Intensity-modulated radiation therapy in head and neck cancers: The Mallinckrodt experience

The purpose of the study was to investigate the feasibility and the optimiz ation of tomotherapy-based intensity-modulated radiation therapy (IMRT) in patients with head and neck cancer. From February 1997 to November 1997, 17 patients with squamous cell carcinoma of the head and neck were treated wi th IMRT. Patients were immobilized with a noninvasive mask and treated usin g a serial tomotherapy device on a 6 MV linear accelerator. Treatment plann ing was performed on a Peacock inverse planning system and prescription opt imization was used to achieve the best plan for target coverage and parotid sparing. The treatment planning system process has a dosimetric characteri stic of delivering different doses to different target structures simultane ously in each daily treatment; therefore, the biological equivalent dose wa s implemented using the linear-quadratic model to adjust the total dose to the target volume receiving a daily dose of less than 1.9 Gy. All eight pat ients with gross disease (six in the nasopharynx, two in the tonsil) and on e patient with recurrent nasopharyngeal carcinoma received concurrent cispl atin chemotherapy. Six postoperative patients were treated with irradiation alone. Median follow-up was 2.2 years (range 2.6-1.8 years). All patients completed the prescribed treatment without unexpected interruption. Acute s ide effects were comparable to those of patients treated with conventional beam arrangements during the same period. No patient required gastrostomy d uring irradiation. The preliminary experience showed that the noninvasive i mmobilization mask yielded high positioning reproducibility for our patient s. To spare the parotid gland, which is in the proximity of the target, a f raction of the target volume may not receive the prescribed dose. In the be st-achievable plan of our studied cohort, only 27% +/- 8% of parotid gland volumes were treated to more than 30 Gy, while an average of 3.3% +/- 0.6% of the target volume received less than 95% of the prescribed dose. This is mainly related to the steep dose gradient in the region where the target a buts the parotid gland. The inverse planning system allowed us the freedom of weighting normal tissue-sparing and target coverage to select the best-a chievable plan. Local control was achieved in eight patients with gross tum or; six were treated postoperatively. Of three reirradiated patients, two h ad symptomatic improvement but persistent disease, and one is without evide nce of disease. In summary, a system for patient immobilization, setup veri fication, and dose optimization for head and neck cancer with parotid spari ng without significantly compromising target coverage is being implemented for a tomotherapy-based IMRT plan at the Mallinckrodt Institute of Radiolog y. The initial clinical experience in tumor control is promising, and no se vere adverse acute side effects have been observed. Further refining of del ivery technology and the inverse planning system, gaining clinical experien ce to address target definition and dose inhomogeneity within the targets, and understanding the partial volume effect on normal tissue tolerance are needed for IMRT to excel in the treatment of head and neck cancer. Int. J. Cancer (Radiat. Oncol. Invest.) 90, 92-103, (2000). (C) 2000 Wiley-Liss, In c.