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Real-time Image-guided Adaptive-predictive Prostate Radiotherapy using Rectal Diameter as a Predictor of Motion
1Radiation Therapy Services, Peter MacCallum Cancer Centre, Bendigo, Victoria, Australia; Medical Imaging & Radiation Sciences, Monash University, Melbourne, Victoria, Australia.
Clinical Oncology (Royal College of Radiologists (Great Britain))
|October 27, 2016
Summary
Measuring maximum rectal diameter (MRD) on pre-treatment cone beam computed tomography (CBCT) can predict prostate motion during adaptive image-guided radiotherapy (IGRT). This helps optimize treatment margins and reduce normal tissue complication probability (NTCP).
Area of Science:
- Radiation Oncology
- Medical Imaging
- Radiotherapy Physics
Background:
- Adaptive image-guided radiotherapy (IGRT) aims to improve treatment accuracy for prostate cancer.
- Intra-fraction prostate motion can impact treatment efficacy and toxicity.
- Predicting and managing prostate motion is crucial for optimizing radiotherapy planning.
Purpose of the Study:
- To investigate the relationship between maximum rectal diameter (MRD) measured on pre-treatment cone beam computed tomography (CBCT) and intra-fraction prostate motion.
- To establish a predictive method for small prostate displacement using MRD.
- To evaluate the impact of adaptive margins on normal tissue complication probability (NTCP) for the rectum and bladder.
Main Methods:
- Retrospective analysis of 2125 CBCTs from 55 patients.
- Measurement of MRD and correlation with prostate displacement using intra-fraction imaging.
- Development of a linear regression model to identify MRD thresholds for predicting prostate motion.
- Comparison of standard and reduced adaptive margin plans to assess NTCP for rectum and bladder.
Main Results:
- With 90% confidence, MRD ≤ 3 cm predicts prostate displacement ≤ 5 mm, and MRD ≤ 3.5 cm predicts displacement ≤ 5.5 mm.
- Adaptive therapy with reduced margins led to median NTCP reductions of 0.5% for the rectum and 1.3% for the bladder.
- Further reductions in NTCP (1.1% for rectum, 2.6% for bladder) were observed with a second adaptive scenario.
Conclusions:
- Maximum rectal diameter (MRD) on pre-treatment CBCT is a viable predictor of intra-fraction prostate motion.
- This finding supports the development of adaptive prostate IGRT strategies.
- Measuring MRD offers a potential method to optimize treatment margins and minimize radiation toxicity.
