Introduction

As more patients are surviving head and neck cancer with non-surgical treatments, the population living with the effects of radiation treatment presents an increasing caseload to surgeons. ^{Reference Thorn, Hansen, Specht and Bastholt1} Following radiotherapy for head and neck cancer, a cohort of patients present with osteoradionecrosis (ORN). The reported incidence of ORN varies greatly between 5 to 38% and presents between 6 and 36 months post-irradiation. ^{Reference Thorn, Hansen, Specht and Bastholt1–Reference Bettoni, Olivetto and Duisit3} Onset is initiated by trauma or infection (from tooth extraction, surgery, biopsy, denture irritation, accidents or infection) to the local area, and the mandible is a particularly high risk and problematic site. Other risk factors include age, sex, medical comorbidities, primary tumour site and stage, tumour location and extent, dental status/hygiene, smoking and alcohol ^{Reference Store and Boysen2,Reference Mendenhall4,Reference Wang, Hu and Eisbruch5} , as well as dose received by the mandible. ^{Reference Aarup-Kristensen, Hansen, Forner, Brink, Erikson and Johansen6}

ORN is a debilitating side effect of radiotherapy that is challenging to treat, and while a definitive consensus on the management of ORN is lacking, the current standard of care for this patient cohort is symptom management. Recognised non-surgical has historically included hyperbaric oxygen therapy and more recently a combination of pentoxifylline, clodronate and vitamin E and long-term antimicrobial therapy. ^{Reference Fan, Kim, Cho, Eo, Lee and Woo7} Response to medical management is variable and unpredictable. In refractory cases, where symptoms become unmanageable, the gold standard of care is mandibular resection and reconstruction such as a fibula osseo-fascio-cutaneous free flap. ^{Reference Hirsch, Bell, Dierks, Potter and Potter8} Radiological assessment of high-resolution CT scans of the maxillofacial skeleton and fibula guides the resection and reconstruction (Figure 1). Locally, this is performed using a patient-specific implant system designed in conjunction with manufacturers specialising in implants and implant systems for craniomaxillofacial surgery (KLS Martin GmbH & Co, Tuttlingen, Germany). Additive manufacturing (3D printing) techniques are then used to produce patient-specific cutting guides and titanium alloy fixation devices to ensure an accurate execution of the surgical plan (Figure 1c). This computer-based virtual surgical planning approach has become the gold standard of care in mandible reconstruction for both malignant and benign pathologies. This process infers significant benefits over the traditional ‘free-hand’, ‘on-table’ approach in terms of accuracy, reducing surgical time and post-operative complications. ^{Reference Levine, Patel, Saadeh and Hirsch9,Reference Ma, Van Dessel and Shujaat10} Unfortunately, this approach has not been universally adopted for osteoradionecrosis surgery as surgeons struggle to commit to a surgical plan without the flexibility to alter it based on the immediate intra-operative findings. Placement of a resection through areas of mandible exposed to high radiotherapy dose increases the risk of surgical failure. The additional information provided by merging radiotherapy dosimetry alongside the pre-surgical planning CT enables a more informed decision regarding the extent of the surgical excision. Areas of high dose can be avoided and resection margins placed in areas of bone with greater re-modelling potential, reducing the risk of further ORN and surgical failure, minimising the patient distress and healthcare expenditure that ensues.

Figure 1.

Virtual surgical planning for resection of the mandible. (a) High definition CT is used to create a rendered image of the maxillofacial skeleton. (b) Radiological and clinical assessments guide the surgical planning. (c) Bone sections (in teal, red blue and green) taken from the patient’s fibula, guided by 3D-printed cutting guides form the reconstructed section replacing the resected mandible.

The exact relationship between radiotherapy dose and ORN in the mandible is thought to be complex and as yet still not perfectly defined, although some evidence suggests a trend between doses greater than 50Gy and the onset of ORN exists, with areas exposed to doses lower than 50Gy reported to be at significantly lower risk of ORN. ^{Reference Thorn, Hansen, Specht and Bastholt1,Reference Aarup-Kristensen, Hansen, Forner, Brink, Erikson and Johansen6,Reference Fan, Kim, Cho, Eo, Lee and Woo7,Reference Tsai, Hofstede and Sturgis11}

We present our experience of a novel approach to pre-operative planning for these complex cases. By incorporating radiotherapy dose registered and deformed onto a high-resolution diagnostic CT, volumes representing high risk of ORN can be incorporated into the 3D surgical design process. Importantly, areas that received low doses of radiotherapy can also be visualised to ensure that osteotomy sites and osteosynthesis plates are located in areas of mandible that received low doses of radiotherapy. To date, this is the first reported implementation of the 3D dose guided surgery (DGS) technique.