Performance of the cone beam computed tomography-based patient positioning system on the Gamma Knife Icon™

Same-day mask-based gamma-knife stereotactic radiosurgery: workflow analysis and impact

OBJECTIVE

Over the last 30 years, there has been a steady move towards the use of mask immobilization in SRS. Benefits of masks include the ability to hypofractionate SRS and improved patient comfort. However, there has been criticism that it eliminates the possibility of same-day, "wheels in to wheels out" treatments, as mask fixation is traditionally done on a separate day. This study evaluates the feasibility of doing mask fabrication and SRS treatment on the same day.

METHODS

Patients who underwent SRS from September 2020 to June 2021 were reviewed. Leksell Gamma Knife (LGK) console data were processed, and operator reports were analyzed for treatment time, number of pauses, alarms, and pause durations.

RESULTS

A total of 100 patients met the inclusion criteria. 52 patients underwent same-day fabrication and treatment, and 48 patients were treated at least one day following mask fabrication. Same-day patients had more frequent pauses and longer average pause durations than different-day patients. However, there were no significant differences in predicted vs. actual treatment times or the number of treatment alarms between groups.

CONCLUSION

Mask-based SRS can be done safely and efficiently in a single day, mirroring the approach of frame-based treatments. There is an increased number of pauses in the same-day group; however, it does not result in a significant prolongation of treatment time. The reduction in the number of visits to a GK facility for SRS may impact the overall subjective experience, increasing patient satisfaction.

Advanced External Beam Stereotactic Radiotherapy for Skull Base Reirradiation

BACKGROUND/OBJECTIVES

Stereotactic body radiation therapy (SBRT) for skull base reirradiation is particularly challenging, as patients have already received substantial radiation doses to the region, and nearby normal organs may have approached their tolerance limit from prior treatments. In this study, we reviewed the characteristics and capabilities of four advanced external beam radiation delivery systems and four modern treatment planning systems and evaluated the treatment plan quality of each technique using skull base reirradiation patient cases.

METHODS

SBRT plans were generated for sixteen skull base reirradiation patients using four modalities: the GK plan for the Elekta Leksell Gamma Knife Perfexion/ICON, the CyberKnife (CK) plan for the Accuray CyberKnife, the intensity-modulated proton therapy (IMPT) plan for the Hitachi ProBeat-FR proton therapy machine, and the volumetric-modulated arc therapy (VMAT) plan for the Varian TrueBeam STx. These plans were evaluated and compared using two novel gradient indices in addition to traditional dosimetry metrics for targets and organs at risk (OARs). The steepest border gradient quantified the percent prescription dose fall-off per millimeter at the boundary between the target and adjacent critical structures. This gradient index highlighted the system's ability to spare nearby critical OARs. The volume gradient assessed the extent of dose spread outside the target toward the patient's body.

RESULTS

All plans achieved comparable target coverage and conformity, while IMPT and VMAT demonstrated significantly better uniformity. The GK plans exhibited the highest border gradient, up to 20.9%/mm, followed by small-spot-size IMPT plans and CK plans. Additionally, IMPT plans showed the benefit of reduced dose spread in low-dose regions and the lowest maximum and mean doses to the brainstem and carotid artery.

CONCLUSIONS

The advanced external beam radiotherapy modalities evaluated in this study are well-suited for SBRT in skull base reirradiation, which demands precise targeting of tumors with highly conformal doses and steep dose gradients to protect nearby normal structures.

Enhancing Gamma Knife Cone-beam Computed Tomography Image Quality Using Pix2pix Generative Adversarial Networks: A Deep Learning Approach

Aims

The study aims to develop a modified Pix2Pix convolutional neural network framework to enhance the quality of cone-beam computed tomography (CBCT) images. It also seeks to reduce the Hounsfield unit (HU) variations, making CBCT images closely resemble the internal anatomy as depicted in computed tomography (CT) images.

Materials and Methods

We used datasets from 50 patients who underwent Gamma Knife treatment to develop a deep learning model that translates CBCT images into high-quality synthetic CT (sCT) images. Paired CBCT and ground truth CT images from 40 patients were used for training and 10 for testing on 7484 slices of 512 × 512 pixels with the Pix2Pix model. The sCT images were evaluated against ground truth CT scans using image quality assessment metrics, including the structural similarity index (SSIM), mean absolute error (MAE), root mean square error (RMSE), peak signal-to-noise ratio (PSNR), normalized cross-correlation, and dice similarity coefficient.

Results

The results demonstrate significant improvements in image quality when comparing sCT images to CBCT, with SSIM increasing from 0.85 ± 0.05 to 0.95 ± 0.03 and MAE dropping from 77.37 ± 20.05 to 18.81 ± 7.22 (p < 0.0001 for both). PSNR and RMSE also improved, from 26.50 ± 1.72 to 30.76 ± 2.23 and 228.52 ± 53.76 to 82.30 ± 23.81, respectively (p < 0.0001).

Conclusion

The sCT images show reduced noise and artifacts, closely matching CT in HU values, and demonstrate a high degree of similarity to CT images, highlighting the potential of deep learning to significantly improve CBCT image quality for radiosurgery applications.

Retrospective Analysis of Treatment Workflow in Frame-Based and Frameless Gamma Knife Radiosurgery

Objective

To improve the efficiency of frame-based and frameless Gamma Knife® Icon™ (GKI) treatments by analyzing the workflows of both treatment approaches and identifying steps that lead to prolonged patient in-clinic or treatment time.

Methods

The treatment processes of 57 GKI patients, 16 frame-based and 41 frameless cases were recorded and analyzed. For frame-based treatments, time points were recorded for various steps in the process, including check-in, magnetic resonance imaging (MRI) completion, plan approval, and treatment start/end times. The time required for completing each step was calculated and investigated. For frameless treatments, the actual and planned treatment times were compared to evaluate the patient tolerance of the treatment. In addition, the time spent on room cleaning and preparation between treatments was also recorded and analyzed.

Results

For frame-based cases, the average in-clinic time was 6.3 hours (ranging from 4 to 8.7 hours). The average time from patient check-in to plan approval was 4.2 hours (ranging from 2.8 to 5.5 hours), during which the frame was placed, stereotactic reference MRI images were taken, target volumes were contoured, and the treatment plan was developed and second-checked. For patients immobilized with a mask, treatment pauses triggered by the intra-fractional motion monitoring system resulted in a significantly longer actual treatment time than the planned time. In 50 (or 55%) of the 91 frameless treatments, the patient on-table time was longer than the planned treatment time by more than 10 minutes, and in 19 (or 21%) of the treatments the time difference was larger than 20 minutes. Major treatment interruptions, defined as pauses leading to a longer than 10-minute delay, were more commonly encountered in patients with a planned treatment time longer than 40 minutes, which accounted for 64% of the recorded major interruptions.

Conclusion

For frame-based cases, the multiple pretreatment steps (from patient check-in to plan approval) in the workflow were time-consuming and resulted in prolonged patient in-clinic time. These pretreatment steps may be shortened by performing some of these steps before the treatment day, e.g., pre-planning the treatment using diagnostic MRI scans acquired a few days earlier. For frameless patients, we found that a longer planned treatment time is associated with a higher chance of treatment interruption. For patients with a long treatment time, a planned break or consideration of fractionated treatments (i.e., 3 to 5 fractionated stereotactic radiosurgery) may optimize the workflow and improve patient satisfaction.

Gamma Knife evolving instrumentation

There have been advances in both the hardware and software used in GKNS. The first major change in hardware had been Gamma Knife PERFEXION which introduced in 2006 had given more space for treatment, and removed the need for helmets, facilitating the treatment of complex conditions. Gamma Knife ICON was commissioned first in 2017. This has two important changes. It is based on the PERFEXION model, but it is constructed to permit frameless treatments. It also has an attached CBCT apparatus which may be used to define the stereotactic space. The Gamma Knife software has also improved in two important respects. The speedy calculations available to modern computer power has enabled improvements in the accuracy of the determination of intracranial radiation absorption between source and target. The other improvement has been the introduction of inverse treatment planning which continues to be under development.

Mask-Based versus Frame-Based Gamma Knife ICON Radiosurgery in Brain Metastases: A Prospective Randomized Trial

BACKGROUND

Radiosurgery is performed with a diversity of instruments relying usually either on a stereotactic frame or a mask for patient head fixation. Comfort and safety efficacy of the 2 systems have never been rigorously evaluated and compared.

MATERIAL AND METHOD

Between February 2016 and January 2017, 58 patients presenting with nonsmall cell lung cancer brain metastases have been treated by Gamma Knife radiosurgery (GKS) with random use of a frame or a mask for fixation were included patients older than 18, with <5 brain metastases (at the exclusion of brainstem and optic pathway's locations) and no earlier history of radiotherapy. The primary outcome measure was the pain scale assessment (PSA) at the beginning of the GKS procedure.

RESULTS

The PSA at the beginning of the GKS procedure was not different between the 2 groups. The PSA at the day before GKS, before magnetic resonance imaging, just after frame application, and the day after radiosurgery (departure) has shown no difference between the 2 groups. At the end of the radiosurgery itself (just after frame or mask removal) and 1 h after, the mean pain scale was higher in patients treated with the frame (p < 0.05 and p < 0.001, respectively) but 2 patients were not able to tolerate the mask discomfort and had to be treated with frame. Tumor control and morbidity probability were demonstrated to be no difference between the 2 groups in this population of patients with BM not in highly functional area. The median of the extra dose to the body due to the cone-beam computed tomography was 7.5 mGy with a maximum of 35 mGy in patients treated with a mask fixation (null in the others treated with frame). Mask fixation was associated to longer treatment time although the beam on time was not different between the 2 groups.

CONCLUSION

In selected patients, with brain oligo-metastases out of critical location, single-dose mask-based GKS can be done with a comfort and a safety efficacy comparable to frame-based GKS. There seems to be no clear patient data that confirm the value of the mask system with regards to comfort.