PV QA 4 - Poster Viewing Q&A 4
Purpose/Objective(s): Radiation pneumonitis (RP) is a significant toxicity in patients (pts) with non-small cell lung cancer (NSCLC) undergoing post-operative radiation therapy (PORT). Although the radiation (RT) doses are lower compared to definitive RT, pts may be at increased risk for RP due to the post-operative nature of treatment and the decreased lung volume after surgery. The purpose of this analysis was to identify clinical and dosimetric factors associated with the development of RP in pts undergoing PORT.
Materials/Methods: We retrospectively reviewed records of pts with NSCLC treated with PORT between 5/04 and 1/17. Dosimetry for all pts was obtained from recalculated or direct plans with the AAA dose calculation algorithm. The endpoint for this study was ≥Grade 2 RP (RP2+) (CTCAE v 4.0). Correlation of clinical and dosimetric variables (Dv the minimum dose received by hottest v%, v 0-100%, steps of 5%; Vd the % volume receiving at least dose d, d 0-60Gy, steps of 2 Gy; mean dose) for lung and heart was determined with uni- and multi- variate Cox modeling with significance defined as 0.05. To provide comparison with other studies, models based on V5Gy were created. Significance of differences in RP2+ rate above and below the median V5 was calculated using Fisher’s exact test.
Results: A total of 285 pts with restored dose distributions were reviewed with a median follow-up time of 23 m (1-117m). The median age was 67 y (range: 28-87y) and the median KPS was 90 (range: 70-100). Most (62%) pts had stage III disease and 82% were current or former smokers. Pts underwent lobectomy (81%), pneumonectomy (7%) or sublobar resection (12%). The rates of R0, R1 and R2 resections were 81%, 19%, and 0%, respectively. Most (92%) pts received chemotherapy (57% preoperative and 43% postoperative) with either cisplatin (63%) or carboplatin (37%) regimens. The median RT dose was 54 Gy (range: 45-70 Gy). Pts were treated with IMRT (71%) or 3DCRT (29%). There were 37 (13%) pts who developed grade 2 or higher RP. There were 3 cases of grade 3 RP and 1 case of grade 4 RP. On univariate analysis, age and carboplatin were significantly correlated with RP2+. Dosimetric variables across a large range of doses to both heart and lungs were highly significant. Dominant variables were Lungs V4Gy and D75%, and Heart V8Gy and D55%. On multivariate analysis, competitive models were age with either Lungs V4Gy or Heart V8Gy. Rate of RP2+ was 10/143 (7%) vs 27/142 (19%) above and below the median value of V5Gy (50.1%; p = 0.008).
Conclusion: In our data age, lung, and heart dose were predictive of radiation pneumonitis in pts with NSCLC undergoing PORT. Particular attention should be given to the range V5-V20 of the lung and heart as low doses to these were of greatest significance. Based upon our data, we recommend a lung V5<50% to keep the RP2 rate < 10%.
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