EPR/alanine dosimetry in LDR brachytherapy--a feasibility study.

In this study, we present the results of in vivo dosimetry, using electron paramagnetic resonance in l-alanine, performed on 13 patients treated for gynaecological cancers. The doses from (137)Cs (12 samples) and (192)Ir (one sample) brachytherapy sources were determined inside vagina. The detectors had a form of small cellulose capsules tightly filled with crystalline alanine. The positions of the detectors were reconstructed from two orthogonal radiographs. The planned doses were calculated with a computer planning system (PLATO, Nucletron). The relative deviations between planned and measured doses ranged from -23 to +14%. The mean deviation from the prescribed dose was relatively low (-5%) with SD of 10%. The main sources of differences between the measured and calculated doses were attributed to uncertainty in the determination of the detector position inside the patient's body and to uncontrolled changes in the detector position during the treatment.

The effect of heating on background and radiation-induced EPR signals in tooth enamel.

The presented study is a continuation of our work performed during participation in the Third International Intercomparison on EPR Tooth Dosimetry. During the process of samples preparation, all 22 enamel samples were accidentally exposed for about 30 min to 150 degrees C temperature. This considerably affected shape of their EPR spectra mainly due to substantial increase in the background signal, which approximately doubled its contribution to the spectra. These effects were studied closer under controlled conditions of the delivered dose and heating temperature using another enamel samples. The observed changes in the spectra shape partially faded within a few days after heating. The heating resulted also in a noticeable generation of a spectral component similar to the dosimetric signal induced in enamel by radiation. The temperature-induced dosimetric component in EPR spectra of the heated samples remained constant for 32 days. Deviations in calculated contributions of the dosimetric signal into total EPR spectra of irradiated sample varied from -12 to +15% of its initial contribution in the non-heated enamel, depending on type of the background spectrum applied in numerical processing of the spectra.

In vivo alanine/EPR dosimetry in daily clinical practice: a feasibility study.

PURPOSE: The objective of this study was evaluation of accuracy of in vivo dosimetry using electron paramagnetic resonance (EPR) in alanine. Additionally, we aimed to identify sources of uncertainty in dose determination and quantitative assessment of physical factors that may result in discrepancies between the measured and planned single-fraction doses. METHODS AND MATERIALS: The measurements were performed using detectors in a form of 1.6 cm x 1.6 cm polyethylene sachets filled with powdered L-alanine. The detectors were taped to the patient's skin and measured the entrance doses for (60)Co and electron beams. Some detectors were covered with buildup material, and some measured the "skin dose." The EPR measurements were performed with a Varian E-4 spectrometer. RESULTS: The calculated uncertainty of EPR measured doses was dependent on measured doses and varied from 6.6% for 0.5 Gy to 3.2% for 2 Gy. The calculated uncertainty was in concordance with experimentally determined reproducibility of EPR signals. However, the deviations between measured and planned doses exceeded the uncertainty range of EPR measurements, which can be attributed to uncertainty in determination of actually delivered doses to the detectors, on the basis of treatment planning data. CONCLUSION: The accuracy of dose determination by EPR measurements was shown to be achievable within the 5% limit recommended by the ICRU for doses above 0.7 Gy. The accuracy of in vivo verification of radiotherapy doses by in vivo EPR dosimetry can be improved by meticulous selection of measurement conditions, i.e., radiation fields and detector positions, ensuring accurate calculation of doses delivered to the dosimeters.