Proton and heavy ion therapy offer superior relative biological effectiveness (RBE) in the treatment of deep-seated tumors compared with conventional photon radiotherapy due to its Bragg-peak feature of energy deposition in organs. Many proton and carbon ion therapy centers are active all over the world. At present, five particle radiotherapy institutes have been built and are receiving patient in China, mainly including Wanjie Proton Therapy Center (WPTC), Shanghai Proton Heavy Ion Center (SPHIC), Heavy Ion Cancer Treatment Center (HIMM), Chang Gung Memorial Hospital (CGMH), and Ruijin Hospital affiliated with Jiao Tong University. Many cancer patients have benefited from ion therapy, showing unique advantages over surgery and chemotherapy. By the end of 2020, nearly 8,000 patients had been treated with proton, carbon ion or carbon ion combined with proton therapy. So far, there is no systemic review for proton and carbon ion therapy facility and clinical outcome in China. We reviewed the development of proton and heavy ion therapy, as well as providing the representative clinical data and future directions for particle therapy in China. It has important guiding significance for the design and construction of new particle therapy center and patients’ choice of treatment equipment.

Flourish of Proton and Carbon Ion Radiotherapy in China

This study aims to measure the linear energy transfer (LET) spectra of therapeutic carbon ion beams with a new 2D 6 mm thick ripple filter (RiFi) by using a CR-39 detector. A water phantom was irradiated by three different single energy carbon beams (86.2 MeV/u, 276.5 MeV/u, and 430.0 MeV/u) at Shanghai Proton and Heavy Ion Center (SPHIC), CR-39 detectors were used to measure the LET spectra with and without the RiFi. The Monte Carlo toolkit Geant4 was employed to perform the simulations. The dose-averaged LET (LETd) was calculated according to the LET spectra. The results showed that the 2D RiFi broadens the Bragg peak width and LETd distribution. The simulation LET spectra of primary carbon ions were in good agreement with the experimental results. The LETd can be well estimated by using the measured LET spectra. This result indicated that the RiFi affects the depth-dose distribution and the shape of LET spectra for mono-energetic carbon beams. The CR-39 detector is suitable for LET spectra measurement. It is hoped that this work could provide a new reference method for the cross-validation of basic data in carbon ion clinical quality assurance and benefit clinical treatment. 

Measurements of linear energy transfer (LET) distributions by CR-39 for a therapeutic carbon ion beam with a new 2D ripple filter

Comparison of morphological characteristics for alpha tracks in CR-39 using different radon monitors

To obtain more information about incident particles, a new method for measuring three-dimensional track profiles formed on CR-39s based on the photometric stereo method was developed. A new optical microscope system with 16 lasers and a complementary metal-oxide-semiconductor camera was built to automatically capture the reflecting track images illuminated by the laser beams from different angles, and the track profiles were three-dimensionally reconstructed using a self-developed software. To verify the reconstruction results of the track profiles, both the openings and depth were measured with an atomic force microscope. The results showed that the relative deviations between the two methods of the openings were about 5.5% and the deviations of the depth were about 8.0%. At present, the reconstruction speed of a three-dimensional track profile is a factor of 400 greater than that of the atomic force microscope. The new method shows great potential for rapid reconstruction of numerous track morphologies. It is expected to be helpful for further studies on the energy and angle discrimination of incident particles in the field of nuclear measurements.

Measurement of three-dimensional track profiles on CR-39s based on the photometric stereo method.

This work aims to investigate the changes in the linear energy transfer (LET) spectra distribution and the beam spot width of a therapeutic carbon ion beam in density heterogeneous phantoms. Three different heterogeneous phantoms were fabricated using a combination of solid water, lung, and bone tissue slabs and irradiated by a single energy carbon beam (276.5 MeV u−1). CR-39 detectors were used for experimental measurements and the Monte Carlo toolkit Geant4 was employed for theoretical simulations. The results demonstrated that the measured LET spectra agree well with the simulation results. The lung and bone tissues displayed no obvious effect on the spectral distribution of LET. The dose-average LET was invariant and showed no obvious difference in the different materials, while the track-average LET increased in the lung and decreased in the bone materials. Similarly, the beam spot size increased in the lung, and decreased in the bone materials. Additionally, the fluence of the secondary fragments varied in different tissues. These findings are expected to provide cross-validation data for the quality assurance of carbon ion therapy and to be beneficial for validating the base data in treatment planning systems.

Changes of the linear energy transfer (LET) and beam width of therapeutic carbon ion beam in density heterogeneous phantoms

The motivation of this study was to explore a new method to test the particle spatial distribution for a therapeutic carbon beam. The CR-39 plastic nuclear track detectors (PNTD) were irradiated to a 276.5 MeV/u mono-energy carbon beam at the heavy ion facility in SPHIC (Shanghai Proton and Heavy Ion Center). The spatial distribution of primary carbon beam and secondary fragments in a water phantom were systematically analyzed both in transverse direction (perpendicular to the projection direction of primary beam) and at different depths in longitudinal direction (along the projection direction of primary beam) with the measured tracks on the CR-39 detectors. Meanwhile, the theoretically spatial distribution and linear energy transfer (LET) spectra of primary beam and secondary fragments were calculated using the Monte Carlo toolkit Geant4. The results showed that the CR-39 detectors are capable to provide high lateral resolution of carbon ion at different depths. In the range of primary carbon beam, the beam width simulated with MC is in good agreement with that of experimental measurement. The track size registered in the CR-39 has a good correlation with the particle LET. These findings indicate that the CR-39 can be used for measuring both the particle flux and its spatial distribution of carbon ions.

Measurement of therapeutic 12C beam in a water phantom using CR-39

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Measurement of therapeutic 12C beam in a water phantom using CR-39