Radiation Protection and Occupational Exposure on 68Ga-PSMA-11-Based Cerenkov Luminescence Imaging Procedures in Robot-Assisted Prostatectomy

Abstract

Cerenkov luminescence imaging (CLI) was successfully implemented in the intraoperative context as a form of radioguided cancer surgery, showing promise in the detection of surgical margins during robot-assisted radical prostatectomy. The present study was designed to provide a quantitative description of the occupational radiation exposure of surgery and histopathology personnel from CLI-guided robot-assisted radical prostatectomy after the injection of ⁶⁸Ga-PSMA-11 in a single-injection PET/CT CLI protocol. Methods: Ten patients with preoperative ⁶⁸Ga-PSMA-11 administration and intraoperative CLI were included. Patient dose rate was measured before PET/CT (n = 10) and after PET/CT (n = 5) at a 1-m distance for 4 patient regions (head [A], right side [B], left side [C], and feet [D]). Electronic personal dosimetry (EPD) was used for intraoperative occupational exposure (n = 10). Measurements included the first surgical assistant and scrub nurse at the operating table and the CLI imager/surgeon at the robotic console and encompassed the whole duration of surgery and CLI image acquisition. An estimation of the exposure of histopathology personnel was performed by measuring prostate specimens (n = 8) with a germanium detector. Results: The measured dose rate value before PET/CT was 5.3 ± 0.9 (average ± SD) μSv/h. This value corresponds to a patient-specific dose rate constant for positions B and C of 0.047 μSv/h⋅MBq. The average dose rate value after PET/CT was 1.04 ± 1.00 μSv/h. The patient-specific dose rate constant values corresponding to regions A to D were 0.011, 0.026, 0.024, and 0.003 μSv/h⋅MBq, respectively. EPD readings revealed average personal equivalent doses of 9.0 ± 7.1, 3.3 ± 3.9, and 0.7 ± 0.7 μSv for the first surgical assistant, scrub nurse, and CLI imager/surgeon, respectively. The median germanium detector-measured activity of the prostate specimen was 2.96 kBq (interquartile range, 2.23-7.65 kBq). Conclusion: Single-injection ⁶⁸Ga-PSMA-11 PET/CT CLI procedures are associated with a reasonable occupational exposure level, if kept under 110 procedures per year. Excised prostate specimen radionuclide content was below the exemption level for ⁶⁸Ga. Dose rate-based calculations provide a robust estimation for EPD measurements.

Keywords: Cerenkov luminescence imaging; margin assessment; prostate cancer; radical prostatectomy; radioguided surgery.

Graphical abstract

FIGURE 1.

One-stop-shop protocol, including tracer administration (A), PET/CT imaging (B), and CLI during prostatectomy (C–E), permitted by remainder of ⁶⁸Ga-PSMA-11 uptake in prostate. Temporal sequence (black arrow) shows median time points after injection (p.i.) and decay-corrected whole-body activity expected for each step of protocol.

FIGURE 2.

Setup in operating theater and respective distances used for calculated personal equivalent doses based on patient-specific dose rate constants.

FIGURE 3.

Dose rate measurements at predefined positions (Pos.) (A) and respective linear regression lines (B). Positions are as follows: A = at head; B = right side; C = left side; D = at feet. Post-PET/CT = dose rate readings immediately before entering operating room; Pre-PET/CT = measurements immediately after tracer injection.

FIGURE 4.

EPD measurements (black bars) alongside computed values based on point source (PS) model (medium gray bars) at measured distance r. Variations of minus −10 cm (dark gray bars) and +10 cm (light gray bars) from distance r using PS assumption are shown.

FIGURE 5.

Activity quantification of excised prostate specimens decay corrected to time of excision. Black bars represent PET-based quantification (median, 3.83 kBq; IQR, 2.83–8.50 kBq). Gray bars represent HPGe measurement (GeDet) (median, 2.96 kBq; IQR, 2.23–7.65 kBq).