Factors influencing intrafractional target shifts in lung stereotactic body radiation therapy

A planning-based feasibility study of MR-Linac treatment for anal cancer radiation therapy

The hybrid magnetic resonance image (MRI) scanner and radiation therapy linear accelerator (MR-Linac) has the potential to enhance clinical outcomes for anal cancer (AC) patients with improved soft tissue visualization and daily plan adaption but has planning and delivery limitations due to the incorporation of MRI. We aimed to identify if Elekta Unity MR-Linac-based radiation therapy is feasible for anal cancer. Ten prospectively enrolled AC patients treated with radical chemoradiotherapy were replanned for MR-Linac treatment using departmental planning criteria. For comparison, and to reduce interobserver variability, volumetric modulated arc radiation therapy (VMAT) plans were also created for each patient by the same single senior radiation therapist. Plans were compared using departmental dosimetric plan criteria, as well as conformity and homogeneity indices, monitor units (MUs) and measured plan delivery (beam-on) time. Results were deemed clinically acceptable. Target and organ at risk (OAR) doses were comparable between MR-Linac plans and VMAT plans, although PTV45Gy D98% coverage was compromised in 3 of 10 MR-Linac plans due to caudocranial length exceeding the limits of the MR-Linac. MR-Linac plans had lower MUs, median of 689.1 vs 849.65 (p = 0.002), but took over twice as long to deliver, 529.5s vs 224s (p = <0.0001) as VMAT plans. MR-Linac planning and treatment of AC is feasible for a subset of patients. The current physical limitations of the Elekta Unity system mean patients with large caudocranial elective PTV45Gy target volumes may not be covered dosimetrically to the required clinical standard. Longer image verification and treatment delivery times of the MR-Linac also mean patient selection and intrafractional IGRT are likely to be integral to ensuring high quality clinical outcomes in this rare cancer.

Influence of Clinical and Tumor Factors on Interfraction Setup Errors With Rotation Correction for Vacuum Cushion in Lung Stereotactic Body Radiation Therapy

Purpose

To explore the influence of clinical and tumor factors over interfraction setup errors with rotation correction for non-small cell lung cancer (NSCLC) stereotactic body radiation therapy (SBRT) patients immobilized in vacuum cushion (VC) to better understand whether patient re-setup could further be optimized with these parameters.

Materials and Methods

This retrospective study was conducted on 142 NSCLC patients treated with SBRT between November 2017 to July 2019 in the local institute. Translation and rotation setup errors were analyzed in 732 cone-beam computed tomography (CBCT) scans before treatment. Differences between groups were analyzed using independent sample t-test. Logistic regression test was used to analyze possible correlations between patient re-setup and clinical and tumor factors.

Results

Mean setup errors were the largest in anterior-posterior (AP) direction (3.2 ± 2.4 mm) compared with superior-inferior (SI) (2.8 ± 2.1 mm) and left-right (LR) (2.5 ± 2.0 mm) directions. The mean values were similar in pitch, roll, and rtn directions. Of the fractions, 83.7%, 90.3%, and 86.6% satisfied setup error tolerance limits in AP, SI, and LR directions, whereas 95% had rotation setup errors of <2° in the pitch, roll, or rtn directions. Setup errors were significantly different in the LR direction when age, body mass index (BMI), and "right vs. left" location parameters were divided into groups. Both univariate and multivariable model analyses showed that age (p = 0.006) and BMI (p = 0.002) were associated with patient re-setup.

Conclusions

Age and BMI, as clinical factors, significantly influenced patient re-setup in the current study, whereas all other clinical and tumor factors were not correlated with patient re-setup. The current study recommends that more attention be paid to setup for elderly patients and patients with larger BMI when immobilized using VC, especially in the left-right direction.

Assessment of IGRT variability for lung SBRT

PURPOSE

The purpose of this project was to assess factors that may influence variability in the pre-treatment kilovoltage cone beam computed tomography (kV CBCT) image matching process for lung stereotactic body radiation therapy (SBRT).

METHODS AND MATERIALS

Pre-treatment CBCT and planning CT data sets of previously-treated lung SBRT patients were gathered and anonymized from four radiotherapy centers in Alberta. Eight radiation therapists (RTTs) and four radiation oncologists (ROs) were recruited from the same four cancer centers for image matching. Identical data sets were provided to each user, but the order of image sets was randomized independently for each user to remove any learning bias. Inter-user variabilities were then investigated as functions of various factors, including image origin (source institution/machine), user's institution (local matching protocol), profession (RTT vs. RO), years of experience and image quality (presence/absence of added noise).

RESULTS

Very little variation in image matching between different users was observed. The mean differences from the consensus means for different image sets were less than 1 mm in all directions, and cases that exceeded 3 mm (i.e. clinically significant differences) were extremely rare. Image origin, user's institution, and profession (RTT vs. RO) didn't lead to any meaningful clinical differences, while image quality didn't introduce any statistically significant differences. In addition, no discernible trend was seen between user's experience and deviation from the user mean. Overall, no meaningful differences in inter-user variabilities for the different factors investigated were found in this study.

CONCLUSIONS

There appears to be an adequate standardization across the province of Alberta in terms of CBCT image matching process. No clinically significant differences were observed as functions of various factors investigated in this study. Consistency in matching between RTTs and ROs in this study suggests that RTTs do not need systematic RO approval of their lung CBCT match. It should be noted that RTTs at the centers in this study receive comprehensive training in CBCT-based image matching.

A randomised comparison of three different immobilisation devices for thoracic and abdominal cancers

Introduction

Patient immobilisation is critically important for both highly conformal conventionally fractionated radiotherapy and for stereotactic body radiotherapy. Different immobilisation devices are available to maintain patient position for radiotherapy but the most suitable one remains unknown.

Methods

Forty‐five patients were randomly allocated to one of three immobilisation devices; the Q fix arm shuttle, BodyFIX without wrap or BodyFIX with wrap. Patients were imaged before and after treatment to ascertain intra‐fraction and inter‐fraction motion. Bony anatomy was used for matching to determine the positional accuracy of each device. Treatments were timed using a standard method. Patient comfort and staff satisfaction questionnaires were also issued to determine comfort, ease of use and preferences for each device.

Results

The BodyFIX without wrap was the more accurate device; however, the differences between the devices were not statistically significant. The BodyFIX with wrap was found to take significantly longer to set up and set down compared to the arm shuttle and the BodyFIX without wrap (all P < 0.001). Patients (37%) marginally preferred the BodyFIX with wrap. Most (81%) staff preferred the BodyFIX without wrap.

Conclusion

Immobilisation using the BodyFIX without wrap was deemed to be suitable for clinical use. It was a clinically accurate device, the more efficient in terms of set up and set down time, the most preferred by staff and was accepted by patients.

4DCT and CBCT based PTV margin in Stereotactic Body Radiotherapy(SBRT) of non-small cell lung tumor adhered to chest wall or diaphragm

Background

Large tumor motion often leads to larger treatment volumes, especially the lung tumor located in lower lobe and adhered to chest wall or diaphragm. The purpose of this work is to investigate the impacts of planning target volume (PTV) margin on Stereotactic Body Radiotherapy (SBRT) in non-small cell lung cancer (NSCLC).

Methods

Subjects include 20 patients with the lung tumor located in lower lobe and adhered to chest wall or diaphragm who underwent SBRT. Four-dimensional computed tomography (4DCT) were acquired at simulation to evaluate the tumor intra-fractional centroid and boundary changes, and Cone-beam Computer Tomography (CBCT) were acquired during each treatment to evaluate the tumor inter-fractional set-up displacement. The margin to compensate for tumor variations uncertainties was calculated with various margin calculated recipes published in the exiting literatures.

Results

The means (±standard deviation) of tumor centroid changes were 0.16 (±0.13) cm, 0.22 (±0.15) cm, and 1.37 (±0.81) cm in RL, AP, and SI directions, respectively. The means (±standard deviation) of tumor edge changes were 0.21 (±0.18) cm, 0.50 (±0.23) cm, and 0.19 (±0.44) cm in RL, AP, and SI directions, respectively. The means (±standard deviation) of tumor set-up displacement were 0.03 (±0.24) cm, 0.02 (±0.26) cm, and 0.02 (±0.43) cm in RL, AP, and SI directions, respectively. The PTV margin to compensate for lung cancer tumor variations uncertainties were 0.88, 0.98 and 2.68 cm in RL, AP and SI directions, which were maximal among all margin recipes.

Conclusions

4DCT and CBCT imaging are appropriate to account for the tumor intra-fractional centroid, boundary variations and inter-fractional set-up displacement. The PTV margin to compensate for lung cancer tumor variations uncertainties can be obtained. Our results show that a conventional 1.0 cm margin in the SI plane dose not suffice to compensate the geometrical variety of the tumor located in lower lobe and adhered to chest wall and diaphragm.

Influence of different treatment techniques and clinical factors over the intrafraction variation on lung stereotactic body radiotherapy

PURPOSE

In the present study we compared three different Stereotactic body radiation therapy (SBRT) treatment delivery techniques in terms of treatment time (TT) and their relation with intrafraction variation (IFV). Besides that, we analyzed if different clinical factors could have an influence on IFV. Finally, we appreciated the soundness of our margins.

MATERIALS AND METHODS

Forty-five patients undergoing SBRT for stage I lung cancer or lung metastases up to 5 cm were included in the study. All underwent 4DCT scan to create an internal target volume (ITV) and a 5 mm margin was added to establish the planning target volume (PTV). Cone-beam CTs (CBCTs) were acquired before and after each treatment to quantify the IFV. Three different treatment delivery techniques were employed: fixed fields (FF), dynamically collimated arcs (AA) or a combination of both (FA). We studied if TT was different among these modalities of SBRT and whether TT and IFV were correlated. Clinical data related to patients and tumors were recorded as potential influential factors over the IFV.

RESULTS

A total of 52 lesions and 147 fractions were analyzed. Mean IFV for x-, y- and z-axis were 1 ± 1.16 mm, 1.29 ± 1.38 mm and 1.17 ± 1.08 mm, respectively. Displacements were encompassed by the 5 mm margin in 96.1 % of fractions. TT was significantly longer in FF therapy (24.76 ± 5.4 min), when compared with AA (15.30 ± 3.68 min) or FA (17.79 ± 3.52 min) (p < 0.001). Unexpectedly, IFV did not change significantly between them (p = 0.471). Age (p = 0.003) and left vs. right location (p = 0.005) were related to 3D shift ≥2 mm. In the multivariate analysis only age showed a significant impact on the IFV (OR = 1.07, p = 0.007).

CONCLUSIONS

The choice of AA, FF or FA does not impact on IFV although FF treatment takes significantly longer treatment time. Our immobilization device offers enough accuracy and the 5 mm margin may be considered acceptable as it accounts for more than 95 % of tumor shifts. Age is the only clinical factor that influenced IFV significantly in our analysis.

The development of stereotactic body radiotherapy in the past decade: a global perspective

In the past 10 years, there has been an exponential increase in the incorporation of stereotactic body radiotherapy, also known as stereotactic ablative radiotherapy, into the armamentarium against various types of cancer in different settings worldwide. In this article in the 10th year anniversary issue of Future Oncology, representatives from the USA, Canada, Japan, Germany, The Netherlands, Australia and Singapore will provide individual perspectives of the development of stereotactic body radiotherapy in their respective countries.