Design of static and dynamic ridge filters for FLASH–IMPT: A simulation study

Zhang, Guoliang; Gao, Wenchao; Peng, Hao

doi:10.1002/mp.15717

Cited by 20 publications

(24 citation statements)

References 37 publications

(103 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The base of the range modulator is shaped to act as a range compensator to match the distal contour of the tumor. It has been shown that this set-up could easily achieve dose rate of at least 40 Gy/s [18,7].…”

Section: Introductionmentioning

confidence: 98%

See 1 more Smart Citation

Optimization of patient-specific range modulators for conformal FLASH proton therapy

Deffet¹,

Souris²,

Sterpin³

2023

Preprint

View full text Add to dashboard Cite

Background: In proton therapy, current pencil beam scanning (PBS) systems cannot deliver intensity modulated proton therapy (IMPT) treatment with a FLASH dose rate. A promising approach to enable FLASH conformal proton therapy is to passively degrade a single energy layer using a patient-specific range modulator. This range modulator can be seen as a combination of a ridge filter and a range shifter to achieve both uniformity and conformality. Several studies have already proved the feasibility of this approach. However, in those published works, the optimization of the range modulators is more akin to dose mimicking as it is not performed with respect to the constraints used to design the original IMPT plan. In addition, a complex simulation pipeline with an external dose engine is required to deal with the parameterized geometries of the range modulators. Purpose: We propose an innovative method to directly optimize the geometrical characteristics of the range modulator and the treatment plan with respect to user defined constraints, similarly to state-of-the-art IMPT inverse planning. Methods: The kind of range modulators proposed in this study is a voxelized object which can be placed in the CT for dose computation, which simplifies the simulation pipeline. Both the geometrical characteristics of the range modulator and the weights of the PBS spots were directly optimized with respect to constraints on the dose using a first-order method. A modified Monte Carlo dose engine was used to provide an estimate of the gradient of the relaxed constraints with respect to the elevation values of the range modulator. Results: Assessed on a head and neck case, dose conformity logically appeared to be significantly degraded compared to IMPT. We then demonstrated that this degradation came mainly from the use of a large range shifter and therefore from physical limitations inherent in the passive degradation of beam energy. The geometry of the range modulator, on the other hand, was shown to be very close to being optimal. PBS dose rates were computed and discussed with respect to FLASH objectives. Conclusions: The voxelized range modulators optimized with the proposed method were proven to be optimal on a head and neck case characterized by two rather large volumes, with irregular contours and variable depths. The optimized geometry differed from conventional ridge filters as it was arbitrarily set by the optimizer. This kind of range modulators can be directly added in the CT for dose computation and is well suited for 3D printing.

show abstract

Section: Introductionmentioning

confidence: 98%

“…To plan a conformal PBS FLASH treatment it is therefore necessary to optimize a patient-specific range modulator and the weights of the PBS spots. Several methods have already been proposed [13,7,18]. Although different, they are based on two common principles:…”

Section: Introductionmentioning

confidence: 99%

Optimization of patient-specific range modulators for conformal FLASH proton therapy

Deffet¹,

Souris²,

Sterpin³

2023

Preprint

View full text Add to dashboard Cite

show abstract

“…Alternative approaches have been proposed for FLASH planning using spread-out single-energy proton beams, in which patient-specific range compensators were used to pull back the BPs to the target exit edge and pin-shaped ridge filters (RFs) were customized to spread out the BPs to the proximal edge of the target. [24][25][26] Nevertheless, either using the customized range compensators alone or combining the patient-specific pin-shaped RFs and range compensators for FLASH planning has limitations in adapting to patient anatomical changes that often occur during the treatment courses, such as tumor regression, since a time-consuming process for re-making the range compensators and/or pin-shaped RFs may be required.…”

Section: Introductionmentioning

confidence: 99%

“…In these studies, the uniform range shifters (RSs) and patient‐specific universal range compensators were employed to align the BPs of the high‐energy proton beams to the distal edge of the target from multiple beam directions, which demonstrated improved OAR sparing with sufficient target dose coverage and comparable FLASH dose rate coverage compared to the TB‐only planning. Alternative approaches have been proposed for FLASH planning using spread‐out single‐energy proton beams, in which patient‐specific range compensators were used to pull back the BPs to the target exit edge and pin‐shaped ridge filters (RFs) were customized to spread out the BPs to the proximal edge of the target 24–26 . Nevertheless, either using the customized range compensators alone or combining the patient‐specific pin‐shaped RFs and range compensators for FLASH planning has limitations in adapting to patient anatomical changes that often occur during the treatment courses, such as tumor regression, since a time‐consuming process for re‐making the range compensators and/or pin‐shaped RFs may be required.…”

Section: Introductionmentioning

confidence: 99%

Feasibility study of hybrid inverse planning with transmission beams and single‐energy spread‐out Bragg peaks for proton FLASH radiotherapy

Yang

Chang

et al. 2023

Medical Physics

View full text Add to dashboard Cite

Background: Ultra-high dose rate (FLASH) proton planning with only transmission beams (TBs) has limitations in normal tissue sparing. The single-energy spread-out Bragg peaks (SESOBPs) of the FLASH dose rate have been demonstrated feasible for proton FLASH planning. Purpose: To investigate the feasibility of combining TBs and SESOBPs for proton FLASH treatment. Methods: A hybrid inverse optimization method was developed to combine the TBs and SESOBPs (TB-SESOBP) for FLASH planning. The SESOBPs were generated field-by-field from spreading out the BPs by pre-designed general bar ridge filters (RFs) and placed at the central target by range shifters (RSs) to obtain a uniform dose within the target.The SESOBPs and TBs were fully placed field-by-field allowing automatic spot selection and weighting in the optimization process. A spot reduction strategy was conducted in the optimization process to push up the minimum MU/spot assuring the plan deliverability at beam current of 165 nA. The TB-SESOBP plans were validated in comparison with the TB only (TB-only) plans and the plans with the combination of TBs and BPs (TB-BP plans) regarding 3D dose and dose rate (dose-averaged dose rate) distributions for five lung cases. The FLASH dose rate coverage (V 40Gy/s ) was evaluated in the structure volume receiving > 10% of the prescription dose. Results: Compared to the TB-only plans, the mean spinal cord D 1.2cc drastically reduced by 41% (P < 0.05), the mean lung V 7Gy and V 7.4 Gy moderately reduced by up to 17% (P < 0.05), and the target dose homogeneity slightly increased in the TB-SESOBP plans. Comparable dose homogeneity was achieved in both TB-SESOBP and TB-BP plans. Besides, prominent improvements were achieved in lung sparing for the cases of relatively large targets by the TB-SESOBP plans compared to the TB-BP plans. The targets and the skin were fully covered with the FLASH dose rate in all three plans. For the OARs, V 40Gy/s = 100% was achieved by the TB-only plans while V 40Gy/s > 85% was obtained by the other two plans. Conclusion:We have demonstrated that the hybrid TB-SESOBP planning was feasible to achieve FLASH dose rate for proton therapy. With pre-designed general bar RFs,the hybrid TB-SESOBP planning could be implemented for proton adaptive FLASH radiotherapy. As an alternative FLASH planning approach to TB-only planning, the hybrid TB-SESOBP planning has great potential in dosimetrically improving OAR sparing while maintaining high target dose homogeneity.

show abstract

“…However, such SOBP delivery can hardly reach the dose rate of FLASH RT mainly because: first, the beam current decreases dramatically as proton energy decreases due to beam transmission efficiency loss in the energy selection system 22,23 ; second, the typical energy switch time is ∼900 ms for energy degradation‐based cyclotron systems 24 and on a scale of >1000 ms for synchrotron systems, 25 which also prolongs the beam‐on time. Ridge‐filter‐based SOBP 26 and compensator‐based single‐energy Bragg peak 15 delivery techniques were proposed to improve the dose rate by eliminating the necessity of energy switching while maintaining dose conformity compared to transmission delivery. However, high‐energy transmission delivery, which is characteristic of high current and less sensitivity to range uncertainties, is more practical to accommodate FLASH dose rates to be used for preclinical studies on animals 14,27,28 .…”

Section: Introductionmentioning

confidence: 99%

Implementation of novel measurement‐based patient‐specific QA for pencil beam scanning proton FLASH radiotherapy

et al. 2023

View full text Add to dashboard Cite

Background Several studies have shown pencil beam scanning (PBS) proton therapy is a feasible and safe modality to deliver conformal and ultra‐high dose rate (UHDR) FLASH radiation therapy. However, it would be challenging and burdensome to conduct the quality assurance (QA) of the dose rate along with conventional patient‐specific QA (psQA). Purpose To demonstrate a novel measurement‐based psQA program for UHDR PBS proton transmission FLASH radiotherapy (FLASH‐RT) using a high spatiotemporal resolution 2D strip ionization chamber array (SICA). Methods The SICA is a newly designed open‐air strip‐segmented parallel plate ionization chamber, which is capable of measuring spot position and profile through 2 mm‐spacing‐strip electrodes at a 20 kHz sampling rate (50 μs per event) and has been characterized to exhibit excellent dose and dose rate linearity under UHDR conditions. A SICA‐based delivery log was collected for each irradiation containing the measured position, size, dwell time, and delivered MU for each planned spot. Such spot‐level information was compared with the corresponding quantities in the treatment planning system (TPS). The dose and dose rate distributions were reconstructed on patient CT using the measured SICA log and compared to the planned values in volume histograms and 3D gamma analysis. Furthermore, the 2D dose and dose rate measurements were compared with the TPS calculations of the same depth. In addition, simulations using different machine‐delivery uncertainties were performed, and QA tolerances were deduced. Results A transmission proton plan of 250 MeV for a lung lesion was planned and measured in a dedicated ProBeam research beamline (Varian Medical System) with a nozzle beam current between 100 to 215 nA. The worst gamma passing rates for dose and dose rate of the 2D SICA measurements (four fields) compared to TPS prediction (3%/3 mm criterion) were 96.6% and 98.8%, respectively, whereas the SICA‐log reconstructed 3D dose distribution achieved a gamma passing rate of 99.1% (2%/2 mm criterion) compared to TPS. The deviations between SICA measured log, and TPS were within 0.3 ms for spot dwell time with a mean difference of 0.069 ± 0.11 s, within 0.2 mm for spot position with a mean difference of −0.016 ± 0.03 mm in the x‐direction, and −0.036 ± 0.059 mm in the y‐direction, and within 3% for delivered spot MUs. Volume histogram metric of dose (D95) and dose rate (V40Gy/s) showed minimal differences, within less than 1%. Conclusions This work is the first to describe and validate an all‐in‐one measurement‐based psQA framework that can fulfill the goals of validating the dose rate accuracy in addition to dosimetric accuracy for proton PBS transmission FLASH‐RT. The successful implementation of this novel QA program can provide future clinical practice with more confidence in the FLASH application.

show abstract

Design of static and dynamic ridge filters for FLASH–IMPT: A simulation study

Cited by 20 publications

References 37 publications

Optimization of patient-specific range modulators for conformal FLASH proton therapy

Optimization of patient-specific range modulators for conformal FLASH proton therapy

Feasibility study of hybrid inverse planning with transmission beams and single‐energy spread‐out Bragg peaks for proton FLASH radiotherapy

Implementation of novel measurement‐based patient‐specific QA for pencil beam scanning proton FLASH radiotherapy

Contact Info

Product

Resources

About