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 Table of Contents  
ORIGINAL ARTICLE
Year : 2022  |  Volume : 13  |  Issue : 4  |  Page : 242-246

The dosimetric comparison between tandem-ovoid and tandemring applicator in cervical cancer brachytherapy


1 Department of Radiation Oncology, Tata Main Hospital, Jamshedpur, Jharkhand, India
2 Department of Radiation Oncology, Meherbai Tata Memorial Hospital, Jamshedpur, Jharkhand, India

Date of Submission30-May-2022
Date of Decision07-Jul-2022
Date of Acceptance30-Jul-2022
Date of Web Publication04-Nov-2022

Correspondence Address:
Dr. Neelima Pokala
Department of Radiation Oncology, Meherbai Tata Memorial Hospital, Jamshedpur, Jharkhand
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jrcr.jrcr_35_22

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  Abstract 

Aim: The study aims to evaluate the differences in dosimetry between tandem-ovoid (TO) and tandem-ring (TR) gynecologic brachytherapy applicators using different optimizing techniques in image-based brachytherapy. Background: Conventionally, TO applicators are in use to deliver doses to tumor in intracavitary brachytherapy. Nowadays, different types of applicators are available for cervical cancer brachytherapy treatment such as TR, tandem-cylinder, hybrid intracavitary, and interstitial applicators. Materials and Methods: In the present study, we used a TR and Fletcher-style TO applicator in the same patient, in two different sessions of brachytherapy. Four plans were generated for each patient, utilizing two different optimization techniques for each applicator used. A dose of 9 Gy (Gray) was prescribed and plans were normalized to left point A, and in other techniques, the optimization is done to achieve the recommended organ at risk (OAR) dose–volume constraints. Dose–volume and dose point parameters were compared. Results: The results indicate that the (OAR doses assessed by dose–volume histogram criteria were lower than the International Commission on Radiation Units and Measurements (ICRU) point doses for bladder and rectum with both TO and TR applicators for point A normalized plans. Both bladder and sigmoid received higher doses in TO than in TR but were statistically not significant (NS), but the rectum doses are higher in TR than in TO and it was statistically significant. The isodose volumes are higher in point A normalized plans than in OAR-based optimized plans in both applicators. The ICRU point doses are lower in OAR optimized plans than in point A normalized plans in both applicators. Conclusions: TO and TR applicators are commonly used gynecological intracavitary applicators. In this present study we did not find any significant difference between doses delivered to ICRU Point and Isodose volumes, after using both applicators .Critical OAR doses were also comparable. The only advantage of the ring applicator is, it provides an additional degree of freedom to load the vaginal sources over the ovoids and easy application in cases of narrow fornices with greater reproducibility.

Keywords: Applicators, brachytherapy, cervix cancer, dosimetry, optimization techniques, tandem-ovoid, tandem-ring


How to cite this article:
Prakash A, Mandal K, Pokala N, Amanapu GR. The dosimetric comparison between tandem-ovoid and tandemring applicator in cervical cancer brachytherapy. J Radiat Cancer Res 2022;13:242-6

How to cite this URL:
Prakash A, Mandal K, Pokala N, Amanapu GR. The dosimetric comparison between tandem-ovoid and tandemring applicator in cervical cancer brachytherapy. J Radiat Cancer Res [serial online] 2022 [cited 2022 Dec 4];13:242-6. Available from: https://www.journalrcr.org/text.asp?2022/13/4/242/360472


  Introduction Top


Cervical cancer is the third-most common cancer and the second-most leading cause of death in the Indian population.[1] Most of the patients present with locally advanced stage at presentation, and it is associated with high mortality. Concurrent chemoradiation is the mainstay of curative treatment of locally advanced cervical cancers.[2] The external beam radiation includes pelvic lymph nodes, parametria, and primary tumor, to a dose adequate to control only microscopic disease, so the addition of brachytherapy is crucial to achieving a high dose to the gross tumor to improve disease control and survival.[3] It is the only way to provide high dose to the tumor, required to control cervical cancer (>85–90 Gy), sparing the surrounding normal structures without causing undue side effects.[4] Brachytherapy plays an anchor role in the management of cervical cancer and intracavitary brachytherapy (ICBT) remains the most commonly practiced form of cervical brachytherapy treatment.

High-dose-rate (HDR) brachytherapy enables short treatment times and the ability to optimize the dose distribution by changing dwell times and allows greater control of the dose distribution.[5] A choice of the applicator is rather arbitrary and depends on availability, patient's pelvic anatomy, and extent of disease. Hence, the selection of an appropriate applicator according to the anatomy is needed.[6] The most commonly used type of applicator for curative definitive cervical cancer brachytherapy is the tandem-ovoid (TO) applicator, followed by the tandem-ring (TR) applicator. TO treatment offers a range of sizes and allows for configuration adjustment, whereas the advantages of the TR application include the different loading positions and repeatability due to its compact configuration.[7]

Objectives

The recommended dose–volume objective for clinical target volume is to deliver a minimum of 100% of the prescribed dose to 90% volume of the clinical target volume. Moreover, recommended dose–volume constraints for organs at risk (OARs) are: <75 Gy EQD2–2cc volume of the contoured rectum and sigmoid colon and <90 Gy EQD2–2cc volume of contoured of the urinary bladder. Our study aims to compare dose–volume and point dose parameters in both applicators on the same patient. Here, we used two planning techniques as 9 Gy to left point A and optimized using graphical optimization to achieve the recommended OAR dose–volume constraints.


  Materials and Methods Top


In our study, 20 patients were included during October 2020–July 2021, aged 40–70 years, with cancer of the cervix FIGO (International Federation of Gynecology and Obstetrics (FIGO) uterine cervical cancer staging system) Stages II–IVa.

Patient characteristics

  • Total cases: 20
  • Mean age: 51 years
  • Staging: II-IV a
  • Histopathology: Squamous cell carcinoma.


All patients received external beam therapy to the whole pelvis at a dose of 50 Gy in 25 fractions on Varian TrueBeam machine by 3D-conformal radiotherapy technique along with the weekly intravenous injection of cisplatin 40 mg/m2. External beam radiation therapy was followed by clinical evaluation and two brachytherapy sessions by Ir192 of 9 Gy each to point A, with a gap of 1 week.

The procedure was carried out in the HDR room (High Dose Rate Brachytherapy Room) in lithotomy position after sedation. A Foley's catheter was placed and the balloon was filled with 7cc of contrast (2cc contrast with 5cc distilled water). Intracavitary brachytherapy (ICBT) application was done, either with tandem and ovoid or tandem and ring applicator. The type of applicator and sequence of insertion were randomly assigned.[8] Patients were randomly assigned to receive the first insertion using either ring or ovoid applicator and the other type is used for the second insertion [Figure 1].
Figure 1: (a) Tandem-ovoid applicators. (b) Tandem-ovoid applicator insertion in patient with isodose line. (c) Tandem-ring applicators. (d) Tandem-ring applicator insertion in patient with isodose line

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Tandem was selected between 15° and 30° depending on the anatomy of the cervix. The appropriate length of the tandem was determined by uterine sound and placed after dilatation of the cervical canal. For applications, 4 cm and 6 cm tandem lengths were commonly used. The most common size of the ovoid for TO applications was 2.5 cm. The most common tandem angle used for TO and TR applicators was 30°. Vaginal packing was done adequately to displace the rectum and bladder. Computed tomography simulation was done for all patients and 3 mm slices were taken for planning. The urinary bladder inclusive of the Foley's catheter bulb, bladder, rectum, and sigmoid was countered as OAR. The International Commission on Radiation Units and Measurements (ICRU) reference points, namely point A (right and left), left point B, bladder, and rectal points.

Planning was done on the Eclipse planning system by Varian. A 3D plan was generated after the reconstruction of the applicators. After catheter reconstruction, activation of dwell positions was done in the same pattern for both applicators. A standard loading pattern was followed for both TO and TR applicators [Table 1]. Usually, we prefer a 9 Gy dose to point A. As described above, four plans were created by a physicist for two insertions and saved for each patient for dosimetric comparison. Dose–volume histograms were generated and D2cc (dose to 2cc volume), D1cc (dose to 1cc volume), and D0.1cc (dose to 0.1cc volume) were recorded for the bladder, rectum, and sigmoid. V 90 (volume covered by 90% isodose), V 100 (volume covered by 100% isodose), and V 200 (volume covered by 200% isodose) were documented. Dose point parameters such as bladder point, rectal point, point A, and point B doses were recorded for both the applicators.
Table 1: Dwell positions for both applicators

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Statistical analysis

For data analysis, we used GraphPad Prism 8.4 (GraphPad Software Inc, San Diego, California, USA). Statistical analysis was performed using paired t-test to assess the relationship between dosimetric values of TO and TR applicators.


  Results Top


In our study, we compared both applicators by creating plans with two different optimization techniques. Details of 40 ICBT applications in 20 patients were analyzed.

Point A normalization plans comparison for both applicators

ICRU point doses with TR and TO applicators are shown in [Table 2]. There was no statistically significant difference with both applicators except rectal point dose and the standard error of difference = 0.288.
Table 2: International Commission on Radiation Units and Measurements point doses with tandem-ring and tandem-ovoid applicators in point A normalization plans

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Volumetric OAR doses, D2cc, D1cc, and D0.1 cc to the bladder, rectum, and sigmoid are shown in [Table 3]. There was no statistically significant difference with both applicators in terms of OAR doses. The difference in D2cc rectum doses is considered to be statistically significant and the difference in D1cc and D0.1cc of the rectum is considered to be not statistically significant. The standard error of difference = 0.366 for D2cc of the rectum.
Table 3: Organ at risk doses with tandem-ovoid and tandem-ring applicators in point A normalization plans

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Volumes treated with different isodose lines are shown in [Table 4]. There was no statistically significant difference with both applicators for volumes such as V90, V100, and V200.
Table 4: Volumes of different isodose lines in point A normalization plans

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Optimized plans (with recommended organ at risk constraints)

ICRU point doses with TR and TO applicators are shown in [Table 5]. There was no statistically significant difference with both applicators except rectal point dose and the standard error of difference = 0.287.
Table 5: International Commission on Radiation Units and Measurements point doses with tandem-ovoid and tandem-ring applicators in optimized plans

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Volumes treated with different isodose lines are shown in [Supplementary Table 1]. There was no statistically significant difference with both applicators for volumes such as V90, V100, and V200.




  Discussion Top


The geometry of both applicator systems is different even though both are based on the Manchester system. The TO application system consists of three applicators and has flexible geometry as the separation and the relative longitudinal position of the applicators can be adjusted. The ring applicator system is a fixed-geometry two-applicator system, where the tandem and the single ring applicator can be fixed only at a particular slot.

Erickson et al., in their study, showed significantly higher bladder and rectal point doses with TO applicator compared to TR applicator, and brachytherapy planning was X-ray based in their study.[9],[10] However, in our study, since brachytherapy planning was CT-based we documented volumetric doses such as D2cc, D1cc, and D0.1cc to OARs such as the rectum, bladder, and sigmoid. The present study shows a significantly higher bladder and sigmoid dose with the TR applicator but is statistically NS.

A study by Rangarajan et al. and Levin et al. showed that there were no significant differences in point A dose and OAR doses with both TR and TO applicators. The TR applicators treated a smaller volume compared to TO applicators and the difference was statistically significant.[11],[12] Even though in our study, there is no difference in point A doses and OAR doses except rectum doses with both TR and TO applicators and a significantly larger treatment volume with the TO applicator.

The Vinin et al.'s study showed no significant difference in point A dose, volumetric OAR doses, and volumes treated with different isodose with TR and TO applicators and suggested that both applicators are dosimetrically equivalent.[13] In our study, both applicators using both optimizing techniques also show similar results except rectum doses and treatment volumes.


  Conclusions Top


TO and TR applicators are commonly used gynecological intracavitary applicators. Our study shows that they delivered the same point doses, and critical organ doses were comparable. The only advantage of the ring is, it provides an additional degree of freedom to load the vaginal sources over the ovoids and easy application in cases of narrow fornices with greater reproducibility.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
  References Top

1.
Sung H, Ferlay J, Siegel RL, Laversanne M, Soerjomataram I, Jemal A, et al. Global cancer statistics 2020: GLOBOCAN estimates of incidence and mortality worldwide for 36 cancers in 185 countries. CA Cancer J Clin 2021;71:209-49.  Back to cited text no. 1
    
2.
Chopra S, Gupta M, Mathew A, Mahantshetty U, Engineer R, Lavanya G, et al. Locally advanced cervical cancer: A study of 5-year outcomes. Indian J Cancer 2018;55:45-9.  Back to cited text no. 2
[PUBMED]  [Full text]  
3.
Banerjee R, Kamrava M. Brachytherapy in the treatment of cervical cancer: A review. Int J Womens Health 2014;6:555-64.  Back to cited text no. 3
    
4.
Viswanathan AN, Beriwal S, De Los Santos JF, Demanes DJ, Gaffney D, Hansen J, et al. American Brachytherapy Society consensus guidelines for locally advanced carcinoma of the cervix. Part II: High-dose-rate brachytherapy. Brachytherapy 2012;11:47-52.  Back to cited text no. 4
    
5.
Uyeda M, Friedrich F, Pellizzon AC. High dose rate (HDR) brachytherapy in gynecologic cancer regression: A review of the literature. Appl Cancer Res 2018;38:1-5.  Back to cited text no. 5
    
6.
Viswanathan AN, Thomadsen B, American Brachytherapy Society Cervical Cancer Recommendations Committee, American Brachytherapy Society. American Brachytherapy Society consensus guidelines for locally advanced carcinoma of the cervix. Part I: General principles. Brachytherapy 2012;11:33-46.  Back to cited text no. 6
    
7.
Gursel SB, Serarslan A, Meydan AD, Okumus N, Yasayacak T. A comparison of tandem ring and tandem ovoid treatment as a curative brachytherapy component for cervical cancer. J Contemp Brachytherapy 2020;12:111-7.  Back to cited text no. 7
    
8.
Brachytherapy Techniques and Systems. J ICRU 2013;13:21-35. doi: 10.1093/jicru/ndw008. PMID: 27335475.  Back to cited text no. 8
    
9.
Nag S, Erickson B, Thomadsen B, Orton C, Demanes JD, Petereit D. The American Brachytherapy Society recommendations for high-dose-rate brachytherapy for carcinoma of the cervix. Int J Radiat Oncol Biol Phys 2000;48:201-11.  Back to cited text no. 9
    
10.
Erickson B, Jones R, Rownd J, Albano K, Gillin M. Is the tandem and ring applicator a suitable alternative to the high dose rate selectron tandem and ovoid applicator? J Brachyther Int 2000;16:131-44.  Back to cited text no. 10
    
11.
Rangarajan R. Dosimetric evaluation of image based brachytherapy using tandem ovoid and tandem ring applicators. Rep Pract Oncol Radiother 2018;23:57-60.  Back to cited text no. 11
    
12.
Levin D, Menhel J, Rabin T, Pfeffer MR, Symon Z. Dosimetric comparison of tandem and Ovoids vs. tandem and ring for intracavitary gynecologic applications. Med Dosim 2008;33:315-20.  Back to cited text no. 12
    
13.
Vinin NV, Dharmarajan A, Sahin PM, Jones J, Bharathan RK, Yahiya N, et al. Dosimetric comparison of tandem and ovoids with tandem and ring for intracavitary brachytherapy for carcinoma cervix. Oncol Radiotherapy 2019;1:039-42.  Back to cited text no. 13
    


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    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5]



 

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