Radiation transmission study of silicone elastomer for mammary prosthesis

Dose perturbations due to contrast medium and air in MammoSite® treatment: An experimental and Monte Carlo study

In the management of early breast cancer, a partial breast irradiation technique called MammoSite (Proxima Therapeutic Inc., Alpharetta, GA) has been advocated in recent years. In MammoSite, a balloon implanted at the surgical cavity during tumor excision is filled with a radio-opaque solution, and radiation is delivered via a high dose rate brachytherapy source situated at the center of the balloon. Frequently air may be introduced during placement of the balloon and/or injection of the contrast solution into the balloon. The purpose of this work is to quantify as well as to understand dose perturbations due to the presence of a high-Z contrast medium and/or an air bubble with measurements and Monte Carlo calculations. In addition, the measured dose distribution is compared with that obtained from a commercial treatment planning system (Nucletron PLATO system). For a balloon diameter of 42 mm, the dose variation as a function of distance from the balloon surface is measured for various concentrations of a radio-opaque solution (in the range 5%-25% by volume) with a small volume parallel plate ion chamber and a micro-diode detector placed perpendicular to the balloon axis. Monte Carlo simulations are performed to provide a basic understanding of the interaction mechanism and the magnitude of dose perturbation at the interface near balloon surface. Our results show that the radio-opaque concentration produces dose perturbation up to 6%. The dose perturbation occurs mostly within the distances <1 mm from the balloon surface. The Plato system that does not include heterogeneity correction may be sufficient for dose planning at distances > or = 10 mm from the balloon surface for the iodine concentrations used in the MammoSite procedures. The dose enhancement effect near the balloon surface (<1 mm) due to the higher iodine concentration is not correctly predicted by the Plato system. The dose near the balloon surface may be increased by 0.5% per cm3 of air. Monte Carlo simulation suggests that the interface effect (enhanced dose near surface) is primarily due to Compton electrons of short range (<0.5 mm). For more accurate dosimetry in MammoSite delivery, the dose perturbation due to the presence of a radio-opaque contrast medium and air bubbles should be considered in a brachytherapy planning system.

Radiotherapy for breast cancer in patients undergoing breast reconstruction or augmentation

Due to increasing indications for postmastectomy radiotherapy and a growing demand for breast reconstruction or augmentation, increasing numbers of patients are currently being exposed to both these treatments. In view of the wide range of available techniques for breast reconstruction, either prosthetic or autologous, and their various sequencing in relation to radiotherapy, physicians can be faced with numerous clinical situations requiring comprehensive knowledge of the topic. This review discusses physical, radiobiological and clinical aspects of combining breast reconstruction and radiotherapy. The available data indicate the feasibility of such combinations, although at the expense of increased risk of complications and less satisfactory cosmesis. Of the two methods of breast reconstruction: using autologous tissue or prosthesis, the former seems to provide better cosmesis and a lower risk of complications in conjunction with radiotherapy. To minimize the risk of unfavourable outcome, the techniques and timing of both breast reconstruction and radiotherapy should be given meticulous attention.

Changes in photon dose distributions due to breast prostheses

PURPOSE

Subcutaneous prosthetic implants had been routinely used for cosmetic augmentation and for tissue replacement following mastectomy over the last 15 years. The implants come in many forms as the gel filler material and surrounding shell material(s) vary significantly.

METHODS AND MATERIALS

This study uses a thin window parallel-plate chamber and thermoluminescent dosimeters to quantify and dosimetric changes to surrounding breast tissue due to the presence of the prosthesis. A mammographic phantom was compared to four commercial prostheses, namely two silicon gel fillers within two different shells (silicon or silicon/polyurethane), a tri-glyceride within silicon and a bio-oncotic gel within silicon/polyurethane. The latter two implants were designed with a low-Z fill for diagnostic imaging benefits.

RESULTS

Ion chamber results indicate no significant alteration of depth doses away from the implant with only minor canceling (parallel opposed) interface perturbations for all implants. In addition the physical changes to the irradiated prostheses were quantified by tonometry testing and qualified by color change. Each implant exhibited color change following 50 Gy, and the bio-oncotic gel became significantly less formable following irradiation, and even less formable 6 weeks postirradiation.

CONCLUSION

The data indicates that prostheses do not affect the photon beam distribution, but radiation does affect the prostheses.

Breast carcinoma post-augmentation mammaplasty: therapy with limited surgery and radiation

Due to the recent surgical and technical developments in aesthetic surgery and occasional dissatisfaction of women with their external contour, augmentation mammaplasty has become a common occurrence in the surgical practice of the aesthetic surgeon. Breast carcinomas, incidentally associated with augmentation mammaplasty, have been sporadically reported in the literature and have all been treated with a mastectomy when resection was possible. We present a case of breast carcinoma occurring 5 years after augmentation mammaplasty performed with silicone-gel-filled implants. Therapy of this carcinoma was achieved through a segmental mastectomy followed by postoperative radiation. The patient remains well 15 months postoperatively. A large number of breast implants are performed each year and the likelihood of a higher incidence of incidental breast carcinomas seen with implants is certainly possible as these patients become older; thought should be given to the notion that possibly not all of these cases need to be managed with radical surgery.

Carcinoma of the breast behind a prosthesis--comparison of ultrasound, mammography and MRI (case report)

Silicone prostheses are known to impair the diagnostic evaluation of the breast. The authors report about a case of a small carcinoma of the breast, which was examined by MRI, ultrasound and mammography. The diagnostic capabilities of these imaging modalities are discussed and MRI is presented as a new possible tool for an improved evaluation of breasts with silicone implants.