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.
For patients failing standard Bacillus Calmette-Guerin based immunotherapy for Non-Muscle Invasive Bladder Cancer (NMIBC), PDT may delay or prevent cystectomy. A Phase IB clinical trial evaluated the feasibility and safety of TLD1433, a novel Ruthenium coordination-complex as photosensitizer (PS) for PDT. The clinical trial combined PS instillation for one hour and the use of strongly attenuated green (525nm) light to reduce PDT caused damage to the bladder wall. The low and high PS doses were defined as 0.35mg and 0.7mg TLD1433 per cm^2 bladder surface (N=3 each) and 90+/-9J/cm^2 as target radiant exposure on the bladder wall. The PS concentration in the urine and blood at 24hrs post instillation was below 1ng/ml indicating rapid drug clearing. In all patients, the average target radiant exposure was attained as verified by irradiance sensors in the bladder. The average measured irradiance was ~ 15mW/cm^2, never exceeding 35mW/cm2 at the sensor positions. At 30 days post-treatment, all patients receiving the low PS dose tolerated the procedure well with no grade 3, 4 or 5 AEs. Three patients were then treated at the Therapeutic Dose, again with no grade 3, 4 or 5 AEs, and an identical pharmacokinetic profile to the half dose. At half dose, all patients had recurrent, but no progressive NMIBC noted at the 180-day cystoscopy. At therapeutic dose, 2 of 3 patients were tumour-free at the 180-day cystoscopy. Moderate bladder irritability was reported at full dose which primarily resolved within 90 days.
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