MIRD Commentary: Proposed Name for a Dosimetry Unit Applicable to Deterministic Biological Effects—The Barendsen (Bd)

Abstract

A good name is better than precious ointment. Hebrew Ecclesiastes 7:1The fundamental physical quantity for relating all biologic effects to radiation exposure is the absorbed dose, the energy imparted per unit mass of tissue. Absorbed dose is expressed in units of joules per kilogram (J/kg) and is given the special name gray (Gy). Exposure to ionizing radiation may cause both deterministic and stochastic biologic effects. To account for the relative effect per unit absorbed dose that has been observed for different types of radiation, the International Commission on Radiological Protection (ICRP) has established radiation weighting factors for stochastic effects. The product of absorbed dose in Gy and the radiation weighting factor is defined as the equivalent dose. Equivalent dose values are designated by a special named unit, the sievert (Sv). Unlike the situation for stochastic effects, no well-defined formalism and associated special named quantities have been widely adopted for deterministic effects. The therapeutic application of radionuclides and, specifically, a-particle emitters in nuclear medicine has brought to the forefront the need for a well-defined dosimetry formalism applicable to deterministic effects that is accompanied by corresponding special named quantities. This commentary reviews recent proposals related to this issue and concludes with a recommendation to establish a new named quantity.

21 years of Biologically Effective Dose

“…This suggestion was made within the last year by a group from MIRD [50] and is under consideration by the ICRU and IAEA. It would be called the Barendsen (Bv) in honour of his many scientific contributions, as emphasised in the present account, that Eddie Barendsen has made, from his obtaining of LQ shaped cell survival curves in the early 1960s to the finding of rapid repopulation in human-origin tumours implanted into rats at a time when it was not known that repopulation is common in tumours during continued irradiation, and culminating in the concept of using the initial slopes of cell survival curves to define the log cell kill which is the basic concept of the present BED as explained above [12].…”

Testis dosimetry in individual patients by combining a small-scale dosimetry model and pharmacokinetic modeling-application of111In-Ibritumomab Tiuxetan (Zevalin®)

“…Owing to the small extension of the testes compared to other body regions it was considered important to make explicit attenuation correction, and was achieved using a pixel-based quantification scheme where an X-ray scout image is used as attenuation correction map. The internal dosimetry community continuously discusses the necessity for improvements to bring about more detailed tissue and cellular dosimetry (Hobbs et al 2012;Howell et al 2006;ICRU 2002;Sgouros and Hobbs 2014;Sgouros et al 2009). One direction has been the development of detailed small-scale dosimetry models but the practical use is so far unfortunately limited due to the difficulties in determining detailed activity localization for the tissue in question.…”

“…A need has been established for developing more detailed dosimetry models based on tissue structures in internal dosimetry (Howell et al 2006;ICRU 2002;Sgouros et al 2009). Our group recently published a small-scale dosimetry model developed for detailed testis dosimetry (Larsson et al 2012).…”

The BJR and progress in radiobiological modelling

“…Such an idea was first put forward in embryonic form in 2009 [5], the suggestion then being made specifically by the nuclear medicine community to help establish easier comparison between the results of targeted radionuclide therapy with those seen with conventional external beam therapy. But, as Fowler points out [3], the establishment of a dedicated unit for BED would have wider benefit and impact, not least because it would help to remove some wider confusion.…”

“…But, as Fowler points out [3], the establishment of a dedicated unit for BED would have wider benefit and impact, not least because it would help to remove some wider confusion. The suggested name for the BED unit is the barendsen (symbol Bd), in recognition of the seminal work of Professor GW Barendsen [3][4][5]. The process of considering a unit for expressing deterministic effects in radiation oncology is likely to be a protracted process (it will require international agreement on concepts, quantities and units), but the need has been established.…”