Rates of unacceptable variation (UV) of normal tissue constraints in patients undergoing chest wall/breast and regional nodal irradiation (RNI) in a routine clinical practice.

Abstract

67 Background: TheNSABP B51/RTOG 1304 clinical trial defines dose-volume constraints for targets/normal tissue receiving RNI. We sought to evaluate UV rate in normal tissue based on the NSABP B51/RTOG 1304 protocol in patients receiving chestwall/breast (CW/B) and RNI in daily practice. Methods: Treatment records of CW/B+RNI patients from 2/2012-5/2015 were studied for: CW or B radiotherapy (RT), RT type (intensity modulated [IMRT] or 3D conformal [3DCRT]), internal mammary node (IMN) inclusion, primary site boost, and nodal boost. No case is enrolled on B51/1304. Dose volume histogram (DVH) was analyzed for the rate of ≥ 1 UV for the following normal tissue constraints: Heart mean dose ≤ 5 Gy; ipsilateral lung (IL): V20 ≤ 35%, V10 ≤ 60%, V5 ≤ 70%; contralateral lung (CL) V5 ≤ 15%; contralateral breast (CB) V4.1 ≤ 5%. Logistic regression is used to test the association between UV and key variables. Results: 203 consecutive cases received CW/B+RNI (105 left, 98 right). RT was to CW in 170 (84%), B in 33 (16%), primary site boost 133 (66%), and IMN 170 (84%). 38 (19%) received IMRT and 14 (6.9%) had a nodal boost. 46 patients (22.6%) had ≥ 1 UV. 19 patients (9.4%) had ≥ 2 UV, all in IMRT patients. 2 patients (1.0%) had a heart UV at 5.2 Gy and 5.6 Gy. The most common UV was CB (n = 32, 15.7%) and IL V5 (n = 22, 10.8%). Higher UV rates are associated with use of IMRT (vs. 3DCRT): 86.8% vs. 7.9%, OR = 77.2 (95% CI 25.7-231.4, p < 0.0001); IMN irradiation: OR = 11.5 (95% CI 1.5-86.8, p = 0.02); and use of nodal boost: OR = 7.4 (95% CI 2.3-23.4, p = 0.001). The most common UVs in IMRT cases are CB (n = 27, 71%), IL V5 (n = 19, 50%), CL V5 (n = 14, 37%) and for 3DCRT are IL V20 (n = 5, 3%), CB (n = 5, 3%) and IL V5 (n = 3, 1.8%). On multivariate analysis, use of IMRT (OR = 64.7, 95% CI 20.8-201.5, p < 0.001) and use of nodal boost (OR = 5.5, 95% CI 1.1-27.1, p = 0.04) but not IMN irradiation (OR = 2.7, 95% CI 0.3-22.0, p = 0.35) were independently associated with higher UV rate. Conclusions: The rate of UV per B51/1304 criteria with 3DCRT in routine clinical practice is low (7.9%). Women treated with IMRT had a significantly higher overall UV rate and clinicians should be aware of this as they initiate treatment planning for RNI.