Lijun Ma1, Steve E Braunstein2, Encouse Golden2, Shannon Fogh2, Jean Nakamura2, Michael W McDermott3, Penny K Sneed2. 1. Department of Radiation Oncology, University of California San Francisco (UCSF), San Francisco, CA, USA. lijun.ma@ucsf.edu. 2. Department of Radiation Oncology, University of California San Francisco (UCSF), San Francisco, CA, USA. 3. Department of Neurosurgery, University of California San Francisco (UCSF), San Francisco, CA, USA.
Abstract
OBJECTIVE: The present proof-of-principle study investigated radiobiological effects of redistributing central target dose hot spots across different treatment fractions during hypofractionated stereotactic radiosurgery (HSRS) of large intracranial tumors. METHODS: Redistribution of central target dose hot spots during HSRS was simulated, and its effects were evaluated in eight cases of brain metastases. To assess dose variations in the target across N number of treatment fractions, a generalized biologically effective dose (gBED) was formulated. The gBED enhancement ratio was defined as the ratio of gBED in the tested treatment plan (with central target dose hot spot redistributions across fractions) to gBED in the conventional treatment plan (without central target dose hot spot redistributions). RESULTS: At a median α value of 0.3/Gy, the tested treatment plans resulted in average gBED increases of 15.6 ± 3.5% and 8.3 ± 1.8% for α/β ratios of 2 and 10 Gy, respectively. In comparison with conventional treatment plans, the differences in the Paddick conformity index and gradient index did not exceed 2%. CONCLUSION: Redistributing central target dose hot spots across different treatment fractions during HSRS may be considered promising for enhancing gBED in the target. It may be beneficial for management of large intracranial neoplasms; thus, it warrants further clinical testing.
OBJECTIVE: The present proof-of-principle study investigated radiobiological effects of redistributing central target dose hot spots across different treatment fractions during hypofractionated stereotactic radiosurgery (HSRS) of large intracranial tumors. METHODS: Redistribution of central target dose hot spots during HSRS was simulated, and its effects were evaluated in eight cases of brain metastases. To assess dose variations in the target across N number of treatment fractions, a generalized biologically effective dose (gBED) was formulated. The gBED enhancement ratio was defined as the ratio of gBED in the tested treatment plan (with central target dose hot spot redistributions across fractions) to gBED in the conventional treatment plan (without central target dose hot spot redistributions). RESULTS: At a median α value of 0.3/Gy, the tested treatment plans resulted in average gBED increases of 15.6 ± 3.5% and 8.3 ± 1.8% for α/β ratios of 2 and 10 Gy, respectively. In comparison with conventional treatment plans, the differences in the Paddick conformity index and gradient index did not exceed 2%. CONCLUSION: Redistributing central target dose hot spots across different treatment fractions during HSRS may be considered promising for enhancing gBED in the target. It may be beneficial for management of large intracranial neoplasms; thus, it warrants further clinical testing.
Authors: Lijun Ma; Shannon Fogh; Nalin Gupta; Andrew Hwang; Dilini Pinnaduwage; Jean Nakamura; Igor Barani; Michael McDermott; Penny K Sneed; David A Larson; Arjun Sahgal Journal: J Radiosurg SBRT Date: 2012