Patient Position Verification Research Articles

Depth Dose According to Depth during Cone Beam Computed Tomography Acquisition and Dose Assessment in the Orbital Area Using a Three-Dimensional Printer

Background: Cone beam computed tomography (CBCT) is essential for correcting and verifying patient position before radiation therapy. However, it poses additional radiation exposure during CBCT scans. Therefore, this study aimed to evaluate radiological safety for the human body through dose assessment for CBCT.Materials and Methods: For CBCT dose assessment, the depth dose was evaluated using a cheese phantom, and the dose in the orbital area was evaluated using a human body phantom self-fabricated with a three-dimensional printer.Results and Discussion: The evaluation of radiation doses revealed maximum doses of 14.14 mGy and minimum doses of 6.12 mGy for pelvic imaging conditions. For chest imaging conditions, the maximum doses were 4.82 mGy, and the minimum doses were 2.35 mGy. Head imaging conditions showed maximum doses of 1.46 mGy and minimum doses of 0.39 mGy. The eyeball doses using a human body phantom model averaged at 2.11 mGy on the left and 2.19 mGy on the right. The depth dose ranged between 0.39 mGy and 14.14 mGy, depending on the change in depth for each imaging mode, and the average dose in the orbit area using a human body phantom was 2.15 mGy.Conclusion: Based on the experimental results, CBCT did not significantly affect the radiation dose. However, it is important to maintain a minimal radiation dose to optimize radiation protection following the as low as reasonable achievable principle.

Patterns of practice of image guided particle therapy for cranio-spinal irradiation: A site specific multi-institutional survey of European Particle Therapy Network

PurposeTo investigate the current practice patterns in image-guided particle therapy (IGPT) for cranio-spinal irradiation (CSI). MethodsA multi-institutional survey was distributed to European particle therapy centres to analyse all aspects of IGPT. Based on the survey results, a Delphi consensus analysis was developed to define minimum requirements and optimal workflow for clinical practice. The centres participating in the institutional survey were invited to join the Delphi process. ResultsEleven centres participated in the survey. Imaging for treatment planning was rather similar among the centres with Computed Tomography (CT) being the main modality. For positioning verification, 2D IGPT was more commonly used than 3D IGPT. Two centres performed routinely imaging for plan adaptation, by the rest ad hoc. Eight centres participated in the Delphi consensus analysis. The full consensus was reached on the use of CT imaging without contrast for treatment planning and the role of magnetic resonance imaging (MRI) in target and organs-at-risk delineation. There was an agreement on the necessity to perform patient position verification and correction before each isocentre. The most important outcome was the clear need for standardization and harmonization of the workflow. ConclusionThere were differences in CSI IGPT clinical practice among the European particle therapy centres. Moreover, the optimal workflow as identified by experts was not yet reached. There is a strong need for consensus guidelines. The state-of-the-art imaging technology and protocols need to be implemented into clinical practice to improve the quality of IGPT for CSI.

2894: Patient position verification in non-coplanar SRS with dual X-ray projections via 2D-3D registration

2894: Patient position verification in non-coplanar SRS with dual X-ray projections via 2D-3D registration

Treatment robustness of total body irradiation with volumetric modulated arc therapy

This study evaluated the robustness of multi-isocenter Volumetric Modulated Arc Therapy Total Body Irradiation dose distribution in the overlapping region between the head-first and feet-first computed tomography scans, considering the longitudinal isocenter shifts recorded during treatment delivery. For 15 out of 22 patients, the dose distribution in the overlapping region fulfilled all three the robustness criteria. The overlapping region dose distribution of the remaining 7 cases fulfilled two robustness criteria. The dose distribution was found to be robust against daily recorded longitudinal isocenter shifts, as a consequence of the patient position verification procedure, of up to 16 mm.

Use of Low Melting Point Alloy Mcp-96 Filter on Gammagraphic Optimization of Patient Position Verification with Telecobalt 60 Machine

Verification of the patient's position is a stage in external radiotherapy that aims to ensure the accuracy of radiation therapy administration according to plan. Equipment for the patient position verification process that is often used is Electronic Portal Image Devices (EPID) and film portals. However, not all Telecobalt 60 machines are equipped with EPID, so it requires alternative equipment to verify patient positions. One modality that can be utilized is Computed Radiography (CR). The study was conducted to analyze the use of MCP-96 low melting point alloy filters in imaging, verifying patient positions with CR devices on telecobalt 60 machine can calibrate radiation doses and provide good image quality and anatomical information. The study used a posttest-only control group design by comparing radiation dose, image quality, and anatomical information of the patient's position verification image. Imaging was performed using a phantom pelvis as an object and using CR equipment and low melting point alloy MCP-96 as a filter. The results showed that low melting points alloy MCP-96 with a thickness of 1 cm, 2 cm and 4 cm can calibrate the radiation dose output of the telecobalt 60 machine in accordance with recommendations for kilovoltage imaging. There was no significant difference in SNR and CNR images from imaging verification of patient positions with filter thicknesses of 1 cm, 2 cm, and 4 cm. Filter thickness of 1 cm produces images with optimal image quality and anatomical information in gammagraphic imaging verification of patient position using CR on telecobalt 60 machine. Thus, the use of low melting point alloy MCP-96 thickness of 1 cm and CR devices can be used in gammagraphic imaging of patient position verification on a telecobalt 60 machine as an alternative if you do not have EPID.

PO-2265 Patient position verification for multi isocenter total body irradiation with VMAT

PO-2265 Patient position verification for multi isocenter total body irradiation with VMAT

Accuracy of the catalyst surface guidance system for patient monitoring during cranial SRS treatments.

The use of surface guided imaging in cranial stereotactic radiotherapy provides a non-ionising form of patient position verification that gives information on when patient position errors may require corrections to be applied. This work assessed the accuracy of Catalyst+ HD system for treatment geometries commonly used in cranial SRS. Average Catalyst reported error as a function of couch rotation agreed with measured kV and MV walkout within 0.5mm for the lateral and longitudinal directions. Change in Catalyst reported error with isocentre depth relative to the monitoring region of interest (ROI) from the surface was assessed and showed variation above 0.5mm, but within 1mm for isocentre depths ranging from 3 to 15cm from the phantom surface. Gantry occlusion of Catalyst cameras caused a shift in reported position error that was also dependent on isocentre depth relative to the monitoring ROI. SRS MapCHECK patients specific QA results showed improvement in gamma passing rates for a workflow where Catalyst reported errors above 0.5mm were corrected.

Robustness of a multi-isocenter VMAT Total Body Irradiation (TBI) dose distribution against daily patient setup errors

<h3>Objectives</h3> A VMAT technique using a rotatable tabletop for TBI in supine position is newly applied at UMC Utrecht. We aimed to assess the dose distribution robustness against daily isocenter shifts. <h3>Methods</h3> The tabletop enables rotation from head-first (HF) to feet-first (FF) supine position while the patient remains immobilized in an individualized whole-body vacuum matrass and a thermoplastic facemask. The treatment plan was optimized on the HF and FF CT-scans, co-registered on the overlapping anatomical region (20 cm longitudinal). Depending on patient-length, 4 to 6 isocenters with overlapping arcs (4 cm longitudinal) were used. Prescription dose (PD) was 12Gy in 6 fractions with mean dose constraints for lungs/kidneys <10Gy and lenses <8Gy. Daily patient-position verification procedure (PV) comprised: pelvic HF-iso3 (CBCT + online corrected); thoracic HF-iso2 (CBCT only, no correction); knee region FF-iso (CBCT + online corrected). Brain HF-iso1 and FF-iso4 or -iso5 (patient length dependent) not imaged. HF (FF) radiation delivery followed HF (FF)-PV. After each fraction, the dose distribution of the first 3 treated patients (length range 110-195 cm) was recalculated applying the registered isocenter corrections/shifts. Then, the 6-fraction rigidly accumulated dose distribution was compared to the original. <h3>Results</h3> The maximum shift for HF-iso2 was 0.4 cm lateral, 0.8 cm longitudinal and 0.9 vertical and for the knee region FF-iso 0.7 cm lateral, 0.4 cm longitudinal and 0.5 cm vertical over all patients/fractions. Over all patients, the differences in PTV volume receiving 80%, 90% and 120% PD between accumulated and original dose distribution were <1%, while a +3% V110% PD maximum difference was found. The maximum mean dose difference for lenses, lungs and kidneys between accumulated and original dose distributions was +1.0 Gy, +0.2 Gy and +0.6 Gy, respectively. <h3>Conclusion</h3> The dose distribution of the described VMAT technique for TBI, is proven to be robust against daily observed isocenter shifts.

First clinical experience with real-time portal imaging-based breath-hold monitoring in tangential breast radiotherapy.

Background and purposeReal-time treatment monitoring with the electronic portal imaging device (EPID) can conceptually provide a more accurate assessment of the quality of deep inspiration breath-hold (DIBH) and patient movement during tangential breast radiotherapy (RT). A system was developed to measure two geometrical parameters, the lung depth (LD) and the irradiated width (named here skin distance, SD), along three user-selected lines in MV EPID images of breast tangents. The purpose of this study was to test the system during tangential breast RT with DIBH.Materials and methodsMeasurements of LDs and SDs were carried out in real time. DIBH was guided with a commercial system using a marker block. Results from 17 patients were assessed. Mean midline LDs, <mLDs>, per tangent were compared to the planned mLDs; differences between the largest and smallest observed <mLDs> (<mSDs>) per tangent were calculated.ResultsFor 56% (162/288) of the tangents tested, <mLDs> were outside the tolerance window. All but one patient had at least one fraction showing this behaviour. The largest difference found between an <mLD> and its planned mLD was −16.9 mm. The accuracy of patient positioning and the quality of marker-block-based DIBH guidance contributed to the differences. Fractions with patient position verification using a single EPID image taken before treatment showed a lower rate (34%), suggesting reassessment of setup procedures.ConclusionsReal-time treatment monitoring of the internal anatomy during DIBH delivery of tangential breast RT is feasible and useful. The new system requires no additional radiation for the patient.

Assessing of a Radiation Therapy Sessionʼs Duration at the Stage of Pre-Radiation Preparation

The treatment planning process includes a review of the radiation treatment plan which leads to a decision on the patientʼs treatment technique. The scope of this study was to create a mathematical model for calculating of a radiation therapy session duration during the pre-radiation planning stage.For dosimetric planning of radiation treatment the authors provided a formula and an algorithm for determining of a patientʼs irradiation session duration. Radiation therapy session parameters such as radiation technique, number of monitor units, characteristics of radiotherapy equipment, number of radiation fields, radiation field parameters (angles of rotation of the radiotherapy coach, collimator, gantry), presence / absence of dose-modulating devices, dose rate, and duration of patient position verification procedures have all been taken into account during the development of software. The developed application explains how to define typical timing characteristics for various items as well as how to select a template from a built-in drop-down menu. If the dosimetric plan does not match for one of the templates, the program provides a space for defining of all parameters manually.The anticipated deviations of the true indicators from the expected indicators of the duration of the radiation therapy session were assessed. A total of 300 cases have been completely measured, with 100 cases studied for each irradiation technique (IMRT, VMAT, 3D). The maximum detection confidence value for the 3DCRT irradiation technique is 2.3 %, while the deviation for the IMRT and VMAT irradiation techniques is less than 1 %. The magnitude and degree of the deviation of the measured value from the expected one for a variety of characteristics and features have been revealed to depend on the actions of the personnel.The program developed allows medical physicists to analyze the timing parameters of the specified dosimetric planning methodologies directly on the treatment planning workstation. Evaluation of the duration of a radiation therapy session during the treatment planning stage, selection of various radiation treatment modalities, and consideration of the characteristics of the radiation session in each clinical case are available for analysis and further justified action.

Interprofessional Image Verification Workshop for Physician and Physics Residents: A Multi-Institutional Experience

Verification of patient position through pretreatment setup imaging is crucial in modern radiation therapy. As treatment complexity increases and technology evolves, physicist-physician collaboration becomes imperative for safe and successful radiation delivery. Despite the importance of both, residency programs lack formal interprofessional education (IPE) activities or structured training for image verification. Here we show the impact of an interprofessional image verification workshop for residents in a multi-institutional setting. The workshop included a lecture by the attending physicist and physician, and hands-on image registration practice by learners (medical physics residents, MP; and radiation oncology residents, RO). All participants filled out pre- and postactivity surveys and rated their comfort from 1 to 10 in (A) selecting what type of imaging to order for a given case and (B) independently assessing the setup quality based on imaging. A paired 1-tailed t test (α=0.05) was used to evaluate significance; Spearman rank correlation coefficient was used to assess correlation of ratings and RO postgraduate year (PGY). Surveys had free-response questions about IPE and image verification activities in residency. A total of 71 residents from 7 institutions participated between 2018 and 2020. Pre- and postsurveys were completed by 50 residents (38RO, 12MP) and showed an increase in (A) from 5.5 ± 2.2 to 7.1 ± 1.6 (P < .001) and in (B) from 5.1 ± 2.3 to 6.8 ± 1.5 (P < .001), with significant increases per subgroup (AΔ, RO=1.8 ± 1.7, P < .001; BΔ, RO=1.9 ± 1.8, P <. 001; AΔ, MP=1.1 ± 1.4, P=.012; BΔ, MP=1.2 ± 1.6, P=.016). RO confidence scores moderately correlated with PGY. Survey responses indicated that image verification training is mostly unstructured, with extent of exposure varying by program and attending; most with little-to-no training. Time constraints were identified as the main barrier. IPE was noted as a useful way to incorporate different perspectives into the process. Formal image verification training increases resident comfort with setup imaging review and provides opportunities for interprofessional collaboration in radiation oncology residency programs.

Carbon ion radiotherapy using fiducial markers for prostate cancer in Osaka HIMAK: Treatment planning.

PurposeCarbon ion radiotherapy for prostate cancer was performed using two fine needle Gold Anchor (GA) markers for patient position verification in Osaka Heavy Ion Medical Accelerator in Kansai (Osaka HIMAK). The present study examined treatment plans for prostate cases using beam‐specific planning target volume (bsPTV) based on the effect of the markers on dose distribution and analysis of target movements.Materials and MethodsGafchromic EBT3 film was used to measure dose perturbations caused by markers. First, the relationships between the irradiated film density and absolute dose with different linear energy transfer distributions within a spread‐out Bragg peak (SOBP) were confirmed. Then, to derive the effect of markers, two types of markers, including GA, were placed at the proximal, center, and distal depths within the same SOBP, and dose distributions behind the markers were measured using the films. The amount of internal motion of prostate was derived from irradiation results and analyzed to determine the margins of the bsPTV.ResultsThe linearity of the film densities against absolute doses was constant within the SOBP and the amount of dose perturbations caused by the markers was quantitatively estimated from the film densities. The dose perturbation close behind the markers was smallest (<10% among depths within the SOBP regardless of types of markers) and increased with depth. The effect of two types of GAs on dose distributions was small and could be ignored in the treatment planning. Based on the analysis results of internal motions of prostate, required margins of the bsPTV were found to be 8, 7, and 7 mm in left–right (LR), anterior–posterior (AP), and superior–inferior (SI) directions, respectively.ConclusionWe evaluated the dose reductions caused by markers and determined the margins of the bsPTV, which was applied to the treatment using fiducial markers, using the analysis results of prostate movements.

Patient position verification in magnetic-resonance imaging only radiotherapy of anal and rectal cancers

Magnetic resonance (MR)-only treatment pathways require either the MR-simulation or synthetic-computed tomography (sCT) as an alternative reference image for cone beam computed tomography (CBCT) patient position verification. This study assessed whether using T2 MR or sCT as CBCT reference images introduces systematic registration errors as compared to CT for anal and rectal cancers. A total of 32 patients (18 rectum,14 anus) received pre-treatment CT- and T2 MR- simulation. Routine treatment CBCTs were acquired. sCTs were generated using a validated research model. The local clinical registration protocol, using a grey-scale registration algorithm, was performed for 216 CBCTs using CT, MR and sCT as the reference image. Linear mixed effects modelling identified systematic differences between modalities. Systematic translation and rotation differences to CT for MR were -0.3 to+0.3mm and -0.1 to 0.4° for anal cancers and -0.4 to 0.0mm and 0.0 to 0.1° for rectal cancers, and for sCT were -0.4 to+0.8mm, -0.1 to 0.2° for anal cancers and -0.6 to+0.2mm, -0.1 to+0.1° for rectal cancers. T2 MR or sCT can successfully be used as reference images for anal and rectal cancer CBCT position verification with systematic differences to CT <±1 mm and <±0.5°. Clinical enabling of alternative modalities as reference images by vendors is required to reduce challenges associated with their use.

Helium radiography with a digital tracking calorimeter—a Monte Carlo study for secondary track rejection

Radiation therapy using protons and heavier ions is a fast-growing therapeutic option for cancer patients. A clinical system for particle imaging in particle therapy would enable online patient position verification, estimation of the dose deposition through range monitoring and a reduction of uncertainties in the calculation of the relative stopping power of the patient.Several prototype imaging modalities offer radiography and computed tomography using protons and heavy ions. A Digital Tracking Calorimeter (DTC), currently under development, has been proposed as one such detector. In the DTC 43 longitudinal layers of laterally stacked ALPIDE CMOS monolithic active pixel sensor chips are able to reconstruct a large number of simultaneously recorded proton tracks.In this study, we explored the capability of the DTC for helium imaging which offers favorable spatial resolution over proton imaging. Helium ions exhibit a larger cross section for inelastic nuclear interactions, increasing the number of produced secondaries in the imaged object and in the detector itself. To that end, a filtering process able to remove a large fraction of the secondaries was identified, and the track reconstruction process was adapted for helium ions.By filtering on the energy loss along the tracks, on the incoming angle and on the particle ranges, 97.5% of the secondaries were removed. After passing through 16 cm water, 50.0% of the primary helium ions survived; after the proposed filtering 42.4% of the primaries remained; finally after subsequent image reconstruction 31% of the primaries remained. Helium track reconstruction leads to more track matching errors compared to protons due to the increased available focus strength of the helium beam. In a head phantom radiograph, the Water Equivalent Path Length error envelope was 1.0 mm for helium and 1.1 mm for protons. This accuracy is expected to be sufficient for helium imaging for pre-treatment verification purposes.

Does Active Coaching Reduce Overall Treatment Duration For Mask-Based, Frameless Gamma Knife Stereotactic Radiosurgery?

Frameless stereotactic radiosurgery (SRS) has become a preferred supplement to frame-based Gamma Knife SRS due to its non-invasive nature and allowance for fractionation. To account for intra-fraction motion, radiation is automatically gated whenever a real-time tracking system detects patient displacement larger than a user-specified threshold. Treatment delivery pauses and a cone-beam CT is acquired to verify patient position if the excess displacement persists. This gating technique, although effective with high accuracy, is sensitive to patient’s involuntary motions. Overall treatment duration is increased with each pause, and this can result in a prolonged treatment duration. The purpose of this study is to investigate whether active coaching during frameless SRS can reduce overall treatment duration. Patients treated at a single institution with frameless SRS on a Gamma Knife Icon from 2017 to 2020 were retrospectively identified. Beginning in January 2019, all patients treated with frameless SRS were actively coached: Prior to treatment, each patient was instructed on how to adjust his/her head position following prompts from staff. During treatment, the patient motion was closely monitored. Once a large displacement was observed, the patient was instructed to gently tuck/untuck or tilt his/her chin to reduce the displacement. Patient characteristics and treatment plans were compared between the cohorts of patients treated with and without active coaching. Linear regressions between the planned and overall treatment duration were performed on either cohort. ANOVA and Wilcoxon tests were used with a p-value less than 0.05 considered as significant. A total of 45 patients and 107 frameless SRS treatment sessions were identified, 27 (60.0%) of which underwent 51 (47.7%) frameless SRS treatment sessions with active coaching. There was no significant difference in patient characteristics or treatment plans between two cohorts (p<0.001). Patients treated with active coaching underwent significantly fewer CBCTs during sessions (Median: 1 vs. 2; p<0.01). The median planned and overall treatment durations were 27.1 min (range: 12.2-110.9) and 41.3 min (range: 13.7-202.2) for the non-coached cohort, and 30.9 min (range: 10.6-89.5) and 41.6 min (range: 10.6-144.4) for the coached cohort. Linear regressions analysis revealed that the overall treatment duration was 1.29 times longer than the planned beam-on duration with active coaching (R2 = 0.95) and 1.60 times without (R2 = 0.75). The difference between the slopes was statistically significant (p<0.001), which indicated a significant reduction in the overall treatment duration with active coaching. Our results suggested that active coaching was associated with significant reductions of overall treatment duration. This simple intervention can be clinically implemented to improve clinical efficiency and possibly patient comfort during frameless Gamma Knife SRS.

Flat-panel imager energy-dependent proton radiography for a proton pencil-beam scanning system

In proton-based radiotherapy, proton radiography could allow for direct measurement of the water-equivalent path length (WEPL) in tissue, which can then be used to determine relative stopping power (RSP). Additionally, proton radiographs allow for imaging in the beam’s-eye-view. In this work, a proton radiography technique using a flat-panel imager and a pencil-beam scanning (PBS) system is demonstrated in phantom. Proton PBS plans were delivered on a Varian ProBeam system to a flat-panel imager. Each proton plan consisted of energy layers separated by 4.8 MeV, and a field size of 25 cm × 25 cm. All measured data is binned into a layer-by-layer delivery in post processing. To build a calibration curve correlating detector response to WEPL, the plans were delivered to slabs of solid water of increasing thickness. Pixel-by-pixel detector response in the time/energy domain is then fit as a function of WEPL. Tissue equivalent phantoms are imaged for evaluation of WEPL accuracy. A spatial resolution phantom and a head phantom are also imaged. For all experiments, the detector was run with an effective pixel size of 0.4 mm × 0.4 mm. The proposed method reconstructed RSP with mean errors of 2.65%, −0.14%, and 0.61% for lung, soft tissue, and bone, respectively. In a 40 mm thick spatial resolution phantom, a 2 mm deep pinhole with 1 mm diameter can be seen. The accuracy and spatial resolution of the method show that it could be implemented for patient position verification. Further development could lead to patient-specific verification of RSP to be used for treatment guidance.

High quality proton portal imaging using deep learning for proton radiation therapy: a phantom study

Purpose; For shoot-through proton treatments, like FLASH radiotherapy, there will be protons exiting the patient which can be used for proton portal imaging (PPI), revealing valuable information for the validation of tumor location in the beam’s-eye-view at native gantry angles. However, PPI has poor inherent contrast and spatial resolution. To deal with this issue, we propose a deep-learning-based method to use kV digitally reconstructed radiographs (DRR) to improve PPI image quality. Method; We used a residual generative adversarial network (GAN) framework to learn the nonlinear mapping between PPIs and DRRs. Residual blocks were used to force the model to focus on the structural differences between DRR and PPI. To assess the accuracy of our method, we used 149 images for training and 30 images for testing. PPIs were acquired using a double-scattered proton beam. The DRRs acquired from CT acted as learning targets in the training process and were used to evaluate results from the proposed method using a six-fold cross-validation scheme. Results; Qualitatively, the corrected PPIs showed enhanced spatial resolution and captured fine details present in the DRRs that are missed in the PPIs. The quantitative results for corrected PPIs show average normalized mean error (NME), normalized mean absolute error (NMAE), peak signal-to-noise ratio (PSNR) and structural similarity (SSIM) index of −0.1%, 0.3%, 39.14 dB, and 0.987, respectively. Conclusion; The results indicate the proposed method can generate high quality corrected PPIs and this work shows the potential to use a deep-learning model to make PPI available in proton radiotherapy. This will allow for beam’s-eye-view (BEV) imaging with the particle used for treatment, leading to a valuable alternative to orthogonal x-rays or cone-beam CT for patient position verification.

Comparison of CBCT based synthetic CT methods suitable for proton dose calculations in adaptive proton therapy

In-room imaging is a prerequisite for adaptive proton therapy. The use of onboard cone-beam computed tomography (CBCT) imaging, which is routinely acquired for patient position verification, can enable daily dose reconstructions and plan adaptation decisions. Image quality deficiencies though, hamper dose calculation accuracy and make corrections of CBCTs a necessity. This study compared three methods to correct CBCTs and create synthetic CTs that are suitable for proton dose calculations. CBCTs, planning CTs and repeated CTs (rCT) from 33 H&N cancer patients were used to compare a deep convolutional neural network (DCNN), deformable image registration (DIR) and an analytical image-based correction method (AIC) for synthetic CT (sCT) generation. Image quality of sCTs was evaluated by comparison with a same-day rCT, using mean absolute error (MAE), mean error (ME), Dice similarity coefficient (DSC), structural non-uniformity (SNU) and signal/contrast-to-noise ratios (SNR/CNR) as metrics. Dosimetric accuracy was investigated in an intracranial setting by performing gamma analysis and calculating range shifts. Neural network-based sCTs resulted in the lowest MAE and ME (37/2 HU) and the highest DSC (0.96). While DIR and AIC generated images with a MAE of 44/77 HU, a ME of −8/1 HU and a DSC of 0.94/0.90. Gamma and range shift analysis showed almost no dosimetric difference between DCNN and DIR based sCTs. The lower image quality of AIC based sCTs affected dosimetric accuracy and resulted in lower pass ratios and higher range shifts. Patient-specific differences highlighted the advantages and disadvantages of each method. For the set of patients, the DCNN created synthetic CTs with the highest image quality. Accurate proton dose calculations were achieved by both DCNN and DIR based sCTs. The AIC method resulted in lower image quality and dose calculation accuracy was reduced compared to the other methods.

A Method for Real-Time Patient Positioning Verification in Radiotherapy Using Multi-Angular Images with Conventional Video Cameras

Background: Accurate patient positioning and the corresponding position verification play a key role in precision radiotherapy. The conventional position verification techniques, such as cone-beam computed tomography (CBCT), used in radiotherapy deliver additional radiation doses to patients; thus some complications may occur in the surrounding normal tissue. Additionally, the present registration and fusion algorithms require a long time to verify and monitor the patient's position in real-time. Method: A new simple method using three conventional video cameras from different directions for observing the changes in the patient's position and taking the multiangular surface images of the patient without delivering additional doses of radiation is proposed in this paper. Real-time patient position verification could be achieved through this Oriented FAST and Rotated BRIEF (ORB) algorithm modified by us. Results: A plastic patient model immobilized with thermoplastic shell on a simulation couch was used to verify the accuracy and feasibility of our method. Testing results showed that the position and angle offset errors identified with our system were less than 1 mm and 1°, respectively. Moreover, the modified ORB algorithm was fast enough for real-time images comparison. Conclusion: This proposed method shows a great potential for application in verifying and monitoring the patient's position in real time during radiotherapy.

A Novel Deep Learning Architecture for Deformable Imaging Registration applied to Image-Guided Radiotherapy

Most clinical image-guided radiotherapy workflows make use of alignment algorithms to map a plan to a daily cone-beam CT (CBCT) onto a patient’s simulation CT (simCT). Current methodologies of rigid and deformable registration have not demonstrated accuracy high enough to enable automated alignment or adaptive recontouring. Here we investigate a novel deep-learning framework for diffeomorphic deformable image registration (DIR) and analyze its performance with regard to adaptive recontouring. Our institutional treatment planning system and CBCT directory were queried for head and neck plans that were delivered to patients between 2016-2018. A self-normalizing, generative convolutional deep network was developed using the PyTorch API and trained on a platform with 8 NVIDIA K80 GPUs. Network input consisted of a concatenated simCT/CBCT pair and an output of a deformable vector field (DVF). This DVF was then applied to the simCT to warp the simCT onto the CBCT. The network was trained in an unsupervised fashion on the combination of three losses: the Kullback-Leibler loss to promote spatially smooth transforms, a novel bottleneck feature-map loss to prioritize complex anatomic features, and a pixelwise intensity difference loss to drive spatially accurate image reconstruction. In order to test the performance of the network, patient-specific contours were warped onto the CBCT using the DVF output by the network. Patients who underwent repeat planning during their radiotherapy were sampled and the 3D-dice coefficient of overlap was calculated between their initial contours and replanned contours and between the warped contours and replanned contours. All initial and replanned contours were generated by a board-certified radiation oncologist. A dataset of 48 patients was compiled, yielding 1728 simCT/CBCT pairs and 64 unique radiotherapy plans and structure sets. 36 patients were used for the training set, representing 1246 simCT/CBCT pairs. Training was performed over 100 epochs. Resulting warped scans showed strong registration by visual review and 3D dice comparison of the external contours. Quantitatively, the model showed a significantly improved 3D dice overlap of the warped contours to the replanned ground-truth contours (see table). The inference time on the trained model was less than 4 seconds. Our implementation of a novel deep-learning architecture shows fast, robust DIR in the setting of IGRT. Our results highlight the applicability of the recent advancements in deep-learning to essential components of radiation treatment: patient position verification and creation of treatment volumes. Further validation is required prior to implementing such a workflow in the radiation clinic for rapid IGRT.Abstract 1180; Table 1Initial-to-Replanned Contour 3D-Dice OverlapWarped-to-Replanned Contour 3D-Dice OverlappGTV0.781 ± 0.0620.873 ± 0.0450.041CTV0.822 ± 0.0510.901 ± 0.0330.032External0.907 ± 0.0690.948 ± 0.0510.028 Open table in a new tab