SU-E-J-168: 4D-PET for Target Volume Delineation in Respiratory-Gated Radiation Therapy

Area of Science:

• Medical Imaging
• Radiation Oncology
• Nuclear Medicine

Background:

• Respiratory motion significantly impacts tumor delineation and radiation therapy planning.
• Respiratory-gated PET (4D-PET) offers potential for improved accuracy in target volume definition.
• Accurate tumor delineation is crucial for effective radiation therapy while minimizing dose to surrounding organs.

Purpose of the Study:

• To determine an optimized workflow for utilizing 4D-PET in target volume delineation for tumors undergoing respiratory-gated radiation therapy.
• To evaluate the impact of respiratory motion on tumor volume and organ at risk (OAR) doses.
• To identify the most advantageous CT phase for treatment planning.

Main Methods:

• Studied 15 patients with lung and pancreas tumors exhibiting >5mm respiratory motion.
• Utilized 4D-PET with a Philips Gemini BigBore scanner and Varian RPM gating system.
• Identified the internal target volume (ITV) using a SUV=2.2 threshold and expanded to create the planning target volume (PTV), simulating plans on four breathing phases.

Main Results:

• Maximum tumor motion ranged up to 19.2mm in the superior-inferior direction.
• BTV volume standard deviation across phases was 6%-13.7%.
• Planning on a single phase consistently resulted in reduced OAR doses compared to non-gated techniques (p<0.05).

Conclusions:

• 4D-PET confirms tumor motion can be adequately represented by four phases.
• No single optimal phase was identified, suggesting patient-specific planning is necessary.
• Planning and delivery on a single phase achieved consistent dose sparing compared to non-gated methods.