Presenter of 1 Presentation
TREATMENT PLANNING AND DELIVERY FOR FLASH PROTON THERAPY WITH BRAGG PEAK
Abstract
Background and Aims
We developed a treatment delivery and planning approach to achieve a high dose rate while meeting the initial goals of an IMPT plan for dose conformity.
Methods
First, the proton fluence at the exit of the nozzle was maximized by transmitting beam at maximum energy through the beam line and using a range shifter to match the maximum proton range to the distal edge of the PTV. Spread-out Bragg peaks (SOBP) were obtained by modulating the range of the protons via a patient-specific ridge filter placed between the patient and the nozzle. To calculate the characteristics of this ridge filter, an IMPT plan was first computed to obtain the list of energies and associated weights that the filter should reproduce from beamlets at maximum energy. The filter was then optimized using an analytical model to allow a comparison in acceptable computational time with the reference dose. Finally, the scanning pattern was optimized with respect to local constraints on the dose rate.
Results
A patient-specific ridge filter is shown in Fig. 1. Corresponding SOBPs were simulated by Monte Carlo with the ridge filter inserted in the CT.
Conclusions
We proposed a treatment approach relying on the use of a patient-specific ridge filter to increase the dose rate without compromising the potential of the Bragg peak. The ridge filter and the spot scanning trajectory were optimized based on a standard IMPT plan by using an analytical algorithm inside MIROpt (http://openmiropt.org/), alongside the MCsquare dose engine (http://www.openmcsquare.org/).
Author Of 2 Presentations
TREATMENT PLANNING AND DELIVERY FOR FLASH PROTON THERAPY WITH BRAGG PEAK
Abstract
Background and Aims
We developed a treatment delivery and planning approach to achieve a high dose rate while meeting the initial goals of an IMPT plan for dose conformity.
Methods
First, the proton fluence at the exit of the nozzle was maximized by transmitting beam at maximum energy through the beam line and using a range shifter to match the maximum proton range to the distal edge of the PTV. Spread-out Bragg peaks (SOBP) were obtained by modulating the range of the protons via a patient-specific ridge filter placed between the patient and the nozzle. To calculate the characteristics of this ridge filter, an IMPT plan was first computed to obtain the list of energies and associated weights that the filter should reproduce from beamlets at maximum energy. The filter was then optimized using an analytical model to allow a comparison in acceptable computational time with the reference dose. Finally, the scanning pattern was optimized with respect to local constraints on the dose rate.
Results
A patient-specific ridge filter is shown in Fig. 1. Corresponding SOBPs were simulated by Monte Carlo with the ridge filter inserted in the CT.
Conclusions
We proposed a treatment approach relying on the use of a patient-specific ridge filter to increase the dose rate without compromising the potential of the Bragg peak. The ridge filter and the spot scanning trajectory were optimized based on a standard IMPT plan by using an analytical algorithm inside MIROpt (http://openmiropt.org/), alongside the MCsquare dose engine (http://www.openmcsquare.org/).
PROTON BEAM FLASH ONLINE MONITORING AT ARRONAX CYCLOTRON
Abstract
Background and Aims
The beam monitoring tools used in conventional irradiation may not be suitable in the case of irradiation using ultra-high dose rate > 40 Gy/sec (FLASH conditions). To monitor the beam, a fast detector coupled with a high dynamic range is needed. A photomultiplier tube measuring the nitrogen fluorescence produced by the beam-air interaction
can be a solution (figure below).
Methods
The ARRONAX facility has been used to deliver proton beams (68 MeV) ranging from low (0.25 Gy/s) to very high (30 kGy/s) dose rates. An in-house prototype consisting of a photomultiplier coupled to an air cavity was used. The signal intensity can be adjusted by changing the solid angle. To verify the measured beam charge, several aluminum targets were irradiated and the produced activities of the radioisotope 24Na were measured after the end of the beam. Several beam time structures with a high number of pulses were tested. In the case of a low doses, radiochromic films (for which we have shown a response independent of the dose rate) were used.
Results
The measured beam charge using the photomultiplier tube was found in good agreement with the produced activity (1.5 %) and with the film responses (< 5 %). A wide range of dose rates was successfully monitored in the linear response region of the photomultiplier using multiple detectors.
Conclusions
We have established a new robust noninvasive method to measure doses in Flash irradiations. The next step is to use the same technology to measure beam geometrical characteristics.