Determination of optimal drug dose and light dose index to achieve minimally invasive focal ablation of localised prostate cancer using WST11‐vascular‐targeted photodynamic (VTP) therapy

Objective To determine the optimal drug and light dose for prostate ablation using WST11 (TOOKAD® Soluble) for vascular‐targeted photodynamic (VTP) therapy in men with low‐risk prostate cancer. Patients and Methods In all, 42 men with low‐risk prostate cancer were enrolled in the study but two who underwent anaesthesia for the procedure did not receive the drug or light dose. Thus, 40 men received a single dose of 2, 4 or 6 mg/kg WST11 activated by 200 J/cm light at 753 nm. WST11 was given as a 10‐min intravenous infusion. The light dose was delivered using cylindrical diffusing fibres within hollow plastic needles positioned in the prostate using transrectal ultrasonography (TRUS) guidance and a brachytherapy template. Magnetic resonance imaging (MRI) was used to assess treatment effect at 7 days, with assessment of urinary function (International Prostate Symptom Score [IPSS]), sexual function (International Index of Erectile Function [IIEF]) and adverse events at 7 days, 1, 3 and 6 months after VTP. TRUS‐guided biopsies were taken at 6 months. Results In all, 39 of the 40 treated men completed the follow‐up. The Day‐7 MRI showed maximal treatment effect (95% of the planned treatment volume) in men who had a WST11 dose of 4 mg/kg, light dose of 200 J/cm and light density index (LDI) of >1. In the 12 men treated with these parameters, the negative biopsy rate was 10/12 (83%) at 6 months, compared with 10/26 (45%) for the men who had either a different drug dose (10 men) or an LDI of 1 resulted in treatment effect in 95% of the planned treatment volume and a negative biopsy rate at 6 months of 10/12 men (83%).