Utilization of tomotherapy-based topotherapy for emerging breast radiation techniques: boost integration and accelerated partial breast irradiation.

Abstract

Abstract Abstract #5148 Background: Helical Tomotherapy-based intensity modulated radiation therapy (IMRT) can be delivered using fixed gantry angles, known as Topotherapy, with daily image guidance. With the advent of accelerated or hypofractionated treatment schemes to shorten courses of radiation, conformality and accuracy is imperative for breast radiotherapy techniques since high doses of targeted radiation are used. The purpose of this study was to characterize the dosimetry of Topotherapy for delivery of Accelerated Partial Breast Irradiation (APBI) and hypofractionated Simultaneous Integrated Boost (SIB) breast irradiation in comparison with conventional techniques.
 Materials and Methods: Ten patients with early stage left sided breast cancer were evaluated for this study using Topotherapy planning. The planning target volume (PTV) was contoured as the lumpectomy cavity with a 1.5cm margin, and the breast was defined by the tissue encompassed by tangent fields minus the PTV and 5mm of skin. To evaluate SIB, nine patients were comparatively planned using a standard sequential treatment of 50Gy tangents to the whole breast with a 10Gy electron boost in 30 fractions versus Topotherapy integrated boost with the same cumulative dose in 25 fractions versus hypofractionated Topotherapy with 42.4Gy to the breast and 51.2Gy to the PTV in 16 fractions. For evaluation of APBI, 3cm hypothetical lumpectomy cavities were contoured in the four breast quadrants of a single patient, with a similar 1.5cm expansion and breast volume. Plans to deliver 38.5Gy in 10 fractions were generated for each lesion using Topotherapy and compared to 3-dimensional conformal radiation therapy (3DCRT) and IMRT using the dosimetric guidelines from the National Surgical Adjuvant Breast and Bowel Project B-39/Radiation Therapy Oncology Group 0413 protocol.
 Results: Target coverage and dose to heart and lung were clinically equivalent when comparing Topotherapy APBI and SIB to conventional techniques. For ABPI, the Topotherapy conformality index was superior to 3DCRT for all breast quadrants, but inferior to IMRT for lesions located in the medial quadrants of the breast. For SIB, Topotherapy provided an improvement in conformality over conventional sequential techniques, however there was no intensity modulated comparison. Equivalent target uniformity was observed in all APBI techniques however for SIB, Topotherapy provided a superior uniformity index for the whole breast target.
 Discussion: Topotherapy is capable of delivering clinically acceptable dosimetry for accelerated or hypofractionated breast radiation without compromising dose to structures at risk. This treatment modality will be utilized in the near future pending FDA approval. Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 5148.