Feasibility and early toxicity of intraoperative radiotherapy for breast cancer using the papillon + system: First results

Abstract

Background and purpose: Breast intra operative radiation therapy has been evaluated with different systems delivering 20-21 Gy with treatment times around 30 min. Papillon + ^TM Contact X-ray machine was designed to produce a 50 kVp beam with a high dose rate ≥ 15 Gy/minute. A pilot study with the first prototype was conducted in Nice.

Materials and methods: The inclusion criteria were age ≥ 60 years, unifocal ductal breast adenocarcinoma ≤ 2.5 cm, grade 1-2. Surgical local excision with sentinel node dissection was performed and the applicator was placed in the tumor bed after excision with a prescribed dose of 20 Gy. The main end point of the study was the doses measured with the Gafchromic films; two were located at the skin surface and two in the excision cavity. Secondary endpoints were early toxicity and relapse free survival.

Results: Between 10/2018 and 09/2019, 26 patients were included. Mean Gafchromic doses were 18.8 Gy ± 2 Gy at the south pole, 15.6 Gy ± 2.81 Gy at the equator and 2.5 Gy ± 1.67 Gy at the skin. With a median follow-up time of 12 months, no skin or subcutaneous toxicity > grade 2, no local relapse and no metastasis were observed.

Conclusion: This is the first phase II study testing the Papillon + ^tm system for breast IORT with in vivo dosimetry measurements and reassuring clinical data.

Keywords: Brachytherapy; Breast IORT; High dose rate; Papillon+ system.

Fig. 1

The Papillon +^tm unit with the X-ray tube (black arrow) mounted at the end of the X-ray generator.Schematic sketch of the X-ray tube (micronode ^tm) of the Papillon+ ^tm unit. The tungsten anode is at the outside end of the tube providing an isotropic beam of 310°. A mineral oil cooling fluid is circulating around the X-ray tube and the anode allowing a high dose rate close to 20 Gy/ minute at the applicator surface.

Fig. 2

Percentage depth dose profiles for all applicator sizes measured with Gafchromic EBT3 film NBA: Nice Breast Applicator (diameter).

Fig. 3

Schematic artist representation of the dose measured using gafchromic film. It can be seen that the dark blue area (receiving between 20 and 11 Gy is irregular (irregular mammary gland cavity after tumor local excision). The dose measured close to the applicator, depending on this irregularity and close contact of the gafchromic film, can vary between 20 Gy (south pole) and 13 Gy. (equator right). This mammary gland surface dose inhomogeneity has no impact on the dose between 5 and 10 mm depth (clear blue area) which is always between 10 and 7 Gy. The mean dose to this volume of tissue is around 12 Gy with little variation for the same applicator diameter. This mean dose is larger with the 4.5 cm diameter applicator than with the 3.5 cm. In this sketch the applicator diameter is 4 cm. The irradiated volume (dark and clear blue) is close to 40 cm³ (14 % of the sphere on the north pole receiving no dose). As the two gafchromic films positioned at the skin surface close to the surgical incision are at>1 cm from the applicator surface they receive a small dose close to 2 or 3 Gy in one minute. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)