A tissue-mimicking prostate phantom for 980 nm laser interstitial thermal therapy

R Geoghegan,A Santamaria,A Priester,L Zhang,H Wu,W Grundfest,L Marks,S Natarajan

doi:10.1080/02656736.2019.1660811

R Geoghegan, A Santamaria + Show 6 more

Open Access

https://doi.org/10.1080/02656736.2019.1660811

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Abstract

Purpose: To develop a phantom with optical and thermal properties matched to human prostate. This phantom will provide a platform for the development and characterization of 980 nm laser interstitial thermal therapy (LITT) systems.Methods: A polyacrylamide gel was doped with Naphthol Green B, Intralipid, and Bovine Serum Albumin (BSA). The necessary concentration of each ingredient was determined by measuring the optical properties via fluence measurements and light diffusion theory. LITT was then performed under the same conditions as a previous clinical trial in which temperature was monitored via a thermal probe. The thermal data and induced coagulation zone were compared to clinical data to illustrate the similarity between the phantom and patient. LITT was also performed under magnetic resonance thermometry (MRT).Results: The requisite concentrations of Naphthol Green B, Intralipid and BSA were found to be 0.144% (w/v), 8.06% (v/v) and 31.4% (v/v) respectively. In the native state, the absorption coefficient and reduced scattering coefficient () were found to be 0.66 ± 0.06 cm−1 and 8.27 ± 0.50 cm−1 respectively, with increasing to 17.63 ± 1.41 cm−1 after coagulation. The thermal response of the phantom was similar to that observed clinically with maximum thermal probe measurements of 64.2 °C and 66.9 °C respectively. The shape of the induced coagulation zone was qualitatively and quantitatively similar to the MRT zone of elevated temperature and the coagulation zone observed clinically.Conclusions: A phantom which simulates optical and thermal response to 980 nm LITT was constructed and demonstrated to be similar to human prostate.

Highlights

Laser interstitial thermal therapy (LITT), known as focal laser ablation (FLA), has been demonstrated to be a promising method of focal therapy for prostate cancer [1–4]
The optical properties of these models may not be sufficiently similar to human prostate and the experimental approach is complicated by their biohazardous nature
In contrast to Iizuka et al, we utilized a polyacrylamide gel doped with Bovine Serum Albumin (BSA) to ensure that the coagulation temperature can be adjusted using the pH method demonstrated by McDonald et al We demonstrate that the thermal response of the phantom can be measured via interstitial thermal probes and magnetic resonance thermometry (MRT)

Summary

Introduction

Laser interstitial thermal therapy (LITT), known as focal laser ablation (FLA), has been demonstrated to be a promising method of focal therapy for prostate cancer [1–4]. The induced zone of coagulative necrosis is primarily dependent on laser power, exposure duration and device characteristics such as diffuser length. Understanding the effect of these parameters on the resulting damage zone is critical for clinical success. Prior work investigating thermal response has relied on animal models [5–7] and cadaveric prostate [8]. Such models are heterogeneous across specimens, resulting in the requirement for a large number of samples to accurately assess laser-tissue interaction. The zone of thermal necrosis is difficult to quantify and requires histologic analysis. There is a need to develop a tissue-mimicking phantom to provide a standardized, controllable model for investigations of both the optical and thermal response of prostatic tissue to 980nm LITT

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Conclusion