Factors Affecting the Tumor Volume Reduction Rate During Adjuvant Radiation Therapy (RT) in Patients with Glioblastoma Multiforme (GBM)
BACKGROUND Glioblastoma multiforme is the commonest primary brain tumor in adults, responsible for 45.2% of primary brain tumors. It is considered a highly aggressive brain tumor with a grave prognosis. Standard treatment for GBM (Glioblastoma Multiforme) consists of maximal safe resection, adjuvant RT (Radiation Therapy), and temozolomide chemotherapy. Despite all the treatments, survival for GBM remains 15-18 months post-diagnosis. Several studies have demonstrated the prognostic significance of different factors, including age, performance status, extent of surgery, and status of molecular markers such as tumor MGMT promoter methylation and IDH mutation. Among the various factors, studies have shown that delaying the start of radiation therapy decreases survival in these patients. METHODS This retrospective study was conducted from January 2020 to June 2024 on 47 patients diagnosed with GBM. All these patients underwent surgical resection followed by adjuvant chemoradiation therapy and 6 cycles of maintenance temozolomide. Patient demographics, tumor, and treatment-related details were extracted from retrospectively collected, prospectively curated data. The patients who had been previously treated for a primary brain tumor or for whom pre-RT and follow-up scans were not available were excluded. RESULTS The median age at presentation was 45 years. The extent of surgical resection was subtotal in 91.5% of patients. Following surgery, tumor size greater than 4 cm was noted in 63.8% of the patients. The course of adjuvant and maintenance chemoradiation therapy could be completed by 86% of the patients. Among the factors influencing the tumor volume reduction during adjuvant RT, a delay in initiating RT beyond 3 weeks and a residual tumor greater than 4 cm were significantly associated with reduced mean percentage volume change. CONCLUSIONS This study provides an important insight into the various prognostic factors affecting the tumor volume reduction rate in GBM patients. We found that greater residual tumor volume following surgery and prolonged interval to RT significantly negatively influenced the rate of tumor volume reduction in GBM patients. Our study strengthens the fact that adjuvant RT should be started as early as possible after surgery. Future studies are warranted to elucidate the impact of the extent of surgical resection and the interval before initiating RT on patient survival.