Trial Information

Interstitial High Dose-Rate Brachytherapy for Partial Breast Irradiation in Early Breast Cancer: Results of Phase II Prospective Study

Patients included in our phase II trial of PBI with interstitial HDR brachytherapy are at
low-risk of relapse. Implants are positioned during surgery or postoperatively, within 12
weeks. Treatment schedule is 4 Gy twice a day, with a time relapse of at least 6 hours
between each fraction, for four days, for a total dose 32 Gy. Before post-operative
implantation, all patients undergo a breast computed tomography (CT) scan to visualize and
expand the excision cavity and obtain the planning target volume (PTV), i.e. the lumpectomy
cavity plus a margin of 1-2 cm around it. Through virtual simulation with a 3D treatment
planning system (TPS), we define the implant catheter position. After implantation, in all
patients a breast CT scan checked implant geometry. On CT images transferred to a TPS the
surgical cavity is outlined and expanded, the PTV defined, and inactive and active source
lengths measured.CT-based 3D software is used to identify and reconstruct the catheters,
outline and expand the surgical cavity and obtain the PTV. Dwell positions are activated for
each catheter, and inactive and active lengths defined.Prescribed dose was 85% of the basal
dose. Dwell weights are optimised in the basal points applying the volume and distance
method and best values were chosen independently of strategy. A dose-volume histogram that
records the volume covered by 100% and 150% of the prescribed dose (V100 and V150) was
obtained for each patient. DHI, defined as V150 - V100/ V100 (7), is recognized as the most
suitable quality index.