Evaluation of a New Detector Design for Measuring Superficial 2D Dose Distributions in Proton Therapy for Skin Cancer

Abstract

Each year, the incidence of skin cancer continues to rise worldwide. Radiotherapy remains a well-established treatment option; however, its effectiveness can be limited by technical constraints. In clinical practice, a water-equivalent material known as a bolus is often placed over the tumor site to restore electronic equilibrium near the skin surface. As the tumor shrinks during treatment, air gaps may develop between the bolus and the skin, potentially leading to significant underdosage of the prescribed radiation dose. Proton therapy offers a promising alternative for the treatment of superficial tumors. Owing to the characteristics of the Bragg peak, proton beams enable highly localized dose delivery, even at shallow depths, thereby eliminating the need for a bolus. However, currently available commercial devices do not allow accurate dose measurements at the skin level. In this context, we are developing a new device for real-time, two-dimensional measurement of dose and dose rate at the skin surface. The current design consists of an ionization chamber operating in integrating mode, enabling measurement of the total collected charge produced by the proton beam. For beam positioning, an optical readout system is implemented, combining a scintillator, a mirror, and a camera to provide spatial information on the beam location. Both subsystems are designed to interface with the FASTER data acquisition system. Initial tests have been conducted at CYCLHAD using the DOSION ionization chamber to evaluate the superficial dose at skin-equivalent depths with a clinical proton beam generated by the ProteusONE system (IBA). In this contribution, we provide an overview of the project and present preliminary results obtained with DOSION, including linearity assessments. A patient-specific quality assurance case is also analyzed and discussed. Finally, the perspectives of this work are outlined, including its potential application in comparative clinical studies between photon and proton therapies.