ESTRO 2024 - Abstract Book

S356

Beachytherapy - Physics

ESTRO 2024

The Axxent Rectal Surface Applicator is designed to be used with the Axxent Electronic Brachytherapy System to provide minimally invasive superficial x-ray therapy to rectal surfaces, with visualization furnished by a customer supplied standard HD endoscopic camera system The prototype has been designed for the treatment of rectal cancer with the Axxent device whose source is a vacuum tube (10 mm in length, 2 mm in diameter), encased in a cooling catheter (5.6 mm diameter). It is typically operated at 50 kVp with 300 μA of electrons striking a thin tungsten film target on the inner surface of a ceramic X-ray-transparent anode. The absorbed dose has been verified at 0.5 cm (clinical prescription point) from the treatment window of the applicator with an Exradin A20 (Standard Imaging Inc.) ionization chamber and profiles have been measured with the same chamber.

EBT3 radiochromic films have also been used for the measurement of PDDs and symmetry and homogeneity in the treatment window.

The applicator (Fig 1) consists of 4 possible treatment windows of, 15mm, 20mm, 25mm and 30mm apertures, measurements have been performed for all of them. The analysis of the films has been carried out with Image J.

Treatment plans for the different windows have also been designed in Eclipse v.15 (Varian Inc.) and measured in order to create atlases available in the operating theatre for each patient, also verified with EBT3 radiochromic film.

Results:

In the plans designed for the different treatment windows, homogeneity results of better than 5% and symmetry results of better than 3% were obtained.

The PDDs were equivalent to those obtained for the Axxent source in other configurations with equivalent beam hardening.

Radiochromic films irradiated with the designed plans are considered clinically appropriate for the treatment of superficial rectal lesions (Fig 2).

Conclusion: