Preoperative CT Simulation of Iliosacral Screws for Treating Unstable Posterior Pelvic Ring Injury

BackgroundPercutaneous iliosacral screw placement is an important surgical method for the treatment of pelvic unstable fractures, but either intraoperative X-ray screws or navigational screws may be misplaced. This study aimed to demonstrate a safe, effective, and rapid medthod for placing iliosacral screws for the treatment of unstable posterior pelvic ring injury according to preoperative computed tomography (CT) planning using simulated screws. MethodsAfter preoperative CT simulation of iliosacral screws planning screw insertion point and trajectory, intraoperative percutaneous iliosacral screws were used to treat unstable pelvic posterior ring injury.The mechanism of injury, Tile classification, number of screw implants, operative time of each screw implantation, radiation exposure time of each screw implantation screw position, complications, and postoperative follow-up time were collected.Screw position grading was evaluated by Smith grading. ResultsA total of 24 screws were implanted in 21 patients (9 men and 12 women;mean age 41.3 years:range 14-71 years). Tile classification included:Tile B:15 patients;Tile C:6 patients. The mean placement time of each screw was 19.5 minutes (range 14-32min); Radiation exposure time: 0.6 min (range 0.5-0.9min); Two screws were inserted in 3 patients; One screw was inserted in 18 patients; According to Smith grading standard, grade0:20 cases; and Grade1:1 case; Mean postoperative follow-up time was 17.1months (range12-25 months); None of the patients showed nonunion. ConclusionsPreoperative CT simulation of iliosacral screws for placement planning, screw trajectory, and intraoperative placement of screws is a safe method that can be used to reduce surgical time, radiation exposure, and accurate screw placement.

Volumetric and dosimetric impact of Post-Surgical MRI guided radiotherapy for Glioblastoma: A pilot study

Objectives: Glioblastoma (GBM) radiotherapy (RT) target delineation requires MRI, ideally concurrent with CT simulation (pre-RT MRI). Due to limited MRI availability, <72 h post-surgery MRI is commonly used instead. Whilst previous investigations assessed volumetric differences between post-surgical and pre-RT delineations, dosimetric impact remains unknown. We quantify volumetric and dosimetric impact of using post-surgical MRI for GBM target delineation. Methods: Gross tumour volumes (GTVs) for five GBM patients receiving chemo-RT with post-surgical and pre-RT MRIs were delineated by three independent observers. Planning target volumes (PTVs) and RT plans were generated for each GTV. Volumetric and dosimetric differences were assessed through: absolute volumes, volume-distance histograms, and dose-volume histogram statistics. Results: Post-surgical MRI delineations had significantly (p < 0.05) larger GTV and PTV volumes (median 16.7 and 64.4 cm3 respectively). Post-surgical RT plans, applied to pre-RT delineations, had significantly decreased (p < 0.01) median PTV doses (ΔD99% = −8.1 Gy and ΔD95% = −2.0 Gy). Median organ at risk (OAR) dose increases (brainstem ΔD5% =+0.8, normal brain mean dose =+2.9 and normal brain ΔD10% = 5.3 Gy) were observed. Conclusion: Post-surgical MRI delineation significantly impacted RT planning, with larger normal-appearing tissue volumes irradiated and increased OAR doses, despite a reduced coverage of the pre-RT defined target. Advances in knowledge: We believe this is the first investigation assessing the dosimetric impact of using post-surgical MRI for GBM target delineation. It highlights the potential of significantly degraded RT plans, showing the clinical-need for dedicated MRI for GBM RT.

RADT-07. DETERMINATION OF THE OPTIMAL TIME INTERVAL BETWEEN POST-OPERATIVE MRI AND CT SIMULATION FOR STEREOTACTIC RADIOSURGERY PLANNING

BACKGROUND The incidence of brain metastasis is approximately 200,000 worldwide annually. Stereotactic radiation therapy of post-operative cavity reduces local recurrence. Surgical cavity size changes significantly with 96.5% demonstrating volumetric change during post-operative period. We sought to define the optimal time interval that preserved the volumetric dimensions between the post-surgical MRI and the CT simulation used for stereotactic radiosurgery planning. METHODS Seven patients with brain metastasis that underwent surgical resection and stereotactic radiation treatment at Albany Medical Center from February 2019 to April 2020 were included in the study. A total of 8 target lesions were included. Brain lab planning system was used for contouring the target volume. A postoperative MRI within 24-48 hours after surgery was obtained. 3 patients required an additional interim MRI 16-50 days after surgery. The planning CT simulation was performed 2 days prior and up to 15 days after the post-operative/interim MRI and target volumes were compared. RESULTS The average volume of the post-surgical cavity contoured by the neurosurgeons on the post-operative/interim MRI was 15.96 cc (± 7.79 cc, range of 6.54 -24.9 cc). The average volume of the post-surgical cavity contoured by the radiation oncologists on the planning CT was 15.71 (± 7.49 cc, range of 6.53 -24.31 cc). There was no noticeable change in volume size between post-operative/interim MRI and planning CT up to the period of 15 days. LIMITATION This was a retrospective pilot study with a small sample size and patients recruited from a single center. CONCLUSION There is no change in size of the cavity volume for up to 15 days between post-operative/interim MRI and planning CT. This knowledge will help understand the optimal time interval between post-operative MRI and CT simulation for the stereotactic radiation therapy planning.

Online MR evaluation of inter- and intra-fraction uterus motions and bladder volume changes during cervical cancer external beam radiotherapy

Purpose/objective(s) The purpose of the study was to assess the uterus motions and bladder volume changes of fractional movements in cervical sites throughout the external beam radiotherapy (EBRT) treatment. Materials/methods A prospective online MR imaging tracking study was conducted in EBRT 43 patients with at least 4 scans during each treatment (before: ultrasound scan, MRI scan, CBCT scan, after: MRI scan) were included. In order to improve the treatment repeatability, each patient was instructed to empty the bladder and drink 500 ml water 1 h before CT simulation and each treatment. If the ultrasound scan result reached the CT simulation volume of bladder, the treatment began. Bladder was outlined on the T2 weighted axial sequence and CBCT image by the two observers to avoid the influence of contouring. The data of bladder volume and scanning time were accurately recorded. The bladder volumes, filling rates and uterus motion were retrospectively analyzed by MIM software. Results Inter-fraction variation of the bladder volume was significant (p < 0.0001). Intra-fraction mean increase of the bladder volume was modest (30 cc) but significant (p < 0.001). Both inter- and intra-fraction of the uterus motion were significant. The average time between the pre-and post-fraction MRI scans was 27.82 ± 7.12 min (range 10–55 min) for IMRT plans and 24.14 ± 5.86 min (range7-38 min) for VMAT plan. Average bladder filling rate was 3.43 ml/min. The bladder filling rate did not change significantly with the course of treatment, but the bladder was more intolerant. Conclusion This is the most detailed assessment of intra-fraction and inter-fraction motion during EBRT for cervical cancer. Finally, this study will inform appropriate treatment margins for online adaptive radiotherapy. We suggest that at least one image scan is needed before the EBRT. The portable US scanner provides a quick but unreliable measurement of the bladder volume. There is a significant statistical difference between the results of ultrasonic scanning and that of image scanning.

Use of Continuous Positive Airway Pressure (CPAP) to Limit Diaphragm Motion—A Novel Approach for Definitive Radiation Therapy for Inoperable Pleural Mesothelioma: A Pilot Study

Malignant pleural mesothelioma (MPM) is a deadly disease and radiotherapy (RT) plays an important role in its management. Recent developments in technique have made it is possible to deliver RT to MPM in the intact lung. However, it is imperative to reduce normal lung doses. We present a pilot study examining the use of CPAP and VMAT radiotherapy to reduce toxicity when treating MPM, involving three consecutive patients with MPM, not amenable to surgery, who were treated according to Helsinki committee approval. Patients were simulated using four-dimentional CT simulation with the assistance of CPAP lung inflation, then were treated using both IMRT and VMAT techniques. Radiation lung dose was optimized based on accepted lung dose constraints. Patients were followed for toxicity as well as local control and survival. Results: Three patients were treated with CPAP-based IMRT treatment. These patients tolerated the treatment and DVH constraints were able to be met. The comparison plans among the four VMAT arcs and the IMRT static field treatment were able to accomplish the treatment planning objectives without significant advantages with either technique. The treatment combined with CPAP reduced the normal lung dose in MPM patients with intact lungs. This technique is worthy of further investigation.

Dosimetric comparison and TCP-NTCP modelling for lung, heart, left anterior descending and right coronary artery in left sided breast cancer conventional and hypofractionated radiotherapy

BackgroundThe aim of this study was to evaluate the dose distribution, and also tumor control probability (TCP) and normal tissue complications probability (NTCP) models of left sided breast cancer females for 3D-CRT, 6 and 9 fields IMRT and hypofractionated tangential plans.MethodsSixty left sided breast cancer females were included in this study. CT simulation images of the patients were imported on the treatment planning software (TiGRT, LinaTech, China), and the tangential treatment plans of the mentioned methods were done for each patient. The dosimetric evaluation, and TCP-NTCP models of stated modalities were done using Poisson Linear-Quadatric (PLQ) and Lyman-Kutcher-Burman (LKB) models on the MATLAB and R softwares.ResultsThe mean (± SD) dose to ipsilateral lung, heart, LAD and RCA with/without internal mammary fields for 6FIMRT was lower compared to other modalities. Furthermore, V20Gy for Ipsilateral lung and V25Gy for heart, LAD and RCA of 6FIMRT was lower than other methods. In addition, the PTV dose coverage was higher for 9FIMRT and hypofractionated RT, while it may be lower for 3D-CRT among the studied methods. Although TCP values of 9 and 6fieds and hypofractionated was not significantly different, the TCPs of them were higher compared to 3D-CRT. However, the NTCP for ipsilateral lung, heart, LAD and RCA of 6FIMRT was lower than others.Conclusion6FIMRT is suitable choice for RT of breast cancer patients compared to other mentioned modalities, as a result of providing adequate PTV dose coverage and TCP, and also lower imposed dose and NTCP for OARs. Hypofractionated RT is a good alternative to reduce treatment time for the breast cancer patients.Trial registrationThis study was approved by the ethical board of Isfahan University of Medical Sciences, Isfahan, Iran (IR.MUI.MED.REC.1399.677).

Infection Control and Modified Workflow Strategies in Radiation Oncology Department during COVID 19 Crisis: An Institutional Experience

Purpose: To build safe environment for cancer fighters and radiation personnel during COVID-19 pandemic by focusing on infection control, workflow and radiotherapy dose schedules modification strategies in radiation oncology departments. Material and Methods: A meeting was called post lock down in radiation oncology department to prepare infection control policies and workflow strategies in time of COVID-19 Pandemic.Results: Strategies and policies were formed during COVID-19 crises taking following points into consideration 1) Infection control policies 2) CT simulation policies 3) Day care admission and chemotherapy administration policies 4) Radiation treatment plan modification and delivery strategies 5) Brachytherapy delivery strategies.Conclusion: Management of cancer patients is an issue running parallel to the present condition of COVID-19 pandemic. Further randomized trial on hypofractionated radiotherapy schedules should be encouraged. Positivity, awareness and systematic approach are most important step in balancing the current scenario.

New algorithms for computed tomography image reconstruction to eliminate artifacts

Computed tomography (CT) relies on computational algorithms to reconstruct images from CT projections. Current filtered backprojection reconstruction methods have inherent limitations in situations with sharp density gradients and limited beam views. In this thesis two novel reconstruction algorithms were introduced: the Algebraic Image Reconstruction (AIR) algorithm, and the Geometric Image Reconstruction Algorithm (GIRA). A CT simulation was developed to test these novel algorithms and compare their images to filtered backprojection images. AIR and GIRA each demonstrated their proof of principle in these preliminary tests. AIR and its extension, the Parsed AIR algorithm (PAIR), were able to reconstruct optimal images compared to filtered backprojection after empirically determining parameters relevant to the algorithms. While GIRA reconstructed optimal images in preliminary tests, reconstruction was complicated by error propagation for larger imaging domains. The initial success of these novel approaches justifies continued research and development to determine their feasibility for practical CT image reconstruction.