Abstract
Simple SummaryCell killing and tumor response in cancer patients depends not only on the absorbed radiation dose but also on the dose rate and delivery time. In this study, a biodosimetry assay based on the frequency of dicentrics chromosomes scored in peripheral blood lymphocytes from prostate cancer patients and PC3 human prostate cancer cell line was used to investigate the radiobiological impact of the relative prolonged dose delivery time and/or decreased dose rate met in advanced modulated radiotherapy techniques (VMAT and IMRT) compared to conventional non-modulated (3D-CRT) in prostate patient plan irradiations. The results showed a small but statistically significant decrease in the number of dicentrics following radiation with the modulated techniques, suggesting a corresponding decrease on the radiation dose efficiency. The biodosimetry assay could be used as an alternative to the laborious conventional clonogenic assay, while both lymphocytes and cancer cell line could effectively be used for estimation of the biological absorbed dose.While rapid technological advances in radiotherapy techniques have led to a more precise delivery of radiation dose and to a decreased risk of side effects, there is still a need to evaluate the efficacy of the new techniques estimating the biological dose and to investigate the radiobiological impact of the protracted radiotherapy treatment duration. The aim of this study is to compare, at a cytogenetic level, advanced radiotherapy techniques VMAT and IMRT with the conventional 3D-CRT, using biological dosimetry. A dicentric biodosimetry assay based on the frequency of dicentrics chromosomes scored in peripheral blood lymphocytes from prostate cancer patients and PC3 human prostate cancer cell line was used. For each patient blood sample and each subpopulation of the cultured cell line, three different irradiations were performed using the 3D-CRT, IMRT, and VMAT technique. The absorbed dose was estimated with the biodosimetry method based on the induced dicentric chromosomes. The results showed a statistically significant underestimation of the biological absorbed dose of ~6% for the IMRT and VMAT compared to 3D-CRT irradiations for peripheral blood lymphocytes, whereas IMRT and VMAT results were comparable without a statistically significant difference, although slightly lower values were observed for VMAT compared to IMRT irradiation. Similar results were obtained using the PC3 cell line. The observed biological dose underestimation could be associated with the relative decreased dose rate and increase irradiation time met in modulated techniques compared to the conventional 3D-CRT irradiations.
Highlights
New technologies in radiotherapy techniques and treatment planning over the past few years had a great impact in the clinical outcome of cancer patients [1,2]
The maximum difference of 1.19% was observed for volumetric-modulated arc therapy (VMAT) technique, this discrepancy was marginally greater than the Monte Carlo statistical uncertainty of 1%; it was not deemed important
The results showed a decrease in the number of dicentrics following radiation with the modulated intensity-modulated radiation therapy (IMRT) and VMAT techniques compared to 3D conformal radiation therapy (3D-CRT) irradiation, for the majority of prostate cancer patient blood samples leading to a statistically significant decrease of ~6% in the median biological dose absorbed for the same fractional dose of 2Gy
Summary
New technologies in radiotherapy techniques and treatment planning over the past few years had a great impact in the clinical outcome of cancer patients [1,2]. Radiation therapy (RT) is often used in conjunction with other therapies such as chemotherapy or resection as an integral part of both curative and palliative cancer treatments [1,3] Modern radiotherapy techniques such as intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT) have improved local tumor control with accuracy in dose delivery of the radiation, decreasing the dose of radiation to critical tissues near the tumor [1,2,3,4]. Both techniques have the potential to provide a safer dose escalation for a target [5,6] by increasing the radiation delivery time. Both the rate of monitor units per minute (MU rate) and collimation are varied over the course of a fraction, leading to different dose rates in every voxel of the calculation volume at any time during radiotherapy [8]
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