Clinical delivery of intensity modulated conformal radiotherapy for relapsed or second-primary head and neck cancer using a multileaf collimator withdynamic control

Background and purpose: Concave dose distributions generated by intensity m odulated radiotherapy (IMRT) were applied to re-irradiate three patients wi th pharyngeal cancer. Patients, materials and methods: Conventional radiotherapy for oropharyngea l (patients 1 and 3) or nasopharyngeal (patient 2) cancers was followed by relapsing or new tumors in the nasopharynx (patients 1 and 2) and hypophary nx (patient 3). Six non-opposed coplanar intensity modulated beams were gen erated by combining non-modulated beamparts with intensities (weights) obta ined by minimizing a biophysical objective function. Beamparts were deliver ed by a dynamic MLC (Elekta Oncology Systems, Crawley, UK) forced in step a nd shoot mode. Results and conclusions: Median PTV-doses (and ranges) for the three patien ts were 73 (65-78), 67 (59-72) and 63 (48-68) Gy. Maximum point doses to br ain stem and spinal cord were, respectively, 67 Gy (60% of volume below 30 Gy) and 32 Gy (97% below 10 Gy) for patient 1; 60 Gy (69% below 30 Gy) and 34 Gy (92% below 10 Gy) for patient 2 and 21 Gy (96% below 10 Gy) at spinal cord for patient 3. Maximum point doses to the mandible were 69 Gy for pat ient 1 and 64 Gy for patient 2 with, respectively, 66 and 92% of the volume below 20 Gy. A treatment session, using the dynamic MLC, was finished with in a 15-min time slot. (C) 1999 Elsevier Science Ireland Ltd. All rights re served.