Do metallic ports in tissue expanders affect postmastectomy radiation delivery?
OBJECTIVE
Postmastectomy radiation therapy (PMRT) is often delivered to patients with permanent breast implants. On occasion, patients are irradiated with a tissue expander (TE) in place before their permanent implant exchange. Because of concern of potential under-dosing in these patients, we examined the dosimetric effects of the Magna-Site (Santa Barbara, CA) metallic port that is present in certain TEs.


METHODS
We performed ex vivo film dosimetry with single 6-MV and 15-MV photon beams on a water phantom containing a Magna-Site disc in two orientations. Additionally, using in vivo films, we measured the exit dose from 1 patient's TE-reconstructed breast during chest wall treatment with 15-MV tangent beams. Finally, we placed thermoluminescent dosimeters (TLDs) on 6 patients with TEs who received PMRT delivered with 15-MV tangent beams.


RESULTS
Phantom film dosimetry revealed decreased transmission in the region of the Magna-Site, particularly with the magnet in the parallel orientation (at 22 mm: 78% transmission with 6 MV, 84% transmission with 15 MV). The transmission measured by in vivo films during single beam treatment concurred with ex vivo results. TLD data showed acceptable variation in median dose to the skin (86-101% prescription dose).


CONCLUSIONS
Because of potential dosimetric effects of the Magna-Site, it is preferable to treat PMRT patients with permanent implants. However, it is not unreasonable to treat with a TE because the volume of tissue affected by attenuation from the Magna-Site is small. In this scenario, we recommend using 15 MV photons with compensating bolus.
Damast
Shari
S
Department of Radiation Oncology, Memorial Sloan-Kettering Cancer Center, New York, NY 10021, USA.
Beal
Kathryn
K
Ballangrud
Ase
A
Losasso
Thomas J
TJ
Cordeiro
Peter G
PG
Disa
Joseph J
JJ
Hong
Linda
L
McCormick
Beryl L
BL
D000328:Adult; D001943:Breast Neoplasms / Q000532:radiotherapy* / Q000601:surgery; D005260:Female; D005373:Film Dosimetry / Q000379:methods; D006801:Humans; D008408:Mastectomy; D008670:Metals; D008875:Middle Aged; D019047:Phantoms, Imaging; D011184:Postoperative Period; D011879:Radiotherapy Dosage; D013819:Thermoluminescent Dosimetry / Q000379:methods; D015625:Tissue Expansion Devices
D008670:Metals