(P106) Dosimetric Comparisons of Treatment by Different Radiotherapy Techniques for Stage III Non–Small-Cell Lung Cancer

April 30, 2015

For both the 60-Gy and 74-Gy dose levels, significant dosimetric advantages (normal tissue sparing) were observed with IMRT, and a larger benefit was observed for 74-Gy dose plans. The dose to the esophagus, heart, and lung are likely to be clinically meaningful in terms of toxicity. VMAT provided benefit over conventional IMRT at the 60-Gy dose level. Additional studies are warranted to further investigate the impact of advanced radiotherapy techniques for the delivery of high-dose thoracic radiotherapy.

Veronica Finnegan, MD, Kiernan May, CMD, Jeffrey Bogart, MD, Paul Aridgides, MD, Varun Chowdhry, MD, Seung Hahn, MD; SUNY Upstate; Massachusetts General Hospital

PURPOSE: Standard dose for stage III non–small-cell lung cancer was established 30 years ago with Radiation Therapy Oncology Group (RTOG) 7301, where patients treated to 60 Gy had improved outcomes. Phase I and II studies have shown that higher doses are safe but have not been investigated in a phase III trial until recently. Optimal radiation dose was investigated in RTOG 0617, demonstrating that 60 Gy (standard) was superior to 74 Gy (high dose) with chemoradiotherapy ± cetuximab. We hypothesize that this is due to increased normal tissue toxicity. We performed a comparative dosimetric study between different radiation techniques.

MATERIALS AND METHODS: Review of 10 patients treated according to RTOG 0617. Dosimetric differences to normal organs were compared using three-dimensional (3D), intensity-modulated radiation therapy (IMRT), and volumetric-modulated arc therapy (VMAT).

RESULTS: A paired-difference test (two-sample t-test) for various dose parameters was performed. For plans to 74 Gy, there were statistically significant differences for lung V20 (P = .016), mean lung (P = .015), and mean esophagus (P = .046) between 3D and IMRT. There were statistically significant differences for the spinal cord (P = .38), mean lung (P = .021), mean esophagus (P = .001), esophagus V60 (P = .001), heart V60 (P = .031), heart V45 (P = .022), and heart V40 (P = .011) between 3D and VMAT. Comparing IMRT and VMAT, there was a statistically significant difference for mean esophagus dose (P = .013). These results were similar for plans to 60 Gy. There were statistically significant differences for lung V20 between 3D and IMRT. There were statistically significant differences for the spinal cord, mean esophagus, and heart V45 between 3D and VMAT.

CONCLUSION: For both the 60-Gy and 74-Gy dose levels, significant dosimetric advantages (normal tissue sparing) were observed with IMRT, and a larger benefit was observed for 74-Gy dose plans. The dose to the esophagus, heart, and lung are likely to be clinically meaningful in terms of toxicity. VMAT provided benefit over conventional IMRT at the 60-Gy dose level. Additional studies are warranted to further investigate the impact of advanced radiotherapy techniques for the delivery of high-dose thoracic radiotherapy.

Proceedings of the 97th Annual Meeting of the American Radium Society - americanradiumsociety.org