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Purpose Characterize the intra‐fraction motion management (IFMM) system found on the Gamma Knife Icon (GKI), including spatial accuracy, latency, temporal performance, and overall effect on delivered dose. Methods A phantom was constructed, consisting of a three‐axis translation mount, a remote motorized flipper, and a thermoplastic sphere surrounding a radiation detector. An infrared marker was placed on the translation mount secured to the flipper. The spatial accuracy of the IFMM was measured via the translation mount in all Cartesian planes. The detector was centered at the radiation focal point. A remote signal was used to move the marker out of the IFMM tolerance and pause the beam. A two‐channel electrometer was used to record the signals from the detector and the flipper when motion was signaled. These signals determined the latency and temporal performance of the GKI. Results The spatial accuracy of the IFMM was found to be <0.1 mm. The measured latency was <200 ms. The dose difference with five interruptions was <0.5%. Conclusion This work provides a quantitative characterization of the GKI IFMM system as required by the Nuclear Regulatory Commission. This provides a methodology for GKI users to satisfy these requirements using common laboratory equipment in lieu of a commercial solution.

Purposes To report our experience in a prospective study of implementing a transperineal ultrasound system to monitor intra‐fractional prostate motion for prostate stereotactic body radiotherapy (SBRT). Material and Methods This IRB‐approved prospective study included 23 prostate SBRT patients treated between 04/2016 and 11/2019 at our institution. The prescription doses were 36.25 Gy to the Low‐Dose planning target volume (LD‐PTV) and 40 Gy to the High‐Dose PTV (HD‐PTV) in five fractions with 3 mm planning margins. The transperineal ultrasound system was successfully used in 110 of the 115 fractions. For intra‐fraction prostate motion, the real‐time prostate displacements measured by ultrasound were exported for analysis. The percentage of time prostate movement exceeded a 2 mm threshold was calculated for each fraction of all patients. T‐test was used for all statistical comparisons. Results Ultrasound image quality was adequate for prostate delineation and prostate motion tracking. The setup time for each fraction under ultrasound‐guided prostate SBRT was 15.0 ± 4.9 min and the total treatment time per fraction was 31.8 ± 10.5 min. The presence of an ultrasound probe did not compromise the contouring of targets or critical structures. For intra‐fraction motion, prostate movement exceeded 2 mm tolerance in 23 of 110 fractions for 11 of 23 patients. For all fractions, the mean percentage of time when the prostate moved more than 2 mm in any direction during each fraction was 7%, ranging from 0% to 62% of a fraction. Conclusion Ultrasound‐guided prostate SBRT is a good option for intra‐fraction motion monitoring with clinically acceptable efficiency.

This technical evaluation aims to provide practice ‘how to’ guidelines for radiation therapists (RTs) when positioning a transperineal ultrasound (TPUS) probe during prostate radiotherapy. Recommendations and practical tips will be provided for the best practice in TPUS‐guided workflow to obtain optimal ultrasound images for accurate interpretation and registration of the prostate gland. This will assist the RTs in making consistent and accurate clinical decision in an ultrasound‐guided radiotherapy workflow for prostate treatment. The implementation process and the associated successes and challenges will also be described to assist institutions who may be investigating the potential of implementing this system. This technical note aims to provide practice guidelines for radiation therapists (RTs) when positioning a transperineal ultrasound (TPUS) probe during prostate radiotherapy. Recommendations and practical tips were provided for best practice in TPUS‐guided workflow to obtain optimal ultrasound images for accurate interpretation and registration of the prostate gland. This will assist the RTs in making consistent and accurate clinical decision in an ultrasound‐guided radiotherapy workflow for prostate treatment.

Introduction Accurate delivery of radiation while reducing dose to organs at risk is essential in prostate treatment. The Calypso motion management system detects and corrects both inter‐ and intra‐fraction motion which offers potential benefits over standard alignment to fiducial markers. The aims of this study were to implement Calypso with Dynamic Edge™ gating and to assess both the motion seen, and interventions required. Methods An implementation group was formed which assessed changes needed to standard workflows. Three patients had Calypso beacons inserted into their prostate. All patients were treated using volumetric modulated arc therapy to a dose of 80 Gy in 40 fractions. Standard inter‐fraction motion correction using either kilovoltage (kV) orthogonal paired imaging or cone beam computed tomography (CBCT) image‐guided radiotherapy techniques, were used along with the Calypso system to compare accuracy. A gating threshold of >0.5 cm was used during treatment. Workflow variations along with inter‐ and intra‐fraction motion and interventions required were assessed. Results A total of 116 fractions were treated using Calypso with Dynamic Edge™ gating. There was a strong concordance between aligning beacons using kV orthogonal imaging or CBCT and Calypso (mean variation ≤0.06 cm). The mean intra‐fraction motion detected was ≤0.2 cm in all directions with the largest motion recorded being 2.2 cm in the left direction while the treatment beam was off. Prostate rotation was largest in the pitch direction and 28 fractions exceeded the 10° tolerance. A total of 78 couch shift corrections of ≥0.3 cm were required, usually following standard imaging, and before treatment starting. Three gating events due to intra‐fraction motion occurred during treatment. Conclusions Intra‐fraction motion monitoring with Calypso was successfully implemented. Greatest movement was seen between time of standard imaging and treatment starting with more than half the treatments requiring a ≥0.3 cm adjustment. This would not have been detected without intra‐fraction monitoring. Accurate delivery of radiation while reducing dose to organs at risk is essential in prostate treatment. The Calypso motion management system detects and corrects both inter‐ and intra‐fraction motion which offers potential benefits over standard alignment to fiducial markers. The aims of this study were to implement Calypso with dynamic edge gating and to assess both the motion seen, and interventions required.

Background/Objectives: An on-board imager on a linear accelerator allows the acquisition of kV-2D images during irradiation. Overlaying specific structures on these images enables the visual verification of movement at regular frequencies. Our aim was to validate this tracking method for the stereotactic treatment of bone metastases. Methods: Shifts in three translational directions were simulated using an anthropomorphic phantom. For these simulated shifts, planar images were acquired at different angles of incidence, with overlaid volumes of interest. A blinded test was then administered to the 18 participants to evaluate their decisions regarding whether to stop treatment. The results considered the experience of the operators. Quantitative analyses were performed on the intra-fractional images of 29 patients. Results: Participants analyzed each image with an average (standard deviation) decision time of 3.0 s (2.3). For offsets of 0.0, 1.0, 1.5, and 2.0 mm, the results were 78%, 93%, 90%, and 100% for the expert group and 78%, 70%, 79%, and 88% for the less-experienced group. Clinical feedback confirmed this guidance technique and extended it to non-spinal bony metastases. Sudden movements exceeding the 2.0 mm threshold occurred in 3.3% of the analyzed fractions, with a detection rate of 97.8% for vertebral locations. For non-vertebral bone locations, movements exceeding a threshold of 3.0 mm occurred in 3.5% of cases and were detected in 96.5%. Conclusions: The clinical use of planar OBI and superimposed structures for visual-image guidance in bone stereotactic treatment was validated using an anthropomorphic phantom and clinical feedback.

The objective was to investigate the possibility of using ExacTrac X-ray (ETX) for 6D image guidance in stereotactic body radiation therapy (SBRT) of bone metastasis and to propose a patient management protocol. The analyses were first obtained from measurements on a pelvic phantom and on 19 patients treated for bone metastasis. The phantom study consisted of applying known offsets and evaluating the ETX level of accuracy, where results were compared with kV-cone beam computed tomography (kV-CBCT). Two groups of patients, 10 spinal and 9 nonspinal SBRT cases, were analyzed to evaluate ETX imaging for different bone localisations. A comparison was made between kV-CBCT and ETX prior to the treatment fractions. During treatments, two other kV-CBCT/ETX image pairs were also acquired and a total of 224 shifts were compared. A second study, using the ETX monitoring module, analyzed the intrafraction motion of 8 other patients. In the phantom study, the root mean square (RMS) of the translational and rotational discrepancies between ETX and kV-CBCT were < 0.6 mm and < 0.4°, respectively. For both groups of patients, the RMS of the discrepancies observed between the two imaging systems were greater than the phantom experiment while still remaining < 1 mm and < 0.7°. In the nonspinal group, three patients (2 scapulas and 1 humerus) did not have consistent shift values with ETX due to a lack of anatomical information. When ETX monitoring was used during irradiation, the setup errors measured were on average less than 1 mm/1°. The results obtained validated the use of ETX for 6D image guidance during bone SBRT. Real-time tracking of the target position improves the accuracy of the irradiation. This strategy allowed for faster correction of out-of-tolerance positioning errors. The registration of bone lesions with poor anatomical information is a limitation of this 2D-kV imaging system.

Gamma knife radiosurgery saw the light of the day when the Swedish physician \"Lars Leksell\" postulated the salient first principles of stereotactic radiosurgery. Prior to being realized in its new 'avatar' \"The ICON\", Leksell Gamma Knife (LGK) \"Perfexion\" has been the most practiced model and is still in practice in most of the centers in India. The Gamma Knife ICON (the sixth generation model) utilizes the concept of the Cone-Beam Computed Tomography (CBCT) module, thus allowing non-invasive immobilization of the skull employing frameless treatments without jeopardizing accuracy to sub-millimeters. The LGK ICON however has the same stereotactic delivery and patient positioning system as Perfexion and mesmerizes the care givers with the added technically sound feature of the CBCT imaging arm, that is, CBCT and an intra-fraction motion management system. The experience with ICON on both the sub-sets of patients has been intriguing and awe-inspiring. Despite its challenges of being detected with significant intra-fraction errors, we realized that the non-invasive thermoplastic mask fixation system has its own set of specific characteristics: fairly simple dosimetry; short radiation delivery times; and calm, composed, co-operative patients. We have been successful in conducting frameless gamma knife surgeries in ~25% of patients planned for gamma knife surgery. We look forward to witness this avant-garde pioneering scientific automation being practiced in a higher number of patients.

OBJECTIVE Movement in early-stage laryngeal radiotherapy is an important factor in the success of the treatment. Thyroid cartilage may move by swallowing, breathing, sound production, and reflexes. During the treatment, the intra-fraction target movement was monitored by CBCT scans. In this study, we investigated the effects of laryngeal movement on the target volume. METHODS CT scans were performed to 16 patients with maximum neck extension and treatment plans were prepared with VMAT fields with 6MV energy. CBCT scanning was performed to all patients before the treatment and necessary corrections were made. Then, simultaneous intrafraction CBCT scanning with the VMAT field was performed during the treatment. When the treatment field was over, the deviation amounts between CT and CBTC in the lateral, vertical and longitudinal axes were determined. RESULTS The deviation amount ? ±0.1cm was determined with 293 fractions in the lateral axis, 260 fractions in the vertical axis and 263 fractions in the longitudinal axis. Maximum deviation values were determined as 0.2 cm in the lateral axis, 0.5cm in the vertical axis and 0.5cm in the longitudinal axis. If the treatment has a 0.2cm CTV-PTV margin (for 305 fractions), treatment can be performed at a confidence interval of 100% on the lateral axis, 96.1% on the vertical axis and 94.1% on the longitudinal axis. CONCLUSION With the help of intra-faction monitoring, we are able to adjust the target margins and doses more precisely in laryngeal radiotherapy, especially for stereotactic treatment. To reduce possible movements in laryngeal radiotherapy, a maximum neck extension should be performed.

Background Internal Target Volume (ITV) is one of the most common strategies to passively manage tumour motion in Radiotherapy (RT). The reliability of this approach is based on the assumption that the tumour motion estimated during pre-treatment 4D Computed Tomography (CT) acquisition is representative of the motion during the whole RT treatment. With the introduction of Magnetic Resonance-guided RT (MRgRT), it has become possible to monitor tumour motion during the treatment and verify this assumption. Aim of this study was to investigate the reliability of the ITV approach with respect to the treatment fraction time (TFT) in abdominal and thoracic lesions. Methods A total of 12 thoracic and 15 abdominal lesions was analysed. Before treatment, a 10-phase 4DCT was acquired and ITV margins were estimated considering the envelope of the lesion contoured on the different 4DCT phases. All patients underwent MRgRT treatment in free-breathing, monitoring the tumour position on a sagittal plane with 4 frames per second (sec). ITV margins were projected on the tumour trajectory and the percentage of treatment time in which the tumour was inside the ITV (%TT) was measured to varying of TFT. The ITV approach was considered moderately reliable when %TT ≥ 90% and strongly reliable when %TT ≥ 95%. Additional ITV margins required to achieve %TT ≥ 95% were also calculated. Results In the analysed cohort of patients, ITV strategy can be considered strongly reliable only for lung lesions with TFT ≤ 7 min (min). The ITV strategy can be considered only moderately reliable for abdominal lesions, and additional margins are required to obtain %TT ≥ 95%. Considering a TFT ≤ 4 min, additional margins of 2 mm in cranio-caudal (CC) and 1 mm in antero-posterior (AP) are suggested for pancreatic lesions, 3 mm in CC and 2 mm in AP for renal and liver ones. Conclusions On the basis of the analysed cases, the ITV approach appears to be reliable in the thorax, while it results more challenging in the abdomen, due to the higher uncertainty in ITV definition and to the observed larger intra and inter-fraction motion variability. The addition of extra margins based on the TFT may represent a valid tool to compensate such limitations.

Background To measure intra-fraction displacement (IFD) in post-prostatectomy patients treated with anisotropic margins and daily soft tissue matching. Methods Pre-treatment cone beam computed tomography (CBCT) scans were acquired daily and post-treatment CBCTs for the first week then weekly on 46 patients. The displacement between the scans was calculated retrospectively to measure IFD of the prostate bed (PB). The marginal miss (MM) rate, and the effect of time between imaging was assessed. Results A total of 392 post-treatment CBCT’s were reviewed from 46 patients. The absolute mean (95% CI) IFD was 1.5 mm (1.3–1.7 mm) in the AP direction, 1.0 mm (0.9–1.2 mm) SI, 0.8 mm (0.7–0.9 mm) LR, and 2.4 mm (2.2–2.5 mm) 3D displacement. IFD ≥  ± 3 mm and ≥  ± 5 mm was 24.7% and 5.4% respectively. MM of the PB was detected in 33 of 392 post-treatment CBCT (8.4%) and lymph nodes in 6 of 211 post-treatment CBCT images (2.8%). Causes of MM due to IFD included changes in the bladder (87.9%), rectum (66.7%) and buttock muscles (6%). A time ≥ 9 min between the pre and post-treatment CBCT demonstrated that movement ≥ 3 mm and 5 mm increased from 19.2 to 40.5% and 5 to 8.1% respectively. Conclusions IFD during PB irradiation was typically small, but was a major contributor to an 8.4% MM rate when using daily soft tissue match and tight anisotropic margins.