Dose-volume analysis of planned versus accumulated dose as a predictor for late gastrointestinal toxicity in men receiving radiotherapy for high-risk prostate cancer.

BACKGROUND AND PURPOSE

Significant dose deviations have been reported between planned (D) and accumulated (D) dose in prostate radiotherapy. This study aimed to develop multivariate analysis (MVA) models associating Grade 1 and 2 gastrointestinal (GI) toxicity with clinical and D or D dosimetric variables separately.

MATERIALS AND METHODS

Dose volume (DV) metrics were compared between D and D for 150 high-risk prostate cancer patients. MV models were generated from significant clinical and dosimetric variables (p < 0.05) at univariate level. Dose-based-region of interest (DB-ROI) metrics were included. Model performance was measured, and additional subgroup analysis were performed.

RESULTS

Rectal D demonstrated a higher intermediate-high dose (V and DB-ROI at 15-50 mm) compared to D. Conversely, at the very high dose region, rectal D (V and DB-ROI at 5-10 mm) were significantly lower. In MVA, rectal DB-ROI at 10 mm was predictive for Grade ≥ 1 GI toxicity for D and D. Age, rectal D for D, and rectal D for DB-ROI 10 mm were predictors for Grade 2 GI toxicity. Subgroup analysis revealed that patients ≥ 72 years old and a rectal D of ≥ 78.2 Gy were highly predictive of Grade 2 GI toxicity.

CONCLUSIONS

The dosimetric impact of a higher dose rectal dose in D due to volumetric changes was minimal and was not predictive of detrimental clinical toxicity apart from rectal D ≥ 78.2 Gy for Grade 2 GI toxicity. The use of the DB-ROI method can provide equivalent predictive power as the DV method in toxicity prediction.