Purpose <p>We aim to compare the thorax tilt arm support with the manifold (M-fold) arm support in positioning and immobilization during breast cancer radiotherapy. Additionally, we seek to identify which technique is more effective in terms of dosimetric coverage, reproducibility, and patient comfort.</p> Materials and Methods <p>This is a two-arm observational study that included 40 patients. Arm 1 consists of patients using M-fold arm support, while Arm 2 involves patients using the Thorax Tilt arm support. After positioning, computer tomography (CT) scans were taken. The images were exported to the treatment planning system (TPS), contoured, and planning was performed. Dosimetric parameters, reproducibility in six directions, and comfort scores were recorded in both groups. Statistical analysis was conducted using the chi-square test, t-test, and calculations of mean and standard deviation.</p> Results <p>In our study, patients’ parameters and target coverage were similar in both groups. The thorax tilt arm had a lower mean dose to both lungs compared to the M-fold arm, with a significant <i>P</i>-value. Additionally, V20% and V5% of the heart were lower in the thorax tilt arm, with no statistically significant difference. Reproducibility was similar in both arms. The thorax tilt group reported higher comfort levels than the M-fold group, with a significant <i>P</i>-value.</p> Conclusion <p>For patients with breast cancer receiving adjuvant radiotherapy, the thorax tilt group position provides greater comfort and reduces the radiation dose to the heart and lungs. Both the thorax tilt group and the M-fold group devices ensuring reproducible setup and delivering acceptable dosimetry.</p>