610 poster ACCELERATED PARTIAL BREAST IRRADIATION: A DOSIMETRIC COMPARISON OF PERI- AND POSTOPERATIVE IMPLANTS

the lumpectomy cavity is comprised at least 0.5 cm in radial direction by the balloon pressure. Although breast tissue is essentially uncompressible, i.e. density is nearby constant, it can be stretched. Let us consider CTV as a spherical crown of 1.5 cm width around a theoretical spherical lumpectomy cavity with radius RCAV. If the cavity radius were expanded by the balloon, CTV would be contained into a spherical crown of 1 cm width at some balloon radius, RBALLOON > RCAV. In this way, the minimum balloon volume required to cover up CTV by the prescription dose can be calculated as a cavity volume function. Results: An approximate solution is (volume unit in cc): VBALLOON 0.52(1.46VCAV 0.33 + 1.59) [eq. 1]. If we consider also air or seroma inside the CTV up to 10% in volume, uniformly distributed on a ring fitted to the balloon, we obtain: VBALLOON 0.52(1.42VCAV 0.33 + 1.26) [eq 2]. Exact calculations (points) and approximations (continuous curves) for both cases are showed in the graph. Horizontal lines indicate the available diameter range of spherical mammosite balloons: 4-5 cm and 5-6 cm.