Dose deformation-invariance in adaptive prostate radiation therapy: implication for treatment simulations

Area of Science:

• Radiation Oncology
• Medical Physics
• Image-guided Radiation Therapy

Background:

• Adaptive radiation therapy (ART) aims to adjust treatment based on anatomical changes during therapy.
• Prostate cancer treatment often involves intensity-modulated radiation therapy (IMRT).
• Evaluating dose deformation-invariance is crucial for efficient ART.

Purpose of the Study:

• To investigate the accuracy of assuming dose deformation-invariance in adaptive prostate radiation treatment.
• To quantify the error introduced by this assumption in IMRT plans.

Main Methods:

• A cohort of 19 prostate cancer patients with multiple CT scans was analyzed.
• 79.2 Gy IMRT plans were created using 6 and 18 MV beams.
• Dose distributions were evaluated by recalculating dose on each image versus copying the initial plan, simulating shifts and deformations.

Main Results:

• The per-voxel mean percent dose difference was minimal (<1.6% for 6 MV, <1% for 18 MV).
• Root-mean-square-percentage-errors for critical structures (CTV, rectum, bladder) were generally below 2%.
• Dose differences showed no significant correlation with anatomical similarity (Dice coefficients).

Conclusions:

• Assuming dose deformation-invariance in adaptive prostate IMRT plans introduces less than 2% error in key dose-volume metrics.
• This assumption can potentially reduce online re-planning time.
• It may enable pre-planning strategies based on tissue deformation models.