Abstract:Purpose: To investigate the response of detectors for proton dosimetry in the presence of magnetic fields. Material&Methods: Four ionization chambers, two thimble-type and two plane-parallel-type, and a diamond detector were investigated. All detectors were irradiated with homogeneous single-energy-layer fields, using 252.7 MeV proton beams. A Farmer ionization chamber was additionally irradiated in the same geometrical configuration, but with a lower nominal energy of 97.4 MeV. The beams were subjected to mag… Show more
“…Dosimetric measurements were cross-checked by Monte Carlo simulations, agreeing with measured data. The chamber response for proton irradiation was previously shown to be affected by magnetic fields [22] , requiring a correction factor for absolute dosimetry. Before performing this study, a respective correction factor was determined also for carbon ions using the set-up described above and applied accordingly.…”
Section: Discussionmentioning
confidence: 99%
“…Within ±5 mm around the center of the SOBP, dose agreement was always within 1.7% compared to the center of the SOBP (see Figure 2 ). Correction factors for the Farmer chamber due to the influence of the transverse magnetic fields were measured previously and applied accordingly [22] . Figure 2 (a): Monte Carlo simulated irradiation field at the measuring depth for protons (top) and 12C (bottom).…”
“…Dosimetric measurements were cross-checked by Monte Carlo simulations, agreeing with measured data. The chamber response for proton irradiation was previously shown to be affected by magnetic fields [22] , requiring a correction factor for absolute dosimetry. Before performing this study, a respective correction factor was determined also for carbon ions using the set-up described above and applied accordingly.…”
Section: Discussionmentioning
confidence: 99%
“…Within ±5 mm around the center of the SOBP, dose agreement was always within 1.7% compared to the center of the SOBP (see Figure 2 ). Correction factors for the Farmer chamber due to the influence of the transverse magnetic fields were measured previously and applied accordingly [22] . Figure 2 (a): Monte Carlo simulated irradiation field at the measuring depth for protons (top) and 12C (bottom).…”
“…Modelling on MR-integrated proton therapy for liver cancer has shown clear dosimetric benefits as well as significant reduction in normal tissue complication probability in comparison with other imaging modalities, including offline MR-guided proton therapy and MR-linac ( 137 ). Recent studies have made progress in quantifying the impact of the magnetic field on detectors for proton dosimetry and demonstrating the technical feasibility of low-field MR guidance on phantoms in a static research beam line ( 138 , 139 ). Additional studies have investigated methods for calculating stopping power ratios from MRI to generate an MRI-based “synthetic” CT image for treatment planning and range verification ( 140 ).…”
The major aim of radiation therapy is to provide curative or palliative treatment to cancerous malignancies while minimizing damage to healthy tissues. Charged particle radiotherapy utilizing carbon ions or protons is uniquely suited for this task due to its ability to achieve highly conformal dose distributions around the tumor volume. For these treatment modalities, uncertainties in the localization of patient anatomy due to inter- and intra-fractional motion present a heightened risk of undesired dose delivery. A diverse range of mitigation strategies have been developed and clinically implemented in various disease sites to monitor and correct for patient motion, but much work remains. This review provides an overview of current clinical practices for inter and intra-fractional motion management in charged particle therapy, including motion control, current imaging and motion tracking modalities, as well as treatment planning and delivery techniques. We also cover progress to date on emerging technologies including particle-based radiography imaging, novel treatment delivery methods such as tumor tracking and FLASH, and artificial intelligence and discuss their potential impact towards improving or increasing the challenge of motion mitigation in charged particle therapy.
“…Dose planning feasibility, considering just the impact of the magnetic field of the MRI surrounding the patient, has been modeled and shown to be successful 6–12 . A comprehensive study on the performance of radiation detectors in magnetic fields with proton beams has recently been published with promising results 13 . And finally, a proof of concept system exists in Germany 14,15 .…”
Section: Introductionmentioning
confidence: 99%
“…[6][7][8][9][10][11][12] A comprehensive study on the performance of radiation detectors in magnetic fields with proton beams has recently been published with promising results. 13 And finally, a proof of concept system exists in Germany. 14,15 However, online MRI-guided proton therapy will require significant technological development to integrate real time imaging, treatment planning, and beam delivery.…”
Purpose
To present a first study on the treatment planning feasibility in perpendicular field MRI‐integrated proton therapy that considers the full transport of protons from the pencil beam scanning (PBS) assembly to the patient inside the MRI scanner.
Methods
A generic proton PBS gantry was modeled as being integrated with a realistic split‐bore MRI system in the perpendicular orientation. MRI field strengths were modeled as 0.5, 1, and 1.5 T. The PBS beam delivery and dose calculation was modeled using the TOPAS Monte Carlo toolkit coupled with matRad as the optimizer engine. A water phantom, liver, and prostate plans were evaluated and optimized in the presence of the full MRI field distribution. A simple combination of gantry angle offset and small PBS nozzle skew was used to direct the proton beams along a path that closely follows the reference planning scenario, that is, without magnetic field.
Results
All planning metrics could be successfully achieved with the inclusion of gantry angle offsets in the range of 8∘$^{\circ }$–29∘$^{\circ }$ when coupled with a PBS nozzle skew of 1.6∘$^{\circ }$–4.4∘$^{\circ }$. These two hardware‐based corrections were selected to minimize the average Euclidean distance (AED) in the beam path enabling the proton beams to travel inside the patient in a path that is close to the original path (AED smaller than 3 mm at 1.5 T). Final dose optimization, performed through further changes in the PBS delivery, was then shown to be feasible for our selection of plans studied yielding comparable plan quality metrics to reference conditions.
Conclusions
For the first time, we have shown a robust method to account for the full proton beam deflection in a perpendicular orientation MRI‐integrated proton therapy. These results support the ongoing development of the current prototype systems.
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