Impact of induction chemotherapy on estimated risk of radiation pneumonitis in small cell lung cancer.

Introduction: Induction chemotherapy in patients with bulky small cell lung cancer (SCLC) could lead to decreased tumor burden, smaller radiation fields, and less pulmonary toxicity. This study compared radiation therapy (RT) plans based on pre- and postchemotherapy computed tomography (CT) scans of patients with SCLC to estimate the reduced risk of radiation pneumonitis (RP) after receiving chemotherapy.

Methods: Between 2003 and 2009, 23 patients with stage IV SCLC were treated with chemotherapy alone (no surgery or RT) and had computed tomography scans pre- and post two cycles of platin-based chemotherapy. Simulated RT plans were created as if to deliver 45 Gy to the thoracic disease. The percent of lung receiving ≥20 Gy (V20), mean lung dose, and normal tissue complication probability (NTCP) was evaluated in patients who had a partial response (≥30% volumetric reduction) in gross tumor volume.

Results: One (4.3%) patient had a complete response, 18 (78.3%) had a partial response, and four (17.4%) had stable disease. Among 18 responders, the absolute decrease in V20 was 7.4% (p < 0.01), in mean lung dose was 3.3 Gy (p < 0.01), and in NTCP was 5.5% (p < 0.01). Patients with a prechemotherapy V20 ≥35% versus V20 less than 35% had an average absolute reduction in NTCP of 10% versus 2% (p < 0.01).

Conclusion: Patients with limited stage SCLC with a V20 ≥35% may benefit from induction chemotherapy as there is an estimated reduction of RP of 10%. This reduction in risk of RP after induction chemotherapy should be weighed against risks and benefits of delaying upfront RT.