Treatment Outcomes and Predictors of Relative Dose Intensity Among Patients Receiving Chemotherapy for Colorectal Cancer in Nakuru County, Kenya: a Retrospective Cohort Study

Colorectal cancer is an increasing cause of cancer morbidity and mortality in Africa, where late diagnosis and constrained oncology services may compromise treatment delivery. Relative dose intensity is an important measure of chemotherapy delivery, but evidence describing its predictors and relationship with outcomes in Kenyan public oncology practice remains limited. The aim of the study was to determine chemotherapy RDI, identify factors associated with achieving optimal RDI, evaluate treatment response and survival, and examine the relationship between RDI and treatment outcomes among patients with colorectal cancer receiving chemotherapy at a county referral hospital in Kenya. A retrospective cohort study was conducted using records of adults with colorectal cancer treated between January 2020 and December 2024 at Nakuru County Referral Hospital. A simple random sample was drawn from 300 eligible records; 186 records were selected, and 185 complete records were analysed. Data were abstracted using a structured tool. RDI was calculated as the actual dose intensity divided by the planned dose intensity × 100 and classified as optimal (≥85%) or suboptimal (<85%). Descriptive statistics, chi-square tests, binary logistic regression, Kaplan-Meier analysis, log-rank tests, and unadjusted Cox regression were performed using SPSS version 26. The mean RDI was 82.95% (SD 5.35; range 60.0-98.0%), with 44.9% achieving optimal RDI and 55.1% suboptimal RDI. Treatment delays occurred in 91.9% of patients, with toxicity the most common reason; dose reductions or adjustments occurred in 42.7%. Age group, dose reduction/adjustment (AOR 0.34, 95% CI 0.13-0.87; p = 0.025), and treatment response (overall p = 0.007) were independently associated with optimal RDI. Median overall survival was 15 months for suboptimal RDI and not reached for optimal RDI (HR 0.093, 95% CI 0.052-0.168). Corresponding progression-free survival results were 14 months and not reached (HR 0.103, 95% CI 0.060-0.179). Suboptimal chemotherapy RDI was common, characterised by frequent treatment delays and dose modification. Optimal RDI was strongly associated with better observed survival, although the unadjusted survival analyses do not establish causality. Routine toxicity management, treatment schedule monitoring, medication availability, and RDI monitoring may help strengthen chemotherapy delivery in comparable resource-constrained settings.