Clinical Effectiveness of an Adaptive Treatment Planning Algorithm for Intensity Modulated Radiation Therapy Versus 3D Conformal Radiation Therapy for Node-Positive Breast Cancer Patients Undergoing Regional Nodal Irradiation/Postmastectomy Radiation Therapy.

Purpose: Clinical trials support adjuvant regional nodal irradiation (RNI) after breast-conserving surgery or mastectomy for patients with lymph node-positive breast cancer. Advanced treatment planning techniques (eg, intensity modulated radiation therapy [IMRT]) can reduce dose to organs at risk (OARs) in this situation. However, uncertainty persists about when IMRT is clinically indicated (vs 3-dimensional conformal radiation therapy [3DCRT]) for RNI. We hypothesized that an adaptive treatment planning algorithm (TPA) for IMRT adoption would allow OAR constraints for RNI to be met when 3DCRT could not without significantly changing toxicity and locoregional recurrence (LRR) patterns.

Methods And Materials: Since 2013, all RNI patients also underwent an adaptive TPA that began with 3DCRT and then changed to IMRT when OAR constraints (mean heart dose ≤500 cGy; ipsilateral lung V20 ≤35%) could not be met. Patients received 2 Gy/d to the prospectively contoured target volumes (including internal mammary nodes). We retrospectively evaluated the dosimetry and clinical outcomes of the treatment groups (IMRT vs 3DCRT). The primary endpoint was the cumulative incidence of LRR as the site of first recurrence, and we specifically address patterns of failure based on dose to the posterior supraclavicular nodal region (SCL-post).

Results: Two hundred forty patients (60% stage III; mean 4.0 + nodes) underwent an adaptive-TPA for RNI after mastectomy (74%) or breast-conserving surgery (26%), resulting in 168 patients treated with 3DCRT and 72 patients treated with IMRT. There were 7 LRRs (2 IMRT, 5 3DCRT) resulting in 4-year LRR of 2.8% for IMRT versus 1.8% for 3DCRT (P = .99). Three patients (2 IMRT, 1 3DCRT) had SCL nodal failures (1 in the SCL-post).

Conclusions: An adaptive TPA for use of IMRT when 3DCRT does not meet critical OAR constraints resulted in rare high-grade toxicity and no difference in failure patterns between patients treated with IMRT and 3DCRT. These data should provide reassurance that IMRT maintains the therapeutic ratio by preserving cancer control outcomes without excess toxicity when 3DCRT fails to meet OAR constraints.