|Year : 2017 | Volume
| Issue : 4 | Page : 163-164
Necessity of reference dosimetry, periodic quality assurance, and dosimetry audit in preclinical and radiobiology research
Radiological Physics and Advisory Division, Bhabha Atomic Research Centre, Mumbai, Maharashtra, India
|Date of Web Publication||8-Jan-2018|
Dr. S D Sharma
Radiological Physics and Advisory Division, Bhabha Atomic Research Centre, Mumbai, Maharashtra
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Sharma S D. Necessity of reference dosimetry, periodic quality assurance, and dosimetry audit in preclinical and radiobiology research. J Radiat Cancer Res 2017;8:163-4
|How to cite this URL:|
Sharma S D. Necessity of reference dosimetry, periodic quality assurance, and dosimetry audit in preclinical and radiobiology research. J Radiat Cancer Res [serial online] 2017 [cited 2018 Jan 23];8:163-4. Available from: http://www.journalrcr.org/text.asp?2017/8/4/163/222445
Different types of radiation generators (e.g., kV X-ray machines, gamma chamber, telecobalt machines, accelerators generating high-energy electron, and X-ray beams) are used for irradiating varieties of biological samples (and animals, e.g., rats) in preclinical and radiobiology research to establish dose-effect relationship. The dose-effect relationship so obtained is generally useful in radiation therapy of cancer patients. International Commission on Radiological Units and Measurements (ICRU) in its report 24 requires the overall accuracy of ±5% in the delivery of absorbed dose to tumor volume because a change of 7%–10% dose to target volume results in clinically significant change in tumor control probability. The requirement of ICRU 24 should also be applied to the preclinical and biological research as inadequate dosimetry can impair the significance or cause misinterpretation of the radiobiological findings. Thus, dosimetry accuracy is of paramount importance in correlating correctly the biological outcomes of the study with the radiation dose delivered.
Recent survey on dose verification of radiobiological irradiators used in preclinical and biomedical research by Pedersen et al. has found that only one out of five laboratories has delivered the dose to target within 5% of the prescribed dose. Desrosiers et al. have reported that radiation dose measurements in preclinical and radiobiology studies are frequently inadequate, and hence, the reliability and reproducibility of the results of such studies are questionable. Further, the dose-response variability within tissues, species, strains, and cell types are significant. Although many radiobiological studies do not require precision in delivered dose of more than 10%, some biological end-points are sensitive to change in radiation dose requiring precision in dose much better than 10%. It is therefore important to enhance the dosimetry accuracy and precision in preclinical and radiobiology experiments.
Reference dosimetry can be done for those tele-irradiators (e.g. kV x-ray beams from standard X-ray machine, telecobalt machine, and medical linear electron accelerators) where reference conditions recommended by international dosimetry protocols can be established., Relative dosimetry parameters along central beam axis and for off-axis points can also be measured and recorded. The reference dose rate and relative dosimetry parameters will be useful in calculating dose to a point inside the biological samples/animals to be irradiated. The use of dosimetry data measured as per the methodologies recommended by dosimetry protocols will enhance the accuracy and precision of dose delivered to the subject and will also facilitate the meaningful comparison of end results of similar biological experiments conducted by different groups/laboratories. Reference dosimetry may not be possible for some of the tele-irradiators used in radiobiological experiments due to their geometrical limitations and existence of nonreference conditions. Recent dosimetry protocol of International Atomic Energy Agency (IAEA), provides solutions to these problems where recommendations are available for dosimetry of machine specific reference fields/small fields. Irradiator-specific dosimetry guidelines can be prepared using the concept outlined in IAEA dosimetry protocols and implemented for enhancing the local dosimetry accuracy.
The tele-irradiator used in preclinical and radiobiology research is generally simple electromechanical device. However, the stability of acquired dosimetry data and the accuracy/precision of dose delivery depends on the stability of the irradiator performance (e.g. mechanical, electrical). It is necessary to implement a simple periodic quality assurance (QA) program for evaluating the irradiator performance to ascertain the stability of dose delivery. QA programs and guidelines for standard medical irradiators are available, but it requires necessary modifications as per the technology of the equipment when applying the standard QA protocol for radiobiology irradiators.
Third party evaluation of the accuracy of dose delivered to a sample/animal, reference dose rate, and dosimetry data are important for enhancing the confidence of the investigator and findings of the preclinical/radiology experiments. It is, therefore, important to include the concept of periodic dosimetry audit for radiobiology laboratories. These audits can be conducted by a variety of well-established dosimeters including tissue equivalent dosimetry film (e.g. Radiochromic/Gafchromic films). In addition, the concept of in vivo/on-line dosimetry should also be incorporated in radiobiology experiments to generate the point dose data as well as 2-dimensional dose distributions either through the use of active or passive dosimeters. In recent times, these dosimetry works can be carried out without requiring much infrastructure and significant man-hour.
It is a general observation that the professionals involved in preclinical and radiobiology studies are having partial familiarization with the dosimetric aspects and parameters of the irradiators which can influence the accuracy and precision of dose intended to be delivered to the subject in the planned study. Accordingly, the reports of such studies include a superficial description of irradiation conditions which may not be sufficient to compare the similar studies of different research groups/laboratories from dosimetry point of view. It is highly required that such professionals should either be fully trained in relevant aspects of radiation physics and radiation dosimetry or avail the services of available experts.
| References|| |
International Commission on Radiological Units and Measurements (ICRU). Determination of Absorbed Dose in a Patient Irradiated by Beams of x- or Gamma Rays in Radiotherapy Procedures. ICRU Report 24. Bethesda, MD, USA: International Commission on Radiological Units; 1976.
Pedersen KH, Kunugi KA, Hammer CG, Culberson WS, DeWerd LA. Radiation biology irradiator dose verification survey. Radiat Res 2016;185:163-8.
Desrosiers M, DeWerd L, Deye J, Lindsay P, Murphy MK, Mitch M, et al.
The importance of dosimetry standardization in radiobiology. J Res Natl Inst Stand Technol 2013;118:403-18.
International Atomic Energy Agency (IAEA). Absorbed Dose Determination in External Beam Radiotherapy: An International Code of Practice for Dosimetry Based on Standards of Absorbed Dose to Water. Technical Report Series 398. Vienna: International Atomic Energy Agency; 2000.
International Atomic Energy Agency (IAEA). Dosimetry of Small Static Field Used in External Beam Radiotherapy: An International Code of Practice for Reference and Relative Dose Determination. Technical Report Series 483. Vienna: International Atomic Energy Agency; 2017.