Petra S. Kroon’s research while affiliated with University Medical Center Utrecht and other places

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Publications (57)


Individualized 3D-printed applicators for magnetic resonance imaging-guided brachytherapy in nasal vestibule cancer
  • Article

August 2024

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25 Reads

Physics and Imaging in Radiation Oncology

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Milena Smolic

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Maarten Kastelijns

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[...]

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Background and purpose Brachytherapy is treatment of choice for early stage nasal vestibule cancer. Over the years improvements were achieved by means of image guided target definition, interstitial implant techniques and also individual mold techniques. The aim of this study was to improve the technique of the implant so that the need for interstitial catheters can be limited by making use of patient individualized 3D-printed applicators. Materials and Methods In 19 patients 3D-printed applicators were used to deliver pulse dose rate (PDR) brachytherapy. All patients underwent computed tomography (CT) and magnetic resonance imaging (MRI). A pre-plan with tumor delineation and manually optimized catheter positions to achieve tumor coverage was made. Based on the pre-plan a 3D-printed applicator was manufactured. Dose was evaluated by several indices: Conformity Index, Healthy Tissues Conformity Index, Dose Homogeneity Index, Dose non-uniformity ratio, Conformal index and high dose (HD) index. Results A high target coverage was achieved, with a median V100%CTV of 99.1 % (range, 81.8–100 %) and median CI of 0.99 (range, 0.82–1.00), as well as a median V0.7GyGTV of 100 % (range, 93.0–100 %). The median HD was 0.39 (range, 0.20–0.83). Interstitial catheters were needed in 12 patients. None of the patients developed grade ≥ II toxicity within the median follow up of 18 months. Conclusions This study shows that using 3D-printed applicators limits the need for interstitial catheters and also limits the high doses in normal tissue.


Fig. 1. Schematic overview of MR imaging during the brachytherapy cervical treatment procedure. MRpreApp: before the first applicator insertion, MRshort if adaptations are to be expected, MRplan for treatment planning, MRpreRad just before irradiation, MRpostRad after irradiation when interventions are performed based on MRpreRad. Colored in dark blue for every patient, in light blue optional. N is the number of insertions for applications and scans for imaging.
Fig. 2. Examples of the effect of different interventions. Sagittal T2 MR images before (left) and after (right) adaptations prior to MRplan or just before irradiation. a) Applicator not in right position followed by replacement, b) needle adaptation; the needle indicated by the yellow arrow was placed deeper, c) extra rectal degassing to decrease the rectal dose, d) filling the bladder to reduce the bowel dose.
Fig. 3. Effect in dose difference due to extra rectal degassing. Boxplots of the dose difference of the rectum between the prescribed dose and the dose according to the MRpreRad scan before extra degassing, in orange. And in grey the dose difference between the prescribed dose of the rectum and the dose according to the scan after extra degassing (the delivered dose). The boxplot indicates the 25-75th percentiles, minimum, median (line), mean (X) and outlier points.
Fig. 4. Total delivered dose minus prescribed dose. Boxplots showing the dose differences as total delivered minus total prescribed dose of bladder, rectum, sigmoid and bowel, for 70 patients. The box plot indicates the 25-75th percentiles, minimum, median (line), mean (X) and outlier points.
Total delivered minus total prescribed D 2cm3 for bladder, rectum, sigmoid and bowel in Gy EQD2 3 . At the left from this study, compared to a previous study [3] at the right. The values in bold indicates the large difference since our adaptive workflow.
Adaptive brachytherapy for cervical cancer in combined 1.5 T MR/HDR suite: Impact of repeated imaging
  • Article
  • Full-text available

July 2024

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27 Reads

Technical Innovations & Patient Support in Radiation Oncology

Introduction At our department we have a dedicated 1.5 Tesla MRI/HDR brachytherapy suite, which provides the possibility of repeated MRI scanning before, during and after applicator insertion and before and/or after irradiation for patients with advanced cervical cancer. In this study we analysed the effect of this adaptive workflow. We investigated the number of interventions, their impact on organ doses (OAR) and the respective dose differences between total prescribed and total delivered doses. Materials and methods Seventy patients with locally advanced cervical cancer FIGO2009 stages IB-IVA, treated from June 2016 till August 2020, were retrospectively analysed. The standard brachytherapy schedule consisted of two applicator insertions and delivery of three or four HDR fractions. OARs were recontoured on the repeated MRI scans. The D2cm3 dose difference between total prescribed and total delivered dose for bladder, rectum, sigmoid and bowel were calculated. Results In total 153 interventions were performed, 3 replacements of the applicator, 23 adaptations of needle positions, bladder filling was changed 74 times and repeated rectal degassing 53 times. The impact of the rectal interventions was on average −1.2 Gy EQD23. Dose differences between total delivered and total prescribed D2cm3 for bladder, rectum, sigmoid and bowel were −0.6, 0.3, 2.2 and −0.6 Gy EQD23, respectively. Conclusions An MRI scanner integrated into the brachytherapy suite enables multiple interventions based on the scans before treatment planning and dose delivery. This allows for customized treatment according to the changing anatomy of the individual patient and a better estimation of the delivered dose.

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Bringing online adaptive radiotherapy to a standard C-arm linac

June 2024

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18 Reads

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3 Citations

Physics and Imaging in Radiation Oncology

Current online adaptive radiotherapy (oART) workflows require dedicated equipment. Our aim was to develop and implement an oART workflow for a C-arm linac which can be performed using standard clinically available tools. A workflow was successfully developed and implemented. Three patients receiving palliative radiotherapy for bladder cancer were treated, with 33 of 35 total fractions being delivered with the cone-beam computed tomography (CBCT)-guided oART workflow. Average oART fraction duration was 24 min from start of CBCT acquisition to end of beam on. This work shows how oART could be performed without dedicated equipment, broadening oART availability for application at existing treatment machines.





Surface guided radiotherapy practice in paediatric oncology: a survey on behalf of the SIOPE Radiation Oncology Working Group

March 2024

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36 Reads

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1 Citation

The British journal of radiology

Introduction Surface guided radiotherapy (SGRT) is increasingly being implemented to track patient’s surface movement and position during radiation therapy. However, limited information is available on the SGRT use in paediatrics. The aim of this double survey was to map SIOPE (European Society for Paediatric Oncology) -affiliated centres using SGRT and to gain information on potential indications, observed or expected benefits. Materials and methods A double online survey was distributed to 246 SIOPE-affiliated radiotherapy centres. Multiple choices, yes/no and open answers were included. The first survey (41 questions) was active from February to March 2021. A shortened version (13 questions) was repeated in March 2023 to detect trends in SGRT use within the same community. Results Respectively, 76/142 (54%) and 28/142 (20%) responding centres used and planned to use SGRT clinically, including 4/34 (12%) new centres since 2021. Among the SGRT users, 33/76 (43%) already applied this technology to paediatric treatments. The main benefits of improved patient comfort, better monitoring of intrafraction motion and more accurate initial patient set-up expected by future users did not differ from current SGRT-users (P = 0.893). Among non-SGRT users, the main hurdles to implement SGRT were costs and time for installation. In paediatrics, SGRT is applied to all anatomical sites. Conclusion This work provides information on the practice of SGRT in paediatrics across SIOPE-affiliated radiotherapy centres which can serve as a basis for departments when considering the purchase of SGRT systems. Advances in knowledge Since little information is available in the literature on the use of SGRT in paediatrics, the results of this double survey can serve as a basis for departments treating children when considering the purchase of an SGRT system.


Example of registered T2, T1 and T1 with gadolinium (T1-gd) to the planning CT (pCT) with the pancreatic tail (orange) and spleen (blue) delineated. Interfraction motion is defined as positional changes between pCT and T2, whereas intrafraction motion is defined as positional changes between T2 and T1/T1-gd
Amplitude of respiratory motion (mm) for the pancreatic tail and spleen, calculated on the 4DCT, is shown as a function of the three directions left-right (LR), anterior-posterior (AP) and cranial-caudal (CC)
Intrafraction motion (mm) of the pancreatic tail (Pancreas) and spleen for ten patients having six intrafraction movements. Motion is shown in three directions (left-right (LR), anterior-posterior (AP) and cranial-caudal (CC)). The dose difference (Gy) between the contours delineated on the pCT and the different MRI-scans are shown on the right
Interfraction motion (mm) of the pancreatic tail (Pancreas) and spleen for ten patients having three interfraction movements. Motion is shown in three directions (left-right (LR), anterior-posterior (AP) and cranial-caudal (CC)). The dose difference (Gy) between the contours delineated on pCT and the different MRI-exams are shown on the right
MRI-based inter- and intrafraction motion analysis of the pancreatic tail and spleen as preparation for adaptive MRI-guided radiotherapy in neuroblastoma

October 2023

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47 Reads

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2 Citations

Radiation Oncology

Background In pediatric radiotherapy treatment planning of abdominal tumors, dose constraints to the pancreatic tail/spleen are applied to reduce late toxicity. In this study, an analysis of inter- and intrafraction motion of the pancreatic tail/spleen is performed to estimate the potential benefits of online MRI-guided radiotherapy (MRgRT). Materials and methods Ten randomly selected neuroblastoma patients (median age: 3.4 years), irradiated with intensity-modulated arc therapy at our department (prescription dose: 21.6/1.8 Gy), were retrospectively evaluated for inter- and intrafraction motion of the pancreatic tail/spleen. Three follow-up MRIs (T2- and T1-weighted ± gadolinium) were rigidly registered to a planning CT (pCT), on the vertebrae around the target volume. The pancreatic tail/spleen were delineated on all MRIs and pCT. Interfraction motion was defined as a center of gravity change between pCT and T2-weighted images in left-right (LR), anterior-posterior (AP) and cranial-caudal (CC) direction. For intrafraction motion analysis, organ position on T1-weighted ± gadolinium was compared to T2-weighted. The clinical radiation plan was used to estimate the dose received by the pancreatic tail/spleen for each position. Results The median (IQR) interfraction motion was minimal in LR/AP, and largest in CC direction; pancreatic tail 2.5 mm (8.9), and spleen 0.9 mm (3.9). Intrafraction motion was smaller, but showed a similar motion pattern (pancreatic tail, CC: 0.4 mm (1.6); spleen, CC: 0.9 mm (2.8)). The differences of Dmean associated with inter- and intrafraction motions ranged from − 3.5 to 5.8 Gy for the pancreatic tail and − 1.2 to 3.0 Gy for the spleen. In 6 out of 10 patients, movements of the pancreatic tail and spleen were highlighted as potentially clinically significant because of ≥ 1 Gy dose constraint violation. Conclusion Inter- and intrafraction organ motion results into unexpected constrain violations in 60% of a randomly selected neuroblastoma cohort, supporting further prospective exploration of MRgRT.




Citations (31)


... Proton radiotherapy has been used with good results in a study between 1987 and 2014 on 55 patients, 35 males and 20 females, with a mean age of 5 years and a 1 to 2-year overall survival of 91.9% [82]. Another possibility is brachytherapy [83]. ...

Reference:

Alveolar Rhabdomyosarcoma of Nasopharynx and Paranasal Sinuses in Children Diagnosis and Treatment—Review of the Literature and Case Report
Brachytherapy for rhabdomyosarcoma: Survey of international clinical practice and development of guidelines
  • Citing Article
  • April 2024

Radiotherapy and Oncology

... However, IMRT involves the use of multiple small subfields, and any positioning errors before treatment can affect the target dose distribution, potentially increasing side effects or reducing tumor control (12). Accurate positioning for each radiotherapy treatment is crucial for precise radiation delivery (13,14). Studies by Anees Dhabaan et al (15) and Hattel et al (16) using surface-guided radiation therapy (SGRT) systems observed that patients experienced deviations in both translational and rotational directions during real-time monitoring. ...

Surface guided radiotherapy practice in paediatric oncology: a survey on behalf of the SIOPE Radiation Oncology Working Group
  • Citing Article
  • March 2024

The British journal of radiology

... The advancement of precision radiotherapy techniques, such as volumetric modulated arc therapy (VMAT), stereotactic body radiotherapy (SBRT), and particle therapy, allows for the delivery of highly conformal doses to targets. However, the delivery of highly conformal doses to targets in the abdomen and thorax is challenging due to the respiratory motion affecting the treatment [1,2]. To guide the implementation of respiratory motion management, the American Association of Physicists in Medicine (AAPM) has released several relevant guidelines, including TG-76 report [3] for photon therapy, TG-101 report [4] for SBRT, and TG-290 report [5] for particle therapy. ...

MRI-based inter- and intrafraction motion analysis of the pancreatic tail and spleen as preparation for adaptive MRI-guided radiotherapy in neuroblastoma

Radiation Oncology

... The Dutch 3D study, an ongoing endeavor, encompasses 126 patients who have undergone craniospinal RT for CNS tumors, with a predominant focus on medulloblastoma (90 patients), as well as other histologies and treatment sites. This study aims to compile and standardize digital radiotherapy records from various multi-center resources, with the ultimate objective of enabling the future calculation of organ-specific radiation doses for childhood cancer survivors who received treatment during the 3D era [25]. Therefore, while 3D-CRT technique may have advantages in terms of reducing the volume of low dose bath, the use of advanced techniques such as IMRT, VMAT, and proton therapy can also reduce the risk of secondary malignancy by minimizing the dose to the surrounding normal tissues [22]. ...

Adverse late health outcomes among children treated with 3D radiotherapy techniques: Study design of the Dutch pediatric 3D‐RT study

... Interpretable methods have been associated with various tasks in radiomics, including image segmentation, lesion and organ detection, image registration, computer-aided diagnosis and staging, prognosis, radiotherapy planning, disease progression monitoring, classification, and image reconstruction [165]. In one study, multi-modal volumetric concept activation was used to provide an explanation, which showed that the detection was mainly based on the location of metastatic PCa in CT anatomy, and the reliability of PET detection was high [166]. In another study, a model fused with multiple DL methods was used to examine PCa with MRI images, and then XAI explained how the model differentiated benign or malignant PCa [167]. ...

Multi-modal Volumetric Concept Activation to Explain Detection and Classification of Metastatic Prostate Cancer on PSMA-PET/CT
  • Citing Chapter
  • October 2022

Lecture Notes in Computer Science

... However, these imaging modalities may provide a suboptimal visualization of gross disease and organs-at-risk (OARs) due to limitations in visualizing low-density structures, especially when adjacent or abutting [1]. Magnetic resonance (MR)-guided radiotherapy (MRgRT) is a novel technology featuring advanced imaging and rapid replanning capabilities using ontable images [2] that may improve clinical outcomes by facilitating safe dose escalation and reducing toxicity, especially for tumors in challenging anatomic locations [3,4] that have suboptimal outcomes when treated with CT-guided linear accelerators (Linacs) [3,[5][6][7][8][9]. ...

Impact of magnetic resonance-guided versus conventional radiotherapy workflows on organ at risk doses in stereotactic body radiotherapy for lymph node oligometastases

Physics and Imaging in Radiation Oncology

... The Danish guidelines are characterised by very steep dose gradients within the PTV, while the British guidelines yield a more uniform PTV dose. By investigating these diverse guidelines, we aim to enhance the international relevance of our findings, since most international guidelines exhibit dose heterogeneity levels that lie somewhere between these two guidelines [2e4, 13,14]. Furthermore, this could reveal the impact of PTV dose inhomogeneity on the applicability of the van Herk margin recipe. ...

First multicentre experience of SABR for lymph node and liver oligometastatic disease on the unity MR-Linac

Technical Innovations & Patient Support in Radiation Oncology

... 4 Advancements in daily imaging guidance have enabled us to identify inter-fractional bladder variations due to differences in bladder filling and inhomogeneous bladder wall elasticity among patients. [5][6][7][8][9][10][11][12] The adaptive planning approach allows clinicians to create patient-specific treatment plans tailored to individual anatomical variations, which can further reduce normal tissue toxicity and allow potential dose escalation to target. 13 There are three major strategies for performing adaptive radiation therapy on bladder cancer patients: offline adaptive planning, plan of the day selection (PoD), and daily online adaptation. ...

Comparison of Library of Plans with two daily adaptive strategies for whole bladder radiotherapy

Physics and Imaging in Radiation Oncology

... the reviewed publications, only two articles reported QoL [47,49], while toxicity was mostly reported by the radiation oncologists, using CTCAE. Although our search terms did not include QoL, we did expect to find more articles that describe QoL in addition to toxicity. ...

Progression-free survival in patients with 68 Ga-PSMA-PET-directed SBRT for lymph node oligometastases

Acta oncologica (Stockholm, Sweden)

... To reduce a possible measurement error, it would be recommended to have more repeated measurements per patient. Furthermore, to account for the individual variation of diurnal spinal reduction a patient-specific approach by using online adaptive radiotherapy can be considered in the treatment of pediatric patients [33]. ...

The potential role of MR-guided adaptive radiotherapy in pediatric oncology: Results from a SIOPE-COG survey

Clinical and Translational Radiation Oncology