title: Influence of total-body mass on the scaling of S-factors for patient-specific, blood-based red-marrow dosimetry.
abstract: To perform patient-specific, blood-based red-marrow dosimetry, dose conversion factors (the S factors in the MIRD formalism) have to be scaled by patients' organ masses. The dose to red marrow includes both self-dose and cross-irradiation contributions. Linear mass scaling for the self-irradiation term only is usually applied as a first approximation, whereas the cross-irradiation term is considered to be mass independent. Recently, the need of a mass scaling correction on both terms, not necessarily linear and dependent on the radionuclide, has been highlighted in the literature. S-factors taking into account different mass adjustments of organs are available in the OLINDA/EXM code. In this paper, a general algorithm able to fit the mass-dependent factors S(rm<--tb) and S(rm<--rm) is suggested and included in a more general equation for red-marrow dose calculation. Moreover, parameters to be considered specifically for therapeutic radionuclides such as (131)I, (90)Y and 177Lu are reported. The red-marrow doses calculated by the traditional and new algorithms are compared for (131)I in ablation therapy (14 pts), 177Lu- (13 pts) and (90)Y- (11 pts) peptide therapy for neuroendocrine tumours, and (90)Y-Zevalin therapy for NHL (21 pts). The range of differences observed is as follows: -36% to -10% for (131)I ablation, -22% to 5% for 177Lu-DOTATATE, -9% to 11% for (90)Y-DOTATOC and -8% to 6% for (90)Y-Zevalin. All differences are mostly due to the activity in the remainder of the body contributing to cross-irradiation. This paper quantifies the influence of mass scaling adjustment on usually applied therapies and shows how to derive the appropriate parameters for other radionuclides and radiopharmaceuticals.
authors.affiliation: Sezione di Fisica Medica, U.O. Fisica Sanitaria, Azienda Ospedaliero-Universitaria Pisana, Pisa, Italy.
authors.forename: A C
authors.initials: AC
authors.lastname: Traino
authors.forename: M
authors.initials: M
authors.lastname: Ferrari
authors.forename: M
authors.initials: M
authors.lastname: Cremonesi
authors.forename: M G
authors.initials: MG
authors.lastname: Stabin
mesh_terms: D000886:Anthropometry / Q000379:methods*; D015992:Body Mass Index; D001853:Bone Marrow / Q000502:physiology* / Q000528:radiation effects*; D003198:Computer Simulation; D006801:Humans; D008954:Models, Biological; D011829:Radiation Dosage; D011874:Radiometry / Q000379:methods*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D020266:Radiotherapy, Conformal / Q000379:methods*; D012062:Relative Biological Effectiveness; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity