Transurethral Photoacoustic Endoscopy for Prostate Cancer: A Simulation Study

Abstract

The purpose of this study was to optimize the configuration of a photoacoustic endoscope (PAE) for prostate cancer detection and therapy monitoring. The placement of optical fiber bundles and ultrasound detectors was chosen to maximize the photoacoustic imaging penetration depth. We performed both theoretical calculations and simulations of this optimized PAE configuration on a prostate-sized phantom containing tumor and various photosensitizer concentrations. The optimized configuration of PAE with transurethral light delivery simultaneously increases the imaging penetration depth and improves image quality. Thermal safety, investigated via COMSOL Multiphysics, shows that there is only a 4 mK temperature rise in the urethra during photoacoustic imaging, which will cause no thermal damage. One application of this PAE has been demonstrated for quasi-quantifying photosensitizer concentrations during photodynamic therapy. The sensitivity of the photoacoustic detection for TOOKAD was 0.18 ng/mg at a 763 nm laser wavelength. Results of this study will greatly enhance the potential of prostate PAE for in vivo monitoring of drug delivery and guidance of the laser-induced therapy for future clinical use.

Photoacoustic imaging of prostate cancer

“…2(d) and 2(h)). In addition, as demonstrated by Tang et al 60 and Peng et al, 59 the prostate is asymmetrically illuminated under transrectal light delivery, which largely favors the detection of tumors located proximal to the rectum. To achieve whole-prostate imaging, a more uniformly distributed illumination is desired.…”

“…1(b)), as well as transurethral light delivery coupled with transrectal US detection. 61 Although transurethral US detection yielded optimal image quality in Monte Carlo simulations performed by Tang et al 60 (Figs. 2(c) and 2(g)) and El-Gohary et al, 55 a transrectal US transducer is more frequently used in urology.…”

“…1(a)), transurethral light delivery and US detection 55,60 ( Fig. 1(b)), as well as transurethral light delivery coupled with transrectal US detection.…”

“…55 The human prostate is located beyond this penetration limit from the skin surface 56 ; therefore, human prostate PAI with an external light source is currently unfeasible. Fortunately, the feasibility of prostate PAI using endoscopic light delivery has been well demonstrated through phantom studies, 57,58 simulation studies, 55,59,60 and animal studies. 57,58 One of the major challenges of human prostate PAI is the delivery of the light source.…”

“…55,59,60 In transrectal light delivery, the light must penetrate through the rectum wall before it reaches the prostate. At the wavelength of 1000 nm, the rectal absorption and scattering coe±cients, a and s , are greater than those in the prostate by factors of 2 and 5, respectively.…”