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Planning Target Volume Margin in Prostate Sterotactic Radiation Therapy Treatment (SBRT). Experience of Centro Medico Dean Funes

E Garrigo1*, S Sabadias2 , C Descamps3 , D Franco4 , E Aon5 , E falco6 , (1) Centro Medico Dean Funes, Cordoba, X, (2) Instituto Balseiro ,Bariloche, ,(3)Centro Medico Dean Funes ,Cordoba, ,(4)Centro Medico Dean Funes ,Cordoba, ,(5)Centro Medico Dean Funes ,Cordoba, ,(6)Centro Medico Dean Funes ,Cordoba,


(Sunday, 7/14/2019)  

Room: ePoster Forums

Purpose: SBRT is a technique that uses ablative doses; a high degree of confidence in the accuracy of the dose delivered to the target and in the protection of surrounding normal tissues is the key to succesfull treatment. The aim of this work was to use the three-dimensional imaging system incorporated in the linear accelerator, in order to evaluate systematic and random errors in the treatment process.

Methods: Ten prostate cancer patients were treated using SBRT with a dose of 36.25 Gy in 5 fractions with RapidArcTM. Before and immediately after each treatment, a cone beam computed tomography (CBCT) guidance was performed. Prostate matching between CBCT and planning CT was performed by a Therapist and accepted by a Physician. The shift of both CBCT (before and after treatment) in the three dimensions was recorded. To respect the ALARA principle and avoid a third CBCT among patients, the system residual shifts were evaluated using a CIRS phantom.

Results: The Van Herk formalism with a confidence level of 99% and a level dose of 99% was used. The systematic error and the random error were calculated for each patient over all fractions and for the group respectively. The PTV margin found was 2.5mm (vertical), 2.1mm (longitudinal) and 1.9mm (lateral).

Conclusion: The incorporation of an isotropic margin of 3mm in the case of prostate cancer with SBRT is sufficient to overcome the geometric uncertainties associated with our system;it is also necessary to evaluate the uncertainties in the delineation volume process.


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