Planning CT Research Articles

Accuracy of Ultrahigh-Resolution Photon-counting CT for Detecting Coronary Artery Disease in a High-Risk Population.

Background Recently introduced photon-counting CT may improve noninvasive assessment of patients with high risk for coronary artery disease (CAD). Purpose To determine the diagnostic accuracy of ultrahigh-resolution (UHR) coronary CT angiography (CCTA) in the detection of CAD compared with the reference standard of invasive coronary angiography (ICA). Materials and Methods In this prospective study, participants with severe aortic valve stenosis and clinically indicated CT for transcatheter aortic valve replacement planning were consecutively enrolled from August 2022 to February 2023. All participants were examined with a dual-source photon-counting CT scanner using a retrospective electrocardiography-gated contrast-enhanced UHR scanning protocol (tube voltage, 120 or 140 kV; collimation, 120 × 0.2 mm; 100 mL of iopromid; no spectral information). Subjects underwent ICA as part of their clinical routine. A consensus assessment of image quality (five-point Likert scale: 1 = excellent [absence of artifacts], 5 = nondiagnostic [severe artifacts]) and a blinded independent reading for the presence of CAD (stenosis ≥50%) were performed. UHR CCTA was compared with ICA using area under the receiver operating characteristic curve (AUC). Results Among 68 participants (mean age, 81 years ± 7 [SD]; 32 male, 36 female), the prevalence of CAD and prior stent placement was 35% and 22%, respectively. The overall image quality was excellent (median score, 1.5 [IQR, 1.3-2.0]). The AUC of UHR CCTA in the detection of CAD was 0.93 per participant (95% CI: 0.86, 0.99), 0.94 per vessel (95% CI: 0.91, 0.98), and 0.92 per segment (95% CI: 0.87, 0.97). Sensitivity, specificity, and accuracy, respectively, were 96%, 84%, and 88% per participant (n = 68); 89%, 91%, and 91% per vessel (n = 204); and 77%, 95%, and 95% per segment (n = 965). Conclusion UHR photon-counting CCTA provided high diagnostic accuracy in the detection of CAD in a high-risk population, including subjects with severe coronary calcification or prior stent placement. Published under a CC BY 4.0 license. Supplemental material is available for this article. See also the editorial by Williams and Newby in this issue.

Does coronary artery calcium score have an impact on overall survival for locally advanced non-small cell lung cancer treated with definitive radiotherapy

Background and purposeCoronary artery calcium score (CACs) is an excellent marker for survival in non-cancer patients, but its role in locally advanced non-small cell lung cancer (LA-NSCLC) patients remains uncertain. In this study, we hypothesize that CACs is a prognostic marker for survival in a competing risk analysis in LA-NSCLC patients treated with definitive radiotherapy. Materials and methodsWe included 644 patients with LA-NSCLC treated in 2014-2015 in Denmark. Baseline patient characteristics were derived from the Danish Lung Cancer Registry. Radiotherapy planning CT scans were used for manual CACs measurements, and the patients were divided into four groups, CACs 0, 1-99, 100-399, and ≥400. A multivariable Cox model utilizing bootstrapping for cross-validation modeled overall survival (OS). ResultsThe median follow-up time was seven years, and the median OS was 26 months (95% CI 24-29). Within each CAC group 0, 1-99, 100-399, and ≥400 were 172, 182, 143, and 147 patients, respectively. In the univariable analysis, the survival decreased with increasing CACs. However, after adjustment for age, PS, radiotherapy dose, and logarithmic GTV, CACs did not have a statistically significant impact on OS with hazard ratios of 1.04 (95% CI 0.85-1.28), 1.11 (95%CI 0.89-1.43), and 1.16 (95%CI 0.92-1.47) for CACs 1-99, CACs 100-399 and ≥400, respectively. Elevated CACs was observed in 73 % of the patients suggesting a high risk of cardiac comorbidity before radiotherapy. ConclusionCACs did not add prognostic information to our population's classical risk factors, such as tumor volume, performance status, and age; the lung cancer has the highest priority despite the risk of baseline cardiac comorbidity.

Prediction of pathologic complete response after single-dose MR-guided partial breast irradiation in low-risk breast cancer patients: the ABLATIVE-2 trial—a study protocol

BackgroundPartial breast irradiation (PBI) is standard of care in low-risk breast cancer patients after breast-conserving surgery (BCS). Pre-operative PBI can result in tumor downstaging and more precise target definition possibly resulting in less treatment-related toxicity. This study aims to assess the pathologic complete response (pCR) rate one year after MR-guided single-dose pre-operative PBI in low-risk breast cancer patients.MethodsThe ABLATIVE-2 trial is a multicenter prospective single-arm trial using single-dose ablative PBI in low-risk breast cancer patients. Patients ≥ 50 years with non-lobular invasive breast cancer ≤ 2 cm, grade 1 or 2, estrogen receptor-positive, HER2-negative, and tumor-negative sentinel node procedure are eligible. A total of 100 patients will be enrolled. PBI treatment planning will be performed using a radiotherapy planning CT and -MRI in treatment position. The treatment delivery will take place on a conventional or MR-guided linear accelerator. The prescribed radiotherapy dose is a single dose of 20 Gy to the tumor, and 15 Gy to the 2 cm of breast tissue surrounding the tumor. Follow-up MRIs, scheduled at baseline, 2 weeks, 3, 6, 9, and 12 months after PBI, are combined with liquid biopsies to identify biomarkers for pCR prediction. BCS will be performed 12 months after radiotherapy or after 6 months, if MRI does not show a radiologic complete response. The primary endpoint is the pCR rate after PBI. Secondary endpoints are radiologic response, toxicity, quality of life, cosmetic outcome, patient distress, oncological outcomes, and the evaluation of biomarkers in liquid biopsies and tumor tissue. Patients will be followed up to 10 years after radiation therapy.DiscussionThis trial will investigate the pathological tumor response after pre-operative single-dose PBI after 12 months in patients with low-risk breast cancer. In comparison with previous trial outcomes, a longer interval between PBI and BCS of 12 months is expected to increase the pCR rate of 42% after 6–8 months. In addition, response monitoring using MRI and biomarkers will help to predict pCR. Accurate pCR prediction will allow omission of surgery in future patients.Trial registrationThe trial was registered prospectively on April 28th 2022 at clinicaltrials.gov (NCT05350722).

Clinical experience in the use of 3D printing as a rapid replacement of traditional radiation therapy immobilization materials.

Patient positioning and immobilization devices are commonly employed in radiation therapy. Unfortunately, cases can arise where the devices need to be reconstructed or improved. This work describes clinical processes to use a planning CT, to design and 3D print immobilization devices for reproducible patient positioning within a clinically feasible time frame when traditional methods can no longer be used or are insufficient. Three clinical cases required rapid 3D printing of an immobilization device mid-treatment due to the following: (1) a lost headrest cushion, (2) needed improvement in lumbar spine positioning, and (3) a partially deflated vacuum immobilization mattress. In the three cases, the 3D printed immobilization devices were clinically implemented successfully; two of the devices were fully designed and printed in 1 day. The 3D printed immobilization devices achieved a positioning accuracy sufficient to avoid the necessity to repeat the simulation and planning process. If traditional immobilization devices fail or are misplaced, it is feasible to have a 3D printed replacement within the time span of 1 day. The design and fabrication methods, as well as the experiences gained, are described in detail to assist clinicians to implement 3D printing for similar situations.

Cone Beam Computed Tomography-Based Evaluation of the Accuracy of Implant Surgery with Conventional (Free Hand) Implant Placement vs Computer Fabricated 3D Guide Implant Placement.

Dental implants have been used in a variety of conventional technique-based forms for many years which had its own drawbacks. With the advent of cone beam CT, proper surgical and prosthetic planning is possible now a days. To achieve ideal implant placement, good prosthetic fabrication and overall successful prognosis computer fabricated guide aided surgery have been developed. The aim of this study was to compare and evaluate the accuracy of implant placement in partially edentulous patients with conventional free hand technique and computer fabricated guide of implant placement by comparing pre- and post-CBCT data. The present split mouth study design was conducted with forty sample size on twenty randomly selected patients who were treated with bilateral partially edentulous sites requiring dental implants. Patients were treated with both conventional (free hand) technique and computer fabricated 3D guide aided technique of implant placement. Comparison of accuracy of implant placement was done by comparing the pre- and postoperative CBCT data in terms of mean coronal deviation, mean apical deviation and mean angular deviation. The results showed that there is no statistically significant difference between mean coronal deviation, mean apical deviation and mean angular deviation of planned and placed implants in both conventional technique (free hand technique) and computer fabricated 3D guide aided implant placement technique. Hence, this study concluded that conventional technique of implant placement is equally efficient in comparison with computer fabricated guide aided surgery in terms of accuracy of implant placement.

Virtual Surgical Reduction in Atrophic Edentulous Mandible Fractures: A Novel Approach Based on “in House” Digital Work-Flow

Atrophic edentulous mandible fractures are a challenge for maxillo-facial surgeons because of low vascularization, low bone regeneration, and lack of occlusion. Whereas occlusion is the main guide in the reduction of mandibular fractures, the aim of our study is to show the advantages of using virtual surgical planning (VSP) in surgery when the occlusal guide is absent. This work is a prospective study that shows the in-house digital workflow for the management of these fractures in the Maxillo-Facial Surgery Unit of Federico II University Hospital of Naples. Four patients who satisfied the criteria were included in the study. For each patient, the same defined CAD/CAM-based was applied. The workflow followed four steps: (1) bone segmentation and virtual reduction of fracture fragments; (2) three-dimensional printing of virtually reduced mandible and modelling of 2.4 reconstruction plate on printed resin model; (3) surgery aided by the pre-formed plate; (4) digital and clinical outcomes analysis. In the last step, a distance colour map was conducted to compare the virtual planning and postoperative CT outcome. In all cases, the discrepancies values between the two images were lower than 1.5 mm, and good clinical outcomes in terms of facial symmetry, absence of sensory disturbance, and possibility of prosthetic rehabilitation were obtained. In conclusion, the VSP, with our in-house workflow brings benefits in the management of atrophic edentulous mandible fractures in terms of the high accuracy of bone repositioning.

Cochlear sparing in LINAC-based radiosurgery for vestibular schwannoma: a dosimetric comparison of dynamic conformal arc, IMRT and VMAT treatment plans

BackgroundStereotactic radiosurgery (SRS) is the preferred treatment for vestibular schwannoma (VS) in patients with preserved hearing and tumour diameter < 3 cm. Emerging evidence suggests restricting cochlear dose could preserve hearing. This retrospective replanning study aims to compare dynamic conformal arc therapy (DCAT), intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) plans for superiority of cochlear dose sparing without compromising tumour coverage.MethodsEligibility criteria included sporadic VS, serviceable hearing and availability of CT and MRI for planning. The original gross tumour volume and brainstem OAR volume were retained; the cochlea was newly contoured on the planning CT scan (bone window). Each case was replanned using the three above techniques, prescribing 12 Gy to the 80% isodose line. No dose constraint was applied to the cochlea.ResultsEighteen patients were replanned. Mean tumour volume was 2.25 cc. Tumour coverage and tumour mean dose (DCAT: 14.2, IMRT: 14.6, VMAT: 14.5 Gy) were comparable. Paddick and RTOG conformity indices were better for DCAT (0.66 and 1.6) and VMAT (0.69 and 1.5) compared to IMRT (0.56 and 1.9). DCAT had superior gradient index (3.0) compared to VMAT (3.4) and IMRT (3.4). VMAT delivered the lowest mean brainstem maximum dose (8.3 Gy) and decreased the mean cochlear dose (3.4 Gy) by 2.3 and 2.1 Gy, and the mean cochlear maximum dose (3.6 Gy) by 2.4 and 2.5 Gy relative to DCAT and IMRT, respectively.ConclusionLINAC-based SRS treatment using VMAT can achieve better cochlear dose sparing than DCAT or IMRT while maintaining tumour coverage.

New Imaging Techniques.

The chapter discusses the advancement of new imaging techniques, the role of imaging in CCA diagnosis, anatomical and morphological classification, ultrasound screening of CCA, ultrasound findings of MF-CCA, PI-CCA, ID-CCA, the use of CT in CCA diagnosis, staging and treatment planning, CT volumetry and estimation of future liver remnant, post-treatment follow-up and surveillance, MRI imaging, Positron Emission Tomography (PET)/CT, limitations to contrast studies and resolution, internal receivers for CCA imaging, and in vitro imaging of CCA.

An Investigation of Dosimetric Consequences of the Anatomic Changes at First Fraction in VMAT of Prostate Cancer Cases using Deformable Planning CT and KVCBCT Image Registration

An Investigation of Dosimetric Consequences of the Anatomic Changes at First Fraction in VMAT of Prostate Cancer Cases using Deformable Planning CT and KVCBCT Image Registration

A probability model for anatomical robust optimisation in head and neck cancer proton therapy

Objective. Develop an anatomical model based on the statistics of the population data and evaluate the model for anatomical robust optimisation in head and neck cancer proton therapy. Approach. Deformable image registration was used to build the probability model (PM) that captured the major deformation from patient population data and quantified the probability of each deformation. A cohort of 20 nasopharynx patients was included in this retrospective study. Each patient had a planning CT and 6 weekly CTs during radiotherapy. We applied the model to 5 test patients. Each test patient used the remaining 19 training patients to build the PM and estimate the likelihood of a certain anatomical deformation to happen. For each test patient, a spot scanning proton plan was created. The PM was evaluated using proton spot location deviation and dose distribution. Main results. Using the proton spot range, the PM can simulate small non-rigid variations in the first treatment week within 0.21 ± 0.13 mm. For overall anatomical uncertainty prediction, the PM can reduce anatomical uncertainty from 4.47 ± 1.23 mm (no model) to 1.49 ± 1.08 mm at week 6. The 95% confidence interval (CI) of dose metric variations caused by actual anatomical deformations in the first week is −0.59% ∼ −0.31% for low-risk CT D 95, and 0.84–3.04 Gy for parotid D mean. On the other hand, the 95% CI of dose metric variations simulated by the PM at the first week is −0.52 ∼ −0.34% for low-risk CTV D 95, and 0.58 ∼ 2.22 Gy for parotid D mean. Significance. The PM improves the estimation accuracy of anatomical uncertainty compared to the previous models and does not depend on the acquisition of the weekly CTs during the treatment. We also provided a solution to quantify the probability of an anatomical deformation. The potential of the model for anatomical robust optimisation is discussed.

Introduce a rotational robust optimization framework for spot-scanning proton arc (SPArc) therapy

Objective. Proton dosimetric uncertainties resulting from the patient’s daily setup errors in rotational directions exist even with advanced image-guided radiotherapy techniques. Thus, we developed a new rotational robust optimization SPArc algorithm (SPArcrot) to mitigate the dosimetric impact of the rotational setup error in Raystation ver. 6.02 (RaySearch Laboratory AB, Stockholm, Sweden). Approach. The initial planning CT was rotated ±5° simulating the worst-case setup error in the roll direction. The SPArcrot uses a multi-CT robust optimization framework by taking into account of such rotational setup errors. Five cases representing different disease sites were evaluated. Both SPArcoriginal and SPArcrot plans were generated using the same translational robust optimized parameters. To quantitatively investigate the mitigation effect from the rotational setup errors, all plans were recalculated using a series of pseudo-CT with rotational setup error (±1°/±2°/±3°/±5°). Dosimetric metrics such as D98% of CTV, and 3D gamma analysis were used to assess the dose distribution changes in the target and OARs. Main results. The magnitudes of dosimetric changes in the targets due to rotational setup error were significantly reduced by the SPArcrot compared to SPArc in all cases. The uncertainties of the max dose to the OARs, such as brainstem, spinal cord and esophagus were significantly reduced using SPArcrot. The uncertainties of the mean dose to the OARs such as liver and oral cavity, parotid were comparable between the two planning techniques. The gamma passing rate (3%/3 mm) was significantly improved for CTV of all tumor sites through SPArcrot. Significance. Rotational setup error is one of the major issues which could lead to significant dose perturbations. SPArcrot planning approach can consider such rotational error from patient setup or gantry rotation error by effectively mitigating the dose uncertainties to the target and in the adjunct series OARs.

MRI-based adaptive radiotherapy has the potential to reduce dysphagia in patients with head and neck cancer

PurposeThis study explored the potential of MRI-based adaptive radiotherapy to spare dysphagia and aspiration related structures (DARS) in a heterogeneous cohort of patients (n=23) who received radiotherapy (RT) for different sites of head and neck cancer. MethodsPharyngeal constrictor muscles (PCM), cricopharyngeal muscle (CPM), proximal part of the esophagus (PE), supraglottic larynx (SGL), and transglottic larynx (TGL) were contoured in weekly MRI during the treatment and considered as DARS. To compare dysphagia-optimized radiotherapy (DORT) and MRI-based dysphagiaoptimized adaptive radiotherapy (DOART), two data sets were created for each patient using synthetic CTs created by deforming the initial planning CT. Dose-volume histograms (DVHs) of accumulated doses were generated and dosimetric parameters V50Gy – V70Gy and mean doses were measured for DARS and for both DORT and DOART. ResultsThe significant improvements in DARS-sparing were observed in regions of the highest doses (95% confidence interval, p<0.05). For example, V70Gy in PCM decreased from 7.8±5.5% to 2.6±4.4% – this was a reduction by 67% (p<0.001). Similarly, the relative decreases of V65 Gy in PCM, V60 Gy in SGL, V60 Gy in TGL, and V55 Gy in CPM were 37%, 32%, 46%, and 27%, respectively. ConclusionsIt was shown that MRI-based DOART has the potential to significantly reduce the radiation burden of DARS as a response to the decreasing volume of primary tumor or lymphatic nodes. Findings of this study provide novel evidence to suggest that the concept of MRI-based DOART could contribute to spare DARS.

Repeatability of MRI for radiotherapy planning for pelvic, brain, and head and neck malignancies

Objectives: The objective of this study was to assess the repeatability of MRI for the purpose of radiotherapy treatment planning by considering the difference in registering MRI to MRI compared to registering CT and MRI.Methods: Fifty patients undergoing radiotherapy planning for gynaecological, prostate, rectal, head and neck and CNS malignancies had a planning CT followed by two T2-weighted MRIs. Anatomical landmarks were contoured on each dataset and the images were rigidly registered. Centre of Mass (COM), Dice Similarity Coefficient (DSC), and Mean Distance to Agreement (MDA) were calculated to assess structure volume and position comparing CT-MRI and MRI-MRI.Results: DSC and MDA demonstrated more consistency in delineated volumes for MRI-MRI than for the CT-MRI comparison. The median DSC values were ≥0.8 for 15 of 46 contoured structures for the CT-MRI comparison and 21 of 23 structures for the MRI-MRI comparison. MDA values were ≤1 mm for 11 of 46 structures for the CT-MRI comparison and 18 of 23 structures for the MRI-MRI comparisons. COM were also more consistent between MRI-MRI than between CT-MRI.Conclusion: There was less variability of anatomical structures between repeated MRIs than registered CT and MRI datasets, demonstrating consistency of MRI for volume delineation in radiotherapy planning.

Improved accuracy of auto-segmentation of organs at risk in radiotherapy planning for nasopharyngeal carcinoma based on fully convolutional neural network deep learning

ObjectiveWe examined a modified encoder-decoder architecture-based fully convolutional neural network, OrganNet, for simultaneous auto-segmentation of 24 organs at risk (OARs) in the head and neck, followed by validation tests and evaluation of clinical application. Materials and methodsComputed tomography (CT) images from 310 radiotherapy plans were used as the experimental data set, of which 260 and 50 were used as the training and test sets, respectively. An improved U-Net architecture was established by introducing a batch normalization layer, residual squeeze-and-excitation layer, and unique organ-specific loss function for deep learning training. The performance of the trained network model was evaluated by comparing the manual-delineation and the STAPLE contour of 10 physicians from different centers. ResultsOur model achieved good segmentation in all 24 OARs in nasopharyngeal cancer radiotherapy plan CT images, with an average Dice similarity coefficient of 83.75%. Specifically, the mean Dice coefficients in large-volume organs (brainstem, spinal cord, left/right parotid glands, left/right temporal lobes, and left/right mandibles) were 84.97% − 95.00%, and in small-volume organs (pituitary, lens, optic nerve, and optic chiasma) were 55.46% − 91.56%. respectively. Using the STAPLE contours as standard contour, the OrganNet achieved comparable or better DICE in organ segmentation then that of the manual-delineation as well. ConclusionThe established OrganNet enables simultaneous automatic segmentation of multiple targets on CT images of the head and neck radiotherapy plans, effectively improves the accuracy of U-Net based segmentation for OARs, especially for small-volume organs.

Incorporating uncertainty bounds in daily deformable dose accumulation for adaptive radiation therapy of head-and-neck cancer.

The widespread use of deformable dose accumulation (DDA) in adaptive radiotherapy (ART) has been limited due to the lack of clinically compatible methods to consider its related uncertainties. We estimate dose reconstruction uncertainties in daily DDA during CT-guided radiotherapy of head-and-neck cancer (HNC). We project confidence intervals of cumulative dose-volume parameters to the parotids and determine threshold values to guide clinical decision-making in ART. Doses from daily images (megavoltage CTs [MVCTs]) of 20 HNC patients treated with tomotherapy were reconstructed and accumulated in the planning CT (PCT) utilizing a commercial DDA algorithm (PreciseART, Accuray, Inc.). For each mapped fraction, we warped the planning contours to the MVCT. Dose-volume histograms (DVHs) calculated in the MVCT (with warped contour and native dose) and the PCT (with native contour and mapped dose) were compared; the observed inconsistencies were associated with dose reconstruction errors. We derived uncertainty bounds for the transferred dose to voxels within the structure of interest in the PCT. The confidence intervals of cumulative dose-volume parameters were mid-treatment projected and evaluated as predictors of the end of treatment cumulative metrics. The need for plan adaptation was tested by comparing the projected uncertainty bounds with the treatment constraint points. Among all cases, the uncertainty in mean values of daily dose distributions mapped to the reference parotid's contours averaged between 2.8% and 3.8% of typical single fraction planning values and less than 1% for the planning target volume (PTV) D95%. These daily inconsistencies were higher in the ipsilateral compared to the contralateral parotid and increased toward the end of treatment. The magnitude of the uncertainty bounds for the cumulative treatment mean dose, D50%, and V20Gy to the parotids, and PTV D95% were on average 3.5%, 6.6%, 4.6%, and 0.4% of the planned or prescribed values, with confidence intervals of 97.1%-107.0%, 98.2%-110.4%, 95.6%-111.1%, and 98.2%-100.2% respectively. The uncertainty intervals projected at mid-treatment intersected with the end of treatment bounds in 82% of the parotid's metrics; half of them presented an overlapping percentage greater than 60%. In five patients, the cumulative mean doses were projected at mid-treatment to exceed the total treatment constraint point by at least 3%; this threshold was exceeded at the end of treatment in the five cases. Underdosing was projected in only one case; the cumulative PTV D95% at the end of treatment was below the clinical threshold. Uncertainty bounds were incorporated into the results of a commercial DDA tool. The cohort's statistics showed that the parotids' cumulative DVH metrics frequently exceeded the planning values if confidence intervals were included. Most of the uncertainty bounds of the PTV metrics were kept within the clinical thresholds. We verified that mid-treatment violation projections led to exceeding the constraint point at the end of the treatment. Based on a 3% threshold, approximately one fourth of the patients are expected to be replanned at mid-treatment for parotids sparing during HNC radiotherapy.

Clinical application of a template-guided automated planning routine.

Determine the dosimetric quality and the planning time reduction when utilizing a template-based automated planning application. A software application integrated through the treatment planning system application programing interface, QuickPlan, was developed to facilitate automated planning using configurable templates for contouring, knowledge-based planning structure matching, field design, and algorithm settings. Validations are performed at various levels of the planning procedure and assist in the evaluation of readiness of the CT image, structure set, and plan layout for automated planning. QuickPlan is evaluated dosimetrically against 22 hippocampal-avoidance whole brain radiotherapy patients. The required times to treatment plan generation are compared for the validations set as well as 10 prospective patients whose plans have been automated by QuickPlan. The generations of 22 automated treatment plans are compared against a manual replanning using an identical process, resulting in dosimetric differences of minor clinical significance. The target dose to 2% volume and homogeneity index result in significantly decreased values for automated plans, whereas other dose metric evaluations are nonsignificant. The time to generate the treatment plans is reduced for all automated plans with a median difference of 9' 50″±4' 33″. Template-based automated planning allows for reduced treatment planning time with consistent optimization structure creation, treatment field creation, plan optimization, and dose calculation with similar dosimetric quality. This process has potential expansion to numerous disease sites.

4DCT ventilation function image-based functional lung protection for esophageal cancer radiotherapy.

4DCT (four-dimensional computed tomography) can effectively obtain functional lung ventilation images for patients and integrate them into radiotherapy treatment planning. Studies have not been performed on esophageal cancer, and there is no clear consensus on the optimal functional lung threshold for functional lung. Functional lung images were generated for 11patients with esophageal cancer. The correlation between the dose-volume parameters of functional lung (FL) as defined by different thresholds and the change of PFT/PDFT (pulmonary [diffusion] function test) metrics before and after radiotherapy were evaluated. FL-sparing planning was generated for each patient to preserve the functional lung and compared to conventional anatomical CT (non-sparing) planning. There was asignificant positive correlation between the FL0.8 (defined Jacobian value ≤ 0.8), FL0.84, and FL0.9 dose-volume parameters and ΔFEV1/FVC (reduction before and after radiotherapy), and the FL0.8‑V30 correlation was the strongest (r = 0.819, P < 0.01). The FL-sparing planning had atarget area conformity index and homogeneity index comparable to the non-sparing planning (P > 0.05). For FL, the FL-sparing planning achieved lower FL-MLD (6.30 ± 2.14 Gy vs. 7.83 ± 2.70 Gy), V10 (17.13 ± 7.70% vs. 27.40 ± 9.48%), and V20 (6.96 ± 3.85% vs. 11.63 ± 7.19%) compared to the non-sparing planning (P < 0.05), while heart and spinal cord doses were not significantly different between the two planning groups. The 4DCT-based FL irradiation dose for esophageal cancer was significantly associated with adecrease in FEV1/FVC. The optimal FL defined as a Jacobian value ≤ 0.8 or about 21% of the whole lung volume may be a good choice. FL-sparing planning significantly reduced the FL dose without compromising target area coverage.

GPP02 Presentation Time: 8:10 AM: Evaluating the Relationship Between Vaginal Apex ``Dog Ears'' and Patterns of Recurrence in Endometrial Cancer Following Adjuvant Image Guided Vaginal Cuff Brachytherapy

<h3>Purpose</h3> The vaginal cuff is a common site of tumor recurrence following surgery for endometrial cancer, and adjuvant vaginal cuff brachytherapy (VCB) is indicated to reduce the risk of local recurrence. Following hysterectomy, many patients have redundant tissue at the lateral apex of the vaginal cuff ("dog ears"). This extra tissue may extend irregularly beyond the typical cylindrical dose distribution of radiation delivered during single channel VCB and it is hypothesized that they are a potential site of local treatment failure even after VCB. The effects of the presence and size of vaginal cuff "dog ears" on tumor recurrence is not yet fully understood. The aim of this study is to evaluate the prevalence and size of extra tissue at the vaginal apex, and whether these factors predict disease recurrence in patients treated with adjuvant VCB for endometrial cancer. <h3>Materials and Methods</h3> We retrospectively reviewed the medical records of 219 patients with early-stage endometrial cancer treated with image-guided single channel VCB at our institution from 2012 - 2021 with available brachytherapy planning CT simulation images. "Dog ears" were defined as the presence of additional soft tissue extending at least 10 mm from the apex of the vaginal cuff perpendicular to the surface of the brachytherapy applicator as defined on a coronal or axial CT simulation. Patient characteristics and outcomes including stage, size and laterality of dog ears, presence of air gaps, and patterns of failure were collected. Vaginal cuff recurrence (VCR) failure free survival was calculated from time of first brachytherapy to VCR and was estimated by the product limit method of Kaplan and Meier. Fisher's exact test was used to compare categorical variables and a multivariate logistic regression model was developed to evaluate the association of overall treatment failure with various factors of interest. <h3>Results</h3> We found that 57.5% of patients (n = 126) met our criteria for having "dog ears," which, on average, extended 23.8 mm (SD = 6.4) from the brachytherapy applicator. In total, 13 patients (5.9%) developed a VCR, 12 (5.5%) developed a regional recurrence, and 16 (7.3%) developed distant recurrence. There was no statistically significant difference in VCRs between patients with dog ears and those without dog ears (7.1% vs 4.3%, p=0.56). The various surgical approaches (abdominal, laparoscopic, transvaginal) did not have an increased propensity to result in dog ears (p=0.74). The 3-year probability of VCR failure-free survival is 86%. On multivariate analysis (MVA), no factors predicted for overall treatment failure including the presence of dog ears, maximum dimension of dog ears, FIGO stage, presence of air gaps at the applicator surface on post insertion CT images, or brachytherapy duration. There was a trend toward increased risk of recurrence with higher grade histology on MVA (p=0.0805). <h3>Conclusions</h3> In this investigation of a single institution experience with single-channel image-guided VCB, the presence of "dog ears" at the vaginal apex is prevalent; however, VCR remains low with distant metastases being the predominant site of failure. While dog ears appear to have little impact on overall recurrence patterns, these may be a factor to consider when planning adjuvant brachytherapy including choosing alternate applicators.

PO10: Case Presentation and Workflow for a 3D Printed Mold for HDR Brachytherapy of the Lower Lip

<h3>Introduction</h3> Interstitial head and neck brachytherapy is a versatile tool but requires intense patient and clinical resources as well as a high level of physician skill. For certain lesions, 3D printed brachytherapy molds may provide an "easier" alternative to interstitial brachytherapy. Recently, a patient presented with a progressive recurrent squamous cell carcinoma (SCC) in situ of the lower lip two years after prior Mohs surgery. As surgery for removal of the lesion would be disfiguring, radiotherapy was pursued. Electron radiotherapy would be difficult due to the curved surface. Thus, brachytherapy options were considered, however the use of interstitial brachytherapy would have been technically difficult as well as invasive. Commercial surface brachytherapy applicators would not fit the lesion and location, and therefore, a 3D printed brachytherapy applicator was utilized. <h3>Materials and Methods</h3> To create the 3D printed mold, two CT scans were required prior to mold design - one scan with radiopaque wires to define the target volume on the CT scan, and a second scan without wires, used to accurately define the patient surface for the 3D-printed mold. In this instance, the lower lip had to be rolled outward to expose the lesion and had to be immobilized in this position. Immobilization of the lower lip was achieved with adhesive attached to the lip and chest (Figure 1.a.). A standard bite block was inserted into the patient's mouth to keep the teeth in a reproducible position with the final intent that the 3D mold could be designed to attach to this bite block. CT scans were acquired at 1.25 mm thickness. A 3D mold was designed using our standard process in the Adaptiiv 3D bolus software. A pre-plan was created with the mold design in BrachyVision (Varian, Palo Alto, CA) to determine if the desired dosimetry to the target volume was achievable. Once a final mold design was approved, printing utilized an Axiom20 3D printer with Cheetah TPU. <h3>Results</h3> The final mold is shown in Figure 1.b and 1.c., illustrating that the mold was designed to fit over the pegs of the bite block. Several mold designs were considered, and ultimately an open bottomed mold was selected (Figure 1.d.) to allow for visualization of setup and also in case the lip swelled during treatment. A final CT of the patient with the mold in place was obtained to evaluate final mold fit and perform final CT planning (Figure 1.f.), as well as to acquire setup measurements (Figure 1.e.). Air gaps were minimal and only in two locations over the treatment volume which were all ≤1.5mm. The patient received 40 Gy in 10 fractions every other day. Near the end of treatment, topical lidocaine was applied to the patient's lip to help with applicator tolerance. Follow-up pictures are shown in Figure 1.g-i. Some moist desquamation was visible at the 1 week follow-up but resolved by six weeks posttreatment. At 10 months, the patient shows no signs of recurrence and no significant treatment-related toxicities. <h3>Conclusions</h3> A recurrent SCC in situ of the lower lip was successfully immobilized, planned, and treated with HDR brachytherapy using a custom 3D-printed mold. The benefits of the 3D mold allow for rigid immobilization of the lip for a reproducible and comfortable setup. Further research is needed into the optimal indications and applicator designs for 3D-printed applicators for head and neck brachytherapy.

Virtual non-contrast reconstructions improve differentiation between vascular enhancement and calcifications in stereotactic planning CT scans of cystic intracranial tumors

PurposeTo assess the diagnostic value of spectral-detector CT (SDCT) derived virtual non-contrast images (VNC) for differentiation between vascular enhancement and wall calcifications of cystic intracranial tumors in contrast-enhanced stereotactic planning examinations. Method48 patients with cystic intracranial tumors who underwent stereotactic SDCT examinations between 02/2017 and 02/2020 were retrospectively included. In each patient, two separate hyperattenuating structures along the cyst wall were defined as either enhancement or calcification, respectively, using reference MRI examinations. Quantitative analysis was performed ROI-based in conventional images (CI) and VNC. In the subjective analysis, two radiologists diagnosed the predefined peri-cystic structures in binary decisions as either enhancement or calcification using CI and the combination of CI and VNC, and rated diagnostic confidence, image noise and removal of iodine in VNC. Moreover, a potential diagnostic benefit of VNC was indicated. ResultsAttenuation in CI was higher as compared to VNC across all assessed ROI (all p < 0.01). In VNC, CNR between calcification and white matter was significantly higher as compared to CNR between vascular enhancement and white matter (2.6 vs 1.3, p < 0.01), while there was no significant difference in CI. In the qualitative assessment, diagnostic accuracy was significantly higher using both VNC and CI compared to using CI alone. Raters reported less image noise in VNC as compared to CI. An additional diagnostic benefit of VNC was indicated in 84.4 % of all cases. ConclusionsSDCT-derived VNC images facilitate differentiation between peri-cystic contrast enhancement in blood vessels and calcifications in stereotactic planning scans of cystic intracranial tumors.