, all systems reported median values within 1.0% difference of each other, however they were all different from Eclipse. Considering mean values, Pinnacle, RayStation, and Elements averaged at 1.038, 1.046, 1.024 respectively, while MIM, Mobius, ProKnow, and Velocity reported 1.026, 1.050, 1.033 and 1.022 respectively relative to Eclipse. Smaller dose grid size improved agreement between the systems marginally without statistical significance. For structure volumes relative to Eclipse, larger differences are seen across all systems with a range in median values up to 3.0% difference and mean up to 10.1% difference. ConclusionLarge variations were observed between all systems. Eclipse generally reported, at statistically significant levels, lower values than all other evaluated systems. The non-significant change resulting from lowering the dose grid resolution indicates that this resolution may be less important than other aspects of calculating DVH curves, such as the 3D modeling of the structure.

Spot Scanning Proton Therapy for Pregnant Patients with Brain and Head and Neck Tumors

When radiotherapy is medically necessary, x-ray based treatments (XRT) have traditionally been used to treat pregnant patients. Treatment planning and delivery techniques may be modified to minimize dose to the fetus but results in less optimal plans due to avoiding posterior beams or arcs. Monte Carlo calculations and published case studies suggest spot scanning proton therapy (PRT) reduces the equivalent dose to the fetus by a factor of 10 compared to XRT and does not require modified treatment planning techniques. However, due to concern for dose uncertainties and neutron scatter with PRT, few centers have adopted PRT over XRT for pregnant patients. The purpose of this work is to perform a retrospective study on the pregnant patients previously treated at our institution with XRT to measure the equivalent dose that would be delivered to the fetus with spot scanning PRT compared to XRT. PRT plans were made for seven pregnant patients, 4 brain tumors and 3 head and neck tumors, who had received XRT. Due to the finite range of protons, the fetal exposure is dominated by neutrons and not the primary beam. Thus, no beam arrangement modifications were required to minimize fetal dose for PRT plans. Fetal dose measurements were performed with the patient plans using a Rando phantom and Wendi-2 (Thermo Scientific) meter placed at the phantom's abdomen. The Wendi-2 measures ambient dose equivalent, which accounts for the biological effect of the neutron energies. Measurements were made at various distances from isocenter to the center of the detector. The total dose equivalent from PRT at several out of field distances was compared to that from XRT. Patient specific measurements were used to determine the total fetal dose from each modality, accounting for the changing position of the fetus each week of the mother's treatment. The imaging dose for standard of practice imaging, including verification CT scans and daily alignment imaging, was also evaluated using a similar setup with a Fluke 451 dose meter. The average measured fetal equivalent dose for the brain plans was 0.4 mSv for PRT and 7 mSv for XRT. For the head and neck plans, it was 6 mSv for PRT and 90 mSv for XRT. The dose from PRT was consistently at least a factor of 10 less than the XRT plans. In addition, the PRT plans were preferred by the physicians when considering tumor coverage and other normal tissue sparing. Daily imaging added between 0.05 and 1.5 mSv to the total dose in the PRT treatments. This retrospective study showed that when treating brain or head and neck tumors in pregnant patients, the equivalent dose a fetus would receive with PRT is approximately a factor of 10 less than XRT without making any compromises in treatment planning. These results support changing the standard of practice to utilizing spot scanning PRT as the preferred method for treating pregnant patients with brain or head and neck tumors when available instead of XRT. We have brought this process to clinic at our center.

Daily Head and Neck Treatment Assessment for Optimal Proton Planning Robustness

Daily setup variation can affect the quality of treatment and robust optimization is used to ensure adequate target coverage. We aimed to assess quality assurance by evaluating fractional plan quality and its impact on plan robustness. Eligible head and neck plans with full field of view cone beam CT (CBCT) for >75% of daily fractions were classified into 2 categories 1) Primary only (PO) coverage and 2) Primary and neck nodal (PNN) coverage. Registration used at the machine was utilized for each daily CBCT to generate a synthetic CT (sCT), and the clinical target volumes (CTVs) and organs at risk (OARs) were manually edited by the reviewing physician. The daily dose for the CTVs and OARs were compared to the expected range from the robustness bands using 3.5% range uncertainty and 3mm versus 5mm setup uncertainty, fractional error was defined as volume and dose outside of uncertainty constraints. Statistical significance was calculated using students t-test. There was 203 eligible daily fractions from 6 patients were included for analysis. The average percentage of fractions that deviated from planning CTV volumes as well as average error in delivered dose using 3mm and 5mm robustness can be seen in (Table 1). In PO plans, there was minimal change in percentage of fractions that deviated from planned CTV volumes and overall low average error in delivered dose at both 3mm and 5mm robustness, 0.35% and 0.26%, respectively. In comparison, PNN plans had greater percentage of fractions that deviated from planning CTV and consequently greater average error in delivered dose, 1.00% versus 0.37% at 3mm and 5mm robustness, respectively. There was a significant difference in the percentage of fractional error with 3mm robustness between PO patients, 0.22%, and PNN patients, 0.98%, p<0.01. No statistical difference in percentage of fractional error was found with 5mm robustness for PO and PNN patients, 0.24% and 0.52%, respectively. All OARS maintained mean daily dose within or below 3mm robustness calculations. Based on our analysis, there was a difference in error of delivered dose between 3mm and 5mm robustness for head and neck proton plans, particularly for PNN coverage. Clinically, up to 1% error to CTV volumes is often not significantly meaningful and treating centers should consider utilizing 3mm robustness to maximize OAR sparing while maintaining proper target coverage. sCTs analysis is important for determining planning guidelines and may be able to identify patients needing an adaptive plan instead of currently utilized verification CTs.

Clinical Implementation of an Automated IMRT/VMAT Treatment Planning Tool

To create an in-house automated treatment planning tool for IMRT/VMAT treatments and evaluate the dosimetric plan quality against manually generated plans. A scripting application programming interface is employed to interact with a commercial treatment planning system (TPS) to implement automatic plan evaluation and update optimization parameters by mimicking the human planning process. The automated planning performs in an iterative fashion until reaching an acceptable tradeoff among target coverage/dose homogeneity and sparing of critical organs at risk. In each iteration, the dose constraints, priorities, and optimization structures for are automatically updated based on the results of the current iteration. Twenty previously treated plans (10 prostate and 10 head and neck), were preliminarily used to evaluate the performance of the automated planning tool. The differences in target and organ-at-risk metrics from the manually generated clinical plans were analyzed using paired t-test to evaluate clinical acceptability of tour automated planning tool. The current in-house-developed automated planning solution is able to create plans for different disease sites, including head & neck, prostate, pelvis, and lung. So far, the VMAT plans for more than 150 different cases have been generated with the tool. The results for these were also evaluated. Compared to the manually generated clinical head and neck plans, all auto plans achieved PTV D95% coverage and critical organs at risk sparing without statistically significant change in average global Dmax (107.4% for manual vs 107.3% for automated plans). The auto-planning solution provided reduced maximum doses to brainstem and spinal cord (average reductions with standard deviations of 5.1 ± 2.6 Gy and 2.9 ± 1.4 Gy, respectively, all p <0.03), reduced average mean doses to contralateral parotid, ipsilateral parotid, contralateral submandibular gland, pharynx, esophagus, cochleae (reductions of 2.2 ± 2.9 Gy, 4.8 ± 4.7 Gy, 3.6 ± 5.2 Gy, 2.0 ± 7.1 Gy, 3.9 ± 2.6 Gy, 3.8 ± 5.0 Gy, respectively, all p < 0.045). Similar results were observed for the prostate plans. With the same PTV coverage and without statistically significant change in average global Dmax (106.5% for manual vs 106.8% for automated plans), the automated solution provided superior sparing for both bladder and rectum. Bladder V75, V70, V65 were reduced by 0.6% ± 2.1%, 0.8% ± 2.5%, and 0.9% ± 2.9% (all p <0.04), respectively. Rectum V75, V70, V65, V60 were reduced by 1.0% ± 2.3%, 1.2% ± 2.8%, 1.3% ± 3.2%, 1.6% ± 3.6% (all p < 0.01), respectively. Our automated treatment planning solution is capable of efficiently generating VMAT plans for different disease sites with superior dosimetric indices compared to manually generated plans. Our tool is integrated within a commercial TPS platform, so it has the advantage of seamless adoption into the standard workflow to improve plan quality and treatment planning efficiency in our clinic.

Clinical Evaluation of an Automated Iterative Optimization System for Radiation Oncology

Automation of radiotherapy treatment planning improves efficiency and consistency, while reducing planning time and errors. The objective of this study was to validate an Iterative Optimization Engine (IOE) within an existing automated IMRT/VMAT planning framework. The IOE was designed to reduce remaining manual intervention within the automation framework through measuring and codifying common user intervention within a commercial planning system. The IOE was developed for external beam IMRT/VMAT treatment planning on the Monaco Treatment Planning System. The IOE was built on an existing automation framework, utilizing the Application Programming Interface (API) to create completely automated treatment plans. A network of 40 centers in Australia evaluated automated treatment plans for head and neck disease sites where users decided manual intervention was required post automated planning to achieve clinician approval. The modifications to automated plans were recorded, analyzed, and codified into the API to remove the requirement for manual intervention. A subset of the automated plans was then retrospectively processed by the IOE with resulting plans being scored in three categories of 1) superior, 2) equivalent and 3) inferior based on DVH assessment with the original clinician approved plan as the baseline. The automation framework generated 546 head and neck plans from January 1 to February 1, 2023, of which 45% required manual intervention to achieve dosimetric criteria. After being processed by the IOE, 86% of plans showed equivalent or superior coverage and maximum dose, and 95% of plans demonstrated equivalent homogeneity or improved homogeneity. Multi-target plans showed equivalent or improved target dose for 67% of intermediate dose targets and 39% of low dose targets when multiple targets were treated simultaneously. Analysis of organs at risk showed 38% of plans with reduced Parotid mean dose, 92% improved Larynx mean dose, 43% reduced Spinal Cord maximum dose, 57% decreased Brainstem maximum dose, 85% reduced Oral Cavity mean dose and 56% reduced Pharynx mean dose. The addition of an IOE achieved a clinical improvement to target and OAR metrics in the assessed clinical plans. The automation framework will incorporate this work into clinical production to improve the overall effectiveness of the automated planning framework.

Comparison of Progressive Resolution Optimizer and Photon Optimizer algorithms in RapidArc delivery for head and neck SIB treatments.

The aim of this study is to analyze and verify characterization of two different algorithms using simultaneous integrated boost (SIB) in head and neck (H&N) plans. In our study 15 patients were selected, who received radiation therapy by using Eclipse volumetric modulated arc therapy (VMAT) Progressive Resolution Optimizer (PRO) algorithm 15.1. The same cases were re-optimized using a Photon Optimizer (PO) algorithm 15.6.A total of 30 treatment plans (15 PRO-VMAT plans and 15 PO-VMAT plans) were produced in the present study. All plans were created using double full arcs, keeping the identical constraints, cost functions and optimization time. Plan evaluation was done using planning target volume (PTV) parameters (D98%, D95%, D50%, D2% mean dose and V105%), homogeneity index (HI), conformity index (CI), Monitor unit (MU) per degree with control points (CP), organ at risk (OAR) doses and gamma verification (Portal dosimetry and ArcCHECK) values were evaluated. Treatment was delivered in Varian Truebeam 2.5, energy 6 MV with Millennium 120 multileaf collimator (MLC). The PTV coverage (D95%) for PRO and PO were 98.7 ± 0.8 Gy, 98.8 ± 0.9 Gy, HI were 0.09 ± 0.02 and 0.09 ± 0.02, CI were 0.98 ± 0.01 and 0.99 ± 0.01. Monitor units (MU) for PRO and PO were 647.5 ± 137.9, 655.2 ± 138.4. The Portal dose results were [3%, 3mm (%) & 1 %, 1 mm (%)] for PO and PRO 100 ± 0.1, 95.1 ± 1.4 and 100 ± 0.1, 95.2 ± 1.3. For ArcCHECK were 99.9 ± 0.1, 94.7 ± 3.0 and 99.9 ± 0.1, 93.5 ± 3.9, respectively. Results showed that PTV coverage and OAR doses were comparable. For individual patients CI and HI of PO showed slightly higher values than PRO. MUs for PO were slightly increased as compared to PRO. MU per degree with each individual control points generated by PO showed a high degree of modulation compared to PRO. Hence, new PO optimizer can produce a comparable degree of plan while using the same PRO objectives.

A comparative study of deep learning-based knowledge-based planning methods for 3D dose distribution prediction of head and neck.

In this paper, we compare four novel knowledge-based planning (KBP) algorithms using deep learning to predict three-dimensional (3D) dose distributions of head and neck plans using the same patients' dataset and quantitative assessment metrics. A dataset of 340 oropharyngeal cancer patients treated with intensity-modulated radiation therapy was used in this study, which represents the AAPM OpenKBP - 2020 Grand Challenge dataset. Four 3D convolutional neural network architectures were built. The models were trained on 64% of the data set and validated on 16% for voxel-wise dose predictions: U-Net, attention U-Net, residual U-Net (Res U-Net), and attention Res U-Net. The trained models were then evaluated for their performance on a test data set (20% of the data) by comparing the predicted dose distributions against the ground-truth using dose statistics and dose-volume indices. The four KBP dose prediction models exhibited promising performance with an averaged mean absolute dose error within the body contour <3Gy on 68 plans in the test set. The average difference in predicting the D99 index for all targets was 0.92Gy (p=0.51) for attention Res U-Net, 0.94Gy (p=0.40) for Res U-Net, 2.94Gy (p=0.09) for attention U-Net, and 3.51Gy (p=0.08) for U-Net. For the OARs, the values for the and indices were 2.72Gy (p<0.01) for attention Res U-Net, 2.94Gy (p<0.01) for Res U-Net, 1.10Gy (p<0.01) for attention U-Net, 0.84Gy (p<0.29) for U-Net. All models demonstrated almost comparable performance for voxel-wise dose prediction. KBP models that employ 3D U-Net architecture as a base could be deployed for clinical use to improve cancer patient treatment by creating plans with consistent quality and making the radiotherapy workflow more efficient.

Remote EPID-based dosimetric auditing using DVH patient dose analysis

Objective. The aim of this work was to develop and validate a method for remote dosimetric auditing that enables dose-volume histogram parameter comparisons of measured and planned dose in the patient CT volume. Approach. The method is derived by adapting and combining a remote electronic portal imaging (EPID) based auditing method (Virtual Epid based Standard Phantom Audit—VESPA) and a method to estimate 3D in-patient dose distributions from planar dosimetric measurements. The method was tested with a series of error-induced plans including monitor unit and multileaf collimator (MLC) positioning errors. A pilot audit study was conducted with eleven radiotherapy centres. IMRT plans from two clinical trials, a post-prostatectomy (RAVES trial) plan and a head and neck (HPV trial) plan were utilized. Clinically relevant DVH parameters for the planned dose and estimated measured dose were compared. Main results. The method was found to reproduce the induced dose errors within 0.5% and was sensitive to MLC positioning errors as small as 0.5 mm. For the RAVES plan audit all DVH results except one were within 3% and for the HPV plan audit all DVH results were within 3% except three with a maximum difference of 3.2%. Significance. The results from the audit method produce clinically meaningful DVH metrics for the audited plan and could enable an improved understanding of a centre’s radiotherapy quality.

Deep Learning–Based Dose Prediction for Automated, Individualized Quality Assurance of Head and Neck Radiation Therapy Plans

This study aimed to use deep learning-based dose prediction to assess head and neck (HN) plan quality and identify suboptimal plans. A total of 245 volumetric modulated arc therapy HN plans were created using RapidPlan knowledge-based planning (KBP). A subset of 112 high-quality plans was selected under the supervision of an HN radiation oncologist. We trained a 3D Dense Dilated U-Net architecture to predict 3-dimensional dose distributions using 3-fold cross-validation on 90 plans. Model inputs included computed tomography images, target prescriptions, and contours for targets and organs at risk (OARs). The model's performance was assessed on the remaining 22 test plans. We then tested the application of the dose prediction model for automated review of plan quality. Dose distributions were predicted on 14 clinical plans. The predicted versus clinical OAR dose metrics were compared to flag OARs with suboptimal normal tissue sparing using a 2 Gy dose difference or 3% dose-volume threshold. OAR flags were compared with manual flags by 3 HN radiation oncologists. The predicted dose distributions were of comparable quality to the KBP plans. The differences between the predicted and KBP-planned D1%,D95%, and D99% across the targets were within -2.53% ± 1.34%, -0.42% ± 1.27%, and -0.12% ± 1.97%, respectively, and the OAR mean and maximum doses were within -0.33 ± 1.40 Gy and -0.96 ± 2.08 Gy, respectively. For the plan quality assessment study, radiation oncologists flagged 47 OARs for possible plan improvement. There was high interphysician variability; 83% of physician-flagged OARs were flagged by only one of 3 physicians. The comparative dose prediction model flagged 63 OARs, including 30 of 47 physician-flagged OARs. Deep learning can predict high-quality dose distributions, which can be used as comparative dose distributions for automated, individualized assessment of HN plan quality.

Cobalt compensator-based IMRT device: A treatment planning study of head and neck cases

PurposeOur goal is to develop a novel cobalt-compensator-based IMRT device for low- and middle-income countries that is reliable and cost-effective while delivering treatment plans of equal quality to those from linac-MLC devices. The present study examines the quality of treatment plans using this device. MethodsA commercial treatment planning system (TPS; RayStation v.8B) was commissioned for this device using Monte Carlo simulations from the Geant4 toolkit. Patient-specific compensators were created as regions-of-interest. Thirty clinical head & neck cases were planned and compared to clinical plans with a 6MV linac using IMRT. The mock head and neck plan from TG-119 was used for further validation. ResultsPTV objectives were achieved in all 30 plans with PTV V95% >95 %. OAR sparing was similar to clinical plans. There were 14 cases where OAR dose limits exceeded the recommended QUANTEC limits in the clinical plan in order to achieve target coverage. OAR sparing was better in the cobalt compensator plan in 8 cases and worse in 3 cases, in the latter cases exceeding the clinical plan doses by an average of 8.22 % (0.0 %–13.5 %). Average field-by-field gamma pass-rate were 93.7 % (2 %/2mm). Estimated treatment times using the Co-60 compensator device were 1 min 27 s vs 1 min 2 s for the clinical system. ConclusionThis system is the first of its kind to allow for IMRT with a Co-60 device. Data here suggests that the delivery meets plan quality criteria while maintaining short treatment times which may offer a sustainable and cost-low option for IMRT on the global scale.

Cobalt Compensator-Based IMRT for Head and Neck Treatment in Low- and Middle-Income Countries: Equivalence to LINAC-Based IMRT

<h3>Purpose/Objective(s)</h3> Cobalt intensity modulated radiation therapy (IMRT) has the potential to impact global oncology by improving access to precision radiation therapy, particularly in low- and middle-income countries. A novel compensator-based design is under development. Previously, cobalt compensator-based IMRT and LINAC-based IMRT were shown to achieve similar target goals and dose constraints for 30 head and neck clinical cases. The current study further investigates the fidelity of these calculations. <h3>Materials/Methods</h3> An example case was analyzed to compare dose statistics between an IMRT plan and cobalt compensator plan. Planning tool simulations were performed to validate prior dose calculations. For a compensator plan, data was recorded at a depth of 10 cm in a 50 × 50 × 50 cm water phantom and beam-by-beam gamma analysis was performed. A mock IMRT head and neck plan per AAPM Task Group-119 was modeled using a cobalt compensator machine and a 6 MV LINAC. The study was IRB approved. <h3>Results</h3> Dose statistics of an example case showed similar target coverage and normal tissue sparing between an IMRT plan and cobalt compensator plan (Table 1). The average gamma analysis pass rate was 93.7% (range 85.5-99.1%). Similar target coverage was achieved between IMRT plans using a cobalt compensator machine and a 6 MV LINAC. Additionally, there was similar dose sparing of the spinal cord and parotid glands. Table 1: Dose statistics of an IMRT plan compared to a cobalt compensator plan with a primary PTV treated to 7000 cGy and bilateral neck irradiation. <h3>Conclusion</h3> Cobalt compensator-based IMRT may provide comparable quality treatment plans to LINAC-based IMRT for head and cancer patients. Physical development of the cobalt compensator device is ongoing, and further research will assess clinical outcomes.

Validating TG119 VMAT Commissioning on a Volumetric Phantom

<h3>Purpose/Objective(s)</h3> The present work adapts AAPM TG119 on a volumetric detector array and evaluates its feasibility for VMAT commissioning for two different Treatment Planning Systems (TPS). <h3>Materials/Methods</h3> TG119 describes a group of test plans for standard structure sets following prescription and dose constraints objectives. These plans were calculated and evaluated using both Elekta Monaco V5.0 (Montecarlo) and Varian Eclipse v15.6 (AAA algorithm) TPS. TG119 structure sets were inserted on virtual CT images for volumetric Quality Assurance (QA) phantom. A set of plans calculated on both TPS were delivered on a 6MV photon beam on an Elekta Synergy Linac. A set of plans was generated only on Eclipse for a Varian Halcyon Linac with 6MV Flattening Filter Free beam. Generated plans were delivered, dose distribution was concurrently measured with Ion Chamber (IC) point doses using a cavity plug holder inserted on the QA phantom. Dose constraints and goals comparison between TPS was executed. Gamma analysis was performed for 3%3mm and 3%2mm global gamma index and Confidence Limits (CL) according to the TG119 definition of Normal quantile were calculated. Measured and planned point doses on relevant positions were compared. <h3>Results</h3> TG119 goals were mostly satisfied except for some critical situations: PTV D99 goal on head & neck plan calculated on Eclipse TPS and Superior Target D10 goal on Multitarget Plan for Monaco TPS calculation. Gamma Analysis for 3%3mm range of passing rate was 96.8% to 100% while CLs range between 4.1% and 4.7% for a Normal quantile for Monaco TPS. For Eclipse TPS range of passing rate achieved was among 97.2% and 99.9%, CLs range was between 3.2% and 3.1%. For Eclipse plans delivered on Halcyon, the passing rate range was among 98.6% and 99.8%, CLs between 1.6% and 1.7%. 3%2mm global gamma index analysis shows a range of passing rate of 93.5% and 100% for Monaco TPS while CLs range between 4.8% and 8.3%. For Elekta plans on Eclipse TPS range of passing rate was 95.6% and 98.8%, CLs range was between 5.1% and 4.5%. The gamma passing rate range for Halcyon plans was between 94.5% and 99.3 and CLs between 3.4% and 6.0%. IC measurements for Synergy Linac showed an average dose difference of 0.84% between measured and calculated plans on Monaco, range among -3.15% and 7.01%, the greatest differences were found on C-Shape plan for high gradient regions measurements. For Eclipse TPS, the average dose difference was 1.28%, range between -1.04% and 10.26%, the highest difference was found in high gradient region C-Shape plan. For Halcyon plans, IC measurements showed an average dose difference of 0.74%, ranging between -0.27% and 3.38%. <h3>Conclusion</h3> CLs agreed with TG119 reference values even when stricter requirements were used. New criteria are more appropriate for modern treatments, but TG119 methodology remains a valid procedure for VMAT. The methodology described for commissioning VMAT technique on a volumetric QA phantom shows to be robust and consistent for various TPS and lilacs.

The impact of gadolinium-based MR contrast on radiotherapy planning for oropharyngeal treatment on the MR Linac.

Gadolinium-based contrast agents (GBCAs) may add value to magnetic resonance (MR)-only radiotherapy (RT) workflows including on hybrid machines such as the MR Linac. The impact of GBCAs on RT dose distributions however have not been well studied. This work used retrospective GBCA-enhanced datasets to assess the dosimetric effect of GBCAs on head and neck plans. Ten patients with oropharyngeal squamous cell carcinoma receiving RT from November 2018 to April 2020 were included in this study. RT planning included contrast-enhanced computed tomography (CT) and MR scans. A contrast agent "contour" was defined by delineating GBCA-enhanced regions using an agreed window/level threshold, transferred to the planning CT and given a standardized electron density (ED) of 1.149 in the Monaco treatment planning system (Elekta AB). Four plans were per patient calculated and compared using two methods: (1) optimized without contrast (Plan A) then recalculated with ED (Plan B), and (2) optimized with contrast ED (Plan C) then without (Plan D). For target parameters minimum and maximum doses to 1cc of PTVs, D95 values, and percent dose differences were calculated. Dose differences for organs-at-risk (OARs) were calculated as a percentage of the clinical tolerance value. For the purposes of this study,±2% over the whole treatment course was considered to be a clinically acceptable dose deviation. Wilcoxon-signed rank tests were used to determine any dose differences within and between the two methods of optimization and recalculation (p<0.05). Pearson's correlations were used to establish the relationship between gadolinium uptake volume in a structure (i.e., proportion of structure covered by a density override) and the resulting dose difference. The median percent dose differences for key reportable dosimetric parameters between non-contrast and simulated contrast plans were<1.2% over all fractions over all patients for reportable target parameters (mean 0.34%, range 0.22%-1.02%). The percent dose differences for maximum dose to 1cc of both PTV1 and PTV2 were significantly different after application of density override (p<0.05) but only in method 2 (Plan C vs. Plan D). For D95 PTV1, there was a statistically significant effect of density override (p<0.01), however only in method 1 (Plan A vs. Plan B). There were no significant differences between calculation methods of the impact of contrast in most target parameters with the exception of D95 PTV1 (p<0.01) and for D95 PTV2 (p<0.05). The median percent dose differences for reportable OAR parameters as a percentage of clinical planning tolerances were<2.0% over a full treatment course (mean 0.65%, range 0.27%-1.62%). There were no significant differences in dose to OARs within or between methods for contrast impact assessment. Dose differences to targets and OARs in oropharyngeal cancer treatment due to the presence of GBCA were minimal, and this work suggests that prospective in vivo evaluations of impact may not be necessary in this clinical site. Accounting for GBCAs may not be needed in daily adaptive workflows on the MR Linac.

Low-Cost, Multi-Center, Longitudinal Remote Training Improves Confidence in Head and Neck Contouring

<h3>Purpose/Objective(s)</h3> Remote training programs have been shown as a cost-effective way to bridge education and training gaps for radiation oncology providers in low- and middle-income countries (LMICs) and could be used to improve contouring skill. Given the expansion of 3D and intensity-modulated radiotherapy and high interest in contouring training in the Philippines, we seek to measure and report the efficacy of a pilot head and neck contouring curriculum. <h3>Materials/Methods</h3> A 13-week, 13-session remote training program on head and neck contouring and plan evaluation was provided at no cost to 8 participating radiation oncology residency programs in the Philippines. The program consisted of weekly 1-hour live video conferencing sessions with interactive didactics and case-based learning through a cloud-based contouring platform. Resident participants were assigned a pre-curriculum and a post-curriculum stage T3N2M0 oropharynx cancer case with 27 OARs. The cases were respectively rated as 2.67/5 and 3.83/5 in difficulty by 6 U.S. educator head and neck radiation oncologists involved in the curriculum. Participants self-rated their confidence in their performance according to a 1-5 Likert scale at the time of each submission regarding three categories: organs at risk (OARs), nodal contouring, and primary target contouring. A team of 4 educators later independently graded contours, according to a 1-5 grading rubric for the same three categories. Cases received 1-2 grades total, which were averaged for analysis. Contour submission was required for a certificate of participation, however no incentives for higher scores were provided. <h3>Results</h3> 41 residents in the Philippines (10 R1, 12 R2, 11 R3, and 9 R4) participated in the curriculum. Average participation per session was 26 (range 12-39, SD = 7.2). 26 (63.4%) participants completed pre-contours for evaluation and 17 (41.5%) post-contours for evaluation. Of these, 14 participants were eligible for paired pre- vs. post-curriculum analysis. Paired pre- and post-curriculum confidence scores (out of 5) were 3.0 and 3.77 for OARs (<i>P</i> = 0.003), 3.08 and 3.54 for nodal stations (<i>P</i> = 0.056), and 2.85 and 3.31 for primary target contouring (<i>P</i> = 0.027), respectively. Overall confidence in contouring the assigned case rose from 2.85 to 3.54 (<i>P</i> < 0.001). Paired pre- and post-curriculum educator grades were 2.96 and 3.38 for OARs (<i>P</i> = 0.135), 2.61 and 1.96 for nodal coverage (<i>P</i> = 0.019), and 2.54 and 2.73 for primary target contours (<i>P</i> = 0.292), respectively. Qualitative observations included greater participant uniformity of left and right parotid glands. <h3>Conclusion</h3> Longitudinal telehealth training integrating cloud-based tools for radiation oncology professionals is a viable and scalable method for providing head and neck contouring education in a LMIC setting. Our findings suggest that work remains to assess the concordance of confidence with performance, especially in challenging cases, and that further contouring education is needed in LMIC regions.