[en] The Peter MacCallum Cancer Centre has established a stereotactic lung radiosurgery program for the treatment of isolated lung metastases. The aim of this study was to critically assess the technical feasibility of performing stereotactic lung radiosurgery in an Australian institution. A single 26-Gy fraction of radiotherapy was delivered to patients with positron emission tomography (PET) staged solitary lung metastases. Motion management was addressed using four-dimensional computed tomographic simulation, and cone beam CT (CBCT) online soft-tissue matching. Treatments were with multiple coplanar and non-coplanar asymmetric beams. Patients were immobilised in a dedicated stereotactic body cradle. Quality assurance (QA) of treatment plans with both ion chamber and film measurements was performed accounting for patient-specific respiratory motion. Between February 2010 and February 2011, nine patients received stereotactic lung radiosurgery. One grade 1 toxicity and one grade 2 toxicity were recorded after treatment. The mean planning target volume was 22.6 cc. A median of eight beams were delivered per treatment plan (range 7–10) with a median of two non-coplanar beams (range 0–6). At treatment plan QA, the difference between planned and delivered dose was ≤1.76% in all static and dynamic ion chamber recordings. A mid-treatment CBCT was performed at a median time of 21 min, with the mean displacement discrepancy from initial set-up being 0.4 mm (range 0–2 mm). Stereotactic radiosurgery to the lung was both feasible and tolerable at our institution. Intrafractional immobilisation within 2 mm was reproducible. Excellent concordance between planned and delivered treatments was achieved in the phantom QA.

[en] Hypofractionated image guided radiotherapy of extracranial targets has become increasingly popular as a treatment modality for inoperable patients with one or more small lesions, often referred to as stereotactic ablative body radiotherapy (SABR). This report details the results of the physical quality assurance (QA) program used for the first 33 lung cancer SABR radiotherapy 3D conformal treatment plans in our centre. SABR involves one or few fractions of high radiation dose delivered in many small fields or arcs with tight margins to mobile targets often delivered through heterogeneous media with non-coplanar beams. We have conducted patient-specific QA similar to the more common intensity modulated radiotherapy QA with particular reference to motion management. Individual patient QA was performed in a Perspex phantom using point dose verification with an ionisation chamber and radiochromic film for verification of the dose distribution both with static and moving detectors to verify motion management strategies. While individual beams could vary by up to 7 %, the total dose in the target was found to be within ±2 % of the prescribed dose for all 33 plans. Film measurements showed qualitative and quantitative agreement between planned and measured isodose line shapes and dimensions. The QA process highlighted the need to account for couch transmission and demonstrated that the ITV construction was appropriate for the treatment technique used. QA is essential for complex radiotherapy deliveries such as SABR. We found individual patient QA helpful in setting up the technique and understanding potential weaknesses in SABR workflow, thus providing confidence in SABR delivery.