In Vivo Laser Light Distribution in Human Prostatic Carcinoma

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Abstract
The extent of laser light diffusion within prostatic tumor is of major importance in the treatment of localized prostatic cancer with photodynamic therapy (PDT). The penetration of 633 nm. wavelength red light was studied in eleven patients with suspected prostatic cancer using a novel method suitable for in situ measurements. Light delivery and detector fiber, placed interstitially within the gland, determined light attenuation at different interfiber separations. Of 11 patients, 10 had bilateral and 1 had single lobe studies. The mean +/- the standard error of the mean attenuation coefficients (sigma eff) for benign and malignant prostate tissue were 0.35 +/- 0.02 mm-1 and 0.36 +/- 0.02 mm-1, respectively, indicating similar optical densities (p = .58). Patients with bilateral lobe involvement showed little intraglandular variation in sigma eff (p = 0.23). However, there was interpatient variation (sigma eff = 0.28 to 0.48 mm-1) reflecting biological differences which, though therapeutically important, were not statistically significant (p = 0.057). This study showed that treatment requires individualization and predicted that 4 cylindrical diffusers are expected to destroy 25 ml. of prostatic tumor with PDT.