Geometric variability of organs at risk in head and neck radiotherapy
| PhD ceremony: | dr. ir. C.L. (Charlotte) Brouwer |
| When: | October 19, 2016 |
| Start: | 12:45 |
| Supervisor: | prof. dr. J.A. (Hans) Langendijk |
| Co-supervisors: | dr. ir. N.M. (Marianna) Sijtsema, dr. R.J.H.M. Steenbakkers |
| Where: | Academy building RUG / Student Information & Administration |
| Faculty: | Medical Sciences / UMCG |
Many patients with head and neck cancer suffer from side effects due to radiation therapy. Xerostomia (having a dry mouth) is a serious and common side effect, which can persist long after treatment. Predictive models are used to calculate the probability of the occurrence of a certain complication, the 'normal tissue complication probability (NTCP)'. NTCP models for xerostomia often use the average dose to the major salivary gland (parotid gland). The NTCP can be used to select patients for an advanced treatment. However, variation exists in the delineation of organs at risk, such as the parotid gland. Also, the shape and size of the parotid gland may change during the course of radiotherapy. These variations in geometry lead to variations in the average dose, and therefore to inconsistent values of NTCP.
In this dissertation, the size and the effect of variations in delineation and changing anatomy are studied, and solutions to reduce these variations or limit their consequences are proposed. The most important results are internationally approved delineation guidelines, which have been implemented world-wide. This will reduce interobserver variability and allow the generic application of NTCP models.
In addition, a method is proposed to select patients with a large dose variation in the parotid gland for adaptive radiotherapy. In this way, the risk of xerostomia will be reduced and quality of life improved.