[Comparison of Measured Dose and Calculated Dose by Various Algorithms in an Early-stage Glottic Cancer Treatment Model].

PURPOSE: To evaluate the dose calculation accuracy in areas exposed to air on a radiotherapy treatment planning system using a phantom model simulating early-stage glottic cancer.

METHODS

An air gap was placed between water-equivalent phantoms, and 6 MV X-rays were delivered at 200 MU. The absorbed dose in the depth direction was measured using Gafchromic film. These measurements were compared with calculations from Pinnacle3 (collapsed cone convolution: CCC) and RayStation (photon Monte Carlo: pMC, CCC).

RESULTS

The difference between the measured film values after passing through the air gap and the calculated values of each algorithm was up to 14.4% with RayStation CCC and -3.8% with RayStation pMC.

CONCLUSION

The pMC method offers higher accuracy in calculating surface dose at air-tissue boundaries than the CCC method, which overestimates the absorbed dose at the surface. When the dose around heterogeneous regions involving air is clinically very important, using RayStation pMC allows for more accurate dose calculations.