An updated approach for deriving PTV margins using image guidance and deformable dose accumulation

Area of Science:

• Radiation Oncology
• Medical Physics

Background:

• Accurate planning target volume (PTV) margins are crucial for effective image-guided radiotherapy.
• Current methods may not fully account for inter-patient anatomical variations.

Purpose of the Study:

• To introduce and validate an updated, semi-automated approach for deriving PTV margins.
• To ensure consistent clinical target volume (CTV) coverage in volumetric image-guided radiotherapy.

Main Methods:

• A semi-automated workflow combining dose accumulation and the bidirectional local distance (BLD) metric was developed.
• Patient cohorts were divided into derivation and validation sets for margin calculation and testing.
• Deformable image registration was used to accumulate doses from idealized zero-margin plans.

Main Results:

• Derived PTV margins were 3 mm for oropharyngeal cancer and 5 mm for early-stage breast cancer.
• The method ensured 95% prescription dose to 98% of the CTV for 90% of patients.
• Validation confirmed CTV coverage criteria were met in at least 90% of patients.

Conclusions:

• This methodology provides a robust approach for deriving PTV margins in realistic radiotherapy scenarios.
• The approach is applicable across various disease sites, enhancing understanding of treatment outcomes.
• This technique can optimize PTV margin selection for image-guided radiotherapy.