Performance Evaluation of Calypso^®4D Localization and Kilovoltage Image Guidance Systems for Interfraction Motion Management of Prostate Patients

Abstract

Prostate cancer represents a model site for advances in understanding inter- and intrafraction motion for radiotherapy. In this study, we examined the correlation of the electromagnetic transponder system/Calypso 4D Localization System with conventional on-board imaging (OBI) using kilovoltage imaging. Initially using a quality assurance (QA) phantom and subsequently using data of seven patients, the vector distances between Calypso- and OBI-recorded shifts were compared using the t-test. For the 30 phantom measurements, the average differences between the measured Calypso offset and the calculated OBI shift were 0.4 ± 0.4, 0.2 ± 0.3, and 0.4 ± 0.3 mm in the lateral, longitudinal, and vertical directions, respectively (p = 0.73, p = 0.91, and p = 0.99, respectively), and the average difference vector for all sessions was 0.8 ± 0.4 mm. For the 259 patient measurements, the average differences between the measured Calypso offset and the calculated OBI shift were 0.7 ± 0.5, 1.1 ± 0.9, and 1.2 ± 0.9 mm in the lateral, longitudinal, and vertical directions, respectively (p = 0.45, p = 0.28, and p = 0.56, respectively), and the average difference vector for all sessions was 2.1 ± 1.0 mm. Our results demonstrated good correlation between Calypso and OBI. While other studies have explored the issue of Calypso/OBI correlation, our analysis is unique in our use of phantom validation and in our performing the patient analysis on an initial population prior to routine setup using Calypso without OBI. Implications for Calypso's role as a QA tool are discussed.

In Vivo Validation of Elekta's Clarity Autoscan for Ultrasound-based Intrafraction Motion Estimation of the Prostate During Radiation Therapy

“…Willoughby et al (16) reported mean and maximum 3D errors of 1.5 mm (SD, 1.1 mm) and 3.8 mm, respectively, over 44 fractions in 11 patients. Ogunleye et al (33) found mean differences of 1.2 mm (SD, 0.9 mm), 1.1 mm (SD, 0.9 mm), and 0.7 mm (SD, 0.5 mm) in the anterior-posterior, superior-inferior, and left-right directions, respectively. Foster et al (34) found mean differences of –0.81 mm (95% LOAs, −2.83 to 2.67 mm), –0.41 mm (95% LOAs, −3.41 to 2.59 mm), and 0.06 mm (95% LOAs, −1.97 to 2.09 mm) for the anterior-posterior, superior-inferior, and left-right directions, respectively, over 250 fractions.…”

“…The mean and maximum 3D errors were 1.7 mm (SD, 1.0 mm) and 4.6 mm, respectively (18) . Only Calypso interfraction motion estimation validations have been reported 16 , 33 . Willoughby et al (16) reported mean and maximum 3D errors of 1.5 mm (SD, 1.1 mm) and 3.8 mm, respectively, over 44 fractions in 11 patients.…”

Intrafraction displacement of prone versus supine prostate positioning monitored by real‐time electromagnetic tracking

“…The accuracy of the Beacons has been verified to millimeter and even submillimeter accuracy both in phantoms and in vivo when compared to X‐ray and CT imaging. ( 13 , 14 ) …”

Electromagnetic Transponders Indicate Prostate Size Increase Followed by Decrease During the Course of External Beam Radiation Therapy

“…Each Beacon in a set of three has a unique frequency response; therefore, each is color coded with its intended position. The accuracy of the Beacons has been verified to millimeter and even submillimeter accuracy both in phantoms and in vivo when compared with x-ray and computed tomography (CT) imaging (12,13).…”