N Kovalchuk¹*, L Vitzthum¹, D Pham¹, C Chuang¹, M Gensheimer¹, A Da Silva², B Han¹, D Chang¹, M Surucu¹, (1) Stanford University Cancer Center, Stanford, CA, (2) RefleXion Medical, Inc, Hayward, CA

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  N Kovalchuk

TU-I345-IePD-F4-3 (Tuesday, 7/12/2022) 3:45 PM - 4:15 PM [Eastern Time (GMT-4)]

Exhibit Hall | Forum 4

Purpose: The first clinical biology-guided radiotherapy (BgRT) system – RefleXion X1 – was commissioned for clinical IMRT/SBRT use at our institution. While BgRT delivery is undergoing FDA review, BgRT treatment planning is enabled on research treatment planning system (TPS) using diagnostic PET scans. The purpose of this study was to evaluate the feasibility of BgRT treatment planning for various treatment sites.

Methods: Five cancer patients previously treated to retropharyngeal node, liver met, para-aortic node, adrenal gland, and inguinal node with 40Gy in 5fx were selected for this study. BgRT-GTV was contoured using one of the phases of 4DCT (moving targets) or free-breathing planning CT (static). BgRT-PTV was created using 5mm expansion to compensate for BgRT tracking uncertainties and image registration uncertainties. The biology tracking zone (BTZ) defining the area for PET tracking was created using 10mm expansion from ITV (moving targets) or GTV (static). For each case, the BgRT plan was generated following our institutional planning constraints using 10mm jaw setting. BgRT plans were optimized to achieve PTV D95% coverage with 100% of prescription dose. Clinically relevant metrics, including Normalized Target Signal (NTS), mean concentration in BTZ, PTV Dmax, organs-at-risk constraints, and treatment time were evaluated.

Results: Clinically acceptable BgRT plans meeting institutional constraints were obtained for all 5 cases. The average BgRT-PTV volume was 24.4±15.8cc, range 5.9-46.2cc. For all plans, NTS (5.5±3.1) and mean concentration in BTZ (10.9±5.4kBq/ml) were above the acceptable threshold of 2.7 and 5kBq/ml, respectively. PTV-Dmax (119.5±6.6%) was below 125% of prescription dose for all plans. The lower DVH bounds of PTV-D95% and upper DVH bounds of PTV-Dmax generated to consider changes in NTS and setup uncertainty were 90.8±4.4% and 125.4±6.3% of prescription, respectively. BgRT treatment beam-on time was 22.7±8.6min, range 14.9-32.9min.

Conclusion: RefleXion X1 TPS provided clinically acceptable BgRT plans for the cases investigated.

Keywords

PET, Treatment Planning

Taxonomy

TH- External Beam- Photons: treatment planning/virtual clinical studies

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