Author: Brett Lewis, Roland Teboh 👨🔬
Affiliation: HUMC, Hackensack University Medical Center 🌍
Purpose: The novel RefleXion SCINTIX BgRT system relies on the FDG uptake distribution from a PET study to plan and deliver dose. One of the patient eligibility criteria is that any uptake outside the tumor region is small within defined thresholds for the system to function as intended. We present a simple and reliable method to assess this criterion.
Methods: The eligibility requires that any uptake outside and up to 2cm beyond the biology tracking zone (BTZ), a zone that encompasses tumor motion extent should not exceed 50% of the maximum uptake within the BTZ region. In our method, we generated a 2cm annulus ring beyond the BTZ called BTZ-Annulus-2cm and thus can define the criterion as Maximum Uptake in (BTZ-Annulus-2cm) < 0.5 * Maximum Uptake in (BTZ). The PET distribution is acquired during the functional modeling (FM) session. The current RefleXion treatment planning system (TPS) can be used to evaluate this criterion qualitatively where the PET distribution is displayed utilizing an appropriate threshold window level. However, other TPS such as Varian Eclipse, was used to evaluate this criterion quantitatively.
Results: We successfully evaluated this method on previously treated patients on our BgRT system and it is now part of the physics initial chart check. In one of the patients, the maximum uptake in (BTZ) was 33.8kBq/ml while the maximum uptake in (BTZ-Annulus-2cm) was 16.6kBq/ml, which is less than 50% of the former therefore eligible for treatment. In another patient, the maximum uptake in (BTZ) was 28.4kBq/ml while the maximum uptake in (BTZ-Annulus-2cm) was 29.6kBq/ml which is more than 50% of the former therefore ineligible for treatment.
Conclusion: We have presented a simple and reliable method, useful to the clinical team when determining which patients are eligible for treatment on the novel BgRT system based on FDG uptake distribution.