Modeling of Acute Rectal Toxicity to Compare Two Patient Positioning Methods for Prostate Cancer Radiotherapy: Can...

Area of Science:

• Radiation Oncology
• Medical Physics
• Clinical Oncology

Background:

• Intensity Modulated Radiation Therapy (IMRT) offers dose reduction for prostate cancer patients.
• Accurate IMRT delivery is challenged by patient positioning errors.
• Monitoring IMRT quality is crucial for minimizing treatment toxicity.

Purpose of the Study:

• To evaluate the potential of modeling acute rectal toxicity for assessing IMRT protocol quality.
• To correlate planning dosimetry with clinical outcomes in prostate cancer patients undergoing IMRT.

Main Methods:

• Compared 79 patients receiving Image and Fiducial Markers Guided IMRT (FMIGRT) with 302 patients receiving trans-abdominal ultrasound guided IMRT (USGRT).
• Modeled rectal toxicity using Lyman Kutcher Burman (LKB) and Univariate Logistic Regression (ULR) models.
• Utilized Receiver Operating Characteristics (ROC) analysis and Area Under the Curve (AUC) to compare model performance.

Main Results:

• Observed grade ≥ 2 acute rectal toxicity was 20% for FMIGRT and 54% for USGRT.
• LKB model parameters for FMIGRT: TD50=56.8 Gy, slope m=0.093, exponent n=0.131.
• The FMIGRT ULR model showed good predictive performance (AUC=0.67), while the USGRT ULR model did not (AUC=0.5).

Conclusions:

• Modeling acute rectal toxicity provides a quantitative link between dosimetry and clinical toxicity.
• A weak correlation between modeled toxicity and actual outcomes may indicate patient positioning errors.
• This approach can serve as a quality assurance tool for IMRT delivery in prostate cancer.