Reproducibility of a novel, vacuum-assisted immobilization for breast stereotactic radiotherapy

Multi-angle acquisition and 3D composite reconstruction for organ-targeted PET using planar detectors

BACKGROUND

This study investigates a multi-angle acquisition method aimed at improving image quality in organ-targeted PET detectors with planar detector heads. Organ-targeted PET technologies have emerged to address limitations of conventional whole-body PET/CT systems, such as restricted axial field-of-view (AFOV), limited spatial resolution, and high radiation exposure associated with PET procedures. The AFOV in organ-targeted PET can be adjusted to the organ of interest, minimizing unwanted signals from other parts of the body, thus improving signal collection efficiency and reducing the dose of administered radiotracer. However, while planar detector PET technology allows for quasi-3D image reconstruction due to the separation between detector heads, it suffers from degraded axial spatial resolution and, consequently, reduced recovery coefficients (RCs) along the axial direction perpendicular to the detectors.

PURPOSE

The purpose of this study was to evaluate the concept of multi-angle image acquisition with two planar PET detectors and composite full 3D image reconstruction. This leverages data collection from multiple polar angles to improve the axial spatial resolution in the direction perpendicular to the detector heads. In such, the concept allows to overcome the intrinsic limitations of planar detectors in axial resolution.

METHODS

This study evaluates the improvement in the quality of images acquired with the Radialis organ-targeted PET camera through multi-angle image acquisition, in both experimental and simulated imaging scenarios. This includes the use of custom-made phantom with fillable spherical hot inserts, the NEMA NU4-2008 image quality (IQ) phantom, and simulations with a digital brain phantom. The analysis involves the comparison of line profiles drawn through the spherical hot inserts, image uniformity, RCs, and the reduction of smearing observed in the axial planes with and without the multi-angle acquisition strategy.

RESULTS

Significant improvements were observed in reducing smearing, enhancing image uniformity, and increasing RCs using the evaluated multi-angle acquisition method. In the composite images, the hot spheres appear more symmetrical in all planes. The image uniformity, calculated from the IQ phantom, improves from 7.79% and 10.98%, as measured in the images from the individual acquisitions, to 2.72% in the composite image. There is also an overall improvement in the RCs as measured from the hot rods of the IQ phantom. Furthermore, the simulation study using the digital human brain phantom demonstrates minimal smearing in the four-angle scan, as opposed to a two-angle scan.

CONCLUSION

The multi-angle acquisition method offers a promising approach to transform planar PET detector technology into a true tomographic organ-targeted PET system and to enable improvement in image quality while preserving a versatility inherent to planar detector technology. Future research will focus on optimizing the multi-angle imaging protocol, including adjustments to detector separations, number of acquisition angles, and reconstruction iterations, alongside incorporating TOF, and reconstruction with point spread function modeling to further improve image quality.

A Prospective Trial of Single-Fraction Radiation to the Tumor Bed with a Novel Breast-Specific Stereotactic Radiation Therapy Device: The GammaPod

Purpose

Radiation therapy for early-stage breast cancer is typically delivered in a hypofractionated regimen to the whole breast followed by a tumor bed boost. This results in a treatment course of approximately 4 weeks. In this study, the tumor bed boost was delivered in a single fraction as part of a safety and feasibility study for FDA clearance of the device.

Methods and Materials

Eligible women with early-stage breast cancer underwent lumpectomy followed by radiation therapy. Patients underwent breast immobilization using a system specific to the GammaPod followed by CT simulation, boost treatment planning, and boost treatment delivery all in a single treatment day. Patients then started whole-breast radiation therapy within 1 week of the boost treatment. Patients and treatments were assessed for safety and feasibility. Acute toxicities were recorded.

Results

A single-fraction boost of 8 Gy was delivered to the tumor bed before a course of whole-breast radiation. The GammaPod treatment was successfully delivered to 14 of 17 enrolled patients. Acute toxicities from all radiation therapy, inclusive of the boost and whole-breast radiation, were limited to grade 1 events.

Conclusions

The GammaPod device successfully delivered a single-fraction boost treatment to the tumor bed with no change in expected acute toxicities. The results of this study led to FDA clearance of the device through the Investigational Device Exemption process at the FDA. The GammaPod is in clinical use at 4e institutions nationally and internationally, with additional sites pending in 2023.

Correlation of treatment time to target volume for GammaPod treatments: A simple second calculation

Purpose

The GammaPod is a novel device for stereotactic breast treatments that employs 25 rotating Co‐60 sources while the patient is continuously translated in three axes to deliver a highly conformal dose to the target. There is no commercial software available for independent second calculations. The purpose of this study is to determine an efficient way to estimate GammaPod treatment times based on target volume and use it as a second calculation for patient‐specific quality assurance.

Methods

Fifty‐nine GammaPod (Xcision Medical Systems, LLC.) breast cancer patient treatments were used as the fitting dataset for this study. Similar to the Curie‐seconds concept in brachytherapy, we considered dose‐rate × time/(prescribed dose) as a function of target volumes. Using a MATLAB (Mathworks, Natick, MA, USA) script, we generated linear (with 95% confidence interval (CI)) and quadratic fits and tested the resulting equations on an additional set of 30 patients.

Results

We found a strong correlation between the dose‐rate × time/(prescribed dose) and patients’ target volumes for both the linear and quadratic models. The linear fit was selected for use and using the polyval function in MATLAB, a 95% CI graph was created to depict the accuracy of the prediction for treatment times. Testing the model on 30 additional patients with target volumes ranging from 20 to 188 cc yielded treatment times from 10 to 25 min that in all cases were within the predicted CI. The average absolute difference between the predicted and actual treatment times was 1.0 min (range 0–3.3 min). The average percent difference was 5.8% (range 0%–18.4%).

Conclusion

This work has resulted in a viable independent calculation for GammaPod treatment times. This method has been implemented as a spreadsheet that is ready for clinical use to predict and verify the accuracy of breast cancer treatment times.