Abstract: A photodynamic therapy treatment of a cavity for providing a predetermined dose of light energy, the cavity being delimited by cells with photosensitizers, having: an external hollow rod, an internal hollow rod to be inserted inside the external rod, an inflatable balloon secured on the external rod, the inside of the balloon being in fluidic communication with the inside of it, a handle made of one single piece. The handle receives an illuminating device for illuminating the balloon to activate the photosensitizers. The handle and the rods are sealingly secured to each other in one single screwing movement. An illumination time is determined by means of a transfer function relating each volume of the balloon to at least one corresponding distribution of light power at its outer surface and a corresponding illumination time for providing the energy dose.