Clinical realization of sector beam intensity modulation for Gamma Knife radiosurgery: a pilot treatment planning study

Radiotherapy of non-tumoral refractory neurological pathologies

Intracranial radiotherapy has been improved, primarily because of the development of stereotactic approaches. While intracranial stereotactic body radiotherapy is mainly indicated for treatment of benign or malignant tumors, this procedure is also effective in the management of other neurological pathologies; it is delivered using GammaKnife® and linear accelerators. Thus, brain arteriovenous malformations in patients who are likely to experience permanent neurological sequelae can be managed by single session intracranial stereotactic body radiotherapy, or radiosurgery, in specific situations, with an advantageous benefit/risk ratio. Radiosurgery can be recommended for patients with disabling symptoms, which are poorly controlled by medication, such as trigeminal neuralgia, and tremors, whether they are essential or secondary to Parkinson's disease. This literature review aims at defining the place of intracranial stereotactic body radiotherapy in the management of patients suffering from non-tumoral refractory neurological pathologies. It is clear that the multidisciplinary collaboration of experienced teams from Neurosurgery, Neurology, Neuroradiology, Radiation Oncology and Medical Physics is needed for the procedures using high precision radiotherapy techniques, which deliver high doses to locations near functional brain areas.

Dosimetric characterization of hypofractionated Gamma Knife radiosurgery of large or complex brain tumors versus linear accelerator-based treatments

OBJECTIVE Noninvasive Gamma Knife (GK) platforms, such as the relocatable frame and on-board imaging, have enabled hypofractionated GK radiosurgery of large or complex brain lesions. This study aimed to characterize the dosimetric quality of such treatments against linear accelerator-based delivery systems that include the CyberKnife (CK) and volumetric modulated arc therapy (VMAT). METHODS Ten patients treated with VMAT at the authors' institution for large brain tumors (> 3 cm in maximum diameter) were selected for the study. The median prescription dose was 25 Gy (range 20-30 Gy) in 5 fractions. The median planning target volume (PTV) was 9.57 cm³ (range 1.94-24.81 cm³). Treatment planning was performed using Eclipse External Beam Planning V11 for VMAT on the Varian TrueBeam system, Multiplan V4.5 for the CyberKnife VSI System, and Leksell GammaPlan V10.2 for the Gamma Knife Perfexion system. The percentage of the PTV receiving at least the prescription dose was normalized to be identical across all platforms for individual cases. The prescription isodose value for the PTV, conformity index, Paddick gradient index, mean and maximum doses for organs at risk, and normal brain dose at variable isodose volumes ranging from the 5-Gy isodose volume (V5) to the 15-Gy isodose volume (V15) were compared for all of the cases. RESULTS The mean Paddick gradient index was 2.6 ± 0.2, 3.2 ± 0.5, and 4.3 ± 1.0 for GK, CK, and VMAT, respectively (p < 0.002). The mean V15 was 7.5 ± 3.7 cm³ (range 1.53-13.29 cm³), 9.8 ± 5.5 cm³ (range 2.07-18.45 cm³), and 16.1 ± 10.6 cm³ (range 3.58-36.53 cm³) for GK, CK, and VMAT, respectively (p ≤ 0.03, paired 2-tailed t-tests). However, the average conformity index was 1.18, 1.12, and 1.21 for GK, CK, and VMAT, respectively (p > 0.06). The average prescription isodose values were 52% (range 47%-69%), 60% (range 46%-68%), and 88% (range 70%-94%) for GK, CK, and VMAT, respectively, thus producing significant variations in dose hot spots among the 3 platforms. Furthermore, the mean V5 values for GK and CK were similar (p > 0.79) at 71.9 ± 36.2 cm³ and 73.3 ± 31.8 cm³, respectively, both of which were statistically lower (p < 0.01) than the mean V5 value of 124.6 ± 67.1 cm³ for VMAT. CONCLUSIONS Significantly better near-target normal brain sparing was noted for hypofractionated GK radiosurgery versus linear accelerator-based treatments. Such a result supports the use of a large number of isocenters or confocal beams for the benefit of normal tissue sparing in hypofractionated brain radiosurgery.

3-D treatment planning system-Leksell Gamma Knife treatment planning system

Leksell Gamma Plan (LGP), the treatment planning system for the Leksell Gamma Knife (LGK) stereotactic radiosurgery, has evolved from the primitive KULA system to the present-day powerful version of image-guided stereotactic radiosurgery. Through many years of development, LGP has improved on its dose calculation accuracy, speed, and user interface. This allows more accurate irradiation of the target while sparing the nearby normal tissues and critical structures better.

Comparison of the efficacy between concurrent chemoradiotherapy with or without adjuvant chemotherapy and intensity-modulated radiotherapy alone for stage II nasopharyngeal carcinoma

OBJECTIVE

This study aimed to explore whether concurrent chemoradiotherapy (CCRT) with or without Adjuvant Chemotherapy (AC) could improved the survival in stage II nasopharyngeal carcinoma (NPC).

METHODS

Patients with stage II NPC treated with CCRT (n=80) or CCRT+AC (n=40) or IMRT alone (n=42) between January 2007 and September 2014 were retrospectively analyzed. The three patient groups were matched based on prognostic factors. All patients were treated with IMRT. The endpoints were overall survival (OS), distant metastasis-free survival (DMFS), locoregional relapse-free survival (LRRFS), and failure-free survival (FFS). The treatment-related acute toxicity reactions between the three groups were compared also.

RESULTS

The three groups indicated similar outcomes: survival of the CCRT group, CCRT+AC group and RT alone group were (93.9%, 95.0%, 95.2%, P=0.937) for OS, (96.8%, 94.9%, 93.0%, P=0.756) for LRRFS, (91.1%, 97.5%, 100%, P=0.185) for DMFS and (84.9%, 92.5%, 93.0%, P=0.597) for FFS. Both the univariate and multivariate analysis indicated that older age predicted lower LRRFS and FFS. The CCRT and CCRT+AC groups showed more acute toxicity reactions, especially in bone marrow suppression, Liver dysfunction, gastrointestinal reactions (nausea/vomiting) and weight loss.

CONCLUSION

CCRT with/without AC could not improve the survival conditions of patients with stage II NPC, but remarkably increased treatment-associated acute toxic reactions when compared with IMRT alone.