Image-guided radiotherapy

Modeling and prediction of set‑up errors in breast cancer image‑guided radiotherapy using the Gaussian mixture model

The aim of the present study was to develop a prediction model for set-up error distribution in breast cancer image-guided radiotherapy (IGRT) using a Gaussian mixture model (GMM). To achieve this, the image-guided set-up errors data of 80 patients with breast cancer were selected, and the GMM was used to develop the set-up errors distribution prediction model. The predicted error center points, covariance and probability were calculated and compared with the planning target volume (PTV) margin formula. A total of 1,200 sets of set-up errors in IGRT for breast cancer were collected. The results of the Gaussian model parameters showed that the set-up errors were mainly in the direction of µ1-µ4 center points. All the raw errors in the lateral, longitudinal and vertical directions were -6.30-4.60, -5.40-1.47 and -2.70-1.70 mm, respectively. According to the probability of each center, the set-up error was most likely to shift in the µ1 direction, reaching 0.53. The set-up errors of the other three centers, µ2, µ3 and µ4, were 0.11, 0.34 and 0.12, respectively. According to the covariance parameters of the GMM, the maximum statistical standard deviation of the set-up errors reached 29.06. In conclusion, the results of the present study demonstrated that the GMM can be used to quantitatively describe and predict the distribution of set-up errors in IGRT for breast cancer, and these findings could be useful as a reference for set-up error control and tumor PTV expansion in breast cancer radiotherapy without routine, daily IGRT.

Reirradiation of bone metastasis: A narrative review of the literature

Patients with bone metastasis are prevalent among those receiving palliative radiotherapy (RT), with approximately 20 % requiring reirradiation (reirradiation). The goal of bone reirradiation may be local control (oligoreoccurrence or oligoprogression of a previously treated lesion or in a previous treatment field) or symptomatic (threatening or painful progression). Published data on bone reirradiation indicate almost two-thirds of overall pain response. The primary organ at risk (especially for spine treatment) is the spinal cord. The risk of radiation myelitis is<1 % for cumulative doses of<50Gy. Intensity-modulated RT (IMRT) and stereotactic RT (SRT) appear to be safer than three-dimensional RT (3DRT), although randomized trials comparing these techniques in reirradiation are lacking. Reirradiation requires multidisciplinary assessment. Alternative treatments for bone metastases (surgery, interventional radiology, etc.) must be considered. Patients should have a performance status≤2, with at least a 1-month interval between treatments. The planning process involves reviewing previous RT plans, cautious dose adjustments, and precise target delineation and dose distribution to minimize toxicity. Cumulative dosimetry, patient consent, and vigilant post-treatment monitoring and dose reporting are crucial.

Personalizing radiotherapy with adaptive radiotherapy: Interest and challenges

Adaptive radiotherapy (ART) is a recent development in radiotherapy technology and treatment personalization that allows treatment to be tailored to the daily anatomical changes of patients. While it was until recently only performed "offline", i.e. between two radiotherapy sessions, it is now possible during ART to perform a daily online adaptive process for a given patient. Therefore, ART allows a daily customization to ensure optimal coverage of the treatment target volumes with minimized margins, taking into account only the uncertainties related to the adaptive process itself. This optimization appears particularly relevant in case of daily variations in the positioning of the target volume or of the organs at risk (OAR) associated with a proximity of these volumes and a tenuous therapeutic index. ART aims to minimize severe acute and late toxicity and allows tumor dose escalation. These new achievements have been possible thanks to technological development, the contribution of new multimodal and onboard imaging modalities and the integration of artificial intelligence tools for the contouring, planning and delivery of radiation therapy. Online ART is currently available on two types of radiotherapy machines: MR-linear accelerators and recently CBCT-linear accelerators. We will first describe the benefits, advantages, constraints and limitations of each of these two modalities, as well as the online adaptive process itself. We will then evaluate the clinical situations for which online adaptive radiotherapy is particularly indicated on MR- and CBCT-linear accelerators. Finally, we will detail some challenges and possible solutions in the development of online ART in the coming years.

ACSwinNet: A Deep Learning-Based Rigid Registration Method for Head-Neck CT-CBCT Images in Image-Guided Radiotherapy

Accurate and precise rigid registration between head-neck computed tomography (CT) and cone-beam computed tomography (CBCT) images is crucial for correcting setup errors in image-guided radiotherapy (IGRT) for head and neck tumors. However, conventional registration methods that treat the head and neck as a single entity may not achieve the necessary accuracy for the head region, which is particularly sensitive to radiation in radiotherapy. We propose ACSwinNet, a deep learning-based method for head-neck CT-CBCT rigid registration, which aims to enhance the registration precision in the head region. Our approach integrates an anatomical constraint encoder with anatomical segmentations of tissues and organs to enhance the accuracy of rigid registration in the head region. We also employ a Swin Transformer-based network for registration in cases with large initial misalignment and a perceptual similarity metric network to address intensity discrepancies and artifacts between the CT and CBCT images. We validate the proposed method using a head-neck CT-CBCT dataset acquired from clinical patients. Compared with the conventional rigid method, our method exhibits lower target registration error (TRE) for landmarks in the head region (reduced from 2.14 ± 0.45 mm to 1.82 ± 0.39 mm), higher dice similarity coefficient (DSC) (increased from 0.743 ± 0.051 to 0.755 ± 0.053), and higher structural similarity index (increased from 0.854 ± 0.044 to 0.870 ± 0.043). Our proposed method effectively addresses the challenge of low registration accuracy in the head region, which has been a limitation of conventional methods. This demonstrates significant potential in improving the accuracy of IGRT for head and neck tumors.

[Does radiation therapy for prostate cancer increase the risk of second cancers?]

PURPOSE

The increased risk of second cancer after prostate radiotherapy is a debated clinical concern. The objective of the study was to assess the risk of occurrence of second cancers after prostate radiation therapy based on the analysis the literature, and to identify potential factors explaining the discrepancies in results between studies.

MATERIALS AND METHODS

A review of the literature was carried out, comparing the occurrence of second cancers in patients all presenting with prostate cancer, treated or not by radiation.

RESULTS

This review included 30 studies reporting the occurrence of second cancers in 2,112,000 patients treated or monitored for localized prostate cancer, including 1,111,000 by external radiation therapy and 103,000 by brachytherapy. Regarding external radiation therapy, the average follow-up was 7.3years. The majority of studies (80%) involving external radiation therapy, compared to no external radiation therapy, showed an increased risk of second cancers with a hazard ratio ranging from 1.13 to 4.9, depending on the duration of the follow-up. The median time to the occurrence of these second cancers after external radiotherapy ranged from 4 to 6years. An increased risk of second rectal and bladder cancer was observed in 52% and 85% of the studies, respectively. Considering a censoring period of more than 10 years after irradiation, 57% and 100% of the studies found an increased risk of rectal and bladder cancer, without any impact in overall survival. Studies of brachytherapy did not show an increased risk of second cancer. However, these comparative studies, most often old and retrospective, had many methodological biases.

CONCLUSION

Despite numerous methodological biases, prostate external radiation therapy appears associated with a moderate increase in the risk of second pelvic cancer, in particular bladder cancer, without impacting survival. Brachytherapy does not increase the risk of a second cancer.

Adenoid Cystic Cancer of the Lacrimal Gland: Management Aspects and Treatment Outcomes

Adenoid cystic carcinoma (ACC) of the lacrimal gland is the most common malignant epithelial tumor of the lacrimal gland. The biological behavior of these tumors is characterized by a slow growth with frequent nerve invasion but rare invasion of the neck nodes. Local extension intracranially with bone erosions is seen in locally advanced tumors. Distant metastasis to lungs bone and liver are commonly reported. Treatments using surgery and radiotherapy are generally preferred for adequate tumor control. However there is still no consensus on the best treatment approach.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12070-023-04426-5.

Observations of the effectiveness, dosage, and prognosis of intensity-modulated radiation therapy under ultrasonic guidance for cervical cancer patients

BACKGROUND

Volumetric modulated arc therapy (VMAT) guided by ultrasound is a novel radiation therapy technique that facilitates the delineation of the tumor target area under image guidance, enhancing the precision of radiation therapy and maximizing the protection of surrounding tissues.

OBJECTIVE

The objective of this paper is to investigate the effectiveness of VMAT under ultrasonic guidance for cervical cancer patients and its impact on radiotherapy dosage and prognosis.

METHODS

A retrospective analysis encompassed 128 instances of cervical cancer patients who were admitted to our medical facility between April 2019 and April 2021. The patients were categorized into an observation cohort and a control cohort, depending on variations in treatment modalities post-admission. The control group underwent conventional radiotherapy, whereas the observation group received VMAT guided by ultrasound. Clinical efficacy, average radiation dosages (in the radiotherapy target area, rectum, and bladder), radiotherapy-related toxicities during treatment, and one-year survival rates were compared between the two groups. Additionally, variances in pre- and post-treatment serum levels of squamous cell carcinoma antigen (SCC-Ag), carcinoembryonic antigen (CEA), and carbohydrate antigen 724 (CA724) were subjected to assessment.

RESULTS

When compared to the control group (64.52%), the observation cohort's comprehensive effectiveness rate was considerably greater (80.30%). The observation group saw lower average radiation exposures and a reduction in the post-treatment concentrations of CEA, SCC-Ag, and CA724. The overall incidence of adverse effects from radiation treatment also declined. The observation group had a greater one-year survival rate (90.48%) than the control group (73.33%). When comparing the observation cohort to the control group, Kaplan-Meier survival analysis showed a significantly higher one-year survival rate (Log-Rank = 6.530, P= 0.011).

CONCLUSION

VMAT guided by ultrasound for patients with cervical cancer demonstrates promising short- and long-term treatment outcomes. It also leads to improvements in serum CEA, SCC-Ag, and CA724 levels, as well as reductions in the average radiation dosages to the radiotherapy target area, rectum, and bladder. This approach warrants attention from clinicians in clinical practice.

Performance assessment of the surface-guided radiation therapy system: Varian Identify

Image-guided radiotherapy (IGRT) systems using ionizing radiation may increase the risk of secondary cancer and normal tissue toxicity due to additional radiation exposure caused by large field sizes or repeated scans during X-ray imaging. As an alternative to these modalities, surface-guided radiotherapy (SGRT) systems which do not employ ionizing radiation have been developed. This study presents a comprehensive performance evaluation of the Varian Identify SGRT system by using an anthropomorphic Alderson Rando phantom in three different aspects: (a) the accuracy and reproducibility of the system in different regions of interest (ROI) for varying couch displacements, (b) the setup accuracy of the system for patient positioning based on different computed tomography (CT) slice thicknesses, and (c) the potential influence of obstructing SGRT cameras by the gantry on the system's overall accuracy and reproducibility. The accuracy and reproducibility of the SGRT system fell within 1 mm and 1°. Nevertheless, in certain situations, these values were observed to exceed prescribed limits. Consequently, concerning SGRT tolerance limits for treatment applications, careful consideration of ROIs and offset values of the system is crucial. We also recommend that patients should ideally be set up during 0° gantry rotation, and the on-board imaging (OBI) system should be retracted to prevent obstruction of the cameras. Additionally, reference CT images with a slice thickness of under 3 mm are recommended for this purpose.

Surface-guided radiotherapy overview: Technical aspects and clinical applications

In radiotherapy, patient positioning has long been ensured by ionizing imaging (kV or MV). Over the past ten years, surface-guided radiotherapy has appeared in radiotherapy departments. It is a continuous three-dimensional acquisition of the surface of the patient, based on the use of several optical cameras. The acquired surface is compared to an expected surface (usually taken from the planning scanner). Operators can constantly appreciate poor position, anatomical deformity or patient shift. Thus, the system allows an aid to the positioning of the patient, possibly without tattooing, but also a follow-up of the patient during the duration of the session. The most obvious contribution of the system concerns the treatment of the breast. In fact, for this location, the bone registration is not ideal and the target is visible in surface-guided radiotherapy. These systems also make it possible to treat in deep inspiration breath hold. But several other locations can benefit from it (pelvis, thorax, etc.).

Photodynamic Therapy: From the Basics to the Current Progress of N-Heterocyclic-Bearing Dyes as Effective Photosensitizers

Photodynamic therapy, an alternative that has gained weight and popularity compared to current conventional therapies in the treatment of cancer, is a minimally invasive therapeutic strategy that generally results from the simultaneous action of three factors: a molecule with high sensitivity to light, the photosensitizer, molecular oxygen in the triplet state, and light energy. There is much to be said about each of these three elements; however, the efficacy of the photosensitizer is the most determining factor for the success of this therapeutic modality. Porphyrins, chlorins, phthalocyanines, boron-dipyrromethenes, and cyanines are some of the N-heterocycle-bearing dyes' classes with high biological promise. In this review, a concise approach is taken to these and other families of potential photosensitizers and the molecular modifications that have recently appeared in the literature within the scope of their photodynamic application, as well as how these compounds and their formulations may eventually overcome the deficiencies of the molecules currently clinically used and revolutionize the therapies to eradicate or delay the growth of tumor cells.

In Silico Studies of the Impact of Rotational Errors on Translation Shifts and Dose Distribution in Image-Guided Radiotherapy

Objective: To compare the 6-dimensional errors of different immobilization devices and body regions based on 3-dimensional cone beam computed tomography for image-guided radiotherapy and to further quantitatively evaluate the impact of rotational corrections on translational shifts and dose distribution based on anthropomorphic phantoms. Materials and Methods: Two hundred ninety patients with cone beam computed tomographies from 3835 fractions were retrospectively analyzed for brain, head & neck, chest, abdomen, pelvis, and breast cases. A phantom experiment was conducted to investigate the impact of rotational errors on translational shifts using cone beam computed tomography and the registration system. For the dosimetry study, pitch rotations were simulated by adjusting the breast bracket by ±2.5°. Roll and yaw rotations were simulated by rotating the gantry and couch in the planning system by ±3.0°, respectively. The original plan for the breast region was designed in the computed tomography image space without rotation. With the same planning parameters, the original plan was transplanted into the image space with different rotations for dose recalculation. The effect of these errors on the breast target and organs at risk was assessed by dose-volume histograms. Results: Most of the mean rotational errors in the breast region were >1°. A single uncorrected yaw of 3° caused a change of 2.9 mm in longitudinal translation. A phantom study for the breast region demonstrated that when the pitch rotations were -2.5° and 2.5° and roll and yaw were both 3°, the reductions in the planning target volumes-V_{50 Gy} were 20.07% and 29.58% of the original values, respectively. When the pitch rotation was +2.5°, the left lung V_{5 Gy} and heart Dmean were 7.49% and 165.76 Gy larger, respectively, than the original values. Conclusions: Uncorrected rotations may cause changes in the values and directions of translational shifts. Rotational corrections may improve the patient setup and dose distribution accuracy.

[What do we need to deliver "online" adapted radiotherapy treatment plans?]

During the joint SFRO/SFPM session of the 2019 congress, a state of the art of adaptive radiotherapy announced a strong impact in our clinical practice, in particular with the availability of treatment devices coupled to an MRI system. Three years later, it seems relevant to take stock of adaptive radiotherapy in practice, and especially the "online" strategy because it is indeed more and more accessible with recent hardware and software developments, such as coupled accelerators to a three-dimensional imaging device and algorithms based on artificial intelligence. However, the deployment of this promising strategy is complex because it contracts the usual time scale and upsets the usual organizations. So what do we need to deliver adapted treatment plans with an "online" strategy?