Evaluation of interfraction patient setup errors for image-guided prostate and head-and-neck radiotherapy using kilovoltage cone beam and megavoltage fan beam computed tomography

Abstract

Purpose: To analyse interfraction setup using two different image guidance modalities for prostate and head-and-neck (H&N) cancer treatment.Materials and methods: Seventy-two prostate and 60 H&N cancer patients, imaged with kilovoltage cone beam computed tomography (KVCBCT) or megavoltage fan beam computed tomography (MVFBCT), were studied retrospectively. The daily displacements in mediolateral (ML), craniocaudal (CC) and anteroposterior (AP) dimensions were investigated. The setup errors were calculated to determine the clinical target volume to planning target volume (CTV-to-PTV) margins.Results: Based on 1,606 KVCBCT and 2,054 MVFBCT scans, average interfraction shifts in ML, CC and AP direction for H&N cases were 0?5 ± 1?5, 20?3 ± 2?0, 0?3 ± 1?7 mm using KVCBCT, 0?2 ± 1?9, 20?2 ± 2?4 and 0?0 ± 1?7 mm using MVFBCT. For prostate cases, average interfraction displacements were 20?3 ± 3?9, 0?2 ± 2?4, 0?4 ± 3?8 mm for MVFBCT and 20?2 ± 2?7, 20?6 ± 2?9, 20?5 ± 3?4 mm for KVCBCT. The calculated CTV-to-PTV margins, if determined by image-guided radiotherapy (IGRT) data, were 5?6 mm (H&N) and 7?8 mm (prostate) for MVFBCT, compared with 4?8 mm and 7?2 mm for KVCBCT. We observed no statistically significant difference in daily repositioning using KVCBCT and MVFBCT in early, middle and late stages of the treatment course. Conclusion:In the absence of IGRT, the CTV-to-PTV margin determined using IGRT data, may be varied for different imaging modalities for prostate and H&N irradiation.

CBCT image guidance in head and neck irradiation: the impact of daily and weekly imaging protocols

“…A large proportion of errors could be picked if daily imaging is used. This is consistent with findings of other researchers 11 – 13 . No significant difference was found in the mean setup error for the daily and hypothetical day 1–3 plus weekly protocols.…”

“…For this direction only, daily imaging would require 3·8 mm margins whereas day 1–3 plus weekly interfraction and day 1–3 residual protocols needed a 5 mm PTV margins. These results are similar to Qi et al’s 11 study that proved that frequent imaging reduces systematic error and PTV margins. Based on the results it appears beneficial to reduce PTV margins on treatment planning when daily imaging is used.…”

“…Finding the most suitable imaging protocol for head and neck cancers is still a controversial issue. Some authors have reported results that support the use of daily imaging 4 , 8 , 9 , 11 , 20 whereas other studies were not in favour of daily imaging 15 – 18 . Some researchers reported average doses per scan for head and neck imaging of 0·07 and 0·03 cGy, therefore reduction in imaging frequency would be preferable 24 , 25 .…”

A review of Image Guided Radiation Therapy in head and neck cancer from 2009–2019 – Best Practice Recommendations for RTTs in the Clinic

“…Where daily IGRT is routine clinical practice 40-80% reductions in margin sizes are possible [11,13,28,29,[58][59][60]. Widespread use of IGRT has given clinicians confidence to reduce CTV-PTV margins to 3 mm reporting reduced patient toxicities with no reduction in local control [61,62].…”

Radiotherapy educational research: a decade of innovation

“…Radiotherapy clinical practice has undergone rapid technological development over the last decade with advances including multimodality imaging, 27 a range of image-guided radiation therapy (IGRT) technology, 28 volumetric arc therapy (VMAT) 29 and proton therapy 30 . Not only have these developments outpaced those in many other professions, but the different uptake rates have created a uniquely diverse range of clinical environments.…”