On dosimetric characteristics of detectors for relative dosimetry in small fields: a multicenter experimental study.

Objective. In this multicentric collaborative study, we aimed to verify whether the selected radiation detectors satisfy the requirements of TRS-483 Code of Practice for relative small field dosimetry in megavoltage photon beams used in radiotherapy, by investigating four dosimetric characteristics. Furthermore, we intended to analyze and complement the recommendations given in TRS-483.Approach. Short-term stability, dose linearity, dose-rate dependence, and leakage were determined for 17 models of detectors considered suitable for small field dosimetry. Altogether, 47 detectors were used in this study across ten institutions. Photon beams with 6 and 10 MV, with and without flattening filters, generated by Elekta Versa HDTMor Varian TrueBeamTMlinear accelerators, were used.Main results. The tolerance level of 0.1% for stability was fulfilled by 70% of the data points. For the determination of dose linearity, two methods were considered. Results from the use of a stricter method show that the guideline of 0.1% for dose linearity is not attainable for most of the detectors used in the study. Following the second approach (squared Pearson's correlation coefficientr2), it was found that 100% of the data fulfill the criteriar2> 0.999 (0.1% guideline for tolerance). Less than 50% of all data points satisfied the published tolerance of 0.1% for dose-rate dependence. Almost all data points (98.2%) satisfied the 0.1% criterion for leakage.Significance. For short-term stability (repeatability), it was found that the 0.1% guideline could not be met. Therefore, a less rigorous criterion of 0.25% is proposed. For dose linearity, our recommendation is to adopt a simple and clear methodology and to define an achievable tolerance based on the experimental data. For dose-rate dependence, a realistic criterion of 1% is proposed instead of the present 0.1%. Agreement was found with published guidelines for background signal (leakage).

Reparative properties of human glioblastoma cells after single exposure to a wide range of X-ray doses.

Radiation therapy induces double-stranded DNA breaks in tumor cells, which leads to their death. A fraction of glioblastoma cells repair such breaks and reinitiate tumor growth. It was necessary to identify the relationship between high radiation doses and the proliferative activity of glioblastoma cells, and to evaluate the contribution of DNA repair pathways, homologous recombination (HR), and nonhomologous end joining (NHEJ) to tumor-cell recovery. We demonstrated that the GO1 culture derived from glioblastoma cells from Patient G, who had previously been irradiated, proved to be less sensitive to radiation than the Sus\fP2 glioblastoma culture was from Patient S, who had not been exposed to radiation before. GO1 cell proliferation decreased with radiation dose, and MTT decreased to 35% after a single exposure to 125 Gγ. The proliferative potential of glioblastoma culture Sus\fP2 decreased to 35% after exposure to 5 Gγ. At low radiation doses, cell proliferation and the expression of RAD51 were decreased; at high doses, cell proliferation was correlated with Ku70 protein expression. Therefore, HR and NHEJ are involved in DNA break repair after exposure to different radiation doses. Low doses induce HR, while higher doses induce the faster but less accurate NHEJ pathway of double-stranded DNA break repair.

Preoperative Stereotactic Radiosurgery of Brain Metastases: Preliminary Results.

INTRODUCTION:  Preoperative stereotactic radiosurgery (pre-SRS) is a recent advancement in the strategy for brain metastasis (BM) management, and available data demonstrate the advantages of pre-SRS before postoperative radiation treatment, including lower rates of local toxicity, leptomeningeal progression, and a high percentage of local control. The authors presented the results of pre-SRS in patients with BM. MATERIALS AND METHODS: Nineteen patients with BM (11 female and eight male) have been treated at N.N. Burdenko Medical Research Center for Neurosurgery (Moscow, Russia) and Gamma-Knife Center (Moscow, Russia) using pre-SRS. A total of 22 symptomatic metastatic lesions were preoperatively irradiated in the series. Eight patients had multiple BM (number of metastases ranged between two and seven). The median target volume for combined treatment was 14.131 cc (volumes varied between 2.995 and 57.098 cc; mean - 19.986 cc). The median of the mean target dose was 18 Gy, ranging between 12.58 and 24.36 Gy.  Results: All patients tolerated pre-SRS well, without any neurological deterioration, and surgical treatment was performed as scheduled. The median follow-up period was 6.3 months (ranging between five weeks and 22.9 months). In 17 out of 19 patients, follow-up magnetic resonance (MR) images obtained two or three months after the combined treatment demonstrated the postoperative cavity without any signs of postradiation alterations in the perifocal tissues. In two observations, peritumoral edema was present. Local recurrences were found in two cases, 5.5 and 17.4 months after treatment. Radionecrosis was present in one observation after 4.6 months of follow-up. Two patients died of disease progression and are presented as illustrative cases. CONCLUSION: The combined treatment of secondary brain tumors has proved to be the best treatment option. Preoperative stereotactic radiosurgery may decrease radiation-induced toxicity and rates of local tumor progression. The potential hazards of pre-SRS associated with the postoperative healing of irradiated soft tissues of the head were not confirmed in our study. The decision of pre-SRS should be made by the tumor board, including specialists in neurosurgery, neuro-oncology, and radiation oncology, if the diagnosis of BM is based on oncological history and visualization data.

Intraosseous Metastasizing of Pineoblastoma into the Anterior Skull Base, Calvarial Bones, and Vertebrae.

Pineoblastoma is a rare malignant tumor of the central nervous system (CNS), which arises from the parenchyma of the pineal gland. It is characterized by aggressive clinical behavior and frequent metastases along the craniospinal axis. Extraneural metastases may occur due to surgical seeding of tumor cells beyond the dura and/or hematogenous spread, ventriculoperitoneal shunting, or through Batson's plexus. To our knowledge, only six documented cases of intraosseous metastases of pineoblastoma are described in the literature. A 23-year-old female patient presented with clinical and radiological symptoms of a pineal tumor causing secondary hydrocephalus. After initial surgical treatment, chemotherapy, and local radiotherapy with craniospinal irradiation, she developed multiple metastases affecting the anterior skull base, intracranial meninges, frontal bone, and finally, the entire vertebral column. The patient received surgical treatment for the anterior skull base metastasis, repeated irradiation of the neuraxis, radiosurgical and radiotherapeutic procedures, and chemotherapy. The patient survived 57 months after the primary disease manifestation and died of multiple metastases. This presented case is the first known description of metastasis of pineoblastoma in the anterior cranial base. Multiple intracranial metastases were suppressed using CyberKnife radiation treatment and chemotherapy until massive involvement of spinal column occurred. Interestingly, no signs of brain radiation necrosis after repeated radiation treatments were observed, and the patient developed only moderate neurocognitive decline.

Successful CyberKnife Irradiation of 1000 cc Hemicranial Meningioma: 6-year Follow-up.

Meningiomas are common benign tumors with accepted treatment approaches and usually don't challenge healthcare specialists. We present a case of a huge unresectable hemicranial meningioma, which was successfully treated with hypofractionated irradiation. A male patient, sixty-two years of age, suffered for over 12 years from headaches, facial deformity, right eye displacement, right eye movement restriction, right-sided ptosis, and facial hypoesthesia. MRI and CT studies revealed an extended hemicranial meningioma. Prior to irradiation, the patient underwent four operations. Eventually, the tumor was irradiated with the CyberKnife in August 2009. Tumor volume composed 1085 cc. The mean dose of 35.3 Gy was delivered in 7 fractions (31.5 Gy at 72% isodose line comprising 95% of tumor volume). The patient was followed during six years and experienced only mild (Grade 1-2 CTCAE) acute skin and mucosa reactions. During the follow-up period, we observed target volume shrinkage for 17% (for 26% after excluding hyperostosis) and regression of intracranial hypertension signs. Due to the extreme volume and complex shape of the tumor, spreading along the surface of the hemisphere as well as an optic nerve involvement, the case presented would not be generally considered suitable for irradiation, especially for hypofractionation. We regard this clinical situation not as a treatment recommendation, but as a demonstration of the underestimated possibilities of hypofractionation regimen and CyberKnife system, both of which are limited with our habit of conventional treatments.