Photodynamic therapy (PDT) of cancer involves the use of a photosensitizer that can be light-activated to eradicate tumors via direct cytotoxicity, damage to tumor vasculature and stimulating the body's immune system. Treatment outcome may vary between individuals even under the same regime; therefore a non-invasive tumor response monitoring system will be useful for personalization of the treatment protocol. We present the combined use of diffuse optical spectroscopy (DOS) and diffuse correlation spectroscopy (DCS) to provide early assessment of tumor response. The relative tissue oxygen saturation (rStO2) and relative blood flow (rBF) in tumors were measured using DOS and DCS respectively before and after PDT with reference to baseline values in a mouse model. In complete responders, PDT-induced decreases in both rStO2 and rBF levels were observed at 3 h post-PDT and the rBF remained low until 48 h post-PDT. Recovery of these parameters to baseline values was observed around 2 weeks after PDT. In partial responders, the rStO2 and rBF levels also decreased at 3 h post PDT, however the rBF values returned toward baseline values earlier at 24 h post-PDT. In contrast, the rStO2 and rBF readings in control tumors showed fluctuations above the baseline values within the first 48 h. Therefore tumor response can be predicted at 3 to 48 h post-PDT. Recovery or sustained decreases in the rBF at 48 h post-PDT corresponded to long-term tumor control. Diffuse optical measurements can thus facilitate early assessment of tumor response. This approach can enable physicians to personalize PDT treatment regimens for best outcomes.

The usefulness of radionuclide imaging studies with 99m-technetium diethylenetriaminepentaacetic acid (Tc-DTPA) for quantitating the glomerular filtration rate (GFR) in children was studied. This was compared to the conventional methods for measuring GFR using 51-chromium-EDTA clearance (Cr-EDTA), creatinine clearance and a height/plasma creatinine formula. In the 22 children studied, the correlation coefficient between renal uptake of DTPA and Cr-EDTA was 0.90 (p less than 0.001). In contrast, there was a poorer correlation between Cr-EDTA and creatinine clearance (r = 0.69) or the derived GFR using height/creatinine formula (r = 0.83). The regression line between Tc-DTPA uptake and Cr-EDTA clearance was used to derive a formula for calculating the predicted GFR. This was tested in 10 additional children, and the correlation between the predicted GFR and measured GFR (using Cr-EDTA clearance studies) was 0.92 (p less than 0.001). Quantitative estimation of the GFR during renal imaging studies is a feasible and convenient method of assessing renal function.

No abstract

Photodynamic therapy (PDT) of cancer works via direct cytotoxicity, causing damage to tumor vasculature and stimulating the body's anti-tumor immune response. PDT outcome depends on the parameters used; therefore an in vivo tumor response monitoring system is useful for optimization of the treatment protocol. The combined use of diffuse optical spectroscopy and diffuse correlation spectroscopy allows us to measure the tissue oxygen saturation (StO 2 ) and relative blood flow (rBF) in tumors. These parameters were measured before and after PDT in mouse tumor models and were calculated as ratios relative to the baseline in each tumor (rStO 2 and rBF). Readings were also measured in drugonly control tumors. In responders (mice with tumor eradication), significant PDT-induced decreases in both rStO 2 and rBF levels were observed at 3h post-PDT. The rStO 2 and rBF readings in these mice remained low until 48h post-PDT, with recovery of these parameters to baseline values observed 2 weeks after PDT. In non-responders (mice with partial or no response), the rStO 2 and rBF levels decreased less sharply at 3h post-PDT, and the rBF values returned toward baseline values at 48h post-PDT. By comparison, the rStO 2 and rBF readings in drug-only control tumors showed only fluctuations about the baseline values. Thus tumor response can be predicted as early as 3h post-PDT. Recovery or sustained decreases in rStO 2 and rBF up till 48h post-PDT were correlated to long-term tumor control. Diffuse optical measurements can thus facilitate early assessment of tumor response to PDT to aid in treatment planning.

No abstract