Prog Med Phys.  2024 Dec;35(4):89-97. 10.14316/pmp.2024.35.4.89.

Evaluation of the Dosimeter Volume Effect on Small-Field Dosimetry Using the Elekta Harmony Pro Linear Accelerator

• Park H
• Jegal J
• Huh Y
• Lee I
• Lee SH
• Choi CH
• Kim JI
• Kang S

• KMID: 2564147
• DOI: http://doi.org/10.14316/pmp.2024.35.4.89

Abstract

Purpose
This study investigated the dose perturbation according to the size of the sensitive volume in the dosimeter in small-field dosimetry.
Methods
The dose profiles with different field sizes were measured using three different dosimeters: the CC13, Razor ion chamber, and Edge solid-state detector. Both the open and wedged beams with different field sizes were employed in the measurement. The profiles were measured in a water phantom at maximum dose depths of 5, 10, and 20 cm. The penumbra and width of the open-beam profiles were compared according to the types of the dosimeters and beam. The dose fall-off between the peak and 20% dose was evaluated for the wedged beam profiles.
Results
In the open-beam measurement, the fall-off of the profile was steeper with the Edge detector, which has the smallest sensitive volume. Meanwhile, the dose in the out-of-field region was the smallest with the Edge detector. The widths of the penumbra were 6.10, 4.47, and 4.03 mm for the profile of the 3×3 cm 2 field measured by the CC13 chamber, Razor chamber, and Edge detector, respectively. The width of the profile was not changed even if different dosimeters were used in the measurement. The wedged beam profiles showed more clear peaks at the field edge when a smaller dosimeter was used.
Conclusions
The results demonstrate the necessity of dosimeters with a small sensitive volume for measuring a small-field beam or a steep dose gradient.

Keyword

Small-field dosimetry; Dose gradient measurement; Ion chamber; Solid-state dosimeter

Figure

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  Fig. 1 Dosimeters used in the measurement. CC13 ion chamber (a), Razor ion chamber (b), and Edge detector (c), along with the measurement setup (d).

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  Fig. 2 Dose profiles along the inline and crossline directions measured at a depth of 10 cm for 6 MV beams with field sizes of 3×3 cm2 (left) and 10×10 cm2 (right).

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  Fig. 3 Dose profiles along the inline and crossline directions measured at a depth of 10 cm for 6 MV-flattening filter free beams with field sizes of 3×3 cm2 (left) and 10×10 cm2 (right).

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  Fig. 4 Dose profiles along the inline and crossline directions measured at a depth of 10 cm for 10 MV beams with field sizes of 3×3 cm2 (left) and 10×10 cm2 (right).

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  Fig. 5 Profile of the wedged beam with an energy of 6 MV and a field size of 10×10 cm2.

Reference

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