Output factor determination for dose measurements in axial and perpendicular planes using a silicon strip detector

Z Abou-Haïdar,A Bocci,A Pérez Vega-Leal,J M Espino,J M Quesada,M A Cortés-Giraldo,M I Gallardo,M A G Alvarez,M C Ovejero,M Ruiz Prieto,F J Pérez Nieto,R Arráns

doi:10.1103/physrevstab.15.042802

Abstract

In this work we present the output factor measurements of a clinical linear accelerator using a silicon strip detector coupled to a new system for complex radiation therapy treatment verification. The objective of these measurements is to validate the system we built for treatment verification. The measurements were performed at the Virgin Macarena University Hospital in Seville. Irradiations were carried out with a Siemens ONCOR™ linac used to deliver radiotherapy treatment for cancer patients. The linac was operating in 6 MV photon mode; the different sizes of the fields were defined with the collimation system provided within the accelerator head. The output factor was measured with the silicon strip detector in two different layouts using two phantoms. In the first, the active area of the detector was placed perpendicular to the beam axis. In the second, the innovation consisted of a cylindrical phantom where the detector was placed in an axial plane with respect to the beam. The measured data were compared with data given by a commercial treatment planning system. Results were shown to be in a very good agreement between the compared set of data.

Highlights

For a given photon beam at a given source to surface distance (SSD), the dose rate at a certain depth d in a phantom depends on the field size
The reference field is a square field of 10 Â 10 cm2 at an SSD of 100 cm; the larger the field size, the higher the dose [1]
For the purpose of verifying our detection system and its calibration, we measured the dose given by various square fields in an in-house designed cylindrical phantom normalized to the reference field, and we refer to it as output factor as well

Summary

Introduction

For a given photon beam at a given source to surface distance (SSD), the dose rate at a certain depth d in a phantom depends on the field size. The output factor (OF) is defined as the ratio of the dose for any field size A Â A cm to the dose for a reference field at the same source to surface distance, and at the same depth d in a slab phantom. In radiation therapy, the output factor is measured in slab phantoms. For the purpose of verifying our detection system and its calibration, we measured the dose given by various square fields in an in-house designed cylindrical phantom normalized to the reference field, and we refer to it as output factor as well

Objectives

Discussion

Conclusion