Development of adaptive stereotactic radiotherapy method in treatment of primary malignant glial tumors in the brain

Abstract

At present, there are some scattered evidence data pertaining to the use of an adaptive technique of radiotherapy in treatment of malignant glial tumors of the brain. Our evidence data obtained in MRI in the course of treatment show that the initial treatment plan may become irrelevant due to some changes observed in the tumor configuration. In its turn, it bears witness to the topicality of developing and introducing adaptive methods and techniques in the brain tumor treatment, which are capable to increase efficacy and tolerability in patients with primary malignant tumors of the brain. Aim. Our aim has been to develop an adaptive stereotactic method of radiotherapy in treatment of primary malignant brain tumors, which shall be capable to increase efficacy and tolerability of radiation therapy as well as reduce radiation dose to normal structures in the brain. Materials and methods. Our method has been elaborated with recruiting a group of 10 patients diagnosed with primary glioblastoma G IV, which have received specialized treatment at the National Medical Research Centre for Oncology at the Ministry of Health, the Russian Federation, in the period 2021-2022. The average age of the above patients is 43,4 years. All patients have undergone microsurgery covering the total resection of the tumor (3 patients) and subtotal removal of the malignant tumor (7 patients). The average time interval between the surgery and radiotherapy is 32,5 days. Before treatment, an intravenous contrast enhancement MRI of the brain with an axial pitch of 1 mm has been conducted employing the contrast T1, contrast-free T1 and T2 FLAIR modes. Planning of radiotherapy for this sort of patients has been carried out employing BrainLab Elements и Varian Medical Systems Eclipse. The CTV was defined as a 2,0 cm margin around GTV with an anatomical correction. The CTV-to-PTV margin was 0,1 cm. Doses have been administered as follows: a single dose of 2 Gy up to a total dose of 60 Gy in 30 fractions. The brain has been MRI-scanned in all patients with the use of intravenously introduced contrast agents with an axial pitch of 1 mm employing enhanced contrast/contrast-free T1 sequences and T2 FLAIR to redefine the radiotherapy targets (GTV, CTV, PTV). At fraction 30 we have completed MRI in order to estimate the treatment outcome. In the average, the radiotherapy course has taken 42-45 days, holidays included. For the purpose of the radiation therapy, used have been the Novalis Tx Varian Tx linear accelerator of kinetic energy of the beam of 6 MeV. Results We have developed our own adaptive stereotactic method of radiotherapy to treat the primary malignant glial tumors in the brain, which is capable of tracing the configuration of the post-surgery cavity, the residual tumor and the brain structures in the course of radiotherapy and adapting the therapy plan thereto that makes possible to reduce tissue volumes exposed to radiation due to a decrease in the tumoral and peritumoral volumes of the tumor and post-operative cavity. Conclusion. Our analysis has shown that in the course of radiotherapy some anatomical changes in the tumor configuration are found. An adaptive approach applied to radiation therapy allows monitoring the above changing volumes and correcting the treatment plan.