Dosimetric and radiobiological comparison of simultaneous integrated boost and sequential boost of locally advanced...

Introduction Some patients with locally advanced cervical cancer (LACC) cannot undergo brachytherapy (BT). Possible treatment includes two-stage external beam radiotherapy (sequential boost - SEQ) or single-stage external beam radiotherapy (simultaneous integrated boost - SIB). The goal of this paper was to carry out dosimetric and radiobiological comparison of these techniques with respect to tumour and organs-at-risk (OARs) irradiation. Methods The anatomic data of six patients with LACC were used for this study. The single-stage SIB-VMAT (25, 27 or 30 fractions) and double-stage SEQ-VMAT (25 + 6 fractions) plans were developed to deliver EQD₂=50 Gy to the pelvic region and EQD₂=90 Gy to the tumour. The developed plans were compared with respect to an EQD₂ dose delivered to a tumour and to the OARs, expected tumour control probability and normal tissue complications probability. Results The developed SIB-VMAT and SEQ-VMAT plans had physical coverage of the CTV tumours with more than 95% of the prescribed dose delivered to more than 95% of the volume. The irradiation of the tumour for both SIB-VMAT and SEQ-VMAT has comparable EQD₂ values close to 87-88 Gy. SIB-VMAT treatment plans provided lower levels of irradiation of OARs than SEQ-VMAT plans. The optimal number of fractions for SIB-VMAT was 27. Conclusion SIB-VMAT is a better treatment option for patients with LACC that are not eligible for BT. Results show that both SIB-VMAT and SEQ-VMAT allowed good coverage of the tumour and high-quality dose delivery. SIB-VMAT allowed minimising irradiation of OARs and shortening the overall treatment time by a week.