79P - Volume Changes with Hypo-Fractionated Radiotherapy in Early Lung Cancer: Time Trends & Outcomes

Abstract

Aim: Hypofractionated Radiotherapy (HFRT) is commonly used for medically inoperable early lung cancer/ oligometastasis in lung. Response to HFRT may be heterogeneous & the pattern of response may be used as an early predictor for outcome. Methods: Twenty-six patients with early lung cancer/ oligometastasis in lung treated with HFRT from 2010 - 2014 were evaluated for their Gross Tumor Volume (GTV) change during the course of RT. Kilo-voltage CTs (KVCT) were acquired before every fraction & GTV volumes were contoured manually using standard ‘lung & mediastinal’ window & level. A total of 176 KVCTs were contoured. Patients were treated using 6/15 MV photons, with 3DCRT, to a dose of 48 - 60Gy in 6- 10#, on alternate days. The Overall survival (OS), Locoregional Recurrence Free Survival (LRFS) & Distant Metastasis Free Survival (DMFS) were computed using Kaplan Meier method. Results: Of the 26 patients, 22 had primary lung cancer & 4 had lung metastasis. Median age was 65.5 yrs (range 23 - 82 yrs). Median GTV was 40.6 cc (range 7.2- 146.5 cc) on CT1 (KVCT for 1st fraction) & 33.3 cc (range 4 - 151.8 cc) on CTlast (KVCT of last fraction) suggesting 18% reduction for the whole group. Increase in tumor volume was noted in 20 (75%) patients at some time point during RT. In the mid treatment scan 13 (50%) patients had higher tumor volume than the CT1, however only 8 (30%) patients' GTV remained larger at the end of treatment compared to baseline. Median follow up was 12 months. The OS, LRFS & DMFS at 12 & 18 months were 63.4%, 85.1%, 59.1% and 57.1%, 73%, 35.5%, while for the patients with lung primaries were 75.2%, 86.3%, 67% & 67.7%, 73.9%, 40.2% respectively. In primary lung cancer patients, the median percentage reduction in GTV at CTlast compared to CT1 was 11%. Tumors that regressed in volume by >11% had significantly worse OS & LRFS compared to those that regressed by <11% (p = 0.003). Conclusions: Significant changes of GTV are seen during HFRT. Early regression in tumor volume may help in deciding early adjuvant treatment interventions. Disclosure: All authors have declared no conflicts of interest.