Radiation Therapy for Locally Advanced Lung Cancer: Which Cases Require Adaptive Planning?

Abstract

The advantages of highly conformal radiation treatments may be negated if patient anatomy changes. Here we characterize the reasons for re-simulation and adaptive re-planning. We conducted a chart-review of patients with locally advanced lung cancer treated with chemo-radiation. Inclusion criteria included: dose of at least 50 Gray (Gy), standard fractionation, treated between 1/2016-12/2018. Both small cell and non-small cell lung histologies were included, definitive and neoadjuvant. Exclusion criteria included SBRT, and adjuvant indications. We included patients that underwent re-simulation and adaptive re-planning during the course of treatment, performed at the discretion of the treating physician based upon carina / tumor miss-match on CBCT or if anatomical changes were observed on the CBCT or unsatisfactory simulation technique. Primary tumor (pGTV) and lymph nodes were contoured according to co-registered FDG PET/CT, without elective node irradiation and CBCT was used for IGRT. Reasons for re-planning for classified as: 1. Change in pGTV volume (> 20% compared with first scan) 2. Other major anatomical changes 3. Change of simulation technique (use of breath hold) Dosimetric parameters of lung V20, mean lung dose (MLD) and volume of heart receiving 40Gy (heart V40) were compared between first and second plan, after normalizing the prescription dose to 60 Gy. Statistical tests used: paired t test, Wilcoxon test. Out of 248 lung cancer patients, 48 cases underwent re-planning (19%). Male were 79%; histology: SCLC 9/48 (19%) and NSCLC 39/48 (81%). Stage 3a-3b in 92%. Mean radiation dose was 59.8 Gy (SD 3.4); planning technique VMAT 29/48 (60.4%), hybrid 8/48 (16.7%), and 3D-conformal 11/48 (23%). Tumor location was central in 26/48 (54%). Timing of re-planning was 1st third; 2nd third; final third in 23%, 46% and 31% respectively. 1. Changes in pGTV were observed in 41/48 (85%) of pts. pGTV decreased in volume in 36/41 (88%) of pts., mean decrease was -140.6 ml (range -7.7--475 ml). pGTV volume enlarged in 5/41(12%), mean increase: 56.8 ml (range 7-144 ml). 2. Other anatomical changes were observed in 18/48 (37%), including: pleural fluid accumulation, new atelectasis, resolution of atelectasis and absorption of pneumothorax. 3. Change in simulation technique was needed in 9/48 (18.7%) including breath hold or continuous positive airway pressure (CPAP) to expand the normal lung. Comparing the dosimetric variables between first and second plan: lung V20: 27.1Gy (SD 7.4) vs. 25.8Gy (SD 7) p=0.07, MLD 15.7Gy (SD 4) vs. 14.7Gy (SD 3.4) p=0.005, heart V40 was 10.9cc (SD 13.0) vs. 6.6cc (SD 9.5) p=0.004. Adaptive re-planning was performed in 19% of LA lung pts. who were monitored with daily IGRT-CBCT. In most cases tumor volume decreased or centrally located tumor caused distal atelectasis that resolved. These anatomical changes could potentially lead to increased toxicity and geographical miss, which can be corrected by adaptive re-planning.