Second cancer risk, concomitant exposures and IRMER(2000)

Abstract

In this issue we publish a Commentary by Dr Roger Harrison [1] on second cancer risk following radiotherapy. Harrison looks at the evidence from various sources, including an NRPB summary, and the complexity of comparing risk in the radiotherapy patient population with that in the normal population. He also addresses the particular problem of ‘‘concomitant dose’’ in radiotherapy planning and verification that has been highlighted by other authors in articles in BJR, particularly Waddington and Mackenzie [2] and Munro [3]. The Ionising Radiation (Medical Exposures) Regulations (IRMER(2000)) [4] require justification of all medical exposures [Reg:6(1)]. Under the optimization regulation [Reg:7], the Practitioner is also required to ‘‘ensure that exposures of target volumes are individually planned, taking into account that doses to non-target volumes and tissues shall be as low as reasonably practicable (ALARP) and consistent with the intended radiotherapeutic purposes of the exposure’’. Neither of these regulations distinguishes between the radiotherapeutic dose and the ‘‘planning and verification doses’’ required by the total process. Also, ALARP has such a different meaning for radiotherapy exposures from that for diagnostic exposures that it is almost inappropriate as a concept. (We may need to develop our own language specifically for protection in radiotherapy, but more of that later.) A specific interpretation is put on these regulations in the Medical and Dental Guidance Notes [5]. In situations where the clinician is required to consider the extra dose from planning and verification exposures independently, ‘‘The IRMER Practitioner responsible for the treatment exposure (the Clinical Oncologist) can justify the concomitant exposures at the outset or during the radiotherapy course, but in doing so must be aware of the likely exposures and the resulting dose so that the benefit and detriment can be assessed. This can be achieved by including likely concomitant (extra-target) exposures within site-specific protocols with a total effective dose agreed’’. Waddington and McKenzie [2] chose to follow the Guidance Notes to demonstrate the possibility of expressing concomitant exposures using ‘‘effective dose’’, and have presented an excellent paper analysing that part of the ‘‘dose’’ from verification images; and at the same time justifying the need to record these doses by looking at the potential for cancer induction. Harrison [1] has taken this a stage further to analyse in more depth the radiation induced cancer issue for radiotherapy patients. One of his conclusions is that to specify and document individual concomitant exposures separately would seem to be unnecessary. This Editorial aims to stimulate further debate on these subjects, which are partly about the need for radiotherapy departments to comply with IRMER(2000) [4], but also about the need for all staff to gain a better understanding on cost-benefits of radiotherapy. It is extremely important that the radiotherapy community addresses this subject and arrives at a consensus that will benefit the patient. In the summary of the current position, which follows, absorbed dose (shortened to ‘‘dose’’) has been used throughout. The use of ‘‘effective dose’’ is questionable in radiotherapy for several reasons: the radiotherapy patient population is a highly selected subgroup of the general population with different longevity; also tissue weighting factors will be different because dose gradients and doses are much greater in radiotherapy than in diagnostic radiography. Therefore it is avoided here.