Introduction. Brachytherapy as a boost in breast cancer, after conservative surgery and whole breast external beam radiotherapy is a well known and accepted type of treatment. Traditionally in breast brachytherapy the dose used to be prescribed over the basal points, following the paris system in a theoretical dosimetry. Nowadays, 3D planification systems have been incorporated, so the PTV can be delineated on the CT-scan . Dosimetric and dose distribution differences can be found between the

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... o types of planification. Purpose. To evaluate the different dose distributions between the prescription over the basal points and the prescription over the PTV points. Materials and methods. We analyze 6 patients 3D brachytherapy dosimetries, and in every case we compare the dose, prescribing over the basal points and prescribing over the PTV points, determining in every type of planification the V150, V200 and D90. Results. When the dose is prescribed over the PTV points, D90 is higher tan when the dose is prescribed over the basal points in every patient. V150 and V200 are also higher when the dose is prescribed over the PTV points, but in any case the V200 exceeds 10 cm 3 , and any case V150 exceeds 15 cm 3 . Conclusions. When a 3D CT-scan planification is done, prescribing over the PTV obtains a better covering of the target and does not exceed the limits of the high dose RTOG recommendations. http://dx.