Applying radiobiological plan ranking methodology to VMAT prostate SBRT

Area of Science:

• Radiation oncology
• Medical physics

Background:

• Volumetric Modulated Arc Therapy (VMAT) stereotactic body radiation therapy (SBRT) is a common prostate cancer treatment.
• Rectal spacers are used to reduce radiation dose to the rectum.
• Optimizing dose escalation while minimizing toxicity is crucial for treatment efficacy.

Purpose of the Study:

• To evaluate the impact of a rectal spacer and increased near-maximum dose on tumor control probability (TCP) and normal tissue complication probabilities (NTCP) in VMAT prostate SBRT.
• To compare treatment plans with and without a rectal spacer at different dose levels.
• To assess the trade-offs between tumor control and toxicity for various planning strategies.

Main Methods:

• Generated four VMAT plans for 11 patients based on CT scans before and after transperineal spacer insertion.
• Plans included two dose levels: D2%⩽37.5Gy (Hom) and D2%⩽40.2Gy (Het).
• Utilized parameter-invariant TCP ranking and Lyman's NTCP model for rectum and bladder.

Main Results:

• Higher dose plans (Het) showed significantly better TCP than standard dose plans (Hom).
• Plans with a rectal spacer generally improved TCP and reduced rectal NTCP compared to plans without.
• Rectal NTCPs for Het plans were similar to Hom plans, but Hom plans with spacers had lower rectal NTCPs than those without.
• Bladder NTCPs were negligible across all plans.

Conclusions:

• Increased near-maximum target dose (D2%⩽40.2Gy) in VMAT prostate SBRT enhances tumor control.
• Rectal spacer use improves tumor control and reduces rectal complication risk.
• Combining a rectal spacer with dose escalation offers a promising strategy for improved prostate SBRT outcomes.