Comparison between isotropic and nonisotropic dosimetry systems during intraperitoneal photodynamic therapy

Abstract

Background and Objective: On-line monitoring of light fluence during intraperitoneal photodynamic therapy (IP PDT) is crucial for safe light delivery. A flat photodiode-based dosimetry system is compared with an isotropic detector-based system in patients undergoing IP PDT. Study Design/Materials and Methods: Flat photodiodes and spherical detectors were placed side by side in the abdomen, for simultaneous light dosimetry in 19 patients. Tissue phantom experiments were performed to provide a preliminary estimate of the tissue optical properties of the peritoneum. Results:The conversion factor between systems for 630-nm light was found to be 1.7 ± 0.12. The eff of the tissues in the abdomen is estimated to vary between 0.5 cm −1 to 1.4 cm −1 assuming a s = 7 cm −1 . Conclusions: The measured conversion factor should allow for comparison of light fluences with future clinical protocols that use an isotropic-based detector system. Differences in the optical properties of the underlying tissues may contribute to the variability in light measurements.

Macroscopic singlet oxygen modeling for dosimetry of Photofrin-mediated photodynamic therapy: an in-vivo study

“…12 This might be responsible for the unpredictable response and variability between clinical dosimetry and PDT outcome. 13,14 To find a better solution for PDT dosimetry, explicit PDT dosimetry has been introduced. Unlike using the given photosensitizer dosage and light fluence as PDT metrics, in explicit PDT dosimetry, the light dose absorbed by the photosensitizer in tissue is measured and defined as PDT dose, which is determined by the product of photosensitizer concentration and light fluence.…”

A Phase II Trial of Intraperitoneal Photodynamic Therapy for Patients with Peritoneal Carcinomatosis and Sarcomatosis

“…The light delivery and dosimetry system were similar to the technique previously described (6). Light doses were monitored with fixed peritoneal diodes located in the right upper quadrant, left upper quadrant, left peritoneal gutter, right peritoneal gutter, and in the midline pelvis anteriorly.…”

The role of photodynamic therapy (PDT) physics

“…33 The effect on the measured fluence rate is significant. 34 Because these probes collect light via multiple scattering, the interface between the scattering tip and the surrounding medium can change the sensitivity of the detector by as much as a factor of 2, requiring careful calibration. 35 Because complete explicit dosimetry requires measurement of three different parameters, it is inherently challenging.…”

“…In our current clinical trials, we deliver a dose of light to the treatment sites based upon measurements made from implanted isotropic light detectors. 34,76 These detectors allow us to prescribe the light dose based upon actual measurements in the prostate rather than the output of the laser. This dosimetric approach also ensures that the same amount of light energy ͑as measured by the isotropic detectors͒ is deposited uniformly in the prostate within each cohort of patients as a specific dose level.…”