An apparatus for performing thermotherapy on at least a portion of a tissue site, said apparatus comprises: a heating probe (10, 170, 220, 320, 515) comprises a fibre and an energy emitting area (180, 270, 370, 514) being a light emitting area; said heating probe (10, 170, 220, 320, 515) is connectable to an energy source for heating said portion of tissue by said energy emitting area (270, 370, 514); a sleeve (160, 200, 300, 430, 510) configured to be interstitially arranged in said tissue site; and wherein said heating probe (10, 170, 220, 320, 515) is arrangable in said sleeve (160, 200, 300, 430, 510), and said sleeve (160, 200, 300, 430, 510) is configured to be slid along said heating probe (10, 170, 220, 320, 515) in a distal and/or proximal direction for positioning of said energy emitting area (180, 270, 370, 514) in said portion of tissue for controlling said thermotherapy; further comprising an arrangement configured to lock said sleeve (160, 200, 300, 430, 510) and said heating probe (10, 170, 220, 320, 515) together when a right position of said sleeve (160, 200, 300, 430, 510) in relation to said energy emitting area (270, 370, 514) is found, characterized in that said arrangement comprises a first hub arranged on and attached to said sleeve (160, 200, 300, 430, 510) at a proximal end thereof, said first hub comprises a protruding element and an opening; a second hub comprising a connector and a locking member wherein said connector comprises fastening and releasing means for connecting said second hub to said protruding element of said first hub by hooking said fastening means to said protruding element; whereby a lumen is arranged through said locking member and thereby through said second hub for introducing said heating probe (10, 170, 220, 320, 515) and wherein said locking member is configured for locking said heating probe (10, 170, 220, 320, 515) intoeposition in said lumen. a heating probe (10, 170, 220, 320, 515) comprises a fibre and an energy emitting area (180, 270, 370, 514) being a light emitting area; said heating probe (10, 170, 220, 320, 515) is connectable to an energy source for heating said portion of tissue by said energy emitting area (270, 370, 514); a sleeve (160, 200, 300, 430, 510) configured to be interstitially arranged in said tissue site; and wherein said heating probe (10, 170, 220, 320, 515) is arrangable in said sleeve (160, 200, 300, 430, 510), and said sleeve (160, 200, 300, 430, 510) is configured to be slid along said heating probe (10, 170, 220, 320, 515) in a distal and/or proximal direction for positioning of said energy emitting area (180, 270, 370, 514) in said portion of tissue for controlling said thermotherapy; further comprising an arrangement configured to lock said sleeve (160, 200, 300, 430, 510) and said heating probe (10, 170, 220, 320, 515) together when a right position of said sleeve (160, 200, 300, 430, 510) in relation to said energy emitting area (270, 370, 514) is found, characterized in that said arrangement comprises a first hub arranged on and attached to said sleeve (160, 200, 300, 430, 510) at a proximal end thereof, said first hub comprises a protruding element and an opening; a second hub comprising a connector and a locking member wherein said connector comprises fastening and releasing means for connecting said second hub to said protruding element of said first hub by hooking said fastening means to said protruding element; whereby a lumen is arranged through said locking member and thereby through said second hub for introducing said heating probe (10, 170, 220, 320, 515) and wherein said locking member is configured for locking said heating probe (10, 170, 220, 320, 515) intoeposition in said lumen.