A strategy to reduce fraction number in peripheral lung stereotactic ablative body radiotherapy

Abstract

Hypo-fractionated lung Stereotactic Ablative Body Radiotherapy (SABR) has often been avoided when tumours are close to the chest wall. Our strategic objective was the reduction of fraction number, while maintaining target biological effective dose coverage without increasing chest wall toxicity (CWT) predictors. Twenty previously treated lung SABR patients were stratified into four cohorts according to distance from PTV to the chest wall, <1 cm, <0.5cm, overlapping up to 0.5cm and 1.0cm. For each patient, four plans were created; a chest wall optimised plan for 54Gy in 3 fractions, the clinical plan re-prescribed for 55Gy in 5, 48Gy in 3 and 45Gy in 3 fractions. For a PTV distance of 0.5-0.0cm, a reduction of the median (range) Dmax from 55.7 (57.5-54.1) Gy to 40.0 (37.1-42.0Gy) Gy was observed for the chest wall optimised plans. The median V30Gy decreased from 18.9 (9.7-25.6) cm3 to 3.1 (1.8-4.5) cm3. For a PTV overlap of up to 0.5cm, the Dmax reduced from 66.5 (64.1-70) Gy to 53.2 (50.6-55.1) Gy. The V30Gy decreased from 21.5 (16.5-29.5) cm3 to 14.9 (11.3-20.2) cm3. For the cohort with up to 1.0cm overlap, there was a reduction in Dmax values of 9.9Gy. The V30Gy for clinical plans, at 66.8 (18.7-188.8) cm3, decreased to 55.3 (15.5-149) cm3. When PTVs are within 0.5cm of chest wall, lung SABR dose heterogeneity can be used to reduce fraction number without increasing CWT predictors.