Abstract P4-10-10: The Gammapod TM: A Novel Breast Specific Stereotactic Body Radiation Therapy (SBRT) for Small Breast Cancers
Authors: Feigenberg SJ , Yu CX , Regine W. 
Published: April 2011

Introduction: SBRT is a novel approach to precisely deliver high doses of radiation therapy to a define target, while normal tissues immediately surrounding the tumor receives a significantly lower (i.e. tolerable) dose. This technique has revolutionized the management of small medically inoperable lung cancer with local control rates recently reported in the co-operative setting of 98% now setting the stage for challenging surgery as the standard of care for select patients with lung cancer. SBRT has not been used in the breast, since the breast is a pliable organ without a suitable immobilization device and the lack of an SBRT system that can create the rapid fall off in dose necessary to deliver ablative doses of radiation safely in the breast. The purpose of this NIH funded project is to develop a dedicated SBRT system for early breast cancer which could eventually lead paradigm shift in the management of breast cancer similar to lung cancer.

Materials and Methods: The SBRT system was developed such that dose distributions produced would be similar to stereotactic radiosurgery in the brain where the the drop off of the prescription isodose to 50% of the prescription dose was less than 5 mm. The device uses 36 non-coplanar Co-60 sources which rotate around a focal point to produce 36 non-coplanar arcs. The system incorporates the use of a floating/dynamic table which together with the rotatable sources enables differential dosing of target volumes similar to intensity modulated RT allowing higher ablative doses to the gross tumor and a lower sub clinical dose to treat microscopic tumor foci. In addition the SBRT system, a breast specific immobilization device was developed. This system consists of 2 layers with an air tight seal in between. Once placed on the breast a small negative pressure secures it to the breast. A prospective trial tested the reproducibility of the breast cup using the centroid of the post-operative clips on 2 consecutive CT simulations separated by 10 to 60 minutes simulating the treatment planning scenerio in the prone position. During this time, patients were also asked to fill out a questionaire regarding the comfort of this approach. Results: The issues within the specific aims of the grant have been effectively solved and have led to a breast specific immobilization device and a breast specific SBRT system — The Gammapod TM. The immobilization device demonstrated a set up error of less than 3 mm a significant decrease from the 10 mm planning target volume expansion as recommended in NSABP B39 for patients undergoing 3 dimensional conformal partial breast radiotherapy. All patients described this experience as more comfortable in comparison to a biopsy and similar to the experience of a mammogram.Dosimetric studies using Monte Carlo simulation demonstrate that tumors up to 5 cm in diameter, and 5 mm from the chest wall, lung/heart receive &lt; 10% of the maximum dose. Conclusions: A breast specific immobilization device and SBRT system has been developed produces dose distributions similar to stereotactic radiosurgery in the brain. The first prospective studies testing this device clinically through a multi-institutional consortium are expected to open in early 2011.

Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P4-10-10.