Patterns of local-regional recurrence following parotid-sparing conformal and segmental intensity-modulated radiotherapy for head and neck cancer

Purpose: To analyze the patterns of local-regional recurrence in patients w ith head and neck cancer treated with parotid-sparing conformal and segment al intensity-modulated radiotherapy (IMRT). Methods and Materials: Fifty-eight patients with head and neck cancer mere treated with bilateral neck radiation (RT) using conformal or segmental IR IRT techniques, while sparing a substantial portion of one parotid gland. T he targets for CT-based RT planning included the gross tumor volume (GTV) ( primary tumor and lymph node metastases) and the clinical target volume (CT V) (postoperative tumor bed, expansions of the GTVs and lymph node groups a t risk of subclinical disease). Lymph node targets at risk of subclinical d isease included the bilateral jugulodigastric and lower jugular lymph nodes , bilateral retropharyngeal lymph nodes at risk, and high jugular nodes at the base of skull in the side of the neck at highest risk (containing clini cal neck metastases and/or ipsilateral to the primary tumor). The CTVs were expanded by 5 mm to yield planning target volumes (PTVs), Planning goals i ncluded coverage of all PTVs (with a minimum of 95% of the prescribed dose) and sparing of a substantial portion of the parotid gland in the side of t he neck at less risk. The median RT doses to the gross tumor, the operative bed, and the subclinical disease PTVs were 70.4 Gy, 61.2 GS, and 50.4 Gy r espectively. All recurrences were defined on CT scans obtained at the time of recurrence, transferred to the pretreatment CT dataset used for RT plann ing, and analyzed using dose-volume histograms, The recurrences were classi fied as 1) "in-field," in which 95% or more of the recurrence volume (V-rec ur) was within the 95% isodose; 2) "marginal," in which 20% to 95% of V-rec ur was within the 95% isodose; or 3) "outside," in which less than 20% of V -recur was within the 95% isodose, Results: With a median follow-up of 27 months (range 6 to 60 months), 10 re gional recurrences, 5 local recurrences (including one noninvasive recurren ce) and 1 stomal recurrence were seen in 12 patients, for a 2-year actuaria l local-regional control rate of 79% (95% confidence interval 68-90%). Ten patients (80%) relapsed in-field tin areas of previous gross tumor in nine patients), and two patients developed marginal recurrences in the side of t he neck at highest risk tone in the high retropharyngeal nodes/base of skul l and one in the submandibular nodes). Four regional recurrences extended s uperior to the jugulodigastric node, in the high jugular and retropharyngea l nodes near the base of skull of the side of the neck at highest risk. Thr ee of these were in-field, in areas that had received the dose intended for subclinical disease. No recurrences were seen in the nodes superior to the jugulodigastric nodes in the side of the neck at less risk, where RT was p artially spared, Conclusions: The majority of local-regional recurrences after conformal and segmental IMRT were "in-field," in areas judged to be at high risk at the time of RT planning, including the GTV, the operative bed, and the first ec helon nodes, These findings motivate studies of dose escalation to the high est risk regions. (C) 2000 Elsevier Science Inc.