Dynamic modeling of interstitial laser photocoagulation: Implications for lesion formation in liver in vivo

Abstract

Background and Objective Interstitial Laser Photocoagulation (ILP) is a minimally invasive cancer treatment technique, whereby optical energy from implanted optical fibers is used to therapeutically heat small, solid tumors. In this work, the potential of ILP without tissue charring is investigated. Study Design/Materials and Methods Optical diffusion and bioheat transfer equations were used to develop dynamic models of interstitial laser heating in liver in vivo. Modifications in the optical properties due to tissue coagulation (T ⩾ 60°C) were incorporated into the physical description. In addition, the effect of three different blood perfusion patterns on temperature distributions was explored. Model‐predicted temperatures were used as an index for thermal damage based on an accumulated temperature injury (Arrhenius) model. Thermal damage dimensions were determined with tissue temperatures constrained to remain below 100°C, so as to minimize the potential for tissue charring and smoke production. Results The model predicts that increases in scattering due to coagulation and choice of perfusion pattern affect substantially thermal damage dimensions. The results indicate that, for single fiber ILP at 2.55 W for 600 s, the maximum achievable thermal damage diameter in liver, without charring, is 9.6 mm. In addition, ILP performed with high‐low power ramping may have an advantage over constant power treatments, in that, larger volumes of thermal damage can be realized earlier in an irradiation. Conclusions For ILP performed with a single spherical emitting fiber, optimal irradiation parameters exist such that thermal lesions in liver up to approximately 10 mm in diameter can be induced while the maximum tissue temperature remains below 100°C, avoiding tissue charring. Lasers Surg. Med. 24:202–208, 1999. © 1999 Wiley‐Liss, Inc.

Considerations for Thermal Injury Analysis for RF Ablation Devices

“…Several investigators have noted that for each degree increase above 43°C in temperature, there is approximately a two-fold decrease in the time required to achieve the same biological effect [28][29][30][31][32][33]. The equivalent time for each second of exposure to temperatures greater than 43°C is calculated by the isoeffect equation [33]: t exp = t critical * 2 (T exp 43) Eq. 1 where T exp and t exp represent the tissue exposure temperature (in Celsius) and time, respectively.…”

“…For a specified exposure temperature and time, the Arrhenius fit parameters determine the probability of cell damage. Arrhenius parameters have been determined in several body tissues, including the liver at high temperatures [31][32][33]38]. In the majority of studies, temperature and tissue injury profiles are calculated sequentially, meaning that Arrhenius calculations are not made until temperature calculations are completed [29][30].…”

MR thermometry‐based feedback control of laser interstitial thermal therapy at 980 nm

“…A number of previous studies have explored the use of 1,064-nm Nd:YAG and 810-nm diode lasers for LITT [1,[19][20][21]. At these wavelengths, water (which is a major component of tissue) exhibits an absorption coefficient of 0.144 cm À1 and 0.0219 cm À1 , respectively [22], and therapies may last up to 30 minutes in some cases [10,13,23,24].…”

Performance evaluation of cylindrical fiber optic light diffusers for biomedical applications

“…The beam from the diode laser (1) was coupled into the fiber via a micro-objective lens (2) overfilling the numerical aperture of the fiber [13]. The Newport optical power meter with a silicon detector head (3) was employed for optical radiation measurement.…”

“…Cylindrical light diffusers coupled to an optical fiber are commonly used in photodynamic therapy [1], interstitial photocoagulation [2], and interstitial hyperthermia [3]. Although there have been numerous publications on fiber diffuser evaluation and applications [4][5][6], a common standard for the photometric evaluation of the diffuser's emission characteristics is not available, making comparisons between products, and evaluating their suitability for a given treatment difficult.…”