Evaluation of surface dose calculations using monaco treatment planning system in an indigenously developed head and neck phantom

Abstract

Objective: The objective of this study is to evaluate the surface doses for 3-dimensional conformal radiation therapy (3DCRT), intensity-modulated radiation therapy (IMRT), and volumetric-modulated arc therapy (VMAT) treatment planning techniques using an inhouse designed head and neck (HN) phantom and to compare the measured surface doses with the doses calculated using the Monaco treatment planning system (TPS). Materials and Methods: An arbitrary clinical target volume was defined with 5 mm planning target volume (PTV) expansion on computed tomography images of an in house designed heterogeneous HN phantom. 3DCRT, IMRT, and VMAT plans were created using Monaco TPS for prescribed dose of 60Gy in 30 fractions to cover 95% of PTV volume. Dose measurements were performed using EBT3 Gafchromic films at 10 selected points on the surface of HN phantom, especially inside the treatment area. Percentage mean dose differences were evaluated between the TPS calculated doses and measured dose values at these identified points. Results: The average dose difference between the TPS calculated doses and film measurements were found to be varying from 11.66% to 19.73%. It was observed that TPS overestimated the surface doses in comparison to measured doses. The results also shows that Gafchromic films can be used for surface dose measurements in patients for in vivo dosimetry in areas where high skin dose is expected during radiotherapy treatment. Conclusion: The limitations of TPS should be considered while evaluating surface doses in radiotherapy plans.