Intermediate rectal dose is associated with late toxicity after prostate SBRT: a dose-volume histogram principal
Amadeo J Wals Zurita1, Ana Illescas Vacas2, Héctor Miras Del Río3
1Department of Radiation Oncology, Hospital Universitario Virgen Macarena, Seville, Spain. amadeoj.wals.sspa@juntadeandalucia.es.
Purpose:
To evaluate whether principal component analysis (PCA) of rectal and bladder dose-volume histograms (DVHs) identifies dose regions associated with late toxicity after prostate stereotactic body radiotherapy (SBRT).
Methods/Patients:
This retrospective single-institution study included 106 patients with linked clinical and dosimetric data after prostate SBRT to 36.25 Gy in five fractions. PCA was applied separately to whole-organ and wall-based rectal and bladder DVHs. Associations with late grade ≥ 2 gastrointestinal (GI) and genitourinary (GU) toxicity at 12 months were explored using Spearman correlation, ROC analysis and deliberately limited logistic regression. Toxicity was extracted retrospectively from institutional follow-up records scored according to CTCAE v5.0.
Results:
Among 84 patients with 12-month follow-up in the DVH-linked dosimetric cohort, grade ≥ 2 toxicity was uncommon, with 3 GI events (3.6%) and 2 GU events (2.4%). Intermediate-dose rectal metrics showed the strongest exploratory signal for late GI toxicity, particularly rectal V18.1 Gy (AUC 0.868, 95% CI 0.740-0.997) and V29 Gy (AUC 0.827). These estimates are based on very few events and should not be interpreted as validated predictive performance or as evidence of a new planning threshold. No bladder or bladder-wall metric showed clinically meaningful discrimination for GU toxicity.
Conclusions:
Intermediate whole-rectum dose was associated with late GI toxicity in this low-event SBRT cohort, but the findings are exploratory and require validation. No isolated dosimetric predictor of late GU toxicity was identified.
