An observational study of post-operative Volumetric Modulated Arc Radiotherapy (VMAT) of breast cancer by immobilizing patients on All-in-one (AIOTM) solution Breast and Lung Board without usingthermoplastic mask: Risk of collusion of gantry with couch exists if acquisition of Cone-beam Computed Tomography (CBCT)is attempted for set-up verification.

Abstract

Background: Automatic Cone-beam computed tomography (CBCT) based image matching for set-up verification is recommended as compared to 2-D match for post-operative local / loco-regional radiotherapy of breast cancer patients by Volumetric Modulated Arc Therapy (VMAT) technique. However, in supine position, off-midline peripheral body Clinical Target Volume (CTV) of unilateral breast cancer patients immobilized on Breast and Lung board of All-in-One (AIO) positioning systemmay necessitate augmented movement of couch in ‘x’ and ‘z’ axis thereby raising the risk of collusion of x-ray sources / detectors system with couch. Methods and Materials: VMAT was planned by a pair of partial arc for whole target volume for seven consecutive post-operative breast cancer patients (five post-mastectomy and two post-breast conservation patients). Tattoo based set-up by shift of treatment table in x-, y- and z-axis as determined by Treatment Planning System followed by X-rays with planar image acquisition and online 2-D imaging matching was performed for set-up verification. In-room 360°rotation of x-ray source and detector system of linear accelerator (linac) was performed before x-ray planar image acquisition. Results: Completion of 360°rotation in-room of x-ray source and detector system of linacaround the machine iso-centre was not possible in six out of seven patients due to possibility of collusion of gantry with contralateral side of the couch. Conclusion: Performing CBCT for generating 3D images for computed tomography (CT) reconstruction may not be practical for patient set-up verification of post-operative radiotherapy of unilateral breast cancer patients positioned supine on breast and lung board.