Continuous three-dimensional radiation dosimetry in tissue-equivalent phantoms using electron paramagnetic resonance in L-alpha-alanine

Clinical applications of alanine/electron spin resonance dosimetry

This paper discusses the clinical applications of electron spin resonance (ESR) dosimetry focusing on the ESR/alanine system. A review of few past studies in this area is presented offering a critical overview of the challenges and opportunities for extending this system into clinical applications. Alanine/ESR dosimetry fulfills many of the required properties for several clinical applications such as water-equivalent composition, independence of the sensitivity for the energy range used in therapy and high precision. Improvements in sensitivity and the development of minidosimeters coupled with the use of a spectrometer of higher microwave frequency expanded the possibilities for clinical applications to the new modalities of radiotherapy (intensity-modulated radiation therapy and radiosurgery) and to the detection of low doses such as those present in some radiological image procedures.

A new 2 methylalanine-PVC ESR dosimeter

The use of polyvinyl chloride (PVC) as a binder to 2-methylalanine (2MA) dosimeters was investigated. It was recently shown by Olsson et al. (Radiat. Res. 157 (2002) 113), that 2MA is approximately 70% more sensitive than L-alanine which makes this substance a good candidate to replace alanine in ESR dosimetry. PVC is a low yield material for free radical production by ionizing radiation and a good binding material easily processed and widely available. PVC can be prepared at room temperature and mixed up to 50% in weight with 2MA to produce a pellet stable in mass and physical dimensions, in large quantities and with low background signal. Pure PVC pellet irradiated at 50 Gy gave weaker ESR signals compared to 2MA at the region of spectral interest. Spectrometer settings such as microwave power, and modulation amplitude were optimized for the measurements. This dosimeter production scheme allows the addition of Mn2+ ions for an internal reference signal, leading to a self-calibrated dosimeter (J. Radional. Nucl. Chem. 240 (1999) 215).

The application of EPR dosimetry for radiotherapy and radiation protection

This paper reports the first clinical trial of the application of the continuous wave electron paramagnetic resonance (CW-EPR) spectrum of alanine to determine the radiation dose received by a patient. The results of these measurements are compared with those obtained using thermoluminescent dosimetry (TLD) simultaneously. The 9 GHz EPR measurements were made at 13 degrees C. The time stability of the radiation induced radicals in alanine was confirmed. The fractionated radiation doses received in the clinical trial were determined from a calibration curve (linear regression coefficient r = 0.9995) obtained by irradiating L-alanine samples with 60-800 cGy doses using cobalt 60 gamma rays obtained from an Eldorado 8 Cobalt 60 unit at a rate of approximately 60 cGy/min. It is shown that the absorbed dose in tissue-equivalent material can be determined using EPR spectroscopy with an accuracy of approximately 3% at low dose levels (60 cGy) whereas the error using TLD is approximately 5% and that this method of dose determination is preferable to the present TLD method because it is simpler and more accurate.

MR imaging of absorbed dose distributions for radiotherapy using ferrous sulphate gels

The measurement of absorbed dose distributions using dosemeter gel and magnetic resonance imaging (MRI) in a standard geometry has been investigated. Absorbed depth-dose curves and profiles measured with this new technique show good agreement with corresponding measurements using diodes. This was proven in a 60Co beam as well as an electron beam. The dosemeter gel is made of agarose and ferrous sulphate solution. The dose response is linear (r = 0.9996) in the investigated dose interval, 0-40 Gy. The sensitivity is a factor of about six higher compared to ordinary ferrous sulphate solution, known as 'Fricke'. This is a true 3D dose measurement technique which will have a number of applications in radiation therapy, since it is possible to mould the gel to arbitrary geometries, mix different radiation qualities and integrate the absorbed dose from different kinds of fields.