Radiobiological Evaluation of Three Common Clinical Radiotherapy Techniques Including Combined Photon‑Electron, Tangential Beams and Electron Therapy in Left‑Sided Mastectomy Patients

The aim of this study was radiobiological evaluation of different radiotherapy (RT) techniques, namely, combined photon‑electron, two tangential photon beams, and electron therapy which are commonly used for treatment of mastectomy patients.

The mentioned techniques were planned on the computed tomography (CT) images of a chest phantom, using TiGRT treatment planning system (TPS). The TPS dose calculations were verified using Thermo Luminescence dosimeters (TLD) measurements. Dose‑volume histogram (DVH) of the plans was generated in the TPS, and also tumor control probability (TCP) and normal tissue complication probability (NTCP) values were calculated using DVH data for each technique. For TCP and NTCP modeling, Poisson Linear‑Quadatric (PLQ) and Lyman‑Kutcher‑Burman (LKB) models were used, respectively.

The TCPs for the chest wall, internal mammary nodes, supraclavicular nodes, and axilla for the combined photon‑electron was 90%, 90%, 90%, and 65%, respectively, which was higher compared to tangential beams (up to 11%, 11%, 5%, and 5%, respectively) and the electron therapy (up to 11%, 11%, 33%, and 23%, respectively) Whereas the NTCPs of the tangential beams for ipsilateral and contralateral lungs, heart, and chest wall–lung interface was 4%, 1%, 3%, and 5.6%, respectively. These NTCP values were considerably lower than electron therapy (up to 42%, 66%, and 40% and 30%, respectively) and combined photon‑electron (up to 55%, 75%, 50%, and 20%, respectively) methods.

Tangential beam is suggested for treating mastectomy patients, due to sufficient value of TCP, and also lower NTCP compared to the other techniques such as electron therapy and combined photon‑electron.