Characterization of the tissue light penetration in prostate photodynamic therapy (PDT) is important to plan the arrangement and weighting of light sources so that sufficient light fluence is delivered to the treatment volume. The optical properties (absorption [μ a ], transport scattering [ ] and effective attenuation [μ eff ] coefficients) of 13 patients with locally recurrent prostate cancer were measured in situ using interstitial isotropic detectors. Measurements were made at 732 nm before and after motexafin lutetium (MLu)-mediated PDT in four quadrants. Optical properties were derived by applying the diffusion theory to the fluence rates measured at several distances (0.5-5 cm) from a point source. μ a and varied between 0.07 and 1.62 cm −1 (mean 0.37 ± 0.24 cm −1 ) and 1.1 and 44 cm −1 (mean 14 ± 11 cm −1 ), respectively. μ a was proportional to the concentration of MLu measured by an ex vivo fluorescence assay. We have observed, on average, a reduction of the MLu concentration after PDT, presumably due to the PDT consumption of MLu. μ eff varied between 0.91 and 6.7 cm −1 (mean 2.9 ± 0.7 cm −1 ), corresponding to an optical penetration depth (δ = 1/μ eff ) of 0.1-1.1 cm (mean 0.4 ± 0.1 cm). The mean penetration depth at 732 nm in human prostate is at least two times smaller than that found in normal canine prostates, which can be explained by a four times increase of the mean value of in human prostates. The mean light fluence rate per unit source strength at 0.5 cm from a point source was 1.5 ± 1.1 cm −2 , excluding situations when bleeding occurs. The total number of measurements was N = 121 for all mean quantities listed above. This study showed significant inter-and intraprostatic differences in the optical properties, suggesting that a real-time dosimetry measurement and feedback system for monitoring light fluences during treatment should be considered for future PDT studies. ¶ Posted on the website on 9 November 2004.

As an important x-ray source, enhancement of x-ray emissions from laser-produced plasmas is significant for various applications. Due to less expanding kinetic loss, gold foam with low initial density can have an enhanced x-ray conversion efficiency compared with solid-density gold. However, low-Z impurities within gold foam targets will diminish the enhancement remarkably, and should be tightly controlled. This paper presents an experimental study of a high brightness laser plasma soft x-ray source, based on a 0.36 g cm −3 gold foam target with negligible impurities irradiated by nanosecond laser pulses with power density around 3 × 10 14 W cm −2 at the Shenguang II laser facility. A conversion efficiency, from multi-eV to multi-keV, of 51.2% is achieved in the x-ray emissions-about 21% relative enhancement compared with a solid-density gold target, and the highest conversion efficiency for Au foam planar targets yet. Good agreement has been achieved between the semi-analytical model prediction and the experimental results.

The enhancement of laser to x-ray conversion efficiencies using low density gold targets [W. L. Shang, J. M. Yang, and Y. S. Dong, Appl. Phys. Lett. 102, 094105 (2013)] is demonstrated. Laser to x-ray conversion efficiencies with 6.3% and 12% increases are achieved with target densities of 1 and 0.25 g/cm3, when compared with that of a solid gold target (19.3 g/cm3). Experimental data and numerical simulations are in good agreement. The enhancement is caused by larger x-ray emission zone lengths formed in low density targets, which is in agreement with the simulation results.

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