The CivaSheet: The new frontier of intraoperative radiation therapy or a pricier alternative to LDR brachytherapy?

Feasibility Study for Controlled Radiation Capsule for High Source Activity for Low Dose Radiation Brachytherapy

In this paper, we propose a new radiation capsule design to enable a high dose rate for a low energy radiation source Iodine-125, conventionally used for low dose radiation (LDR) brachytherapy to lower the radiation risk and reduce the treatment duration for cancer treatment. Conventional LDR has a dose rate of less than 2 Gy/day. The proposed capsule enables a high dose rate of 10 Gy/min or higher due to the ability to control the stoppage of the radiation. The release and stoppage of the radiation from the capsule is conducted by using an electromagnet that repels a permanent magnet, which controls the opening and closing of the window in the capsule. For feasibility of the new capsule design, simulations were conducted using TOPAS, which wraps and extends Geant4 simulation toolkit to make advanced Monte Carlo simulation of radiotherapy. Simulation results show that a 150-micron gold shielding blocks the radiation for a very high source activity of I-125. MATLAB is used to display the TOPAS results to compare the radiation intensity and beamwidth between a conventional LDR seed, the proposed capsule with a small 15 degree opening and a larger 120 degree opening.

Clinical outcomes in borderline and locally advanced pancreatic cancer with the addition of low-dose-rate brachytherapy to standard of care therapy

PURPOSE

Surgical resection remains the only curative therapy for pancreatic cancer. Unfortunately, many patients have borderline or unresectable disease at diagnosis due to proximity of major abdominal vessels. Neoadjuvant chemotherapy and radiation are used to down-stage, however, there is a risk that there will be a positive/close surgical margin. The CivaSheet is a low-dose-rate (LDR) brachytherapy device placed at the time of surgery to target the area of highest risk of margin positivity. The purpose of this study is to assess the clinical value of brachytherapy in addition to standard-of-care therapy in pancreatic therapy.

METHODS AND MATERIALS

Between 2017 and 2022 patients with borderline and locally advanced pancreatic cancer treated with neoadjuvant chemotherapy and radiation followed by surgical resection were included. There were 2 cohorts of patients: (1) Those who had the LDR brachytherapy device placed at the time of surgery and (2) those who did not. Sixteen of 19 (84%) patients who had brachytherapy were enrolled in a prospective clinical trial (NCT02843945). Patients were matched for comorbidities, cancer staging, and treatment details. The primary outcome was progression-free survival (PFS).

RESULTS

Thirty-five patients were included in this analysis, 19 in the LDR brachytherapy group and 16 in the comparison cohort. The 2-year PFS was 21% vs. 0% (p = 0.11), 2-year OS was 26% vs. 13% (p = 0.43), and the pancreatic cancer cause-specific survival was 84% vs. 56% (p = 0.13) in favor of the brachytherapy patients.

CONCLUSIONS

Use of LDR brachytherapy at the time of resection shows a trend towards improved progression free and overall survival for patients with borderline or locally advanced pancreatic cancer treated with neoadjuvant chemoradiation.

CivaSheet® use for soft tissue sarcoma: A single institution experience

OBJECTIVE

CivaSheet is a palladium-103, implantable, intraoperative radiation therapy device which emits unidirectional radiation that enables boost doses in patients who have otherwise received the maximum radiation dose. Here, we present our initial clinical experience with the first 10 cases using this new technology.

METHODS AND MATERIALS

A retrospective chart review of all patients with STS treated with surgical resection and CivaSheet placement at the University of Miami Hospital, a tertiary care center, from January 2018 to December 2019, was performed. Adjuvant radiation was administered by a palladium-103 implant, which delivered an average of 47 Gy (35-55) to a depth of 5 mm.

RESULTS

Nine patients underwent CivaSheet placement from January 2018 until December 2019 for a total of 10 CivaSheets placed (1 patient had 2 CivaSheets inserted) and followed for a mean of 27 months (4-45 months). Four tumors were located in the retroperitoneum, two in the chest, two in the groin, and two within the lower extremity. At the time of tumor resection and CivaSheet placement, tumor sizes ranged from 2.5 cm to 13.8 cm with an average of 7.6 cm. Four patients necessitated musculocutaneous tissue flaps for closure and reconstruction. All patients with Grade 4 complications had flap reconstruction and prior radiation. Four patients' tumors recurred locally for a local recurrence rate of 40%. Three patients had modified accordion Grade 4 complications necessitating additional surgery for CivaSheet removal. Extremity tumors unanimously developed modified accordion Grade 4 adverse events.

CONCLUSIONS

CivaSheet may be an acceptable alternative treatment modality compared to prior brachytherapy methods.

Intensity Modulated High Dose Rate (HDR) Brachytherapy Using Patient Specific 3D Metal Printed Applicators: Proof of Concept

Purpose

In high-dose-rate (HDR) brachytherapy, an anisotropic dose distribution may be desirable for achieving a higher therapeutic index, particularly when the anatomy imposes challenges. Several methods to deliver intensity-modulated brachytherapy (IMBT) have been proposed in the literature, however practical implementation is lacking due to issues of increased delivery times and complicated delivery mechanisms. This study presents the novel approach of designing a patient-specific inner shape of an applicator with 3D metal printing for IMBT using an inverse plan optimization model.

Methods

The 3D printed patient-specific HDR applicator has an external shape that resembles the conventional brachytherapy applicator. However, at each dwell position of the HDR source, the shielding walls in the interior are divided into six equiangular sections with varying thicknesses. We developed a mathematical model to simultaneously optimize the shielding thicknesses and dwell times according to the patient’s anatomical information to achieve the best possible target coverage. The model, which is a bi-convex optimization problem, is solved using alternating minimization. Finally, the applicator design parameters were input into 3D modeling software and saved in a 3D printable file. The applicator has been tested with both a digital phantom and a simulated clinical cervical cancer patient.

Results

The proposed approach showed substantial improvements in the target coverage over the conventional method. For the phantom case, 99.18% of the target was covered by the prescribed dose using the proposed method, compared to only 58.32% coverage achieved by the conventional method. For the clinical case, the proposed method increased the coverage of the target from 56.21% to 99.92%. In each case, both methods satisfied the treatment constraints for neighboring OARs.

Conclusion

The study simulates the concept of the IMBT with inverse planning using the 3D printed applicator design. The non-isotropic dose map can be produced with optimized shielding patterns and tailored to individual patient’s anatomy, to plan a more conformal plan.

Initial Clinical Experience With Novel Directional Low-dose Rate Brachytherapy for Retroperitoneal Sarcoma

BACKGROUND

A novel Palladium-103 low-dose rate (LDR) brachytherapy device was developed to provide dose-escalation to the tumor bed after resection while shielding adjacent tissues. This multicenter report describes the initial experience with this device in patients with retroperitoneal sarcoma (RPS).

MATERIALS AND METHODS

Patients with recurrent RPS, prior radiotherapy, and/or concern for positive margins were considered. An LDR brachytherapy dose of 20-60 Gy was administered, corresponding to biologically effective dose values of 15-53 Gy and equivalent dose values of 12-43 Gy.

RESULTS

Six patients underwent implantation at four institutions. Of these, five had recurrent disease in the retroperitoneum or pelvic sidewall, one had untreated locally advanced leiomyosarcoma, two had prior external beam radiation therapy at the time of initial diagnosis, and four received neoadjuvant external beam radiation therapy plus brachytherapy. The device was easily implanted and conformed to the treatment area. Median follow-up was 16 mo; radiation was delivered to the at-risk margin with minimal irradiation of adjacent structures. No local recurrences at the site of implantation, device migration, or radiation-related toxicities were observed.

CONCLUSIONS

The novel LDR directional brachytherapy device successfully delivered a targeted dose escalation to treat RPS high-risk margins. Lack of radiation-related toxicity demonstrates its safety.

Algorithmic determination of source orientations for the CivaSheet directional brachytherapy device

PURPOSE

The CivaSheet device uses multiple directionally shielded Pd-103 CivaDot sources to produce a directional planar dose distribution. In postplanning, manually digitizing the 3D source orientation is challenging because the 3D vector must be digitized by using 2D displayed images. The aim of this study is to develop an algorithm that will automatically determine the direction of each CivaDot source based on the location of sources adjacent to it.

METHODS AND MATERIALS

The algorithm determines the source direction by averaging the normal directions of multiple local planes established by the adjacent sources. The algorithm was tested on a manually constructed CivaSheet-like device that was CT scanned in known flat geometries and two known curved geometries. Algorithmically determined source directions were compared with the known directions. The algorithm was also used on a postplan for a gynecological pelvic sidewall tumor bed implant and compared against manual digitization of the source directions.

RESULTS

For the flat and curved test geometries, the average angular difference between the algorithm determined and known orientation was 1.2° ± 0.8° (flat geometry), 1.7° ± 2.1° (curve about vertical axis), and 2.3° ± 2.4° (curve about horizontal axis). For the patient case, results showed on average a 23.1° ± 10.8° difference between the manual digitized orientation and the algorithm's predicted orientation.

CONCLUSIONS

The algorithm calculates the source orientation with accuracy better than 2.3° for the controlled experiments. In addition to its accuracy, the algorithm produces consistent results and lessens the difficult challenge of orienting the partially shielded sources.