A permanent breast seed implant as partial breast radiation therapy for early-stage patients: a comparison of palladium-103 and iodine-125 isotopes based on radiation safety considerations.
OBJECTIVE
A permanent breast seed implant (PBSI) technique has been developed as a new form of partial adjuvant radiation therapy for early-stage breast cancer. This study compares iodine-125 ((125)I) and palladium-103 ((103)Pd) isotopes by examining the exposure and effective dose (ED) to a patient's partner.


METHODS
A low-energy survey meter was used to measure exposure rates as a function of bolus thickness placed over (103)Pd or (125)I seeds. A general mathematical expression for the initial exposure rate at 1 m (x(o,1m)) from the skin surface as a function of the implant size, R, and the distance between the skin surface and the implant, d, was derived. Also, a second general equation is proposed to calculate the ED to the patient's partner.


RESULTS
The initial exposure rate at 1 meter and the ED are calculated as follows: x(o,1m) = 3alpha2R(3) ; ;beta(3) [e(-beta(2R+d))(betaR + 1) + e(-betad)(betaR - 1)], and ED = aR(b) [e(-c(2R+d)) (cR + 1) + e(-cd) (cR - 1)]. For (125)I, the parameters are: alpha = 0.154409, beta = 0.388460, a = 197, b = -0.95, and c = 0.38846. For (103)Pd, they are: alpha = 0.06877, beta = 0.421098, a = 18.6, b = -0.78, and c = 0.421098. For implant diameters varying from 2 to 6 cm and skin-to-implant distances varying from 0.7 to 4 cm, the ED is consistently below 2.6 mSv using the (103)Pd isotope, but more than 5 mSv in many instances and possibly up to 20 mSv using (125)I.


CONCLUSIONS
PBSI using (103)Pd seeds appears safe because the patient's partner ED is consistently below 5 mSv. The(125)I isotope is not recommended for PBSI.
Keller
Brian
B
Department of Medical Physics, Sunnybrook and Women's Health Sciences Centre, Toronto, Ontario, Canada.
Sankreacha
Raxa
R
Rakovitch
Eileen
E
O'brien
Peter
P
Pignol
Jean-Philippe
JP
D000465:Algorithms; D001918:Brachytherapy / Q000295:instrumentation / Q000379:methods*; D001943:Breast Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D005260:Female; D006801:Humans; D007457:Iodine Radioisotopes / Q000627:therapeutic use*; D009367:Neoplasm Staging; D010165:Palladium / Q000627:therapeutic use*; D011829:Radiation Dosage; D011835:Radiation Protection; D011868:Radioisotopes / Q000627:therapeutic use*; D011874:Radiometry / Q000379:methods; D018714:Radiotherapy, Adjuvant; D018454:Spouses
D007457:Iodine Radioisotopes; D011868:Radioisotopes; D010165:Palladium