Purpose: Radiotherapy using Proton beam was preformed in the past using upright or “seated” position for head and neck treatment sites, using a fixed Proton beam. Utilizing the system with advanced image guidance techniques and robotic patient positioning, it becomes possible to extend this positioning approach for the treatment of abdominal and pelvic disease sites. In this work, we investigate the feasibility of prostate treatment in seated position using commercial TPS and CT data.
Methods: P-Cure (P-Cure, Shilat, Israel) offers a 360 degrees gantry-less system, for Proton PBS using patient seated position. A custom chair allows a patient CT scanning from head to thigh in the treatment position. We used two scans for comparison: seated using the P-Cure system and supine. The planning was conducted for Proton PBS in upright position and supine using Eclipse (Varian Medical Systems, Palo Alto, CA),for a 70.2 Gy to the prostate and 46.8 Gy to the LN prescribed in 26 fractions. We used RaySearch (RaySearch laboratories, Stockholm, Sweden),for prostate 70.2 Gy (RBE) plan prescribed in 26 fractions. The Proton upright plan was done using two lateral PBS fields with robust optimization, while the supine scan was planned with VMAT.
Results: The seated position was found a lower OAR dosage. The rectal mean dose was about 11.2 Gy (RBE) and about 30 Gy for the seated and supine position respectively. The bladder, small bowel and femoral heads showed lower doses compatible to a common Proton delivery.
Conclusion: We showed that treating prostate patients is feasible using seated position. While showing OAR sparing, one should consider multiple posterior oblique fields for better dose delivery in addition to overcoming the range uncertainty that can be smeared over larger region while taking into account patient stability over delivery time.