Influence of SBRT fractionation on TCP and NTCP estimations for prostate cancer.

INTRODUCTION: Stereotactic body radiation therapy is widely used for the hypofractionated treatment of prostate cancer. The range of total doses used in different clinical trials varies from 33.5 to 50 Gy delivered in 4 or 5 fractions. The choice of an optimal total dose value and fractionation regimen for a particular patient can be carried out using the integral radiobiological criteria, namely tumour control probability (TCP) and normal tissue complication probability (NTCP). In this study, we have investigated the dependence of simulated TCP/NTCP values on total dose in the range of 30-40 Gy delivered in 4 or 5 fractions for patients with low-risk prostate cancer in order to find the optimal total dose value and fractionation regimen. METHODS: The anatomic data (DICOM CT images) of 12 patients with low-risk prostate cancer, who were treated at Tomsk Regional Oncology Centre, were used for the calculation. Dosimetric treatment plans for all patients were simulated using VMAT with 2 arcs in the Monaco treatment planning system v5.10 (Elekta Instrument AB, Stockholm) with a total dose equal to 36.25 Gy. The dosimetric plans were rescaled in the dose range of 30-40 Gy. The TCP and NTCP values were calculated based on differential dose volume histograms using the Niemierko model for both TCP and NTCP, and the Källman-s model for NTCP calculations. The TCP calculation was carried out using the uncertainty of well-known tumour radiobiological parameters values, including α/ß value. NTCP was calculated for an anterior rectal wall, which was the most irradiated organ at risk due to its close contact with the planning target volume. RESULTS: The TCP and NTCP calculations for VMAT of the prostate cancer have shown that the optimal total dose ranges were equal to 32-34 Gy delivered in 4 fractions or 35-38 Gy delivered in 5 fractions. At doses lower than the optimal ones, the TCP values were lower than 95%, while TCP uncertainties were significant (as low as 80%). This fact might bring unexpectedly poor treatment results. At doses higher than optimal ones, the probability of toxicity to the anterior rectal wall became significant. CONCLUSION: The optimization of radiation therapy regimen based on TCP/NTCP criteria could help to determine an optimal total dose and a number of fractions for a particular patient depending on patient-specific anatomic features and planned dose distribution.

Antitumor efficacy of extracellular complexes with gadolinium in Binary Radiotherapy.

In this report the efficacy of extracellular pharmaceutical Gd-DTPA in Binary Radiotherapy was studied. The study was carried out in mice bearing transplantable adenocarcinoma Ca755 using X-ray based contrast enhanced radiotherapy as a practical implementation of Binary Radiotherapy. It was shown that intravenous administration of 0.3 ml of 0.5 M water solution of Gd-DTPA followed by X-irradiation at a dose of 10 Gy provides T/C%=10±3% and leads to complete tumor regression in 25% of mice.

[Increase of X-ray radiotherapy antineoplastic efficacy by use of a gadolinium containing pharmaceutical].

The influence of the gadolinium-containing drug Dipentast (0.5 M water solution of sodium gadopentetate) on the antineoplastic efficacy of X-ray radiotherapy has been studied. Dipentast possesses neither intrinsic antitumor effect, nor tumor-seeking capability. Mice C57Bl/6 with transplanted adenocarcinoma Ca755 were used in the study. The mice were irradiated with an X-ray machine with an anode voltage of 200 kV. The absorbed dose in the tumor after irradiation was 10 Gy for both experimental and control groups. The mice in the experimental group were treated with a single intraperitoneal injection of 0.3 ml of Dipentast. The observation of the tumour growth rate has shown that intraperitoneal administration of Dipentast prior to X-ray irradiation results in a significant tumour growth delay (12 ± 1 days for the experimental group versus 2 ± 1 in the control group), increasing the median life span from 36 ± 1 days in the control group to 43 ± 1 days in the experimental group, and leads to complete disappearance of the tumour in 25 ± 1% of the animals in the experimental group, while in the control group, no tumour regression was observed.

Comparison of BNCT and GdNCT efficacy in treatment of canine cancer.

In this study efficacy of antineoplastic action of gadolinium NCT and boron NCT in cases of canine melanoma and osteosarcoma was compared. Canine spontaneous tumors, such as melanoma and osteosarcoma, have clinical common features with human malignancies, so these tumors in dogs can be considered as clinical model of human melanoma and osteosarcoma. The study has been carried out on 33 dogs with oral cavity melanoma and 9 dogs with osteosarcoma. Dogs with spontaneous melanoma of oral cavity and osteosarcoma of extremities were selected by the results of clinical examination. Irradiation was carried out at the NCT facility of the IRT MEPhI reactor. Neutron irradiation without boron or gadolinium was chosen as a control method to evaluate the efficacy of NCT.