Discovery ct590 rt

The patients underwent CT (Discovery CT590 RT, GE Healthcare, Chicago, IL, USA) with 2.5 mm slice spacing, and then the image sets were transferred to a treatment planning system (Pinnacle3, version 9.8.1, Philips Medical Systems, Madison, WI, USA) for targeting and organ delineation. The patients who underwent head keloidectomy were immobilized by a U-Frame head and neck immobilization system (CIVCO Radiotherapy, Orange City, IA, USA) with the face turned to the contralateral side (Figure 1A). A Body Vac Cushion (Klarity Medical, Newark, OH, USA) was used to immobilize the whole body of patients with keloids on the torso or extremities (Figure 1B). Additionally, a 1 cm bolus was added to the surgical area to provide an adequate surface dose to the scar.

Patients were set up in the supine position and immobilized with a vacuum bag cushion system with their arms over their head. Respiratory pattern was neither mentioned nor coached, so that the patients breathed freely with no alteration. Both helical CT and 4DCT scans were made using the Discovery CT590 RT sixteen-slice scanner (GE Healthcare, UK), with a slice thickness of 2.5 mm and a diameter of field of view of 50 cm. The in-field resolution was 1.0 mm. The helical mode was used for helical CT, and the axial cine mode was used for 4DCT. To further describe 4DCT, a mounted detector with infrared ray tracked an external tracking reflector attached to the epigastric area where respiration caused the largest displacement on the surface. The breath patterns of the patients were monitored and recorded with the Real-time Position Management (RPM) Respiratory Gating System (Varian Medical Systems, USA). After scanning, a 10-phase-gated 4DCT image from 0% to 90% distributed over the whole respiratory cycle was constructed from the raw 4DCT data using the Advantage 4D software (GE Healthcare, UK), in which 0% (phase 0 CT) and 50% (phase 50 CT) indicated end-inspiration and end-expiration, respectively. The maximum phase error of 4DCT which is the maximal variability of breath patterns at the specific phase over all breathing cycles is listed in Table 1.

Computed tomography (CT) simulation with a 2.5 mm slice thickness (Discovery CT590 RT, GE Healthcare, Chicago, IL, USA) was performed for RT treatment planning to delineate the target volume and adjacent OARs. The patients were placed in the supine position and allowed to breathe freely during CT simulation. The radiation volumes included the clinical tumor volume (CTV), including the whole breast or chest wall (CW), and RNI with supraclavicular and infraclavicular regions, any part of the axillary bed at risk, and optional IMN. The planning target volume (PTV) was defined as the CTV plus a 5–8 mm margin for setup error. The RT prescription was a conventional dose of 45–50.4 Gy in 25–28 fractions, or a hypofractionated dose of 40–42.5 Gy in 15–16 fractions with a daily fraction to the breast or chest wall and RNI. An additional 10 to 16 Gy boost dose to the tumor bed or surgical scar was allowed. If there were grossly involved or enlarged unoperated LNs, an additional RT boost could be delivered. The equivalent dose in 2 Gy fractions (EQD2) was evaluated with the α/β ratio of 4 Gy for breast cancer.