Medicina Nuclear e Radioterapia

Comparison of Geometrical Uncertainties in Breast Radiation Therapy with Different Immobilization Methods

Abstract

Kanan Jassal, Bisht S, Kataria T, Sachdev K, Choughle A and Supe S

To compare the set-up uncertainties in breast radiation therapy using two different immobilization methods: vacuum cushion (VC) and standard breast board (BB). The data set comprises of 26 breast cases were divided into two groups based on the type of immobilization used for their radiotherapy treatment, either intensity-modulated radiotherapy (IMRT) or volumetric arc modulated radiotherapy (VMAT). The vacuum cushion group consisted of 14 patients with 143 exposures and the breast board group consisted of 12 patients with 120 exposures. Set-up errors in mediolateral (ML), craniocaudal (CC) and anterioposterior (AP) directions were determined using grey scale matching between the baseline reference and online acquired images by cone beam computed tomography (CBCT) scan. Systematic error (Σ), random error (σ) and mean displacement vector (M) were calculated for both the groups. For Vacuum Cushion group, maximum error observed was 2.75 mm, mean displacement vector was 1.52 mm and mean value of set-up error in ML, CC and AP direction was -0.30 mm, -0.40 mm and 1.60 mm respectively. For Breast Board group, maximum error recorded was 3.87 mm, mean displacement vector was 1.72 mm and mean value of set-up error in ML, CC and AP direction was 0.80 mm, 1.70 mm and 1.50 mm respectively. Setup errors evaluated from the two immobilization methods did not differ significantly (p>0.05). Thus, introduction of the vacuum cushion (VC) into routine breast radiation therapy was seen to be as efficient as BB setup.