Aim: To identify the most reproducible technique of patient positioning and immobilization in patients with carcinoma cervix.

Background: Radiotherapy aims at controlled killing of tumors cells without harming the normal tissue surrounding the disease. The basic aim of radiotherapy planning is to ensure adequate coverage of target with the planned dose and to save the normal tissue. Adequate margins for setup errors are necessary, the margins applied must not be huge as that would adversely affect normal tissue. This study compares the knee rest with thermoplastic pelvic cast in patients with carcinoma cervix with an aim of identifying the most reproducible method.

Material and methods: Cross-sectional study was done in patients of carcinoma cervix undergoing radiotherapy from April 2021 to June 2022 at our institution. Immobilization was performed on 20 patients (Thermoplastic pelvic cast i.e., Pelvic cast pelvic masks=10, Kneerest=10). The systemic error, random error and planning target volume (PTV) margins were calculated for both the techniques and statistically analysed.

Result: The systemic error in lateral (x-axis), longitudinal (y-axis) and vertical (z-axis) in thermoplastic pelvic cast and knee rest are 0.61cm, 0.39cm, 0.15cm and 0.17cm, 0.4cm, 0.32cm respectively. Random error are lateral (x-axis), longitudinal (y-axis), and vertical (z-axis) are 0.07cm, 0.63cm, 0.08cm and 0.10cm, 0.44cm, 0.22cm. CTV-PTV margin using van herk’s formula in lateral (x-axis), longitudinal (y-axis) and vertical axis (z-axis) using thermoplastic pelvic cast and knee rest are 1.59cm, 1.44cm, 0.44cm and 0.49cm, 1.31cm, 0.96cm respectively. CTV-PTV margin using Stroom’s formula in lateral (x-axis), longitudinal (y-axis) and vertical axis (z-axis) using thermoplastic pelvic cast and knee rest are 1.28cm, 1.24cm, 0.36cm and 0.41cm, 1.11cm, 0.80cm respectively.

Conclusion: Among the two techniques, knee rest technique is least time consuming and most economically viable in developing countries.