Dosimetric analysis of rectal filling on rectal doses during vaginal cuff brachytherapy

doi:10.1016/j.brachy.2015.02.391

Brachytherapy

Volume 14, Issue 4, July–August 2015, Pages 458-463

Presented in part at the second European Society for Radiotherapy & Oncology Forum, April 2013, Geneva, Switzerland.

https://doi.org/10.1016/j.brachy.2015.02.391 Get rights and content

Abstract

Purpose

Several studies have analyzed the effect of bladder filling during vaginal cuff brachytherapy (VCB), but the effect of rectum filling has not been studied. We sought to evaluate the effects of rectal volume on rectal doses during postoperative VCB.

Methods and Materials

Brachytherapy planning CT scans (334 sets) obtained from 92 consecutive patients treated with VCB were resegmented (bladder and rectum) and replanned retrospectively using the same parameters to homogenize data and improve analysis. Rectal volume and a set of values derived from dose–volume histograms (DVHs) were extracted (maximal dose [D_max], D_0.1cc, D_1cc, and D_2cc). Univariate and multivariate analyses were carried out to evaluate the association between rectal volume and DVH metrics after adjusting for other clinical factors.

Results

A positive significant correlation was observed between rectal volume correlated and D_max, D_0.1cc, D_1cc, and D_2cc. Multiple linear regression models found that rectal volume, cylinder angle position, and cylinder diameter variables correlated significantly with the different DVH parameters analyzed. These variables explained the 14.5% and 18% of variance on regression models.

Conclusions

Larger rectal volumes are associated with higher rectal dose parameters during VCB fractions. Prospective studies are needed to investigate whether these data are linked to differences in rectal toxicity.

Introduction

Vaginal cuff brachytherapy (VCB) is a leading adjuvant treatment modality in the management of gynecologic neoplasms (1). The dosimetric effect of bladder filling on organs at risk (OARs) has been extensively studied [2], [3], [4], but there are no similar published studies that have addressed the effect of rectum filling. Ideally, a customized plan is recommended for each fraction (5), but when a fixed geometry is assumed at every insertion, it is acceptable to use only one plan for overall treatment, which is the most common VCB procedure. Corso et al. (6) retrospectively analyzed the dosimetric differences between a reimaging and a customized plan at every fraction and the single plan approach for the overall treatment, as well as the economic consequences associated with each approach. Although no statistical dosimetric differences were reported, the reimaging scheme was associated with an excess of $663.06 compared with the single plan approach. Nevertheless, day-to-day variations can limit that assumption. Some of these issues are the dosimetric effects of cylinder tilt (7) or the effect of individualized fraction optimization (8). Differences in bladder filling have been reported to affect differences in bladder doses, so it is of interest to analyze whether differences in rectal volume modify rectal doses. An extensive knowledge of every variable that can modify pelvic anatomy and implant relationship, standardizing clinical variables during different applications for the same patient, might improve clinical results over a single plan for overall treatment.

In long-lasting and low-dose-rate treatments, rectal evacuation before brachytherapy is advised. Nevertheless, for high-dose-rate (HDR) gynecologic brachytherapy, there are no clear directions. European Society for Radiotherapy & Oncology–Groupe Européen de Curiethérapie guidelines advise rectal evacuation but without stating why (9), and the American Brachytherapy Society (ABS) guidelines do not make any recommendation at all (5). Rectal volume can be considered a surrogate of the rectal cleaning efficacy; therefore, we sought to investigate the dosimetric effects of rectal volume on rectal doses during VCB in a population treated without rectal enemas before the VCB procedures.

Section snippets

Methods and materials

A retrospective analysis of 92 consecutive patients who underwent fractionated postoperative HDR–VCB. All patients had undergone hysterectomy followed by HDR–VCB alone (37% of patients) or whole pelvic radiation therapy in conjunction with an HDR–VCB boost (63% of patients). Patients' characteristics are shown in Table 1.

Gynecologic patients (85 endometrial cancer patients and 7 cervical cancer patients) were referred for postoperative radiotherapy after an individual multidisciplinary

CT simulation

Until 2012, it was clinical practice in our department to carry out a CT for each fraction. All patients underwent pelvic CT scans at every brachytherapy fraction, with 2-mm thick slices and no gap between them, in the supine position with a Foley bladder catheter that instilled dilute contrast medium (5 mL of Omnipaque 350 [GE Healthcare Bio-Sciences, S.A.U. La Florida (Madrid), Spain] into 45 mL of saline solution). Rectal contrast medium was instilled at the oncologist's discretion to

Segmentation and planning

To improve analysis and for the purposes of the study, a recontouring of OARs was carried out, together with replanning and redosage of all fractions under the same conditions, regardless of the actual delivered treatment. We did this because doses, active lengths, prescription depth, and the number of fractions varied among patients.

We retrieved 334 CT scans (82% of fractions) from our electronic records and transferred them to a three-dimensional (3D) treatment planning system (Oncentra v.

Statistical analysis

Results are shown as mean (±standard deviation). Bladder and rectal volumes and a set of rectal DVH parameters (D_max, D_0.1cc, D_1cc, and D_2cc) were assessed. Correlation and simple regression were used for univariate analyses. A stepwise multiple linear regression analysis was used to model rectal doses as a function of other variables (the significance levels for addition to and removal from the model were set at p = 0.05 and p = 0.10, respectively). The multiple regression analysis included

Results

Most treatments were done with the largest cylinders (3.5 cm, 66% of patients; 3 cm, 33% of patients). Mean rectal volume was 50.7 ± 22.3 cc. Positive significant correlations appeared between rectal volume and the different rectal dose metrics (r, 0.2035, 0.2245, and 0.2330 for D_max, D_0.1cc, D_1cc, and D_2cc, respectively, all p < 0.005). Univariate regression showed that rectal volume explained about 3.1%, 4.1%, 5%, and 5.4% of the variance in D_max, D_0.1cc, D_1cc, and D_2cc rectal dose–volume

Discussion

Although many studies have focused on the relationship between rectal volume and rectal doses in the context of external radiotherapy, there is lack of research into the brachytherapy settings. Our group has analyzed the effect of rectal filling during VCB, and results presented here demonstrate an increase in rectal doses associated with large rectal volumes, in agreement with previous results of studies into the effect of rectal gas removal during HDR–VCB (12).

The availability of 3D imaging

Conclusions

Our results show an increase in absorbed rectal doses associated with larger rectal volumes during VCB, generalizing previous data. Our data are the first to support measures directed at reducing rectal volume during VCB. Results warrant further research that focuses on the possible benefits related to procedures designed to homogenize rectal volume before brachytherapy.

References (29)

J. Hung et al.
Image-based 3D treatment planning for vaginal cylinder brachytherapy: Dosimetric effects of bladder filling on organs at risk
Int J Radiat Oncol Biol Phys
(2012)
A.J. Stewart et al.
Prospective clinical trial of bladder filling and three-dimensional dosimetry in high-dose-rate vaginal cuff brachytherapy
Int J Radiat Oncol Biol Phys
(2008)
R.Y. Kim et al.
Effects of bladder distension on organs at risk in 3D image-based planning of intracavitary brachytherapy for cervical cancer
Int J Radiat Oncol Biol Phys
(2010)
W. Small et al.
American Brachytherapy Society consensus guidelines for adjuvant vaginal cuff brachytherapy after hysterectomy
Brachytherapy
(2012)
C.D. Corso et al.
Dosimetric and cost comparison of first fraction imaging versus fractional re-imaging on critical organ dose in vaginal cuff brachytherapy
Pract Radiat Oncol
(2013)
Z. Symon et al.
Individual fraction optimization vs. first fraction optimization for multichannel applicator vaginal cuff high-dose-rate brachytherapy
Brachytherapy
(2006)
J.K. Russo et al.
Comparison of 2D and 3D imaging and treatment planning for postoperative vaginal apex high-dose rate brachytherapy for endometrial cancer
Int J Radiat Oncol Biol Phys
(2012)
S. Sabater et al.
In regard to Boyle, et al
Brachytherapy
(2014)
C.L. Holloway et al.
Should the organs at risk be contoured in vaginal cuff brachytherapy?
Brachytherapy
(2011)
A.M. Olszewska et al.
Comparison of dose–volume histograms and dose–wall histograms of the rectum of patients treated with intracavitary brachytherapy
Radiother Oncol
(2001)

F. van den Bergh et al.

The use of a transverse CT image for the estimation of the dose given to the rectum in intracavitary brachytherapy for carcinoma of the cervix

Radiother Oncol

(1998)

M. Cengiz et al.

Effect of bladder distension on dose distribution of intracavitary brachytherapy for cervical cancer: Three-dimensional computed tomography plan evaluation

Int J Radiat Oncol Biol Phys

(2008)

G.S. Merrick et al.

The effect of constipation on rectal dosimetry following prostate brachytherapy

Med Dosim

(2000)

S. Li et al.

Effects of prescription depth, cylinder size, treatment length, tip space, and curved end on doses in high-dose-rate vaginal brachytherapy

Int J Radiat Oncol Biol Phys

(2007)

Cited by (21)

Quantitative analysis of intra-fractional variation in CT-based image guided brachytherapy for cervical cancer patients
2020, Physica Medica
We quantified intra-fractional dose variation and organ movement during CT-based 3D-image guided brachytherapy (3D-IGBT) in cervical cancer patients. Fifteen patients who underwent CT-based 3D-IGBT were studied. For all patients, pre-delivery CT for treatment planning after applicator insertion and post-delivery CT after dose delivery without changing the applicator position were acquired. Pre- and post-delivery CT were rigidly fused by matching the inserted applicator and planned dose on pre-delivery CT (pre-delivery dose) was mapped on post-delivery CT (post-delivery dose). D2, D1, and D0.1 cm³ of the rectum and bladder were compared between pre- and post-delivery doses with contours on each CT image. Organ movement and deformation was evaluated using deformation vector fields calculated by deformable image registration between pre- and post-delivery CT. We also evaluated dose variation and DVF between with and without a catheter to control filling. Differences in all DVH parameters were <±3% in physical dose and ± 5% in EQD2. However, a > 15% dose difference was found in 13.8% of the fractions in rectum D2 cm³ and in 11.1% of those in bladder D2 cm³. The mean value of DVF for bladder was larger than that of rectum, especially for the superior-inferior (S-I) direction. Insertion catheters in bladder reduced mean dose and DVF variation compared with that of without catheters. In fraction groups with large dose increasing, DVF in the S-I direction was significantly larger than that of other fraction groups. Our results indicated that preparation is needed to reduce changes in the S-I direction affect dose variation.
An MRI comparative image evaluation under diagnostic and radiotherapy planning set-ups using a carbon fibre tabletop for pelvic radiotherapy
2019, Cancer/Radiotherapie
To quantitatively and qualitatively evaluate and compare MR images acquired from the usual diagnostic set-up with images acquired in a radiotherapy set-up.
MR images of a phantom and 18 prostate cancer patients imaging using the usual diagnostic set-up with a curved tabletop (DX-set-up) and using a radiotherapy set-up (RT-set-up) with a flat tabletop, were analysed retrospectively. Quantitative assessments were made by measuring signal-to-noise ratio (SNR) and contrast to noise ratio (CNR). Non-parametric tests were used. Qualitative assessments were made independently by three radiologists. Inter-rater reliability was measured as the percentage of agreement and Gwet's AC2 test.
The use of the RT-set-up was linked to 19.3% SNR drop on the phantom image. Up to 24% SNR prostate drop was observed in patients’ images. Up to 34% CNR drop was observed in patients’ images. Although image quality of the RT-set-up was acceptable, all measured domains were worse than the corresponding DX-set-up. Additionally diagnostic images were linked to a better percentage of agreement among raters.
SNR, CNR and image quality were significantly worse when using the RT-set-up than with the DX-set-up although Image quality in the RT-set-up was acceptable.
Évaluer et comparer qualitativement et quantitativement des images d’IRM acquises avec le positionnement diagnostique de routine et celui pour la radiothérapie.
Les images d’IRM d’un fantôme et de 18 patients atteints d’un cancer de la prostate en utilisant la configuration diagnostique habituelle avec une table courbe (configuration DX) et en utilisant une installation de radiothérapie (configuration RT) avec une table plate, ont été analysées rétrospectivement. Des évaluations quantitatives ont été effectuées en mesurant le rapport signal/bruit (SNR) et le rapport contraste/bruit (CNR). Des tests non paramétriques ont été utilisés. Des évaluations qualitatives ont été effectuées indépendamment par trois radiologues. La fiabilité inter-évaluateurs a été mesurée en pourcentage de l’accord et avec le test AC2 de Gwet.
L’utilisation de la configuration RT à montré une réduction du SNR de 19,3 % sur l’image fantôme. Jusqu’à 24 % de baisse du CNR a été observée dans les images des patients. Bien que la qualité d’image de la configuration RT était acceptable, tous les domaines mesurés étaient pires que la configuration DX correspondante. De plus, les images diagnostiques ont montré un meilleur pourcentage d’accord entre les évaluateurs.
Bien que la qualité de l’image dans la configuration RT fût acceptable, le SNR, le CNR et la qualité de l’image étaient nettement mauvais lors de l’utilisation de la configuration RT qu’avec la configuration DX.
Geometric and dosimetric evaluation of the differences between rigid and deformable registration to assess interfraction motion during pelvic radiotherapy
2019, Physics and Imaging in Radiation Oncology
Citation Excerpt :
There was no reduction in integral rectal dose with increased rectal filling. This compares to a study in 92 patients who received brachytherapy to the vaginal vault where there was a significant positive correlation between rectal volume and Dmax, D0.1cc and D1cc and D2cc [26]. In a study of 10 prostate patients, contouring the entire rectum, compared to contouring the proximal and distal rectal volumes separately, led to significantly increased dose to the distal rectum [27].
Appropriate internal margins are essential to avoid a geographical miss in intensity-modulated radiation therapy (IMRT) for endometrial cancer (EC). This study evaluated interfraction target motion using rigid and non-rigid approximation strategies and calculated internal margins based on random and systematic errors using traditional rigid margin recipes. Dosimetric impact of target motion was also investigated.
Cone beam CTs (CBCTs) were acquired days 1–4 and then weekly in 17 patients receiving adjuvant IMRT for EC; a total of 169 CBCTs were analysed. Interfraction motion for the clinical target volume vaginal vault and upper vagina (CTVv) was measured using bony landmarks and deformation vector field displacement (DVFD) within a 1 mm internal wall of CTVv. Patient and population systematic and random errors were estimated and margins calculated. Delivered dose to the CTVv and organs at risk was estimated.
There was a significant difference in target motion assessment using the different registration strategies (p < 0.05). DVFD up to 30 mm occurred in the anterior/posterior direction, which was not accounted for in PTV margins using rigid margin recipes. Underdosing of CTVv D95% occurred in three patients who had substantial reductions in rectal volume (RV) during treatment. RV relative to the planning CT was moderately correlated with anterior/posterior displacement (r = 0.6) and mean relative RV during treatment was strongly correlated with mean relative RV at CBCT acquired days 1–3 (r = 0.8).
Complex and extensive geometric changes occur to the CTVv, which are not accounted for in margin recipes using rigid approximation. Contemporary margin recipes and adaptive treatment planning based on non-rigid approximation are recommended.
The influence of the image registration method on the adaptive radiotherapy. A proof of the principle in a selected case of prostate IMRT
2018, Physica Medica
To analyse the influence of the image registration method on the adaptive radiotherapy of an IMRT prostate treatment, and to compare the dose accumulation according to 3 different image registration methods with the planned dose.
The IMRT prostate patient was CT imaged 3 times throughout his treatment. The prostate, PTV, rectum and bladder were segmented on each CT. A Rigid, a deformable (DIR) B-spline and a DIR with landmarks registration algorithms were employed. The difference between the accumulated doses and planned doses were evaluated by the gamma index. The Dice coefficient and Hausdorff distance was used to evaluate the overlap between volumes, to quantify the quality of the registration.
When comparing adaptive vs no adaptive RT, the gamma index calculation showed large differences depending on the image registration method (as much as 87.6% in the case of DIR B-spline). The quality of the registration was evaluated using an index such as the Dice coefficient. This showed that the best result was obtained with DIR with landmarks compared with the rest and it was always above 0.77, reported as a recommended minimum value for prostate studies in a multi-centre review.
Apart from showing the importance of the application of an adaptive RT protocol in a particular treatment, this work shows that the election of the registration method is decisive in the result of the adaptive radiotherapy and dose accumulation.
A new short daily brachytherapy schedule in postoperative endometrial carcinoma. Preliminary results
2017, Brachytherapy
To evaluate the preliminary results of vaginal-cuff relapses (VCR) and complications of a short brachytherapy (BT) schedule in postoperative endometrial carcinoma.
From September 2011 to December 2014, 102 patients were treated with postoperative BT for endometrial carcinoma. Seventy-four patients received a single 7 Gy dose after external beam irradiation (Group 1), and 28 intermediate-risk patients received three daily fractions of 6 Gy (Group 2). The dose was prescribed at 5 mm from the applicator surface. Toxicity was prospectively evaluated after the objective late effects of normal tissues-subjective, objective, management, analytic scores for vagina and RTOG scores for rectum and bladder. Statistics: χ² and Student's t tests.
The mean followup was 28.85 months (9.6–58.5) in Group 1 and 31.19 months (7.7–62.3) in Group 2. No VCR was found during followup. Late toxicity: vagina toxicity was developed in 24.32% of the patients in Group 1 (G1–G2) and in 21.4% in Group 2 (G1–G2 but 1 G3). Rectal toxicity appeared in only 2.7% of patients in Group 1 (G1). Neither Group 1 nor Group 2 presented late bladder toxicity. No differences were found in late toxicity between Groups 1 and 2.
The present short BT schedule was safe in relation to VCR and late toxicity for the followup period studied. These results are similar to those of two larger previous schedules performed in our center in relation to the same point of followup.
American Brachytherapy Task Group Report: Adjuvant vaginal brachytherapy for early-stage endometrial cancer: A comprehensive review
2017, Brachytherapy
Citation Excerpt :
Hung et al. (108) showed that bladder filling decreased small bowel dose without affecting dose to the bladder, rectum, or sigmoid colon. Effects of rectal filling were dosimetrically studied with larger rectal volumes resulting in higher rectal dose delivered (109). In addition, placement of a vaginal cylinder horizontal to the patient rather than in the “natural” angle of the vagina results in decreased dose to the rectum (110).
This article aims to review the risk stratification of endometrial cancer, treatment rationale, outcomes, treatment planning, and treatment recommendations of vaginal brachytherapy (VBT) in the postoperative management of endometrial cancer patients. The authors performed a thorough review of the literature and reference pertinent articles pertaining to the aims of this review. Adjuvant VBT for early-stage endometrial cancer patients results in very low rates of vaginal recurrence (0–3.1%) with low rates of late toxicity which are primarily vaginal in nature. Post-Operative Radiation Therapy in Endometrial Cancer 2 (PORTEC-2) supports that VBT results in noninferior rates of vaginal recurrence compared to external beam radiotherapy for the treatment of high-intermediate risk patients. VBT as a boost after external beam radiotherapy, in combination with chemotherapy, and for high-risk histologies have shown excellent results as well though randomized data do not exist supporting VBT boost. There are many different applicators, dose-fractionation schedules, and treatment planning techniques which all result in favorable clinical outcomes and low rates of toxicity. Recommendations have been published by the American Brachytherapy Society and the American Society of Radiation Oncology to help guide practitioners in the use of VBT. Data support that patients and physicians prefer joint decision making regarding the use of VBT, and patients often desire additional treatment for a marginal benefit in risk of recurrence. Discussions regarding adjuvant therapy for endometrial cancer are best performed in a multidisciplinary setting, and patients should be counseled properly regarding the risks and benefits of adjuvant therapy.

View all citing articles on Scopus

: Conflict of interest: None to report.

View full text

Dosimetric analysis of rectal filling on rectal doses during vaginal cuff brachytherapy

Abstract

Purpose

Methods and Materials

Results

Conclusions

Introduction

Section snippets

Methods and materials

CT simulation

Segmentation and planning

Statistical analysis

Results

Discussion

Conclusions

Int J Radiat Oncol Biol Phys

Int J Radiat Oncol Biol Phys

Int J Radiat Oncol Biol Phys

Brachytherapy

Pract Radiat Oncol

Brachytherapy

Int J Radiat Oncol Biol Phys

Brachytherapy

Brachytherapy

Radiother Oncol

Radiother Oncol

Int J Radiat Oncol Biol Phys

Med Dosim

Int J Radiat Oncol Biol Phys