Low volume.

Let’s delve a bit more into the planning techniques of the Florence trial. First, for appropriate daily alignment, breast surgeons were asked to place no less than four clips within the cavity at time of lumpectomy. The clinical target volume (CTV) was a 1 cm radius from these clips cropped 3 mm from skin (but not chest wall). The planning target volume (PTV) was another 1 cm expansion again cropped 3 mm from skin and extending no more than 4 mm into lung. Note: this creates a deeper PTV than on other partial breast trials. 100% of the PTV received at minimum 95% of prescription (28.5Gy) with a hotspot ≤105%. No more than 15% of uninvolved breast could receive >50% of prescription and max dose to contralateral breast was 1 Gy. It also called for ipsilateral lung V10 ≤20%, contralateral lung V5 ≤10%, and heart V3 ≤10%. TBL: Inverse planning with well-defined constraints may prove even easier than creating homogenous breast tangents. | Meattini, J Clin Oncol 2020