Application of a Survival-Predicting Nomogram Based Primarily on Whole-Brain Radiation Therapy–Treated Patients With Brain Metastases Yields Significant Underestimates for Radiosurgery-Treated Patients

Abstract

Palo Alto CA) and 6X 1000 MU/Min photons. ITVs were obtained from 4DCT scans and PTVs were formed from a uniform, 5 mm expansion of the ITVs. A single isocenter was determined with lesions required to be well within a 15 cm jaw setting to circumvent machine limitations and to minimize low dose spread into normal lung (from scatter and intraleaf leakage). Planning was done with 3D techniques such that 95% of the individual PTVs received the prescribed dose. MLC fields sharing a common gantry angle were merged as one field. Iteration of the plans was made based on DVH criteria. Results: Characteristics of the 6 patients were: 3 male, 3 female with a median age of 74.2 years (range, 62-83 years). The combined PTVs ranged from 8.7 to 124 cc (median 54 cc). Using RTOG coverage objectives as a scoring criteria, conformality index criteria were met (average Z 1.22 +/0.045). R50% criteria were not met; 2 cases did not meet the D2cm criteria. V20 (%) lung criteria (8.4 +/3.7, rangeZ 2.6%,13.4%) were met with two minor deviations. Conclusions: In general, the plans met the coverage and constraint guidelines by limiting high and low dose spill to regions outside the combined PTV volume and thereby critical structures. This study shows that treating two lesions using a single isocenter can be clinically efficient. Further evaluation is needed to validate that a single isocenter IGRT can accurately localize the treatment targets for safe treatment delivery. Author Disclosure: M. Gulam: None. A. Gopal: None. N. Wen: None. J. Gordon: None. K.J. Levin: None. I.J. Chetty: None. B. Movsas: None. M. Ajlouni: None.