Medical Radiology and Radiation Safety. 2021. Vol. 66. № 3. P. 68–75

Е.S. Sukhikh^1,2, L.G. Sukhikh², A.V. Vertinsky^1,2, P.V. Izhevsky³, I.N. Sheino³,  V.V. Vertoukhova²

Analysis of the Physical and Radiobiological Equivalence of the Calculated
and Measured Dose Distributions for Prostate Stereotactic Radiotherapy

¹Tomsk Regional Oncology Center, Tomsk, Russia

²National Research Tomsk Polytechnic University, Tomsk, Russia

³AI Burnasyan Federal Medical Biophysical Center Moscow, Russia

Contact person: Andrei Vladimirovich Vertinskii: This email address is being protected from spambots. You need JavaScript enabled to view it.

Abstract

Purpose: Carrying out the analysis of the physical and radiobiological equivalence of dose distributions obtained during the planning of hypofractionated stereotactic radiation therapy of the prostate cancer and verification using a three-dimensional cylindrical dosimeter.

Material and Methods: Based on the anatomical data of twelve patients diagnosed with prostate carcinoma, stage T2N0M0 with low risk, plans were developed for stereotactic radiation therapy with volumetric modulates arc therapy (VMAT). The dose per fraction was 7,25 Gy for 5 fractions (total dose 36,25 Gy) with a normal photon energy of 10 MV. The developed plans were verified using a three-dimensional cylindrical ArcCHECK phantom. During the verification process, the three-dimensional dose distribution in the phantom was measured, based on which the values of the three-dimensional gamma index and the dose–volume histogram within each contoured anatomical structures were calculated with 3DVH software.

The gamma index value γ (3 %, 2 mm, GN) at a threshold equal to 20 % of the dose maximum of the plan and the percentage of coincidence of points at least 95 % was chosen as a criterion of physical convergence of the calculated and measured dose distribution according to the recommendations of AAPM TG-218. To analyze the radiobiological equivalence of the calculated and measured dose distribution, the local control probability (TCP) and normal tissue complication probability (NTCP) criteria were used based on the calculated and measured dose–volume histograms. Contours of the target (PTV) and the anterior wall of the rectum were used for the analysis. The approach based on the concept of equivalent uniform dose (EUD) by A. Niemierko was used to calculate the values of TCP/NTCP criteria.

Results: The results of physical convergence of plans for all patients on the contour of the whole body were higher than 95 % for the criteria γ (3 %, 2 mm, GN). The convergence along the PTV contour is in the range (75.5–95.2)%. The TCP and NTCP values obtained from the measured dose-volume histograms were higher than the planned values for all patients. It was found that the accelerator delivered a slightly higher dose to the PTV and the anterior wall of the rectum than originally planned.

Conclusion: The capabilities of modern dosimetric equipment allow us move to the verification of treatment plans based on the analysis of TCP / NTCP radiobiological equivalence, taking into account the individual characteristics of the patient and the capabilities of radiation therapy equipment. 

Key words: 3D gamma analysis, dose-volume histogram, tumor control probability, normal tissue complication probability

For citation: Sukhikh ЕS, Sukhikh LG, Vertinsky AV, Izhevsky PV, Sheino IN, Vertoukhova VV. Analysis of the Physical and Radiobiological Equivalence of the Calculated and Measured Dose Distributions for Prostate Stereotactic Radiotherapy. Medical Radiology and Radiation Safety. 2021;66(3):68-75.

DOI: 10.12737/1024-6177-2021-66-3-68-75

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Conflict of interest. The authors declare no conflict of interest.

Financing. The study had no sponsorship.

Contribution. Article was prepared with equal participation of the authors.

Article received: 23.12.2020. 

Accepted for publication: 20.01.2021.