Plan space: representation of treatment plans in multidimensional space

Area of Science:

• Medical Physics
• Radiation Oncology
• Image Analysis

Background:

• Radiation therapy planning aims to balance target coverage with normal tissue sparing.
• Multiple treatment plans can meet minimum dose-volume criteria, but optimal plan selection remains challenging.
• Existing methods may not fully leverage the potential for superior normal tissue protection.

Purpose of the Study:

• To present a method for comparing radiation therapy treatment plans.
• To aid planners in selecting the "best" plan based on dose-volume conditions.
• To visualize and evaluate the space of possible treatment plans for optimal dose-volume characteristics.

Main Methods:

• Treatment plans are represented as points in a multidimensional plan space.
• Coordinates are defined by minimum target dose and percentage volume of normal tissue receiving a specified dose.
• Plan space images are generated for phantom and clinical cases (thorax, abdomen).

Main Results:

• A feasibility boundary in plan space indicates the limits of a treatment technique.
• Utilizing plans on this boundary maximizes treatment modality benefits.
• Plan adjustments (beam angles, weights) can improve existing plans and select superior normal tissue dose distributions.

Conclusions:

• Selecting the best achievable plan involves evaluating the entire plan space for a patient's anatomy.
• This method avoids assigning a single score, allowing physicians to prioritize structures based on clinical judgment.
• Visualization of plan space empowers informed decisions regarding normal tissue irradiation significance.