Beam intensity modulation using tissue compensators or dynamic multileaf collimation ln three-dimensional conformal radiotherapy of primary cancers of the oropharynx and larynx, including the elective neck

Introduction: The treatment of midline tumors in the head and neck by conve ntional radiotherapy almost invariably results in xerostomia. This study an alyzes whether a simple three-dimensional conformal radiotherapy (3D-CRT) t echnique with beam intensity modulation (BIM) (using a 10-MV beam of the MM 50 Racetrack Microtron) can spare parotid and submandibular glands without compromising the dose distribution in the planning target volume (PTV). Methods: For 15 T2 tumors of the tonsillar fossa with extension into the so ft palate (To) and 15 T3 tumors of the supraglottic larynx (SgL), conventio nal treatment plans, consisting of lateral parallel opposed beams, were use d for irradiation of both the primary tumor (70 Gy) and the elective neck r egions (46 Gy). Separately, for each tumor a 3-D conformal treatment plan w as developed using the 3-D computer planning system, CadPlan, and Optimize, a noncommercial program to compute optimal beam profiles. Beam angles were selected with the intention of optimal sparing of the salivary glands. The intensity of the beams was then modulated to achieve a homogeneous dose di stribution in the target for the given 3D-CRT techniques. The dose distribu tions, dose-volume histograms (DVHs) of target and salivary glands, tumor c ontrol probabilities (TCPs), salivary gland volumes absorbing a biologicall y equivalent dose of greater than 40 or 50 Gy, and normal tissue complicati on probabilities (NTCPs) of each treatment plan were computed. The paramete rs of the 3D-CRT plans were compared with those of the conventional plans. Results: In comparison with the conventional technique, the dose homogeneit y in the target volume was improved by the conformal technique for both tum or sites. In addition, for the SgL conformal technique, the average volumes of the parotid glands absorbing a BED of greater than 40 Gy (V40) decrease d by 23%, and of the submandibular glands by 7% (V40) and 6% (V50). Consequ ently, the average NTCPs for the parotid and submandibular glands were redu ced by 7% and 6%, respectively. For the To conformal techniques, the V40 of the parotid glands was decreased on average by 31%, resulting in an averag e reduction of the NTCP by 49%. Both the average V50 and the NTCP of the su bmandibular glands were decreased by 7%. Conclusion: For primary tumors of the oropharynx, the parotid glands could be spared to a considerable degree with the 3D-CRT technique. However, part icularly the ipsilateral submandibular gland could not be spared. For prima ry tumors of the larynx, the 3D-CRT technique allows sparing of all salivar y glands to a considerable and probably clinically relevant degree, Moreove r, the conformal techniques resulted in an increased dose homogeneity in th e PTV of both tumor sites. (C) 2000 Elsevier Science Inc.