GEC-ESTRO Guidelines Research Articles

CT or MRI for Image-based Brachytherapy in Cervical Cancer

To compare volumes and doses of tumour and organs at risk with computed tomography vs. magnetic resonance imaging in cervical cancer brachytherapy. Seventeen previously untreated patients with cervical cancer suitable for radical treatment were included. All patients underwent brachytherapy using a magnetic resonance imaging-compatible applicator followed by both computed tomography and magnetic resonance imaging. The tumour and organs at risk (bladder, rectum, sigmoid and intestines) were contoured on computed tomography using only clinical findings and on magnetic resonance imaging using GEC-ESTRO guidelines. The volume and doses for tumour and organs at risk were evaluated using two-sided t-test. When magnetic resonance imaging information is not included in contouring on computed tomography images, there is significant underestimation of tumour height and overestimation of the width (P< 0.05). However, there was no significant difference in V(100), D(90) and D(100) for high- and intermediate-risk clinical target volume in computed tomography and magnetic resonance imaging. The volumes and doses to 0.1, 1 and 2 cc for organs at risk were also similar. Magnetic resonance imaging remains the gold standard for tumour delineation, but computed tomography with clinical information can give comparable results, which need to be studied further. Computed tomography-based contouring can be used comfortably for delineation of organs at risk.

Dosimetric Changes during Daily MR-Guided Pulse-Dose-Rate Brachytherapy for Cervix Cancer

Dosimetric Changes during Daily MR-Guided Pulse-Dose-Rate Brachytherapy for Cervix Cancer

SU-GG-T-59: Optimization of the Applicator Position in the Treatment of Vaginal Vault HDR Brachytherapy: A Study Based on GEC-ESTRO Guidelines

Purpose: Rectum and bladder are the most common critical structures in the prophylactic treatment of vaginal vault following surgery of early stage endometrial cancers using high-dose-rate (HDR) brachytherapy. Brachytherapy treatment usually involves employing a single catheter in a vaginal cylinder applicator with dose prescription at 5mm from a variable diameter colpostats leaving very little patient specific customization/optimization options. CT based brachytherapy treatment planning has opened yet another avenue of optimization based on patient's anatomy. Present study focuses to see if changing the applicator angle reduces the doses to the critical structures. Methods & Materials: In this retrospective study, we have used 6 patients with the applicator in natural position as well as in a position parallel to the treatment couch using a simple spirit level. CT scans were obtained in both the positions. Rectum and bladder were segmented in each set by the same physician. An optimized treatment plan, designed to deliver 700cGy at 5mm from the colpostats surface, was generated employing 5cm length along the vagina in both the CT datasets. The treatment plans were evaluated based on GEC-ESTRO guidelines of 0.1, 1 & 2 cc of rectum and bladder. Results: The mean angle of vagina was found to be 10.3° [min=4.4°, max=22.2°] in relation to the treatment couch. Placing the applicator in a position parallel to couch resulted in mean dose reduction of 6, 8.1 & 9.5% for 0.1, 1 & 2 cc of rectum, respectively. However, it resulted in an increase in the respective bladder doses by 15.3, 13.2 & 13.3%. Conclusion: Since the bladder has significantly higher radiation tolerance than the rectum, use of vaginal applicator in a position parallel to the couch reduces rectal dose and potential rectal morbidity. This procedure can be easily adapted in any clinic with minimum additional efforts or hardware cost.

Variation of Rectal, Bladder, Vaginal, and Parametrial Doses using the American Brachytherapy Society HDR Optimization Guidelines of Intracavitary Brachytherapy for Cervical Cancer: A Summary of the Most Possible Clinical Scenarios

Purpose: HDR brachytherapy for cervical cancer is gaining popularity. Dose prescription has evolved from the milligram Radium hour system to 3-D image based treatment-planning passing through ICRU point “A” in LDR and American Brachytherapy Society (ABS) point “H” in HDR. The ABS recommendations are still widely adopted in HDR planning since the clinical outcomes of GEC-ESTRO guidelines are still in the maturation phase. The purpose of this study is to evaluate the variation in rectal, bladder, vaginal,and parametrial doses using ABS guidelines in various case scenarios using different tandem lengths, tandem angles, and ovoid sizes. Materials and Methods: Seven hundred cGy was prescribed to point H, and was optimized using current ABS guidelines. Varian Eclipse software was used in this project. We performed several simulations on a model CT scan of a previously treated patient. We used tandem lengths of 4, 6 and 8 cm; angle of the tandem to the central axis of the patient of 0, 15 and, 30 degrees; and mini (1.6 cm), small (2 cm), medium (2.5 cm) and large (3 cm) ovoid sizes. We performed DVH analysis and recorded D0.1cc, D1 cc, D 2 cc each for the rectum, sigmoid, and bladder. In addition we reported point doses of the bladder, rectum, bilateral vaginal points, and bilateral point B. Results: We performed 36 simulations utilizing the various above mentioned criteria. Our reference case used a 6cm tandem with an angle of 0 degree and medium ovoids (6.0, medium). Doses recorded were as follows: vagina, 1224 cGy; point B, 251 cGy; bladder, 506 cGy and rectum, 493 cGy. The D2cc of the rectum, sigmoid, and bladder were 370 cGy, 265 cGy, and 405 cGy, respectively. The highest (H) and lowest (L) doses of each organ/point with the corresponding parameters is listed in the table below: Table 1OrganDose in cGy (% of Point H Dose)Tandem Length (cm)Tandem Angle (Degree)ovoid sizeVagina H1500 (214%)40miniVagina L1081 (154%)830largePoint B H371 (53%)830largePoint B L151 (22%)40miniBladder H637 (91%)430largeBladder L393 (56%)40miniRectum H597 (85%)60largeRectum L323 (46%)40miniBladder D2cc H560 (80%)430largeBladder D2cc L315 (45%)40miniRectum D2cc H470 (67%)430largeRectum D2cc L245 (35%)40miniSigmoid D2cc H285 (41%)80mediumSigmoid D2cc L180 (26%)430mini Open table in a new tab Conclusions: When using the ABS guidelines, the tandem length is directly related to point B and sigmoid doses. The ovoid size is directly proportional to rectal and bladder doses while inversely proportional to vaginal dose. The tandem angle is directly related to ipsilateral point B and ipsilateral vaginal doses. These numbers are for reference only. Caution should be adopted when using less than optimal parameters, as it would reflect into higher doses to critical structure that may lead to serious complications.

3D CT-based volumetric dose assessment of 2D plans using GEC-ESTRO guidelines for cervical cancer brachytherapy

Purpose To investigate two-dimensional (2D) radiograph-based plans using three-dimensional (3D) dose–volume histogram (DVH) parameters following guidelines from Gynecologic GEC-ESTRO Working Group (GEC-ESTRO). Methods and Materials Nineteen high-dose-rate (HDR) fractions from 8 patients were studied. Prescription was 45 Gy from external beam radiation therapy plus 30 Gy in five fractions from HDR using tandem and ring/ovoids. Both radiographs and CT scan were obtained. Treatment was planned using radiographs following American Brachytherapy Society (ABS) guidelines. Retrospective evaluation of above 2D plans on a 3D volumetric basis was achieved by generating CT image-based 3D plans using same dwell times. Results In 2D plans, International Commission on Radiation Units and Measurement (ICRU) bladder and rectal point doses were 3.8 ± 0.4 and 3.0 ± 0.5 Gy, respectively. In 3D plans, rectum D 2 cc is 4.0 ± 1.0 Gy and bladder D 2 cc is 5.4 ± 0.9 Gy. Position of actual hottest spot in 3D rectum volume was close to the position of ICRU rectal point. ICRU bladder point did not match with the actual hottest spot in 3D bladder volume. In 2D plans, H-point dose was 5.8 ± 0.2 Gy. In 3D plans, dose to CT-based cervix ( D 90) reduced from 7.1 to 4.2 Gy as the cervical volume increased from 12 to 39 cc. Average D 2 cc /ICRU dose ratio was calculated to be 1.36/1.01 for bladder/rectum, respectively. Conclusions The DVH analysis of 2D plans revealed a suboptimal coverage of CT-based cervix and a negative correlation between coverage and cervical size. Rectum dose to 2 cc weakly correlated with ICRU point dose. Currently published constraint for bladder in 3D planning is tighter than ABS guidelines in past 2D planning.

Technical Aspects of the Integration of Three-Dimensional Treatment Planning Dose Parameters (GEC-ESTRO Working Group) into Pre-implant Planning for LDR Gynecological Interstitial Brachytherapy

This study investigates the technical feasibility of pre-implant image-based treatment planning for LDR GYN interstitial brachytherapy(IB) based on the GEC-ESTRO guidelines. Initially, a virtual plan is generated based on the prescription dose and GEC-ESTRO defined OAR dose constraints with a pre-implant CT. After the actual implant, a regular diagnostic CT was obtained and fused with our pre-implant scan/initial treatment plan in our planning software. The Flexi-needle position changes, and treatment plan modifications were made if needed. Dose values were normalized to equivalent doses in 2 Gy fractions (LQED 2 Gy) derived from the linear-quadratic model with alpha/beta of 3 for late responding tissues and alpha/beta of 10 for early responding tissues. D(90) to the CTV, which was gross tumor (GTV) at the time of brachytherapy with a margin to count for microscopic disease, was 84.7 +/- 4.9% of the prescribed dose. The OAR doses were evaluated by D(2cc) (EBRT+IB). Mean D(2cc) values (LQED(2Gy)) for the rectum, bladder, sigmoid, and small bowel were the following: 63.7 +/- 8.4 Gy, 61.2 +/- 6.9 Gy, 48.0 +/- 3.5 Gy, and 49.9 +/- 4.2 Gy. This study confirms the feasibility of applying the GEC-ESTRO recommended dose parameters in pre-implant CT-based treatment planning in GYN IB. In the process, this pre-implant technique also demonstrates a good approximation of the target volume dose coverage, and doses to the OARs.

Single Magnetic Resonance Imaging vs Magnetic Resonance Imaging/Computed Tomography Planning in Cervical Cancer Brachytherapy

Aims To compare differences in dose to the target volume and organs at risk (OARs) for ring and tandem brachytherapy using individualised magnetic resonance imaging (MRI)/computed tomography-based three-dimensional treatment plans for each application vs plans based on a single scan for all fractions. Materials and methods The study was carried out in 10 patients with carcinoma of the uterine cervix, treated with external beam radiotherapy and five fractions of high dose rate brachytherapy. Planning was carried out using MRI for the first fraction and computed tomography for each of the four subsequent fractions. The MRI-based plan was taken as the reference and the single-plan procedure was calculated by using the weights from the reference plan to calculate the dose distribution for each subsequent computed tomography-based plan. The high-risk clinical target volume (HRCTV) and OARs were delineated as per GEC-ESTRO guidelines. Total doses from external beam radiotherapy and brachytherapy were summated and normalised to a 2 Gy fraction size. Results The mean D 90 for the HRCTV was 81.9 Gy when using one plan and 84 Gy when using individual treatment plans. Similarly, the mean D 2cc was 75.68 Gy vs 74.99 Gy for the bladder, 55.84 Gy vs 56.56 Gy for the rectum and 64.8 Gy vs 65.5 Gy for the sigmoid. Ring rotation was identified in three patients, resulting in a change in dwell positions, which otherwise could have led to either a high bladder dose or suboptimal coverage of the HRCTV. Conclusions Our study has shown that a single-plan procedure achieved acceptable dosimetry in most patients. However, the individualised plan improved dosimetry by accounting for variations in applicator geometry and the position of critical organs.

Optimization of Pulsed Dose Rate Intra-uterine Brachytherapy for Cervix Cancer: A Comparison of Target Volume Doses

Optimization of Pulsed Dose Rate Intra-uterine Brachytherapy for Cervix Cancer: A Comparison of Target Volume Doses

Are we hitting the target and if not, can we safely alter the pear?

Purpose: CT-based dosimetry for each HDR fraction has been used at MCW since 2004 for cervical cancer patients receiving brachytherapy to define and limit dose to normal tissues. An MRI at fraction 1 has been obtained to define tumor volume using the GEC ESTRO guidelines. Using CT-based plans we reviewed how well we met the GEC ESTRO guidelines on the MRI scans. In those patients in whom a D90 of 85 Gy was not met, we used an MRI plan with simple modifications to assess the ramifications on the adjacent normal organs of altering the dose distribution to cover the HR CTV.

Translation of point doses from radiograph-based plans to 3D volumetric assessment using GEC-ESTRO guidelines for cervical cancer brachytherapy

Translation of point doses from radiograph-based plans to 3D volumetric assessment using GEC-ESTRO guidelines for cervical cancer brachytherapy