title: Models and measurements of light intensity changes during laser interstitial thermal therapy: implications for optical monitoring of the coagulation boundary location.
abstract: We have developed a multi-region spherical Monte Carlo (MC) model to simulate the dynamic changes in light intensity measured during laser interstitial thermal therapy (LITT). Model predictions were validated experimentally in tissue-simulating albumen phantoms with well-characterized optical properties that vary dynamically with LITT in a way similar to tissue. For long treatments (2.5 W, approximately 1800 s), the transient light intensity changes demonstrated better qualitative agreement with a three-region MC model (with an inner layer of fully coagulated optical properties, a middle layer of partially coagulated properties and an outer region of native properties); for short treatments (4 W, approximately 240 s), better qualitative agreement was seen with a two-region MC model (with an inner layer of fully coagulated properties and outer region of native properties). These differences were attributed to differences in coagulation formation during low- and high-powered heating regimes, respectively. At the end of heating, a three-region coagulation zone was observed for both heating schemes. Quantitatively, final light intensity changes at the end of heating were compared with changes predicted by both two- and three-region MC for the same experimentally measured coagulation size and found to agree within approximately 30% for both models. The developed MC model helps lend insight into the nature of thermal coagulation events occurring for low and high power LITT irradiation schemes.
authors.affiliation: Medical Physics Division, Ontario Cancer Institute/Princess Margaret Hospital, University Health Network, University of Toronto, 610 University Avenue, Toronto, Ontario, Canada M5G 2M9.
authors.forename: Lee C L
authors.initials: LC
authors.lastname: Chin
authors.forename: William M
authors.initials: WM
authors.lastname: Whelan
authors.forename: I Alex
authors.initials: IA
authors.lastname: Vitkin
mesh_terms: D004307:Dose-Response Relationship, Radiation; D017075:Laser Coagulation / Q000379:methods*; D053685:Laser Therapy; D008954:Models, Biological; D016343:Monitoring, Intraoperative / Q000379:methods*; D019047:Phantoms, Imaging; D010783:Photometry / Q000379:methods; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D012709:Serum Albumin / Q000528:radiation effects*; D000075462:Serum Albumin, Human; D025321:Surgery, Computer-Assisted / Q000379:methods*
chemical_list: D012709:Serum Albumin; C402606:albumin Amsterdam; D000075462:Serum Albumin, Human