A randomised trial of Supine versus Prone breast radiotherapy (SuPr study): Comparing set-up errors and respiratory motion

Abstract: Purpose: To test a prone position against the international-standard supine position in women undergoing whole-breast-radiotherapy (WBRT) after wide-local-excision (WLE) of early breast cancer (BC) in terms of feasibility, set-up errors, and respiratory motion. Methods: Following WLE of BC with insertion of tumour-bed clips, patients underwent 4D-CT for WBRT-planning in supine and prone positions (the latter using an in-house-designed platform). Patients were randomised to undergo WBRT fractions 1–7 in one position, switching to the alternate position for fractions 8–15 (40Gy/15-fractions total). Cone-beam CT-images (CBCT) were acquired prior to fractions 1, 4, 7, 8, 11 and 14. CBCT data were matched to planning-CT data using (i) chest-wall and (ii) clips. Systematic and random errors were calculated. Maximal displacement of chest-wall and clips with respiration was measured on 4D-CT. Clinical- to planning-target-volume (CTV–PTV) margins were calculated. Patient-comfort-scores and treatment-times were evaluated. Results: Twenty-five patients were randomized. 192/192 (100%) planned supine fractions and 173/192 (90%) prone fractions were completed. 3D population systematic errors were 1.3–1.9mm (supine) and 3.1–4.3mm (prone) (p =0.02) and random errors 2.6–3.2mm (supine) and 3.8–5.4mm (prone) (p =0.02). Prone positioning reduced chest-wall and clip motion (0.5±0.2mm (prone) versus 2.7±0.5mm (supine) (p <0.001)) with respiration. Calculated CTV–PTV margins were greater for prone (12–16mm) than for supine treatment (10mm). Patient-comfort-scores and treatment times were comparable (p =0.06). Conclusions: Set-up errors were greater using our prone technique than for our standard supine technique, resulting in the need for larger CTV–PTV margins in the prone position. Further work is required to optimize the prone treatment-platform and technique before it can become a standard treatment option at our institution. [Copyright &y& Elsevier]