COMS Calculation

NOTE: When calculating retrospective dosimetry using the COMS protocol it is recommended you set Plaque Simulator's calculation controls for isotropic point source in water (ie disable carrier correction) and use the supplied I-125 (6711 COMS) physics file which has been preconfigured for source strength specification in air kerma strength, Sk, (U = cGy cm^2/hr) and for which the other modifiers have been assigned unity values.

The COMS (Collaborative Ocular Melanoma Study) dosimetry did not recognize radionuclides other than I-125, nor did it recognize linear source geometry, anisotropy, or any of the other TG43 and Plaque Simulator dosimetry enhancements. This protocol was modified in November 1996 to use a simplified form of the AAPM TG43 (Dosimetry of interstitial brachytherapy sources: Recommendations of the AAPM Radiation Therapy Committee Task Group No. 43, Medical Physics, Vol. 22, 1995) formalism.

  • TG43: D(r,o) = Sk * d * [G(r,o) / G(r0,o0)] * g(r) * F(r,o)
  • COMS: D(r) = Sk * d * (1/r^2) * g(r)

To configure PS6 to reproduce the original COMS calculation set the prescription controls as illustrated on the right: Set the shell model to lipped, geometry to point source, isotropy to spherical, and disable all other the corrections including the silicone carrier, gold flouresence, shell collimation and air scatter.