Dosimetric characteristics of the new Papillon+® system for breast intraoperative radiotherapy

The first prototype of the Papillon+® Contact X-ray Brachytherapy system operates at 50 kVp for Breast Intraoperative Radiotherapy at Centre Antoine Lacassagne in Nice. Treatments are delivered with a single fraction of 20 Gy prescribed at the surface of spherical applicators with diameters ranging from 35 to 50 mm. The dosimetric characteristics of these applicators were investigated to support clinical implementation and optimize their use in routine practice.

Dose measurements were performed with EBT-3 GAFChromic films to evaluate surface dose distributions, dose rates at the south pole of the applicators and percentage depth-doses (PDDs) in water. Film measurements were validated using a soft X-ray ionization chamber. A planning target volume (PTV), defined as a 10 mm shell surrounding the applicator was considered. Dose-volume histograms (DVHs) were constructed and dose-volume metrics (D_min, D_1mm, V₉₀, V₈₀, HI) were derived to quantify the target dose distribution.

Surface dose distributions were homogeneous, with relative standard deviations below 3% at the applicator equator. Dose rates ranged from 10.9 to 30.1 Gy.min^-1 depending on applicator diameter and showed good agreement between film and ionization chamber measurements i.e. within 2%. Smaller applicators produced steeper depth-dose gradients while larger applicators resulted in improved target coverage and dose homogeneity within the PTV.

This study provides a comprehensive dosimetric characterization of the Papillon+® breast applicators. The results support applicator selection in clinical practice and provide quantitative guidance in the absence of CT-based treatment planning for breast intra-operative Radiotherapy (IORT).