Dynamic colorectal PDT methods, devices and photosensitizer compositions to treat abnormal cell growth in anal tissue such as perianal and intra-anal intraepithelial neoplasia grade III are presented. Dynamic colorectal PDT method comprises the steps of administering topically, intravenously or orally a photosensitizer composition; irradiating; monitoring treatment parameters before, during and/or after irradiation. Photosensitizer composition comprises Temoporfin and excipients/carriers, appropriate for the application method. An applicator is provided for colorectal PDT treatments enhancing irradiation delivery and monitoring treatment parameters. Preferably, applicator is made of a material, used to monitor the fluence rate simultaneously while doing optical spectroscopy. Measurement probe devices are provided for monitoring PDT treatment parameters in-vivo. A device for colorectal PDT treatment is also provided, comprising laser radiation source operating at about 400 and 800 nm; excitation laser radiation source operating at about 650 nm for fluorescence measurements; multichannel dosimetry device; long pass filter; waveguides and measurement probes.