Quality Assurance of a Multicenter Prospective Phase III Randomized Controlled Trial Investigating the Role of Internal Mammary Lymph Node (IMN) in Node-Positive Breast Cancer: Individual Case Review

Abstract

<h3>Purpose/Objective(s)</h3> Postmastectomy radiotherapy in Node-positive breast cancer with or without Internal mammary nodal irradiation (POTENTIAL) study is an ongoing study investigates the role of IMN irradiation in breast cancer patients. This study reported the result of the dosimetric quality assurance regarding individual case review of target coverage and doses to heart and lungs. <h3>Materials/Methods</h3> Real-time central reviews were performed for the first ten enrolled patients in each center regarding contouring and planning. The target coverage, including planning target volume of all targets and IMN (PTVall, PTVim), clinical target volume of IMN (CTVim), and doses to heart and lungs were evaluated. <h3>Results</h3> Among the 117 patients who were enrolled at 14 centers, 62 (53.0%) patients were randomly assigned to the IMN irradiation group (IMNI) and 55 (47.0%) patients to no IMN group (no IMNI group). Sixty (51.3%) patients received HFRT at dose of 43.5 Gy/15f/2.9 Gy, and 57 (48.7%) patients received CFRT at dose of 50 Gy/25f/2 Gy. A total of 108 (92.3%) patients were irradiated with intensity-modulated radiotherapy (IMRT) technique to the supra/infraclavicular nodal region (SNR) and chest wall (CW) +/- IMN. In 9 (7.6%) patients, the CW +/-IMN were irradiated by electrons, and the SNR was irradiated with IMRT technique. The D95 and D90 of PTVall reached the prescribed dose in 36.8% and 81.2% of the patients, respectively. In the IMN group who were irradiated with IMRT technique, the D95 and D90 of PTVim reached the prescribed dose in 29.8% and 78.9% of the patients, respectively. When the IMN was irradiated with electrons, the mean D95 and D90 of CTVim was 31.1 Gy and 37.1 Gy, significantly lower than that of patients treated with IMRT (P = 0.008). In the no IMNI group, the mean D95 of PTVim was 12.6 Gy and 20.2 Gy for patients treated with HFRT and CFRT, respectively, which was both significantly lower than that of the IMNI group (P < 0.001). For patients treated with HFRT, the Dmean and V5 of the heart was significantly higher in IMNI group compared to those in no IMNI group (5.2 vs 3.4 Gy, p = 0.001; 26.2% vs 14.4%, p< 0.001). The differences were significant in Dmean (12.9 vs 11.3 Gy, p = 0.001), V20 (26.0% vs 22.4%, p = 0.002), and V5 (50.2% vs 46.6%, p=0.009) of the ipsilateral lung, but not in V5 (6.2% vs 4.8%, p = 0.367) of contralateral lung, between IMN and no IMN group. For patients treated with CFRT, there were no significant differences in Dmean (5.4 vs 4.8 Gy, p = 0.366) and V5 (32.1% vs 26.7%, p = 0.169) of the heart between IMNI and no IMNI group. There were significant differences in Dmean (15.1 vs 14.0 Gy, p = 0.004), V20 (28.7% vs 26.0%, p=0.002), and V5 (56.9% vs 52.5%, p=0.001) of the ipsilateral lung, and V5 (12.7% vs 5.5%, p < 0.001) of contralateral lung between IMN and no IMN group. <h3>Conclusion</h3> Individual case review of POTENTIAL study showed that the target coverage was acceptable, and doses to the heart and lung increased in IMNI group compared to no IMNI group.