Inter- and intrafractional dose uncertainty in hypofractionated Gamma Knife radiosurgery

Total workflow uncertainty of frameless radiosurgery with the Gamma Knife Icon cone-beam computed tomography

Objective

Frameless treatment with the Gamma Knife Icon is still relatively new as a treatment option. As a result, additional confidence/knowledge about the uncertainty that exists within each portion of the treatment workflow could be gained especially regarding steps that have not been previously studied in the literature.

Methods

The Icon base delivery device (Perfexion) uncertainty is quantified and validated. The novel portions of the Icon such as mask immobilization, cone‐beam computed tomography image guidance, and the intrafraction motion management methods are studied specifically and to a greater extent to determine a total workflow uncertainty of frameless treatment with the Icon.

Results

The uncertainty of each treatment workflow step has been identified with the total workflow uncertainty being identified in this work as 1.3 mm with a standard deviation of 0.51 mm.

Conclusion

The total uncertainty of frameless treatment with the Icon has been evaluated and this data may indicate the need for setup margin in this setting with data that could be used by other institutions to calculate needed setup margin per their preferred recipe after validation of this data in their context.

Cerebral metastases

Brain metastases are common and deadly. Over the last 25 years GKNS has been established as an invaluable treatment. It may be used as a primary treatment or after either surgery or WBRT. Patients are assessed using one of a number of available scales. GKNS may be repeated for new metastases and for unresponsive tumors. Prescription doses are usually between 18 and 20Gy. The use of advanced MR techniques to highlight sensitive structures like the hippocampi have extended the efficacy of the treatment. More recently GKNS has been used with different target therapies with improved results. More recently frameless treatments have become more popular in this group of very sick patients. GKNS controls tumors in between 80% and over 95% of cases and may even be used for brainstem tumors.

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.

8+ Year Performance of the Gamma Knife Perfexion/Icon Patient Positioning System and Possibilities for Preemptive Fault Detection Using Statistical Process Control

BACKGROUND

The large fractional doses, steep dose gradients, and small targets found in intracranial radiosurgery require extremely low beam delivery uncertainty. In the case of Gamma Knife radiosurgery (GKRS), this includes minimizing patient positioning system (PPS) positioning uncertainty. Existing QA techniques are recipe based, and feature point in time pass/fail tolerances. However, modern treatment machines, including the Gamma Knife Perfexion/Icon systems, record extensive internal data in treatment logs. These data can be analyzed through statistical process control (SPC) methods which are designed to detect changes in process behavior. The purpose of this study was to characterize the long-term (8+ year) performance of a Perfexion/Icon unit and use SPC methods to determine if performance changes could be detected at levels lower than existing QA and internal manufacturer performance tolerances.

METHODS

In-house software was developed to parse Perfexion/Icon log-files and store relevant information on shot delivery in a relational database. A last-in, first-out (LIFO) queuing algorithm was created to heuristically match messages associated with a given delivered shot. Filtering criteria were developed to filter QA and uncompleted shots. The resulting matched shots were extracted. Achieved versus planned PPS position was determined for each PPS motor as well as for the vector magnitude difference in PPS position. Exponentially weighted moving average (EWMA) control charts were plotted to determine when process behavior changed over time.

RESULTS

53833 shots were delivered over an 8+ year span in the study. The mean vector magnitude PPS difference was 32.7 µm, with 97.5% of all shots within 70.1 µm. Several changes in PPS positioning behavior were observed over time, corresponding with control system faults on several occasions requiring PPS recalibration. EWMA control charts clearly demonstrate that these faults could be identified and possibly predicted as many as 3 years before there were faults beyond control system tolerance.

CONCLUSION

The PPS of Gamma Knife Perfexion/Icon systems has extremely low positioning uncertainties. EWMA control chart method can be utilized to track PPS performance over time and can potentially detect changes in performance that may indicate a component requiring maintenance. This would allow planned service visits to mitigate problems and prevent unplanned downtime.

Deep brain stimulation and other surgical modalities for the management of essential tremor

INTRODUCTION

Surgical treatments are considered for essential tremor (ET) when patients do not respond to oral pharmacological therapies. These treatments mainly comprise radiofrequency (RF) thalamotomy, gamma knife radiosurgery (GKRS), deep brain stimulation (DBS), and focused ultrasound (FUS) procedures.

AREAS COVERED

We reviewed the strengths and weaknesses of each procedure and clinical outcomes for 7 RF studies (n = 85), 11 GKRS (n = 477), 33 DBS (n = 1061), and 13 FUS studies (n = 368). A formal comparison was not possible given the heterogeneity in studies. Improvements were about 42%-90% RF, 10%-79% GKRS, 45%-83% DBS, 42%-83% FUS at short-term follow-up (<12 months) and were about 54%-82% RF, 11%-84% GKRS, 18%-92% DBS, and 42%-80% FUS at long-term follow-up (>12 months).

EXPERT OPINION

We found DBS with inherent advantages of being an adjustable and reversible procedure as the most frequently employed surgical procedure for control of ET symptoms. FUS is a promising procedure but has limited applicability for unilateral control of symptoms. RF is invasive, and GKRS has unpredictable delayed effects. Each of these surgical modalities has advantages and limitations that need consideration when selecting a treatment for the ET patients.

Estimation of technical treatment accuracy in fractionated stereotactic radiosurgery

Aim:

The purpose of this study was to estimate technical treatment accuracy in fractionated stereotactic radiosurgery (fSRS) using the Extend™ system (ES) of Gamma Knife (GK).

Methods and materials:

The fSRS with GK relies on a re-locatable ES where the reference treatment position is estimated using repositioning check tool (RCT). A patient surveillance unit (PSU) monitors the head and neck movement of the patient during treatment and imaging. The quality assurance test of RCT was performed to evaluate a standard error (SE) associated with a measurement tool called digital probe. A ‘4-mm collimator shot’ dose plan for a head–neck phantom was investigated using EBT3 films. CT and MR distortion measurement studies were combined to evaluate SEimaging. The combined uncertainty from all measurements was evaluated using statistical methods, and the resultant treatment accuracy was investigated for the ES.

Results:

Four sets of RCT measurements and 20 observations of associated digital probe showed SERCT of ±0·0186 mm and SEdigital probe of ±0·0002 mm. The mean positional shift of 0·2752 mm (σ = 0·0696 mm) was observed for 20 treatment settings of the phantom. The differences between radiological and predefined isocentres were 0·4650 and 0·4270 mm for two independent experiments. SEimaging and SEdiode  tool were evaluated as ±0·1055 and ±0·0096 mm, respectively. An expanded uncertainty of ±0·2371 mm (at 95% confidence level) was observed with our system.

Conclusions:

The combined result of the positional shift and expanded uncertainty showed close agreement with film investigations.

Gamma Knife radiosurgery: Scenarios and support for re-irradiation

Stereotactic radiosurgery (SRS) involves the focal delivery of large, cytotoxic doses of radiation to small targets within the brain, often located in close proximity to radiosensitive normal tissue structures and requiring very low procedural uncertainties to perform safely. Historically, neurosurgeons considered SRS as a one-time, single session procedure. However therapeutic advances and a better understanding of the clinical response to SRS have caused a renewal of interest in a variety of re-irradiation scenarios; including re-irradiation of the same target after prior SRS, SRS treatments after prior broad-field radiation, hypofractionated treatments, and volume-staged treatments. Re-irradiation may in some cases require even greater effort towards minimizing treatment uncertainties as compared to one-time-only treatments. Gamma Knife radiosurgery (GKRS) has evolved over time in ways that directly supports many re-irradiation scenarios while helping to minimize overall procedural uncertainty.

Tailored Treatment Options for Patients with Brain Metastases by a Relocatable Frame System with Gamma Knife Radiosurgery

OBJECTIVE

To report on our experience with the Elekta Extend system, a relocatable frame system used in patients with brain metastases for single-session, hypofractionated, or staged hypofractionated Gamma Knife radiosurgery (GKRS); and the evaluation of its efficacy.

METHODS

From March 2014 to September 2016, 856 patients with brain metastases underwent GKRS at our hospital. Of them, 35 patients who were retrospectively investigated, were selected for treatment with GKRS using the relocatable frame system. Individualized treatment strategy was chosen according to prior treatment history, number, size and location of tumor, or tumor harboring gene mutation.

RESULTS

Thirty-two (91.4%) patients underwent treatment with hypofractionated GKRS or staged hypofractionated GKRS, whereas 3 (8.6%) patients underwent single session GKRS. The mean radial setup difference from the reference measurements was 0.50 ± 0.16 mm. The median follow-up time after GKRS with the Extend system was 12 months (range, 1-45 months). The median overall survival time was 12 months (95% confidence interval 6.43-17.57). On multivariable analysis, performance status and extracranial metastases were independently prognostic factors for overall survival. Radiation necrosis developed in 4 cases (11.4%) during the follow-up period (2 with common terminology criteria for adverse events grade 2 and 2 with its grade 3).

CONCLUSIONS

The relocatable frame system can maintain submillimetric accuracy and provide tailored treatment option with reasonable tumor control and good survival benefits in selected patients with brain metastases. Especially, hypofractionated GKRS or staged hypofractionated GKRS with noninvasive frame is a safe and effective treatment option for large brain metastases or tumor adjacent to eloquent structures.

Monitoring frequency of intra-fraction patient motion using the ExacTrac system for LINAC-based SRS treatments

Purpose

The aim of this study was to investigate the intra‐fractional patient motion using the ExacTrac system in LINAC‐based stereotactic radiosurgery (SRS).

Method

A retrospective analysis of 104 SRS patients with kilovoltage image‐guided setup (Brainlab ExacTrac) data was performed. Each patient was imaged pre‐treatment, and at two time points during treatment (1st and 2nd mid‐treatment), and bony anatomy of the skull was used to establish setup error at each time point. The datasets included the translational and rotational setup error, as well as the time period between image acquisitions. After each image acquisition, the patient was repositioned using the calculated shift to correct the setup error. Only translational errors were corrected due to the absence of a 6D treatment table. Setup time and directional shift values were analyzed to determine correlation between shift magnitudes as well as time between acquisitions.

Results

The average magnitude translation was 0.64 ± 0.59 mm, 0.79 ± 0.45 mm, and 0.65 ± 0.35 mm for the pre‐treatment, 1st mid‐treatment, and 2nd mid‐treatment imaging time points. The average time from pre‐treatment image acquisition to 1st mid‐treatment image acquisition was 7.98 ± 0.45 min, from 1st to 2nd mid‐treatment image was 4.87 ± 1.96 min. The greatest translation was 3.64 mm, occurring in the pre‐treatment image. No patient had a 1st or 2nd mid‐treatment image with greater than 2 mm magnitude shifts.

Conclusion

There was no correlation between patient motion over time, in direction or magnitude, and duration of treatment. The imaging frequency could be reduced to decrease imaging dose and treatment time without significant changes in patient position.

Clinical Positioning Accuracy for Multisession Stereotactic Radiotherapy With the Gamma Knife Perfexion

Multisession stereotactic radiation therapy is increasingly being seen as a preferred option for intracranial diseases in close proximity to critical structures and for larger target volumes. The objective of this study is to investigate the reproducibility of the Extend system from Elekta. A retrospective review was conducted for all patients treated with multisession Gamma Knife between July 2010 and June 2015, including both malignant and benign lesions. Eighty-four patients were treated in this 5-year span. The average residual daily setup uncertainty was 0.48 (0.19) mm. We compare measurements of setup uncertainty from the Extend system to measurements performed with a linac-based approach previously used in our center. The Extend system has significantly reduced setup uncertainty for fractionated intracranial treatments at our institution. Positive results were observed in a small population of edentulous patients. The Extend system compares favorably with other approaches to delivering intracranial stereotactic radiotherapy and is a robust, simple-to-use, and precise method for treating multisession intracranial lesions.