Development and characterization of multi-sensory fluence rate probes

Minimal required PDT light dosimetry for nonmuscle invasive bladder cancer

SIGNIFICANCE

Photodynamic therapy (PDT) could become a treatment option for nonmuscle invasive bladder cancer when the current high morbidity rate associated with red light PDT and variable PDT dose can be overcome through a combination of intravesical instillation of the photosensitizer and the use of green light creating a steep PDT dose gradient.

AIM

To determine how a high PDT selectivity can be maintained throughout the bladder wall considering other efficacy determining parameters, in particular, the average optical properties of the mucosal layer governing the fluence rate multiplication factor, as well as the bladder shape and the position of the emitter in relationship to the bladder wall.

APPROACH

We present three irradiance monitoring systems and evaluate their ability to enable selective bladder PDT considering previously determined photodynamic threshold values for the bladder cancer, mucosa and urothelium in a preclinical model, and the photosensitizer's specific uptake ratio. Monte Carlo-based light propagation simulations performed for six human bladders at the time of therapy for a range of tissue optical properties. The performance of one irradiance sensing device in a clinical phase 1B trial is presented to underline the impact of irradiance monitoring, and it is compared to the Monte Carlo-derived dose surface histogram.

RESULTS

Monte Carlo simulations showed that irradiance monitoring systems need to comprise at least three sensors. Light scattering inside the bladder void needs to be minimized to prevent increased heterogeneity of the irradiance. The dose surface histograms vary significantly depending on the bladder shape and bladder volume but are less dependent on tissue optical properties.

CONCLUSIONS

We demonstrate the need for adequate irradiance monitoring independent of a photosensitizer's specific uptake ratio.

Three-dimensional fluence rate measurement and data acquisition system for minimally invasive light therapies

Light based therapies such as photodynamic therapy are in need of advanced tools for light fluence rate dosimetry and monitoring within the context of therapy planning and light delivery to ensure maximum treatment efficacy. The use of a single, multisensor fiber-based fluorescent probe capable of performing spatially resolved fluence rate measurements along an axis was demonstrated. This work extends the previous technique and describes a fluence rate quantification system able to employ up to 12 multisensor probes to simultaneously measure fluence rate distribution throughout a 3D treatment volume. The system optoelectronics provides for sensor calibration, data acquisition, and weighted least-squares processing to extract localized fluence rate information in real-time. Core components include an integrating cylinder for source sensor calibration, a 2D back thin CCD detector for sensor signal detection from multiple probes, high-speed data acquisition card, and custom software for real-time extraction of fluence rate information from all sensors.