Introduction: The role and use of stereotactic radiotherapy (SABR) is evolving rapidly. A key article by
Hanna et al. (2017) provides an excellent overview of current evidence and suggestion of sensible dose
constraints. Given the topical nature of this discussion we present a short retrospective analysis of treating
multiple lung SABR patients at our centre.
Method: We retrospectively analysed toxicity, both early (within 3 months of SABR) and late, and normal
tissue dose constraints on all patients who had multiple lung lesions treated with SABR (using volumetric
modulated arc therapy (VMAT) technique) at our tertiary centre over a 25-month period from April 2016
until May 2018.
Results: We have treated 78 lung lesions in 37 patients with a combination of synchronous lung cancer
primaries and lung metastases diagnoses. Median follow-up was 9 months. Almost all patients received
treatment on the same day for multiple lesions. We report no grade 3 toxicities in any patient nor any
unexpected side effects. 5 patients (14.7%) developed grade 2 pneumonitis. In all 5 patients, lung V12.5
was >20% (range 20.8-32.2%), yet only 1 patient exceeded acceptable lung V20 constraints. Regarding
long-term toxicity, 66.6% of patients reported no treatment-related effects. Of 9 patients with long-term
toxicity, 8 exceeded V12.5 constraint of <15%, indeed of these 5 were >20%. Lung V20 levels were
acceptable for the majority of these. Local control of treated lesions at median follow-up in all comers was
86.2%.
Discussion: Our findings show that multiple lung SABR is tolerable, safe with minimal long-term toxicity
and acceptable early toxicity. Defining normal lung V12.5 of <15% (optimal) and <20% (acceptable) will
significantly reduce the risk of pneumonitis and longer-term toxicity, proving itself more predictive than
lung V20 levels for toxicity. Additionally, treating multiple lesions concurrently appears to bare no extra
risk to patients.
Conversion of computational human phantoms into DICOM-RT for normal tissue dose assessment in radiotherapy patients
