Mean Dose Difference Research Articles

Normal tissue complication probability model predicting taste impairment in head and neck cancer patients: Evaluating the taste bud bearing tongue mucosa as a predictor.

Taste impairment is a common yet complex toxicity of head and neck cancer (HNC) radiotherapy treatment that may affect quality of life of survivors. This study aimed to predict acute and late taste impairment using taste bud bearing tongue mucosa as a new taste-specific organ-at-risk compared to full oral cavity as identified in previous studies. Included HNC patients were treated with curative radiotherapy between 2007 and 2022. The endpoint was patient-rated moderate-to-severe taste loss scored with the EORTC QLQ-H&N35. The new tongue mucosa structure was derived from the existing oral cavity structure in accordance with published guidelines. An auto-segmentation tool was developed and verified by comparison to manually delineated structures. The performance of the mean dose admitted to this new structure was evaluated with both univariable analysis and a refit of a reference NTCP model substituting the oral cavity with the tongue mucosa. A total of 691 HNC patients were included. Good conformity between manually delineated and auto-segmented structures was observed with no significant differences in mean dose (22.2 Gy vs. 22.1 Gy) or volume (20.7 cm3 vs. 20.3 cm3). Full oral cavity mean dose showed comparable effect size in univariable analysis compared to tongue mucosa mean dose. The NTCP model with tongue mucosa did not outperform the reference model with oral cavity for any evaluated time points. The tongue mucosa mean dose did not outperform the oral cavity mean dose in the logistic regression NTCP model predicting acute and late taste impairment.

Comparative Study of Cardiac Radiation Dose With Different Types of Surgery in Breast Cancer Patients

Background: It has been demonstrated that radiation therapy lowers both the death rate from breast cancer and its recurrence. Precise calculation of the radiation dose is crucial for treating the target site as well as protecting vital organs like the heart since large doses of radiation therapy significantly increase patient morbidity and death. Objective: To compare the mean heart dose of radiation in breast cancer patients between breast-conserving surgery versus mastectomy, between different radiotherapy doses and fractionation schedules, and between right and left breast cancer irradiation. Patients and Methods: This is a cross-sectional descriptive retrospective comparative study that was conducted in Baghdad Radiotherapy Center from January 2018 to June 2018, carried on 174 breast cancer patients of different age groups selected randomly and their mean heart dose data collected from their files and database in Baghdad Radiotherapy Center. Results: The overall average of the mean dose was 372 cGy (range from 76.4 to 716.2). The greatest difference in the mean heart dose was between (BCS) patients who received 5000 cGy with regional nodal irradiation and (BCS) patients who received 4005 cGy also with regional nodal irradiation (difference in the mean is 639.8, the P – value <0.001). Regarding the side of breast cancer, the greatest difference in mean heart dose was seen between left and right breast cancer patients who did the same type of surgery (MRM) and received the same dose of radiotherapy (4256 cGy) (difference in the mean is 565cGy and the P – value <0.001). No statistically significant difference in the mean dose between breast-conserving surgery and mastectomy was recorded. Conclusion: The mean heart dose of radiotherapy is significantly increased in left-sided breast cancer irradiation as compared to the right side. A dose of 5000 cGy has the greatest effect on the dose received by the heart, especially in left breast cancer. The type of surgery whether breast-conserving surgery or mastectomy did not affect the mean dose received by the heart. Keywords: Breast cancer, cardiac radiation dose, breast cancer surgery, breast cancer treatment.

Investigating LETd optimization strategies in carbon ion radiotherapy for pancreatic cancer: a dosimetric study using an anthropomorphic phantom.

Clinical carbon ion beams offer the potential to overcome hypoxia-induced radioresistance in pancreatic tumors, due to their high dose-averaged Linear Energy Transfer (LETd), as previous studies have linked a minimum LETd within the tumor to improved local control. Current clinical practices at the Heidelberg Ion-Beam Therapy Center (HIT), which use two posterior beams, do not fully exploit the LETd advantage of carbon ions, as the high LETd is primarily focused on the beams' distal edges. Different LETd-boosting strategies, such as Spot-scanning Hadron Arc (SHArc), could enhance LETd distribution by concentrating high-LETd values in potential hypoxic tumor cores while sparing organs at risk. This study aims to investigate and verify different LETd-boosting strategies using an anthropomorphic pancreas phantom. Various LETd-boosting strategies were investigated for a cylindrical and a pancreas-shaped target in an anthropomorphic pancreas phantom. Treatment plans were optimized using single field optimization (SFO) or multi field optimization (MFO), with objective functions based on either physical dose (Phys), relative biological effectiveness(RBE)-weighted dose, or a combination of RBE and LETd-based objectives (LETopt). The LETd-boosting planning strategies were optimized with the goal of increasing the minimum LETd in the tumor without compromising its homogeneous dose coverage. Beam configurations investigated included the two-beam in-house clinical standard (2-SFOPhys, 2-SFORBE and 2-MFORBE-LETopt), a three-beam configuration (3-MFORBE and 3-MFORBE-LETopt) and SHArc (SHArcPhys, SHArcRBE and SHArcRBE-LETopt) using step-and-shoot delivery. The different plans were verified using an anthropomorphic pancreas phantom at HIT and compared to treatment planning system (TPS) predictions. All investigated LETd-boosting strategies altered the LETd distribution while meeting optimization goals and constraints, resulting in varying degrees of LETd enhancement. For the cylindrical volume, the SHArc plan resulted in the highest LETd concentration in the tumor core, with the minimum LETd in the GTV scaling up to 91keV/µm. For the pancreas-shaped volume, however, the 3-MFORBE-LETopt achieved a higher minimum LETd in the GTV than SHArcRBE (75.6 and 62.3keV/µm, respectively). When combining SHArc with LETd optimization, a minimum LETd of 76.3keV/µm was achieved, suggesting a potential benefit from this combined approach. Most dosimetric verifications showed dose deviations to the TPS within a 5% range, for both beam-per-beam and total dose. LETd-optimized and SHArc plans exhibited slightly higher mean dose deviations (2.0%-4.6%) compared to the standard RBE-based plans (<1.5%). This study demonstrated the feasibility of enhancing LETd in pancreatic tumors using carbon ion arc delivery coupled with LETd optimization. The possibility of delivering these plans was verified through irradiation of an anthropomorphic pancreas phantom, which showed agreement between dose measurements and predictions.

EBT3 Radiochromic film response in time-dependent thermal environment and water submersion conditions: Its clinical relevance and uncertainty estimation

AimThis study aimed to find the thermal and humidity-dependent behavior of EBT3 film. The changes in the film sensitivity as well as the dosimetric region of interest in the small-size film due to its storage and setup condition were evaluated. Material and methodsThree sets of films were kept at three different thermal storage conditions. 15 films from each set were kept at 2 °C, 20 °C, and 40 °C storage conditions for 24 h and 48 h pre- and post-irradiation. The humidity effect (water submersion) on the film in terms of the film's edge diffusion, and change in the optical density at the central region of the film was estimated by keeping the films underwater. ResultsThe mean relative film sensitivity was found 1.107 ± 0.123 and 0.966 ± 0.028 respectively for the films stored at 40 °C and 2 °C with respect to the sensitivity of the films that were kept at room temperature (20 °C) each for 48 h. The dosimetric result shows that the measured dose in the dose range (2–20 Gy) was overestimated by 7.01 % (percentage mean dose difference (MDD)) in the films stored at 40 °C for 48 h. In contrast, it was underestimated by −4.54 % (MDD) in the films stored at 2 °C for 48 h compared to those kept at an ambient room temperature of 20 °C (MDD = 0.24%). The water-diffusion rate at the border of the EBT3 film used in this study was 0.23 mm/h. An increment of 6.8% in the optical density at the central region of the film was observed for the unexposed control film kept underwater for 24 h. The combined standard uncertainty due to five different sources of uncertainties was 2.91%. ConclusionThe sensitivity of the EBT3 film kept at 40 °C is always higher (overestimate) whereas lower (underestimate) for the films kept at 2 °C as compared to the films at normal room temperature. The correction for the changes in the net optical density due to its storage condition (thermal effect) and the dosimetry condition of water submersion (humidity effect) must be incorporated into the current protocols of film-dosimetry if the facility cannot have temperature-controlled film storage environment and if the film immersion under water is more than 4 h.

Implementation of Patient-Specific Quality Control in Radiotherapy Treatments with ArcCheck

Introduction: Quality control is essential to ensure safety and prevent errors in the administration of ionizing radiation across various radiotherapy techniques. Objective: To evaluate the performance of the ArcCheck detector with the goal of implementing a specific quality control technique for patients treated with dynamic arc therapy. Methods: Fifty patients treated with 6 MV and 10 MV energies on the Clinac® Varian CX were selected. Doses at the isocenter of each treatment plan were analyzed using a PMMA phantom (30 x 30 x 15 cm³) to validate reference values between the treatment planning system and the ionization chamber. The treatment plans were also recreated using the ArcCheck. Results: The mean dose difference at the isocenter was -0.96% and -1.34% for 6 MV and 10 MV, respectively. The average passing rate of the dose distributions in the gamma analysis exceeded 98.0% for both energies. Conclusion: The results demonstrated good concordance with the TG-119 and TG-218 protocols, supporting the use of the detector for quality control in patient-specific treatments.

Implementation and validation of a very-high-energy electron model in the matRad treatment planning system.

While electron beams of up to 20 MeV are commonly used in radiotherapy, the use of very-high-energy electrons (VHEEs) in the range of 100-200 MeV is now becoming a realistic option thanks to the recent advancements in accelerator technology. Indeed, VHEE offers several clinically attractive features and can be delivered using various conformation methods (including scanning, collimation, and focussing) at ultra-high dose rates. To date, there is a lack of research tools for fast simulation of treatment plans using VHEE beams. This work aims to implement and validate a simple and fast dose calculation algorithm based on the Fermi-Eyges theory of multiple Coulomb scattering for VHEE radiation therapy, with energies up to 200 MeV. A treatment planning system (TPS) toolkit with VHEE modality would indeed allow for further preclinical investigations, including treatment plan optimization and evaluation, and thus contribute to the gradual introduction of VHEE radiotherapy in clinical practice. A VHEE pencil beam scanning double Gaussian model was introduced into the open-source TPS matRad environment along with new functions and options dedicated to VHEE dose calculations. Various geometries and field configurations were then calculated in matRad (up to 200 MeV and 15×15 cm2, with complex bone or lung heterogeneities) and the results were compared to Monte Carlo simulations in the TOPAS/Geant4 toolkit. Two types of beam model (divergent or focused) were also tested. Examples of clinical treatment plans were computed, and the results were compared between the two codes. VHEE modality was fully implemented in matRad with GUI capabilities while preserving all original TPS features. New relevant options such as the importation of specific spot-lists or adjustment of the lateral dose calculation cutoff to optimize the calculation speed were validated. Single spot and square field dose distributions were validated in water alone as well as in clinically relevant inhomogeneities. Dose maps from the VHEE model in matRad were in good agreement with TOPAS (2D gamma index [2%/1mm] with passing rates superior to 90%, <6% mean dose differences), except for large interface heterogeneities. This work describes the implementation of a simple but efficient VHEE simulation model in matRad. A few configurations were studied in order to validate the model against accurate Monte Carlo simulations, demonstrating its usefulness for carrying out preliminary studies involving VHEE radiotherapy.

Quality assurance for online adaptive radiotherapy: a secondary dose verification model with geometry-encoded U-Net

Abstract Background &amp; Purpose: In online adaptive radiotherapy (ART), quick computation-based secondary dose verification is crucial for ensuring the quality of ART plans while the patient is positioned on the treatment couch. However, traditional dose verification algorithms are generally time-consuming, reducing the efficiency of ART workflow. This study aims to develop an ultra-fast deep-learning (DL) based secondary dose verification algorithm to accurately estimate dose distributions using CT and fluence maps (FMs). &amp;#xD;Methods: We integrated FMs into the CT image domain by explicitly resolving the geometry of treatment delivery. For each gantry angle, an FM was constructed based on the optimized multi-leaf collimator apertures and corresponding monitoring units (MUs). To effectively encode treatment beam configuration, the constructed FMs were back-projected to 30 cm away from the isocenter with respect to the exact geometry of the treatment machines. Then, a 3D U-Net was utilized to take the integrated CT and FM volume as input to estimate dose. Training and validation were performed on 381 prostate cancer cases, with an additional 40 testing cases for independent evaluation of model performance.&amp;#xD;Results: The proposed model can estimate dose in ~15 ms for each patient. The average γ passing rate (3%/2mm, 10% threshold) for the estimated dose was 99.9% ± 0.15% on testing patients. The mean dose differences for the planning target volume (PTV) and organs at risk (OARs) were 0.07%±0.34% and 0.48%±0.72%, respectively.&amp;#xD;Conclusion: We have developed a geometry-resolved DL framework for accurate dose estimation and demonstrated its potential in real-time online ART doses verification.&amp;#xD;

AVATAR 2.0: next level communication systems for radiotherapy through face-to-face video, biofeedback, translation, and audiovisual immersion.

This paper discusses an advanced version of our audiovisual-assisted therapeutic ambience in radiotherapy (AVATAR) radiolucent display systems designed for pediatric radiotherapy, enabling anesthesia-free treatments, video communication, and biofeedback. The scope of the AVATAR system is expanded here in two major ways: (i) through alternative mounting systems to accommodate a broader range of radiotherapy machines (specifically to fit robotic-arm and toroidal geometry photon radiotherapy and proton radiotherapy systems) and (ii) through additional hardware to provide video-calling, optimized audio for clear communication, and combined video inputs for biofeedback, translation, and other advanced functionalities. Because robustness requires strong parts and radio-transparency requires thin, light parts, three-dimensional printing was used to rapidly prototype hollow structures and to iteratively improve robustness. Two system designs were made: one that mounts superior and another that mounts inferior to the patient's head. Radiation dose measurements and calculations were conducted to assess dose perturbations at surface and depth due to the screen. For 6-MV volumetric modulated arc therapy (VMAT) plans, with and without the screen, the mean and maximum dose differences inside the planning target volume were 0.2% and 2.6% of the 200 cGy prescription, respectively. For a single static beam through the screen, the maximum measured excess surface dose was 13.4 ± 0.5%, and the largest measured dose attenuation at 5-cm water-equivalent depth was 2.1 ± 0.2%. These percentages are relative to the dose without the screen at those locations. The radiolucent screen systems provided here are shown to give minimal dosimetric effects on megavoltage VMAT photon treatments. For static beams, however, surface dose effects should be considered when these beams pass through the thickest components of the screen. Design files are also provided.

Is the IROC H&N credentialing phantom an effective surrogate for different anatomical sites?: Using IROC's H&N phantom for various sites

PURPOSEThe IROC head and neck phantom is used to credential institutions for IMRT delivery for all anatomical sites where delivery of modulated therapy is a primary challenge. This study evaluated how appropriate the use of this phantom is for varied clinical anatomy by evaluating how closely the IROC head and neck phantom described clinical dose errors from beam modeling compared to various anatomical sites. METHODSThe MLC offset, transmission, PDD and seven additional beam modeling parameters for a Varian accelerator were modified in RayStation to match community data at the 2.5, 25, 50, 75 and 97.5 percentile levels. Modifications were evaluated on 25 H&N phantom cases and 25 clinical cases (H&N, prostate, lung, mesothelioma, and brain), generating 2,000 plan perturbations. Differences in mean dose delivered to clinical target volumes (CTV) and organs at risk (OAR) were compared between phantom and clinical plans to assess the relationship between dose deviations in phantom versus clinical CTVs, and as a function of 18 different complexity metrics. RESULTSPerturbations to MLC offset and transmission parameters demonstrated the greatest impact on dose accuracy for phantom and clinical plans (for all anatomic sites). The phantom demonstrated equivalent or greater sensitivity to these parameter perturbations when compared to clinical sites, largely aligning with treatment complexity. The mean MLC Gap best described the impact of errors in TPS beam modeling parameters in phantoms plan and clinical plans from various anatomical sites. CONCLUSIONWhen compared across various anatomical sites, the IROC H&N credentialing phantom exhibited similar or greater sensitivity to errors in the treatment planning system. As such, it is a suitable surrogate device for assessing institutional performance across various anatomical sites. If an institution successfully irradiates the phantom, that result confers confidence that IMRT to a wide range of anatomical sites can be successfully delivered by the institution.

Adaptive intensity modulated proton therapy using 4D robust planning: a proof-of-concept for the application of dose mimicking approach

Objective.A four-dimensional robust optimisation (4DRO) is usually employed when the tumour respiratory motion needs to be addressed. However, it is computationally demanding, and an automated method is preferable for adaptive planning to avoid manual trial-and-error. This study proposes a 4DRO technique based on dose mimicking for automated adaptive planning.Approach.Initial plans for 4DRO intensity modulated proton therapy were created on an average CT for four patients with clinical target volume (CTV) in the lung, oesophagus, or pancreas, respectively. These plans were robustly optimised using three phases of four-dimensional computed tomography (4DCT) and accounting for setup and density uncertainties. Weekly 4DCTs were used for adaptive replanning, using a constant relative biological effectiveness (cRBE) of 1.1. Two methods were used: (1) template-based adaptive (TA) planning and (2) dose-mimicking-based adaptive (MA) planning. The plans were evaluated using variable RBE (vRBE) weighted doses and biologically consistent dose accumulation (BCDA).Main results.MA and TA plans had comparable CTV coverage except for one patient where the MA plan had a higher D98 and lower D2 but with an increased D2 in few organs at risk (OARs). CTV D98 deviations in non-adaptive plans from the initial plans were up to -7.2 percentage points (p.p.) in individual cases and -1.8 p.p. when using BCDA. For the OARs, MA plans showed a reduced mean dose and D2 compared to the TA plans, with few exceptions. The vRBE-weighted accumulated doses had a mean dose and D2 difference of up to 0.3 Gy and 0.5 Gy, respectively, in the OARs with respect to cRBE-weighted doses.Significance.MA plans indicate better performance in target coverage and OAR dose sparing compared to the TA plans in 4DRO adaptive planning. Moreover, MA method is capable of handling both forms of anatomical variation, namely, changes in density and relative shifts in the position of OARs.

Selection for proton radiotherapy of grade 1–3 glioma patients

BackgroundFor adult patients with grade 1–3 gliomas, identifying patients with an indication for proton therapy (PT) can be challenging due to sparse evidence supporting its benefits. In this study, we aimed to ensure national consensus and develop a decision support tool to aid clinicians in identifying patients with grade 1–3 gliomas eligible for PT. MethodsSixty-one historic patients referred for postoperative radiotherapy for glioma grade 1–3 were included in this study and had new photon therapy and PT plans calculated. These plans along with clinical parameters were presented to neurooncologists with experience in treating brain tumours. The patients were presented at three workshops (WSs), where each neurooncologist individually had to choose between photon and proton therapy. Important parameters were selected using cross validation. Multivariable logistic regression was used to predict the neurooncologists’ treatment modality choice. ResultsAt the three WSs 23, 24 and 19 randomly selected patients were presented. Seventy-five percent of the neurooncologists agreed for 14 patients (61%), 16 patients (67%) and 15 patients (79%) at WS1, WS2 and WS3. Age at radiotherapy and difference in mean dose (ΔDmean) to the residual brain were significant predictors of the choice of treatment modality, p < 0.001. Model coefficients were: βage = 0.07 per year (95% confidence interval [CI] = 0.05–0.09), and βΔdose = -0.27 per Gy (95% CI=-0.36--0.18). ConclusionHigher degree of agreement was reached. Age and ΔDmean to the residual brain significantly predicted the choice of radiation modality. We have developed a decision support model which may aid in the selection of patients with glioma grade 1–3 to PT.

Quantifying the Dosimetric Impact of Proton Range Uncertainties on RBE-Weighted Dose Distributions in Intensity-Modulated Proton Therapy for Bilateral Head and Neck Cancer.

In current clinical practice, intensity-modulated proton therapy (IMPT) head and neck cancer (HNC) plans are generated using a constant relative biological effectiveness (cRBE) of 1.1. The primary goal of this study was to explore the dosimetric impact of proton range uncertainties on RBE-weighted dose (RWD) distributions using a variable RBE (vRBE) model in the context of bilateral HNC IMPT plans. The current study included the computed tomography (CT) datasets of ten bilateral HNC patients who had undergone photon therapy. Each patient's plan was generated using three IMPT beams to deliver doses to the CTV_High and CTV_Low for doses of 70 Gy(RBE) and 54 Gy(RBE), respectively, in 35 fractions through a simultaneous integrated boost (SIB) technique. Each nominal plan calculated with a cRBE of 1.1 was subjected to the range uncertainties of ±3%. The McNamara vRBE model was used for RWD calculations. For each patient, the differences in dosimetric metrices between the RWD and nominal dose distributions were compared. The constrictor muscles, oral cavity, parotids, larynx, thyroid, and esophagus showed average differences in mean dose (Dmean) values up to 6.91 Gy(RBE), indicating the impact of proton range uncertainties on RWD distributions. Similarly, the brachial plexus, brain, brainstem, spinal cord, and mandible showed varying degrees of the average differences in maximum dose (Dmax) values (2.78-10.75 Gy(RBE)). The Dmean and Dmax to the CTV from RWD distributions were within ±2% of the dosimetric results in nominal plans. The consistent trend of higher mean and maximum doses to the OARs with the McNamara vRBE model compared to cRBE model highlighted the need for consideration of proton range uncertainties while evaluating OAR doses in bilateral HNC IMPT plans.

Multicriteria optimization of radiation therapy: Towards empowerment and standardization of reverse planning for head and neck squamous cell carcinoma

PurposeThe purpose of this study was to assess if multicriteria optimization could limit interoperator variability in radiation therapy planning and assess if this method could contribute to target volume coverage and sparing of organ at risk for intensity-modulated curative radiation therapy of head and neck cancers. Material and methodsWe performed a retrospective analysis on 20 patients treated for an oropharyngeal or oral cavity squamous cell carcinoma. We carried out a comparative dosimetric study of manual plans produced with Precision® software, compared with the plans proposed using the multicriteria optimization method (RayStation®). We assessed interoperator reproducibility on the first six patients, and dosimetric contribution in sparing organs at risk using the multicriteria optimization method. ResultsMedian age was 69 years, most lesions were oropharyngeal carcinoma (65%), and 35% lesions were stage T3. First, we obtained a high degree of similarity between the four operator measurements for each patient at the level of each organ. Intraclass correlation coefficients were greater than 0.85. Second, we observed a significant dosimetric benefit for contralateral parotid gland, homolateral and contralateral masseter muscles, homolateral and contralateral pterygoid muscles and for the larynx (P<0.05). For the contralateral parotid gland, the mean dose difference between the multicriteria optimization and manual plans was −2.0Gy (P=0.01). Regarding the larynx, the mean dose difference between the two plans was −4.6Gy (P<0.001). ConclusionMulticriteria optimization is a reproducible technique and faster than manual optimization. It allows dosimetric advantages on organs at risk, especially for those not usually taken into consideration in manual dosimetry. This may lead to improved quality of life.

The development of patient-specific quality assurance (PSQA) for a proton wobbling nozzle using PTSim Monte Carlo code

The aim of this study is to develop a Monte Carlo-based platform for patient-specific quality assurance (PSQA) in the proton wobbling nozzle at Chang Gung Memorial Hospital. To efficiently reduce time usage and enhance simulated precision, this platform required an initial fine-tuning of the Guard volume (GV) and lateral displacement (LD) settings. Different GV sizes combined with LD modes were utilized to estimate depth dose profiles in a water phantom. The simulated central axis depth doses were then analyzed using PTSim and compared to measurement using a PTW MP3 water tank and a Markus ionization chamber type 34045. Treatment parameters for a liver case were extracted from the Eclipse DICOM RT Plan file. Simulated doses were compared to measurements using Zebra and MatriXX systems during PSQA process. Furthermore, a geometrical trigger technique was applied to assess the track positions in patient-specific components. The study found that the mean dose difference between measured and simulated values for the optimized LD/GV was below 1% at all depth positions. With passing rates of 97.4% at the middle SOBP and 90.3% at the proximal SOBP, the gamma analysis demonstrated satisfactory results. For the axial dose profile, SOBP flatness was within 2.5%. From the geometric trigger analysis, more than 95–98% of the dose was delivered through the range compensator, while approximately 2–5% originated from scattered protons from the Multi-Leaf Collimator (MLC) and block's edges. The PTSim simulation's performance in conducting PSQA demonstrated its capability and reliability.

Tubarial gland sparing with intensity modulated radiation therapy for oropharyngeal cancers: A pilot study of dosimetric feasibility.

Tubarial glands are a new organ at risk for head and neck cancer radiation therapy (RT). We aimed to study the feasibility of sparing them using intensity-modulated radiation therapy (IMRT). Tubarial glands were delineated for 17 patients with oropharyngeal carcinoma receiving definitive RT, and treatment plans were re-optimized to spare dose to the tubarial glands while maintaining target coverage. A paired t test was performed to compare the mean dose of tubarial glands and target coverage. The difference in mean doses was 4.9 and 7.0 Gy for the ipsilateral and contralateral tubarial glands, respectively (p < 0.01). The mean dose to tubarial gland was ≤39 Gy in 35% versus 47% (ipsilateral) and 70% versus 100% (contralateral) in clinical and re-optimized plans, respectively. Re-optimized ipsilateral tubarial gland mean ≤39 Gy was achieved more commonly in patients with base of tongue versus tonsil primaries (86% vs. 20%, p = 0.02). This pilot study demonstrates the dosimetric feasibility of tubarial gland sparing with IMRT. Dosimetric constraints need to be determined with larger studies.

Clinical implementation of a commercial synthetic computed tomography solution for radiotherapy treatment of glioblastoma

Background and PurposeMagnetic resonance (MR)-only radiotherapy (RT) workflow eliminates uncertainties due to computed tomography (CT)-MR image registration, by using synthetic CT (sCT) images generated from MR. This study describes the clinical implementation process, from retrospective commissioning to prospective validation stage of a commercial artificial intelligence (AI)-based sCT product. Evaluation of the dosimetric performance of the sCT is presented, with emphasis on the impact of voxel size differences between image modalities. Materials and methodssCT performance was assessed in glioblastoma RT planning. Dose differences for 30 patients in both commissioning and validation cohorts were calculated at various dose-volume-histogram (DVH) points for target and organs-at-risk (OAR). A gamma analysis was conducted on regridded image plans. Quality assurance (QA) guidelines were established based on commissioning phase results. ResultsMean dose difference to target structures was found to be within ± 0.7 % regardless of image resolution and cohort. OARs’ mean dose differences were within ± 1.3 % for plans calculated on regridded images for both cohorts, while differences were higher for plans with original voxel size, reaching up to −4.2 % for chiasma D2% in the commissioning cohort. Gamma passing rates for the brain structure using the criteria 1 %/1mm, 2 %/2mm and 3 %/3mm were 93.6 %/99.8 %/100 % and 96.6 %/99.9 %/100 % for commissioning and validation cohorts, respectively. ConclusionsDosimetric outcomes in both commissioning and validation stages confirmed sCT’s equivalence to CT. The large patient cohort in this study aided in establishing a robust QA program for the MR-only workflow, now applied in glioblastoma RT at our center.

Treatment planning evaluation and experimental validation of the magnetic resonance-based intrafraction drift correction

Background and purposeMRI-guided online adaptive treatments can account for interfractional variations, however intrafraction motion reduces treatment accuracy. Intrafraction plan adaptation methods, such as the Intrafraction Drift Correction (IDC) or sub-fractionation, are needed. IDC uses real-time automatic monitoring of the tumor position to initiate plan adaptations by repositioning segments. IDC is a fast adaptation method that occurs only when necessary and this method could enable margin reduction. This research provides a treatment planning evaluation and experimental validation of the IDC. Materials and methodsAn in silico treatment planning evaluation was performed for 13 prostate patients mid-treatment without and with intrafraction plan adaptation (IDC and sub-fractionation). The adaptation methods were evaluated using dose volume histogram (DVH) metrics. To experimentally verify IDC a treatment was mimicked whereby a motion phantom containing an EBT3 film moved mid-treatment, followed by repositioning of segments. In addition, the delivered treatment was irradiated on a diode array phantom for plan quality assurance purposes. ResultsThe planning study showed benefits for using intrafraction adaptation methods relative to no adaptation, where the IDC and sub-fractionation showed consistently improved target coverage with median target coverages of 100.0%. The experimental results verified the IDC with high minimum gamma passing rates of 99.1% and small mean dose deviations of maximum 0.3%. ConclusionThe straightforward and fast IDC technique showed DVH metrics consistent with the sub-fractionation method using segment weight re-optimization for prostate patients. The dosimetric and geometric accuracy was shown for a full IDC workflow using film and diode array dosimetry.

Innovative Education Method for a More Effective, Faster, and Valued Training in Radiation Therapy Treatment Planning

Because of the automation of radiation therapy, competencies of radiation technologists (RTTs) change, and training methods are challenged. This study aims to develop, and pilot test an innovative training method based on lean management principles. A new training method was developed for lung cancer treatment planning (TP). The novelty is summarized by including a stable environment and an increased focus on the how and why of key decision making. Trainees have to motivate their decisions during TP process, and to argue their choices with peers. Six students and 6 RTTs completed this training for lung cancer TP. Effects of the training were measured by (1) quality of TP, using doses in organs at risk and target volumes, (2) perceived experiences (survey), measured at baseline (T0); after peer session (T1); and 6 months later (T2). Finally, training throughput time was measured. At T0, RTTs showed a larger intragroup interquartile range (IIR) (2.63Gy vs 1.51Gy), but lower mean doses to heart and esophagus than students (6.79Gy vs 8.49Gy; 20.87Gy vs 24.62Gy). At T1, quality of TPs was similar between RTTs and students (IIR: 1.39Gy vs 1.33Gy) and no significant differences in mean dose to heart and esophagus (4.48Gy vs 4.69Gy; 17.75Gy vs 18.47Gy). At T2, students still performed equal to RTTs (IIR: 1.07Gy vs 1.45Gy) and achieved lower maximum dose to esophagus (44.75Gy vs 46.45Gy). The training method and peer sessions were experienced positive: at baseline (T0): 8 score on a scale 1-10, directly after the peer sessions; (T1): 8 by the students and 7 by the RTTs, after 9 months; (T2): 9 by the students and 7 by the RTTs. Training throughput time decreased from 12 to 3 months. This training method based on lean management principles was successfully applied to training of RTTs for lung cancer TP. Training throughput time was reduced dramatically and TP quality sustained after 6 months. This method can potentially improve training efficiency in diverse situations with complex decision-making.

The Role of Lung Density in the Voxel-Based Dosimetry of 90Y-TARE Evaluated with the Voxel S-Value (VSV) Method and Fast Monte Carlo Simulation

(1) Background: In 90Y-TARE treatments, lung-absorbed doses should be calculated according to the manufacturer’s instructions, using the MIRD-scheme. This scheme is derived from the assumption that 90Y-microspheres deliver the dose in a water-equivalent medium. Since the density of the lungs is quite different from that of the liver, the absorbed dose to the lungs could vary considerably, especially at the liver/lungs interface. The aim of this work is to compare the dosimetric results obtained by two dedicated software packages implementing a water-equivalent dose calculation and a Monte Carlo (MC) simulation, respectively. (2) Methods: An anthropomorphic IEC phantom and a retrospective selection of 24 patients with a diagnosis of HCC were taken into account. In the phantom study, starting from a 90Y-PET/CT acquisition, the liver cavity was manually fixed with a uniform activity concentration on PET series, while the lung compartment was manually expanded on a CT series to simulate a realistic situation in which the liver and lungs are adjacent. These steps were performed by using MIM 90Y SurePlan. Then, a first simulation was carried out with only the liver cavity filled, while a second one was carried out, in which the lung compartment was also manually fixed with a uniform activity concentration corresponding to 10% lung shunt fraction. MIM 90Y SurePlan was used to obtain Voxel S-Value (VSV) approach dose values; instead, Torch was used to obtain MC approach dose values for both the phantom and the patients. (3) Results: In the phantom study, the percentage mean dose differences (∆D%) between VSV and MC in the first and second simulation, respectively were found to be 1.2 and 0.5% (absolute dose variation, ∆D, of 0.7 and 0.3 Gy) for the liver, −56 and 70% (∆D of −0.3 and −16.2 Gy) for the lungs, and −48 and −60% (∆D of −4.3 and −16.5 Gy) for the Liver/Lungs Edge region. The patient study reports similar results with ∆D% between VSV and MC of 7.0%, 4.1% and 6.7% for the whole liver, healthy liver, and tumor, respectively, while the result was −61.2% for the left lung and −61.1% for both the right lung and lungs. (4) Conclusion: Both VSV and MC allowed accurate radiation dose estimation with small differences (&lt;7%) in regions of uniform water-equivalent density (i.e., within the liver). Larger differences between the two methods (&gt;50%) were observed for air-equivalent regions in the phantom simulation and the patient study.

Treating early-stage centrally-located non-small cell lung cancer with DCAT-SBRT in centers lacking the VMAT technique: a comprehensive study.

Volumetric-modulated arc therapy (VMAT) may have the highest overall performance for stereotactic body radiotherapy (SBRT) treatment of inoperable early-stage NSCLC. However, in centers lacking the VMAT technique, the dynamic conformal arc therapy (DCAT) technique is potentially the best option for small and rounded NSCLC-SBRT. Therefore, we will comprehensively analyze the advantages of the DCAT versus the other techniques except VMAT in terms of dosimetry, plan complexity, delivery time, γ-passing rates and the interplay effect. 36 patients with early-stage centrally located NSCLC with PTV volumes < 65 cc were enrolled. All patients were redesigned with 50Gy/5f, and 100% of the prescribed dose was normalized to cover 95% of the PTV. The other two delivery techniques compared to the DCAT technique include 3-dimensional conformal radiotherapy (3DCRT) and intensity-modulated radiotherapy (IMRT), which use the same parameters for all three techniques. The dosimetric parameters of the 3-group plans all met the RTOG 0813 protocol. Unsurprisingly, plan complexity parameters such as segments and MUs were significantly reduced in the DCAT plans by 159.56 and 925.90 compared to the IMRT plans, respectively (all P < 0.001). The delivery time of the DCAT plans was the least of 164.51 s (all P < 0.05). Compared to the IMRT plans, the γ-passing rates were higher in the DCAT plans (P < 0.001), with the most significant difference of 6.01% in the (2%, 1mm) criteria. As for the interplay effect, the mean dose difference (MDD) in the DCAT plans was as good as the 3DCRT plans at different respiratory amplitudes but better than the IMRT plans (all P < 0.05), and the MDD of DCAT plans did not exceed 3% in all respiratory amplitude. In centers lacking the VMAT technique, implementing SBRT treatment based on the DCAT technique for inoperable early-stage centrally-located NSCLC patients with PTV volumes < 65 cc achieves better treatment efficiency and delivery accuracy while maintaining the plan quality.