Predicting the Biological Effects of Human Salivary Gland Tumour Cells for Scanned 4He-, 12C-, 16O-, and 20Ne-Ion Beams Using an SOI Microdosimeter

Experimental microdosimetry along with the microdosimetric kinetic (MK) model can be utilized to predict the biological effects of ions. To predict the relative biological effectiveness (RBE) of ions and the survival fraction (SF) of human salivary gland tumour (HSGc-C5) cells, microdosimetric quantities measured by a silicon-on-insulator (SOI) MicroPlus-mushroom microdosimeter along the spread-out Bragg peak (SOBP) delivered by pencil beam scanning of 4He, 12C, 16O, and 20Ne ions were used. The MK model parameters of HSGc-C5 cells were obtained from the best fit of the calculated SF for the different linear energy transfer (LET) of these ions and the formerly reported in vitro SF for the same LET and ions used for calculations. For a cube-shaped target of 10 × 10 × 6 cm3, treatment plans for 4He, 12C, 16O, and 20Ne ions were produced with proprietary treatment planning software (TPS) aiming for 10% SF of HSGc-C5 cells over the target volume and were delivered to a polymethyl methacrylate (PMMA) phantom. Afterwards, the saturation-corrected dose-mean lineal energy derived based on the measured microdosimetry spectra, along with the physical dose at various depths in PMMA phantoms, was used for the estimation of the SF, RBE, and RBE-weighted dose using the MK model. The predicted SF, RBE, and the RBE-weighted dose agreed with what was planned by the TPS within 3% at most depths for these ions.publishedVersio

A Monte Carlo study of physical dose perturbation of carbon ion beam in water with Gold Anchor

Purpose: The Gold Anchor is a kind of fiducial marker for radiotherapy. There is a trend toward the greater use of it for IGRT because of its great visibility, instant stability and minimal invasive. It has cut-outs in its structure, which allow itself into a ball or placed as a line during implantation. Towards to use of it for prostate cancer with carbon ion radiotherapy, the physical dose perturbation of carbon ion beam was assessed when a Gold Anchor was located proximal to Bragg peak.Methods: The Gold Anchor have two size types, one is φ 0.28 mm × 20 mm and another is φ 0.28 mm × 10 mm, respectively. They were made of 99.5% Au and 0.5% iron. Because of its small and complex structure, dose profiles were calculated by Monte Carlo tool Geant4. A 5 × 5 cm2 field with pristine 350 MeV/u carbon ion beam was irradiated into water, and a Gold Anchor was located around 2 cm proximal to Bragg peak. Several shapes of Gold Anchor, such as curled, zigzag and tadpole shapes, were considered.Results: The differences of depth dose profiles with and without Gold Anchor along beam axis in water were compared. The maximum peak shift was observed with curled 20 mm length Gold Anchor, it was reached around 1 cm.Conclusion: This study recommends the sparser shapes for reducing the dose perturbation.第121回日本医学物理学会学術大

Longitudinal radiochromic-film dosimetry for carbon-ion radiotherapy

This is a feasibility study for radiochromic film (RCF) dosimetry to measure physical and biological doses for quality assurance of carbon-ion radiotherapy. We used a layer-stacking carbon-ion beam comprised of range-shifted beamlets from the Heavy Ion Medical Accelerator in Chiba (HIMAC) at the National Institute of Radiological Scienecs (NIRS). Using biophysical beam model in a treatment planning system with its measured RCF response, the layer-stacking beam was decomposed into finely arranged beamlets with weights estimated by deconvolution of longitudinal RCF responses. The distributions of physical and biological doses were reconstructed from the estimated weights and were compared with the plan. We have developed a method to measure physical and biological doses by longitudinal dosimetry of quenched response. The method only involves a general optimization algorithm, a radiobiology model, and experimental beamlet data, and requires no extra corrections. Theoretically, this approach is applicable to various dosimeters and to proton and ion beams of any delivery method, regardless of quenching or biological effectiveness.ESTRO Meets Asia 201

Analysis of the uncertainties in the dose audit system using radiophotoluminescent glass dosimeters in Japanese radiotherapy units

A dosimetry audit of radiotherapy units in Japan was performed usingradiophotoluminescent glass dosimeters (RPLDs). This study analyses theuncertainties associated with the procedure for determining the absorbed dose by anRPLD from a high-energy photon beam in radiotherapy units. The absorbed dose isderived using six parameters: the indicated value given by the RPLD, the individualdosimeter sensitivity correction factor for each element, the calibration coefficient forthe reference radiation quality, the correction factor for the radiation quality, thecorrection factor for the phantom material, and the correction factor of nonlinearity. Theuncertainty of each parameter was estimated based on the ISO standard methodology,“Guide to the Expression of Uncertainty in Measurement.” The estimated combinedstandard uncertainty of the dose measured by RPLD was 1.4% under the referencecondition. This value was compared to the standard deviation of the differencebetween the measured and intended doses obtained from the actual audit results(4,447 beams from 577 hospitals) over 13 years. The average percentage differencebetween the measured and calculated doses under the reference condition was 0.4%,with a standard deviation (k=1) of 1.3%. The results were consistent with theuncertainty estimated by this report and demonstrate the reliability of the RPLDdosimetry method

Application of radiophotoluminescent glass dosimeter to radiotherapy dosimetry audit

Background and ObjectivesRadiophotoluminescent glass dosimeter (RPLD) has been used in Japan as dosimeter of postal dose audit in external radiotherapy. Due to its advantages of compactness, repeatable readout, good precision and small fading1), RPLD become a suitable dosimeter for the audit. In Japan, the permanent auditing system using RPLD for external radiotherapy was launched in 2007. Currently, in multicenter clinical studies conducted in the framework of the Forum for Nuclear Cooperation in Asia (FNCA), the RPLD is also used as a dosimeter for brachytherapy dosimetry audit.Material　The glass dosimeter (DOSE ACE, ASAHI TECHNO GLASS CORPORATION; ATG) is silver-activated phosphate glass. Its weight composition is as follows: 11.0% Na, 31.55% P, 51.16% O, 6.12% Al and 0.17% Ag [14]. Its dimensions are 1.5mm in diameter and 12mm in length. A solid-state laser (ultraviolet wavelength) is used for reading. On its reading, 10 to 20 pulses of laser are irradiated per second, and the average value is obtained. In order to suppress variations in light emission amount depending on slight position fluctuation including rotation of the element, sensitive setup of the element is necessary. In addition, the whole reading process is repeated for 5 times, to improve the statistics. Dosimetry audit for external radiotherapy　RPLD elements are embedded in a solid phantom (Tough water phantom, manufactured by Kyoto Science Co., Ltd.), and it is set to be the reference condition of linear accelerator, and the reference dose (1 Gy) is irradiated. Phantom and RPLD are sent to the radiotherapy hospital according to their request. After irradiation, those are sent back to NIRS to evaluate the dose irradiated to the RPLD.Dosimetry audit for brachytherapy　The use of RPLD as a dose auditing tool for image-guided brachytherapy performed as a multicenter clinical study of cervical cancer has been studied. We are planning an end-to-end test that enables validation including the same flow as the actual patient, such as CT acquisition and treatment plan, rather than simple source intensity measurement. Although the beam quality is close to the cobalt irradiation field that calibrates the RPLD, it is affected by the dose gradient caused by the distance from the source close, and it is necessary to consider the volume effect. The phantom photograph produced is shown in the figure below. It was manufactured so that the RPLD element can be inserted into the evaluation points which are clinical dose evaluation points, point A right and left, and representative points of risk organs, bladder and the rectum (ICRU reference point). Currently we are doing Monte Carlo simulation for basic data verification and beam quality correction. Conclusion　RPLD is a useful solid state dosimeter for the external dosimetry audit in radiation therapy.19th International Conference on Solid State Dosimetry (SSD19

Feasibility study of using Stereotactic Field Diode for field output factors measurement and evaluating three new detectors for small field relative dosimetry of 6 and 10 MV photon beams

This study assesses the feasibility of using stereotactic field diode (SFD) as an alternate to gaf chromic films for field output factor (FF) measurement and further evaluating three new detectors for small field dosimetry. Varian 21EX linear accelerator was used to generate 6 and 10 MV beams of nominal square fields ranging from 0.5 × 0.5 cm2 to 10 × 10 cm2. One passive (EBT3 films) and five active detectors including IBA RAZOR diode(RD), SFD, RAZOR nanochamber (RNC), pinpoint chamber (PTW31023), and semiflex chamber (PTW31010) were employed. FFs were measured using films and SFD while beam profiles and percentage depth dose (PDD) distribution were acquired with active detectors. Polarity (kpol) and recombination (ks) effects of ion chambers were determined and corrected for output ratio measurement. Correction factors (CF) of RD, RNC, and PTW31023 in axial and radial orientation were also measured. Stereotactic field diode measured FFs have shown good agreement with films (with difference of <1%). RD and RNC measured beam profiles were within 3% deviation from the SFD values. Variation in kpol with field size for RNC and PTW31023 was up to 4% and 0.4% (for fields ≥ 1 × 1 cm2), respectively, while variation in ks of PTW31023 was <0.2 %. The maximum values of CF have been calculated to be 5.2%, 2.0%, 13.6%, and 25.5% for RD, RNC, PTW31023‐axial, and PTW31023‐radial respectively. This study concludes that SFD with appropriate CFs as given in TRS 483 may be used for measuring FFs as an alternate to EBT3 films. Whereas RD and RNC may be used for beam profile and PDD measurement in small fields. Considering the limit of usability of 2%, RNC may be used without CF for FF measurement in the smallfields investigated in this study