A review of recent developments in image-guided radiation therapy in cervix cancer

Integration of rotatable tandem applicator to conventional ovoid applicator toward complete framework of intensity modulated brachytherapy (IMBT) for cervical cancer

A new tandem applicator with tungsten shield for Ir-192 radiation source used in intra-cavitary brachytherapy (ICBT) enabled intensity modulated brachytherapy (IMBT) in cervical cancer treatment through fluence-modulation by rotating shield. Our previous work employed group-wise and element-wise sparsity constraints for plan optimization of tandem applicator to minimizes the number of activated angles and source dwell points for delivery efficiency. It, however, did not incorporate the ovoid applicators into the optimizing process, which is generally used to prevent cancer recurrence. To integrate ovoid applicators to the new tandem applicator, this work proposed a comprehensive framework that modifies 1) dose deposition matrix for inverse planning, and 2) plan optimizing algorithm. The dose deposition matrix was newly formulated by the Monte-Carlo simulated dose distribution for 10 positions of ovoid applicators, followed by combining those with tandem-associated dose deposition matrix. The plan optimizing algorithm decomposed entire elements into tandem and ovoid applicators, which were governed by different constraints adaptive to specified plan objectives. The integrated framework was compared against conventional ICBT, and IMBT with tandem only for three patients with asymmetric dose distributions. Integrated IMBT framework resulted in the most optimal plans. Including fluence-modulation by rotating-shield outperformed conventional ICBT in dose sparing to critical organs. Adopting ovoid applicators to the optimization yielded more conformal dose distribution around inferior, laterally expanded region of target volume. The resulting plans reduced D_5cc and D_2cc by 30.9% and 27.8% for critical organs over conventional ICBT, and by 20.6% and 21.5% for target volume over IMBT with tandem only.

Plan optimization with L0-norm and group sparsity constraints for a new rotational, intensity-modulated brachytherapy for cervical cancer

The aim of this work is to build a framework that comprehends inverse planning procedure and plan optimization algorithm tailored to a novel directional beam intensity-modulated brachytherapy (IMBT) of cervical cancer using a rotatable, single-channel radiation shield. Inverse planning is required for finding optimal beam emitting direction, source dwell position and dwell time, which begin with creating a kernel matrix for each structure based on Monte-Carlo simulated dose distribution in the rotatable shield. For efficient beam delivery and less transit dose, the number of source dwell positions and angles needs to be minimized. It can be solved by L0-norm regularization for fewest possible dwell points, and by group sparsity constraint in L2,p-norm (0≤p<1) besides L0-norm for fewest active applicator rotating angles. The dose distributions from our proposed algorithms were compared to those of conventional tandem-based intracavitary brachytherapy (ICR) plans for six cervical cancer patients. The algorithmic performance was evaluated in delivery efficiency and plan quality relative to the unconstrained algorithm. The proposed framework yielded substantially enhanced plan quality over the conventional ICR plans. The L0-norm and (group sparsity+L0-norm) constrained algorithms reduced the number of source dwell points by 60 and 70% and saved 5 and 8 rotational angles on average (7 and 11 angles for highly modulated cases), relative to the unconstrained algorithm, respectively. Though both algorithms reduced the optimal source dwell positions and angles, the group sparsity constrained optimization with L0-norm was more effective than the L0-norm constraint only, mainly because of considering physical constraints of the new IMBT applicator. With much fewer dwell points compared to the unconstrained, the proposed algorithms led to statistically similar plan quality in dose volume histograms and iso-dose lines. It also demonstrated that the plan optimized by rotating the applicator resulted in much better plan quality than that of conventional applicator-based plans.

Dosimetry comparison between a 3D printed minimally invasive guidance template and free implantation in the brachytherapy treatment of postoperative recurrent cervical carcinoma

Objective: This study aimed to investigate the dosimetry difference between a 3D printed minimally invasive guidance template and conventional free implantation in brachytherapy of postoperative recurrent cervical carcinoma under the guidance of computed tomography (CT).

Methods: A total of 21 cases of patients with recurrent cervical cancer after operation were enrolled from January 2017 to June 2018. After external irradiation treatment in 1.8-Gy fractions to 45 Gy, patients were randomly divided into two groups to receive brachytherapy: 11 cases were assisted by a 3D-printed minimally invasive guidance template, and the other 10 cases were free implantation. In the template group, needles were inserted according to the main guide channel of the template commissioned in medical photosensitive resin, while patients in the other group were treated with bare hands under the guidance of CT, which was used in both groups to adjust the position and depth of the implant needles. After transmission of the CT images into the Oncentra® Brachy TPS system, the target organs and organs at risk were delineated for further treatment.

Results: The D₉₀ value of the high-risk clinical target volume in the template group was 6.30±0.21 Gy while that in the other group was 6.07±0.32 Gy (P<0.05). In addition, the D2cm³ (illuminated dose of 2 cm³ of organ at risk) value of the bladder, rectum, sigmoid colon, and bowel was significantly decreased in the template group as compared to the free group (P<0.05). The number of needles used for each treatment in the template group was 5.71±1.82, while that for the free injection group was 7.78±2.35 (P<0.05).

Conclusion: Compared with conventional free implantation, the 3D printed minimally invasive guidance template-assisted treatment has an obvious dosimetry advantage in the treatment of postoperative recurrent cervical carcinoma, with shorter time of implantation and better repeatability.

Nonrigid Medical Image Registration Using an Information Theoretic Measure Based on Arimoto Entropy with Gradient Distributions

This paper introduces a new nonrigid registration approach for medical images applying an information theoretic measure based on Arimoto entropy with gradient distributions. A normalized dissimilarity measure based on Arimoto entropy is presented, which is employed to measure the independence between two images. In addition, a regularization term is integrated into the cost function to obtain the smooth elastic deformation. To take the spatial information between voxels into account, the distance of gradient distributions is constructed. The goal of nonrigid alignment is to find the optimal solution of a cost function including a dissimilarity measure, a regularization term, and a distance term between the gradient distributions of two images to be registered, which would achieve a minimum value when two misaligned images are perfectly registered using limited-memory Broyden–Fletcher–Goldfarb–Shanno (L-BFGS) optimization scheme. To evaluate the test results of our presented algorithm in non-rigid medical image registration, experiments on simulated three-dimension (3D) brain magnetic resonance imaging (MR) images, real 3D thoracic computed tomography (CT) volumes and 3D cardiac CT volumes were carried out on elastix package. Comparison studies including mutual information (MI) and the approach without considering spatial information were conducted. These results demonstrate a slight improvement in accuracy of non-rigid registration.

Quantitative CT assessment of a novel direction-modulated brachytherapy tandem applicator

PURPOSE

The purpose of this study was to quantitatively assess the CT metal-induced artifacts from a novel direction-modulated brachytherapy (DMBT) tandem applicator prototype, recently designed for cervical cancer treatments.

METHODS AND MATERIALS

A water-based pelvic phantom was constructed for CT scanning. The DMBT applicator was imaged using our institutional protocol, one with higher kVp and mAs settings, and repetition of these protocols using 3-mm slices. A conventional stainless steel applicator was also scanned. In addition to the standard reconstructed images, applicator images were reconstructed using a commercial metal artifact-reduction (MAR) algorithm and an in-house-developed research algorithm. Subsequently, image quality and artifact severity were evaluated.

RESULTS

Artifact severity, measured in terms of SDs in CT numbers, decreased asymptotically to background water levels with the distance away from the applicator. Artifact-reduction algorithms lead to significant and visible improvements in image quality, with >50% and >20% decrease in artifact severity achieved at a 10-mm distance for the DMBT and stainless steel applicators, respectively. Differences in artifact severity were minimal between the four imaging protocols. DMBT dimensions were the same on images with and without the commercial MAR algorithm, within <1 mm of the theoretical value. Both the commercial and in-house algorithms restored the CT numbers outside the applicator, albeit a better performance was achieved by the in-house algorithm.

CONCLUSIONS

The artifacts produced by both applicators were minimized with the use of MAR algorithms. Adoption of the DMBT and stainless steel applicators for CT-guided brachytherapy is anticipated as MAR algorithms are widely available on CT scanners.

Early clinical outcome of coverage probability based treatment planning for simultaneous integrated boost of nodes in locally advanced cervical cancer

INTRODUCTION

More than 50% of patients with locally advanced cervical cancer (LACC) have pathological nodes. Coverage probability (CovP) is a new planning technique allowing for relaxed dose at the boost periphery minimising collateral irradiation. The aim was to report the first early clinical outcome data for CovP based simultaneous integrated boost (SIB) in LACC.

MATERIAL AND METHODS

Twenty-three consecutive node positive patients were analysed. FIGO stage IB2/IIB/IIIB/IVA/IVB was 1/14/3/1/4. Treatment was radio(chemo)therapy (RT) delivering 45 Gy/25 fx whole pelvis ± para-aortic region (PAN) using volumetric arc therapy (VMAT) followed by magnetic resonance imaging (MRI) guided brachytherapy. PAN RT (13 pts) was given if >2 nodes or if node(s) were present at the common iliac vessels or PAN. Nodal gross tumour volumes (GTV-N) were contoured on both PET-CT and MRI. Clinical target volume (CTV-N) was formed by fusion of GTV-N_CT and GTV-N_MRI. A 5-mm isotropic margin was used for planning target volume (PTV-N). Nodes in the small pelvis were boosted to 55.0 Gy/25 fx. Common iliac and para-aortic nodes received 57.5 Gy/25 fx. Planning aims for CovP were PTV-N D₉₈ ≥ 90%, CTV-N D₉₈ ≥ 100% and CTV-N D₅₀ ≥ 101.5%.

RESULTS

Seventy-four nodes were boosted. A consistent 5.0 ± 0.7 Gy dose reduction from CTV-N D₉₈ to PTV-N D₉₈ was obtained. In total, 73/74 nodes were in complete remission at 3 months PET-CT and MRI. Pelvic control was obtained in 21/23 patients. One patient (IB2, clear cell) had salvageable local disease, while another (IIB) failed in a boosted node. Two patients failed in un-irradiated PAN. One patient age 88 (IIIB) did not receive PAN RT, despite a common iliac node. The other (IIB) recurred above L1. Two further patients (IVB) failed systemically.

CONCLUSION

Since complete remission at 3 months is predictive for favourable long-term nodal control, our study indicates that CovP for SIB is promising.

A Review on Medical Image Registration as an Optimization Problem

Objective:

In the course of clinical treatment, several medical media are required by a phy-sician in order to provide accurate and complete information about a patient. Medical image registra-tion techniques can provide a richer diagnosis and treatment information to doctors and to provide a comprehensive reference source for the researchers involved in image registration as an optimization problem.

Methods:

The essence of image registration is associating two or more different images spatial asso-ciation, and getting the translation of their spatial relationship. For medical image registration, its pro-cess is not absolute. Its core purpose is finding the conversion relationship between different images.

Result:

The major step of image registration includes the change of geometrical dimensions, and change of the image of the combination, image similarity measure, iterative optimization and interpo-lation process.

Conclusion:

The contribution of this review is sort of related image registration research methods, can provide a brief reference for researchers about image registration.

MR Imaging in Gynecologic Brachytherapy

Magnetic resonance-based image-guided adaptive brachytherapy is gaining popularity in the United States in the setting of gynecologic malignancies. This technique improves local control, increases overall survival, and minimizes toxicity to the adjacent organs at risk. The purpose of this article is to familiarize radiologists with image-guided adaptive brachytherapy by describing its history, detailing MR imaging techniques, describing treatment considerations, and reviewing image interpretation.

Dosimetric Comparison between Three-Dimensional Magnetic Resonance Imaging-Guided and Conventional Two-Dimensional Point A-Based Intracavitary Brachytherapy Planning for Cervical Cancer

Objective

The purpose of this study was to comprehensively compare the 3-dimensional (3D) magnetic resonance imaging (MRI)-guided and conventional 2-dimensional (2D) point A-based intracavitary brachytherapy (BT) planning for cervical cancer with regard to target dose coverage and dosages to adjacent organs-at risk (OARs).

Methods

A total of 79 patients with cervical cancer were enrolled to receive 2D point A-based BT planning and then immediately to receive 3D planning between October 2011 and April 2013 at the First Hospital Affiliated to Xi’an Jiao Tong University (Xi’an, China). The dose-volume histogram (DVH) parameters for gross tumor volume (GTV), high-risk clinical target volume (HR-CTV), intermediate-risk clinical target volume (IR-CTV) and OARs were compared between the 2D and 3D planning.

Results

In small tumors, there was no significant difference in most of the DVHs between 2D and 3D planning (all p>0.05). While in big tumors, 3D BT planning significantly increased the DVHs for most of the GTV, HR-CTV and IR-CTV, and some OARs compared with 2D planning (all P<0.05). In 3D planning, DVHs for GTV, HR-CTV, IR-CTV and some OARs were significantly higher in big tumors than in small tumors (all p<0.05). In contrast, in 2D planning, DVHs for almost all of the HR-CTV and IR-CTV were significantly lower in big tumors (all p<0.05). In eccentric tumors, 3D planning significantly increased dose coverage but decreased dosages to OARs compared with 2D planning (p<0.05). In tumors invading adjacent tissues, the target dose coverage in 3D planning was generally significantly higher than in 2D planning (P<0.05); the dosages to the adjacent rectum and bladder were significantly higher but those to sigmoid colon were lower in 3D planning (all P<0.05).

Conclusions

3D MRI image-guided BT planning exhibits advantages over 2D planning in a complex way, generally showing advantages for the treatment of cervical cancer except small tumors.

Quantitative MRI assessment of a novel direction modulated brachytherapy tandem applicator for cervical cancer at 1.5T

BACKGROUND AND PURPOSE

The purpose of this work is to quantitatively investigate the artifacts and image distortions induced in the MR images by a recently proposed direction modulated brachytherapy (DMBT) tandem applicator prototype. This new MRI-compatible applicator allows better sparing of organs-at-risk (OAR) for cervical cancer patients, while providing conformal dose distributions to target volumes.

MATERIALS AND METHODS

Specific phantom and tools were designed and manufactured for this study. The phantom was filled with a tissue-like solution and MR images were acquired with clinical protocols as per GEC-ESTRO recommendations. Images were obtained at 6 different orientations that mimic possible clinical settings and full-width-at-half-maximum (FWHM) was recorded at multiple locations/angles. The accuracy of detecting the centerline of the tandem was assessed using a novel radial-fiducials mount.

RESULTS

FWHM from all line profiles at all angles and all orientations was 6.14±0.7mm (compared to 6mm of the actual DMBT tandem diameter). The in-plane spatial-shift observed at para-axial and para-sagittal views was less than 0.5mm.

CONCLUSIONS

This work demonstrated that the novel DMBT tandem applicator prototype has minimal artifact in T₂-weighted images employed in clinical practice, suggesting the applicator might be a good candidate for MRI-guided adaptive brachytherapy.

Evolving Clinical Cancer Radiotherapy: Concerns Regarding Normal Tissue Protection and Quality Assurance

Radiotherapy, which is one of three major cancer treatment methods in modern medicine, has continued to develop for a long period, more than a century. The development of radiotherapy means allowing the administration of higher doses to tumors to improve tumor control rates while minimizing the radiation doses absorbed by surrounding normal tissues through which radiation passes for administration to tumors, thereby reducing or removing the incidence of side effects. Such development of radiotherapy was accomplished by the development of clinical radiation oncology, the development of computers and machine engineering, the introduction of cutting-edge imaging technology, a deepened understanding of biological studies on the effects of radiation on human bodies, and the development of quality assurance (QA) programs in medical physics. The development of radiotherapy over the last two decades has been quite dazzling. Due to continuous improvements in cancer treatment, the average five-year survival rate of cancer patients has been close to 70%. The increases in cancer patients' complete cure rates and survival periods are making patients' quality of life during or after treatment a vitally important issue. Radiotherapy is implemented in approximately 1/3 to 2/3s of all cancer patients; and has improved the quality of life of cancer patients in the present age. Over the last century, as a noninvasive treatment, radiotherapy has unceasingly enhanced complete tumor cure rates and the side effects of radiotherapy have been gradually decreasing, resulting in a tremendous improvement in the quality of life of cancer patients.

Comparative evaluation of two-dimensional radiography and three dimensional computed tomography based dose-volume parameters for high-dose-rate intracavitary brachytherapy of cervical cancer: a prospective study

BACKGROUND

Dosimetric comparison of two dimensional (2D) radiography and three-dimensional computed tomography (3D-CT) based dose distributions with high-dose-rate (HDR) intracavitry radiotherapy (ICRT) for carcinoma cervix, in terms of target coverage and doses to bladder and rectum.

MATERIALS AND METHODS

Sixty four sessions of HDR ICRT were performed in 22 patients. External beam radiotherapy to pelvis at a dose of 50 Gray in 27 fractions followed by HDR ICRT, 21 Grays to point A in 3 sessions, one week apart was planned . All patients underwent 2D-orthogonal and 3D-CT simulation for each session. Treatment plans were generated using 2D-orthogonal images and dose prescription was made at point A. 3D plans were generated using 3D-CT images after delineating target volume and organs at risk. Comparative evaluation of 2D and 3D treatment planning was made for each session in terms of target coverage (dose received by 90%, 95% and 100% of the target volume: D90, D95 and D100 respectively) and doses to bladder and rectum: ICRU-38 bladder and rectum point dose in 2D planning and dose to 0.1cc, 1cc, 2cc, 5cc, and 10cc of bladder and rectum in 3D planning.

RESULTS

Mean doses received by 100% and 90% of the target volume were 4.24 ± 0.63 and 4.9 ± 0.56 Gy respectively. Doses received by 0.1cc, 1cc and 2cc volume of bladder were 2.88 ± 0.72, 2.5 ± 0.65 and 2.2 ± 0.57 times more than the ICRU bladder reference point. Similarly, doses received by 0.1cc, 1cc and 2cc of rectum were 1.80 ± 0.5, 1.48 ± 0.41 and 1.35 ± 0.37 times higher than ICRU rectal reference point.

CONCLUSIONS

Dosimetric comparative evaluation of 2D and 3D CT based treatment planning for the same brachytherapy session demonstrates underestimation of OAR doses and overestimation of target coverage in 2D treatment planning.

Kinetic Models for Predicting Cervical Cancer Response to Radiation Therapy on Individual Basis Using Tumor Regression Measured In Vivo With Volumetric Imaging

This article describes a macroscopic mathematical modeling approach to capture the interplay between solid tumor evolution and cell damage during radiotherapy. Volume regression profiles of 15 patients with uterine cervical cancer were reconstructed from serial cone-beam computed tomography data sets, acquired for image-guided radiotherapy, and used for model parameter learning by means of a genetic-based optimization. Patients, diagnosed with either squamous cell carcinoma or adenocarcinoma, underwent different treatment modalities (image-guided radiotherapy and image-guided chemo-radiotherapy). The mean volume at the beginning of radiotherapy and the end of radiotherapy was on average 23.7 cm(3) (range: 12.7-44.4 cm(3)) and 8.6 cm(3) (range: 3.6-17.1 cm(3)), respectively. Two different tumor dynamics were taken into account in the model: the viable (active) and the necrotic cancer cells. However, according to the results of a preliminary volume regression analysis, we assumed a short dead cell resolving time and the model was simplified to the active tumor volume. Model learning was performed both on the complete patient cohort (cohort-based model learning) and on each single patient (patient-specific model learning). The fitting results (mean error: ∼ 16% and ∼ 6% for the cohort-based model and patient-specific model, respectively) highlighted the model ability to quantitatively reproduce tumor regression. Volume prediction errors of about 18% on average were obtained using cohort-based model computed on all but 1 patient at a time (leave-one-out technique). Finally, a sensitivity analysis was performed and the data uncertainty effects evaluated by simulating an average volume perturbation of about 1.5 cm(3) obtaining an error increase within 0.2%. In conclusion, we showed that simple time-continuous models can represent tumor regression curves both on a patient cohort and patient-specific basis; this discloses the opportunity in the future to exploit such models to predict how changes in the treatment schedule (number of fractions, doses, intervals among fractions) might affect the tumor regression on an individual basis.

Direction-modulated brachytherapy for high-dose-rate treatment of cervical cancer. I: theoretical design

PURPOSE

To demonstrate that utilization of the direction-modulated brachytherapy (DMBT) concept can significantly improve treatment plan quality in the setting of high-dose-rate (HDR) brachytherapy for cervical cancer.

METHODS AND MATERIALS

The new, MRI-compatible, tandem design has 6 peripheral holes of 1.3-mm diameter, grooved along a nonmagnetic tungsten-alloy rod (ρ = 18.0 g/cm(3)), enclosed in Delrin tubing (polyoxymethylene, ρ = 1.41 g/cm(3)), with a total thickness of 6.4 mm. The Monte Carlo N-Particle code was used to calculate the anisotropic (192)Ir dose distributions. An in-house-developed inverse planning platform, geared with simulated annealing and constrained-gradient optimization algorithms, was used to replan 15 patient cases (total 75 plans) treated with a conventional tandem and ovoids (T&O) applicator. Prescription dose was 6 Gy. For replanning, we replaced the conventional tandem with that of the new DMBT tandem for optimization but left the ovoids in place and kept the dwell positions as originally planned. All DMBT plans were normalized to match the high-risk clinical target volume V100 coverage of the T&O plans.

RESULTS

In general there were marked improvements in plan quality for the DMBT plans. On average, D2cc for the bladder, rectum, and sigmoid were reduced by 0.59 ± 0.87 Gy (8.5% ± 28.7%), 0.48 ± 0.55 Gy (21.1% ± 27.2%), and 0.10 ± 0.38 Gy (40.6% ± 214.9%) among the 75 plans, with best single-plan reductions of 3.20 Gy (40.8%), 2.38 Gy (40.07%), and 1.26 Gy (27.5%), respectively. The high-risk clinical target volume D90 was similar, with 6.55 ± 0.96 Gy and 6.59 ± 1.06 Gy for T&O and DMBT, respectively.

CONCLUSIONS

Application of the DMBT concept to cervical cancer allowed for improved organ at risk sparing while achieving similar target coverage on a sizeable patient population, as intended, by maximally utilizing the anatomic information contained in 3-dimensional imaging. A series of mechanical and clinical validations are to be followed.

Major clinical research advances in gynecologic cancer in 2012

Ten topics were chosen among major clinical research achievements in gynecologic oncology in 2012. For ovarian cancer, comprehensive review of the history of bevacizumab studies was followed by poly adenosine diphosphate [ADP]-ribose polymerase (PARP) inhibitors and other molecular targeted agents such as epidermal growth factor receptor tyrosine kinase inhibitor and AMG 386. For the development of genomic study in gynecologic cancers, BRCA and DICER1 mutations were covered in epithelial and nonepithelial ovarian cancer, respectively. For endometrial cancer, targeted agents including mammalian target of rapamycin (mTOR) inhibitors and bevacizumab were discussed. Radiation therapy "sandwiched" between combination chemotherapy schedules for the treatment of uterine papillary serous carcinoma was also reviewed. Preoperative prediction of lymph node metastasis, definition of low-risk group, and recurrence and survival outcomes of laparoscopic approaches were addressed. For cervical cancer, we reviewed long-term benefit of human papillomavirus test and efficacy of paclitaxel/carboplatin versus paclitaxel/cisplatin in stage IVB, persistent or recurrent disease. In addition, the effect of three dimensional image-based high-dose rate brachytherapy was also reviewed. For vulvar cancer, the diagnostic value of sentinel lymph node biopsy was discussed. For breast cancer, positive results of three outstanding phase III randomized clinical trials, CLEOPATRA, EMILIA, and BOLERO-2 were introduced. Lastly, updates of major practice guidelines were summarized.