Objective: Two opposed tangential photon beams followed by scar boost with electrons is a common technique for post-mastectomy radiotherapy to the chest wall. However with current advances in x-rays (conformal and intensity modulated radiotherapy), the electrons have gained less attention; and most of the centres are using the conventional electron therapy techniques. Here we share our experience of electron conformal therapy (ECT) and modulated electron therapy (MET) for post-mastectomy scar boost.
Materials and methods: For post-mastectomy chest wall irradiation, 25 patients were treated with ECT and MET in five steps (a) virtual simulation and image acquisition using CT scanner Siemens® followed by (b) data transfer to Coherence Siemens® for contouring of skin, clinical target volume (CTV), planning target volume (PTV) and organs at risk (OARs), followed by (c) forward and reverse planning applying segmented fields using Prowess Panther treatment planning system (TPS) Siemens® and shaping of fields on beam’s eye view (BEV), (d) data transfer to computer assisted fabrication device (Autimo 2D) for lead cut outs and wax blocks and finally (e) quality assurance (QA) and modified treatment delivery.
Results: Apart from energy selection and tumor delineation, the ECT and MET showed maximal sparing of OARs (< 70% of prescribed dose), and improved dose conformity compared to single energy single field plans. Phantom and in vivo dosimetric measurements showed excellent agreement with calculated doses with difference ±2%. Conformity improved little beyond allowing three energies due to energy overlap and field-size constraints and conformity improvement was found at the expanse of dose heterogeneity within the PTV.
Conclusions: ECT and MET is time saving and can be utilised for treating superficial targets to improve the treatment outcome and with better QA; however, efforts are required to design commercially available eMLC (electron multileaf collimators) in modern linear accelerators.