title: GAF film dosimetry of a tandem positioned beta-emitting intravascular brachytherapy source train.
abstract: Coronary artery brachytherapy may require treatment of lesions longer than a single source length. A treatment option is tandem positioning of the single source. This study presents relative dosimetric measurements of a cardiovascular brachytherapy source and the dosimetric characteristics in the junction region of tandem treatments. Measurements were carried out using a Novoste Beta Cath 90Sr/90Y 40 mm beta source in a plastic water phantom. Radiochromic MD-55-2 film, calibrated using both 6 MV photon and 6 MeV electron beams from a linear accelerator, was used as the dosimeter. Dose distributions around a single source and in the junction region of tandem irradiation were measured. Measurements of the near field dose as close as 1.2 mm from the source are presented. Significant over- or underdoses in the junction region of tandem irradiation were quantified. At a radial distance of 2 mm from the longitudinal axis of the source, the dose value in the middle of the junction region, normalized to the dose at 2 mm midline single source, was about 182% for a 2-seed overlap and 16% for a 2-seed gap, respectively. Dose distributions in the junction region as a function of source overlap and radial distance have fairly high gradients and exhibit characteristic patterns. The fraction of prescription dose was found to have a sigmoidal dependence on overlap size, for radial distances ranging between 1.2 and 3 mm. The parameters of these sigmoids, quantified as functions of radial distance, could be used to provide quick and reasonable over/underdose estimates, given any potential overlap or gap in the junction area, with an uncertainty within 10%.
authors.affiliation: Department of Radiation Oncology, Brigham and Women's Hospital, Dana-Farber Cancer Institute and Children's Hospital, Harvard Medical School, 75 Francis Street, Boston, Massachusetts 02115-6110, USA. iiftimia@lifespan.org
authors.forename: Ileana
authors.initials: I
authors.lastname: Iftimia
authors.forename: Phillip M
authors.initials: PM
authors.lastname: Devlin
authors.forename: Lee M
authors.initials: LM
authors.lastname: Chin
authors.forename: J M
authors.initials: JM
authors.lastname: Baron
authors.forename: R A
authors.initials: RA
authors.lastname: Cormack
mesh_terms: D001610:Beta Particles; D001918:Brachytherapy / Q000295:instrumentation* / Q000379:methods*; D023903:Coronary Restenosis / Q000532:radiotherapy*; D005373:Film Dosimetry / Q000295:instrumentation* / Q000379:methods*; D006801:Humans; D010879:Piperazines; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation* / Q000379:methods*; D011881:Radiotherapy, Computer-Assisted / Q000295:instrumentation / Q000379:methods; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013326:Strontium Radioisotopes; D014652:Vascular Diseases / Q000532:radiotherapy; D015021:Yttrium Radioisotopes
chemical_list: D010879:Piperazines; D013326:Strontium Radioisotopes; D015021:Yttrium Radioisotopes; C084589:oxypertine