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


CONCLUSIONS
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.
Ciesielski
Bartlomiej
B
Department of Physics, Medical University of Gdansk, Gdansk, Poland. bciesiel@amg.gda.pl
Schultka
Katarzyna
K
Kobierska
Anna
A
Nowak
Renata
R
Peimel-Stuglik
Zofia
Z
D000409:Alanine; D000465:Algorithms; D003037:Cobalt Radioisotopes / Q000627:therapeutic use; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods*; D005240:Feasibility Studies; D006801:Humans; D009369:Neoplasms / Q000532:radiotherapy*; D011874:Radiometry; D011879:Radiotherapy Dosage
D003037:Cobalt Radioisotopes; D000409:Alanine