D. Bettega

Inactivation of human normal and tumour cells irradiated with low energy protons

Purpose : To analyse the cell inactivation frequencies induced by low energy protons in human cells with different sensitivity to photon radiation. Materials and methods : Four human cell lines with various sensitivities to photon irradiation were used: the SCC25 and SQ20B derived from human epithelium tumours of the tongue and larynx, respectively, and the normal lines M/10, derived from human mammary epithelium, and HF19 derived from a lung fibroblast. The cells were irradiated with γ-rays and proton beams with linear energy transfer (LET) from 7 to 33keV/ μ m. Clonogenic survival was assessed. Results : Survival curves are reported for each cell line following irradiation with γ-rays and with various proton LETs. The surviving fraction after 2 Gy of γ-rays was 0.72 for SQ20B cells, and 0.28–0.35 for the other cell lines. The maximum LET proton effectiveness was generally greater than that of γ-rays. In particular there was a marked increase in beam effectiveness with increasing LET for the most resistant cells (SQ20B) whose 2 Gy-survival varied from 0.72 with γ-radiation down to 0.37 with 30keV/ μ m protons. The relative biological effectiveness (RBE(2Gy γ) ) with the 30 keV/ μ m beam, evaluated as the ratio of 2Gy to the proton dose producing the same inactivation level as that given by 2 Gy of γ-rays, was 3.2, 1.8, 1.3 and 0.8 for SQ20B, M/10, SCC25, and HF19, respectively. Conclusions : RBE for inactivation with high-LET protons increased with the cellular radioresistance to γ-rays. The cell line with the greatest resistance to γ-rays was the most responsive to the highest LET proton beam. A similar trend has also been found in studies reported in the literature with He, C, N ions with LET in the range 20–125keV/ μ m on human tumour cell lines.PURPOSE To analyse the cell inactivation frequencies induced by low energy protons in human cells with different sensitivity to photon radiation. MATERIALS AND METHODS Four human cell lines with various sensitivities to photon irradiation were used: the SCC25 and SQ20B derived from human epithelium tumours of the tongue and larynx, respectively, and the normal lines M/10, derived from human mammary epithelium, and HF19 derived from a lung fibroblast. The cells were irradiated with y-rays and proton beams with linear energy transfer (LET) from 7 to 33 keV/microm. Clonogenic survival was assessed. RESULTS Survival curves are reported for each cell line following irradiation with gamma-rays and with various proton LETs. The surviving fraction after 2 Gy of gamma-rays was 0.72 for SQ20B cells, and 0.28-0.35 for the other cell lines. The maximum LET proton effectiveness was generally greater than that of gamma-rays. In particular there was a marked increase in beam effectiveness with increasing LET for the most resistant cells (SQ20B) whose 2 Gy-survival varied from 0.72 with gamma-radiation down to 0.37 with 30 keV/microm protons. The relative biological effectiveness (RBE(2 Gy gamma)) with the 30 keV/microm beam, evaluated as the ratio of 2 Gy to the proton dose producing the same inactivation level as that given by 2 Gy of gamma-rays, was 3.2, 1.8, 1.3 and 0.8 for SQ20B, M/10, SCC25, and HF19, respectively. CONCLUSIONS RBE for inactivation with high-LET protons increased with the cellular radioresistance to gamma-rays. The cell line with the greatest resistance to gamma-rays was the most responsive to the highest LET proton beam. A similar trend has also been found in studies reported in the literature with He, C, N ions with LET in the range 20-125 keV/microm on human tumour cell lines.

Cell transformation by light charged particles : review of available data

Data reported in the literature on neoplastic transformation induced in cultured cells by light charged particles are compared and analyzed as a function of LET and dose protraction. Light charged particles RBE for transformation is maximum between 75 and 120 keV/microm. The majority of the data suggest that RBE values for survival and transformation are of similar magnitude. Dose protraction effects on transformation induction depend on dose, dose rate and on radiation quality.

EP-1764: development and validation of a tool to evaluate prostate motion due to patient’s breathing

Purpose or Objective: An electromagnetic (ELM) system (Calypso, Varian Medical System, Palo Alto, CA, USA) based on sub-millimeter high frequency localization of three transponders permanently implanted in the prostate, was recently introduced for continuous real-time tracking of the tumor. Several studies of the tracks acquired over thousands of patients were reported in literature and allowed to give a detailed insight of intra-fraction prostate motion. Aim of this work was to develop and validate a tool to selectively filter the signal produced by the ELM transponders and to apply it for the evaluation of the amplitude of prostate motion only due to patient’s breathing.

Calculation of Nuclear Particles Production at High-Energy Photon Beams from a Linac Operating at 6, 10 and 15 MV

Production of photonuclear particles in a tissue-equivalent medium has been calculated for linacs at 6, 10 and 15 MV from Varian TrueBeam. Based on the knowledge of bremsstrahlung fluence spectra and linac photon beam parameters, numerical integration was performed on the cross sections for photoparticle production of the constituent elements of tissue (2H,12C,13C,16O,17O,18O,14N,15N). At 15 MV, at the depth of photon maximum dose, the total absorbed dose due to neutrons, protons, alphas and residual nuclei from photon reactions in tissue (5.5E-05 Gy per Gy of photons) is comparable to that due to neutrons from accelerator head. Results reasonably agree with data reported in the literature using Monte Carlo models simulating linac head components. This work suggests a simple method to estimate the dose contributed by the photon-induced nuclear particles for high-energy photon beams produced by linacs in use, as it might be relevant for late stochastic effects.