Overall and GTV subvolumes tumour control probability (TCP) for head and neck cancer treated by 3D-IMRT with inhomogeneous dose distribution
Streszczenie
Introduction. In this study, an original model has been developed to estimate the real TCP that is a product of the TCPs calculated for GTV subvolumes of head and neck cancer based on 3D-IMRT dose planning.
Material and methods. Retrospective pilot group consist of 16 cases of oropharyngeal cancer in stage T1–2N0 previously treated with 3D-IMRT with at least 3-year follow-up. The total dose (TD) was 60–70 Gy in 2.0 Gy fractions delivered over 42–49 days. Within GTV two subvolumes were marked out: SVA with the planned 100% TD, and underdosed (90–95%) SVB. The TCP for both was calculated using the original formula developed by Withers and Maciejewski.
Results. During 3-year follow-up, 8 local recurrences (LR) occurred. In about 70% of SVB “dose cold spots” encompassed more than 50% GTV volume. This resulted in the TCPSVB decrease to 60%. Thus, the real overall TCP was much lower than a priori predicted, and in these cases local recurrences occurred.
Discussion.Both cold spot SVB volumes and their dose deficit strongly correlated with a high risk of LR.
Conclusions.In conclusion the magnitude of dose deficit and the size of cold subvolume within GTV have an independent negative impact on real TCP and demand dose re-planning.
Słowa kluczowe: 3D-IMRT planningcold spots within GTVestimates of partial TCPs within GTV subvolumes
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