Streamlining the image-guided radiotherapy process for proton beam therapy: a service evaluation
Davies, Lucy McHugh, Louise Aznar, Marianne Camille Lindsay, J Eccles, Cynthia L
Davies, Lucy
McHugh, Louise
Aznar, Marianne Camille
Lindsay, J
Eccles, Cynthia L
Citations
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Abstract
Purpose or Objective
Modern radiotherapy requires image-guidance to ensure
precision and accuracy of treatment delivery. To
implement image-guided proton beam therapy (IGPBT) at
our Proton Beam Therapy (PBT) Centre, a 3-step process
was developed. This study reports on an evaluation to
assess the feasibility of reducing this to a 2-step imaging
process, thereby reducing overall treatment time and
unnecessary imaging doses.
Material and Methods
The first 20 consecutive patients treated at the Centre
were included in the study. Patient characteristics are
recorded in Table 1. The initial IGPBT workflow consisted
of: (i) 2-dimensional kilo-voltage (2DkV) image pair
acquisition for gross positioning assessment, (ii) 3-
dimensional cone-beam computed tomography (CBCT) acquisition to assess target volumes and organs at risk, and
(iii) repeat 2DkV pair to verify translation and rotation
corrections before delivering treatment.
Imaging data from fractions 1-5 and then weekly [biweekly
for head and neck treatment sites] was collated to
evaluate (i) initial 2DkV imaging dose using estimated
delivered dose (μGy), (ii) elapsed time between 2DkV and
CBCT acquisition, and (iii) concordance of online matched
values for the 2DkV and CBCT image registrations,
evaluated by registration on bony anatomy and soft tissue,
using ARIA OIS (v13.7, Varian Medical Systems, USA). To
assess the correlation between 2DkV and CBCT image
registration, data was analysed using Pearson’s Correlation
Coefficient and Bland-Altman analysis.
Results 229 fractions were evaluated (per patient: range 8-19,
median 10). 19 (8.3%) fractions required patient
repositioning following the initial 2DkV. Using a 2-step
imaging process would reduce the imaging dose by 3.4mGy
on average for all patients over a whole treatment course.
The use of the 3-step process required a mean additional
time of 5.1 minutes (range: 3.3 to 9.9) compared to the 2-
step process.
Overall image results indicated that correspondence
between the mean displacements from the initial 2DkV and
CBCT images for all treatment sites was high, with R=0.94,
0.94 and 0.80 in the anterior-posterior, superior-inferior
and right-left directions respectively. Bland-Altman
analysis showed there was very little bias and narrow limits
of agreement. However, discrepancies in rotation
correction were observed: although there was only small
bias, there were relatively wide limits of agreement (no
less than +/-0.6o).
Conclusion
The results presented confirmed only a minority of
fractions required patient repositioning after the initial
2DkV. Removing this from the standard 3-step IGPBT
process and streamlining to a 2-step workflow
(commencing with CBCT) would reduce imaging dose and
treatment times, thus improving efficiency and overall
service capacity. The 2-step IGPBT workflow has now been
implemented at our PBT Centre and is standard
verification protocol.
For challenging cases (e.g. paediatric patients under GA)
further investigations are required before the 3-step
workflow can be modified.
Description
Date
2020
Publisher
Collections
Keywords
Type
Meetings and Proceedings
Citation
Davies L, McHugh L, Aznar MC, Lindsay J, Eccles CL. PD-0068: Streamlining the image-guided radiotherapy process for proton beam therapy: a service evaluation. Radiotherapy and Oncology . 2020 Nov;152:S28–9. Available from: http://dx.doi.org/10.1016/S0167-8140(21)00094-3