SU-E-J-07: Image Guided Radiotherapy for Prostate Cancer: To Shift Or to Re-Plan?

Area of Science:

• Radiation Oncology
• Medical Physics
• Image-Guided Therapy

Background:

• Advanced imaging techniques aid patient setup in prostate radiotherapy.
• Current methods struggle with rotational motion and organ deformation, potentially compromising target coverage.
• 3D dose distributions offer a novel approach to enhance accuracy.

Purpose of the Study:

• To investigate the feasibility of using 3D dose distributions for target volume matching.
• To improve target coverage and critical structure sparing in prostate radiotherapy.
• To evaluate the effectiveness of 3D dose matching against standard contour-based methods.

Main Methods:

• Retrospective analysis of 15 prostate cancer patients.
• Weekly CT-on-rails scans before and after Intensity-Modulated Radiation Therapy (IMRT).
• Reconstruction of 98 post-treatment dose distributions for comparison with original plans.
• Isocenter realignment using 3D dose/target volume matching evaluated against contour-based localization.

Main Results:

• Standard contour/anatomy matching resulted in 7.1% of fractions with poor target coverage (Dmin<65Gy).
• Rectal dose constraints were violated in 27.6% (V65<17%) and 26.5% (V40<35%) of fractions.
• 3D dose/target volume matching improved target coverage to >65Gy for all fractions and reduced rectal constraint violations to 14.3% and 18.4%.

Conclusions:

• Current image-guided radiation therapy (IGRT) for isocenter alignment has limitations due to soft-tissue contrast and organ motion/deformation.
• 3D dose/target volume matching enhances target dose coverage and critical structure sparing.
• This approach reduces the necessity for adaptive re-planning in prostate radiotherapy.