Medical Radiology and Radiation Safety. 2014. Vol. 59. No. 2. P. 39-46

RADIATION THERAPY

Yu.V. Gumenetskaya, Yu.S. Mardynsky, I.A. Gulidov, O.B. Karyakin

Results of a Comparative Analysis of the Effectiveness of Different Methods of Palliative Radiation Therapy for Bladder Cancer

Medical Radiological Research Center, Kaluga Region, Obninsk. E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.

ABSTRACT

Purpose: To analyze the results of palliative radiation therapy for bladder cancer and to assess the effects of dose-fractionation regimens on treatment effectiveness.

Material and methods: The immediate and long-term results of palliative radiation therapy in 90 bladder cancer patients who had been treated in the Medical Radiological Research Center within the period from1990 to 2010 were analyzed. Three dose-fractionation regimens were used:

1) Conventional fractionation (CF; single tumor dose 2 Gy, total tumor dose 40–46 Gy; n = 37);

2) Hypofractionation (HF; single tumor dose 3 Gy, total tumor dose 30 Gy, n = 22);

3) Accelerated dynamic dose-fractionation (ADDF; total tumor dose 30 Gy, n = 31).

Results: Palliative radiation therapy could stop and reduce hematuria in 73.1 % and 26.9 % of cases, respectively; alleviate bladder pain syndrome in 75.0 % of cases; achieve objective tumor response to therapy after 6 months and 12 months in 34.4 % and 31.1 % of cases, respectively. Median survival after the palliative treatment was 12.9 ± 1.3 months. After accelerated dynamic fractionation, hematuria was stopped in 91.7 % of cases versus 63.0 % after conventional fractionation (p < 0.05) and 62.5 % of cases after hypofractionation; objective tumor response (6 months after therapy) was achieved in 48.4 % of cases versus 24.3 % after CF (p < 0.05) and 31.8 % of cases after HF. Late bladder complications of grades 1–2 (RTOG/EORTC) were seen in 9.7 % of cases in ADDF group versus 18.2 % in HF group and 18.9 % of cases in CF group (p < 0.2). No complications of grade ≥ 3 occurred. Median survival in CF group was 12.0 ± 1.6 months, in HF group – 12.3 ± 4.4 months, and in ADF group – 14.3 ± 8.5 months.

Conclusion: Radiation therapy is an effective palliative treatment in patients with contraindications for surgical and anti-tumor drug therapy of complications of bladder cancer. Accelerated dynamic dose-fractionation allowed to improve the effectiveness of palliative treatment in bladder cancer patients and to reduce treatment times without complications increasing.

Key words: bladder cancer, palliative radiation therapy, fractionation regimen

Medical Radiology and Radiation Safety. 2018. Vol. 63. No. 2. P. 55–61

RADIATION PHYSICS, TECHNOLOGY AND DOSIMETRY

DOI: 10.12737/article_5ac622371650f7.48983677

Field Junction Technique for Helical Tomotherapy-Based Total Body Irradiation

A.A. Loginova¹, D.A. Tovmasian², A.P. Chernyaev², S.M. Varzar², D.A. Kobyseva¹, A.V. Nechesnyuk¹

1. Dmitry Rogachev National Research Center of Pediatric Hematology, Oncology and Immunology, Moscow, Russia, e-mail: This email address is being protected from spambots. You need JavaScript enabled to view it. ; 2. M.V. Lomonosov Moscow State University, Moscow, Russia

A.A. Loginova – Senior Med. Physicist; D.A. Tovmasian – Master’s Degree Student; A.P. Chernyaev – Head of the Dep., Prof., Dr. Sc. Phys.-Math.; S.M. Varzar – Associate Prof., PhD Phys.-Math.; D.A. Kobyzeva – Pediatric Oncologist; A.V. Nechesnyuk – Head of the Radiother. Dep., PhD Med.

Abstract

Purpose: Combination of total body irradiation (TBI) with chemotherapy is widely used technique for conditioning before hematopoietic stem cell transplantation for patient with hematological malignancies worldwide. Total body irradiation for patients with high height has to be divided into two parts: irradiation of upper part of the patient’s body (including head, body and part of legs) and irradiation of lower part of the patient’s body (including leg). There is an area in which the fields overlap each other – the junction area. The aim of this work is the development and verification of simple junction technique that would provide the dose distribution in the junction area from 90 to 125 % of prescribed dose.

Material and methods: Total body irradiation was performed on the Tomotherapy machine using helical geometry of the beam delivery. Distribution of the dose in junction area was investigated. Simple solution was proposed: during the optimization of the radiotherapy plan certain margin should be maintained between upper and lower targets while dose distribution in junction area satisfies the uniformity requirements for the given irradiation geometry. The dimension of the margin was determined experimentally using a CheesePhantom and radiochromic EBT-2 films. The uniformity of dose distribution in the junction area was monitored by in vivo measurements using radiochromic EBT-2 films located on the skin surface of patients.

Results: The dimension of the margin at which the dose in the junction area is within the range of 90 to 125 % of the prescribed dose was determined experimentally and amounted to 5.25 cm. The values of the measured dose were in the range from 97 to 105 %. In total 18 in vivo measurements of the junction area were performed. According to the results of in vivo dosimetry, the values of the doses measured in the junction area were in the range from 93 ± 3 % to 108 ± 4 %.

Conclusion:The developed planning method with the selected plan geometry ensures satisfactory heterogeneity of the dose distribution in the area of field junction between the upper and lower irradiation regions, despite of the existing uncertainty of patient positioning. Results were confirmed by in vivo measurements. The obtained data can be used for total body irradiation of the patients using Helical Tomotherapy.

Key words: radiotherapy, tomotherapy, total body irradiation, junction area

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For citation: Loginova AA, Tovmasian DA, Chernyaev AP, Varzar SM, Kobyseva DA, Nechesnyuk AV. Junction Technique for Helical Tomotherapy-Based Total Body Irradiation. Medical Radiology and Radiation Safety. 2018;63(2):55-61. Russian. DOI: 10.12737/article_5ac622371650f7.48983677.

PDF (RUS) Full-text article (in Russian)

Medical Radiology and Radiation Safety. 2018. Vol. 63. No. 2. P. 62–69

RADIATION PHYSICS, TECHNOLOGY AND DOSIMETRY

DOI: 10.12737/article_5ac6238f8d7653.20448458

Estimation of the X-rays RBE Uncerainty Related to Determination of Absorbed Dose in Radiobiological Experiments

A.V. Belousov, G.A. Krusanov, A.P. Chernyaev

M.V. Lomonosov Moscow State University, Moscow, Russia, e-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.

A.V. Belousov – Assistant Professor, PhD Phys.; G.A. Krusanov – Graduate Student; A.P. Chernyaev – Head of Dep., Dr. Sc. Phys., Prof.

Abstract

Purpose: Determining the absorbed dose produced by photons, it is often assumed that it is equal to the radiation kerma. This assumption is valid only in the presence of an electronic equilibrium, which in turn is never ensured in practice. It leads to some uncertainty in determining the absorbed dose in the irradiated sample during radiobiological experiments. Therefore, it is necessary to estimate the uncertainty in determining the relative biological effectiveness of X-rays associated with uncertainty in the determination of the absorbed dose.

Material and methods: The monochromatic X-ray photon emission is simulated through a standard 25 cm² plastic flask containing 5 ml of the model culture medium (biological tissue with elemental composition С₅H₄₀O₁₈N). The calculation of the absorbed dose in a culture medium is carried out in two ways: 1) the standard method, according to which the ratio of the absorbed dose in the medium and the ionization chamber is equal to the ratio of kerma in the medium and air; 2) determination of the absorbed dose in the medium and in the sensitive volume of the ionization chamber by computer simulation and calculating the ratio of these doses. For each primary photon energies, 10⁸ histories are modeled, which makes it possible to achieve a statistical uncertainty not worse than 0.1 %. The energy step was 1 keV. The spectral distribution of X-ray energy is modeled separately for each set of anode materials, thickness and materials of the primary and secondary filters. The specification of the X-ray beams modeled in this work corresponds to the standards ISO 4037 and IEC 61267. Within the linear-quadratic model, the uncertainty of determining the RBE_max values is directly proportional to the uncertainty in the determination of the dose absorbed by the sample under study.

Results: At energy of more than 60 keV, the ratios for water and biological tissue practically do not differ. At lower energies, up to about 20 keV, the ratio of the coefficients of air and water is slightly less than that of air and biological tissue. The maximum difference is ~ 1 % than usual and the equality of absorbed doses in the ionization chamber and sample is justified. At photon energy of 60 keV for the geometry in question, the uncertainty in determining the dose is about 50 %. For non-monochromatic radiation, the magnitude of the uncertainty is determined by the spectral composition of the radiation, since the curves vary greatly in the energy range 10–100 keV. It is shown that, depending on the spectral composition of X-ray radiation, uncertainty in the determination of the absorbed dose can reach 40–60 %. Such large uncertainty is due to the lack of electronic equilibrium in the radiation geometry used in practice. The spread of RBE values determined from the data of radiobiological experiments carried out by different authors can be determined both by differences in the experimental conditions and by uncertainty in the determination of the absorbed dose. Using Fricke dosimeters instead of ionization chambers in the same geometry allows you to reduce the uncertainty approximately 2 times, up to 10–30 %.

Conclusion: The computer simulation of radiobiological experiments to determine the relative biological effectiveness of X-ray radiation is performed. The geometry of the experiments corresponds to the conditions for the use of standard flasks placed in the side holders. It is shown that the ratio of absorbed doses and kerma in the layers of biological tissue and air differ among themselves with an uncertainty up to 60 %. Depending on the quality of the beam, the true absorbed dose may differ from the one calculated on the assumption of kerma and dose equivalence by 50 %. Uncertainty in determining the RBE in these experiments is of the same order. The results are presented for X-ray beams with negligible fraction of photons with energies less than 10 keV. For beams of a different quality, the uncertainty in determination can significantly increase. For the correct evaluation of RBE, it is necessary to develop a uniform standard for carrying out radiobiological experiments. This standard should regulate both the geometry of the experiments and the conduct of dosimetric measurements.

Key words: relative biological effectiveness, X-rays, absorbed dose, computer simulation, radiobiological experiments

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For citation: Belousov AV, Krusanov GA, Chernyaev AP. Estimation of the X-rays RBE Uncerainty Related to Determination of Absorbed Dose in Radiobiological Experiments. Medical Radiology and Radiation Safety. 2018;63(2):62-9. Russian. DOI: 10.12737/article_5ac6238f8d7653.20448458.

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Medical Radiology and Radiation Safety. 2018. Vol. 63. No. 2. P. 47-54

RADIATION THERAPY

DOI: 10.12737/article_5ac620f416a449.50054749

On Some Methodological Issues of Studying Cytogenetic Effects in Cancer Patients Treated with Neutron Therapy Using U-120 Cyclotron

V.A. Lisin

Tomsk Cancer Research Institute, Tomsk, Russia, e-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.

V.A. Lisin - Dr. Sc. Tech., Prof.

Abstract

Purpose: To study dosimetric characteristics of neutron radiation field, to determine their role in the formation of the total cytogenetic effect in the patient’s body and to assess the cytogenetic dosimetry capabilities in improving the quality of NT.

Material and methods: A therapeutic beam with the average neutron energy of ~6.3 MeV was obtained from the V-120 cyclotron. The radiation field of the beam was investigated with the help of two ionization chambers with different sensitivity to neutrons. Chamber with high and low sensitivities were made of polyethylene and graphite, respectively. To exclude the uncertainty associated with the change in beam intensity in time, a dosimeter monitor operating in the integral mode was used.

Results: The dependence of the monitor factor on the irradiated area was measured. The distributions of the absorbed dose of neutrons and γ-radiation over the depth of the tissue-equivalent medium were found. The contribution of γ-radiation to the neutron dose was increased from ~10 % at the entry to the medium to ~30 % at a depth of 16 cm. Dose distributions of scattered neutron and γ-radiation in the plane of the end face of the forming device were obtained. The contribution of these radiations to the dose received by the patient’s body was estimated. This contribution was shown to be comparable with that from the therapeutic beam. The analysis of the influence of NT on the estimation of the frequency of chromosome aberrations in the blood of patients was carried out.

Conclusion: The frequency of chromosome aberrations in the blood of patients was determined by the whole-body dose, including dose due to scattered radiation. When using equal focal doses, the cytogenetic effect was found to be dependent on the area of the irradiated field and the depth of the tumor in the patient’s body. The differences in the RBE of neutrons and γ-radiation as well as the instability of the therapeutic neutron beam intensity create uncertainties that do not allow for the necessary control over the doses using the cytogenetic dosimetry. Therefore, cytogenetic dosimetry should be combined with an effective instrument dosimetry method.

The use of biodosimetry based on the assessment of the frequency of chromosome aberrations is promising for controlling the average whole-body dose, on which the overall radiation response of the body depends.

Key words: neutron therapy, cytogenetic effect, cyclotron U-120

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For citation: Lisin VА. On Some Methodological Issues of Studying Cytogenetic Effects in Cancer Patients Treated with Neutron Therapy Using U-120 Cyclotron. Medical Radiology and Radiation Safety. 2018;63(2):47-54. Russian. DOI: 10.12737/article_5ac620f416a449.50054749.

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