This study is intended to assess the feasibility of adjusting a radiation plan during its course to accommodate for a shrinking tumor target. The investigators hypothesize that an adaptive radiotherapy (RT) planning strategy for small cell lung cancer (SCLC) patients with chest-confined disease will allow for safe delivery of higher doses of chest RT than a non-adaptive RT planning approach without subjecting normal critical structures to unacceptable doses of radiotherapy.

Inclusion Criteria:

• patients with histologically or cytologically proven newly diagnosed small cell lung cancer
• chest-confined disease (including bulky intrathoracic disease)
• adequate pulmonary function tests (FEV-1>1.0 L, DLCO>50%)
• patients of childbearing potential must practice adequate contraception
• Age > or = 18 years
• Karnofsky performance status > or = 70
• eligible for concurrent chemoradiotherapy

Exclusion Criteria:

• patients who have undergone complete or subtotal tumour resection
• evidence of non-small cell histology
• prior or concurrent malignancy except non-melanomatous skin cancer unless disease-free for at least 5 years
• prior RT to the thorax or neck
• compromised lung function with inadequate pulmonary function tests (FEV-1<1.0,DLCO<50%)
• pregnant women