Characterization of a 2D ion chamber array for the verification of radiotherapy treatments

Abstract

In this study we investigated the characteristics of a commercial ion chamber array and its performance in the verification of radiotherapy plans. The device was the 2D Array Seven29 model (PTW, Freiburg, Germany). This is a two-dimensional detector array with 729 ionization chambers uniformly arranged in a 27 x 27 matrix with an active area of 27 x 27 cm(2). The detector short-, medium- and long-term reproducibility have been tested through an extensive set of repeated measurements. Short-term reproducibility was well within 0.2%. Medium- and long-term reproducibility were within 1%, including set-up reproducibility errors and linac output fluctuations. Dose linearity was also assessed. The system response to dose was verified to be linear within the range 2-500 MU. Output factors matched very well pinpoint chamber measurements performed in the same experimental conditions with a maximum local percentage difference of 0.4%. Furthermore, the 2D Array sensitivity to millimetric collimator positional changes and to perturbation effect of irradiated area was tested. The comparison with ion chamber data carried out in water was very satisfying. Finally, measurements of wedge-modulated fields and IMRT beam sequence matched very well ion chamber dose profiles acquired in a water tank. The extensive tests performed in this investigation show that the 2D Array Seven29 is a reliable and accurate dosimeter and that it could be a useful tool for the quality assurance and the verification of radiotherapy plans.

Evaluation of monitor unit calculation based on measurement and calculation with a simplified Monte Carlo method for passive beam delivery system in proton beam therapy

“…The PTW 2D Array seven29 has 729 ionization chambers in a 10 mm pitch $27\times 27$ array. Spezi et al (15) reported the successful application of this detector to radiation therapy and verified the performance. The sensitive volume of a unit chamber is $5 \text{mm}\times 5 \text{mm}\times 5 \text{mm}$ and the ionization chambers of the array are open to the air.…”

A method to enhance spatial resolution of a 2D ion chamber array for quality control of MLC

“…The following work shows that this limitation can be solved by taking into account the fact that partial coverage of a volumetric detector by a radiation beam gives a response proportional to the irradiated volume, as described by Yang et al ( 8 ) Spezi et al ( 9 ) studied the response of a 2D ion chamber array when radiation fields gradually increase the coverage of the detector area, and found a close correspondence between detector coverage and its response.…”

“…Several authors have studied the sensitivity and reproducibility parameters of this array and the results obtained are comparable with similar, commonly used detectors. ( 7 , 9 ) The VeriSoft software (PTW‐Freiburg, Germany) was used to record radiation dose readings. The array was optically aligned with the MLC so that each leaf corresponded to one row of detectors.…”

Dosimetric and radiobiological comparison for quality assurance of IMRT and VMAT plans

“…Accuracy of treatment delivery of complex treatment plans is assured through a quality assurance (QA) process using ion chambers, films and more commonly with diode array,1, 2 and ion chamber array measurements 3. Measured data are generally compared against planned data using two‐dimensional (2‐D) gamma analysis.…”