Assessing efficacy and toxicity in rectal cancer radiotherapy: a comparative study of two fractionation regimens

Objectives: Rectal cancer is a significant global health concern, with radiotherapy playing a crucial role in treatment. However, optimal fractionation regimens remain debated, particularly with newer treatment techniques such as the use of Halcyon-based radiotherapy. This study aims to compare dosimetric and radiobiological parameters between two radiotherapy regimes for rectal cancer: 50Gy/25 fractions and 50.4Gy/28 fractions. Methods: A retrospective analysis of 28 treatment plans was conducted. Group A (10 plans) received 50Gy/25 fractions, while Group B (18 plans) received 50.4Gy/28 fractions. The study evaluated parameters including dose volume histograms (DVH), conformity index (CI), homogeneity index (HI), tumor control probability (TCP), normal tissue complication probability (NTCP), equivalent uniform dose (EUD), and biologically effective dose (BED) across the two groups. Results: No significant dose differences were found in normal tissues between the groups. However, it demonstrated a significantly higher conformity index (CI) for the planning target volume (0.98 ± 0.01 vs. 0.96 ± 0.02, p=0.007) and biologically effective dose (BED) (71.82 ± 0.32 vs. 70.08 ± 0.08, p<0.001). Additionally, Group A exhibited a higher normal tissue complication probability (NTCP) for the bladder (0.03 ± # vs. 0.02 ± #, p=0.004). Conversely, Group B had a lower tumor control probability (TCP) compared to Group A. Conclusions: Group A offers better tumor coverage and comparable TCP but has a higher NTCP, indicating a potential increase in normal tissue complications compared to Group B. While the study provides valuable dosimetric and radiobiological insights, its retrospective nature and limited sample size pose constraints on generalizability.