Introduction and purpose: The aim of this study is introducing a new Mono-Isocentric Technique)MIT) for external  radiotherapy of the chest wall in the mastectomy patients with 6MV photon beams and comparing this technique with the Dual-Isocentric Technique(DIT).

Materials and methods: Data of 18 mastectomy patients having chest wall radiotherapy were used. The target tissue was divided into nine regions with 17 points as the appropriate candidates to find the appropriate dose calculation reference point for the MIT. Dose calculations were made for each patient based on the MIT and DIT to determine the dose distributions of the target volume and organs at risk after finding the dose calculation reference point.

Findings: The lateral component of the dose calculation reference point was found to be located at one-third of the distance between the geometrical center and the lateral border of the chest wall in the lateral direction toward the outer border. The longitudinal component of this point was found to be located at the geometrical center of the chest wall with a depth located around 2–3 cm under the patients’ skin. There was no significant difference between the two radiotherapy planning techniques regarding the dose distri­butions in the organs at risk and the 95% of the prescribed dose coverage of the target tissue. However, a significant difference for the 105% of the prescribed dose coverage, maximum dose delivered to the target tissue was found, with the DIT showing higher values

Discussion and conclusion: Because of the good matching and no superposition observed between the treatment fields in the MIT, it was expected and confirmed that the regions with higher and lower doses than the prescribed dose with the MIT are significantly fewer than that of the DIT. Therefore, to perform a better conformal radiotherapy for the patients having mastectomy, it could be recommended to use the MIT instead of the DIT and other conventional techniques.