Coverage-based treatment planning: optimizing the IMRT PTV to meet a CTV coverage criterion.

Area of Science:

• Radiation Oncology
• Medical Physics
• Radiotherapy Planning

Background:

• Ensuring adequate target coverage in radiotherapy is challenged by patient setup errors.
• Current planning methods may not fully account for dosimetric margins and geometric uncertainties.
• Optimizing planning target volume (PTV) margins is crucial for dose escalation and normal tissue sparing.

Purpose of the Study:

• To introduce and evaluate an iterative coverage-based treatment planning approach.
• To assess the method's ability to ensure specified clinical target volume (CTV) coverage under setup uncertainties.
• To quantify the impact of this approach on PTV size and irradiated normal tissue volumes.

Main Methods:

• An iterative algorithm adjusted the clinical target volume to planning target volume (CTV-to-PTV) margin.
• The adjustment continued until a predefined CTV coverage percentage was achieved for a given level of setup error.
• The method was applied to 27 prostate cancer treatment plans.

Main Results:

• The average CTV-to-PTV margin was reduced from 5 mm to 2.8 mm.
• The total volume of normal tissue receiving > or =65 Gy decreased by an average of 19.3% (approx. 48 cc).
• Significant reductions were observed in the irradiated volumes of bladder and periprostatic rectum.

Conclusions:

• Coverage-based treatment planning offers an effective strategy for optimizing radiotherapy plans.
• The iterative approach automatically accounts for dosimetric margins, leading to smaller PTVs and reduced normal tissue toxicity.
• This method advances probabilistic treatment planning and is applicable across various sites and delivery techniques.