A new template for MRI-based intracavitary/interstitial gynecologic brachytherapy: design and clinical implementation

Plan quality score to evaluate the dwell time deviation restricted inverse planning by simulated annealing and graphically optimized treatment plans for template based interstitial brachytherapy

PURPOSE

To evaluate the impact of dwell time deviation constraint (DTDC) on the quality of IPSA-optimized treatment plans in comparison with graphical plans using plan quality scores (PQS).

MATERIAL AND METHODS

Seventy optimized plans (graphical & IPSA with different DTDC values) of ten cervical cancer patients were generated. Various DVH parameters like D₉₀, V₁₀₀, V₁₅₀, V₂₀₀, V₃₀₀ were compared to evaluate the impact of DTDC on target coverage and high dose regions inside target for different plans. Similarly, for the OAR dose, values of D_2cc were compared. Various planning parameters like CI, COIN, DHI, DNR, ODI, EI and gain factor (GF) for different OARs were calculated. Based on these indices a plan quality score (PQS) was formulated and calculated. PQS values were used to see the impact of DTDC on plan quality of IPSA in comparison with dosimetric quality of graphical plan.

RESULTS

We have found that target coverage is similar for IPSA and graphically optimized treatment plans. However, dose homogeneity was improved in IPSA compared to graphical optimization whereas conformality was better in graphically optimized plans. OAR dose was less in IPSA plans. High-dose regions inside the target were also reduced in IPSA comparatively. However, IPSA plans optimized with various values of DTDC did not necessarily reduce high-dose regions beyond 0.6. Plan quality scores (PQS) were 6.31, 6.31, 6.34, and 6.17 for the graphically optimized plan, IPSA with DTDC values of 0.0, 0.4, and 1.0 respectively.

CONCLUSION

We found that IPSA is dosimetrically advantageous over graphical optimization. IPSA with a DTDC value of 0.4 improved overall plan quality. However, DTDC value beyond 0.6 produces dosimetrically sub-optimal plans hence the use of DTDC should be very selective and limited.

Evolution of Brachytherapy Applicators for the Treatment of Cervical Cancer

Brachytherapy applicators have come a long way since Danlos developed early intracavitary applicators to treat cervical cancer patients. Therefore, this review will help in the neoteric designs of intracavitary applicators. A detailed literature survey of the gynecological brachytherapy applicators from the era of preloading to conceptual intensity-modulated brachytherapy applicators has been carried out. Depending on the extent of the disease and patient anatomy, the selection of brachytherapy applicators plays a pivotal role in the treatment of cervical cancer. Furthermore, the selection of the applicators is also based on the imaging modalities to be used for applicator reconstruction and treatment planning. Dose acceleration in the target and reduction in nearby organs at risk can be optimized using an applicator having the capabilities of intensity-modulated brachytherapy. Now, three-dimensional printed applicators are used for patient-specific tailor-made treatment and they are fast replacing the old conventional applicators. Newer advancements in technology have greatly influenced the neoteric designs of intracavitary brachytherapy applicators.

Evaluation of a new bi-valve vaginal speculum applicator design for gynecologic interstitial brachytherapy

Purpose

We designed a bi-valve vaginal speculum high-dose-rate (HDR) interstitial gynecologic brachytherapy applicator. This allows for both a direct view of the cervix and image-guided brachytherapy applicator placement. The purpose of this study was to assess the validity of the new applicator.

Material and methods

The applicator was designed to have a 25-mm arc, which can be spread transversely to 35-mm wide, with 10 insertion holes; it was produced using a stereolithographic printer with biocompatible Dental SG resin. For resin radiodensity was measured in Hounsfield units (HU) using computed tomography (CT). Comparing the new applicator with a conventional intracavitary applicator, we evaluated the treated volume (including dimensions of 100% isodose volume at the central axis), V₁₀₀/D₉₀/D₉₈ for a hypothetical cervix (a 2-cm-long and 4-cm-diameter cylinder), and dose points of organs at risk (OARs) (at 25 and 30 mm from the tandem). Based on dose-volume histogram (DVH) analysis of the cervix and dose points of OARs, the range of tolerance for the percent dose difference in the prescription dose was set at 5%.

Results

The mean radiodensity of the Dental SG resin, which was magnetic resonance imaging compatible, was 118 HU. Dimensions of the 100% isodose volume measured at the central axis were 4.4 × 6.6 × 7.4 cm for the new applicator and 4.3 × 6.0 × 7.7 cm for the intracavitary applicator. The 100% prescription dose volumes were 110 cc and 113 cc for the new and conventional applicator, respectively. The percent difference in the hypothetical cervix V₁₀₀, D₉₀, and D₉₈ between the new and intracavitary applicator were within 5%. The percent differences in dose points of OARs at 25 and 30 mm between the new and conventional applicators were within 5%.

Conclusions

Our speculum applicator can reproduce a conventional pear-shaped dose distribution. Our current clinical practice will use this applicator, which can improve the patient’s treatment results.

Indian Brachytherapy Society Guidelines for radiotherapeutic management of cervical cancer with special emphasis on high-dose-rate brachytherapy

Brachytherapy (BT) for locally advanced cervical cancer is vital for optimal outcomes. There is heterogeneity in brachytherapy treatment practice for cervical cancer across India. In an attempt to standardize various processes involved in cervical cancer brachytherapy, the expert members of the Indian Brachytherapy Society (IBS) developed a document related to radiation therapy treatment of cervical cancer with special emphasis on brachytherapy. The guidelines are based on high quality clinical evidence, expert opinion and consensus wherever evidence was lacking. The document provides a guide for external beam radiation and details of all the processes involved in high-dose-rate (HDR) brachytherapy including patient selection, preparation, principles and technique of BT applications, target and normal tissue definition, dose prescriptions, BT planning, reporting parameters, common complications of BT and their management, scope for research, etc. In summary, we present here practical tips and tricks, recording and reporting of cervical cancer brachytherapy, which can be implemented in various clinical environments and forms the basis of this report.

Review of strategies for MRI based reconstruction of endocavitary and interstitial applicators in brachytherapy of cervical cancer

Brachytherapy plays an essential role in the curative intent management of locally advanced cervical cancer. The introduction of the magnetic resonance (MR) as a preferred image modality and the development of new type of applicators with interstitial components have further improved its benefits. The aim of this work is to review the current status of one important aspect in the cervix cancer brachytherapy procedure, namely catheter reconstruction. MR compatible intracavitary and interstitial applicators are described. Considerations about the use of MR imaging (MRI) regarding appropriate strategies for applicator reconstruction, technical requirements, MR sequences, patient preparation and applicator commissioning are included. It is recommendable to perform the reconstruction process in the same image study employed by the physician for contouring, that is, T2 weighted (T2W) sequences. Nevertheless, a clear identification of the source path inside the catheters and the applicators is a challenge when using exclusively T2W sequences. For the intracavitary component of the implant, sometimes the catheters may be filled with some substance that produces a high intensity signal on MRI. However, this strategy is not feasible for plastic tubes or titanium needles, which, moreover, induce magnetic susceptibility artifacts. In these situations, the use of applicator libraries available in the treatment planning system (TPS) is useful, since they not only include accurate geometrical models of the intracavitary applicators, but also recent developments have made possible the implementation of the interstitial component. Another strategy to improve the reconstruction process is based on the incorporation of MR markers, such as small pellets, to be used as anchor points. Many institutions employ computed tomography (CT) as a supporting image modality. The registration of CT and MR image sets should be carefully performed, and its uncertainty previously assessed. Besides, an important research work is being carried out regarding the use of ultrasound and electromagnetic tracking technologies.

Pre-plan technique feasibility in multi-interstitial/endocavitary perineal gynecological brachytherapy

Purpose

To present the implementation of a magnetic resonance imaging (MRI) pre-planning technique in multi-interstitial perineal and endocavitary gynecological brachytherapy.

Material and methods

We used a new fully MRI-compatible applicator that is capable to engage titanium needles, and an intrauterine tandem, developed in our department for the treatment of gynecological cervical cancer patients. This applicator is an attempt to combine the technical advantages of the Martinez universal perineal interstitial template (MUPIT) with the improvement in dose distribution by adding an intrauterine probe with the imaging advantages of MRI-based brachytherapy, thus preserving the stability, geometry, and robustness of the implant, avoiding possible errors of free-hand needle placement. A pre-brachytherapy MRI T2 acquisition is carried out with the template in place 3-5 days before the implant. On this image set, clinical target volume (CTV) is drawn. The required needles and their depths are selected accordingly to encompass the CTV (as conformal as possible). To facilitate this task, a Java based application linked to the treatment planning system has been developed. From this procedure, each needle identification and its depth are obtained previously to the implantation. With this information, the radiation oncologist proceeds with implant and then, a post-implant MRI is carried out, in which the contouring, needles, tandem reconstruction, and optimization are established.

Results

This pre-planning procedure has been successfully applied in 10 patients. An excellent reproduction of the virtual pre-planning has been achieved.

Conclusions

We describe a virtual pre-planning technique using a multi-interstitial and endocavitary perineal template. It is based on a virtual work with MRI images. This procedure has shown to be feasible and efficient in clinical practice by facilitating the work of specialists, and reducing uncertainties of the application.

A method to incorporate interstitial components into the TPS gynecologic rigid applicator library

PURPOSE

T2 magnetic resonance imaging (MRI) is recommended as the imaging modality for image-guided brachytherapy. In locally advanced cervical carcinoma, combined endocavitary and interstitial applicators are appropriate (Vienna or Utrecht). To cover extensive disease, Template Benidorm (TB) was developed. Treatment planning system applicator libraries are currently unavailable for the Utrecht applicator or the TB. The purpose of this work is to develop an applicator library for both applicators.

MATERIAL AND METHODS

The library developed in this work has been used in the Oncentra Brachytherapy TPS, version 4.3.0, which has a brachytherapy module that includes a library of rigid applicators. To add the needles of the Utrecht applicator and to model the TB, we used FreeCAD and MeshLab. The reconstruction process was based on the points that the rigid section and the interstitial part have in common. This, together with the free length, allowed us to ascertain the position of the tip.

RESULTS

In case of the Utrecht applicator, one of the sources of uncertainty in the reconstruction was determining the distance of the tip of needle from the ovoid. In case of the TB, the large number of needles involved made their identification time consuming. The developed library resolved both issues.

CONCLUSIONS

The developed library for the Utrecht and TB is feasible and efficient improving accuracy. It allows all the required treatment planning to proceed using just a T2 MRI sequence. The additional use of specific free available software applications makes it possible to add this information to the already existing library of the Oncentra Brachytherapy TPS. Specific details not included on this manuscript will be available under request. This library is also currently being implemented also into the Sagiplan v 2.0 TPS.

Development and clinical implementation of a new template for MRI-based intracavitary/interstitial gynecologic brachytherapy for locally advanced cervical cancer: from CT-based MUPIT to the MRI compatible Template Benidorm. Ten years of experience

PURPOSE

To study outcome and toxicity in 59 patients with locally advanced cervix carcinoma treated with computed tomography (CT)-based Martinez universal perineal interstitial template (MUPIT) and the new magnetic resonance imaging (MRI)-compatible template Benidorm (TB).

MATERIAL AND METHODS

From December 2005 to October 2015, we retrospectively analyzed 34 patients treated with MUPIT and 25 treated with the TB. Six 4 Gy fractions were prescribed to the clinical target volume (CTV) combined with external beam radiotherapy (EBRT). The organs at risk (OARs) and the CTV were delineated by CT scan in the MUPIT implants and by MRI in the TB implants. Dosimetry was CT-based for MUPIT and exclusively MRI-based for TB. Dose values were biologically normalized to equivalent doses in 2 Gy fractions (EQD2).

RESULTS

Median CTV volumes were 163.5 cm3 for CT-based MUPIT (range 81.8-329.4 cm3) and 91.9 cm3 for MRI-based TB (range 26.2-161 cm3). Median D90 CTV (EBRT + BT) was 75.8 Gy for CT-based MUPIT (range 69-82 Gy) and 78.6 Gy for MRI-based TB (range 62.5-84.2 Gy). Median D2cm3 for the rectum was 75.3 Gy for CT-based MUPIT (range 69.8-132.1 Gy) and 69.9 Gy for MRI-based TB (range 58.3-83.7 Gy). Median D2cm3 for the bladder was 79.8 Gy for CT-based MUPIT (range 71.2-121.1 Gy) and 77.1 Gy for MRI-based TB (range 60.5-90.8 Gy). Local control (LC) was 88%. Overall survival (OS), disease free survival (DFS), and LC were not statistically significant in either group. Patients treated with CT-based MUPIT had a significantly higher percentage of rectal bleeding G3 (p = 0.040) than those treated with MRI-based TB, 13% vs. 2%.

CONCLUSIONS

Template Benidorm treatment using MRI-based dosimetry provides advantages of MRI volume definition, and allows definition of smaller volumes that result in statistically significant decreased rectal toxicity compared to that seen with CT-based MUPIT treatment.

Metal artefacts in MRI-guided brachytherapy of cervical cancer

The importance of assessing the metal-induced artefacts in magnetic resonance imaging (MRI)-guided brachytherapy is growing along with the increasing interest of integrating MRI into the treatment procedure of cervical cancer. Examples of metal objects in use include intracavitary cervical applicators and interstitial needles. The induced artefacts increase the uncertainties in the clinical workflow and can be a potential obstacle for the accurate delivery of the treatment. Overcoming this problem necessitates a good understanding of its originating sources. Several efforts are recorded in the literature to quantify the extent of such artefacts, in phantoms and in clinical practice. Here, we elaborate on the origin of metal-induced artefacts in the light of brachytherapy applications, while summarizing recent efforts that have been made to assess and overcome the induced distortions.

A practical MRI-based reconstruction method for a new endocavitary and interstitial gynaecological template

PURPOSE

There are perineal templates for interstitial implants such as MUPIT and Syed applicators. Their limitations are the intracavitary component deficit and the necessity to use computed tomography (CT) for treatment planning since both applicators are non-magnetic resonance imaging (MRI) compatibles. To overcome these problems, a new template named Template Benidorm (TB) has been recently developed. Titanium needles are usually reconstructed based on their own artifacts, mainly in T1-weighted sequence, using the void on the tip as the needle tip position. Nevertheless, patient tissues surrounding the needles present heterogeneities that complicate the accurate identification of these artifact patterns. The purpose of this work is to improve the titanium needle reconstruction uncertainty for the TB case using a simple method based on the free needle lengths and typical MRI pellets markers.

MATERIAL AND METHODS

The proposed procedure consists on the inclusion of three small A-vitamin pellets (hyperintense on MRI images) compressed by both applicator plates defining the central plane of the plate's arrangement. The needles used are typically 20 cm in length. For each needle, two points are selected defining the straight line. From such line and the plane equations, the intersection can be obtained, and using the free length (knowing the offset distance), the coordinates of the needle tip can be obtained. The method is applied in both T1W and T2W acquisition sequences. To evaluate the inter-observer variation of the method, three implants of T1W and another three of T2W have been reconstructed by two different medical physicists with experience on these reconstructions.

RESULTS AND CONCLUSIONS

The differences observed in the positioning were significantly smaller than 1 mm in all cases. The presented algorithm also allows the use of only T2W sequence either for contouring or reconstruction purposes. The proposed method is robust and independent of the visibility of the artifact at the tip of the needle.