Statistical effects of dose deposition in track-structure modelling of radiobiology efficiency

Ion-induced cell killing has been reported to depend on the irradiation dose but also on the projectile parameters. In this paper we focus on two approaches developed and extensively used to predict cell survival in response to ion irradiation: the Local Effect Model and the Katz Model. These models are based on a track-structure description summarized in the concept of radial dose. This latter is sensitive to ion characteristics parameters and gives to both models the ability to predict some important radiobiological features for ion irradiations. Radial dose is however an average quantity, which does not include stochastic effects. These radiation-intrinsic effects are investigated by means of a Monte-Carlo simulation of dose deposition. We show that both models are not fully consistent with the nanometric and microscopic dose deposition statistics.Comment: 32 pages ; 8 figure

O2 and glutathione effects on water radiolysis: a simulation study

International audienceWe present a MC simulation of water radiolysis when O2 and glutathione are present in the solution. Our simulation is based on the continuum approximation proposed by Green and co-workers'. We investigate in particular the sensitivity of the yield of HO2•+O2−• to the concentration of O2 and glutathione and to the LET of the ionising radiation. We demonstrate that the production of HO2•/O2−• is highly sensitive to these parameters and that the variation of their yield with the O2 concentration shares remarkable similarities with the O2 effect reported for biological cell damage efficiency

Simulation of ion-induced water radiolysis in different conditions of oxygenation

International audienceWe have investigated the production of free radicals induced by swift ions during the radiolysis of oxygenated water and analyzed the underlying mechanisms in detail. To this aim, we simulated, by Monte-Carlo, the irradiation of water by projectiles with LET values ranging from 1 to 300 keV/μm for a partial pressure of oxygen in air from 0 to 750 mmHg, and for times up to 10 μs after ion impact. For low-LET radiation, we observed an increase in production of (HO2radical dot + O2radical dot−) with oxygen pressure and a saturation. At 1 μs, the saturation occurred at a pressure of 20–30 mmHg and the maximal yield amounted to 0.3 μmol L−1 per Gray. For the same conditions, we observed similar trends for high-LET ions, but we observed a significant reduction in the yield values and an attenuation of the saturation behavior.By underlining similarities between the yield of (HO2radical dot + O2radical dot−) and the oxygen effect observed in radiobiology, we discuss the role of (HO2radical dot + O2radical dot−) in oxygen effect and suggest a general mechanism for this phenomenon

Bénéfice attendu du curage ganglionnaire et de l'exérèse des vésicules séminales pour diminuer la toxicité de la radiothérapie des tumeurs prostatiques de haut risque [Expected benefit of lymph node and seminal vesical dissection to decrease high-risk prostate cancer radiotherapy]

National audiencePurpose In case of pelvic lymph node and seminal vesicle dissection followed by prostate cancer intensity-modulated radiotherapy, the objective of the study was to evaluate the dosimetric benefit of reducing the target volume. Patients and methods A total of 25 patients with high-risk prostate cancer had surgery first followed by intensity-modulated radiotherapy and androgen deprivation. Four treatment planning were simulated for each patient, based on two CT scans performed before and after surgery. The target volumes were: prostate–seminal vesicles–lymph nodes, prostate–lymph nodes, prostate–seminal vesicles and prostate only. The total dose was 46 Gy in the seminal vesicles and lymph nodes, and 80 Gy in the prostate. Results Compared to prostate target volume only, the addition of seminal vesicles and lymph nodes multiplied by a factor of 1.6 and 6.5 the target volume, respectively. Decreasing the target volume from prostate–seminal vesicles–lymph nodes to prostate–seminal vesicles, to prostate only decreased the rectal wall mean dose from 49 Gy to 42 Gy, to 36 Gy, and the risk of late rectal bleeding from 4.4% to 3.2%, to 2.4% (P < 0.05), respectively. The bladder wall mean dose decreased from 51 Gy to 40 Gy, to 35 Gy (P < 0,05), respectively. Not irradiating the lymph nodes decreased the absolute risk of diarrhea by 11%. Conclusion Lymph node and seminal vesicle dissection before prostate cancer intensity-modulated radiotherapy allows decreasing moderately the risk of digestive toxicity. © 2016 Société française de radiothérapie oncologique (SFRO

Radiobiologic Parameters and Local Effect Model Predictions for Head-and-Neck Squamous Cell Carcinomas Exposed to High Linear Energy Transfer Ions

To establish the radiobiologic parameters of head-and-neck squamous cell carcinomas (HNSCC) in response to ion irradiation with various linear energy transfer (LET) values and to evaluate the relevance of the local effect model (LEM) in HNSCC. Methods and Materials Cell survival curves were established in radiosensitive SCC61 and radioresistant SQ20B cell lines irradiated with [33.6 and 184 keV/n] carbon, [302 keV/n] argon, and X-rays. The results of ion experiments were confronted to LEM predictions. Results The relative biologic efficiency ranged from 1.5 to 4.2 for SCC61 and 2.1 to 2.8 for SQ20B cells. Fixing an arbitrary D0 parameter, which characterized survival to X-ray at high doses (>10 Gy), gave unsatisfying LEM predictions for both cell lines. For D0 = 10 Gy, the error on survival fraction at 2 Gy amounted to a factor of 10 for [184 keV/n] carbon in SCC61 cells. We showed that the slope (smax) of the survival curve at high doses was much more reliable than D0. Fitting smax to 2.5 Gy−1 gave better predictions for both cell lines. Nevertheless, LEM could not predict the responses to fast and slow ions with the same accuracy. Conclusions The LEM could predict the main trends of these experimental data with correct orders of magnitude while smax was optimized. Thus the efficiency of carbon ions cannot be simply extracted from the clinical response of a patient to X-rays. LEM should help to optimize planning for hadrontherapy if a set of experimental data is available for high-LET radiations in various types of tumors