Dose–response of EBT3 radiochromic films to proton and carbon ion clinical beams

Abstract

We investigated the dose-response of the external beam therapy 3 (EBT3) films for proton and carbon ion clinical beams, in comparison with conventional radiotherapy beams; we also measured the film response along the energy deposition-curve in water. We performed measurements at three hadrontherapy centres by delivering monoenergetic pencil beams (protons: 63-230 MeV; carbon ions: 115-400 MeV/u), at 0.4-20 Gy dose to water, in the plateau of the depth-dose curve. We also irradiated the films to clinical MV-photon and electron beams. We placed the EBT3 films in water along the whole depth-dose curve for 148.8 MeV protons and 398.9 MeV/u carbon ions, in comparison with measurements provided by a plane-parallel ionization chamber. For protons, the response of EBT3 in the plateau of the depth-dose curve is not different from that of photons, within experimental uncertainties. For carbon ions, we observed an energy dependent under-response of EBT3 film, from 16% to 29% with respect to photon beams. Moreover, we observed an under-response in the Bragg peak region of about 10% for 148.8 MeV protons and of about 42% for 398.9 MeV/u carbon ions. For proton and carbon ion clinical beams, an under-response occurs at the Bragg peak. For carbon ions, we also observed an under-response of the EBT3 in the plateau of the depth-dose curve. This effect is the highest at the lowest initial energy of the clinical beams, a phenomenon related to the corresponding higher LET in the film sensitive layer. This behavior should be properly modeled when using EBT3 films for accurate 3D dosimetry.

Dose detectors, sensors, and their applications

“…Moreover, because of the strong dependence of the optical density for a given dose on the beam LET, special care is required with IMPT fields, since the cumulative field doses result from the superposition of several protons or carbon ions pencil beams with different energies, hence with different LET. In addition, in the case of carbon ions, the effect of various lighter ions produced by nuclear fragmentation increases the complexity of the measurement …”

“…The work of Fuss et al . contains a proposal of measurements with EBT films, while several papers present the dose‐response of the EBT films and the corresponding quenching effect with proton and carbon ions as a function of the ion type and energy, in the plateau region of the depth‐dose curve for mono‐energetic beams …”

Patient-Specific QA of Spot-Scanning Proton Beams Using Radiochromic Film

“…Radiochromic film dosimetry in low-energy proton or ion beams requires a correction of the LET dependent film response [35,36]. Radiochromic film can be used as a reference dosimeter for biomedical experiments with low-energy proton beams if appropriate LET corrections are applied [36].…”

“…Radiochromic film can be used as a reference dosimeter for biomedical experiments with low-energy proton beams if appropriate LET corrections are applied [36]. There are numerous researchers re-ported that under-response of radiochromic film in the presence of proton SOBPs which could be defined as “quenching effect” of the dosimeter in the region [26–33,35–37]. “Quenching” is said to occur when, for a given physical dose, a dosimeter not limited to radiochromic film gives a lower output reading for radiation with high LET than for the same dose of low LET radiation.…”

“…Quenching of dosimeter response is a major issue in the measurement of the radiation dose from proton and other ion beams. The quenching effect of EBT3 film is the highest at the lowest initial energy of the clinical beams, a phenomenon related to the corresponding higher LET in the film sensitive layer [35]. A possible reason for this is attributed to the shape and arrangement of the monomer particles being different in the active components of EBT.…”