Diamond detector in absorbed dose measurements in high‐energy linear accelerator photon and electron beams

Abstract

Diamond detectors (DD) are preferred in small field dosimetry of radiation beams because of small dose profile penumbras, better spatial resolution, and tissue‐equivalent properties. We investigated a commercially available ‘microdiamond’ detector in realizing absorbed dose from first principles. A microdiamond detector, type TM 60019 with tandem electrometer is used to measure absorbed doses in water, nylon, and PMMA phantoms. With sensitive volume 0.004 mm3, radius 1.1 mm, thickness 1×10−3mm, the nominal response is 1 nC/Gy. It is assumed that the diamond detector could collect total electric charge (nC) developed during irradiation at 0 V bias. We found that dose rate effect is less than 0.7% for changing dose rate by 500 MU/min. The reproducibility in obtaining readings with diamond detector is found to be ±0.17% (1 SD) false(n=11false). The measured absorbed doses for 6 MV and 15 MV photons arrived at using mass energy absorption coefficients and stopping power ratios compared well with Nd, water calibrated ion chamber measured absorbed doses within 3% in water, PMMA, and nylon media. The calibration factor obtained for diamond detector confirmed response variation is due to sensitivity due to difference in manufacturing process. For electron beams, we had to apply ratio of electron densities of water to carbon. Our results qualify diamond dosimeter as a transfer standard, based on long‐term stability and reproducibility. Based on micro‐dimensions, we recommend these detectors for pretreatment dose verifications in small field irradiations like stereotactic treatments with image guidance.PACS number(s): 87.56.Da

Characterizing a PTW microDiamond detector in kilovoltage radiation beams

“…5,6 In addition, diamond's atomic number is close to the effective atomic number (Z) of water/tissue, resulting in a relatively low-energy dependence for beam energies used within the therapeutic range, theoretically. 7 When ionizing radiation passes through the DD, electronhole pairs are generated, and collected with an electric field. This collected ionization current is directly proportional to the incoming ionizing radiation.…”

“…Generally, diamond detectors are highly resistant to radiation damage (0.05% loss in sensitivity per kGy) and have excellent spatial resolution (4 active measurement area and 1 μ m thickness) 5,6 . In addition, diamond’s atomic number is close to the effective atomic number (Z) of water/tissue, resulting in a relatively low‐energy dependence for beam energies used within the therapeutic range, theoretically 7 …”

Small field dose measurements using plastic scintillation detector in heterogeneous media

“…The goal of this study was to find a stable measurement point of clinical interest to validate the accuracy of the CyberKnife MultiPlan planning system on a small static field, with particular focus on small cone sizes less than 20 mm using suitable detectors. Plastic scintillation devices (PSD) have been studied for more than 20 yr, and several recent publications have shown that in small fields their performance compares favorably to other detectors including stereotactic diodes, microchambers, and synthetic diamond detectors . Moreover, their properties of tissue equivalence, linearity, energy dependence, small correction factor in homogeneous media, make them an attractive candidate for small field validation in heterogeneous media.…”

Estimating the effect of electron beam interactions with biological tissues

“…Therefore, one must know the stopping power and range values for such materials. Besides developing the new dosimeter materials, it is also important to know the stopping power and range values for the estimating the obtained dose by target [2,3], this makes possible to estimate the effect of the electron beams in the target. These values determined or read from the database in the radiation therapy systems.…”