What are the main causes of interfraction motion of the uterine fundus and cervix?
Cree, Anthea Vasquez Osorio, Eliana Price, G. Van Herk, Marcel Hoskin, Peter J McWilliam, Alan
Cree, Anthea
Vasquez Osorio, Eliana
Price, G.
Van Herk, Marcel
Hoskin, Peter J
McWilliam, Alan
Citations
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Abstract
Purpose or Objective
Interfraction motion of uterus and cervix can be large and
often exceeds applied CTV-PTV margins. There is variation
between patients and different parts of the uterus move
differently. Most strategies accounting for this are based
on bladder filling. However, we hypothesise that there are
other causes of uterine motion. Our study aims to provide
a qualitative assessment of causes of motion of the uterine
fundus and cervix in a large cohort of patients.
Material and Methods
Anonymised scans were retrospectively obtained for 83
patients who received radical radiotherapy for cervical
cancer, with imaging at 3 time points (Fig. 1); diagnostic
MRI scan (1), planning CT, ~2 weeks later (2) and final
week MRI scan, ~6 weeks later (3). Scans were registered
on bony anatomy to the diagnostic MRI for each patient.
The uterus was contoured by a single observer for all 249
scans on a single sagittal slice identified as mid of the
uterus on scan 1. Motion at the cervix and uterine fundus
was evaluated between scans 1-2 (S1-2) and 1-3 (S1-3).
The main cause of motion and direction of motion was
recorded based on visual interpretation. Results
In S1-2, large motion (>1cm) was seen in 44 cases (53%) at
the cervix level and in 65 (78%) at the fundus level. In S1-
3, this was 57 (69%) at the cervix level and 64 (77%) at the
fundus level. Large motion at the cervix rarely occurred
without large motion at the fundus: in S1-2, 3 cases (4%)
and S1-3, 9 cases (11%). The main causes and direction of
motion are summarised in figure 2. For the cervix, the
most common cause of motion in S1-2 was rectal change with 30 cases (36%) and in S1-3 it was tumour regression,
also with 30 cases (36%). Bladder filling differences only
accounted for cervix motion in 5 cases (6%) in S1-2 and 1
case (1%) in S1-3. Main drivers of motion at the fundus
were bladder filling with 23 cases (28%) in S1-2 and 18
cases (22%) in S1-3. However, motion was also related to
rectal changes in 13 cases (16%) in S1-2 and S1-3, to bowel
changes in 21 cases (25 %) in S1-2 and 12 cases (15%) in S1-
3, and to tumour regression in 16 cases (19%) in S1-3. At
the cervix, in S1-2, there was a superior/inferior
component of motion in 20 cases (24%), mainly related to
rectal changes. In S1-3, there was a superior/inferior
component of motion in 38 cases (45%), mainly related to
tumour regression.
Conclusion The main causes of cervical motion in our cohort are
changes in rectal filling and tumour regression, with
bladder filling playing a limited role. Motion at the uterine
fundus is affected by bladder filling but other factors also
have an important role. Rectal motion can lead to changes
in the superior/inferior position of the cervix, which
should be considered if developing an ITV. Our study
suggests that current radiotherapy motion management
strategies based on bladder filling may not account for the
most important causes of cervix motion. Alternative
approaches such as online adaption may be beneficial.
Description
Date
2020
Publisher
Collections
Keywords
Type
Meetings and Proceedings
Citation
Cree A, Osorio EV, Price G, Van Herk M, Hoskin P, Choudhury A, et al. PH-0401: What are the main causes of interfraction motion of the uterine fundus and cervix? Radiotherapy and Oncology . 2020 Nov;152:S214.