comparison of setup errors in prostate cancer radiotherapy: mv epid vs. kv cbct

Introduction: accurate patient setup is essential for precise dose delivery in prostate radiotherapy. this study quantified random and systematic setup errors using mv epid and kv cbct verification techniques to identify the modality associated with minimal setup errors and to determine appropriate planning target volume (ptv) margins.material and methods: setup errors along the x (left–right, lr), y (superior–inferior, si), and z (anterior–posterior, ap) axes were retrospectively extracted from archived electronic records for 100 prostate cancer patients treated between 2015 and 2023. fifty (50) patients had positions verified using mv epid and 50 using kv cbct techniques. setup errors were compared using an independent samples t-test with a significance threshold of p < 0.05. ptv margins were calculated using van herk's formula.results: for kv cbct, random errors were 0.8 (lr), 3.0 (si), and 1.5 mm (ap), and systematic errors were 0.1, 0.4, and 0.2 mm, respectively. for mv epid, corresponding random errors were 0.5 (lr), 14.1 (si), and 8.6 mm (ap), and systematic errors were 0.1, 2.0, and 1.2 mm. no statistically significant difference was found along the lr axis (p = 0.0630), but significant differences were observed along the si and ap axes (p = 0.0022 and p = 0.0001). calculated ptv margins for kv cbct were 0.9 (lr), 3.2 (si), and 1.6 mm (ap), whereas for mv epid, these were 0.5 (lr), 14.8 (si), and 9.0 mm (ap). kv cbct demonstrated superior setup accuracy with reduced margins.conclusion: kv cbct demonstrated superior setup accuracy, enabling tighter ptv margins and reduced normal tissue exposure. its use is recommended for hypofractionated prostate cancer radiotherapy.