Recent progress in pencil beam scanning FLASH proton therapy: a narrative review

Wei, Shouyi; Shi, Chengyu; Chen, Chin-Cheng; Huang, Sheng; Press, Robert H.; Choi, J. Isabelle; Simone, Charles B.; Lin, Haibo; Kang, Minglei

doi:10.21037/tro-22-1

Cited by 7 publications

(6 citation statements)

References 47 publications

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“…Since the plateau region has a relatively homogeneous dose distribution, the whole target can be uniformly irradiated with the FLASH dose rate. This FLASH proton delivery technique is generally available to modern proton units with PBS capability [39,40]. However, since the Bragg peak occurs outside the patient body, there will be an additional exit dose beyond the treatment target, and the advantage of proton use for tissue sparing is lost.…”

Section: Current Flash Deliverymentioning

confidence: 99%

Pencil Beam Scanning Proton Bragg Peak Conformal FLASH in Prostate Cancer Stereotactic Body Radiotherapy

Kaulfers,

Lattery,

Cheng

et al. 2024

Cancers

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Bragg peak FLASH radiotherapy (RT) uses a distal tracking method to eliminate exit doses and can achieve superior OAR sparing. This study explores the application of this novel method in stereotactic body radiotherapy prostate FLASH-RT. An in-house platform was developed to enable intensity-modulated proton therapy (IMPT) planning using a single-energy Bragg peak distal tracking method. The patients involved in the study were previously treated with proton stereotactic body radiotherapy (SBRT) using the pencil beam scanning (PBS) technique to 40 Gy in five fractions. FLASH plans were optimized using a four-beam arrangement to generate a dose distribution similar to the conventional opposing beams. All of the beams had a small angle of two degrees from the lateral direction to increase the dosimetry quality. Dose metrics were compared between the conventional PBS and the Bragg peak FLASH plans. The dose rate histogram (DRVH) and FLASH metrics of 40 Gy/s coverage (V40Gy/s) were investigated for the Bragg peak plans. There was no significant difference between the clinical and Bragg peak plans in rectum, bladder, femur heads, large bowel, and penile bulb dose metrics, except for Dmax. For the CTV, the FLASH plans resulted in a higher Dmax than the clinical plans (116.9% vs. 103.3%). For the rectum, the V40Gy/s reached 94% and 93% for 1 Gy dose thresholds in composite and single-field evaluations, respectively. Additionally, the FLASH ratio reached close to 100% after the application of the 5 Gy threshold in composite dose rate assessment. In conclusion, the Bragg peak distal tracking method can yield comparable plan quality in most OARs while preserving sufficient FLASH dose rate coverage, demonstrating that the ultra-high dose technique can be applied in prostate FLASH SBRT.

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Section: Current Flash Deliverymentioning

confidence: 99%

Pencil Beam Scanning Proton Bragg Peak Conformal FLASH in Prostate Cancer Stereotactic Body Radiotherapy

Kaulfers,

Lattery,

Cheng

et al. 2024

Cancers

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“…We have made breakthrough progress on the proton BP FLASH-RT technique to deliver a highly conformal FLASH dose rate in hypofractionated proton radiotherapy using a single-energy proton beam [29,32]. This method has been demonstrated to achieve a superior inherent normal tissue-sparing dose relative to TB proton FLASH-RT plans with satisfactory FLASH dose rate coverage.…”

Section: Current Limitationsmentioning

confidence: 99%

“…This PRT treatment technique introduces an exit dose in the normal tissue beyond the target, which is not an optimal method for delivery compared to conventional dose rate proton treatments using SOBP techniques and increases the irradiation doses received by critical normal tissues beyond the target volume. Conventional IMPT is the most advanced form of proton therapy and can optimally spare critical structures for cancer patients [ 20 , 29 , 30 ]. However, it historically has not been feasible to reach FLASH dose rates with IMPT due to two major reasons: (1) proton beams with lower energies cannot reach a sufficiently high beam current for FLASH delivery; (2) energy layer switching takes at least a few hundred milliseconds, which prolongs the beam-on time and significantly reduces the mean dose rate to be much lower than the required 40 Gy/s dose rate [ 30 , 31 ].…”

Section: Introductionmentioning

confidence: 99%

“…Conventional IMPT is the most advanced form of proton therapy and can optimally spare critical structures for cancer patients [ 20 , 29 , 30 ]. However, it historically has not been feasible to reach FLASH dose rates with IMPT due to two major reasons: (1) proton beams with lower energies cannot reach a sufficiently high beam current for FLASH delivery; (2) energy layer switching takes at least a few hundred milliseconds, which prolongs the beam-on time and significantly reduces the mean dose rate to be much lower than the required 40 Gy/s dose rate [ 30 , 31 ].…”

Section: Introductionmentioning

confidence: 99%

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Pencil Beam Scanning Bragg Peak FLASH Technique for Ultra-High Dose Rate Intensity-Modulated Proton Therapy in Early-Stage Breast Cancer Treatment

Lattery,

Kaulfers,

Cheng

et al. 2023

Cancers

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Bragg peak FLASH-RT can deliver highly conformal treatment and potentially offer improved normal tissue protection for radiotherapy patients. This study focused on developing ultra-high dose rate (≥40 Gy × RBE/s) intensity-modulated proton therapy (IMPT) for hypofractionated treatment of early-stage breast cancer. A novel tracking technique was developed to enable pencil beaming scanning (PBS) of single-energy protons to adapt the Bragg peak (BP) to the target distally. Standard-of-care PBS treatment plans of consecutively treated early-stage breast cancer patients using multiple energy layers were reoptimized using this technique, and dose metrics were compared between single-energy layer BP FLASH and conventional IMPT plans. FLASH dose rate coverage by volume (V40Gy/s) was also evaluated for the FLASH sparing effect. Distal tracking can precisely stop BP at the target distal edge. All plans (n = 10) achieved conformal IMPT-like dose distributions under clinical machine parameters. No statistically significant differences were observed in any dose metrics for heart, ipsilateral lung, most ipsilateral breast, and CTV metrics (p > 0.05 for all). Conventional plans yielded slightly superior target and skin dose uniformities with 4.5% and 12.9% lower dose maxes, respectively. FLASH-RT plans reached 46.7% and 61.9% average-dose rate FLASH coverage for tissues receiving more than 1 and 5 Gy plan dose total under the 250 minimum MU condition. Bragg peak FLASH-RT techniques achieved comparable plan quality to conventional IMPT while reaching adequate dose rate ratios, demonstrating the feasibility of early-stage breast cancer clinical applications.

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“…Currently, in proton FLASH radiotherapy, single-energy transmission beams are the most feasible solution without any significant beamline modifications. In a cyclotron system, a very high beam current can be achieved by bypassing the energy degraders in the beamline, allowing for ultra-high dose rates and the potential for a FLASH effect ( 1 – 3 ). As proton beams shoot through the body instead of being stopped as in the conventional proton treatment plans, the dosimetric performances are also expected to be very different.…”

Section: Introductionmentioning

confidence: 99%

Dose rate and dose robustness for proton transmission FLASH-RT treatment in lung cancer

et al. 2022

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PurposesTo evaluate the plan quality and robustness of both dose and dose rate of proton pencil beam scanning (PBS) transmission FLASH delivery in lung cancer treatment.Methods and materialsAn in-house FLASH planning platform was used to optimize 10 lung cancer patients previously consecutively treated with proton stereotactic body radiation therapy (SBRT) to receive 3 and 5 transmission beams (Trx-3fds and Trx-5fds, respectively) to 34 Gy in a single fraction. Perturbation scenarios (n=12) for setup and range uncertainties (5 mm and 3.5%) were introduced, and dose-volume histogram and dose-rate-volume histogram bands were generated. Conventional proton SBRT clinical plans were used as a reference. RTOG 0915 dose metrics and 40 Gy/s dose rate coverage (V40Gy/s) were used to assess the dose and dose rate robustness.ResultsTrx-5fds yields a comparable iCTV D2% of 105.3%, whereas Trx-3fds resulted in inferior D2% of 111.9% to the clinical SBRT plans with D2% of 105.6% (p<0.05). Both Trx-5fds and Trx-3fds plans had slightly worse dose metrics to organs at risk than SBRT plans. Trx-5fds achieved superior dosimetry robustness for iCTV, esophagus, and spinal cord doses than both Trx-3fds and conventional SBRT plans. There was no significant difference in dose rate robustness for V40Gy/s coverage between Trx-3fds and Trx-5fds. Dose rate distribution has similar distributions to the dose when perturbation exists.ConclusionTransmission plans yield overall modestly inferior plan quality compared to the conventional proton SBRT plans but provide improved robustness and the potential for a toxicity-sparing FLASH effect. By using more beams (5- versus 3-field), both dose and dose rate robustness for transmission plans can be achieved.

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Recent progress in pencil beam scanning FLASH proton therapy: a narrative review

Cited by 7 publications

References 47 publications

Pencil Beam Scanning Proton Bragg Peak Conformal FLASH in Prostate Cancer Stereotactic Body Radiotherapy

Pencil Beam Scanning Proton Bragg Peak Conformal FLASH in Prostate Cancer Stereotactic Body Radiotherapy

Pencil Beam Scanning Bragg Peak FLASH Technique for Ultra-High Dose Rate Intensity-Modulated Proton Therapy in Early-Stage Breast Cancer Treatment

Dose rate and dose robustness for proton transmission FLASH-RT treatment in lung cancer

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