Vaginal dose assessment in image-guided brachytherapy for cervical cancer: Can we really rely on dose-point evaluation?

Long-term clinical outcomes of preoperative brachytherapy in early-stage cervical cancer

OBJECTIVE

The treatment of early-stage cervical cancer (CC) is primarily based on surgery. Adjuvant (chemo)radiotherapy can be necessary in presence of risk factors for relapse (tumor size, deep stromal invasion, lymphovascular space invasion (LVSI), positive margins, parametrial or lymph node involvement), increasing the risk of treatment toxicity. Preoperative brachytherapy can reduce tumor extension before surgery, potentially limiting the need for adjuvant radiotherapy. This study reports long-term clinical outcomes on efficacy and toxicity of preoperative pulse-dose-rate (PDR) brachytherapy in early-stage CC.

METHODS

All patients treated at Institut Curie between 2007 and 2022 for early-stage CC by preoperative brachytherapy were included. A PDR technique was used. Patients underwent hysterectomy associated with nodal staging following brachytherapy.

RESULTS

73 patients were included. The median time from brachytherapy to surgery was 45 days [range: 25-78 days]. With a median follow-up of 51 months [range: 4-185], we reported 3 local (4 %), 1 locoregional (1 %) and 8 metastatic (11 %) relapses. At 10 years, OS was 84.1 % [95 % CI: 70.0-100], DFS 84.3 % [95 % CI:74.6-95.3] and LRFS 92.8 % [95 % CI:84.8-100]. Persistence of a tumor residue, observed in 32 patients (44 %), was a significant risk factor for metastatic relapse (p = 0.02) and was associated with the largest tumor size before brachytherapy (p = 0.04). Five patients (7 %) experienced grade 3 toxicity. One patient (1 %) developed grade 4 toxicity. Ten patients (14 %) received adjuvant radiotherapy, increasing the risk of lymphedema (HR 1.31, 95 % CI [1.11-1.54]; p = 0.002).

CONCLUSIONS

PDR preoperative brachytherapy for early-stage cervical cancer provides high long-term tumor control rates with low toxicity.

Dose at posterior-inferior border of symphysis point: A predictor for vaginal stricture in cervical cancer

PURPOSE

To study the effect of various dose-volume parameters on the severity of vaginal stricture (VS) and the correlation of the latter with the posterior-inferior border of symphysis (PIBS) points in locally advanced cervical cancer patients treated with concurrent chemoradiation and brachytherapy.

METHODS AND MATERIALS

A prospective study was done on 45 histologically proven locally advanced cervical cancer patients between January 2020 and March 2021. All of them were treated with concurrent chemoradiation with 6 MV photon linear accelerator to a dose of 45 Gy/25 fractions in 5 weeks. Twenty-three patients were treated with intracavitary brachytherapy with a dose of 7 Gy/fraction/week for three fractions. Twenty-two patients were treated with interstitial brachytherapy, with 6 Gy/fraction for four fractions, each fraction 6 h apart. Grading of VS was done as per Common Terminology Criteria for Adverse Events version 5.

RESULTS

The median followup was 21.5 months. About 37.8% of patients had VS with a median duration of 8.0 months (4.0-12 months). About 22.2% had Grade 1, 6.7% had Grade 2, and 8.9% had Grade 3 toxicity. Doses at PIBS and PIBS-2 points had no correlation with vaginal toxicity, however, the dose at PIBS+2 was significantly associated with VS (p = 0.004). The treated length of the vagina at the time of brachytherapy (p = 0.001), initial tumor volume (p = 0.009), and vaginal involvement after completion of external beam radiotherapy (EBRT) (p = 0.01) were also statistically significant with the development of VS of Grade 2 or more.

CONCLUSIONS

Dose at PIBS + 2, treated length of the vagina with brachytherapy, initial tumor volume, and post-EBRT vaginal involvement are strong predictors for the severity of VS.

Vaginal dose-surface maps in cervical cancer brachytherapy: Methodology and preliminary results on correlation with morbidity

PURPOSE

The purpose of the study was to develop a methodology for vaginal dose-surface maps (DSMs) in patients with cervix cancer and to investigate dose-surface histogram metrics as predictors for vaginal stenosis (St) and mucositis (Muc).

METHODS AND MATERIALS

Thirty-one patients with locally advanced cervix cancer with no vaginal St/Muc (CTCAE-v3) G ≥ 2 at baseline were analyzed. Patients were divided in four morbidity groups: 15 with St/Muc G0/1, 6 with St G ≥ 2, 4 with St/Muc G ≥ 2, and 6 with Muc G ≥ 2. Patients received external beam radiotherapy and 4-fraction intracavitary/interstitial high-dose-rate brachytherapy using tandem and ovoids. DSMs were generated from inner/outer vaginal surfaces. DSMs of external beam radiotherapy and brachytherapy (Gy EQD2₃) were added based on a system of homologous points, to generate cumulative DSMs. Dose-surface histogram/dose-volume histogram parameters, location of high/intermediate-dose regions, rectovaginal reference point, vaginal lateral 5 mm point doses, and vagina/implant dimensions were investigated for St and Muc prediction. Average/difference DSMs and one-way analysis of variance were used to compare between groups.

RESULTS

Best predictors of stenosis were D_15-25cm2 and upper-vagina S_65-120Gy(%). Cutoffs of ∼90 Gy EQD2₃ for D_20cm2 and ∼80% for S_65Gy to top 3 cm inner vaginal surface suitably discriminated for stenosis. Spatial dose location on average/difference DSMs showed significantly higher doses (by > 20 Gy, p < 0.001) over longer parts of the dorsolateral vagina and higher rectovaginal reference point doses for any G ≥ 2 morbidity, over the whole circumference of the upper vagina for G ≥ 2 stenosis. Dose-volume histogram parameters were dependent on vaginal wall thickness. An increase of wall thickness from 2 to 4 mm resulted in an increase of D_2cm3 (D_4cm3) of 16% (32%).

CONCLUSIONS

A novel method was developed to generate vaginal DSMs and spatial-dose metrics. DSMs were found to correlate with vaginal stenosis. The findings of this study are promising and should be further validated on a larger patient cohort, treated with different applicators.

Late G2 vagina toxicity in post-operative endometrial carcinoma is associated with a 68 Gy dose equivalent to 2 Gy per fraction(α/β=3Gy) at 2 cm3 of vagina

Purpose

To evaluate if the dose equivalent to 2 Gy per fraction (EQD2)_(α/β=3Gy) at 0.1 cm³, 1 cm³, and 2 cm³ of vagina in vaginal-cuff-brachytherapy (VBT) (high-dose-rate [HDR] ¹⁹²Ir-source) ± external-beam-irradiation (EBRT) is associated with toxicity in post-operative endometrial carcinoma (P-EC).

Material and methods

From June 2014 till November 2015, 67 consecutive P-EC patients underwent VBT ± EBRT; 44 patients received EBRT (median, 45 Gy; range, 44-50.4) + VBT (7 Gy), and 23 exclusive-VBT (6 Gy x 3 fractions). The upper 2.5 cm of vagina was delineated on computed tomography (CT). The active-length source was 2.5 cm, and the brachytherapy dose was prescribed at 5 mm from the applicator. D₉₀, V₁₀₀, and EQD2_(α/β=3Gy) at 0.1 cm³, 1 cm³, and 2 cm³ of the most exposed part of the vagina were calculated. Vaginal toxicity assessment was completed with a LENT-SOMA-objective-criteria. Statistics were done with the use of χ² and Student’s-t test.

Results

The mean follow-up was 23.2 months (7.6-46.8). Median D90 was 7.8 Gy_(α/β=3Gy). Late toxicity: 8 G1 and 9 G2. Median EQD2_(α/β=3Gy) in vagina was 88.6 Gy (62.8-177.6) for 0.1 cm³, 72.4 Gy (57.1-130.4) for 1 cm³, and 69 Gy (53-113.4) for 2 cm³. Exclusive VBT vs. EBRT+VBT showed no differences in vaginal toxicity. There was no relationship between EQD2_(α/β=3Gy) at 0.1 cm³ and 1 cm³ of vagina with G1-G2 toxicity (p = 0.62 and p = 0.58, respectively). G2 toxicity was related to EQD2_(α/β=3Gy) at 2 cm³ (p = 0.03). EQD2_(α/β=3Gy) > 68 Gy caused G2 late toxicity in 20.5% patients. All patients presenting G2 toxicity received > 68 Gy EQD2_(α/β=3Gy).

Conclusions

More than 68 Gy EQD2_(α/β=3Gy) at 2 cm³ was related to G2 toxicity in P-EC-VBT. Further studies including larger number of patients are needed to confirm these results. Patients receiving these doses should be informed of the risk of toxicity, with individualized treatment planning and follow-up to reduce G2 toxicity.

Dose-volume effect relationships for late rectal morbidity in patients treated with chemoradiation and MRI-guided adaptive brachytherapy for locally advanced cervical cancer: Results from the prospective multicenter EMBRACE study

PURPOSE

To establish dose volume-effect relationships predicting late rectal morbidity in cervix cancer patients treated with concomitant chemoradiation and MRI-guided adaptive brachytherapy (IBABT) within the prospective EMBRACE study.

MATERIAL AND METHOD

All patients were treated with curative intent according to institutional protocols with chemoradiation and IGABT. Reporting followed the GEC-ESTRO recommendations ( [Formula: see text] , [Formula: see text] ), applying bioeffect modeling (linear quadratic model) with equieffective doses (EQD2₃). Morbidity was scored according to the CTC-AE 3.0. Dose-effect relationships were assessed using comparisons of mean doses, the probit model and log rank tests on event-free periods.

RESULTS

960 patients were included. The median follow-up was 25.4months. Twenty point one percent of the patients had grade 1 events, 6.0% grade 2, 1.6% grade 3 and 0.1%, grade 4. The mean D_ICRU, [Formula: see text] , and [Formula: see text] were respectively: 66.2±9.1Gy, 72.9±11.9Gy, and 62.8±7.6Gy. Increase of dose was associated with increase in severity of single endpoints and overall rectal morbidity (grade 1-4) (p<0.001-0.026), except for stenosis (p=0.24-0.31). The probit model showed significant relationships between the [Formula: see text] , [Formula: see text] , and D_ICRU and the probability of grade 1-4, 2-4, and 3-4 rectal events. The equieffective [Formula: see text] for a 10% probability for overall rectal grade⩾2 morbidity was 69.5Gy (p<0.0001). After sorting patients according to 6 [Formula: see text] levels, less favorable outcome was observed in the high dose subgroups, for bleeding, proctitis, fistula, and overall rectal morbidity. A [Formula: see text] ⩾75Gy was associated with a 12.5% risk of fistula at 3years versus 0-2.7% for lower doses (p>0.001). A [Formula: see text] <65Gy was associated with a two times lower risk of proctitis than [Formula: see text] ⩾65Gy.

CONCLUSIONS

Significant correlations were established between late rectal morbidity, overall and single endpoints, and dose-volume ( [Formula: see text] , [Formula: see text] ) and dose-point (D_ICRU) parameters. A [Formula: see text] ⩽65Gy is associated with more minor and less frequent rectal morbidity, whereas a [Formula: see text] ⩾75Gy is associated with more major and more frequent rectal morbidity.