ESTRO 2024 - Abstract Book

S588

Clinical - Breast

ESTRO 2024

Post-operative whole-breast radiotherapy (WBRT) is standard treatment after conservative surgery in early stage breast cancer. Through the years, we have evolved from 2D radiotherapy, to three-dimensional radiotherapy (3DRT), a technique which permits a more conformal treatment volume, decreasing dose to organs at risk (OAR), and conserving local control, through the use of medial and lateral tangential fields. 3DRT with field-in-field homogenization is currently a widely used technique for WBRT planning. Concerns remain about high radiation doses to areas of the breast, affected by different factors, like breast shape or size, having an impact in breast cosmesis. Other, more modern radiotherapy techniques, like IMRT/VMAT, have been implemented in breast cancer radiotherapy, achieving more homogeneous treatment plans, and better conformation to PTV, at the cost of increasing the volume of healthy tissue that receives low doses of radiation, which could result in more toxicity, or have an impact in the development of second malignancies, in patients that have an increasing survival rate. Hybrid treatment techniques have been used by different institutions, to try and solve these challenges in WBRT planning. In our centre, we have combined a 3DRT and VMAT hybrid approach, to preserve the advantages of tangential fields in the sparing of OAR, and the exquisite conformation and homogeneity that is brought by the VMAT component to the treatment, practically eliminating high-doses outside of integrated boost PTV. The purpose of this work is to describe our technique, and our dosimetric results.

Material/Methods:

One Hundred Two patients were treated in our centre between March and October 2023. All patients had a simulation CT scan with a breast board in an inclined plane as immobilization. Breast PTV +/- boost PTV were contoured. The radiotherapy treatment plan had a 3DRT component, which contributed to 60% of the prescribed plan dose, as well as a VMAT component, with a 40% contribution. Energy was 6 MV, with and without filter respectively. The 3DRT component of the treatment was comprised of a lateral and medial tangential fields, and the VMAT component had one partial arc, to avoid unnecessary radiation to normal tissues. Treatment planning was performed with TPS Monaco, and delivered in a Versa HD linear accelerator (Elekta AB, Stockholm, Sweden) Figure1.

Daily image-guidance was performed through Cone-beam CT (CBCT). Active Breathing Control (ABC) breathing technique was used in patients who did not meet OAR constraints with free breathing.