# Dosimetric characterization of a Varex VF‐80/μXHP x‐ray unit using open‐ended applicators for superficial radiotherapy

## TL;DR

This study evaluates the dosimetric performance of a low-energy x-ray unit for skin cancer treatment using measurements and simulations.

## Contribution

The study validates the use of a modern ionization chamber and Monte Carlo simulations for dosimetry in low-kV x-ray therapy.

## Key findings

- Percent depth dose data matched literature within 1.9% for 50 kV and 0.5% for 70 kV x-rays.
- Measurements and simulations showed good agreement, confirming the x-ray unit's suitability for superficial radiotherapy.
- Applicator leakage and thickness effects were characterized for various open-ended applicators.

## Abstract

Kilovoltage x‐ray units (50–150 kVp) are widely used for skin cancer treatments, necessitating precise dosimetric characterization to ensure accurate dose delivery. This study validates the depth dose data of the VF‐80/𝜇XHP (80 kV, 100 W) x‐ray system for use in low‐kV therapy with a contemporary detector.

This research aims to characterize the kilovoltage VF‐80/𝜇XHP x‐ray unit with open‐ended PMMA and stainless‐steel applicators of various diameters by utilizing different x‐ray energy values.

Measurements included machine output reproducibility, applicator leakage and thickness effects, measurement of HVL, reference output dosimetry, and applicator‐to‐phantom spacing. PDD curves were obtained using various filter/kV and applicator combinations with a PTW 34013 parallel‐plate ionization chamber in a solid water phantom and through MC simulations with the TOPAS Monte Carlo code in a water phantom, which were validated against literature data.

The study evaluated around 40 x‐ray beams. The PDDs were measured in a solid water phantom using a PTW 34013 ionization chamber and calculated with the TOPAS Monte Carlo code. Both the measured and computed percent depth dose data were compared to the BJR 25 supplementary. The agreement between ionization chamber measurements and MC calculations with BJR 25 supplementary was within [1.9%, 1.5%] for 50 kV x‐rays and within [0.5%, 0.2%] for 70 kV x‐rays.

This research provides the dosimetric analysis of a kilovoltage VF‐80/μXHP x‐ray machine. The primary focus was on using a PTW 34013 ionization chamber to measure the percentage depth dose in a solid water phantom, along with dose calculations performed using the TOPAS Monte Carlo simulation. The findings align well with existing literature, confirming that this x‐ray unit is suitable for low‐kV x‐ray radiotherapy applications.