Abstract Background and purpose During cervical cancer treatment, target volumes change position and shape due to organ motion and tumour regression. An MRI-accelerator will provide information on ...these changes by online magnetic resonance imaging (MRI) guidance throughout each treatment fraction. The purpose of this intensity-modulated radiation therapy (IMRT) planning study is to assess the benefit of online MRI guidance in healthy tissue sparing. Materials and methods Weekly MRI scans of 11 cervical cancer patients were used. We created four IMRT plans per patient, based on these weekly MRI scans, to simulate an online-IMRT approach. We applied a primary and nodal planning target volume (PTV) margin of 4 mm. As reference, we created an IMRT plan based on the pre-treatment MRI scan (pre-IMRT) using a primary and nodal PTV margin of 15 and 10 mm. The weekly defined bladder, rectum, bowel, and sigmoid contours were evaluated on the online-IMRT and pre-IMRT dose distributions at six dose levels (V10Gy , V20Gy , V30Gy , V40Gy , V42.8Gy , and V45Gy ). Results Online-IMRT compared to pre-IMRT significantly reduced the volume of healthy tissue irradiated to all dose levels, except V10Gy. Conclusions Online MRI guidance reduces healthy tissue involvement in patients with cervical cancer.
Abstract Background and purpose During radiation delivery, target volumes change their position and shape due to intrafraction motion. The extent of these changes and the capability to correct for ...them will contribute to the benefit of an MRI-accelerator in terms of PTV margin reduction. Therefore, we investigated the primary CTV motion within a typical IMRT delivery time for cervical cancer patients for various correction techniques: no registration, rigid bony anatomy registration, and rigid soft tissue registration. Materials and methods Twenty-two patients underwent 2–3 offline MRI exams before and during their radiation treatment. Each MRI exam included four sagittal and four axial MRI scans alternately within 16 min. We addressed the CTV motion by comparing subsequent midsagittal CTV delineations and investigated the correlation with intrafraction bladder filling. Results The maximum (residual) motions within 16 min for all points on the CTV contour for 90% of the MRI exams without registration, with rigid bony anatomy registration, and with rigid soft tissue registration were 10.6, 9.9, and 4.0 mm. A significant but weak correlation was found between intrafraction bladder filling and CTV motion. Conclusions Considerable intrafraction CTV motion is observed in cervical cancer patients. Intrafraction MRI-guided soft tissue registration using an MRI-accelerator will correct for this motion.
Study Type – Therapy (case series) Level of Evidence 4
What’s known on the subject? and What does the study add?
The increasing use of imaging techniques resulted in an enormous increase of ...incidentally diagnosed renal cell carcinomas (RCC). At the moment surgery is the only established curative approach for the treatment of RCC. The smaller size of these incidental RCC tumours demands far less invasive treatment techniques, preferably without piercing the tumour.
This study presents the latest developments in the field of radiation therapy, which provides treatment alternatives for tumour sites currently not treated with radiation therapy. Real‐time magnetic resonance imaging guided radiation therapy might become a valuable non‐invasive alternative to treat renal cell carcinoma.
OBJECTIVE To present a new concept for non‐invasive renal tumour ablation using real‐time magnetic resonance imaging (MRI)‐guided radiation therapy. All currently available treatment techniques for localized renal cell carcinoma (RCC) have to be performed in a laparoscopic or percutaneous way.
MATERIALS AND METHODS A technical prototype MRI‐accelerator which performs real‐time 1.5 T MRI imaging during the irradiation has been constructed. We performed a technical feasibility study on real‐time MRI‐guided arc therapy using repeated breath‐holds for renal tumour ablation by (i) investigating renal mobility during breath‐holding, (ii) performing dose calculation and (iii) measuring the radiation delivery time on a phantom. The renal mobility during free breathing and end‐expiration breath‐holding during 15 s was investigated for three patients with renal tumour appearance. Conventional MRI screening data of four patients was used for arc therapy dose calculation. Tumour and normal tissues were delineated and a tumour margin of 3 mm was applied. The radiation delivery time of a 25‐Gy arc therapy plan was measured on a phantom.
RESULTS Renal mobility during free breathing varied from 10 to 25 mm, whereas breath‐holding resulted in nearly non‐moving kidneys (0 to 2 mm) for all patients. Arc therapy dose calculation resulted in an adequate tumour coverage. The radiation delivery time of the arc therapy plan was about 10 min. This means that 20 to 40 repeated breath‐holds of 15 to 30 s will be needed for a single session treatment. A higher maximum dose rate would reduce the number of breath‐holds needed and improve patient comfort. A phase I study will be started to proof the clinical feasibility.
CONCLUSION Real‐time MRI‐guided radiation therapy using an MRI‐accelerator might become a valuable non‐invasive alternative to the current RCC treatment options.
The application of thermal modelling for hyperthermia and thermal ablation is severely hampered by lack of information about perfusion and vasculature. However, recently, with the advent of ...sophisticated angiography and dynamic contrast enhanced (DCE) imaging techniques, it has become possible to image small vessels and blood perfusion bringing the ultimate goal of patient specific thermal modelling closer within reach. In this study dynamic contrast enhanced multi-slice CT imaging techniques are employed to investigate the feasibility of this concept for regional hyperthermia treatment of the prostate. The results are retrospectively compared with clinical thermometry data of a patient group from an earlier trial. Furthermore, the role of the prostate vasculature in the establishment of the prostate temperature distribution is studied. Quantitative 3D perfusion maps of the prostate were constructed for five patients using a distributed-parameter tracer kinetics model to analyse dynamic CT data. CT angiography was applied to construct a discrete vessel model of the pelvis. Additionally, a discrete vessel model of the prostate vasculature was constructed of a prostate taken from a human corpse. Three thermal modelling schemes with increasing inclusion of the patient specific physiological information were used to simulate the temperature distribution of the prostate during regional hyperthermia. Prostate perfusion was found to be heterogeneous and T3 prostate carcinomas are often characterized by a strongly elevated tumour perfusion (up to 70-80 ml 100 g(-1) min(-1)). This elevated tumour perfusion leads to 1-2 degrees C lower tumour temperatures than thermal simulations based on a homogeneous prostate perfusion. Furthermore, the comparison has shown that the simulations with the measured perfusion maps result in consistently lower prostate temperatures than clinically achieved. The simulations with the discrete vessel model indicate that significant pre-heating takes place in the prostate capsule vasculature which forms a possible explanation for the discrepancy. Pre-heating in the larger pelvic vessels is very moderate, approximately 0.1-0.3 degrees C. In conclusion, perfusion imaging provides important input for thermal modelling and can be used to obtain a lower limit on the prostate and tumour temperature in regional hyperthermia. However, it is not sufficient to calculate in detail the prostate temperature distribution in individual patients. The prostate vasculature plays such a crucial role that a patient specific discrete vessel model of the prostate vasculature is required.
Respiratory motion management is important in abdominothoracic radiotherapy. Fast imaging of the tumor can facilitate multileaf collimator (MLC) tracking that allows for smaller treatment margins, ...while repeatedly imaging the full field-of-view is necessary for 4D dose accumulation. This study introduces a hybrid 2D/4D-MRI methodology that can be used for simultaneous MLC tracking and dose accumulation on a 1.5 T Unity MR-linac (Elekta AB, Stockholm, Sweden).
We developed a hybrid 2D/4D-MRI methodology that uses a simultaneous multi-slice (SMS) accelerated MRI sequence, which acquires two coronal slices simultaneously and repeatedly cycles through slice positions over the image volume. As a result, the fast 2D imaging can be used prospectively for MLC tracking and the SMS slices can be sorted retrospectively into respiratory-correlated 4D-MRIs for dose accumulation. Data were acquired in five healthy volunteers with an SMS-bTFE and SMS-TSE MRI sequence. For each sequence, a pre-beam dataset and a beam-on dataset were acquired simulating the two phases of MR-linac treatments. Pre-beam data were used to generate a 4D-based motion model and a reference mid-position volume, while beam-on data were used for real-time motion extraction and reconstruction of beam-on 4D-MRIs. In addition, an in-silico computational phantom was used for validation of the hybrid 2D/4D-MRI methodology. MLC tracking experiments were performed with the developed methodology, for which real-time SMS data reconstruction was enabled on the scanner. A 15-beam 8×7.5 Gy intensity modulated radiotherapy plan for lung stereotactic body radiotherapy with isotropic 3 mm GTV-to-PTV margins was created. Dosimetry experiments were performed using a 4D motion phantom. The latency between target motion and updating the radiation beam was determined and compensated. Local gamma-analyses were performed to quantify dose differences compared to a static reference delivery, and dose area histograms (DAHs) were used to quantify the GTV and PTV coverage.
In-vivo data acquisition and MLC tracking experiments were successfully performed with the developed hybrid 2D/4D-MRI methodology. Real-time liver-lung interface motion estimation had a Pearson's correlation of 0.996 (in-vivo) and 0.998 (in-silico). A median (5th-95th percentile) error of 0.0 (-0.9-0.7) mm and 0.0 (-0.2-0.2) mm was found for real-time motion estimation for in-vivo and in-silico, respectively. Target motion prediction beyond the liver-lung interface had a median root mean square error of 1.6 mm (in-vivo) and 0.5 mm (in-silico). Beam-on 4D MRI reconstruction required a median amount of data equal to an acquisition time of 2:21-3:17 minutes, which was 20% less data compared to the pre-beam derived 4D-MRI. System latency was reduced from 501 ± 12 ms to -1 ± 3 ms (SMS-TSE) and from 398 ± 10 ms to -10 ± 4 ms (SMS-bTFE) by a linear regression prediction filter. The local gamma analysis agreed within -3.8-3.3% (SMS-bTFE) and -5.3-10% (SMS-TSE) with a reference MRI sequence. The DAHs revealed a relative D
GTV coverage between 97-100% (SMS-bTFE) and 100-101% (SMS-TSE) compared to the static reference.
The presented 2D/4D-MRI methodology demonstrated the potential for accurately extracting real-time motion for MLC tracking in abdominothoracic radiotherapy, while simultaneously reconstructing contiguous respiratory-correlated 4D-MRIs for dose accumulation. This article is protected by copyright. All rights reserved.
We determined prostate perfusion in 18 patients with locally advanced prostate carcinoma treated with a combination of external beam irradiation and regional (10) or interstitial (8) hyperthermia.
...Perfusion values were calculated from temperature elevations due to constant applied power and from transient temperature measurements after a change in applied power. Student’s t test was used for comparing perfusion values with time and in the 2 groups.
At the start of regional hyperthermia treatment mean estimated perfusion plus or minus standard deviation was 10 ± 8 ml./100 gm. per minute. At the end of treatment mean perfusion was increased to 14 ± 2 ml./100 gm. per minute (p <0.01). Achieved thermal parameters were a mean temperature of at least 40.3C ± 0.6C in 90% of the prostate, 40.9C ± 0.6C in 50% and a mean maximum temperature of 41.6C ± 0.6C. At the end of interstitial hyperthermia treatment estimated mean perfusion was 47 ± 5 ml./100 gm. per minute, which was significantly different compared with the end of regional hyperthermia (p <0−7). Mean temperature was at least 39.4C ± 0.9C in 90% of the prostate and 41.8C ± 1.6C in 50%, while mean maximum temperature was 53.1C ± 6.3C. Systemic temperature increased during regional hyperthermia up to 38.6C, whereas during interstitial hyperthermia body temperature was not elevated.
During interstitial hyperthermia perfusion values are higher than during regional hyperthermia. Hyperthermia causes increased prostate perfusion.
Purpose:
To perform a feasibility study of three-dimensional spatially controlled interstitial hyperthermia for locally advanced prostate cancer.
Methods and Materials:
Twelve patients with prostate ...cancer (T3NxM0) were treated with conventional external beam radiotherapy and one interstitial hyperthermia treatment. Hyperthermia was delivered with the 27-MHz multielectrode current source (MECS) interstitial hyperthermia technique on an outpatient basis. Guided by transrectal ultrasonography, 12 catheters (range 7–16) were placed in the prostate through a template. Two electrodes per probe were inserted. Thermometry (average 100 sensors) was performed from within the probes for online temperature control. Additional thermometry was done in the prostate, rectum, urethra, and bladder. Reconstruction was done by sonography. Prostate perfusion was estimated from the thermal decay at the end of treatment. The full three-dimensional temperature distribution was calculated.
Results:
No toxicities greater than Grade 2 were recorded. A learning curve for implantation, position verification, reconstruction, and temperature simulation was experienced. Perfusion was 47 mL/100 g/min (range 30–65). The average measured temperature was T
90 (90% of the prostate reached a temperature of at least:) 39.9°C and T
50 44.1°C. The average calculated temperatures were lower: T
90, 39.4°C and T
50, 41.8°C, because the entire prostate was taken into account. The tumor temperatures were T
90, 40.7°C and T
50, 43.0°C. The bladder and rectal temperatures were below the safety limits.
Conclusion:
Multielectrode-current-source interstitial hyperthermia is technically feasible and well tolerated. It was not possible to achieve the goal temperature of 42–43°C because of high perfusion and implantation limitations.
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