Direct minimization of normal-tissue toxicity via an NTCP-based IMPT planning method

Area of Science:

• Radiation Oncology
• Medical Physics
• Cancer Treatment Planning

Background:

• Intensity-modulated proton therapy (IMPT) planning uses physical dose constraints, which may not fully minimize normal-tissue toxicity (NTCP).
• NTCP is crucial for assessing treatment toxicity and guiding patient selection for proton vs. photon therapy.

Purpose of the Study:

• Introduce a novel NTCP-based IMPT (NTCP-IMPT) planning method.
• Directly minimize normal-tissue toxicity while ensuring adequate tumor coverage.

Main Methods:

• NTCP-IMPT optimizes both NTCP and dose-volume histogram (DVH) objectives, respecting minimum monitor unit constraints.
• The interior-point method solves the optimization problem.
• Compared NTCP-IMPT with standard IMPT in four head-and-neck cancer patients, evaluating dose quality and NTCP for xerostomia and dysphagia.

Main Results:

• NTCP-IMPT plans achieved target dose criteria and comparable maximum spinal cord/brainstem doses to standard IMPT.
• Reduced mean doses to OARs including parotid glands, submandibular glands, oral cavity, and pharyngeal constrictor muscles.
• Achieved average NTCP reductions for xerostomia (grade ≥2: 3.67%; ≥3: 1.07%) and dysphagia (grade ≥2: 7.54%; ≥3: 3.72%).

Conclusions:

• NTCP-IMPT effectively minimizes normal-tissue toxicity.
• Improves sparing of organs at risk, reducing associated side effects.
• Maintains comparable tumor coverage to standard IMPT.