Total Body Irradiation (TBI) combined with chemotherapy and Bone Marrow Transplantation (BMT) can successfully treat disseminated malignancies such as, acute leukemia. In order to overcome the very bad prognosis associated with these malignancies, this combination of aggressive treatment modalities has been accepted as being necessary. High dose TBI has the therapeutic task of destroying the malignant stem cells, while intensive chemotherapy is needed to kill the proliferating malignant cells. It is the conditioning role of TBI to provide sufficient immunosuppression and bone marrow depletion to allow subsequent transplantation of HLA-compatible bone marrow^[1]. Several early reactions and late complications are known to occur but are not yet clearly related to the treatment parameters.

From the early applications of BMT/TBI in many centres (in the early 70s), hematologists, immunologists, radiotherapists and medical physicists have tried to increase the success of the treatments. Improvement requires an understanding of all the details, interactions and possible complications of this complex combination of treatment modalities. Retrospective studies should provide more knowledge^[2]. Several thousand TBI/BMT treatments have been performed in European centres and even more in the US. Many (too many) institutions are engaged in TBI/BMT^[3]. The International Bone Marrow Transplant Registries (IBMTR) and the European group for Blood and Marrow Transplantation (EBMT) have collected the parameters and the results of treatments for evaluation. However, there are serious difficulties in the evaluation of the clinical results so far. There are discrepancies in the recorded data, parameters are often defined differently, while data have been determined, recorded, reported and registered in dissimilar ways or incompletely. Parameters have been changed too frequently, usually several at once. Too many clinical, biological and physical parameters determine the cure rate and the failure of treatment, as well as the rates of early and late complication. Experimental data, if available, are not always applicable or comparable to the clinical situation^[4]. Many different treatment schedules are applied; different procedures of both medical and physical treatment planning are used; different definitions of target volume, different dosage and timing schedules have been used in combination with other local treatment data; many different techniques of TBI have been developed, regarding the local technical situation and physical experience: different methods of dosimetry, treatment verification and documentation are used^[5]. Large centres tend to have a sufficient amount of data for internal studies. They all try not to change any of the parameters if the treatments are succesful.

Understanding and improving the TBI/BMT results demands that all disciplines, hematologists, immunologists, radiotherapists, radiobiologists and medical physicists work together and each try to consider all of the clinical, biological as well as the physical aspects.

Several conferences and review articles ^[4,6-18] have addressed this fact. Recent clinical innovations have improved the results dramatically, giving further interest to this complex task^[7,19]. The old desire to optimize and unify the physical parameters has now received new interest^[6,20,21].

The European Late Effects Project Group (EULEP), a European research network supported by the Commission of the European Communities, has recently focussed their activities in a EULEP-EBMT study on late effects after BMT. Several aspects are of interest, for all surviving patients these studies should clarify some aspects of tumor development, evolution of second malignancies after BMT, ophthalmological changes, endocrinologal sequelae of BMT, etc.

These recently formed task groups need a consistent set of parameters and data. Thus, an EULEP-EBMT dosimetry task group was founded in order to help evaluate the data stored in the registries. This goal, however, requires comparable sets of uniformly defined and equally reported parameters which relate to TBI in combination with BMT. With the aim of providing the data, the task group has decided to ask all participating centres to redocument all treatments in an unified, comparable and common form, which will be proposed below.

Although a large amount of data has been collected so far, we must look to the future. Thus, priority has to be given to prospective studies. These too, need clear reporting and registration^[22,23]. As a general rule for this kind of study, it has to be recommended that only one parameter is varied at a time in a randomized trial.

The objectives of this report are to summarize the different approaches that have been taken, as well as to publish the proposed list of specified relevant physical parameters, with the aim of producing some recommendations of physical and dosimetrical methods which are suitable for determining, recording, reporting and registering these data. During its preparation, all experiences, comments and proposals of the participating groups were taken into account. This knowledge has already been included in the EBMT registry -Minimum Essential Data- (MED A-B form), in order to guarantee the evaluation of clinical results, and hopefully, it will also be incorporated into the IBMTR.

The reporting of TBI result needs to describe the spatial and temporal distribution of dose which corresponds to individual data, but which is independent of the technique used to achieve it. In addition, typical data on the treatment and dosimetry conditions will be of interest as standard data.