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Dosimetric Impact of Tissue Expanders with Magnetic Port On Breast Irradiation

C Venencia

G Rivelli , C Venencia*, E Garrigo , S Zunino , Instituto de Radioterapia - Fundacion Marie Curie, Cordoba, ARGENTINA


SU-I-GPD-T-428 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: Recent studies investigated dose attenuation in the presence of magnetic ports on breast irradiation. Artifact corrections were proposed to improve TPS dose calculations. The aims of this study were to review dose attenuation, propose a dose compensation method for field-in-field (sIMRT) technique and investigate possible dose increment due to backscatter radiation from the magnetic port. Dose calculations accuracy of a commercial TPS is evaluated taking into account the overall dosimetric impact of the magnetic port.

Methods: Constructed dental wax phantoms with magnetic ports placed parallel and perpendicular to the surface were used for measurements. A homogeneous wax phantom was used as reference. Dose calculations was done using iPlan v4.5.3 (Brainlab) TPS and compared with film dosimetry (EDR2 and EBT3) and ion chamber measurements. Magnetic port was outlined and its HU was overwritten to 3050. For artifact dose corrections additional segments were added to the medial and external fields, in our sIMRT breast technique. Films were placed through the wax and magnetic port interface at different distances ranging from 0.5 to 5cm.

Results: Ion chamber and film measurements showed dose attenuation of 7% and 19% under the magnetic port in parallel and perpendicular direction. Film measurements showed that additional segments in sIMRT plan were able to compensate attenuation produced by the magnetic port. Films measurement showed a dose increment in the perpendicular direction of field incidence on magnetic port of 8% in contact and 3% at 8mm. The TPS was unable to model backscatter dose increment.

Conclusion: Magnetic port caused dose attenuation under the magnetic port and surface dose increment in the perpendicular direction of field’s incidences. Additional segments on sIMRT technique improve dose calculation distal to the magnetic port. The clinical impact of dose increment due backscatter close to breast surface encourages us to further investigate this issue.

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