[Prostatic carcinoma: problems in the interpretation of rectal dose-volume histograms]

Area of Science:

• Radiation Oncology
• Medical Physics

Background:

• Dose-volume histograms (DVHs) are essential for predicting late radiation side effects.
• The predictive value of rectal DVHs is debated, potentially due to inconsistent organ contouring.
• Specifically, the cranial and caudal borders of the rectum are not uniformly defined in existing literature.

Purpose of the Study:

• To investigate the impact of varying rectal border definitions on DVHs.
• To assess whether these variations influence the prediction of rectal bleeding after prostate cancer radiotherapy.

Main Methods:

• Analyzed DVHs from 12 prostate cancer patients undergoing conformal radiotherapy.
• Compared DVHs of 6 patients with mild rectal bleeding to 6 matched controls without bleeding.
• Generated four distinct DVHs per patient by altering rectal border definitions, calculating volume fractions (V50, V80, V95, aV50, aV80, aV95).

Main Results:

• Significant variations in volume fractions were observed based on rectal border definitions for all patients.
• Bleeding patients consistently showed higher mean and median percent and absolute volume fractions compared to non-bleeding patients.
• No single DVH metric could definitively distinguish between patients who experienced bleeding and those who did not.

Conclusions:

• High variability exists in rectal DVH metrics due to inconsistent definition of rectal borders.
• A standardized definition for rectal borders is necessary for consistent comparison and interpretation of rectal DVHs.
• This standardization is vital for improving the accuracy of predicting radiation-induced rectal toxicity.