A comparison of the target volume and dosimetric variance between supine and prone positions for external-beam partial breast irradiation after breast-conserving surgery

Abstract

Objective To investigate the difference of target volumes and dosimetric parameters between supine and prone positions for external-beam partial breast irradiation (EB-PBI) after breast-conserving surgery (BCS). Methods Thirty breast cancer patients with T1N0M0 stage who underwent three-dimensional conformal radiation therapy (3D-CRT) EB-PBI after BCS were enrolled from July 2016 to April 2017. Supine and prone scan sets were acquired during free breathing for all patients. Target volumes and organs at risk (OARs) including heart, ipsilateral lung and bilateral breast were contoured by the same radiation oncologist. The tumor bed (TB) was determined based on surgical clips. The clinical target volume (CTV) consisted of the TB plus 1.0 cm margin and the planning target volume (PTV) was CTV plus 0.5 cm. Dosimetric parameters for target volumes and OARs were compared between supine and prone positions. Results The median volumes of the TB, the CTV and the PTV in supine were 14.40 cm3, 57.35 cm3, 108.85 cm3 and 14.10 cm3, 62.60 cm3, 113.70 cm3 for prone positions, respectively. The CTV and PTV in prone position were significantly greater than those in supine position, respectively (Z=-3.01, -2.87, P 0.05). The median homogeneity indexs (HI) in supine position was less than those in prone position (Z=-3.137, P 0.05). Conclusions It was feasible to carry out 3D-CRT EB-PBI in prone position in free breathing for Chinese breast cancer patient, with primary advantages of better CI and the significantly lower radiation dose to the ipsilateral lung. Key words: Post breast-conserving surgery; External-beam irradiation; Position; Target volume; Dose