Brachytherapy is not always possible or suitable, due to medical or technical reasons or patient refusal. In these cases, an external beam boost using IMRT (intensity modulated radiotherapy) or VMAT (volumetric modulated arc therapy) is usually considered. However, the typical dose of 16-20 Gy in 8-11# is not usually curative. There is also evidence of lower survival in patients who are treated with an external beam boost¹³.

MR-guided SABR boost provides an alternative treatment option for patients where brachytherapy is not feasible. The MR Linac offers improved soft tissue visualisation, enabling protection for organs at risk (OAR, notably bladder, rectum and bowel) as well as improved targeting, leading to fewer side effects and improved dose to the target.

At GenesisCare, providing the option of a SABR boost delivered on the MR Linac means we can now offer a high-precision, non-invasive treatment option in 5# over five alternate days to patients with cervical cancer unable to receive brachytherapy. This could lead to improved target coverage and therefore improved survival outcomes.

Our referrals process is designed to be straightforward and rapid.

Patients deemed suitable for MR-guided SABR will be referred from a Gynae MDT to one of our MRIdian-credentialled clinical oncologists. All cases will be discussed in the GenesisCare SABR MDT before a decision is made.

The minimum data set required for referrals is:

• Cervical radiotherapy consent form
• MR-Linac supplementary consent form
• Booking form (electronic/paper)
• Referral letter (referring the patient to the clinical oncologist
• Histology report
• Staging pelvis MRI, CT, CAP and PET-CT
• Week 5 diagnostic MRI (to assess response prior to SABR boost)
• GenesisCare MRIdian assessment pro forma

This treatment is available to patients with private medical insurance. Uninsured UK residents can access this treatment through our Expanded Access Pathway

Please note, on occasions some insurers may ask for a medical report.

• Locally advanced (FIGO stage 1B3-IVA) or medically inoperable (FIGO stage 1) cervical cancer
• Patient is undergoing radical chemoradiotherapy or radical radiotherapy and unable to receive a brachytherapy boost
• Reviewed through NHS gynae MDT (outcome ‘radiotherapy’ is acceptable)
• Patient is aware that HDR brachytherapy is the gold-standard of treatment and that MRIdian MRI-guided SABR boost is being offered as a suitable alternative as HDR brachytherapy is not possible
• Patient fit for out-patient treatment and able to travel daily to the department for treatment
• Clinical Target Volume (CTV) <150cc (typical range 30-100cc)
• Larger CTV can be considered but should be reviewed by the clinician and planning team as early as possible
• Referral should be prior to completion of the initial course of radiotherapy. However, understandably cases may be referred in week 6 after a failed brachytherapy attempt. For these referrals it may not be possible to achieve the full treatment course within the 56-day target. The referring clinician will be updated and appropriate course of action discussed

• Patient has pacemaker, ICEDs defibrillator or neuro-stimulator
• Intra-orbital foreign bodies and metallic foreign bodies which may be affected by the MR Linac magnetic field
• Aneurysm clips
• Severe claustrophobia
• Lesion/cervix not visible on MRI
• Tumour involvement of bladder or bowel at week 5 MRI is not an absolute contra-indication but clear counselling of the patient is necessary in this circumstance

As chemoradiotherapy followed by brachytherapy boost remains standard of care for locally advanced cervical cancer, studies of alternatives to brachytherapy are limited. However, studies have shown external radiotherapy to be a reasonable option when brachytherapy is not an option, with more recent research supporting the use of SABR as an alternative to brachytherapy.

MR-guided SABR as an alternative to brachytherapy in cervical cancer is a cutting-edge treatment option with limited published data available in the literature. The rationale for using MRI guidance to deliver SABR is clear though and has been demonstrated in other areas of oncology. For example, the Phase III MIRAGE trial showed an advantage to patients with prostate cancer treated with MR-guided SABR compared with those treated with CT-guided SABR. MR-guided SABR is increasingly being used to treat cancers elsewhere, including in the breast, abdomen and lung.

Evidence for dose recommendation as a boost for cervix cancer is supported by the EMBRACE-1 study, where patients received external beam radiotherapy, concurrent chemotherapy and MRI-based image-guided adaptive brachytherapy (MR-IGABT). Analysis of data from 1,318 patients supported the recommendation of a dose of 85Gy to 90% of the high-risk clinical target volume (CTV) which led to a 3-year local control of 95% for squamous cell and 86% for adeno/adenosquamous carcinoma histology.

Patient selection is an important consideration. In general, MR-guided SABR boost as an alternative to brachytherapy should only be considered for patients with locally advanced cervical cancer who are unable to have brachytherapy boost. Studies using linac based SABR with high dose per fraction have raised toxicity concerns as well as lower-than-expected efficacy outcomes.

A series of trial plans have been performed at GenesisCare using a 5# regimen using the MRIdian MR-Linac and have been able to achieve mean dose of90% of the CTV of 92.3Gy, with a PTV D98 of 69.5Gy and PTVD90 of 78.7Gy whilst remaining within EMBRACE2 guidelines for organ at risk doses.

At GenesisCare, MR-guided SABR is delivered by our expert team of clinical oncologists, therapy radiographers, dosimetrists and physicists, supporting by our experienced nursing team.

All referrals are reviewed by the GenesisCare SABR Advisory Team (SAT), an expert multi-disciplinary team of doctors specialising in the relevant tumour areas.

Since introducing the MRIdian MR Linac in 2019, we have provided MR-guided SABR to more than 2000 patients across a range of cancers. Together with our academic collaboration with the University of Oxford, we continue to support research and contribute to the growing body of evidence for this innovative method of treatment.

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