Target miss using PTV-based IMRT compared to robust optimization via coverage probability concept in prostate cancer

Area of Science:

• Radiation Oncology
• Medical Physics
• Oncology

Background:

• Prostate Intensity-Guided Radiation Therapy (IGRT) planning target volume (PTV) margins significantly impact cure and toxicity rates.
• Optimizing PTV margins is crucial for dose-escalated prostate radiotherapy to balance target coverage and organ at risk (OAR) sparing.
• Conventional PTV-based IMRT may not adequately account for prostate motion and deformation, potentially compromising treatment efficacy and safety.

Purpose of the Study:

• To evaluate the efficacy of the coverage probability (CovP) concept for robust plan optimization in dose-escalated prostate radiotherapy.
• To compare CovP-based IMRT with conventional PTV-based IMRT regarding OAR sparing and compensation for prostate motion.
• To assess the feasibility of probabilistic dose-escalated IMRT in a prospective study.

Main Methods:

• A prospective study involving 27 intermediate-risk prostate cancer patients treated with 78 Gy/39 fractions.
• CovP-plans were evaluated using three separate CT scans to capture organ motion and deformation.
• CovP-dose distribution was optimized considering probabilities of systematic organ displacement, compared to conventional PTV-based IMRT plans.

Main Results:

• CovP-concept demonstrated superior robustness in target volume coverage compared to PTV-based IMRT.
• PTV-based IMRT frequently resulted in target misses and cold spots, whereas CovP-concept mitigated these issues.
• While dose escalation was comparable at certain levels, PTV-based IMRT led to increased OAR doses, particularly in high-dose regions.

Conclusions:

• Probabilistic dose-escalated IMRT using the CovP-concept is feasible and offers significant advantages over conventional PTV-based IMRT.
• The CovP-concept provides superior target coverage and enhanced OAR sparing by implementing a robust optimization strategy for organ motion and deformation.
• CovP-based IMRT represents a promising approach towards adaptive IGRT, potentially reducing the need for daily re-planning.