A Novel Lightning Dose Optimizer for Radiosurgery of Irregular-Shaped Arteriovenous Malformations and Pituitary Adenomas

Abstract

<h3>Purpose/Objective(s)</h3> To demonstrate the clinical feasibility of a novel inverse planning algorithm via dose optimizer (DO) on a treatment planning system (TPS)for generating high-quality treatment plans with significantly faster planning times for Stereotactic Radiosurgery (SRS) of the complex and difficult cases of arteriovenous malformation (AVM) and pituitary adenomas. <h3>Materials/Methods</h3> After completing the in-house end-to-end phantom testing and independent dose verification of recently upgraded DO on TPS using one institution's IROC anthropomorphic SRS head phantom irradiation credentialing, twenty previously treated SRS patients (10 AVM, average volume 3.61 cc) and (10 pituitary adenomas, average volume 0.86 cc) who underwent manual forward planning on TPS were retrospectively re-planned via DO under IRB protocol. DO finds the target curvature boundary by well formulated linear programming objectives, and inversely optimize SRS plan by isocenter placement, optimization, and sequencing. For identical tumor dose, the DO and original manual plans were compared for target conformity, gradient index, dose to critical organs, and surrounding normal brain. Additionally, various treatment delivery parameters including beam on time were recorded. <h3>Results</h3> For both patient cohorts, DO provided similar target coverage with better dose conformity, tighter radiosurgical dose distribution with lower value of gradient indices (all p < 0.001), and lower dose to critical organs. For AVM, significant reduction of normal brain V10, V12 and V14 by 4.74 cc, 3.67 cc, and 2.67 cc (all p < 0.001), on average via DO was observed at the cost of as many as twice the numbers of shots (p < 0.001), and relatively longer beam on time (p = 0.012) by a factor of 1.44, compared to the clinical manual plans. For pituitary adenoma, DO provided systematically lower values of V10, V12 and V14 by 1.08 cc, 0.86 cc and 0.68 cc (all p < 0.001), on average and lower maximal dose to optic pathway by 0.7 Gy (p = 0.005), but had almost twice the numbers of shots (p < 0.001) and increased beam on time (p = 0.005) by a factor of 1.2, compared to the original manual plans. However, for both patient groups, average planning time for the DO was < 5 minutes, compared to estimated 30-60 min of manual planning times. <h3>Conclusion</h3> SRS treatment via new inverse DO provided highly conformal target coverage, steep dose gradient, spared critical organs, and significantly reduced normal brain dose for complex targets who presented with very irregular nidus or pituitary adenoma. DO generated high quality treatment plans and could yield significant time saving in planning the treatment, particularly for inexperienced SRS users–improving patient compliance, and clinic workflow. If available, DO algorithm is suggested for validation and clinical use for irregular, complex and difficult SRS cases in the future.