Does Limited-Margin Radiotherapy Change the Recurrence Pattern and Survival of Patients With IDH-Wild-Type Glioblastoma? Analysis and Validation of a Different Approach.

Purpose: We aimed to analyze our radiotherapy protocol by evaluating its effect on recurrence patterns and survival outcomes.

Methods: We assessed 69 patients diagnosed with IDH-wild-type glioblastoma who underwent chemoradiotherapy at our institution from January 2014 to January 2021. A high-risk clinical target volume (CTV_high) was created with a 1 cm margin in all directions from the GTV, while a low-risk clinical target volume (CTV_low) was established with a 2 cm margin. Planned treatment volumes with a 2-3 mm margin in all directions were created, and doses of 60 and 50 Gy were prescribed in 30 fractions. Recurrence patterns were classified as central, in-field, marginal, or distant based on the 60 and 50 Gy D95 isodose lines.

Results: With a median follow-up of 21 months, 88.4% of patients experienced recurrence. The overall survival rates at 1, 2, and 5 years were 84.1%, 51.5%, and 17%, respectively. The progression-free survival rates at the same intervals were 44.9%, 21.5%, and 9.5%, respectively. Recurrence patterns were central in 63.9%, in-field in 18%, marginal in 4.9%, and distant in 13.1%.

Conclusion: The recurrence pattern remained unchanged with our protocol. With longer survival times, distant recurrence rates increase, yet central and in-field recurrences remain dominant. Despite the decrease in the volume that received the 60 Gy dose, marginal recurrences remained at a notably low level.