SU-E-T-573: Quality and Deliverability of Intensity Modulated Neutron Radiotherapy (IMNRT) Plans.

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Technology

Background:

• Intensity Modulated Neutron Radiotherapy (IMNRT) is a new clinical technique.
• The number of segments in IMNRT plans is restricted by the speed of the multi-leaf collimator (MLC).
• Guidelines for IMNRT plan complexity are needed to ensure quality and deliverability.

Purpose of the Study:

• To evaluate the quality and deliverability of static IMNRT treatment plans.
• To establish guidelines for the maximum number of segments per IMNRT plan.
• To assess compliance with TG-119 dose constraints for varying plan complexities.

Main Methods:

• Treatment plans were optimized using the Varian Eclipse Treatment Planning System (TPS).
• A 4MV photon beam served as a surrogate for neutron beam optimization.
• MLC segments were generated for three complexity levels: very limited (15-23), limited (24-31), and unlimited.
• Dose-volume histograms (DVHs) were analyzed for TG-119 compliance.
• Estimated delivery times were calculated based on known parameters.

Main Results:

• The prostate case met all TG-119 constraints across all complexity levels.
• Other cases failed to meet at least one constraint at certain complexity levels.
• The number of met constraints increased with complexity: 16 (very limited), 17 (limited), 19 (unlimited) out of 23 total.
• Mean delivery times were 34, 40, and 68 minutes for very limited, limited, and unlimited complexity, respectively.

Conclusions:

• Current MLC capabilities limit the quality of IMNRT plans.
• IMNRT plans should be restricted to approximately 25 segments.
• This segment limitation ensures a treatment time under 45 minutes.
• Most TG-119 dose constraints can be met even with a limited number of segments.