Understanding the impact of intensity modulated radiation therapy on dental and oral tissues in oropharyngeal cancer patients

Student thesis: Doctoral ThesisDoctor of Philosophy


Osteoradionecrosis (ORN) of the jaw remains one of the most feared late toxicity complications of head and neck radiotherapy (RT). With the introduction of intensity modulated radiation therapy (IMRT) many hypothesised the complications would be consigned to the history books based on the ability to deliver more focused and targeted radiation. However, in contrast, the opposite has been seen with ORN still persisting and arguably increasing. The latter has been identified particularly in the oropharyngeal cancer (OPC) group more than any other sub-site. In the IMRT era, incidence of ORN in head and neck cancer (HNC) was approximately 5.5%. However, when considering the OPC alone it is almost double (10.5%). The two main factors for ORN; the dentition and RT dose are both of clinical significance in explaining the rise of ORN in OPC patients.

The overall dental status of OPC patients is vastly superior compared to many of the other common HNC patients. OPC patient often present with more teeth with less active dental disease compared to other HNC sub-sites. This fact is further strengthened when the OPC patients are divided by their HPV status with HPV positive patients having a vastly superior dentition. This is based on them presenting with more teeth including third molars, more complex restored teeth and less periodontal disease. Hence, though they have suffered dental disease burden, efforts have been made to retain their teeth. This trend is opposite to the various other common HNC sub-sites who present with fewer teeth and active dental disease in line with a pattern of dental neglect and low oral health priority. Hence, the retention of teeth leaves a significant risk factor for the development of ORN.

RT to the oropharynx via IMRT inadvertently includes the jaws, particularly in the HPV positive patient who presents with late stage disease due to its indolent nature. Hence large areas of the jaws are subjected to doses in excess of 30 Grays (Gy) following which radiation induced microvasculature depletion is evident in the hard and soft tissue of the oral cavity. This phenomenon worsens with increasing RT doses and over time. Both apply to the OPC patient. The posterior dentition often receives in excess of 40 Gy which is the minimum threshold for ORN. In addition, favourable survival particularly in the HPV positive group allows the progressive development of radiation induced fibrosis. Hence, high tooth retention, irradiated dento-alveolar bone with limited reparative potential and fibrosed oral mucosa as a poor protector creates a finely balanced oral conflict for the development of ORN with increase time.

It is therefore evident that the OPC patient is vulnerable to developing ORN possessing all the key factors for creating a ‘perfect storm’. With HPV positive patients being a clear outlier to the typical HNC patient and the epidemic rise of this tumour it only compounds the complication further in a group already presenting with an elevated risk.
Date of Award1 Sept 2020
Original languageEnglish
Awarding Institution
  • King's College London
SupervisorMark McGurk (Supervisor), Lucy Di-Silvio (Supervisor) & Michael Fenlon (Supervisor)

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