A QA Analysis of a Contrast Localized Linac-Based Technique for Hypo-Fractionated Partial Breast Radiotherapy

Abstract

AIM: Partial-Breast Radiotherapy following lumpectomy is an effective treatment for women with early stage breast cancer, with the technique of either brachytherapy or external beam treatment broadly being implemented in clinics. However, the current popular brachytherapy treatments are still limited to treating somewhat regularly shaped targets, with an additional limitation defined by the skin and rib radiation tolerances. A linac-based method that utilizes frame fixation, a contrast enhanced cavity/fiducial location approach, image localization guided treatment techniques, and special immobilization techniques was demonstrated to be accurate method to deliver radiotherapy to a site in the breast, a task that has challenged clinicians for decades. Methods: A prospective study of ten patients (six Left Breasts and four Right Breasts) had placed three internal gold-seed markers inside the surgical bed post-surgery (provided by CIVCO Corporation)/prior to planning and six external markers (made by Beckley). (Two sets of three fiducials) were placed in an axial plane above and below the surgery site) Prior to the Computerized Tomography (CT) scan performed for planning, contrast is introduced into the cavity to allow localization of the breast cavity during planning. A simulation was performed in a large-bore 3rd generation scanner with a patient’s breast affixed using an Electa Body frame to improve localization and to control breathing variances. The planning was performed on an Eclipse treatment planning system, and the treatment was performed using a Varian CD Linear accelerator. Results: Small volumes field sizes, sometimes as small as 4 × 4, and Mutli-Leaf Collimators (MLCs) were required to deliver patient dose verification. This process was performed prior to treatment using diodes (including planar isodose to evaluate the MLCs required to deliver compared to the plan verification when using Map Check. (Diode Array Radiation Dosimeter made by Sun Nuclear Corporation) Conclusions: A Quality Analysis (QA) was performed. Five to seven fields were used, indicating good statistical and clinical agreement in these 10 cases. All fields were imaged daily prior to treatment using 2 Dimensional (2D) MV portal imaging and correlated and evaluated by the Radiation Oncologist using the Acculoc patient positioning system.