Mild-dose IMRT for Early-staged Extranodal Nasal-type NK/T-cell Lymphoma With CR Tumor After GELOX Chemotherapy

Definitive radiotherapy(RT) is mainstay in combined-modality treatment for patients with early-staged extranodal nasal-type NK/T-cell lymphoma(ENKTL),it can be used upfront or after short courses of chemotherapy. The typical dose of RT is recommended as 50-56Gy in conventional fractionations with 3 dimensional conformal RT or intensity-modulated radiation treatment(IMRT). Asparaginase-based chemotherapy regimens are being investigated, and primary results showed superior to previous anthracycline-based (eg. CHOP) chemotherapy. GELOX is a new asparaginase-based chemotherapy regimen designed and published in our institute, and the rate of complete remission(CR) is well improved. We hypothesis the reduced-dose radiation treatment(IMRT in 46Gy) is sufficient to control the disease in patients with early-staged ENKTL, who have got CR after GELOX chemotherapy, and to validate in this phase II study. 1. Patients: * All patients should sign a written informed consent form before enrollment, and the study should be approved by the Sun Yat-sen University Cancer Center Ethics Board. * Baseline of patients: Computed tomography (CT) scans of the chest, abdomen, and pelvis, magnetic resonance imaging studies of the head and neck, and bilateral bone marrow aspiration or biopsy. Positron emission tomography-CT scans (optional). Epstein-Barr virus (EBV) DNA blood levels, titer of EBV antibody (EA-IgA, VCA-IgA). * Recheck before and after GELOX chemotherapy and IMRT: Epstein-Barr virus (EBV) DNA blood levels, titer of EBV antibody (EA-IgA, VCA-IgA), computed tomography (CT) scans of the chest, abdomen, and pelvis, magnetic resonance imaging studies of the head and neck, positron emission tomography-CT scans (optional). 2. Treatment Protocol: 1. The GELOX regimen consist of the following drugs: gemcitabine：1250 mg/ m2 on days 1,iv drip; oxaliplatin：85 mg/m2 on day 1, iv drip; pegaspargase: 2500 IU/m 2 daily on day 1,intramuscular. The treatment cycle is repeated every 14 days. 2. IMRT is delivered using 6-8MeV linear accelerator using extended involved-field intensity-modulated radiation treatment planning. The RT dose is 46.2 grays (Gy) in 22 fractions, and a simultaneous-boost method is used. * We assign gross tumor volume (GTV) to 46.2Gy/22F, which is delineated according to the initial gross tumor volume identified with imaging and physical examination, including the primary tumor and involved regional lymph nodes. * The high-risk clinical target volume (CTV1) is assigned to 41.8Gy/22F, which is delineated including the first batch of adjacent structures around GTV, and lymph node group apt for involvement according to clinical feature of individual tumors. * The low-risk clinical target volume (CTV2) is assigned to 36.3Gy/22F, which is delineated including the extrapolated structures outside of CTV1 sites, and LN groups adjacent to CTV1 LN groups.