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Defining the risk of developing grade 2 proctitis following 125I prostate brachytherapy using a rectal dose-volume
K M Snyder1, R G Stock, S M Hong
1Department of Radiation Oncology, Mount Sinai School of Medicine, New York, NY 10029, USA.
Summary
Minimizing rectal dose in 125I prostate implantation significantly reduces radiation proctitis risk. Keeping the delivered dose below rectal volume thresholds is crucial for patient outcomes.
Area of Science:
- Radiation Oncology
- Medical Physics
- Urology
Background:
- Radiation proctitis is a common morbidity following 125I prostate brachytherapy.
- Predictive models are needed to assess and mitigate rectal toxicity.
Purpose of the Study:
- To establish rectal tolerance limits for Grade 2 radiation proctitis.
- To correlate rectal dose-volume histogram (DVH) parameters with proctitis development after 125I prostate implantation.
Main Methods:
- A cohort of 212 patients with T1-T2 prostate cancer treated with 125I implantation underwent CT-based dosimetry.
- Rectal volumes and doses were analyzed using TG43 formalism.
- Dose-response analysis identified critical rectal volume thresholds for Grade 2 proctitis.
Main Results:
- Grade 2 proctitis developed in 22 patients, with a median onset between 1-2 years post-implantation.
- Rectal volume receiving the prescription dose (160 Gy) was significantly associated with proctitis risk.
- A rectal volume of ≤1.3 cc receiving 160 Gy correlated with a 5% proctitis rate at 5 years, versus 18% for >1.3 cc (p=0.001).
Conclusions:
- Rectal DVH analysis is a valuable tool for predicting Grade 2 proctitis risk after 125I prostate implantation.
- Adhering to defined rectal volume dose thresholds can minimize rectal morbidity.
- Modifying prostate implant techniques based on DVH data can improve patient outcomes.