Risk of extracranial secondary cancer after radiosurgery: comparison of Gamma Knife Perfexion, Cyberknife and Novalis

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1 Risk of extracranial secondary cancer after radiosurgery: comparison of Gamma Knife Perfexion, Cyberknife and Novalis Dr Alison Cameron, Clinical Oncologist, Bristol, UK Ian Paddick, Consultant Physicist, Medical Physics Limited, UK

2 Conflict of Interest Elekta have paid prior meeting attendances and consultation

3 Background: Radiation Causes Cancer Cancer risk in 680,000 people exposed to computed tomography scans in childhood or adolescence: data linkage study of 11 million Australians Matthews et al BMJ year with FU to ,674 had cancer diagnosed 6.2% (680,211) had a CT scan (excluding those within 1 year cancer diagnosis) Cancer Incidence 24% greater in CT scan group Risk increased by 16% for each additional CT scan Absolute excess was 9.38 per 100,000 as at 2007 (likely to increase with longer FU) 608 excess cancers seen

4 Background: Radiation Causes Cancer Risk of cancer from occupational exposure to ionising radiation (International Nuclear Workers Study) BMJ :h5359 Richardson et al 308,297 nuclear industry workers UK, USA & France, of whom 66,632 have died (17,957 due to solid tumours) Exposure to ionising radiation linked to death registries 8.2 million person years of follow up Linear increase in risk of death from solid tumour per Gy, including from 0-100mGy range 48% increase in death from solid tumour per Gy

5 Lifetime Risk of Secondary Tumour after a single CT scan per million RED BLUE Wall et al 2011 Health Protection Agency 0-9 yr- 1.5 extra cancer per yr 1.1 extra cancer per yr 0.5 extra cancer per yr 0.08 extra cancer per 1000

6 Dose to the body from intracranial SRS Cyberknife = yellow Linac = brown Perfexion Gamma Knife= blue Lindquist and Paddick Neurosurgery suppl

7 Methods Dose to body has been measured and published in the literature for different SRS platforms. Dose to mid-sternum and mid-abdomen for average adult size from SRS to mid point in brain was established for and for Gamma Knife Perfexion, Cyberknife, and Novalis Dose received was estimated as equivalent number of CT thorax and CT abdomen-pelvis (accepting this is oversimplification) UK Health Protection Agency published lifetime risk of cancer related to single CT scan exposure at all age cohorts Estimated lifetime risk of cancer secondary to SRS from combining the CT equivalent and known risks from CT scans for 0-39 year patient

8 Potential lifetime increased risk of body cancer per million post SRS on Gamma Knife, Novalis and Cyberknife GK GK Novalis Novalis CyK CyK

9 Potential excess risk body cancer per 1000 patients treated with Novalis v Gamma Knife 0-9yr 10-19yr 20-29yr 30-39yr

10 Potential excess risk body cancer per 1000 patients treated with Cyberknife v Gamma Knife 0-9yr 10-19yr 20-29yr 30-39yr

11 Potential excess risk body cancer per 1000 patients treated with Cyberknife v Novalis 0-9yr 10-19yr 20-29yr 30-39yr

12 Relative Lifetime Risk of Body Cancer Post SRS Gamma Knife Novalis Cyberknife 0-9Yr 0 7x 35x 30-39Yr 0 7x 34x 0-9Yr 0 8x 46x 30-39Yr 0 8x 43x

13 Therapeutic Reference Level CT scanners have a diagnostic reference level allowing easy comparison between machines and resulted in reduction of CT doses Therapeutic Reference Level enable comparison between different radiosurgery platforms Suggest aim 0.01% prescription isodose at 60cm Protect patients from needless secondary cancer later in life

14 Conclusion Radiation causes secondary cancer Small body doses from intracranial cancer result in small increase lifetime risk of cancer, particularly important children and young adults Different platforms result in different body dose and therefore different risk of cancer Recommend Therapeutic Reference Level (TRL): 0.01% at 60cm Absolute figures theoretical, but trend is clear for 0-39year old: Novalis: 7-8x increased relative risk cancer cf Perfexion Gamma Knife Cyberknife: 34-46x increased relative risk cancer cf Perfexion Gamma Knife