|Year : 2018 | Volume
| Issue : 3 | Page : 230-232
A dosimetric comparison between applicators used for brachytherapy in carcinoma cervix – A single-institute prospective study
Aparna Suryadevara, M Vijay Kumar, E Vasundhara, Krishnam R Alluri, Shabbir Ahamed, Srikanth Guduru
Department of Radiation Oncology, Basavatarakam Indo American Hospital and Research Institute, Hyderabad, Telangana, India
|Date of Web Publication||28-Jan-2019|
Dr. Aparna Suryadevara
Department of Radiation Oncology, Basavatarakam Indo American Hospital and Research Institute, Hyderabad, Telangana
Source of Support: None, Conflict of Interest: None
INTRODUCTION: Cervical cancer is the second most common cancer among Indian women. Radical radiotherapy with external beam radiation therapy (EBRT) and brachytherapy is the standard treatment for FIGO stage IB2 to IVA. An appropriate selection of brachytherapy applicator is needed according to the patient's anatomy. The two most commonly used applicators for intracavitary radiotherapy (ICR), Fletcher's and Henschke, have dosimetric differences which are not well studied with two-dimensional (2D)-based planning which is the most common method used for women with carcinoma cervix in India. The purpose of our study was to compare and evaluate the dosimetric differences between these two applicators, which would help in better selection of the applicator in cervical cancer patients. MATERIALS AND METHODS: This is a single-institute prospective study. Fifty patients randomly included in the study received EBRT and ICR by Ir192 HDR remote afterloading technique with computer-based 2D planning. Fletcher's and Henschke applicators were used alternately for first two fractions. RESULTS: The results of the study showed lower bladder and rectal doses with Fletcher's applicator and similar doses to point A for both applicators. However, point B doses are lower with Fletcher's applicator. CONCLUSION: Our results showed a favorable dosimetry with Fletcher's applicator in ICR of carcinoma cervix. The feasibility of placement is much better for Henschke but dosimetric advantages of Fletcher's encourage use of Fletcher's applicator for patients with favorable anatomy to reduce organs at risk doses but with the disadvantage of lower dose to point B.
Keywords: Applicators, brachytherapy, cervix, India
|How to cite this article:|
Suryadevara A, Kumar M V, Vasundhara E, Alluri KR, Ahamed S, Guduru S. A dosimetric comparison between applicators used for brachytherapy in carcinoma cervix – A single-institute prospective study. Indian J Cancer 2018;55:230-2
|How to cite this URL:|
Suryadevara A, Kumar M V, Vasundhara E, Alluri KR, Ahamed S, Guduru S. A dosimetric comparison between applicators used for brachytherapy in carcinoma cervix – A single-institute prospective study. Indian J Cancer [serial online] 2018 [cited 2019 Feb 15];55:230-2. Available from: http://www.indianjcancer.com/text.asp?2018/55/3/230/250901
| » Introduction|| |
Cervical cancer is the second most common cancer after breast cancer among Indian women., Radical chemoradiotherapy with external beam radiation therapy (EBRT) and brachytherapy is the standard treatment for FIGO stage IB2 to IVA., An appropriate selection of brachytherapy applicator for intracavitary radiotherapy (ICR) in carcinoma cervix is needed according to the patient's anatomy.
The two commonly used applicators in ICR of cervix are Fletcher's applicator and Henschke's applicator. The conventional Fletcher's applicator has a stainless steel tandem and two colpostats or ovoids which are fixed to hollow handles for loading of radioactive sources. The rigid tandem used in Fletcher's applicators has curvatures like 15°, 30°, or 45°.,, The Henschke's applicator also has tandem and colpostats which are rigid and fixed to hollow handles, but the axes of vaginal radioactive sources are parallel to the intrauterine source while in Fletcher's applicator they are transverse.
The dose distribution for these two applicators is different, particularly with reference to the rectum and bladder doses. These differences were studied in two studies, with small sample size and conflicting results on computed tomography (CT)-based brachytherapy planning systems. The literature on the two-dimensional (2D) planning with two different applicators is limited and reviewed for different radiation treatment regimens and radionuclides than those followed today.
The differences in brachytherapy applicators is not well studied with 2D-based planning which is the most common method used for carcinoma cervix in India. The purpose of our study was to compare and evaluate the dosimetric differences between the two applicators, namely, Henschke and Fletcher, for better selection of the applicator in cervical cancer patients.
| » Materials and Method|| |
This is a single-institute prospective study done on carcinoma cervix patients diagnosed and treated at our institute from June 2016 to May 2017. Our institute is a cancer hospital and research center, treating about 600–700 carcinoma cervix patients per year. We treat the patients with 50 Gy in 25 fractions EBRT and ICR of 21 Gy in three fractions by Ir192 HDR remote afterloading technique. Brachytherapy is incorporated during EBRT treatment depending on the treatment response.
Fifty patients with carcinoma cervix were included in the study. Any patient with favorable anatomy for placement of Fletcher's applicator was included in the study. The study was done in two phases, first in June–August 2016 with 20 patients, followed by phase 2, where 30 patients were included (from March to May 2017). They were on EBRT and receiving ICR starting at 30 Gy of EBRT, based on treatment response, as an institute protocol. All patients were assessed clinically and treated with Ir192 HDR remote afterloading technique with a dose of 7 Gy per fraction to point A, total of 21 Gy after simulation and computer-based 2D planning performed by BrachyVision treatment planning system using TG-43 dose calculation formalism, using ICRU 38 point-based dosimetry.
All study patients were treated with ICR using Fletcher's and Henschke's applicators alternately for the first two fractions. The applicator with favorable dosimetric parameters was used for the third ICR treatment. The ICR treatments were given 1 week apart and all ICR applications were done by the same radiation oncologist, to decrease the variability in applicator placement. Simulation was done for both applicators, and planning was done by the same physicist and reviewed by a second physicist, to minimize variations in planning. All the plans were reevaluated at the end of the study and analyzed for tumor and organs at risk (OARs) doses. The bladder doses were calculated using the ICRU 38 bladder point.
The bladder point is identified by inflating the bulb of Foley catheter with 7 cc volume of radiopaque dye. The bladder point is located in the AP radiograph at the center of the Foley bulb, and in the lateral radiograph it is located on a line passing through the center of the bulb at the posterior surface.
The rectal doses at our institute are calculated at the modified ICRU rectal point. The modified ICRU rectal point is calculated after placement of rectal tube with radiopaque rectal dummy for calculation as shown in [Figure 1].
|Figure 1: The ICRU 38 rectal point (RL ICRU) and modified ICRU rectal point (RL ICRU M), which is used in this study|
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The modified ICRU rectal point is identified in AP radiograph on a line joining the centers of the right and left femoral heads at the intersection of the rectal marker, and in lateral radiograph it is identified at the same level on the rectal marker. In [Figure 1], the modified ICRU rectal point (RL ICRU M) used in the study is shown in the lateral radiograph. In this patient, vaginal packing was done with radiopaque contrast material (liquid barium) to show the ICRU rectal point (RL ICRU) which is identified as 0.5 cm from the posterior wall of vagina at the level of line drawn through the center of ovoids. Statistical analysis was done using paired t-test method and a P < 0.05 was considered as statistically significant.
| » Results|| |
There were totally 50 patients in the study. The median age of the patients was 45 years. There were 30 patients with stage IIB disease while the remaining presented with stage IIIB disease. The results of the study are summarized in [Table 1] and [Figure 1], [Figure 2], [Figure 3]. On comparing the brachytherapy plans for Fletcher's and Henschke's applicators, the OAR doses were lower for Fletcher's applicator. The results were statistically significant for bladder (P = 0.0002) and rectum (P = 0.0178). Point B doses were lower (P = 0.0001) for Fletcher's applicator, but point A doses were not statistically different between the two applicators.
|Table 1: Results of dosimetry for the two types of applicators used in the study patients (n=50)|
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|Figure 2: The intarcavitary brachytherapy plan for carcinoma cervix with Fletchers applicator. The tandem and ovoids are curved/angled posteriorly, decreasing doses to OARs|
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|Figure 3: The brachytherapy plan with Henschke applicator for the same patient|
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| » Discussion|| |
There are dosimetric differences in the two different applicators, Fletcher and Henschke, used for ICR in carcinoma cervix patients. But the literature identifying these dosimetric differences is sparse. There are two studies comparing the dosimetric differences between these two applicators with one favoring the Fletcher's and the other favoring the Henschke's applicator in relation to OAR doses., Among these two studies, one used the three-dimensional (3D) CT-based planning and showed the dosimetric advantages of Fletcher's over Henschke's applicator  while the second study used 2D dosimetry based on ICRU 38 points, showing advantages of Henschke's over Fletcher's applicator.
Our study showed lower point B doses with Fletcher's applicator, similar to the study done on 3D CT-based planning by Basu et al. Our results also showed a favorable dosimetry with Fletcher's applicator for OAR doses. Fletcher's applicator used at our institute is a 30° angled applicator. This curvature, as shown in [Figure 2] and [Figure 3] gives favorable OAR doses, particularly for bladder. The lower bladder dose is due to the anisotropy of dose distribution arising from finite size of the source, that is, dose along the length source is lower as compared to that across the source (isodose dip at tip). As bladder and rectum lie along the length of the source in Fletcher geometry, an obvious decrease in dose is observed in comparison to Henschke. This could explain our results showing significantly lower bladder doses with Fletcher's over Henschke's applicator in ICR.
Overall, lower isodose volume is observed for Fletcher's applicator, due to its compact design, especially the distance between the outer surface of ovoids, than Henschke's. This is the reason for lower isodoses in entirety [Table 1], of Fletcher's applicator for a given point A dose.
During the placement of the applicator, the feasibility of placement is much better for Henschke's applicator due to its shape but dosimetric advantages of Fletcher's with lower OAR doses encourage us to use Fletcher's applicator for ICR in carcinoma cervix patients, but the disadvantage of lower dose to point B should also be noted. In addition, care must be taken during placement and removal of Fletcher's applicator, particularly in patients with narrow vagina.
The results of this study encourage the use of Fletcher's applicator for better OAR doses even in institutes using 2D dosimetric planning system with Ir192-based HDR remote afterloading technique.
The studies described in literature were single-institute studies and gave conflicting results., This study is also a single-institute prospective study. But the sample size in our study was big (n = 50) compared to other dosimetric studies (n = 20) described in literature. However, the curvature and other parameters are not very clear in the literature, which have been mentioned in this study. Further studies with other Fletcher's applicators need to be done, as variations in the applicator curvature and angulations could affect the dosimetry.
| » Conclusion|| |
There are dosimetric differences between the two applicator types used in intracavitary brachytherapy in carcinoma cervix. Fletcher's applicator gives lower OAR doses, without compromising the dose at point A and is the preferred applicator for patients with favorable anatomy if we desire lower OAR doses but with the disadvantage of lower point B doses.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3]