The Use of Stereotactic Body Radiotherapy (SBRT) for Treatment of Early Stage Lung Cancers Carmel McDerby Clatterbridge Centre for Oncology, Merseyside,UK On behalf of the SBRT team Sheffield Hallam Radiotherapy in Practice Conference, October 2010 1

Background A stereotactic lung radiotherapy treatment technique (SBRT) has been introduced at Clatterbridge Centre for Oncology (CCO). The advantage of this technique is that patients with early stage lung cancers, who are unfit for radical surgery, appear to have better local control and disease specific survival than conventional radiotherapy[1-3]. The serious toxicity (grade 3 or above) reported in literature is below 5% [4]. Due to the hypo-fractionated nature of the technique, treatment accuracy is essential. At CCO, this is verified prior to each treatment using the Cone Beam CT (CBCT) facility of the Varian On-board Imager (OBI), providing kV volumetric imaging data which can be compared to planning CT scans. Following the establishment of the UK Stereotactic Body Radiotherapy Consortium in 2007, using standard immobilisation equipment and image guidance.

Immobilisation A frameless stereotactic technique is used. Patients are immobilised using a Q-fix breast board with the addition of an in-house individualised chin strap to prevent head movement, bum stop and knee roll (see images below). The use of a diaphragm control technique is considered on an individual patient basis and could be utilised for patients with very mobile tumours. Patient in treatment position showing chin strap, diaphragm control and RPM gating box Q-fix board

Method 12 patients have been treated using this technique so far All patients are CT planned using a 4D technique to enable the PTV volume to be accurately defined using Maximum Intensity Projection (MIP) reconstructed CT images. The MIP shows the tumour-motion-encompassing target volume. For each patient, the Varian Real-time Position Management (RPM) gating system is used to monitor the breathing rate and amplitude during the planning CT and at each treatment. A gating window is set on the regular breathing levels which ensures that the gating system switches off the beam should the patient take an unusually deep breath.

Varian RPM System

Treatment Process Experienced radiographers trained in lung CBCT registration SBRT physicist Clinical oncologist The fractionation schedule is either 5 x 11 Gy or 3 x 18 Gy, depending on tumour location. Patients are set up for treatment as at the planning stage, the RPM gating box is positioned and the breathing amplitude verified. CBCT scans are acquired before and after treatment .This multi-disciplinary team are present at each fraction 5 x 11Gy if by ribs or bracial plexus

Treatment Process Figure 1 Figure 2 Figure 3 CT image registration is performed using 3 different registration tools using a 3 step process. Couch corrections are performed if the PTV registration shows isocentre positioning error of 2mm or above. This is confirmed by the oncologist and isocentre correction performed prior to treatment. The CBCT scan is repeated directly following treatment to establish confidence in the immobilisation method used for this technique.

CBCT Bone Match – Step 1 manual match /bone windows June 2010 Slide 8

CBCT PTV Match – Step 2 manual match, lung windows

CBCT PTV Match – Step 3 auto match,PTV,1cm margin / lung windows

Results The graph shows the absolute displacement (averaged over all #) at the pre- and post treatment CBCTs for all three directions. The shaded area represents the positional action level of 2 mm. Any displacement greater than this value was corrected for prior to treatment. The post treatment scan shows any residual positional displacement combined with intra-fraction movement. For almost all patients the positional error during (and after) treatment was within tolerance.

Set-up Accuracy Results The post-trt systematic and random set-up uncertainties show the residual displacement error together with intra-# motion Gives confidence in immobilisation / treatment accuracy

Results In-room timings showed this SBRT technique is an efficient use of linac time. It also gives the additional advantage of a reduced number of hospital visits for the patient. 13

Summary Stereotactic lung radiotherapy can be implemented safely and efficiently by using cone beam CT verification methods. A 2 mm isocentre correction strategy is appropriate if the Varian On-Board Imaging system and RPM monitoring technique is utilised. The image guidance provided by the OBI equipment provides confidence in the treatment technique using a frameless immobilisation approach. The implementation of this technique requires the commitment of the multi-disciplinary team and patient compliance is essential.

Acknowledgements The SBRT Team at CCO

References 1. F.J. Lagerwaard, C.J. Haasbeek, E.F. Smit, et al., Outcomes of risk-adapted fractionated stereotactic radiotherapy for stage I non-small-cell lung cancer. IJROBP, 2008. 70(3): p. 685-92. 2. Y. Nagata, K. Takayama, Y. Matsuo, et al., Clinical outcomes of a phase I/II study of 48 Gy of stereotactic body radiotherapy in 4 fractions for primary lung cancer using a stereotactic body frame. IJROBP, 2005. 63(5): p. 1427. 3. R. Timmerman, L. Papiez, R. McGarry, et al., Extracranial Stereotactic Radioablation: Results of a Phase I Study in Medically Inoperable Stage I Non-small Cell Lung Cancer. Chest, 2003. 124(5): p. 1946. 4. C.J. Haasbeek, S. Senan, E.F. Smit, et al., Critical review of nonsurgical treatment options for stage I non-small cell lung cancer. Oncologist, 2008. 13(3): p. 309-19.