Initial experience of using intensity modulated radiation therapy (IMRT) for recurrent nasopharyngeal carcinoma

Abstract

Purpose/Objective: To report initial experience using intensity modulated radiation therapy (IMRT)(feasibility, toxicity and tumor control) for re-treatment recurrent nasopharyngeal carcinoma. Materials/Methods: 49 patients (KPS≥80) with local-regional recurrence in nasopharynx were treated with IMRT from Jan. 2001 to Feb. 2002 at Cancer Center, Zhongshan University, Guangzhou, China. The average time for local-regional in recurrence nasopharynx was 30.16 months after initial conventional radiotherapy. The isocenter dose on nasopharynx had medean dose 70Gy (60.88-78Gy) in 49 patients initial conventional radiotherapy. The number of patients with stage II, III and IV disease were 4, 9, 10 and 26 respectively. T1, T2, T3 and T4 disease were 4, 9, 11 and 25 cases respectively. N0, N1 and N3 disease were 46, 2 and 1 cases respectively. Of them, the invasion of nasal cavity, maxillary sinus, ethmoid sinus, sphenoid sinus, cavernous sinus and the erosion of base skull were found in 8, 1, 3, 8, 15 and 20 cases respectively. The GTV were contoured according to ICRU 62 guideline. Two CTV (CTV1 and CTV2) were set-up for the subclinical disease in nasopharynx. The CTV1 was defined 0.5-1cm away from the border of GTV. The CTV2 was defined 1-1.5cm away from the border of CTV1. The critical structures were contoured and the doses to critical structures were constrined according to ICRU 50 guideline. The inverse planning IMRT were created with CORVUS 3.0 planning system (Peacock,NOMOS) and treated with segmental tomotherapy techniques (MIMiC).The gantry rotation arc was 105 to 255 degree and beamlet changed every 5 degree. The GTV in nasopharynx and the lymph nodes in the neck received prescription dose of 68-70Gy and 60Gy respectively. All patients received full course IMRT. Three patients who had positive the lymph nodes were treated with 5-6 courses of chemotherapy(Cisplatin + 5-FU) after IMRT. Results: The plans showed that the dose of PTV covering GTV D95 in nasopharynx was 68.09Gy, and the volume of GTV V95 was 98.46%. The mean dose of GTV, CTV1 and CTV2 were delivered by IMRT in 49 patients (Table 1). At a median follow-up of 7 months (range 1 to 13 months), the local-regional progression-free survival was 100%. 3 cases (6.1%) of local-regional residual diseases were seen in 49 patients by the end of IMRT. 14 patients (28.6%) were complicated by radio-necrosis of varying degree in the nasopharynx. Three patients have developed metastases at a distant site: 2 in the bone, 1 in the liver and lung at 13 months follow-up. Acute toxicity in 49 patients was evaluated according to the RTOG radiation morbidity scoring criteria by the end of IMRT treatment. 19, 19 and 1 patients had grade 0, 1 and 2 skin toxicity respectively. Grade 0, 1, 2 and 3 toxicity in oral mucosa were 16, 10, 21 and 2 patients respectively. 26, 18 and 5 patients had grade 1, 2 and 3 xerostomia respectively. Conclusions: The improvement in tumor target coverage and significant sparing of adjacent critical structures allow the feasibility of IMRT as a re-treatment option for recurrent NPC after initial radiotherapy. However, high dose IMRT for re-treatment can result in radio-necrosis of nasopharynx. We recommend that the prescription dose of GTV to be decreased and concurrent chemotherapy to be used in this setting. Tabled 1Critical StructuresMean Dose (Gy)Mean Volume (cc)Brain Stem28.5123.04Spinal Cord20.195.44Optical Chiasm21.560.87Pituitary32.590.21Len(L)3.910.20(R)4.100.20Optical Nerves(L)19.560.60(R)19.200.62Temporal Lobes(L)20.9840.46(R)22.1439.22Parotids(L)20.9710.98(R)18.4414.24T-M Joints(L)27.891.77(R)28.841.85Mandible bone(L)20.1936.30(R)19.7135.79 Open table in a new tab