Water‐equivalent dosimeter array for small‐field external beam radiotherapy

Abstract

With the increasing complexity of dose patterns external beam radiotherapy, there is a great need for new types of dosimeters. We studied the first prototype of a new dosimeter array consisting of water-equivalent plastic scintillating fibers for dose measurement in external beam radiotherapy. We found that this array allows precise, rapid dose evaluation of small photon fields. Starting with a dosimeter system constructed with a single scintillating fiber coupled to a clear optical fiber and read using a charge coupled device camera, we looked at the dosimeter's spatial resolution under small radiation fields and angular dependence. Afterward, we analyzed the camera's light collection to determine the maximum array size that could be built. Finally, we developed a prototype made of ten scintillating fiber detectors to study the behavior and precision of this system in simple dosimetric situations. The scintillation detector showed no measurable angular dependence. Comparison of the scintillation detector and a small-volume ion chamber showed agreement except for 1 x 1 and 0.5 x 5.0 cm (2) fields where the output factor measured by the scintillator was higher. The actual field of view of the camera could accept more than 4000 scintillating fiber detectors simultaneously. Evaluation of the dose profile and depth dose curve using a prototype with ten scintillating fiber detectors showed precise, rapid dose evaluation even with placement of more than 75 optical fibers in the field to simulate what would happen in a larger array. We concluded that this scintillating fiber dosimeter array is a valuable tool for dose measurement in external beam radiotherapy. It possesses the qualities necessary to evaluate small and irregular fields with various incident angles such as those encountered in intensity-modulated radiotherapy, radiosurgery, and tomotherapy.

Measuring output factors of small fields formed by collimator jaws and multileaf collimator using plastic scintillation detectors

“…The plastic scintillator was shown to measure higher output factors than the other detectors for all field sizes with the sole exception of the 5 mm field size, where the diode showed higher output and the ionization chamber was not tested due to its large size. Archambault et al 25 showed that a 1.4 mm 3 plastic scintillating fiber measured an output factor that was ϳ4% higher than that measured by a 7 mm 3 ionization chamber using a 1 ϫ 1 cm 2 jaw-defined, 6 MV linac beam. This is close to the disparity we see in our 1 ϫ 1 cm 2 output factors for jaw-defined fields ͓see Fig.…”

“…[15][16][17][18][19][20][21] Plastic scintillation dosimetry in the setting of small-field irradiation has been studied by several investigators using a variety of systems. [22][23][24][25] However, no close examination has been made of the dependence of the measurement of output factors on the way in which the small fields are defined. The aim of the study reported here was to explore this dependence using plastic scintillation dosimetry and the fielddefining mechanisms associated with a clinical IMRT linac and to expand the body of knowledge concerning the viability of plastic scintillators for accurately measuring small radiation fields.…”

Fiber‐optic detector for real time dosimetry of a micro‐planar x‐ray beam

“…Plastic scintillator based fiber-optic dosimeters have been widely studied for use and applications in radiation therapy measurements. [20][21][22][23] Prior work has shown the ability of fiber-optic dosimeters that feature 5 mm-long plastic scintillators to measure small radiation fields down to 1 cm diameter. 24 Similarly, fiber-optic sensors assembled in 2D arrays have been demonstrated to measure radiation field sizes down to 1.5×5 cm with a resolution of 5 mm.…”

Feasibility study on development of Cerenkov fiber-optic dosimeter for radiotherapy application

“…As an alternative to conventional dosimeters, different types of scintillating fiber-optic dosimeters (SFODs) using various organic scintillators have been developed [1][2][3][4]. For radiotherapy dosimetry, the SFODs offer a number of advantages, including small sensitivity volume, substantial flexibility, tissue or water equivalence, remote and real-time sensing, and immunity to electromagnetic interference (EMI), because they use optical fibers to guide light signal containing dose information.…”