Ultra-High Dose Rate Transmission Beam Proton Therapy for Conventionally Fractionated Head and Neck Cancer: Treatment Planning and Dose Rate Distributions

Marlen, Patricia van; Dahele, Max; Folkerts, Michael; Abel, Eric; Slotman, Ben J.; Verbakel, Wilko F.A.R.

doi:10.3390/cancers13081859

Cited by 25 publications

(24 citation statements)

References 42 publications

(80 reference statements)

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“…( 8) only gives a conservative crude estimate of a "global" dose rate for the 4-spot pattern due to the nonuniform spatial distribution of the dose rate within the field (the areas corresponding to the center of each spot have higher "local" or voxel-specific dose rate compared to the central region of the field where the spots overlap). Definition of the dose rate in the context of FLASH for the scanning beams is not straightforward 33,34 and is beyond the scope of this work.…”

Section: Optimization Of the Range Modulatormentioning

confidence: 99%

Spread‐out Bragg peak proton FLASH irradiation using a clinical synchrocyclotron: Proof of concept and ion chamber characterization

et al. 2021

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Purpose The purpose of this work is to (a) demonstrate the feasibility of delivering a spread‐out Bragg peak (SOBP) proton beam in ultra‐high dose rate (FLASH) using a proton therapy synchrocyclotron as a major step toward realizing an experimental platform for preclinical studies, and (b) evaluate the response of four models of ionization chambers in such a radiation field. Methods A clinical Mevion HYPERSCAN® synchrocyclotron was adjusted for ultra‐high dose rate proton delivery. Protons with nominal energy of 230 MeV were delivered in pulses with temporal width ranging from 12.5 μs to 24 μs spanning from conventional to FLASH dose rates. A boron carbide absorber and a range modulator block were placed in the beam path for range modulation and creating an SOBP dose profile. The radiation field was defined by a brass aperture with 11 mm diameter. Two Faraday cups were used to determine the number of protons per pulse at various dose rates. The dosimetric response of two cylindrical (IBA CC04 and CC13) and two plane‐parallel (IBA PPC05 and PTW Advanced Markus®) ionization chambers were evaluated. The dose rate was measured using the plane‐parallel ionization chambers. The integral depth dose (IDD) was measured with a PTW Bragg Peak® ionization chamber. The lateral beam profile was measured with EBT‐XD radiochromic film. Monte Carlo simulation was performed in TOPAS as the secondary check for the measurements and as a tool for further optimization of the range modulators’ design. Results Faraday cups measurement showed that the maximum protons per pulse is 39.9 pC at 24 μs pulse width. A good agreement between the measured and simulated IDD and lateral beam profiles was observed. The cylindrical ionization chambers showed very high ion recombination and deemed not suitable for absolute dosimetry at ultra‐high dose rates. The average dose rate measured using the PPC05 ionization chamber was 163 Gy/s at the pristine Bragg peak and 126 Gy/s at 1 cm depth for the SOBP beam. The SOBP beam range and modulation were measured 24.4 mm and 19 mm, respectively. The pristine Bragg peak beam had 25.6 mm range. Simulation results showed that the IDD and profile flatness can be improved by the cavity diameter of the range modulator and the number of scanned spots, respectively. Conclusions Feasibility of delivering protons in an SOBP pattern with >100 Gy/s average dose rate using a clinical synchrocyclotron was demonstrated. The dose heterogeneity can be improved through optimization of the range modulator and number of delivered spots. Plane‐parallel chambers with smaller gap between electrodes are more suitable for FLASH dosimetry compared to the other ion chambers used in this work.

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Section: Optimization Of the Range Modulatormentioning

confidence: 99%

Spread‐out Bragg peak proton FLASH irradiation using a clinical synchrocyclotron: Proof of concept and ion chamber characterization

et al. 2021

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“…This spread of dose across the beam spot is a noted difficulty with delivering FLASH using PBS however the necessary instantaneous, mean or threshold dose over a region of interest, has not yet been quantitatively defined ( 177 ). The impact of deadtimes is also unclear, as PBS parameters (components in Section 2.2) determine the dose output and timing ( 178 ). Hybrid delivery schemes and 3D modulation devices have been suggested for reaching FLASH dose rates across the entire volume however higher beam intensities are needed to compensate particle losses.…”

Section: Emerging Applicationsmentioning

confidence: 99%

“…Furthermore, as ensuring precise beam delivery and positioning is difficult, transmission or ‘ shoot-through ’ FLASH ( 186 ) with protons is performed where exploitation of the BP may be considered redundant to maintain a high, effective mean dose rate whilst also resulting in the FLASH effect ( 184 ). Several transmission studies have been reported ( 177 , 178 , 187 ) as this method is achievable with current technologies. This bypasses the need for additional beam modification devices, minimizing range uncertainties and delivery requirements.…”

Section: Emerging Applicationsmentioning

confidence: 99%

Future Developments in Charged Particle Therapy: Improving Beam Delivery for Efficiency and Efficacy

2021

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The physical and clinical benefits of charged particle therapy (CPT) are well recognized. However, the availability of CPT and complete exploitation of dosimetric advantages are still limited by high facility costs and technological challenges. There are extensive ongoing efforts to improve upon these, which will lead to greater accessibility, superior delivery, and therefore better treatment outcomes. Yet, the issue of cost remains a primary hurdle as utility of CPT is largely driven by the affordability, complexity and performance of current technology. Modern delivery techniques are necessary but limited by extended treatment times. Several of these aspects can be addressed by developments in the beam delivery system (BDS) which determines the overall shaping and timing capabilities enabling high quality treatments. The energy layer switching time (ELST) is a limiting constraint of the BDS and a determinant of the beam delivery time (BDT), along with the accelerator and other factors. This review evaluates the delivery process in detail, presenting the limitations and developments for the BDS and related accelerator technology, toward decreasing the BDT. As extended BDT impacts motion and has dosimetric implications for treatment, we discuss avenues to minimize the ELST and overview the clinical benefits and feasibility of a large energy acceptance BDS. These developments support the possibility of advanced modalities and faster delivery for a greater range of treatment indications which could also further reduce costs. Further work to realize methodologies such as volumetric rescanning, FLASH, arc, multi-ion and online image guided therapies are discussed. In this review we examine how increased treatment efficiency and efficacy could be achieved with improvements in beam delivery and how this could lead to faster and higher quality treatments for the future of CPT.

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“…In proton FLASH-RT, transmission proton beams have been the most favorable choice of delivery owing to the sufficiently high beam current achievable with existing clinical systems. Recent efforts have reported combining transmission proton PBS with FLASH-RT, to translate the technology from bench to preclinic experiments, in aspects including proton systems (11)(12)(13)(14)(15), treatment planning (18)(19)(20)(21)(22)(23), and biological investigations (24,25). Proton PBS FLASH treatment planning plays a crucial role just as conventional treatment planning, but it faces new and unique challenges as the dose rate considerations must be included when evaluating the plan quality.…”

Section: Introductionmentioning

confidence: 99%

“…Currently, several treatment planning studies have applied proton PBS FLASH beams to the head and neck (H&N) (19,20,34) and lung cancers (18,22,23,35), with theoretical proton delivery parameters. van de Water et al (19) discussed the feasibility of achieving transmission FLASH with existing and theoretical machine settings, especially the beam current, with the dose rate quantified using the dose-averaged dose rate (DADR).…”

Section: Introductionmentioning

confidence: 99%

FLASH Radiotherapy Using Single-Energy Proton PBS Transmission Beams for Hypofractionation Liver Cancer: Dose and Dose Rate Quantification

et al. 2022

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PurposeThis work aims to study the dose and ultra-high-dose rate characteristics of transmission proton pencil beam scanning (PBS) FLASH radiotherapy (RT) for hypofractionation liver cancer based on the parameters of a commercially available proton system operating under FLASH mode.Methods and MaterialsAn in-house treatment planning software (TPS) was developed to perform intensity-modulated proton therapy (IMPT) FLASH-RT planning. Single-energy transmission proton PBS plans of 4.5 Gy × 15 fractions were optimized for seven consecutive hepatocellular carcinoma patients, using 2 and 5 fields combined with 1) the minimum MU/spot chosen between 100 and 400, and minimum spot time (MST) of 2 ms, and 2) the minimum MU/spot of 100, and MST of 0.5 ms, based upon considerations in target uniformities, OAR dose constraints, and OAR FLASH dose rate coverage. Then, the 3D average dose rate distribution was calculated. The dose metrics for the mean dose of Liver-GTV and other major OARs were characterized to evaluate the dose quality for the different combinations of field numbers and minimum spot times compared to that of conventional IMPT plans. Dose rate quality was evaluated using 40 Gy/s volume coverage (V40Gy/s).ResultsAll plans achieved favorable and comparable target uniformities, and target uniformity improved as the number of fields increased. For OARs, no significant dose differences were observed between plans of different field numbers and the same MST. For plans using shorter MST and the same field numbers, better sparing was generally observed in most OARs and was statistically significant for the chest wall. However, the FLASH dose rate coverage V40Gy/s was increased by 20% for 2-field plans compared to 5-field plans in most OARs with 2-ms MST, which was less evident in the 0.5-ms cases. For 2-field plans, dose metrics and V40Gy/s of select OARs have large variations due to the beam angle selection and variable distances to the targets. The transmission plans generally yielded inferior dosimetric quality to the conventional IMPT plans.ConclusionThis is the first attempt to assess liver FLASH treatment planning and demonstrates that it is challenging for hypofractionation with smaller fractional doses (4.5 Gy/fraction). Using fewer fields can allow higher minimum MU/spot, resulting in higher OAR FLASH dose rate coverages while achieving similar plan quality compared to plans with more fields. Shorter MST can result in better plan quality and comparable or even better FLASH dose rate coverage.

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Ultra-High Dose Rate Transmission Beam Proton Therapy for Conventionally Fractionated Head and Neck Cancer: Treatment Planning and Dose Rate Distributions

Cited by 25 publications

References 42 publications

Spread‐out Bragg peak proton FLASH irradiation using a clinical synchrocyclotron: Proof of concept and ion chamber characterization

Spread‐out Bragg peak proton FLASH irradiation using a clinical synchrocyclotron: Proof of concept and ion chamber characterization

Future Developments in Charged Particle Therapy: Improving Beam Delivery for Efficiency and Efficacy

FLASH Radiotherapy Using Single-Energy Proton PBS Transmission Beams for Hypofractionation Liver Cancer: Dose and Dose Rate Quantification

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