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Six UK studies investigating stereotactic ablative radiotherapy (SABR) are currently open. Many of these involve the treatment of oligometastatic disease at different locations in the body. Members of all the trial management groups collaborated to generate a consensus document on appropriate organ at risk dose constraints. Values from existing but older reviews were updated using data from current studies. It is hoped that this unified approach will facilitate standardised implementation of SABR across the UK and will allow meaningful toxicity comparisons between SABR studies and internationally.

An image-guidance process for using cone-beam computed tomography (CBCT) for stereotactic body radiation therapy (SBRT) of peripheral lung lesions is presented. Respiration correlated CBCT on the treatment unit and four dimensional computed tomography (4DCT) from planning are evaluated for assessing respiration-induced target motion during planning and treatment fractions. Image-guided SBRT was performed for 12 patients (13 lesions) with inoperable early stage non-small cell lung carcinoma. Kilovoltage (kV) projections were acquired over a 360 degree gantry rotation and sorted based on the pixel value of an image-based aperture located at the air-tissue interface of the diaphragm. The sorted projections were reconstructed to provide volumetric respiration correlated CBCT image datasets at different phases of the respiratory cycle. The 4D volumetric datasets were directly compared with 4DCT datasets acquired at the time of planning. For ten of 12 patients treated, the lung tumour motion, as measured by respiration correlated CBCT on the treatment unit, was consistent with the tumour motion measured by 4DCT at the time of planning. However, in two patients, maximum discrepancies observed were 6 and 10 mm in the anterior-posterior and superior-inferior directions, respectively. Respiration correlated CBCT acquired on the treatment unit allows target motion to be assessed for each treatment fraction, allows target localization based on different phases on the breathing cycle, and provides the facility for adaptive margin design in radiation therapy of lung malignancies. The current study has shown that the relative motion and position of the tumour at the time of treatment may not match that of the planning 4DCT scan. Therefore, application of breathing motion data acquired at simulation for tracking or gating radiation therapy may not be suitable for all patients - even those receiving short course treatment techniques such as SBRT.

The impact of radiotherapy on the heart has become an area of interest in recent years. Many different cardiac dose-volume constraints have been associated with cardiac toxicity and survival; however, no consistent constraint has been found. Many patients undergoing treatment for lung cancer have risk factors for cardiovascular disease or known cardiac comorbidities; however, there is little evidence on the effects of radiotherapy on the heart in these patients. We aim to provide a summary of the existing literature on cardiac toxicity of lung cancer radiotherapy, propose strategies to avoid and manage cardiac toxicity, and suggest avenues for future research.

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Risks of radiation-induced second primary cancer following prostate radiotherapy using 3D-conformal radiotherapy (3D-CRT), intensity-modulated radiotherapy (IMRT), volumetric modulated arc therapy (VMAT), flattening filter free (FFF) and stereotactic ablative radiotherapy (SABR) were evaluated. Prostate plans were created using 10 MV 3D-CRT (78 Gy in 39 fractions) and 6 MV 5-field IMRT (78 Gy in 39 fractions), VMAT (78 Gy in 39 fractions, with standard flattened and energy-matched FFF beams) and SABR (42.7 Gy in 7 fractions with standard flattened and energy-matched FFF beams). Dose-volume histograms from pelvic planning CT scans of three prostate patients, each planned using all 6 techniques, were used to calculate organ equivalent doses (OED) and excess absolute risks (EAR) of second rectal and bladder cancers, and pelvic bone and soft tissue sarcomas, using mechanistic, bell-shaped and plateau models. For organs distant to the treatment field, chamber measurements recorded in an anthropomorphic phantom were used to calculate OEDs and EARs using a linear model. Ratios of OED give relative radiation-induced second cancer risks. SABR resulted in lower second cancer risks at all sites relative to 3D-CRT. FFF resulted in lower second cancer risks in out-of-field tissues relative to equivalent flattened techniques, with increasing impact in organs at greater distances from the field. For example, FFF reduced second cancer risk by up to 20% in the stomach and up to 56% in the brain, relative to the equivalent flattened technique. Relative to 10 MV 3D-CRT, 6 MV IMRT or VMAT with flattening filter increased second cancer risks in several out-of-field organs, by up to 26% and 55%, respectively. For all techniques, EARs were consistently low. The observed large relative differences between techniques, in absolute terms, were very low, highlighting the importance of considering absolute risks alongside the corresponding relative risks, since when absolute risks are very low, large relative risks become less meaningful. A calculated relative radiation-induced second cancer risk benefit from SABR and FFF techniques was theoretically predicted, although absolute radiation-induced second cancer risks were low for all techniques, and absolute differences between techniques were small.