A methodology to determine margins by EPID measurements of patient setup variation and motion as applied to immobilization devices

Investigation of intrafractional spinal cord and spinal canal movement during stereotactic MR-guided online adaptive radiotherapy for kidney cancer

BACKGROUND AND PURPOSE

This study aimed to investigate the intrafractional movement of the spinal cord and spinal canal during MR-guided online adaptive radiotherapy (MRgART) for kidney cancer.

MATERIALS AND METHODS

All patients who received stereotactic MRgART for kidney cancer between February 2022 and February 2024 were included in this study. Patients received 30-42 Gy in 3-fraction MRgART for kidney cancer using the Elekta Unity, which is equipped with a linear accelerator and a 1.5 Tesla MRI. MRI scans were performed at three points during each fraction: for online planning, position verification, and posttreatment assessment. The spinal cord was contoured from the upper edge of Th12 to the medullary cone, and the spinal canal was contoured from Th12 to L3, using the first MRI. These contours were adjusted to the second and third MR images via deformable image registration, and movements were measured. Margins were determined via the formula "1.3×Σ+0.5×σ" and 95% prediction intervals.

RESULTS

A total of 22 patients (66 fractions) were analyzed. The median interval between the first and third MRI scans were 38 minutes. The mean ± standard deviation of the spinal cord movements after this interval were -0.01 ± 0.06 for the x-axis (right-left), 0.01 ± 0.14 for the y-axis (caudal-cranial), 0.07 ± 0.05 for the z-axis (posterior-anterior), and 0.15 ± 0.08 for the 3D distance, respectively. The correlation coefficients of the 3D distance between the spinal cord and the spinal canal was high (0.92). The calculated planning organ at risk volume margin for all directions was 0.11 cm for spinal cord. The 95% prediction intervals for the x-axis, y-axis, and z-axis were -0.11-0.09 cm, -0.23-0.25 cm and -0.14-0.03 cm, respectively.

CONCLUSIONS

Margins are necessary in MRgART to compensate for intrafractional movement and ensure safe treatment delivery.

Effects of remedies made in patient setup process on residual setup errors and margins in head and neck cancer radiotherapy based on 2D image guidance

AIM

Patient setup errors were aimed to be reduced in radiotherapy (RT) of head-and-neck (H&N) cancer. Some remedies in patient setup procedure were proposed for this purpose.

BACKGROUND

RT of H&N cancer has challenges due to patient rotation and flexible anatomy. Residual position errors occurring in treatment situation and required setup margins were estimated for relevant bony landmarks after the remedies made in setup process and compared with previous results.

MATERIALS AND METHODS

The formation process for thermoplastic masks was improved. Also image matching was harmonized to the vertebrae in the middle of the target and a 5 mm threshold was introduced for immediate correction of systematic errors of the landmarks. After the remedies, residual position errors of bony landmarks were retrospectively determined from 748 orthogonal X-ray images of 40 H&N cancer patients. The landmarks were the vertebrae C1-2, C5-7, the occiput bone and the mandible. The errors include contributions from patient rotation, flexible anatomy and inter-observer variation in image matching. Setup margins (3D) were calculated with the Van Herk formula.

RESULTS

Systematic residual errors of the landmarks were reduced maximally by 49.8% (p ≤ 0.05) and the margins by 3.1 mm after the remedies. With daily image guidance the setup margins of the landmarks were within 4.4 mm, but larger margins of 6.4 mm were required for the mandible.

CONCLUSIONS

Remarkable decrease in the residual errors of the bony landmarks and setup margins were achieved through the remedies made in the setup process. The importance of quality assurance of the setup process was demonstrated.

Assessment and quantification of patient set-up errors in nasopharyngeal cancer patients and their biological and dosimetric impact in terms of generalized equivalent uniform dose (gEUD), tumour control probability (TCP) and normal tissue complication probability (NTCP)

OBJECTIVE

The aim of this study is to assess and quantify patients' set-up errors using an electronic portal imaging device and to evaluate their dosimetric and biological impact in terms of generalized equivalent uniform dose (gEUD) on predictive models, such as the tumour control probability (TCP) and the normal tissue complication probability (NTCP).

METHODS

20 patients treated for nasopharyngeal cancer were enrolled in the radiotherapy-oncology department of HCA. Systematic and random errors were quantified. The dosimetric and biological impact of these set-up errors on the target volume and the organ at risk (OARs) coverage were assessed using calculation of dose-volume histogram, gEUD, TCP and NTCP. For this purpose, an in-house software was developed and used.

RESULTS

The standard deviations (1SDs) of the systematic set-up and random set-up errors were calculated for the lateral and subclavicular fields and gave the following results: ∑ = 0.63 ± (0.42) mm and σ = 3.75 ± (0.79) mm, respectively. Thus a planning organ at risk volume (PRV) margin of 3 mm was defined around the OARs, and a 5-mm margin used around the clinical target volume. The gEUD, TCP and NTCP calculations obtained with and without set-up errors have shown increased values for tumour, where ΔgEUD (tumour) = 1.94% Gy (p = 0.00721) and ΔTCP = 2.03%. The toxicity of OARs was quantified using gEUD and NTCP. The values of ΔgEUD (OARs) vary from 0.78% to 5.95% in the case of the brainstem and the optic chiasm, respectively. The corresponding ΔNTCP varies from 0.15% to 0.53%, respectively.

CONCLUSION

The quantification of set-up errors has a dosimetric and biological impact on the tumour and on the OARs. The developed in-house software using the concept of gEUD, TCP and NTCP biological models has been successfully used in this study. It can be used also to optimize the treatment plan established for our patients.

ADVANCES IN KNOWLEDGE

The gEUD, TCP and NTCP may be more suitable tools to assess the treatment plans before treating the patients.

A prospective analysis of inter- and intrafractional errors to calculate CTV to PTV margins in head and neck patients

PURPOSE

To evaluate an institute-specific CTV-PTV margin for head and neck (HN) patients according to a 3-mm action level protocol.

METHODS/PATIENTS

Twenty-three HN patients were prospectively analysed. Patients were immobilized with a thermoplastic mask. Inter- and intrafractional set-up errors (in the three dimensions) were assessed from portal images (PI) registration. Digitally reconstructed radiographs (DRRs) were compared with two orthogonal PI by matching bone anatomy landmarks. The isocenter was verified during the first five consecutive days of treatment: if the mean error detected was greater than 2 mm the isocenter position was corrected for the rest of the treatment. Isocenter was checked weekly thereafter. Set-up images were obtained before and after treatment administration on 10, 20 and 30 fractions to quantify the intrafractional displacement. For the set-up errors, systematic (Σ), random (σ), overall standard deviations, and the overall mean displacement (M), were determined. CTV to PTV margin was calculated considering both inter- and intrafractional errors.

RESULTS

A total of 396 portal images was analysed in 23 patients. Systematic interfractional (Σ(inter)) set-up errors ranged between 0.77 and 1.42 mm in the three directions, whereas the random (σ (inter)) errors were around 1-1.31 mm. Systematic intrafractional (Σ(intra)) errors ranged between 0.65 and 1.11 mm, whereas the random (σ (intra)) errors were around 1.13-1.16 mm.

CONCLUSIONS

A verification protocol (3-mm action level) provided by EPIDs improves the set-up accuracy. Intrafractional error is not negligible and contributes to create a larger CTV-PTV margin. The appropriate CTV-PTV margin for our institute is between 3 and 4.5 mm considering both inter- and intrafractional errors.

Development of a phantom to evaluate the positioning accuracy of patient immobilization systems using thermoplastic mask and polyurethane cradle

PURPOSE

The purpose of this study was to develop a new phantom to evaluate the positioning accuracy of patient immobilization systems.

METHODS

The phantom was made of papers formed into a human shape, paper clay, and filling rigid polyester. Acrylonitrile butadiene styrene (ABS) pipes were inserted at anterior-posterior (A-P) and right-left (R-L) directions in the phantom to give static load by pulling ropes through the pipes. First, the positioning precision of the phantom utilizing a target locating system (TLS) was evaluated by moving the phantom on a couch along inferior-superior (I-S), A-P, and R-L directions in a range from -5 mm to +5 mm. The phantom's positions detected with the TLS were compared with values measured by a vernier caliper. Second, the phantom movements in a tensile test were chosen from patient movements determined from 15 patients treated for intracranial lesions and immobilized with a thermoplastic mask and polyurethane cradle. The phantom movement was given by minimum or maximum values of patient movements in each direction. Finally, the relationship between phantom movements and the static load in the tensile test was characterized from measurements using the new phantom and the TLS.

RESULTS

The differences in all positions between the vernier caliper measurement and the TLS detected values were within 0.2 mm with frequencies of 100%, 95%, and 90% in I-S, A-P, and R-L directions, respectively. The phantom movements according to patient movements in clinical application in I-S, A-P, and R-L directions were within 0.58 mm, 0.94 mm, and 0.93 mm from the mean value plus standard deviation, respectively. The regression lines between the phantom movements and static load were given by y = 0.359x, y = 0.241x, and y = 0.451x in I-S, A-P, and R-L directions, respectively, where x is the phantom movement (mm) and y is the static load (kgf). The relationship between the phantom movements and static load may represent the performance of inhibiting patient movements, so the accuracy of the immobilization system in the intracranial lesion will be estimated in advance by basic tensile test on the new phantom.

CONCLUSIONS

The newly developed phantom was useful to evaluate the accuracy of immobilization systems for a Cyberknife system for intracranial lesions.

Correction of systematic set-up error in breast and head and neck irradiation through a no-action level (NAL) protocol

PURPOSE

To quantify systematic and random patient set-up errors in breast and head and neck conventional irradiation and to evaluate a no-action level (NAL) protocol for systematic set-up error off-line correction in head and neck cancer and breast cancer patients.

MATERIAL AND METHODS

Verification electronic portal images of orthogonal set-up fields were obtained daily for the initial four consecutive fractions for 20 patients treated for breast cancer and for 20 head and neck cancer patients. The calculated systematic error was used to shift the isocentre accordingly on the fifth treatment day. From then until the end of the treatment course, pair orthogonal portal images of set-up fields were obtained weekly. To assess the impact of the protocol, pre- and post-correction systematic errors were compared and PTV margins were estimated before and after correction using published margin recipes.

RESULTS

Population systematic set-up error decreased in the breast cancer patient group after the implementation of NAL protocol from 4.0 to 1.7 mm on the x-axis, from 4.7 to 2.1 mm on the y-axis and from 2.8 to 0.9 mm on the z axis. The percentage of patients with individual systematic set-up error reduction was 80%, 90% and 80% on the x-, y and z-axes respectively. Population systematic set-up error decreased also in the head and neck cancer patient group from 2.3 to 1.1 mm on the x-axis, from 1.6 to 1.4 mm on the y-axis and from 1.7 to 0.7 mm on the z-axis. The percentage of patients with individual systematic set-up error reduction was 70%, 65% and 85% on the x-, y- and z-axes respectively. Margin reduction achievable with NAL protocol implementation on the x-, y- and z-axes was 6.3, 7.2 and 4.8 mm for breast cancer patients and 3.3, 0.6 and 2.8 mm for head and neck cancer patients.

CONCLUSION

NAL off-line protocol is useful for systematic set-up error correction and PTV margin reduction in conventional breast and head and neck irradiation.

Adaptive radiation therapy for head and neck cancer-can an old goal evolve into a new standard?

Current head and neck intensity-modulated radiotherapy (IMRT) techniques cause significant toxicity. This may be explained in part by the fact that IMRT cannot compensate for changes in the location of disease and normal anatomy during treatment, leading to exposure of at-risk bystander tissues to higher-than-anticipated doses. Adaptive radiotherapy (ART) is a novel approach to correct for daily tumor and normal tissue variations through online or offline modification of original IMRT target volumes and plans. ART has been discussed on a conceptual level for many years, but technical limitations have hampered its integration into routine care. In this paper, we review the key anatomic, dosimetric, and treatment delivery issues at play in current investigational development of head and neck ART. We also describe pilot findings from initial clinical deployment of head and neck ART, as well as emerging pathways of future research.

Contemplation of head and neck intensity-modulated radiotherapy

Intensity-modulated radiootherapy (IMRT) is being rapidly embraced as a radiotherapy technique in many cancer centres across the world. This paper aims to highlight the reported problems associated with the use of IMRT for the treatment of head and neck cancer. Specific areas of concern that are mentioned are the identification of tumour volumes, reproducibility of treatment, issues of tumour resistance and tumour recurrence. Radiotherapy departments are advised to make haste slowly when considering the implementation of this technique.

Possible fractionated regimens for image-guided intensity-modulated radiation therapy of large arteriovenous malformations

The aim of this study was to estimate a plausible alpha/beta ratio for arteriovenous malformations (AVMs) based on reported clinical data, and to design possible fractionation regimens suitable for image-guided intensity-modulated radiation therapy (IG-IMRT) for large AVMs based on the newly obtained alpha/beta ratio. The commonly used obliteration rate (OR) for AVMs with a three year angiographic follow-up from many institutes was fitted to linear-quadratic (LQ) formalism and the Poisson OR model. The determined parameters were then used to calculate possible fractionation regimens for IG-IMRT based on the concept of a biologically effective dose (BED) and an equivalent uniform dose (EUD). The radiobiological analysis yields a alpha/beta ratio of 2.2 +/- 1.6 Gy for AVMs. Three sets of possible fractionated schemes were designed to achieve equal or better biological effectiveness than the single-fraction treatments while maintaining the same probability of normal brain complications. A plausible alpha/beta ratio was derived for AVMs and possible fractionation regimens that may be suitable for IG-IMRT for large AVM treatment are proposed. The sensitivity of parameters on the calculation was also studied. The information may be useful to design new clinical trials that use IG-IMRT for the treatment of large AVMs.

Quantifying Appropriate PTV Setup Margins: Analysis of Patient Setup Fidelity and Intrafraction Motion Using Post-Treatment Megavoltage Computed Tomography Scans

PURPOSE

To present a technique that can be implemented in-house to evaluate the efficacy of immobilization and image-guided setup of patients with different treatment sites on helical tomotherapy. This technique uses an analysis of alignment shifts between kilovoltage computed tomography and post-treatment megavoltage computed tomography images. The determination of the shifts calculated by the helical tomotherapy software for a given site can then be used to define appropriate planning target volume internal margins.

METHODS AND MATERIALS

Twelve patients underwent post-treatment megavoltage computed tomography scans on a helical tomotherapy machine to assess patient setup fidelity and net intrafraction motion. Shifts were studied for the prostate, head and neck, and glioblastoma multiforme. Analysis of these data was performed using automatic and manual registration of the kilovoltage computed tomography and post-megavoltage computed tomography images.

RESULTS

The shifts were largest for the prostate, followed by the head and neck, with glioblastoma multiforme having the smallest shifts in general. It appears that it might be more appropriate to use asymmetric planning target volume margins. Each margin value reported is equal to two standard deviations of the average shift in the given direction.

CONCLUSION

This method could be applied using individual patient post-image scanning and combined with adaptive planning to reduce or increase the margins as appropriate.

Measurements of patient's setup variation in intensity-modulated radiation therapy of head and neck cancer using electronic portal imaging device

Purpose:

To measure the interfraction setup variation of patient undergoing intensity-modulated radiation therapy (IMRT) of head and neck cancer. The data was used to define adequate treatment CTV-to-PTV margin.

Materials and methods:

During March to September 2006, data was collected from 9 head and neck cancer patients treated with dynamic IMRT using 6 MV X-ray beam from Varian Clinac 23EX. Weekly portal images of setup fields which were anterior-posterior and lateral portal images were acquired for each patient with an amorphous silicon EPID, Varian aS500. These images were matched with the reference image from Varian Acuity simulator using the Varis vision software (Version 7.3.10). Six anatomical landmarks were selected for comparison. The displacement of portal image from the reference image was recorded in X (Left-Right, L-R), Y (Superior-Inferior, S-I) direction for anterior field and Z (Anterior-Posterior, A-P), Y (S-I) direction for lateral field. The systematic and random error for individual and population were calculated. Then the population-based margins were obtained.

Results:

A total of 135 images (27 simulation images and 108 portal images) and 405 match points was evaluated. The systematic error ranged from 0 to 7.5 mm and the random error ranged from 0.3 to 4.8 mm for all directions. The population-based margin ranged from 2.3 to 4.5 mm (L-R), 3.5 to 4.9 mm (S-I) for anterior field and 3.4 to 4.7 mm (A-P), 2.6 to 3.7 mm (S-I) for the lateral field. These margins were comparable to the margin that was prescribed at the King Chulalongkorn Memorial Hospital (5-10 mm) for head and neck cancer.

Conclusion:

The population-based margin is less than 5 mm, thus the margin provides sufficient coverage for all of the patients.

Multiple regions-of-interest analysis of setup uncertainties for head-and-neck cancer radiotherapy

PURPOSE

To analyze three-dimensional setup uncertainties for multiple regions of interest (ROIs) in head-and-neck region.

METHODS AND MATERIALS

In-room computed tomography (CT) scans were acquired using a CT-on-rails system for 14 patients. Three separate bony ROIs were defined: C2 and C6 vertebral bodies and the palatine process of the maxilla. Translational shifts of 3 ROIs were calculated relative to the marked isocenter on the immobilization mask.

RESULTS

The shifts for all 3 ROIs were highly correlated. However, noticeable differences on the order of 2-6 mm existed between any 2 ROIs, indicating the flexibility and/or rotational effect in the head-and-neck region. The palatine process of the maxilla had the smallest right-left shifts because of the tight lateral fit in the face mask, but the largest superior-inferior movement because of in-plane rotation and variations in jaw positions. The neck region (C6) had the largest right-left shifts. The positioning mouthpiece was found effective in reducing variations in the superior-inferior direction. There was no statistically significant improvement for using the S-board (8 out of 14 patients) vs. the short face mask.

CONCLUSIONS

We found variability in setup corrections for different regions of head-and-neck anatomy. These relative positional variations should be considered when making setup corrections or designing treatment margins.

Analysis of interfractional set-up errors and intrafractional organ motions during IMRT for head and neck tumors to define an appropriate planning target volume (PTV)- and planning organs at risk volume (PRV)-margins

BACKGROUND AND PURPOSE

To analyze the interfractional set-up errors and intrafractional organ motions and to define appropriate planning target volume (PTV)- and planning organs at risk volume (PRV)-margins in intensity-modulated radiotherapy (IMRT) for head and neck tumors.

PATIENTS AND METHODS

Twenty-two patients with head and neck or brain tumors who were treated with IMRT were enrolled. The set-up errors were defined as the displacements of the coordinates of bony landmarks on the beam films from those on the simulation films. The organ motions were determined as the displacements of the coordinates of the landmarks on the images recorded every 3 min for 15 min on the X-ray simulator from those on the initial image.

RESULTS

The standard deviations (SDs) of the systematic set-up errors (Sigma-INTER) and organ motions (Sigma-intra) distributed with a range of 0.7-1.3 and 0.2-0.8 mm, respectively. The average of the SDs of the random set-up errors (sigma-INTER) and organ motions (sigma-intra) ranged from 0.7 to 1.6 mm and from 0.3 to 0.6 mm, respectively. Appropriate PTV-margins and PRV-margins for all the landmarks ranged from 2.0 to 3.6 mm and from 1.8 to 2.4 mm, respectively.

CONCLUSIONS

We have adopted a PTV-margin of 5mm and a PRV-margin of 3mm for head and neck IMRT at our department.

Clinical use of electronic portal imaging

Accurate and routine target localization is necessary for successful outcome in radiation therapy treatments. Electronic portal imaging devices (EPIDs) provide an advanced tool with digital technology to improve target localization and maintain clinical efficiency. EPIDs are ubiquitous in the radiation therapy clinic, and they provide a powerful and flexible tool to collect and process data in a quantitative manner to improve treatment accuracy for virtually any treatment site. This manuscript provides an overview of the clinical implementation process for effective use of EPIDs. It continues with a review of correction strategies and finally highlights numerous examples of effective clinical application of EPID.