The Potential Value of MRI in External-Beam Radiotherapy for Cervical Cancer

Cree, Anthea; Livsey, Jacqueline E; Barraclough, Lisa H; Dubec, Michael; Hambrock, Thomas; Herk, Marcel van; Choudhury, Ananya; McWilliam, A.

doi:10.1016/j.clon.2018.08.002

Cited by 24 publications

(24 citation statements)

References 139 publications

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“…Standard therapy for locally advanced cervical cancer is a combination of concurrent chemo-RT followed by brachytherapy [109]. Despite the wide application of daily image-guidance and advanced RT techniques including IMRT and VMAT, long-term urogenital and gastrointestinal side-effects are still frequent [110].…”

Section: Clinical Sitesmentioning

confidence: 99%

“…MR-guided brachytherapy is gradually becoming standard of care by allowing superior sparing of surrounding radiosensitive organs combined with dose escalation compared to conventional 2D-planning [114–117]. Based on the excellent results of MR-guidance in brachytherapy, it has been questioned for EBRT of cervical cancer, whether MRI could not only be applied for advanced tumor delineation but also for image-guidance [110, 114, 118]. The CTV for EBRT comprises the cervix and the uterus which are known to show significant inter- and intra-fractional motion due to the close proximity to hollow OARs [110, 119].…”

Section: Clinical Sitesmentioning

confidence: 99%

“…Based on the excellent results of MR-guidance in brachytherapy, it has been questioned for EBRT of cervical cancer, whether MRI could not only be applied for advanced tumor delineation but also for image-guidance [110, 114, 118]. The CTV for EBRT comprises the cervix and the uterus which are known to show significant inter- and intra-fractional motion due to the close proximity to hollow OARs [110, 119]. Large safety margins are usually needed in CBCT-imaged-guided RT to account for random and patient-specific organ movement [110, 119].…”

Section: Clinical Sitesmentioning

confidence: 99%

“…The CTV for EBRT comprises the cervix and the uterus which are known to show significant inter- and intra-fractional motion due to the close proximity to hollow OARs [110, 119]. Large safety margins are usually needed in CBCT-imaged-guided RT to account for random and patient-specific organ movement [110, 119]. Due to the potential regression of cervical cancer of up to 60–80% of the pre-therapeutic tumor volume during EBRT, further pelvic organ motion might be expected during RT [118, 120].…”

Section: Clinical Sitesmentioning

confidence: 99%

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MR-guidance in clinical reality: current treatment challenges and future perspectives

et al. 2019

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Magnetic Resonance-guided radiotherapy (MRgRT) marks the beginning of a new era. MR is a versatile and suitable imaging modality for radiotherapy, as it enables direct visualization of the tumor and the surrounding organs at risk. Moreover, MRgRT provides real-time imaging to characterize and eventually track anatomical motion. Nevertheless, the successful translation of new technologies into clinical practice remains challenging. To date, the initial availability of next-generation hybrid MR-linac (MRL) systems is still limited and therefore, the focus of the present preview was on the initial applicability in current clinical practice and on future perspectives of this new technology for different treatment sites. MRgRT can be considered a groundbreaking new technology that is capable of creating new perspectives towards an individualized, patient-oriented planning and treatment approach, especially due to the ability to use daily online adaptation strategies. Furthermore, MRL systems overcome the limitations of conventional image-guided radiotherapy, especially in soft tissue, where target and organs at risk need accurate definition. Nevertheless, some concerns remain regarding the additional time needed to re-optimize dose distributions online, the reliability of the gating and tracking procedures and the interpretation of functional MR imaging markers and their potential changes during the course of treatment. Due to its continuous technological improvement and rapid clinical large-scale application in several anatomical settings, further studies may confirm the potential disruptive role of MRgRT in the evolving oncological environment.

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Section: Clinical Sitesmentioning

confidence: 99%

Section: Clinical Sitesmentioning

confidence: 99%

Section: Clinical Sitesmentioning

confidence: 99%

Section: Clinical Sitesmentioning

confidence: 99%

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MR-guidance in clinical reality: current treatment challenges and future perspectives

et al. 2019

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“…Organ at risk and target visualisation can be improved with daily MRI compared to CBCT, which can permit plan adaptation, leading to the potential for improved PTV coverage, dose escalation or reduction in toxicity . Plan adaptation allowing a biologically effective dose of >70 Gy was associated with a longer overall survival in a retrospective analysis of patients treated with MRgRT for locally advanced or borderline resectable pancreatic cancer, although this finding requires validation in a prospective manner with a phase II trial being initiated (NCT03621644).…”

Section: Magnetic Resonance‐guided Radiation Therapymentioning

confidence: 99%

Magnetic resonance‐guided radiation therapy: A review

et al. 2019

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Summary Magnetic resonance‐guided radiation therapy (MRgRT) is a promising approach to improving clinical outcomes for patients treated with radiation therapy. The roles of image guidance, adaptive planning and magnetic resonance imaging in radiation therapy have been increasing over the last two decades. Technical advances have led to the feasible combination of magnetic resonance imaging and radiation therapy technologies, leading to improved soft‐tissue visualisation, assessment of inter‐ and intrafraction motion, motion management, online adaptive radiation therapy and the incorporation of functional information into treatment. MRgRT can potentially transform radiation oncology by improving tumour control and quality of life after radiation therapy and increasing convenience of treatment by shortening treatment courses for patients. Multiple groups have developed clinical implementations of MRgRT predominantly in the abdomen and pelvis, with patients having been treated since 2014. While studies of MRgRT have primarily been dosimetric so far, an increasing number of trials are underway examining the potential clinical benefits of MRgRT, with coordinated efforts to rigorously evaluate the benefits of the promising technology. This review discusses the current implementations, studies, potential benefits and challenges of MRgRT.

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Characterizing local dose perturbations due to gas cavities in magnetic resonance‐guided radiotherapy

et al. 2020

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PurposeDue to differences in attenuation and the electron return effect (ERE), the presence of gas can increase the risk of toxicity in organs at risk (OAR) during magnetic resonance‐guided radiotherapy (MRgRT). Current adaptive MRgRT workflows using density overrides negate gas from the dose calculation, meaning that the effects of ERE around gas are not taken into account. In order to achieve an accurate adaptive MRgRT treatment, we should be able to quickly evaluate whether gas present during treatment causes dose constraint violation during an MRgRT fraction. We propose an analytic method for predicting dose perturbations caused by air cavities in OARs during MRgRT.MethodTen virtual water phantoms were created: nine containing a centrally located spherical air cavity and a reference phantom without an air cavity. Monte Carlo dose calculations were produced to irradiate the phantoms with a single 7 MV photon beam under the influence of a 1.5 T transverse magnetic field (Monaco 5.19.02 Treatment Panning System (TPS) (Elekta AB, Stockholm, Sweden)). Dose distributions of the phantoms with and without air cavities were compared. We used a spherical coordinate system originating in the center of the cavity to sample the dose distributions and calculate the dose perturbation as a result of the presence of each air cavity, ∆D%(θ,Φ)calc.. Dose effects due to ERE and differences in attenuation due to density changes were considered separately. Least squared analysis was used to fit the calculated dose perturbations to mathematical functions. Effects due to ERE were fit to a modulated sinusoidal function and those due to attenuation differences were fit to a 2D Gaussian function. We used the fits to derive a single equation describing dose perturbations around spherical air cavities as a function of angles, θ, Φ, distance from cavity surface, d, and cavity radius, r. We measured the fitting error by calculating the residual error (RE); the difference between the calculated and fitted dose perturbation.ResultsBoth ERE and differences in attenuation contribute toward the total dose effects of air cavities in MRgRT. Whereas ERE dominates close to the surface of the cavities, attenuation effects dominate at distances >0.5 cm from the cavities. We showed that dose effects around a spherical air cavity (≤1 cm from the surface) due to ERE fit a modulated sinusoidal function with mean (RE) ≤−1.4E‐5% and root mean square error (rms) (RE) ≤4.1%. Effects due to attenuation differences fit a Gaussian function with mean (RE) ≤0.7% and rms (RE) ≤1.8%. Our general equation, which we verified using multiple sizes of spherical and cylindrical air cavity, fits Monte Carlo simulated data with mean (RE) ≤±0.9% and rms (RE) ≤6.9%.ConclusionWe show that local dose perturbations around unplanned spherical air cavities during MRgRT can be well characterized analytically. We present an equation that can be incorporated into the clinical workflow to allow for fast evaluation of dose effects of unplanned gas. We also envision this method contributing to the clinical implementation of real time adaptive radiotherapy (ART) for MRgRT using MRI planning.

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The Potential Value of MRI in External-Beam Radiotherapy for Cervical Cancer

Cited by 24 publications

References 139 publications

MR-guidance in clinical reality: current treatment challenges and future perspectives

MR-guidance in clinical reality: current treatment challenges and future perspectives

Magnetic resonance‐guided radiation therapy: A review

Characterizing local dose perturbations due to gas cavities in magnetic resonance‐guided radiotherapy

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