MRI-guided 3D optimization significantly improves DVH parameters of pulsed-dose-rate brachytherapy in locally advanced cervical cancer

MRI assessment of cervical cancer for adaptive radiotherapy

PURPOSE

To assess the importance of the information obtained from MRI for adaptive cervix cancer radiotherapy.

PATIENTS AND METHODS

49 patients with cervix cancer, treated by external-beam radiotherapy (EBRT) and MRI-assisted high-dose-rate brachytherapy +/- concomitant cisplatin, underwent MRI at diagnosis and at the time of brachytherapy fractions. 190 MRI examinations were performed. Pretreatment scans were correlated with clinical examination (CE) findings. Measurements in 3-D of the tumor extension and also of the distance from the tumor to the pelvic side wall were performed using both MRI and CE. The tumor volume regression induced initially by EBRT and the subsequent regression after each brachytherapy fraction were assessed.

RESULTS

MRI and CE showed 92% agreement in overall parametrial staging and 73% agreement in terms of vaginal involvement. There was, however, disagreement in parametrial side (right/left) classification in 25% of the parametria examined. These were patients with unilateral displacement of the cervix and contralateral invasion of the parametrium. The mean tumor volume on the pretreatment MRI scan (GTVD) was 61 cm(3). At the time of the four brachytherapy fractions the mean was 16 cm(3), 10 cm(3), 9 cm(3), and 8 cm(3), defined as the GTVBT plus the gray zones in the parametria.

CONCLUSION

CE and MRI findings agree well in terms of overall staging. The clinical assessment of side-specific parametrial invasion improved when having access to the additional knowledge obtained from MRI. The greatest decrease in tumor volume occurs during EBRT, whereas tumor regression between the first and subsequent brachytherapy fractions is minor.

Dose-volume histogram parameters and local tumor control in magnetic resonance image-guided cervical cancer brachytherapy

PURPOSE

To investigate the value of dose-volume histogram (DVH) parameters for predicting local control in magnetic resonance (MR) image-guided brachytherapy (IGBT) for patients with cervical cancer.

METHODS AND MATERIALS

Our study population consists of 141 patients with cervical cancer (Stages IB-IVA) treated with 45-50 Gy external beam radiotherapy plus four times 7 Gy IGBT with or without cisplatin. Gross tumor volume (GTV), high-risk clinical target volume (HRCTV), and intermediate-risk clinical target volume (IRCTV) were contoured, and DVH parameters (minimum dose delivered to 90% of the volume of interest [D90] and D100) were assessed. Doses were converted to the equivalent dose in 2 Gy (EQD2) by applying the linear quadratic model (alpha/beta = 10 Gy). Groups were defined for patients with or without local recurrence (LR) in the true pelvis for tumor size at diagnosis (GTV at diagnosis [GTVD] of 2-5 cm (Group 1) or greater than 5 cm (Group 2) and for tumor size response at IGBT (HRCTV) of 2-5 cm (Group 2a) or greater than 5 cm (Group 2b).

RESULTS

Eighteen LRs were observed. The most important DVH parameters correlated with LR were the D90 and D100 for HRCTV. Mean D90 and D100 values for HRCTV were 86 +/- 16 and 65 +/- 10 Gy, respectively. The D90 for HRCTV greater than 87 Gy resulted in an LR incidence of 4% (3 of 68) compared with 20% (15 of 73) for D90 less than 87 Gy. The effect was most pronounced in the tumor group (Group 2b).

CONCLUSIONS

We showed an increase in local control in IGBT in patients with cervical cancer with the dose delivered, which can be expressed by the D90 and D100 for HRCTV. Local control rates greater than 95% can be achieved if the D90 (EQD2) for HRCTV is 87 Gy or greater.

Correlation of dose-volume parameters, endoscopic and clinical rectal side effects in cervix cancer patients treated with definitive radiotherapy including MRI-based brachytherapy

PURPOSE

Correlation of dosimetric parameters for MRI-based 3D treatment planning with rectoscopic findings and clinical rectal side effects.

METHODS AND MATERIALS

Rectosigmoidoscopy and rectal morbidity assessment were performed on 35 cervical cancer patients treated with external beam radiotherapy (EBRT) and HDR-intracavitary brachytherapy (ICB). The total doses, normalised to 2 Gy fractions (EQD2, alpha/beta=3 Gy), in 0.1, 1.0 and 2.0 cm(3) (D(0.1 cc), D(1 cc), D(2 cc)) of rectum were determined by summation of EBRT and ICB plans. Correlation analysis between clinical symptoms (LENT/SOMA) and rectoscopic changes (Vienna Rectoscopy Score, VRS) was performed. For dose-response analyses, the logit model was applied.

RESULTS

Mean follow-up was 18 months. LENT/SOMA score was 1 in 4 patients, 2 in 8 patients, 4 in 1 patient. Telangiectasia was found in 26 patients (74%), five of them had ulceration corresponding to the 0.1 cm(3) volume (anterior wall). Mean values D(0.1 cc), D(1 cc), and D(2 cc) were 81+/-13, 70+/-9 and 66+/-8 Gy, respectively. The ED50 values for VRS > or = 3 and for LENT/SOMA > or = 2 significantly increased with decreasing volumes. D(2 cc) was higher in patients with VRS > or = 3 compared to VRS<3 (72+/-6 vs 62+/-7 Gy; p<0.001) and in symptomatic vs asymptomatic patients (72+/-6 vs 63+/-8 Gy; p<0.001). VRS correlated with the LENT/SOMA score.

CONCLUSIONS

Rectosigmoidoscopy is sensitive in detecting mucosal changes, independent of clinical symptoms. The localization of these changes corresponds to the high dose volumes as defined by imaging. The development of mucosal and clinical changes in the rectum follows a clear dose-effect and volume-effect. DVH parameters could be established.

Image-guided intracavitary high-dose-rate brachytherapy for cervix cancer: A single institutional experience with three-dimensional CT-based planning

PURPOSE

To evaluate and report volumetric dose specification of clinical target volume (CTV) and organs at risk with three-dimensional CT-based brachytherapy. In this study, we analyzed CTV volumes and correlated the dose specification from CT-based volumes with doses at classical point A and International Commission on Radiation Units and Measurements (ICRU) points.

METHODS AND MATERIALS

Ten patients who underwent definitive high-dose-rate brachytherapy for cervical cancer between May 2006 and March 2007 were retrospectively identified for this study. Each patient underwent five intracavitary insertions with CT-compatible ring and tandem applicators using a universal cervical Smit sleeve. Dose of 6.0Gy per fraction was prescribed to the 100% isodose line. The dose distribution was modified using the feature of "geometry optimization" to achieve maximum CTV coverage and to spare the organs at risk. The minimal doses for most irradiated 2, 1, 0.1cm(3) of bladder (D(BV2) , D(BV1), and D(BV0.1)) and rectum (D(RV2), D(RV1), and D(RV0.1)) were determined from dose-volume histograms and were compared with the doses estimated at the ICRU reference points.

RESULTS

The mean CTV of the 10 patients had a shrinkage trend over the five fractions, with a mean of 77.4cm(3) from the first fractions and a mean of 65.5cm(3) from the last fractions (r=-0.911, p=0.031). CTV volumes directly correlated with dose to point A (r=0.785, p=0.007). Eight of 10 patients achieved an average dose received by at least 90% of volume (D(90)) >/=6.0Gy. For bladder, the doses determined from the 3-dimensional (3D) plan correlated significantly with the doses to the ICRU reference bladder point, for example, D(BV2) (r=0.668, p<0.001), D(BV1) (r=0.666, p<0.001), and D(BV0.1) (r=0.655, p<0.001). However, for rectum, the estimated doses to the ICRU reference rectal point did not correlate significantly with doses determined from 3D plan, for example, D(RV2) (r=0.251, p=0.079), D(RV1) (r=0.279, p=0.049), and D(BV0.1) (r=0.282, p=0.047).

CONCLUSIONS

Our experience showed that excellent dose coverage of CTV can be achieved with image-guided CT-based planning with geometric optimization although maximal sparing of rectum was not achieved. Careful dose constraints and standardization of D(90) should be considered when optimizing doses to target tissues such that normal tissue constraints can be met.

Clinical impact of computed tomography-based image-guided brachytherapy for cervix cancer using the tandem-ring applicator - the Addenbrooke's experience

AIMS

We report our initial 3-year experience of chemoradiotherapy for cervical cancer with computed tomography-based image-guided high dose rate (HDR) brachytherapy using the tandem-ring applicator.

MATERIALS AND METHODS

Twenty-eight patients were treated between February 2005 and December 2007. All patients received initial external beam radiotherapy (EBRT) followed by HDR brachytherapy (planned dose 21 Gy to point A in three fractions over 8 days). For each insertion, a computed tomography scan was obtained with the brachytherapy applicator in situ. The cervix, uterus and organs at risk (OAR) were contoured on the computed tomography images to create an individualised dosimetry plan. The D(90) (the dose delivered to 90% of the tumour target), V(100) (the percentage of tumour target volume receiving 100% of the prescribed dose) and the minimum dose in the most exposed 2 cm(3) volume (D(2 cc)) of rectum, bladder and bowel were recorded. The equivalent dose in 2 Gy fractions delivered by EBRT and brachytherapy was calculated.

RESULTS

The 3-year cancer-specific survival was 81%, with a pelvic control rate of 96%. In 24 patients, a D(90)>or=74 Gy (alpha/beta10) was achieved. The only patient with local recurrence had a D(90) of 63.8 Gy(alpha/beta10). The overall actuarial risk of serious late morbidity was 14%. Seventeen patients had satisfactory OAR doses using the standard loading pattern. Seven patients had modifications to reduce the risk of toxicity, whereas two had modifications to improve the tumour dose. Comparison with a previous cohort of patients treated with chemoradiotherapy and a conventionally planned low dose rate triple source brachytherapy technique showed an improvement in local pelvic control of 20% (P=0.04).

CONCLUSIONS

The implementation of a computed tomography-based tandem-ring HDR brachytherapy technique in conjunction with individual dose adaptation has resulted in a significant improvement in local control at Addenbrooke's without increasing the risk of serious toxicity, and with little effect on radiotherapy resources.

Inter-observer comparison of target delineation for MRI-assisted cervical cancer brachytherapy: application of the GYN GEC-ESTRO recommendations

BACKGROUND AND PURPOSE

To investigate the inter-observer variation of target contouring when using the GYN GEC-ESTRO recommendations for MR image-guided brachytherapy (IGBT) for cervical cancer.

MATERIALS AND METHODS

Nineteen cervical cancer patients, treated by radiotherapy at the Institut Gustave Roussy (IGR) in France (n=9) or at the Medical University of Vienna (AKH) in Austria (n=10) were included in this study. IGBT was used for all patients. Two radiation oncologists, one from IGR and the other from AKH, outlined the target volumes on MRI at the time of brachytherapy according to the GYN GEC-ESTRO recommendations. The absolute, common and encompassing volumes and their conformity indices (CIs) were assessed for the GTV, HR CTV and IR CTV. D90 and D100 for each volume were assessed. Visual evaluation was made to assess the reasons for the most frequent inter-observer differences.

RESULTS

The mean volumes of GTV and HR CTV did not differ significantly between the observers, p>0.05. Significant differences were observed only for the mean volumes of the IR CTV of both centres, p<0.05. CIs ranged from 0.5 to 0.7. DVH-parameter analyses did not reveal any statistical differences, except for the D100 for the GTV at AKH, and the D90 for the IR CTV at IGR, p<0.05. Underlying reasons for inter-observer differences included image contrast adjustment and neglecting to consider anatomical borders.

CONCLUSIONS

The results of this inter-observer study show that the application of the GYN GEC-ESTRO recommendations for IGBT contouring at two different institutions with two different traditions for applicators, CTV assessment, MR image acquisition and dose prescription is feasible, and it produces acceptable inter-observer variability.

Applicator reconstruction in MRI 3D image-based dose planning of brachytherapy for cervical cancer

BACKGROUND AND PURPOSE

To elaborate a method for applicator reconstruction for MRI-based brachytherapy for cervical cancer.

MATERIALS AND METHODS

Custom-made plastic catheters with a copper sulphate solution were made for insertion in the source channels of MR-CT compatible applicators: plastic and titanium tandem ring applicators, and titanium needles. The applicators were CT and MR scanned in a phantom for accurate 3D assessment of applicator visibility and geometry. A reconstruction method was developed and evaluated in 19 patient MR examinations with ring applicator (plastic: 14, titanium: 5). MR applicator reconstruction uncertainties related to inter-observer variation were evaluated.

RESULTS

The catheters were visible in the plastic applicator on T1-weighted images in phantom and in 14/14 clinical applications. On T2-weighted images, the catheters appeared weaker but still visible in phantom and in 13/14 MR clinical applications. In the titanium applicator, the catheters could not be separated from the artifacts from the applicator itself. However, these artifacts could be used to localize both titanium ring applicator (5/5 clinical applications) and needles (6/6 clinical applications). Standard deviations of inter-observer differences were below 2 mm in all directions.

CONCLUSION

3D applicator reconstruction based on MR imaging could be performed for plastic and titanium applicators. Plastic applicators proved well to be suited for MRI-based reconstruction. For improved practicability of titanium applicator reconstruction, development of MR applicator markers is essential. Reconstruction of titanium applicator and needles at 1.5 T MR requires geometric evaluations in phantoms before using the applicator in patients.

[Implementation of GEC-ESTRO recommendations on 3-D based image brachytherapy]

Even if the prognosis of patients with cervical cancer has been dramatically improved with concomitant chemoradiation, brachytherapy still plays fundamental role in the therapeutic approach of patients with Figo stage I-IV cervical carcinoma. The development of imaging with three-dimensional dosimetry has contributed to the improvement in target and organs at risk knowledge. In 2005 and 2006, GEC-ESTRO recommendations on 3-D based image brachytherapy have defined the different volumes of interest. These recommendations have been validated with intercomparison delineation studies. Data on dose to normal tissues are better known with dose volume-histograms analysis. Dose limits to the bladder are high in the range of 90 Gy to the 2 cm3 while 2 cm3 limits to the rectum do not differ from ICRU point. The sigmoid is currently under study as this organ was not extensively studied before the era of imaging. Doses to the tumour (HR-CTV or IR-CTV) are not clearly stated and will likely depend on tumour extension.

Present status and future of high-precision image guided adaptive brachytherapy for cervix carcinoma

INTRODUCTION

Image guided adaptive brachytherapy (IGABT) for cervical cancer, using mainly MRI, is an evolving method, increasingly replacing the 2D approach based on conventional radiography. During the complex 4D chain of this procedure image-assistance is provided for disease assessment, provisional treatment planning ("pre-planning"), applicator placement and reconstruction, as well as for contouring, definitive treatment planning and quality control of dose delivery. With IGABT changes of topography adjacent to the applicator, caused by tumour regression, oedema, organ changes and dilation are identified. Thus, the CTV for IGABT is primarily based on the tumour volume at the time of BT and takes into account both time and spatial domains. IGABT requires systematic concepts for target, OAR, biological modelling, DVH analysis, and dose-volume-adaptation.

METHODS AND RESULTS

This report focuses on the advantages and uncertainties, dose-effect relations and clinical results of the IGABT procedure addressing the current status and future perspectives. Uncertainties during the 4D chain of IGABT are mainly related to target contouring, applicator reconstruction, as well as to inter-fraction, intra-fraction and inter-application variability, as caused by tumour response and organ changes. Different from EBRT where set-up uncertainties are compensated by adding a margin to the CTV, no margins to the lateral and anterior-posterior directions can be used for IGABT.

DISCUSSION

By 3D treatment planning for IGABT significant improvement of the DVH parameters is achieved compared to 2D library plans. In small tumours the benefit is primarily obtained by a decrease of dose to nearby OAR while in large tumours the use of supplementary interstitial techniques and optimization may double the target volume that can be treated at a therapeutic dose level. The clinical impact of IGABT could recently be demonstrated by the establishment of some correlations between target- and organ-related DVH parameters versus disease control and side effects, which need further clarification. Overall, a very high local control rate can be achieved with minor treatment related morbidity. This favourable therapeutic ratio seems to be now reproducible under different conditions at various treatment centres. These results have to be validated within the upcoming multi-centre prospective IntErnational study on MRI-guided brachytherapy in locally advanced cervical cancer (EMBRACE).

Inter- and intraobserver variation in HR-CTV contouring: intercomparison of transverse and paratransverse image orientation in 3D-MRI assisted cervix cancer brachytherapy

AIM

To analyze agreement between target volumes, delineated by two observers on transverse (T) and paratransverse (perpendicular to the long cervical axis - PT) MR images for cervix cancer brachytherapy.

MATERIALS AND METHODS

In 13 patients, High Risk-CTV (HR-CTV) was outlined by two observers in T and PT MR image plane, respecting the GYN GEC-ESTRO recommendations for 3D-image based cervix cancer brachytherapy [1]. Contouring time was measured. HR-CTV sizes were compared, and conformity index (CI) was assessed. Interobserver variations in contour-extent along eight radial directions were compared between delineation planes. After applying a standard treatment plan, an intercomparison of DVH-parameters V100, D90, and D100 for the HR-CTV was carried out.

RESULTS

Contouring time was slightly longer in T than PT orientation. Interplane CI did not differ significantly between observers (0.72 vs. 0.71), nor did the interobserver CI between planes (0.79 vs. 0.78). Variations in contour-extent between different radial directions and interplane deviations in DVH parameters were non-significant.

CONCLUSION

Contouring in PT, as compared to T plane, allows for a "circumferential view of the cervix" and facilitates comprehensive understanding of spatial relations between the applicator and patho-anatomical structures. It is marked by a lower contouring difficulty and leads to a comparable outcome in terms of DVH parameters. Interobserver inconsistencies can be minimized by systematic training and following the published recommendations.

Consequences of random and systematic reconstruction uncertainties in 3D image based brachytherapy in cervical cancer

BACKGROUND AND PURPOSE

The purpose of this study was to evaluate the impact of random and systematic applicator reconstruction uncertainties on DVH parameters in brachytherapy for cervical cancer.

MATERIAL AND METHODS

Dose plans were analysed for 20 cervical cancer patients with MRI based brachytherapy. Uncertainty of applicator reconstruction was modelled by translating and rotating the applicator. Changes in DVH parameters per mm of applicator displacement were evaluated for GTV, CTV, bladder, rectum, and sigmoid. These data were used to derive patient population based estimates of delivered dose relative to expected dose.

RESULTS

Deviations of DVH parameters depend on direction of reconstruction uncertainty. The most sensitive organs are rectum and bladder where mean DVH parameter shifts are 5-6% per mm applicator displacement in ant-post direction. For other directions and other DVH parameters, mean shifts are below 4% per mm. By avoiding systematic reconstruction errors, uncertainties on DVH parameters can be kept below 10% in 90% of a patient population. Systematic errors of a few millimetres can lead to significant deviations.

CONCLUSION

Comprehensive quality control of afterloader, applicators and imaging procedures should be applied to prevent systematic errors in applicator reconstruction. Random errors should be minimised by using small slice thickness. With careful reconstruction procedures, reliable DVH parameters for target and OAR's can be obtained.

Image-guided adaptive brachytherapy for cervix carcinoma

Sectional imaging has played an important role in the management of cervical cancer, in particular for staging, and is now considered for image-guided treatment planning, in particular for brachytherapy. Image-based three-dimensional brachytherapy is a relatively new approach that is increasingly replacing the traditional two-dimensional X-ray-based method. This overview focuses on the potential and some practicalities of this approach. The pros and cons of computed tomography- and magnetic resonance imaging-based brachytherapy are considered and an overview of the current state of research is given. The first encouraging clinical results are presented and future perspectives are discussed.