Journal of Medical Physics
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ORIGINAL ARTICLE
Year : 2019  |  Volume : 44  |  Issue : 4  |  Page : 254-262

Dose shadowing and prosthesis involvement for megavoltage photon In vivo diode dosimetry


Department of Medical Physics, University of the Free State, Bloemfontein, South Africa

Correspondence Address:
Dr. Nicholas Ade
Department of Medical Physics, University of the Free State, PO Box 339, Bloemfontein 9300
South Africa
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jmp.JMP_59_19

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Aim: The aim of the study is to investigate the photon beam perturbations induced by an in vivo diode in combination with prosthesis involvement in a human-like phantom. Materials and Methods: Beam perturbations for 6 MV and 10 MV photons caused by an EDP-203G in vivo diode in combination with prosthesis involvement were studied in a unique water-equivalent pelvic phantom, equipped with bony structures and Ti prosthesis using single fields between 2 × 2 and 15 cm × 15 cm as well as 10 MV lateral opposing fields and a four-field plan. Dose distributions were measured with Gafchromic EBT3 films with and without the diode included in the beams on the prosthesis (prosthetic fields) and non-prosthesis (non-prosthetic fields) sides of the phantom. Differences between prosthetic and non-prosthetic field dose data were determined to assess the effect of the prosthesis on the diode-induced beam perturbations inside the phantom. Results: Photon beam dose perturbations ranged from 2% to 7% and from 5% to 12% for prosthetic and non-prosthetic fields, respectively, with relative differences between 2% and 4%. In addition, d50depths ranging from 8.7 to 11.5 cm and from 11.5 to 15 cm were acquired in the phantom for prosthetic and non-prosthetic fields, respectively, with relative differences between 2% and 5%. Conclusion: On the basis of accuracy requirements in radiotherapy noting that a small underdose to tumors could yield a decrease in the probability of tumor control, the diode-induced beam perturbations in combination with prosthesis involvement in the photon fields may affect treatment outcome, as there would be a reduction in the prescribed target dose during treatment delivery.


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