This method provides an effective quality control mechanism for evaluating the DVHs of the OARs. Adoption of such a method will advance the quality of current IMRT planning, providing better treatment plan consistency.

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Purpose To assess results of a multi-institutional study of Intensity-Modulated Radiation Therapy (IMRT) for early oropharyngeal cancer. Patients and Methods Patients with oropharyngeal carcinoma stage T1-2, N0-1, M0 requiring treatment of the bilateral neck were eligible. Chemotherapy was not permitted. Prescribed planning target volumes (PTVs) doses to primary tumor and involved nodes was 66 Gy at 2.2 Gy/fraction over 6 weeks. Sub-clinical PTVs received simultaneously 54-60 Gy at 1.8-2.0 Gy/fraction. Participating institutions were pre-approved for IMRT, and quality assurance review performed by the Image–Guided Therapy Center. Results 69 patients accrued from 14 institutions. At median follow-up for surviving patients 2.8 years, 2-year estimated local-regional failure (LRF) rate was 9%. 2/4 patients (50%) with major under-dose deviations had LRF, compared with 3/49 (6%) without such deviations (p=0.04). All cases of LRF, metastasis, or second primary cancer, occurred among patients who were current/former smokers, and none among patients who never smoked. Maximal late toxicities grade ≥ 2 were skin 12%, mucosa 24%, salivary 67%, esophagus 19%, osteoradionecrosis 6%. Longer follow-up revealed reduced late toxicity in all categories. Xerostomia grade ≥ 2 was observed in 55% of patients at 6 months but reduced to 25% and 16% at 12 and 24 months, respectively. In contrast, salivary output did not recover over time. Conclusions Moderately accelerated hypofractionatd IMRT without chemotherapy for early oropharyngeal cancer is feasible, achieving high tumor control rates and reduced salivary toxicity compared with similar patients in previous RTOG studies. Major target under-dose deviations were associated with higher LRF rate.

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