Gynecologic OncologyDose distribution of brachytherapy for locally advanced (stage IIB) cervical cancer
Introduction
The traditional radiotherapy mode of combining external radiotherapy with intracavitary(IC) brachytherapy normalized to Point A has been adopted for over 100 years in treating locally advanced cervical cancer, and its efficacy has proven to be superior ([1], [2], [3], [4]). In recent years, image-guided adaptive brachytherapy has played an increasingly important role in the local control of tumors and the reduction of toxic side effects to normal tissues ([5], [6]). Image-guided adaptive brachytherapy assesses the size of the tumor, based on imaging techniques such as CT and MRI performed during diagnosis and brachytherapy, as well as gynecological examinations. The target is subsequently delineated according to the actual size of the tumor, and an individualized plan is created based on the tumor and the normal tissue organs ([7], [8], [9], [10], [11], [12]).
At present, combined IC and interstitial (IS) implant is an important technique in image-guided brachytherapy for cervical cancer. This method adds extra implant needles on the basis of the traditional model of oval body, circulator, vaginal column, and the vagina and has been demonstrated to be effective for patients with large tumors or 7 parauterine infiltrations ([13], [14], [15]). Report 89 of the International Commission on Radiation Units and Measurements (5, 13, 16) suggested that in combined IC and IS (IC/IS) brachytherapy, the contribution of the IC component should reach at least 80–90% of the total dose, whereas that of the IS component should be limited to 10–20%. Such dose limitation requires additional implant needles to be added beyond those in the original cavity (uterine tandem and ovoid) as a dose supplement to the IC areas that have received an insufficient dose. Combined intrauterine cavity and IS implant can achieve a good dose distribution in patients with large local masses, irregular tumors, and severe parauterine infiltrations, as the high-risk (HR) clinical target volume (CTV) D90 and dose distribution of the target area can be nearly perfect. However, the dose contributed by the IC treatment is minor, and the dose to the central region of the cervix is lower than that of IC treatment alone. Some studies have already investigated the low-dose issue in the central region of the cervix (17, 18).
To solve the problem of insufficient dose in the central region of the cervix during IS implant, our center adopted an inverse optimization method that adds a local boost to the central cervical area to escalate the dose to that area. In this study, the dosimetric advantage of adding a local boost to HR-cervix during combined IC/IS implant was described. In addition, the dosimetric differences of four different planning methods were compared: IC brachytherapy using two different planning methods: IC (Point A) and IC (three-dimensional [3D]); and combined IC/IS brachytherapy using two methods: IC/IS and IC/IS + HR-cervix local boost.
Section snippets
Patient characteristics
A total of 46 patients with locally advanced cervical cancer (International Federation of Gynecology and Obstetrics stage IIB) seen between August 2017 and April 2018 were enrolled in the study. Inclusion criteria included a lack of clear tumor regression after 45 Gy/25 F external radiotherapy (intensity-modulated radiotherapy), local lesion size ≥5 cm, and no prior treatment with brachytherapy. All work described here has been carried out in accordance with the International Code of Medical
Results
The main findings are outlined below. First, compared with the IC/IS group (Table 1), the relative uterine tandem dwell time of the IC/IS + HR-cervix group was significantly extended (p < 0.001). In addition, the V150 and V200 volumes of HR-cervix increased significantly (p < 0.001), from the original 63.94% and 30.80% of the IC/IS group to 91.54% and 64.06%, respectively. These results indicate that when using a combined IC/IS implant to treat locally advanced cervical cancer, a locally
Discussion
Brachytherapy is an important tool in treating locally advanced cervical cancer. Traditional 2D (Point A) 3-catheter IC brachytherapy now has over 100 years of application history, and its efficacy has been proven to be superior ([2], [3], [4]). In recent years, with the continuous and rapid development of medical imaging and brachytherapy technologies, image-guided 3D brachytherapy and combined IC/IS implants have become the major techniques for treating locally advanced cervical cancer and
Disclosure
The authors report no proprietary or commercial interest in any product mentioned or concept discussed in this article. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
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