Clinical implementation of kVCT-guided tomotherapy with ClearRT.

A helical fan-beam kilovoltage computed tomography (kVCT) was recently introduced into Tomotherapy units. This study aims to share the initial experience of kVCT in clinical workflow, compare its performance with that of the existing megavoltage computed tomography (MVCT), and explore its potential in adaptive planning. We retrospectively enrolled 23 patients who underwent both MVCT and kVCT scans. The clinical performance data regarding image acquisition time, nominal dose length product (DLP), registration time and registration corrections were extracted and compared. Image quality was scored by six experienced radiation therapists and quantified based on phantom measurements. CT number stability and the implementation of adaptive radiotherapy were dosimetrically evaluated by performing the dose recalculation on kVCT. Compared to MVCT, kVCT significantly reduced DLP (except the highest kVp protocol), image acquisition and registration time. KVCT obtained higher scores than MVCT on all criteria except artifacts. Phantom measurements also revealed a better image performance characterization of kVCT except for image uniformity. The CT number variation could lead to a dose difference of 0.5% for D95% of target and Dmean of organ-at-risk. For the treatment planning with kVCT, a systematic dose difference (> 1%) in PTV dose metrics was observed at regions with large longitudinal density discontinuities compared to the reference plans. The new kVCT imaging provides enhanced soft-tissue visualization. The improved efficiency with kVCT-guided treatment will allow more patients to be treated each day. In most cases, the dose calculation accuracy of kVCT images is acceptable except for regions with severe artifacts.

MRI-guided adaptive brachytherapy for locally advanced cervix cancer: Treatment outcomes from a single institution in Hong Kong.

BACKGROUND: Paradigm has shifted from 2D to image-guided adaptive brachytherapy (IGABT) for locally advanced cervix cancer (LACC). Increasing reports from pioneering institutions and large retrospective multicenter series have demonstrated improvements in outcome and reduction in toxicity with IGABT. However, there is scarcity of data on magnetic resonance (MR)-IGABT in Chinese patients. PURPOSE: To evaluate the clinical outcome of MR-IGABT for LACC in a single institution in Hong Kong. MATERIAL AND METHODS: Patients with FIGO stage IB-IVA LACC treated with definitive external beam radiotherapy +/- concurrent cisplatin followed by MR-IGABT from January 2015 to January 2018 were included. Brachytherapy planning and dose reporting followed the GEC-ESTRO recommendations. Dosimetric and clinical outcomes including local control (LC), pelvic control (PC), cancer-specific survival, overall survival (OS), and toxicity were analyzed. RESULTS: Forty-two consecutive patients were included. 71% were FIGO stage IIB or above; 52% had pelvic node involvement. Median high-risk clinical target volume (HRCTV) was 34.7 cm3 (12.3-155.1 cm3). Median dose to HRCTV D90 was 88.5 Gy (63.4-113.4 Gy) (EQD210). Median doses to the D2cc of bladder, rectum, sigmoid, and small bowel were 83.1 Gy, 67.5 Gy, 69.0 Gy, and 68.9 Gy (EQD23), respectively. Median followup was 20.3 months (4.0-35.1 months). 24-month actuarial LC, PC, cancer-specific survival, and OS were 90%, 84%, 90%, and 90%, respectively. Stratification by clinical variables showed that FIGO stage had significant impact on LC and dose to HRCTV on both LC and PC. Treatment was well tolerated without any severe late toxicity. CONCLUSIONS: Intermediate-term results from systematic MR-IGABT for LACC demonstrate very promising outcomes with minimal toxicity. This fills the gap in evidence for MR-IGABT in Chinese patients.