Likelihood of unacceptable normal tissue doses in breast cancer patients undergoing regional nodal irradiation in routine clinical practice

Abstract

Purpose: As indications for regional nodal irradiation (RNI) for breast cancer have expanded, so too has scrutiny over potential late toxicity from radiotherapy. This emphasizes the need for careful radiation treatment planning to maximize the therapeutic ratio. We sought to evaluate how often unacceptable doses (UDs) to organs at risk (OARs) occur and the associated factors for patients receiving RNI in daily practice.

Methods and materials: Treatment records of patients who received RNI from February 2012 to May 2015 were studied. The NSABP B51/RTOG 1304 clinical dose-volume constraints for targets/OARs receiving RNI were used as the benchmark. Dose-volume histograms were analyzed for the rate of ≥1 UD delivered to the following organs: heart, mean >5 Gy; ipsilateral lung, V20 >35%, V10 >60%, V5 >70%; contralateral lung (CL), V5 >15%; and contralateral breast, V4.1 >5%. Logistic regression was used to test the association between UDs to OAR and key variables.

Results: Two hundred three consecutive cases received RNI (105 left, 98 right), to the chest wall in 171 (84%) and to the internal mammary nodes in 170 (84%); 77.4% of cases met all OAR constraints. The most common OAR UDs were delivered to the contralateral breast (n = 32, 15.7%) and ipsilateral lung V5 (n = 22, 10.8%). On multivariate analysis, use of intensity modulated radiation therapy (odds ratio [OR], 64.7; 95% confidence interval, 20.8-201.5; P < .001) and use of nodal boost (OR, 5.5; 95% confidence interval, 1.1-27.1; P = .04), but not internal mammary node irradiation (OR, 2.7; P = .35) or reconstruction (OR, 0.62; P = .33), were independently associated with higher OAR UD rate. For 3-dimensional conformal radiation therapy plans, 7.9% had OAR UDs.

Conclusion: The OAR UD rate with 3-dimensional conformal radiation therapy ± deep inspiration breath-hold in routine clinical practice is low and not independently associated with internal mammary node irradiation or reconstruction presence. Women treated with intensity modulated radiation therapy had a significantly higher overall OAR UD rate, and clinicians should be aware of this as they initiate RNI treatment planning.