Background: Local control plays an important role in high risk metastatic and MYCN-amplified (MNA) localized neuroblastoma, as part of the multimodality treatment approach. In a subset of 100 patients with complete imaging and radiotherapy (RT) data sets treated in the current HR-NBL1/SIOPEN trial, we previously reported on the radiotherapy quality assurance (RTQA), identifying unjustified deviations in 17% of patients. The majority of these were an inappropriate target volume and/or an inappropriate dose.
Methods: The aim of this analysis was 1) to investigate local control and event-free survival (EFS) in the full cohort of 1467 patients (stage 4: 1180, MNA: 170, unknown: 117) having received irradiation according to the HR-NBL1/SIOPEN trial recommendation after high dose chemotherapy and autologous stem cell reinfusion between 2002-2015. 2) to correlate local control with RTQA in the subset of 100 patients with previously performed RTQA.
Results: In the group of 1467 patients no difference was detected neither in the cumulative incidence of local relapse nor in event-free survival between patients receiving < 21Gy, 21Gy as prescribed or > 21Gy. However, only in the subgroup of 170 patients with localized MNA disease a trend towards improved 5-year EFS was observed in patients receiving 21Gy as prescribed in contrast to those patients who did not (5yr-EFS:70% versus 62%). In the subset of 100 patients with previous RTQA a significantly increased local recurrence rate of 44% (10/23pts) was found when RT had not been delivered according to protocol in contrast to 22% (17/77pts) in patients treated with correct volume and dose (p=0,042).
Conclusion: These early results show the importance of RTQA for local control in the treatment of neuroblastoma. Further confirmation in a larger patient population is currently being performed. Prospective central validation of RT planning prior to RT delivery could improve overall disease control.