Respiratory motion of adrenal gland metastases: Analyses using four-dimensional computed tomography images

Stereotactic Magnetic Resonance-Guided Adaptive and Non-Adaptive Radiotherapy on Combination MR-Linear Accelerators: Current Practice and Future Directions

Stereotactic body radiotherapy (SBRT) is an effective radiation therapy technique that has allowed for shorter treatment courses, as compared to conventionally dosed radiation therapy. As its name implies, SBRT relies on daily image guidance to ensure that each fraction targets a tumor, instead of healthy tissue. Magnetic resonance imaging (MRI) offers improved soft-tissue visualization, allowing for better tumor and normal tissue delineation. MR-guided RT (MRgRT) has traditionally been defined by the use of offline MRI to aid in defining the RT volumes during the initial planning stages in order to ensure accurate tumor targeting while sparing critical normal tissues. However, the ViewRay MRIdian and Elekta Unity have improved upon and revolutionized the MRgRT by creating a combined MRI and linear accelerator (MRL), allowing MRgRT to incorporate online MRI in RT. MRL-based MR-guided SBRT (MRgSBRT) represents a novel solution to deliver higher doses to larger volumes of gross disease, regardless of the proximity of at-risk organs due to the (1) superior soft-tissue visualization for patient positioning, (2) real-time continuous intrafraction assessment of internal structures, and (3) daily online adaptive replanning. Stereotactic MR-guided adaptive radiation therapy (SMART) has enabled the safe delivery of ablative doses to tumors adjacent to radiosensitive tissues throughout the body. Although it is still a relatively new RT technique, SMART has demonstrated significant opportunities to improve disease control and reduce toxicity. In this review, we included the current clinical applications and the active prospective trials related to SMART. We highlighted the most impactful clinical studies at various tumor sites. In addition, we explored how MRL-based multiparametric MRI could potentially synergize with SMART to significantly change the current treatment paradigm and to improve personalized cancer care.

Two-institution results of Stereotactic Body Radiation Therapy (SBRT) for treating adrenal gland metastases from liver cancer

OBJECTIVE

Stereotactic Body Radiation Therapy (SBRT) has been found beneficial for adrenal gland metastases (AGMs) with a high local control rate and low toxicity. The role of SBRT for AGMs in patients with liver cancer has not been well-discussed before. We, therefore, report our two-institution experience to further elaborate on the feasibility and effectiveness of SBRT in the treatment of AGMs from liver cancer.

METHODS

A total of 23 liver cancer patients (19 males, 4 females) with 24 AGMs treated by SBRT from July 2006 to April 2021 were retrospectively included in this study. Toxicity was assessed based on clinical adverse events using the Common Terminology Criteria for Adverse Events (CTCAE) version 5.0. The effectiveness was assessed based on local control (LC), progression-free survival (PFS), and overall survival (OS), which were calculated using the Kaplan-Meier method. Univariate analyses were compared by log-rank test. The relevant covariates were evaluated using Cox proportional hazards models.

RESULTS

The median dose was 40 Gy in 5 fractions, with the corresponding median biological effective dose (BED10, α/β = 10 Gy) of 72 Gy. The median overall follow-up time was 15.4 months (range: 4.2-70.6 months). The complete response (CR), partial response (PR), stable disease (SD) and progressive disease (PD) rates were 25.0%, 20.8%, 33.3%, and 20.8%, respectively. All 6 patients with AGMs accompanying symptoms had varying degrees of alleviation after SBRT. The 0.5-, 1-year and 2-year LC rates were 87.5%, 77.8%, and 77.8%, respectively. The 0.5-, 1-year and 2-year OS rates were 95.5%, 66.8%, and 41.1%, respectively. The treatments were all tolerated with only one patient reporting a grade-3 hepatic injury. The univariate analysis concluded that only gross tumor volume (GTV) < 34.5 ml (p = 0.039) was associated with a favorable LC rate. After multivariate analysis, favorable predictors correlated with OS were GTV < 34.5 ml (p = 0.043), systemic therapy (p = 0.017), and without additional organ metastasis after SBRT (p = 0.009).

CONCLUSION

Our results suggest that SBRT is a safe and effective technique to treat AGM from liver cancer, especially for small GTV (< 34.5ml). Moreover, the small metastatic lesion volume, fewer metastatic lesions, and intervention of systemic therapy are more likely to improve OS.

Breath-hold versus mid-ventilation in SBRT of adrenal metastases

PURPOSE

To improve local control in radiotherapy of adrenal metastases precise dose delivery without increasing toxicity is vital. Decreasing the Clinical Target Volume (CTV) - Planning Target Volume (PTV) margins by reducing breathing movement can achieve this. Few data were published concerning the effect of a breath-hold technique. This study investigates the potential of Active Breathing Control (ABC) to limit adrenal breathing movement and reduce CTV-PTV margins.

METHODS

We compared adrenal gland movement in free-breathing, making use of the Mid-ventilation (MidV) technique, and with ABC. The coordinates of the adrenal glands obtained on ten phases of a free breathing 4D-CT and on several repeat inspiration ABC CT-scans were measured. Separate coordinates, the random margin component and the margin vector norm were computed and compared between the two techniques.

RESULTS

We compared the two techniques in 11 patients (21 adrenal glands) and found the largest movement in the Z-direction, with values of 8.7 ± 4.2 mm for MidV and 2.4 ± 1.5 mm for ABC. In 71% of the cases ABC resulted in a smaller margin component than MidV, although non-significant (p ≥ 0.4).

CONCLUSION

Movement of the adrenal gland is largest in the Z-direction. The mean difference in the margin vector norm between both techniques was small with large variations over the patient group, the clinical effect of these differences is unknown. Applying an individualised motion management strategy could be beneficial. If a peak-to-peak amplitude above 15 mm in the Z-direction is observed in the MidV scan we advise to examine if a breath-hold technique could reduce margins.

Real-time control of respiratory motion: Beyond radiation therapy

Motion management in radiation oncology is an important aspect of modern treatment planning and delivery. Special attention has been paid to control respiratory motion in recent years. However, other medical procedures related to both diagnosis and treatment are likely to benefit from the explicit control of breathing motion. Quantitative imaging - including increasingly important tools in radiology and nuclear medicine - is among the fields where a rapid development of motion control is most likely, due to the need for quantification accuracy. Emerging treatment modalities like focussed-ultrasound tumor ablation are also likely to benefit from a significant evolution of motion control in the near future. In the present article an overview of available respiratory motion systems along with ongoing research in this area is provided. Furthermore, an attempt is made to envision some of the most expected developments in this field in the near future.

Role of Daily Plan Adaptation in MR-Guided Stereotactic Ablative Radiation Therapy for Adrenal Metastases

PURPOSE

To study interfractional organ changes during magnetic resonance (MR)-guided stereotactic ablative radiation therapy for adrenal metastases and to evaluate the dosimetric advantages of online plan adaptation.

METHODS AND MATERIALS

Seventeen patients underwent a total of 84 fractions of video-assisted, respiration-gated, MR-guided adaptive radiation therapy to deliver either 50 Gy (5 fractions), 60 Gy (8 fractions), or 24 Gy (3 fractions). An MR scan was repeated before each fraction, followed by rigid coregistration to the gross tumor volume (GTV) on the pretreatment MR scan. Contour deformation, planning target volume (PTV) (GTV + 3 mm) expansion, and online plan reoptimization were then performed. Reoptimized plans were compared with baseline treatment plans recalculated on the anatomy-of-the-day ("predicted plans"). Interfractional changes in organs at risk (OARs) were quantified according to OAR volume changes within a 3 cm distance from the PTV surface, center of mass displacements, and the Dice similarity coefficient. Plan quality evaluation was based on target coverage (GTV and PTV) and high dose sparing of all OARs (V_36Gy, V_33Gy, and V_25Gy).

RESULTS

Substantial center of mass displacements were observed for stomach, bowel, and duodenum, 17, 27 and 36 mm, respectively. Maximum volume changes for the stomach, bowel, and duodenum within 3 cm of PTV were 23.8, 20.5, and 20.9 cm³, respectively. Dice similarity coefficient values for OARs ranged from 0.0 to 0.9 for all fractions. Baseline plans recalculated on anatomy-of-the-day revealed underdosage of target volumes and variable OAR sparing, leading to a failure to meet institutional constraints in a third of fractions. Online reoptimization improved target coverage in 63% of fractions and reduced the number of fractions not meeting the V_95% objective for GTV and PTV. Reoptimized plans exhibited significantly better sparing of OARs.

CONCLUSIONS

Significant interfractional changes in OAR positions were observed despite breath-hold stereotactic ablative radiation therapy delivery under MR-guidance. Online reoptimization of treatment plans led to significant improvements in target coverage and OAR sparing.

Definition of the margin of major coronary artery bifurcations during radiotherapy with electrocardiograph-gated 4D-CT

PURPOSE

The aim was to measure the cardiac motion-induced displacements of major coronary artery bifurcations utilizing electrocardiography (ECG)-gated four-dimensional computed tomography (4D-CT) and to determine the margin of coronary artery bifurcations.

METHODS

Thirty-seven female patients who underwent retrospective ECG-gated 4D-CT in inspiratory breath hold (IBH) were enrolled. The left main coronary artery bifurcation (LM), the obtuse marginal branch bifurcation (OM), the first diagonal branch bifurcation (D₁), the second diagonal branch bifurcation (D₂), the caudal portion of the left anterior descending branch (APX), the first right ventricular artery bifurcation (V) and the acute marginal branch bifurcation (AM) were contoured. The center of the contour of the coronary arterial bifurcations at end systole was defined as the standard, and the margin were then calculated.

RESULTS

The margin in the left-right (LR), cranio-caudal (CC), and anterior-posterior (AP) coordinates were as follows: LM 3, 3, and 3 mm; D₁ 6, 3, and 3 mm; D₂ 3, 3, and 3 mm; APX 4, 4, and 4 mm; OM 4, 6, and 5 mm; V 6, 8, and 7 mm; and AM 6, 8, and 7 mm, respectively.

CONCLUSION

Coronary artery bifurcations should be considered a separate organ at risk (OAR), and different margin should be provided due to the differences resulting from motion displacement. The maximum margin in the LR, CC, and AP coordinates of left coronary artery bifurcations were 6, 6, and 5 mm, and those of the right coronary artery bifurcations were 6, 8, and 7 mm, respectively.