Simulation study using the spots deletion technique in spot scanning proton beam therapy for prostate cancers

Area of Science:

• Radiation Oncology
• Medical Physics
• Cancer Treatment

Background:

• Spot scanning proton beam therapy (PBT) is an advanced radiation technique.
• Optimizing dose distribution and beam delivery time is crucial for PBT efficacy and safety.
• The spot deletion technique offers a potential method for plan optimization.

Purpose of the Study:

• To investigate the impact of spot deletion on dose distribution and beam delivery time in PBT.
• To evaluate two distinct spot deletion strategies: by weighting deposition and by distance from the clinical target volume (CTV).
• To assess the dosimetric changes in organs at risk (OAR) and the target volume (exCTV) for prostate cancer patients.

Main Methods:

• A spot scanning plan was created for 30 prostate cancer patients.
• Two modification processes were applied: Process A (deleting low-weighting spots) and Process B (deleting spots distant from CTV).
• Dose distributions, including V50 Gy(RBE) for rectum/bladder, V60 Gy(RBE) for urethral bulb, and exCTV inhomogeneity index (INH), were compared between initial and modified plans.

Main Results:

• Process B significantly improved dose distribution, reducing V50 Gy(RBE) to the rectum and bladder and V60 Gy(RBE) to the urethral bulb.
• Process B resulted in a slight increase in the exCTV inhomogeneity index.
• Process A did not significantly alter OAR doses, exCTV parameters, or beam delivery time.

Conclusions:

• Systemic deletion of spots distant from the CTV (Process B) in spot scanning PBT can effectively reduce radiation dose to OAR.
• This optimization strategy holds promise for enhancing treatment safety in PBT without compromising treatment delivery.
• Further investigation into the clinical implications of these dosimetric improvements is warranted.