Multimodality treatment for cerebral arteriovenous malformations: complementary role of proton beam radiotherapy

Out-of-Field Doses Produced by a Proton Scanning Beam Inside Pediatric Anthropomorphic Phantoms and Their Comparison With Different Photon Modalities

Since 2010, EURADOS Working Group 9 (Radiation Dosimetry in Radiotherapy) has been involved in the investigation of secondary and scattered radiation doses in X-ray and proton therapy, especially in the case of pediatric patients. The main goal of this paper is to analyze and compare out-of-field neutron and non-neutron organ doses inside 5- and 10-year-old pediatric anthropomorphic phantoms for the treatment of a 5-cm-diameter brain tumor. Proton irradiations were carried out at the Cyclotron Centre Bronowice in IFJ PAN Krakow Poland using a pencil beam scanning technique (PBS) at a gantry with a dedicated scanning nozzle (IBA Proton Therapy System, Proteus 235). Thermoluminescent and radiophotoluminescent dosimeters were used for non-neutron dose measurements while secondary neutrons were measured with track-etched detectors. Out-of-field doses measured using intensity-modulated proton therapy (IMPT) were compared with previous measurements performed within a WG9 for three different photon radiotherapy techniques: 1) intensity-modulated radiation therapy (IMRT), 2) three-dimensional conformal radiation therapy (3D CDRT) performed on a Varian Clinac 2300 linear accelerator (LINAC) in the Centre of Oncology, Krakow, Poland, and 3) Gamma Knife surgery performed on the Leksell Gamma Knife (GK) at the University Hospital Centre Zagreb, Croatia. Phantoms and detectors used in experiments as well as the target location were the same for both photon and proton modalities. The total organ dose equivalent expressed as the sum of neutron and non-neutron components in IMPT was found to be significantly lower (two to three orders of magnitude) in comparison with the different photon radiotherapy techniques for the same delivered tumor dose. For IMPT, neutron doses are lower than non-neutron doses close to the target but become larger than non-neutron doses further away from the target. Results of WG9 studies have provided out-of-field dose levels required for an extensive set of radiotherapy techniques, including proton therapy, and involving a complete description of organ doses of pediatric patients. Such studies are needed for validating mathematical models and Monte Carlo simulation tools for out-of-field dosimetry which is essential for dedicated epidemiological studies which evaluate the risk of second cancers and other late effects for pediatric patients treated with radiotherapy.

Radiosurgery as a microsurgical adjunct: outcomes after microsurgical resection of intracranial arteriovenous malformations previously treated with stereotactic radiosurgery

OBJECTIVE

Microsurgical resection of arteriovenous malformations (AVMs) can be aided by staged treatment consisting of stereotactic radiosurgery followed by resection in a delayed fashion. This approach is particularly useful for high Spetzler-Martin (SM) grade lesions because radiosurgery can reduce flow through the AVM, downgrade the SM rating, and induce histopathological changes that additively render the AVM more manageable for resection. The authors present their 28-year experience in managing AVMs with adjunctive radiosurgery followed by resection.

METHODS

The authors retrospectively reviewed records of patients treated for cerebral AVMs at their institution between January 1990 and August 2019. All patients who underwent stereotactic radiosurgery (with or without embolization), followed by resection, were included in the study. Of 1245 patients, 95 met the eligibility criteria. Univariate and multivariate regression analyses were performed to assess relationships between key variables and clinical outcomes.

RESULTS

The majority of lesions treated (53.9%) were high grade (SM grade IV-V), 31.5% were intermediate (SM grade III), and 16.6% were low grade (SM grade I-II). Hemorrhage was the initial presenting sign in half of all patients (49.5%). Complete resection was achieved among 84% of patients, whereas 16% had partial resection, the majority of whom received additional radiosurgery. Modified Rankin Scale (mRS) scores of 0-2 were achieved in 79.8% of patients, and 20.2% had poor (mRS scores 3-6) outcomes. Improved (44.8%) or stable (19%) mRS scores were observed among 63.8% of patients, whereas 36.2% had a decline in mRS scores. This includes 22 patients (23.4%) with AVM hemorrhage and 6 deaths (6.7%) outside the perioperative period but prior to AVM obliteration.

CONCLUSIONS

Stereotactic radiosurgery is a useful adjunct in the presurgical management of cerebral AVMs. Multimodal therapy allowed for high rates of AVM obliteration and acceptable morbidity rates, despite the predominance of high-grade lesions in this series of patients.