SU-E-J-105: Evaluating Auto-Contouring of Prostate KV Conebeam CTs

Area of Science:

• Radiation Oncology
• Medical Physics
• Image-guided radiotherapy

Background:

• Online adaptive radiotherapy requires accurate auto-contouring of daily kV conebeam CTs (kVCBCT).
• Assessing the suitability of auto-contouring algorithms is crucial for effective adaptive planning.

Purpose of the Study:

• To identify the most effective geometric and dosimetric measures for evaluating kVCBCT auto-contouring algorithms in prostate adaptive radiotherapy.
• To compare the performance of auto-contouring with physician-generated contours.

Main Methods:

• Six prostate cancer patients undergoing IMRT were included.
• kV conebeam CT (kVCBCT) contours were generated using ABAS software and by a physician.
• Prostate D100, D98, and mean dose were assessed.
• Rectal and bladder V70 (volume receiving 70% of the prescription dose) and mean dose were evaluated.
• Dice's Coefficient (DC) and a restricted DC (rDC) were calculated.

Main Results:

• Prostate accuracy is best assessed by D100, with no correlation to Dice's Coefficient (DC).
• Mean dose is not a reliable indicator of contour suitability for any organ.
• Rectal and bladder V70 showed high sensitivity to contour suitability, despite no correlation with DC.
• Restricted Dice's Coefficient (rDC) demonstrated optimal correlation with V70 for rectum and bladder.

Conclusions:

• V70 is the most sensitive metric for rectal and bladder contour suitability in adaptive radiotherapy.
• D100 is the most discerning metric for prostate contouring due to treatment margins.
• Dice's Coefficient and mean dose are not suitable for assessing contour accuracy.
• Restricted Dice's Coefficient (rDC) can serve as an alternative to V70, potentially simplified by proximity to the prostate contour.