Impact of dose prescription variation on local control for SBRT patients treated at a single academic institution

Dose prescription variation in radiation oncology has become common place and is dependent on several factors including dosimetrist experience, physician experience, institution trends, and standard practices. The intra-institutional variation can approach and at times exceed the limits that have been historically associated with affecting local control. SBRT data of 250 patients from a single academic institution were collected. Patient data was binned using prognostic factors including disease site, tumor stage, and tumor volume. Dosimetric parameters D₉₅, D₉₈, and D₂ were extracted from dose volume histogram data for analysis and were correlated with recurrence data from an institutional database for each patient. Kaplan-Meier disease free progression analysis was performed using correlated data. Kaplan-Meier disease free progression analysis for patients with various stages of liver and spine cancers indicated no impact on local control based on the intra-institution variation between dose prescription and planned dose. However, disease free progression analysis on early-stage lung cancers indicated a statistically significant impact on local control due to variations in dose prescription. Stage 1 lung cancers exhibited greater local control for patients that received greater than 120% of the prescribed dose to 2% of the target volume. Due to the relatively small variation in dose prescription at a single academic institution, local control for liver and spine cancers remained unaffected. However, increasing dose to the near-maximum dose point on early-stage lung cancers resulted in a local control benefit.