Room: Exhibit Hall | Forum 4
Purpose: Elderly multiple primary or oligometastases (< 5 lesions) patients may not retain their treatment position for long traditional SBRT treatments with individual isocenters for each lesion. Treating multiple lesions synchronously using a single-isocenter volumetric arc therapy (VMAT) plan would be more efficient using recently adopted Photon Optimizer (PO) MLC algorithm (sparsely sampling point dose cloud model for defining structures and sampling dose using one single matrix over the image) and improve patient comfort. Herein, we quantified clinical performance of PO versus its processor progressive resolution optimizer (PRO) algorithm for single-isocenter/multiple-lesions lung SBRT.
Methods: Fourteen patients with early-stage non-small-cell lung cancer lesions (two to five, uni/bilateral lungs) received highly conformal single-isocenter non-coplanar VMAT SBRT. Patients were treated with 6X-FFF beam and Acuros-based algorithm with single-isocenter placed between/among the lesions using PO MLC optimization. Average isocenter to tumors distance was 5.6Â±1.9 cm. Mean combined PTV derived from 4D-CT scans was 38.7Â±22.7cc. Doses were 54 Gy/50 Gy in 3/5 fractions prescribed to 70-80% isodose line. Plans were re-optimized using PRO algorithm. Plans were compared via ROTG-0915 protocol criteria for target conformity, heterogeneity and gradient indices, and dose to organs-at-risk (OAR). Additionally, total monitor units (MU), modulation factor (MF) and beam-on time were compared.
Results: All plans met SBRT protocol requirement for target coverage and OAR doses and comparison of these showed no statistical significance between the plans. PO had 1042Â±753 (p<0.001) less MU than PRO resulting in a beam-on time of about 0.7 Â± 0.5min (p<0.001) less, on average. For similar dose distribution, significant reduction of beam delivery complexity was observed with PO (average MF=3.7Â±0.7) vs. PRO (average MF=4.4Â±1.3) (p<0.001).
Conclusion: PO MLC algorithm can improve treatment efficiency without compromising plan quality when compared to PRO algorithm. Faster treatment time can potentially reduce intrafraction motion errors and improve patient compliance.