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 Table of Contents    
ORIGINAL ARTICLE
Year : 2022  |  Volume : 47  |  Issue : 4  |  Page : 322-330
 

Commissioning and dosimetric results of an indigenously developed intra-vaginal template for interstitial plus intracavitary high dose rate image-guided brachytherapy of advanced cervix cancer


Division of Radiation Oncology, Medanta Cancer Institute, Medanta the Medicity, Gurgaon, Haryana, India

Date of Submission10-Jun-2022
Date of Decision23-Sep-2022
Date of Acceptance16-Oct-2022
Date of Web Publication10-Jan-2023

Correspondence Address:
Dr. Susovan Banerjee
Division of Radiation Oncology, Medanta Cancer Institute, Medanta the Medicity, Gurgaon, Haryana
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jmp.jmp_50_22

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   Abstract 

Aim: The goal of this study is to discuss the commissioning and dosimetric parameters achieved during the clinical implementation of an indigenously developed intracavitary (IC) plus interstitial (IS) template for high dose rate (HDR) image-guided brachytherapy (IGBT) in cancer (Ca) cervix. We want to discuss our achieved values of cumulative equi-effective doses (EQD2) for high-risk clinical target volume (HRCTV) and organ at risk (OAR) and compare it with available published results. Materials and Methods: Medanta anterior oblique/lateral oblique template has a total of 19 needles including the central tandem. For commissioning the template with needles, the indigenously made acrylic phantom was used. Oblique and straight needles were placed inside the acrylic phantom and a computed tomography (CT) scan was performed. Sixteen patients were treated in HDR IGBT using this template after external-beam radiotherapy. The IGBT plans were evaluated based on EQD2 of target coverage i.e., dose received by 98% (D98%_HRCTV), 90% (D90%_HRCTV), and 50% (D50%_HRCTV) volume of HRCTV, and dose received by 2 cc (D2cc) and 0.1 cc (D0.1cc) of OAR using linear quadratic (LQ) radiobiological model. Results: The autoradiographic in radiochromic film shows that the distance between the needle tip and the middle of the source position is 6 mm. The mean D98%_HRCTV and D90%_HRCTV was 76.8 Gy (range: 70-87.7 Gy, P < 0.01) and 84.49 Gy (range: 76.6-96.7 Gy, P < 0.01), respectively. Mean EQD2 of D2cc of the bladder, rectum, and sigmoid was 85.6 Gy (range: 77.5-99.6 Gy, P < 0.03), 74.3 Gy (range: 70.9-76.7 Gy, P < 0.05), and 58.3 Gy (range: 50.6-67.9 Gy, P = 0.01), respectively. The mean total reference air kerma at a 1 m distance is 0.489cGy (range: 0.391-0.681cGy). Conclusions: The indigenously developed template could attain satisfactory standards in terms of set parameters for commissioning and acceptable dose volume relations in our clinical use for treating the advanced Ca cervix patients who need IC + IS type of HDR IGBT. The comparative analysis with contemporary applicators was acceptable.


Keywords: Brachytherapy, cervix cancer, commissioning, high-risk clinical target volume


How to cite this article:
Kaliyaperumal V, Banerjee S, Kataria T, Abraham SK, Kamaraj D, Tamilselvan S, Gupta D, Bisht SS, Narang K, Shishak S. Commissioning and dosimetric results of an indigenously developed intra-vaginal template for interstitial plus intracavitary high dose rate image-guided brachytherapy of advanced cervix cancer. J Med Phys 2022;47:322-30

How to cite this URL:
Kaliyaperumal V, Banerjee S, Kataria T, Abraham SK, Kamaraj D, Tamilselvan S, Gupta D, Bisht SS, Narang K, Shishak S. Commissioning and dosimetric results of an indigenously developed intra-vaginal template for interstitial plus intracavitary high dose rate image-guided brachytherapy of advanced cervix cancer. J Med Phys [serial online] 2022 [cited 2023 Feb 5];47:322-30. Available from: https://www.jmp.org.in/text.asp?2022/47/4/322/367423



   Introduction Top


Cervical cancer is the second most common malignancy in the world, and it has an incidence of 8.4 among overall cancer in India.[1],[2] Brachytherapy (BT) should be an integral part of radiotherapy treatment for cancer (Ca) cervix and omitting it in radiotherapy of cancer cervix significantly worsens the local control and survival.[3],[4] A standard point A-based BT plan by the conventional intracavitary (IC) applicators is now considered inadequate, especially for advanced cancer cases. It not only fails to provide adequate target coverage in the advanced cases but also delivers an unacceptably high dose to the surrounding organs at risk (OARS) in many instances. Intracavitary (IC) plus interstitial (IS) applications are now validated through numerous studies in improving the target coverage but limiting OAR doses at the same time.[5] There are various templates and applicators available for the Ca cervix for high dose rate (HDR) image-guided BT (IGBT),[6] and generally, three types of templates/applicators are used for treating gynecological malignancies in HDR brachytherapy, namely (1) tandem and ovoid, (2) tandem and ring, and (3) cylinder and tandem. All such applicators have now been modified to accommodate IS needles for IC + IS applications. In such modified applicators, the sole principle has been to allow positioning of straight and divergent needles while preserving the basic structure. These modifications allow us to first plan a standard IC planning and subsequently modify it to IC + IS loading pattern to treat advanced cervix cases where the HRCTV volume is non-conforming within the standard pear shape dose cloud. Such advanced BT application and planning also allow a dose individualization for clinical target volumes (escalation/de-escalation) and sparing of OARs by catheter loadings.

In clinical situations of IGBT, where only IC loading has been used, the tandem-ring applicator provides better dosimetry for EQD2 for the D90 of HR-CTV and OAR (bladder and rectum) when compared to the tandem-ovoid applicator.[7] However, in the modified IC + IS applications, no applicator has proved itself superior to others in terms of dosimetric findings of clinical results. Precise quality assurance (QA) techniques for commissioning and applicator geometry for source placements and imaging modalities can reduce the dose uncertainties up to 4% in IC, image-guided cervical cancer BT using HDR Ir-192 as a source.[8] In commissioning and validation of any template or applicator used in IGBT, reconstruction of source channels is crucial, as a small error in needle reconstruction can lead to a larger dose uncertainty to the target and OARs. Hellebust et al.[9] studied some important parameters regarding uncertainties of commissioning and applicator reconstruction in 3D image-based treatment planning and stated that clear and correct methods should be adopted to minimize the geometrical errors which otherwise can lead to major dose deviations for target and OARs from the prescribed goals.

The International Commission on Radiation Units and Measurements report no 89 (ICRU89)[10],[11] states that IGBT for cervix cancer IC/IS, delivering the high radiation equieffective dose at 2 Gy (EQD2) of ≥5 Gy to the HRCTV could increase the local control up to ≥90% at 3 years in stage I and II and 85% in stage III and IV, respectively. Studies have shown better local control (90%-92%) with cumulative EQD2 of more than 84 Gy when compared to local control of around (82%) when the EQD2 is <84 Gy for patients with HRCTV volume is more than 30 cc.[12] The therapeutic outcome including target coverage and sparing of critical structures can be improved, if the dose is prescribed to an image-based CTV considering the OAR dosimetric constraints.[13]

With this concept in the background, we developed an indigenous applicator in our department for the treatment of advanced cervix cancer cases. The details are already published before.(14) Our applicator was subjected to multiple dosimetric studies including commissioning before clinical use.(15) The main aim of this study is to share our experience of commissioning the indigenous IC + IS applicator and to evaluate the dosimetric parameters achieved in our treated cases with this template. Another purpose of this study is to compare the cumulative EQD2 from external-beam radiotherapy (EBRT) and BT doses for HRCTV and OARs to standard published literature.


   Materials and Methods Top


Applicator design and initial dosimetric studies

Medanta anterior oblique/lateral oblique (MAOLO) intra-vaginal template has a total of 19 needles including the central tandem, with the diameter of 3 cm and 4 cm [Figure 1]a and [Figure 1]b. The medical-grade Teflon was used to make a template that has 2 mm diameter holes to accommodate the plastic needles (M/S Kalyani Radiotherapy Specialty India (P) Ltd) and 6 mm holes for inserting intra-uterine tandem made up of stainless steel (Elekta AB, Stockholm, Sweden) and this template can be reused after sterilization. The cylinder is symmetrical on the right and left sides and each side has three anterior-oblique (AO), three lateral obliques (LO), and two straight needles. One straight and two posterior needles are accommodated on the anterior and posterior sides of the cylinder to optimize the dose to the bladder and rectum regions. Three anterior needles on the right and left sides can create the ovoid shape dose distribution along with the central tandem. The lateral needles are used to extend the dose distribution from point A which covers the lateral parametrial residual disease which cannot be covered by the standard point A-based plan.[14] The superior part of the template has a 60° inclination from the anterior-posterior direction for proper fixation in the cervical internal orifice (OS). The angulation of AO needles from tandem is 17° and the LO needle has an angle of 16° from the proximal surface of the cylinder. The angulation of the LO needles is decided in such a way that it could cover the cervical parametrial region which is 3 cm from point A and the angulation was decided based on 21 clinically feasible HR-CTV drawings and its coverage (through planning simulation). The dosimetric study has been performed for various HRCTV volumes to verify the feasibility of target coverage of 3 cm and 4 cm template before implementing its clinical use.[15]
Figure 1: (a) Three-Dimensionally reconstructed indigenously developed template with interstitial needles with central tandem. (b) CAD of the IC + IS template (bisect view) with needles. CAD: Computer-aided design

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Template commissioning

The commissioning process is of paramount importance for the new applicator/template used for brachytherapy. The geometry and reference source position from the surface of the needle/applicator could be decided from this process and estimate the accurate needle positioning to avoid dosimetric uncertainty. For this, the indigenously made acrylic phantom was used with the cylinder [Figure 2]a and [Figure 2]b. AO, LO, and straight (each one) needle is placed to check the angulation and its dimension. CT scan with 1, 1.5, and 2 mm slice thickness was acquired with a radio-opaque marker inside the plastic needle, and images were exported to the BT treatment planning system (TPS). The needles were reconstructed with a tracking methodology (Oncentra Brachy version 4.6, Elekta AB, Stockholm, Sweden) and the tip of the needle was carefully marked. The plastic needle was positioned on graph paper and attached with radiochromic film [Figure 2]c (3a is Oncentra shots in the manuscript on page 16). The indexer length was determined using the source position simulator (Elekta AB, Stockholm, Sweden) and according to length the dwell time of 0.5 sec was executed with the corresponding position in the graph sheet. The total offset is calculated (distance between the needle tip and actual source position) based on the center point of the exposed source position in radiochromic film [Figure 2]d. After this commissioning, the applicator was considered for clinical use.
Figure 2: (a) Front view and (b) side view of the indigenously made phantom for applicator commissioning. (c) autoradiograph for the plastic interstitial needles and (d) needle offset determination with radiochromic film

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Patient selection and external-beam radiotherapy

Between March 2019 to February 2022, 16 patients with the International Federation of Gynecology and Obstetrics (FIGO) staging from IIB to IIIC2 who underwent HDR-BT using this template after EBRT were taken for this study. The median age of the patients was 62. On histopathology, the squamous cell carcinoma and adenocarcinoma were among 13 and 3 patients, respectively [Table 1]. All the patients received the dose of 45 Gy in 25 fractions in EBRT and nodal boost up to 60 Gy by IGRT technique. The treatment plan was made with volumetric modulated arc therapy (VMAT) in the linear accelerator (Infinity, TPS-Monaco® Elekta AB, Stockholm, Sweden) or Helical Tomotherapy (Accuray, TPS-Precision® Sunnyvale, CA, USA). The dosimetric parameters such as dose receiving 2 cc (D2cc) and 0.1 cc volume (D0.1cc) of bladder, rectum, and sigmoid were evaluated in EBRT using dose volume histogram (DVH) statistics. After the completion of EBRT, patients were assessed for BT based on post-EBRT clinical examination and MRI (done after 7 days from EBRT).[16] The use of the IC + IS template was considered when the patient was found to have distal parametrium in the post EBRT evaluations.
Table 1: Patient demographics (n=16)

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Brachytherapy procedure

HDR BT was delivered with Ir-192 (microSelectron HDR, Elekta AB, Stockholm, Sweden) in an integrated BT unit (IBU). Based on post-EBRT clinical findings, and MRI, the number of needles and the placement were preplanned. On the day of the BT procedure, transrectal ultrasonography (TRUS) was used to locate the OS and view the extent of residual disease and lateral parametrial involvement.[17] The length and angle of the central tandems were determined from the clinical examination and TRUS examination of the uterus. Once the intra uterine (IU) tandem with the angle of 15° or 30° (Elekta AB, Stockholm, Sweden) was inserted into the cervical OS, the cylinder assembly was placed through the distal end of the tandem. Thereafter the cylinder template was fixed with the central tandem by use of the indigenously developed customized lock having a total of three screws. The sterilized plastic needles (total length 21 cm) with sharp end were inserted in sequence as previously planned and the needles were simultaneously numbered using sterilized adhesive tape before inserting into template to avoid any uncertainty during treatment. For bladder filling, open catheterized with maximum drained out protocol was followed for all the patients and in rectum, the flatus rubber rectal tube was used. After the BT procedure, the patient underwent a CT scan with a slice thickness of 2 mm (Siemens biograph mCT, Siemens Healthcare GmbH, Germany). The HRCTV, bladder, rectum, and sigmoid were drawn in a BT treatment planning system (TPS) and catheter reconstruction was performed (Oncentra Brachy version 4.6.1, Elekta AB, Stockholm, Sweden). Using IU tandem and AO needles (on both sides), the point A (IC) based plan was created [Figure 3]a and [Figure 3]b. The dwell position of sources was chosen in the LO and straight needles within HRCTV avoiding the rectum, bladder and sigmoid with additional margin of 2 mm. The HRCTV-based plan [Figure 3]c and [Figure 3]d was made using manual optimization i.e., 10%-15% dwell times for the needle loading from the standard point A (IC) based plan.[18],[19]
Figure 3: Standard IC plan based on Point A using central tandem and AO needles in IC + IS template (a) coronal and (b) sagittal view. (c) Coronal view of target-based plan using IC standard plan with AO, LO, and straight needs loading (IS). (d) sagittal view of the HRCTV based plan. HRCTV: High-risk clinical target volume

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The plans were evaluated based on target coverage i.e., dose to 98% (D98%_ HRCTV), 90% (D90%_ HRCTV), and 50% (D50%_ HRCTV) volume of HRCTV and D2cc and D0.1cc of OARS using linear quadratic (LQ) radiobiological model. The α/β ratio of 10 and 3 were used for EQD2 calculation for target and OAR respectively. The plans were selected based on the criteria that total EQD2 (EBRT + BT) for D90%_ HRCTV should be >80 Gy and for rectum and sigmoid, D2cc EQD2 should be <75 Gy and for bladder, it should be <90 Gy.[20] Once the desirable plan was obtained, a verification of the indexer length using a source position simulator and catheter offset (in the TPS) was performed by the medical physicist. Generally, most of the patients were scheduled for two applications, 2 fractions of 6 Gy each (with the minimum gap of 6 h) were delivered in each application, thus delivering a total of 24 Gy in 4 fractions. Some patients (due to logistic and anesthetic risk) were treated at single application with a dose of 6 Gy into 4 fractions or 8 Gy into 3 fractions (with the minimum gap of 6 h maintained). The needle positions before each treatment were verified from skin markings and the C arm images obtained in our IBU. The dosimetric quantities for HRCTV, OARs, and other parameters were reported as per ICRU89.

Statistical analysis

Descriptive statistics for HRCTV and target parameters were evaluated and a dosimetric comparison was done between earlier published results[5],[21] and values calculated in this study for HRCTV and OARs. One-way ANOVA test was performed using IBM SPSS Statistics for Windows, version 24 (IBM Corp., Armonk, N. Y., USA) to analyze the mean difference and its significance. The data are statistically significant if the P < 0.05 and it was termed statistically significant


   Results Top


The autoradiographic for the plastic catheter in radio chromic film shows that the distance between the actual catheter and the middle of the source position is 6 mm [Figure 2]d. This study shows that the catheter reconstruction error was less in 1 mm CT slice thickness when comparing axial view to the sagittal and coronal section concerning 1.5 and 2 mm slice thicknesses. The mean D98%_ of HRCTV was 76.8 Gy EQD2 (range 70-87.7 Gy, SD = 4.48 Gy, P < 0.01). It was above 80 Gy for 3 patients (19%), 7 (44%), and 6 (37%) patients who received doses of 75-80 Gy and 70-75 Gy, respectively. Similarly, the mean D90%_ HRCTV and D50%_ HRCTV was 84.49 Gy (range: 76.6-96.7 Gy, SD = 5.4 Gy, P < 0.01) and 109.7 Gy (range: 97.2-112 Gy, SD = 8.8 Gy, P < 0.02), respectively [Figure 4]a and [Figure 4]b. Many studies[10],[11] show that the crucial parameter for determining the target coverage is D90%_ HRCTV. By using this template set, in our study 14 (88%) patients achieved a D90 of more than 80 Gy, and 2 patients (12%) were receiving 76 Gy EQD2 to the HRCTV [Table 2].
Figure 4: (a) EQD2 of D98% and D50% for HRCTV versus HRCTV (cc). (b) EQD2Gy of D90%_ HRCTV versus HRCTV (cc). EQD: Equieffective dose, HRCTV: High-risk clinical target volume

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Table 2: Dose-volume parameters of target and organ at risk

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While analyzing the dose received by the OARs, the bladder mean EQD2 dose for D2cc was 85.6 Gy (range 77.5-99.6 Gy, SD = 5.31 Gy, P < 0.03. The mean EQD2 of D0.1cc was 101.4 Gy (range 90.3-114.5-Gy, SD = 6.64 Gy, P < 0.004. Except for two patients (13%), all other 14 (87%) patients received an EQD2 of less than 90 Gy for the D2cc of the bladder. The two patients receiving the D2cc for the bladder were 99.61 Gy and 91.78 Gy [Figure 5]a. The mean dose to the D2cc of the rectum was 74.3 Gy (range: 70.9-76.7 Gy, SD = 1.66 Gy, P < 0.005. Ten (63%) patients received an EQD2 of less than 75 Gy when comparing the D2cc of rectum volume and the six (37%) patients exceeded the EQD2 of 75 Gy, but the maximum dose was within 77 Gy [Figure 5]b. The mean D0.1cc of the rectum was 87.43 Gy (range: 81.8-94.7 Gy, SD = 3.72 Gy, P < 0.01). Cumulative EQD2 of sigmoid D2cc received by Sigmoid was well within the tolerance level for all the patients. EQD2 to D2cc and D0.1cc of sigmoid was 58.3 Gy (range: 50.6-67.9 Gy, SD = 6.14 Gy, P = 0.01) and 66.1 Gy (range: 55.3-80.1 Gy, SD = 8.36 Gy, P < 0.02) respectively [Figure 5]c. The mean total reference air kerma (TRAK) at a 1 m distance is 0.491 cGy (range: 0.391-0.681 cGy, SD = 0.09).
Figure 5: (a) Cumulative (EBRT + BT) EQD2 of D2cc and D0.1cc for Bladder. (b) cumulative (EBRT + BT) EQD2 of D2cc and D0.1cc for the rectum. (c) cumulative (EBRT + BT) EQD2 of D2cc and D0.1cc for sigmoid. EQD: Equieffective dose, EBRT: External beam radiotherapy, BT: Brachytherapy

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   Discussion Top


We designed, dosimetrically verified, commissioned, and successfully implemented our template in the clinical practice of IGBT in cancer cervix treatment. The commissioning and dosimetric outcomes of the first 16 patients treated by the indigenously designed IC plus IS applicator were analyzed in this study. Several authors have discussed the applicator positional uncertainties and their impact on HDR BT dose distribution [22],[23],[24]. In our commissioning study, we found that the reconstruction of the needles should be based on sagittal and coronal sections with the help of axial CT images. The sagittal CT slices show the tip of the dummy markers exactly at the same point as in the axial section with a 1 mm slice thickness [Figure 6]a and [Figure 6]b. In 2 mm slice thickness, the actual position of the tip of the catheter was slightly deviated (1.6 mm) with the axial image but it could be taken care of by catheter offset in TPS. Due to limitations in the image artifacts and volume averaging effect, the 2 mm slice thickness should be used for reconstructing needles with the set offset value [Figure 6]c. The important parameter is the RO marker insertion and its distance (inside) from the tip of the plastic needle. In case, the RO marker is not reaching the tip of the plastic needle, the offset value of the needle is not correctly quantified. It is mandatory to ensure the insertion of the RO marker inside the plastic needles with an autoradiograph.
Figure 6: Catheter reconstruction uncertainty analysis using (a) 1 mm (b) 1.5 (c) 2 mm CT slice thickness

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Schindel J et al.[25] studied the dosimetric impacts due to applicator reconstruction and its displacement and his study found that the reconstruction error should be less than ± 1.5 mm to achieve a dose deviation within 10%. In our study, the radiochromic-based evaluation showed that the 6 mm offset was needed to correct the actual position of the source inside our plastic needles, but it may vary with different needle manufacturers. The plastic needles with the radio-opaque markers provided a better reconstruction ability when compared to the same exercise without the RO markers even in the CT-based planning. The main disadvantage while reconstructing the catheters without an RO marker (in CT images) is visualizing the tip of the plastic catheter. This uncertainty may provide an erroneous position of the plastic needle tip, and this problem may get compounded if the plastic needle tip is merged with air in the patient body cavity. In our study, all the patients were planned in 2 mm slice thickness images with needle offset (6 mm).

The Groupe Européen de Curiethérapie and the European Society for Radiotherapy and Oncology (GEC-ESTRO) recommend the target delineation in MRI as the gold standard. The CT-based delineation (with the use of complementary information from other imaging and clinical examination findings) of the HRCTV was proposed by several authors[26],[27],[28],[29] and has recently been accepted as a standard approach. This superior target coverage can give higher local control without any additional toxicity, especially in advanced cases with a residual disease where the HRCTV volume is >30 cc.[30] The ICRU89 recommends the reporting of the minimum target (equivalent dose to 2 Gy) dose and OAR dose for D0.1 cc and D2cc. The minimum dose to the target could represent the outer area of the target, D90% has been recommended for reporting due to random uncertainties for the absolute value of the minimum dose which is D100% and 10% of the target volume is omitted due to steep dose gradients at the edges of the target. Walter et al.[21] studied the IC + IS procedure using the Venezia® applicator and reported the mean D98%_ HRCTV and D90%_ HRCTV is 80.4 Gy and 90.7 Gy respectively. Further, the study stated that the IC plus IS type of applicator could provide a superior D90% for target coverage, and at the same time, it spares the normal structures when compared with standard IC applicators.[20]

In this study, with the use of this indigenously developed template, we achieved a mean dose of 76.8 Gy and 84.5 Gy to D98% and D90% of the HRCTV respectively [Figure 4]a and [Figure 4]b. The deviation in D98% and D90% between these two applicators is due to HRCTV volume and in this study, the mean volume of HRCTV is 73.74 cc. The same dosimetric parameters were compared with Tandem and Ovoid with IC plus IS applicators with earlier published results.[5] The mean difference in D98%_ HRCTV was 2.8 Gy (Ovoid IC/IS Vs MAOLO) and 5.4 Gy (Tandem IC/IS Vs MAOLO) and D90%_ HRCTV, the MD is 4.1 (Ovoid IC/IS Vs MAOLO) Gy and 6.7 Gy (Tandem IC/IS Vs MAOLO) [Figure 7]. In this comparison also, the deviation was mainly due to HRCTV volume and its lateral extension. In the MAOLO template, the lateral divergent needle can be placed at a distance of 3.2 cm from the midline at the level of point A, thus providing adequate coverage up to 3.6 cm on either side from the central axis of the uterus at the height of point A. If the HRCTV extends laterally beyond that width, the coverage will be compromised (reducing dose at lateral parametrium), and the planning aim in this area could be 85% isodose coverage instead of 100% which causes the overall EQD reduction. In our previous study, the Martinez universal perineal IS template (MUPIT) was compared with MAOLO using various optimization methods and the dosimetric results for both templates were comparable.[31] CT-based delineation of HRCTV is an overestimation compared to gold standard MRI imaging, so our volumes were probably bigger than the true HRCTV. Now, with the availability of standardized CT-based guidelines, we will be more accurate to delineate the HRCTV, improving the target coverage and OAR sparing more efficiently. The above discrepancy could be attributed to CT-based delineation of HRCTV and residual disease extension.
Figure 7: Comparison between various applicators and MAOLO for dosimetric parameters of Target and OARs. OAR: Organ at ris

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Georg et al.[32] studied the dose-effect relationship for late side effects of the urinary bladder and rectum in cervix cancer using HDR BT and stated that the 5% possibility of rectal toxicity if D2cc of EQD2 ranges from 60 to 80 Gy. The 5% probability of grade 2 to grade 4 in rectal toxicity was observed if the D2cc was receiving the mean EQD2 of 67 Gy (range: 30-79 Gy) and 10% was at 78 Gy (range 68-110 Gy). The probability of rectal fistula incidence is less than 2.7% if the D2cc EQD2 of the rectum receives ≤75 Gy.[33] The other critical parameter of rectal toxicity is EQD2 of D0.1cc and it was observed that the probability of 5% rectal side effect could happen if the D0.1cc is exceeding 83 Gy.[32] In our study, the mean EQD2 of D2cc and D0.1cc of the rectum is 74.2 Gy and 83.9 respectively [Figure 5]b. Based on the earlier study,[32] the probability of rectal toxicity by using this template could be less than 6%-8% even with bigger HRCTVs in our study. The probability of bladder toxicity versus EQD2 was analyzed in an earlier study[32] using the EQD2 of D2cc and D0.1cc. The 5%-10% of probability of bladder toxicity with the EQD of D2cc is 70-101 Gy and D0.1cc is 61-178 Gy.[32] In our study, the D2cc and D0.1cc for the urinary bladder are 85.5 Gy and 114.2 Gy respectively. For two patients the EQD2 for the D2cc bladder was high due to the residual disease involvement of the posterior bladder wall. The same was observed for the rectum also but none of the patients had bladder or rectal toxicity. Corresponding with an earlier complication probability study,[32] our template could control bladder toxicity by 6%-7%.

The overall aim of this study is to commission and evaluate the earlier dosimetric results of indigenously developed IC plus IS template for cervix cancer in HDR brachytherapy. Based on initial dosimetric results, the indigenously developed template seems useful in BT treatment of advanced cervix cancer patients who need IC plus IC type of application. The main advantage of this template is its ability to cover the lateral extent of the target well extending beyond point A, without increasing doses to the OARS.


   Conclusions Top


The advantages of this indigenously developed template are the superior tumor coverage despite greater target volume and extending the prescription dose even 3 cm laterally from point A. The limitation of this template is compatibility with MRI and currently, it is suitable for CT-based planning. The development of MRI compatibility for this template is in progress and it can provide a better alternate solution for commercially available applicators with economic feasibility for developing countries.

Acknowledgements

The author wishes to thank Mr. Christy Alekchander, Chief Medical Physicist, Patel Hospital, Jalandar, Punjab for providing technical feedback.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7]
 
 
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