Statistics from Altmetric.com
Orbital haemangiopericytoma is a rare, potentially malignant vascular tumour, which can affect any part of the orbit. The treatment of choice is complete surgical excision but because of its vascular nature and tissue friability during surgery this is frequently not achieved.1,2 Difficulties in correctly diagnosing this tumour preoperatively compound this problem. Incomplete excision is associated with increased risk of local recurrence and metastatic disease, which are reported to occur in up to 43% and 15% of cases respectively, and can take many years to become manifest.2,3 Treatment options for orbital recurrence include orbital exenteration, further attempts at complete excision, or local excision and adjuvant therapy with radiotherapy,4 brachytherapy,5 or chemotherapy.3 To our knowledge the use of proton beam therapy in controlling recurrent orbital haemangiopericytoma has never been described. We therefore report such a case.
A 61 year old woman presented with a second recurrence of a left medial orbital haemangiopericytoma 2 years following radical excision of the tumour via a transfrontal approach, and 14 years after initial excision. She was found to have non-axial proptosis of the globe associated with a soft tissue swelling at the medial canthus (fig 1). Her visual acuities were unchanged from initial presentation at 6/6 in the right eye and 6/9 in the left eye. She also had restriction of the left globe on dextroversion resulting in diplopia, which, although longstanding, had deteriorated considerably as shown by the field of binocular single vision. Neurosurgical review was arranged and it was thought that further attempts at complete excision would be unsuccessful. This, together with the patient’s desire not to undergo further major surgery, led us to explore other treatment options. She therefore underwent further local excision via a medial orbital approach to debulk the tumour mass followed by proton beam therapy with a total irradiation dose of 50 Gy equivalent in 20 fractions over 28 days. The protocol for this management plan employed standard parameters, with treatment margins of 2.5 mm on either side of the tumour, and 2.0 mm at its posterior limit. She responded well to this treatment with a reduction in tumour size radiologically, and a subjective improvement in ocular motility. In the 7 years following her proton beam treatment serial magnetic resonance imaging (MRI) has revealed no further growth of the residual tumour mass (fig 2). She maintained a visual acuity of 6/9 in the left eye for 3 years following treatment but subsequently developed ischaemic optic neuropathy reducing her acuity to 5/60.
This patient, having already undergone extensive orbital surgery on two occasions, was reluctant to consider a further procedure. Although there is evidence to support the use of adjuvant external beam radiotherapy after conservative surgery,4 it was felt that because of the size and location of our patient’s tumour, the dose required was likely to cause significant damage to surrounding structures. A decision was therefore taken to explore proton beam therapy as a potential adjuvant treatment for our patient, particularly as our department has gained experience with its use in the management of uveal melanomas. Following discussion with our colleagues at the Douglas Cyclotron, Clatterbridge Centre for Oncology, it was decided that owing to the relatively superficial location of the tumour, proton beam therapy would be a feasible option.
High energy heavy charged particle irradiation with proton beams offers several advantages over external radiotherapy. The particles have minimal scatter and can be collimated into small beams delivering maximal ionisation as they stop. This results in the phenomenon of the Bragg peak which is “modulated” with depth to produce a precise uniform dose volume.6 As the depth of penetration can be controlled, the radiation can be targeted almost exclusively at the tumour mass with minimal irradiation of surrounding tissues.7 The radiation dose of 50 Gy equivalent was chosen empirically and based on the normal dose used for the treatment of choroidal melanomas as there is no precedent in using this treatment for orbital haemangiopericytoma.
Unfortunately, this patient developed ischaemic optic neuropathy which is a recognised complication of proton beam therapy, particularly when more than 2 mm of optic nerve is irradiated at 30 Gy equivalent.8 Because of the size and location of our patient’s tumour, there was a high risk of this complication occurring, as there would have been had external beam radiotherapy been used instead. Nevertheless, this report demonstrates that proton beam therapy can be effective in controlling recurrent orbital haemangiopericytoma and perhaps its use should therefore be considered as an adjuvant in the treatment of recurrent disease, particularly when the tumour is in a superficial location.