Imaged-guided brachytherapy in cervical cancer: treatment planning before each fraction
Baltrons Martori Clara,
Spain
PO-1883
Abstract
Imaged-guided brachytherapy in cervical cancer: treatment planning before each fraction
Authors: Baltrons Martori Clara1, Rochera Alba JosĂ© Pascual2, Herreros MartĂnez Antonio1, Arranz DĂaz Pablo1, Rovirosa Casino Ă€ngels2
1Hospital ClĂnic de Barcelona, Radiation Oncology, Barcelona, Spain; 2Hospital ClĂnic de Barcelona, Radiation Oncology , Barcelona, Spain
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Purpose or Objective
Cervical
Cancer (CC) is one of the most frequent tumours in women worldwide. In CC
organs at risk (OAR) can receive a significant brachytherapy dose due to their
proximity to the cervical tumour depending on its position in relation to the
cervix and the external radiotherapy dose distribution.
To
determine whether image-guided brachytherapy (IGBT) planning of each treatment
session allows dosimetric benefits in the OARs (bladder, rectum, intestine and
sigma) compared to planning only in the first fraction and considering the same
D2cm3 obtained in the following sessions.
Material and Methods
The doses
to OAR were retrospectively compared in 42 patients with CC treated from
September 2017 to August 2021. The patients received 4 sessions with the same
application using the Utrecht applicator +/- parametrial interstitial implant.
CTV-HR
EQD2 > 85 Gy were administered on 3 consecutive days (1st day 1 fraction,
2nd day 2 fractions separated by 6h and 3rd day the last 1
fraction). In the 1st fraction, planning was performed by magnetic resonance (MR)
and the following with computerized tomography (CT). The doses to OAR were
compared considering two strategies (S1 and S2). In S1 we performed treatment
planning on the first day and the D2cm3 OAR dose values obtained were
applied in the remaining fractions. In S2 treatment planning was performed in
the first session based on MR findings, and in the following fractions treatment
planning was performed using the dwell times of the 1st fraction and, if D2cm3
of any OAR exceeded tolerance, the plan was recalculated, optimized or the dose
decreased based on the dose received by OAR. Statistics: Shapiro's test,
Student's t-test and Wilcoxon's test.
Results
| Bladder
|
| Rectum
|
|
EQD2 a/b = 3 Gy
| Average value daily calculation
| Mean value 1 calculation
| Average value daily calculation | Mean value 1 calculation |
| 75.11
| 76.55
| 63.16
| 63.36
|
Difference (%)
| -1.87
|
| -0.32 |
|
p-valor Student, Wilcoxon
| 0.04
|
| 0.68
|
|
|
|
|
|
|
| Bowel
|
| Sigmoid
|
|
EQD2 a/b = 3 Gy | Average value daily calculation | Mean value 1 calculation | Average value daily calculation | Mean value 1 calculation |
| 55.85
| 56.4
| 62.63
| 63.12
|
Difference (%) | -0.97
|
| -0.78
|
|
p-valor Student, Wilcoxon | 0.46
|
| 0.74
|
|
There
were significant differences in D2cm3 bladder between S1 and S2 (p =
0.042), with the mean dose in the bladder being 1.4 Gy higher in S1. No
differences were found in the final dose to the D2cm3 for rectum (p
= 0.68), intestine (p = 0.46) and sigma (p = 0.74).
In 27/42
patients (64%), variations in the filling of the OAR or movements relative to
the applicator required treatment be re-planned in one, two or three of the
remaining fractions to obtain doses below the tolerance values of each OAR.
Conclusion
In CC
IGBT daily planning allows a mean dose reduction, specifically to the bladder
in which significant dosimetric differences were observed between the two
planning strategies, demonstrating that treatment planning in each fraction
allows fulfilling the tolerance doses in OAR.