Patterns of failure in relation to radiotherapy fields in supratentorial primitive neuroectodermal tumor

Supratentorial primitive neuroectodermal tumor (PNET) accounts for 2-3% of all pediatric brain tumors. We retrospectively reviewed all supratentorial PNET cases treated with radiotherapy (RT) at our institutions.

A total of 25 patients (17 males and 8 females, median age 9 years) were treated with RT between 1980 and 2001. The primary site location was the pineal region in 7 (28%), temporal lobe in 5 (20%), thalamus in 5 (20%), frontal lobe in 4 (16%), parietal lobe in 2 (8%), and suprasellar region in 2 (8%). Five patients (20%) had neuraxis dissemination (M+ disease) at initial diagnosis. The RT treatment volumes were craniospinal (CS) in 17 (68%), whole brain (WB) followed by a boost in 2 (8%), and primary site (PS) alone in 6 (24%). The median dose to the primary site was 54 Gy (range, 31-55.8 Gy). The median dose to patients receiving WB and spinal fields was 36 Gy (range, 23.4-39.6 Gy). Sixteen patients (64%) received chemotherapy; the most common type was the "8 in 1" chemotherapy regimen in 9 children. The median follow-up of surviving patients was 70 months (range, 34-251 months).

The 5-year and 10-year progression-free survival rate was 36% and 27%, respectively, and the median time to progression was 22 months. The 5-year and 10-year progression-free survival rate was 47.1% and 47.1% for those receiving CSRT and 12.5% and 0% for those receiving WBRT or PSRT, respectively. The 5-year and 10-year progression-free survival rate for those with M0 disease was 40.0% and 30.0%, respectively; for those with M+ disease, the corresponding figures were 20.0% and 0%. On multivariate analysis, only M status (p = 0.01) and RT volume (p = 0.02) were statistically significant according to the Cox proportional hazards model. The primary site control rate at 5 and 10 years was 62%. Failure at nontreated neuraxis sites was a common cause of progression in patients receiving WBRT or PSRT, as seen in 6 (75%) of 8 cases. Of the 17 patients undergoing CSRT, 8 had no recurrence. Eight of the nine CSRT relapses had a leptomeningeal component. Four (80%) of 5 M+ children and 4 (33%) of 12 M0 children who underwent CSRT developed recurrence in the neuraxis (p = 0.1, Fisher's exact test).

The craniospinal axis is the standard volume that needs to be treated in supratentorial PNET. Leptomeningeal dissemination was the main obstacle for cure even in patients receiving CSRT, regardless of M status.