IOP PUBLISHING PHYSICS IN MEDICINE AND BIOLOGY Phys. Med. Biol. 56 (2011) 4771–4783 doi:10.1088/0031-9155/56/15/009 A model to estimate the outcome of prostate cancer photodynamic therapy with TOOKAD Soluble WST11 Nacim Betrouni 1 ,2 ,3, 4 , Renaud Lopes 1 , Philippe Puech 1 ,2,3 , Pierre Colin 1 ,2,3 and Serge Mordon 1 ,2 ,3 1 Inserm U703, 152 rue du Docteur Yersin, 59120 Loos, France 2 Universit´ e Lille Nord de France, F-59000 Lille, France 3 CHU Lille, F-59000 Lille, France E-mail: n-betrouni@chru-lille.fr Received 17 January 2011, in final form 6 June 2011 Published 13 July 2011 Online at stacks.iop.org/PMB/56/4771 Abstract Interstitial photodynamic therapy is becoming an interesting modality to treat some early stage prostate cancers. A light-sensitive drug is injected to the patient and activated by light using optical fibres inserted inside the prostate. In this work, we were interested in the characterization of the light action model for the WST11 (Tookad R  Soluble) drug. A retrospective analysis was performed on results from 28 patients enrolled in phase I and II trials with the WST11 drug. A drug dose of 4 mg/kg patient, dose light of 200 J cm −1 and wavelength of 753 nm were used. Correlation between the illuminated volume and the obtained necrosis, measured at day 7 MR images, was clearly established. This result suggests that photodynamic therapy planning is possible based on this model. (Some figures in this article are in colour only in the electronic version) 1. Introduction Current therapeutic recommendations for localized prostate cancer consist of radical options aiming to treat the prostatic gland in its totality (radical prostatectomy, radiotherapy, brachytherapy or HIFU). New therapeutic alternatives, allowing for the focal treatment of prostate lesions, are being explored. Focal therapy (or subtotal resection) is defined as a technique permitting the resection of a known prostate cancerous zone, sparing the normal glandular parenchyma. The goal of this preservation is to reduce side effects (impotence and urinary incontinence) resulting from the proximity of neurovascular bundles and striated sphincter. 4 Author to whom any correspondence should be addressed. 4771