title: A directional103Pd brachytherapy device: Dosimetric characterization and practical aspects for clinical use.
abstract: A brachytherapy (BT) device has been developed with shielding to provide directional BT for preferentially irradiating malignancies while sparing healthy tissues. The CivaSheet is a flexible low-dose-rate BT device containing CivaDots with103Pd shielded by a thin Au disk. This is the first report of a clinical dosimetric characterization of the CivaSheet device.
  
  
  
  Radiation dose distributions near a CivaDot were estimated using the MCNP6 radiation transport code. CivaSheet arrays were also modeled to evaluate the dose superposition principle for treatment planning. The resultant data were commissioned in a treatment planning system (TPS) (VariSeed 9.0), and the accuracy of the dose superposition principle was evaluated for summing individual elements comprising a planar CivaSheet.
  
  
  
  The dose-rate constant (0.579 cGy/h/U) was lower than for103Pd seeds due to Au L-shell x-rays increasing the air-kerma strength. Radial dose function values at 0.1, 0.5, 2, 5, and 10 cm were 1.884, 1.344, 0.558, 0.088, and 0.0046, respectively. The two-dimensional anisotropy function exhibited dramatic reduction between the forward (0°) and rearward (180°) directions by a factor of 276 at r = 0.1 cm, 24 at r = 1 cm, and 5.3 at r = 10 cm. This effect diminished due to increasingly scattered radiation. The largest gradient in the two-dimensional anisotropy function was in contact with the device at 92° due to the Au disk shielding. TPS commissioning and dose superposition accuracies were typically within 2%.
  
  
  
  Simulations of the CivaDot yielded comprehensive dosimetry parameters that were entered into a TPS and deemed acceptable for clinical use. Dosimetry measurements of the CivaSheet are also of interest to the BT community.
authors.affiliation: Department of Radiation Oncology, Tufts University School of Medicine, Boston, MA. Electronic address: markjrivard@gmail.com.
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Rivard
mesh_terms: D016880:Anisotropy; D001918:Brachytherapy / Q000295:instrumentation* / Q000379:methods; D003198:Computer Simulation; D006801:Humans; D009010:Monte Carlo Method; D010165:Palladium / Q000627:therapeutic use*; D011868:Radioisotopes / Q000627:therapeutic use*; D011874:Radiometry; D011879:Radiotherapy Dosage
chemical_list: D011868:Radioisotopes; D010165:Palladium
keywords: CivaSheet; Dosimetry; Monte Carlo methods