Thermoluminescence Dosimetry for Quality Assurance in Radiation Therapy

Abstract

A methodology based on thermoluminescence dosimetry was developed to check the output of teletherapy units and the given doses. It was applied in a hospital as a part of an extemal quality audit programme. Over a 7 year period the mean ratios of the output doses measured by TLDs calibrated free-in-air to the doses measured at the hospital in a 6 MV X ray and in a 60Co unit were 1.000 +/- 0.024 (n = 86) and 0.997 +/- 0.027 (n=61), respectively. TLDs in capsules were attached to the patient's body or to a phantom to assess entrance, exit and midline doses and transmission. Factors were determined experimentally to relate the doses measured with TLDs in capsules and inside the body. The accuracy in given doses with pelvic and tangential breast fields and assessed via 752 in vivo measurements, was considered to be adequately good, taking into account the limitations of the equipment available in the hospital.

Characteristics of mobile MOSFET dosimetry system for megavoltage photon beams

“…TLDs [8910] were most commonly used for in vivo dosimetry due to the small size of the dosimeter and that it could be easily placed on the patient surface for this purpose. However, the use of TLD is laborious and time-consuming.…”

“…the “threshold voltage”, is permanently altered by the absorption of radiation. [9131415161718192021222324]…”

In vivo dosimetry to radiotherapy and radiology patient for error determination

“…It was found that ratio of doses was close to 1.00 when the Plexiglas caps were used for both 6 and 15 MV X-ray beams. In a similar study at IUH a ratio of 1.00 was found when 6 MV X-ray beams were used [95,107]. The TLDs over responded at 6 MV fields, when located in Cu or S.S. cups but not in Al.…”

“…TLD-100, compared to other detectors is composed of tissue equivalent material beside other valuable advantages [64]. TLDs with build-up caps are previously reported as being suitable for in vivo dosimetry [95][96][97][98][99]. With tissue equivalent material (Plexiglas) [95,], Polystyrene [96] or high atomic build up caps materials with powder, Aluminium [97], polytetrafluoroethylene (PTFE) [98] or a mixture of different materials (S.Steel, Paraffin, Perspex) [99], an accuracy of ±2 was achieved (Table 5…”

“…TLDs per cap, but those made of Plexiglas of 10 mm pockets may accommodate up to three TLDs. The build caps were manufactured in a private workshop in Larissa, while the Plexiglas one is manufactured by Kalef-Ezra et al [95].…”