Abstract
.Sapphire capillary needles fabricated by edge-defined film-fed growth (EFG) technique hold strong potential in laser thermotherapy and photodynamic therapy, thanks to the advanced physical properties of sapphire. These needles feature an as-grown optical quality, their length is tens of centimeters, and they contain internal capillary channels, with open or closed ends. They can serve as optically transparent bearing elements with optical fibers introduced into their capillary channels in order to deliver laser radiation to biological tissues for therapeutic and, in some cases, diagnostic purposes. A potential advantage of the EFG-grown sapphire needles is associated with an ability to form the tip of a needle with complex geometry, either as-grown or mechanically treated, aimed at controlling the output radiation pattern. In order to examine a potential of the radiation pattern shaping, we present a set of fabricated sapphire needles with different tips. We studied the radiation patterns formed at the output of these needles using a He–Ne laser as a light source, and used intralipid-based tissue phantoms to proof the concept experimentally and the Monte-Carlo modeling to proof it numerically. The observed results demonstrate a good agreement between the numerical and experimental data and reveal an ability to control within wide limits the direction of tissue exposure to light and the amount of exposed tissue by managing the sapphire needle tip geometry.
Highlights
Laser radiation is widely applied in medical treatments,[1,2,3] in photodynamic therapy (PDT) and laser thermal therapy (LTT), for achieving photochemical and photothermal effects in tissues aimed at destruction of malignant and benign neoplasms.[4,5]
In order to examine a potential of various geometries of the sapphire needle tip for shaping the output radiation pattern, in this paper, we present a set of fabricated needles featuring either as-grown or mechanically treated tips of different shapes, including conical, hypoand hyper-hemispherical, parabolic, and drop-like ones
We have studied the potential of the sapphire capillary needles grown by the edge-defined film-fed growth (EFG) technique to form different radiation patterns by changing their tip geometry
Summary
Laser radiation is widely applied in medical treatments,[1,2,3] in photodynamic therapy (PDT) and laser thermal therapy (LTT), for achieving photochemical and photothermal effects in tissues aimed at destruction of malignant and benign neoplasms.[4,5] The general mechanism of PDT is a laser-radiation-induced activation of photosensitizers—i.e., special drugs introduced into patient’s body and accumulated in pathological tissues. PDT is extensively applied for cancer treatment,[9,10,11,12,13] whereas LTT provides treatment of varicose vein,[14] lipolysis,[15] epilepsy,[16] as well as cancers of the skin,[8] pancreas,[17] liver,[18] prostate,[19] lung,[20] breast,[21] and brain.[22,23,24] Both PDT and LTT admit interstitial application, turning into interstitial photodynamic therapy (I-PDT)[25,26,27] and laser interstitial thermal therapy (LITT),[28,29,30] aimed to deliver laser radiation directly to the internal region of interest (ROI) without an extensional surgical incision, using optical fibers.[2,6,31] A common technique for light delivery implies introduction of an optical fiber (or a bundle of fibers) into tissues via application of entirely or partly transparent needles or catheters, which are usually removed in order to ensure a direct contact between a fiber and a tissue for increased photochemical and photothermal effects.[2] In some cases, fiber can be protected from interaction with aggressive biological environments, as well as from overheating by special caps or domes.[15,32] Such protectors often enable circulation of a liquid coolant,[20,33,34] but complicate the instrument as well. This justifies a bright future of sapphire capillary needles in the laser therapy technologies
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