Measurement of percentage depth dose and lateral beam profile for kilovoltage x-ray therapy beams

Abstract

In this work, nine commonly used dosimetry detectors have been investigated to determine suitable relative dosimeters for kilovoltage x-ray beams. By comparison with the Monte Carlo calculated data, it was determined that for the detectors studied the PTW N23342, Markus and NACP parallel-plate chambers are more suitable for the measurement of percentage depth dose (PDD) data for this beam quality range with an uncertainty of about 3%. A diode detector may be used to measure the PDD for the 100 kVp beam, but it is not suitable for higher energies (300 kVp). The Capintec parallel-plate chamber may be adequate for medium-energy photons, but it has a slightly higher uncertainty for low-energy x-rays (100 kVp). For the measurement of beam profiles, diode and film yield incorrect profile tails, which can be corrected using the RK ionization chamber.

Computed tomography dosimetry with high‐resolution detectors commonly used in radiotherapy — an energy dependence study

“…Hill et al (20) reported a rapidly increasing RDR for the Markus chamber as the energy of the incident X‐ray beam decreases from 280 kVp down to 50 kVp. Contrary to this, Li et al (21) found a decreasing RDR in the range from 300 kVp down to 200 kVp, which was not confirmed by Hill and colleagues. However, from 200 kVp down to 50 kVp, the Li study reported an increasing RDR.…”

“…If higher spatial resolution is needed, Compact Chamber IBA CC04 or PTW 31015 or PTW 31016 PinPoint chambers with Al central electrodes can also be used. Energy response of these detectors has been analyzed by the method proposed by Li et al (21) and Hill et al (20) Besides the general characterization of the detectors spectral sensitivity, the RDR can be used as a correction factor for kV dosimetry in radiation fields of similar HVL. The rotational symmetry of these detectors is of major advantage for CT dosimetry and, in conclusion, absorbed dose profile measurements as well as point dose measurements in a suitable phantom for estimation of organ doses are enabled.…”

“…All investigated detectors, except the parallel plate chambers, possess rotation‐symmetric designs, which is crucial for CT dosimetry. The parallel plate chambers were included in this study for comparison with previous studies 20 , 21 …”

“…The relative detector response (RDR) of an ionization chamber or dosimetry diode was determined according to the previously published method 20 , 21 . The RDR for a detector of interest RDR(E) x at a particular beam quality, E, was determined as follows: $RDR{(E)}_x=P_Q{(E)}_{\mathit{f}}\cdot \frac{M{(E)}_{\mathit{\text{Ref}}}}{M{(E)}_x}$ where $P_Q{false(Efalse)}_{Ref}$ is the air‐kerma beam quality correction factor (see Table 1) for the PTW 60004 reference diode provided by the manufacturer within the calibration sheet, $M{false(Efalse)}_{Ref}$ is the electrometer reading for the PTW 60004 reference diode, and $M{false(Efalse)}_x$ is the reading for the ionization chamber or diode under investigation.…”

“…In previous studies, several ionization chambers designed primarily for dosimetry of megavoltage photon beams have been investigated in terms of their usability in X‐ray therapy 19 , 20 , 21 . These studies showed the general feasibility of these detectors for kV dosimetry, provided that detector‐specific correction factors for the spectral composition of the radiation fields are taken into consideration.…”