Molecular radiobiology
Enhanced intrinsic radiosensitivity after treatment with stereotactic radiosurgery for an acoustic neuroma

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Abstract

Enhanced radiosensitivity is an uncommon phenomenon attributable to deficient DNA repair after radiotherapy which can be assessed with the γ-H2AX assay. Reports of radiosensitivity after stereotactic radiosurgery (SRS) are uncommon. We describe a case where the clinical, radiological and laboratory findings suggest enhanced radiosensitivity after SRS for an acoustic neuroma.

Section snippets

SRS

The RS patient was treated on a Varian 6/100 linear accelerator (Varian Medical Systems, Palo Alto, CA, USA) following the RAH SRS technique [10] and BrainLAB (Munich, Germany) software using a single isocenter with six non-coplanar 6 MV photon arcs each with 29.5 mm diameter circular collimators at the isocenter. A limited amount of target volume shaping was achieved by altering position, weight or arc length for some beams. The tumour marginal dose (80% isodose) was 12 Gy.

γ-H2AX assay

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Clinical symptoms of NTT

RS patient was treated in May 2009 with SRS for a right-sided AN measuring 27 × 19 × 18 mm (Fig. 1A). Fig. 1B shows the CT treatment plan with a prescribed dose to the tumour margin of 12 Gy. Eight months later she developed new right sided facial numbness and tingling (5th cranial nerve-CNV). An MRI (Fig. 1C) showed reduction in tumour size to 20 × 16 × 14 mm (white arrow head) with an adjacent area of enhancement – reported as being consistent with radiation toxicity – at the right lateral

Discussion

Radiosensitivity is an inherent characteristic associated with an increased effect of IR on cells, tissues and organisms. The combination of clinical, radiological and laboratory findings presented here provide compelling evidence that the RS patient has increased radiosensitivity. To our knowledge this is the first report of such a finding in a patient undergoing SRS for an AN.

SRS is safe for ANs less than 3 cm in maximum diameter. Tumour control rates (defined as no need for further

Summary

This case describes a patient where the clinical and radiological responses to stereotactic radiosurgery treatment for an acoustic neuroma are highly suggestive of increased intrinsic radiosensitivity. Since no validated test for radiosensitivity exists we explored the novel application of the γ-H2AX assay to assess radiosensitivity. The results clearly demonstrate that the patient has defects in DNA repair mechanisms, consistent with current concepts of the mechanism of intrinsic

Conflict of interest statement

No actual or potential conflicts of interest.

Acknowledgements

The project was partly supported by the Intramural Program of the National Cancer Institute, National Institute of Health, USA. It was presented as a poster at the 62nd Annual Scientific Meeting of the Royal Australian and New Zealand College of Radiologists (RANZCR) in October 2011, Melbourne, Australia.

We are grateful to Dr. Tony Cambareri, Institute of Medical and Veterinary Science (SA Pathology), Adelaide for organising a laboratory facility in Adelaide for our study, to Dr. Christophe

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    1

    Present address: Princess Alexandra Hospital, Brisbane, Queensland, Australia.

    2

    These authors contributed equally to this work.

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