A dosimetric comparison of two high-dose-rate brachytherapy planning systems in cervix cancer: standardized template planning vs. computerized treatment planning.
ABSTRACT High-dose-rate brachytherapy is an important component of the curative treatment for cervical cancer. Some institutions use standardized template planning (STP), based on a precalculated table of dose rates, instead of computerized treatment planning (CTP), based on digitized orthogonal X-ray films. STP can be used as a backup check in case of computer hardware malfunction, and/or as a way to minimize treatment planning time. We performed a dosimetric comparison of STP and CTP to determine dose differences at point A and the International Commission on Radiation Units and Measurements Report 38 bladder and rectal reference points.
We retrospectively reviewed the treatment plans of 62 patients (135 applications) treated with a tandem and two ovoids using the CTP method. For each of these plans, we calculated the dwell times required to deliver the same prescription dose had STP been used. We also used the planning computer to vary tandem and ovoid geometry and develop a table of dose rates based on geometric parameters.
The mean dose at point A was 7.6 Gy using CTP, increasing to 8.4 Gy when the STP approach was used (p<0.05). The mean doses at the International Commission on Radiation Units and Measurements Report 38 bladder and rectal points were both 4.5 Gy with CTP and increased to 4.9 and 5.0 Gy, respectively using STP (p<0.05). Our table of dose rates showed significant dose rate dependency on the applicators geometry.
Our study shows that if the STP approach had been used, a significantly higher dose would have been delivered, and that STP tables accounting for differences in implant geometry should be carefully considered.
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ABSTRACT: To present issues to be considered in, and make proposals for, image-based brachytherapy for cervical cancer. The Image-Guided Brachytherapy Working Group, consisting of representatives from the Gynecology Oncology Group (GOG), Radiologic Physics Center (RPC), American Brachytherapy Society (ABS), American College of Radiology (ACR), American College of Radiology Imaging Network (ACRIN), American Association of Physicists in Medicine (AAPM), Radiation Therapy Oncology Group (RTOG), and American Society for Therapeutic Radiology and Oncology (ASTRO), proposed guidelines for image-based brachytherapy for cervical cancer. This report was based on their aggregate clinical experience and a review of the literature. It reflects only the personal opinions of the authors and is not meant to be an endorsement from any of the above organizations. The Group recommended T(2)-weighted MRI using a pelvic surface coil with MRI-compatible brachytherapy applicators in place for image-based intracavitary brachytherapy for cervical cancer. Imaging must be performed with the patient in the treatment position, with all other treatment conditions duplicated as closely as possible. Future use of positron emission tomography or positron emission tomography/CT may obviate the need for special applicators. The group proposed the following terminology for image-based brachytherapy. The GTV((I)) is defined as the gross tumor volume as defined through imaging, GTV is defined as the GTV((I)) plus any clinically visualized or palpable tumor extensions, and GTV + cx is defined as the GTV plus the entire cervix. The dose-volume histograms (DVH) of the GTV, GTV((I)), GTV + cx should be performed, and the dose to 100%, 95%, or 90% of the GTV (D(100), D(95), and D(90), respectively) and the percentage of the GTV covered by Point A dose (V(100)) should be reported. Similarly, the DVH of the bladder and rectum wall should be performed, and the maximal dose at any point within the bladder and rectal wall should be reported, along with the maximal dose to a contiguous 1, 2, and 5 cm(3) volume of the bladder and rectum, respectively. In addition, the dose at the International Commission on Radiation Units and Measurements reference point for the bladder and rectum should be reported. The Group thought that the current dose prescription method in use for cervical cancer brachytherapy (i.e., to prescribe to Point A in most institutions) should not be changed as yet, because image-based dosimetry is not ready for routine practice. The Group proposes that for research purposes, individual centers and cooperative groups (e.g., GOG, RTOG, ACRIN) collect image-based dosimetry information and perform DVHs and correlate these data with the clinical outcome to determine which of the above parameters are relevant. The Group encourages external funding for image-based dosimetry and recommends that brachytherapy manufacturers develop image-compatible applicators. Although current institutional brachytherapy prescription for cervical cancer should continue, image-based data collection and analysis are needed to optimize cervical cancer brachytherapy. Proposals are made for research in image-based brachytherapy for cervical cancer.International Journal of Radiation OncologyBiologyPhysics 12/2004; 60(4):1160-72. · 4.52 Impact Factor
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ABSTRACT: The reproducibility of high dose rate gynaecological brachytherapy applicator position in the same patient at repeated treatments has been studied. Measurements on antero-posterior and lateral radiographs to detect relative positions of tube and ovoid to the bony pelvis, bladder and rectum were made. Major variations within the same patient in craniocaudal positioning of the applicators and in antero-posterior movement was seen. The position of the anterior rectal wall was found to move a median of 10.5 mm (range, 0-22) in relation to the ovoid source between first and second insertions. These changes can be accounted for in differences in technique between first and second insertion and in particular the use of posterior vaginal packing and exterior clamping. The importance of individual dosimetry for each high dose rate insertion is clear with major differences in dosimetry to critical normal structures having been found.Radiotherapy and Oncology 08/1996; 40(1):59-62. · 4.52 Impact Factor
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ABSTRACT: This retrospective analysis aims to report results of patients with cervix cancer treated by external beam radiotherapy (EBR) and high-dose-rate (HDR) brachytherapy. From September 1992 to December 1996, 138 patients with FIGO Stages II and III and mean age of 56 years were treated. Median EBR to the whole pelvis was 45 Gy in 25 fractions. Parametrial boost was performed in 93% of patients, with a median dose of 14.4 Gy. Brachytherapy with HDR was performed during EBR or following its completion with a dose of 24 Gy in four weekly fractions of 6 Gy to point A. Median overall treatment time was of 60 days. Patient age, tumor stage, and overall treatment time were variables analyzed for survival and local control. Cumulative biologic effective dose (BED) at rectal and bladder reference points were correlated with late complications in these organs and dose of EBR at parametrium was correlated with small bowel complications. Median follow-up time was 38 months. Overall survival, disease-free survival, and local control at 5 years was 53.7%, 52.7%, and 62%, respectively. By multivariate and univariate analysis, overall treatment time up to 50 days was the only statistically significant adverse variable for overall survival (p = 0.003) and actuarial local control (p = 0.008). The 5-year actuarial incidence of rectal, bladder, and small bowel late complications was 16%, 11%, and 14%, respectively. Patients treated with cumulative BED at rectum points above 110 Gy(3) and at bladder point above 125 Gy(3) had a higher but not statistically significant 5-year actuarial rate of complications at these organs (18% vs. 12%, p = 0.49 and 17% vs. 9%, p = 0.20, respectively). Patients who received parametrial doses larger than 59 Gy had a higher 5-year actuarial rate of complications in the small bowel; however, this was not statistically significant (19% vs. 10%, p = 0.260). This series suggests that 45 Gy to the whole pelvis combined with four fractions of 6 Gy to point A with HDR brachytherapy is an effective and safe fractionation schedule in the treatment of Stages II and III cervix cancer if realized up to 50 days. To decrease the small bowel complications, we decreased the superior border of the parametrial fields to the S2-S3 level and the total dose to 54 Gy.International Journal of Radiation OncologyBiologyPhysics 09/2001; 50(5):1123-35. · 4.52 Impact Factor