Investigation of whether in-room CT-based adaptive intracavitary brachytherapy for uterine cervical cancer is robust against interfractional location variations of organs and/or applicators

Brachytherapy Workflow Practices: Analysis of Different Workflow Scenarios in Patients With Cervical Cancer and Impact on IGBT Implementation-An IAEA Study

PURPOSE

The workflow of brachytherapy (BT) is an essential aspect of treatment to consider in image-guided brachytherapy (IGBT). It has an overarching effect influencing patient throughput and the number of cancer treatments that can be performed as it occupies equipment, space, and personnel. There is limited research addressing this issue. Under the International Atomic Energy Agency's Coordinated Research Activity titled IGBT for cervix cancer: An implementation study, our study analyzes various scenarios in the clinical workflow of BT delivery for cervical cancer. It aims to determine the extent to which these scenarios allow the routine implementation of IGBT. With this information, current barriers and individualized adaptations to efficient workflows can be identified to enhance the global application of IGBT, leading to better cervical cancer treatment.

MATERIALS AND METHODS

A web-based poll of questions regarding practices in BT workflow was presented to 62 participants from low-, lower middle-, upper middle-, and high-income countries (19 countries).

RESULTS

This study highlighted diversity in BT practices across countries, income levels, and regions. It identified variations in workflow, patient throughput, and resource availability, which can have implications for the efficiency and quality of BT treatments. Scenario A, utilizing multiple locations for the steps of the BT procedure, was the most commonly used. The availability of resources, such as imaging devices and trained personnel, varied among the participating centers and remained challenging for IGBT implementation and sustainability.

CONCLUSION

The design of the BT facility plays a vital role in improving efficiency, with a dedicated BT suite contributing to an efficient workflow but limiting patient throughput, especially for high-volume centers. Although IGBT is effective, its implementation requires consideration of various logistical challenges and should be individualized.

Dosimetry and plan parameters study of three-dimensional-printed template-based intra-cavitary/interstitial interpolation technology using computed tomography-guided high-dose-rate brachytherapy in locally advanced cervical cancer

Purpose

To explore differences in dosimetry and planning parameters between intra-cavitary/interstitial interpolation (IC + ISBT) three-dimensional (3D)-printed template-based (3D-printed) and simple intra-cavity (ICBT) radiation techniques using a fixed Rotterdam three-tube applicator (TT) for computed tomography-guided high-dose-rate brachytherapy in locally advanced cervical cancer.

Material and methods

This retrospective study included 100 patients (n = 50 each in 3D-printed and Rotterdam three-tube applicator treatment groups) with FIGO stages IIB-IVB cervical cancer from May 2019 to May 2022. Using high-risk clinical target volume, 377 of 400 plans categorized at intervals of 10 cm3 into 20-30, 30-40, 40-50, 50-60, 60-70, and 70-80 cm3; 23 plans with < 20 and > 80 cm3 volume were excluded. Dosimetry parameters (D90 and D98 of high-risk clinical target volume, and D2cc of organs at risk, including bladder, rectum, sigmoid, and bowel) and planning parameters (homogeneity index [HI], conformation number [CN], and organ at risk sparing factor) were compared between the two groups separately for six high-risk clinical target volume plan categories.

Results

For the 3D-printing group, target coverage, organs at risk protection, and plan conformity and uniformity were better than those for the Rotterdam three-tube group. Particularly, in high-risk clinical target volume plans between 50-60 cm3, the mean D90 and D98 of high-risk clinical target volume were approximately 0.35 and 0.3 Gy higher, while the average D2cc of the bladder, rectum, sigmoid, and bowel were approximately 1.3, 0.9, 0.9, and 0.8 Gy significantly lower than those of the Rotterdam three-tube group, respectively (p < 0.05). The above-mentioned planning parameters differed significantly between the groups (p < 0.05).

Conclusions

For the 3D-printing group, IC/ISBT reduced the dose for organs at risk while ensuring target coverage and conformation. This was especially noticeable for plans with high-risk clinical target volume of 50-60 cm3.

Feasibility Study of Robust Optimization to Reduce Dose Delivery Uncertainty by Potential Applicator Displacements for a Cervix Brachytherapy

Brachytherapy is an important technique to increase the overall survival of cervical cancer patients. However, a possible shift of the applicators in relation to the target and organs at risk may occur between imaging and treatment. Without daily adaptive brachytherapy planning, these applicator displacements can lead to a significant change in dose distribution. In order to resolve it, a robust optimization method had been developed using a genetic algorithm combined with a median absolute deviation as a robustness evaluation function. The resulting robustness plans from our strategy might be worth considering according to the GEC-ESTRO guidelines. From the point of view of dose delivery uncertainty from applicator displacement, the robust optimization may be considered with caution in a single-plan approach for High Dose Rate brachytherapy treatment planning and should be confirmed by a more thorough investigation.

The Dosimetric Impact of Interfractional Organ-at-Risk Movement During Liver Stereotactic Body Radiation Therapy

PURPOSE

Stereotactic body radiation therapy (SBRT) is an effective therapy for treating liver malignancies. However, little is known about interfractional dose variations to adjacent organs at risk (OARs). We examine the effects of interfractional organ movement and setup variation on dose delivered to OARs in patients receiving liver SBRT.

METHODS AND MATERIALS

Thirty patients treated with liver SBRT were analyzed. Daily image guidance with diagnostic quality computed tomography-on-rails imaging was performed before each fraction. In phase 1, these daily images were used to delineate all OARs including the liver, heart, right kidney, esophagus, stomach, duodenum, and large bowel in 10 patients. In phase 2, only OARS in close proximity to the target were contoured in 20 additional patients. Dose distribution on each daily computed tomography was generated, and daily doses to each OAR were recorded and compared with clinical thresholds to determine whether a daily dose excess (DDE) occurred.

RESULTS

In phase 1, significant interfractional dose differences between planned and delivered dose to OARs were observed, but differences were rarely clinically significant, with just 1 DDE. In phase 2, multiple DDEs were recorded for OARs close to the target, mainly involving the stomach, heart, and esophagus. Tumors in the hilum and liver segments I, IV, and VIII were the most common locations for DDEs. On root cause analysis, 3 etiologies of DDE emerged: craniocaudal shift (69.2%), anatomic changes (28.2%), and anteroposterior shifts (2.6%).

CONCLUSIONS

OARs close to liver lesions may receive higher doses than expected during SBRT owing to interfractional variations in OARs relative to the target. These differences in planned versus expected dose can lead to toxicity. Efforts to better evaluate OARs with daily image guidance may help reduce risks. Application of adaptive replanning and improved and real-time image guidance could mitigate risks of toxicity, and further study into their applications is warranted.