Abstract
BackgroundStereotactic-Radio-Surgery (SRS) using Conformal-Arc-Therapy (CAT) is a well established irradiation technique for treatment of intracranial targets. Although small safety margins are required because of very high accuracy of patient positioning and exact online localisation, there are still disadvantages like long treatment time, high number of monitor units (MU) and covering of noncircular targets. This planning study analysed whether Rapid Arc (RA) with stereotactic localisation for single-fraction SRS can solve these problems.MethodsTen consecutive patients were treated with Linac-based SRS. Eight patients had one or more brain metastases. The other patients presented a symptomatic vestibularis schwannoma and an atypic meningeoma. For all patients, two plans (CAT/RA) were calculated and analysed.ResultsConformity was higher for RA with additional larger low-dose areas. Furthermore, RA reduced the number of MU and the treatment time for all patients. Dose to organs at risk were equal or slightly higher using RA in comparison to CAT.ConclusionsRA provides a new alternative for single-fraction SRS irradiation combining advantages of short treatment time with lower number of MU and better conformity in addition to accuracy of stereotactic localisation in selected cases with uncomplicated clinical realization.
Highlights
Stereotactic-Radio-Surgery (SRS) using Conformal-Arc-Therapy (CAT) is a well established irradiation technique for treatment of intracranial targets
Conflicts existed in some plans resulting from the position of organs at risk (OAR)’s relative to the target volume, gross tumour volume (GTV) coverage was 100% in both different treatment techniques for all patients
Conformity indices were clearly better for Rapid Arc (RA) in all analysed GTV localisation and treatment volumes with a median of 0.56 compared to 0.37 for CAT
Summary
Stereotactic-Radio-Surgery (SRS) using Conformal-Arc-Therapy (CAT) is a well established irradiation technique for treatment of intracranial targets. Small safety margins are required because of very high accuracy of patient positioning and exact online localisation, there are still disadvantages like long treatment time, high number of monitor units (MU) and covering of noncircular targets. This planning study analysed whether Rapid Arc (RA) with stereotactic localisation for single-fraction SRS can solve these problems. Three dynamic parameters can be continuously varied to create IMRT dose distributions: The speed of rotation, beam shaping aperture, and delivery dose rate [11] The variation of these three dynamic parameters is used to cover the planning target volume with clinical acceptable dose and to minimise the dose to organs at risk (OAR) and normal tissue. The volume of low dose areas of the normal tissue is higher in RA delivery, and should be considered for selection of application technique, especially for young patients
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