Session Item

Supraclavicular fossa position reproducibility and accuracy has been an existing challenge for breast cancer radiotherapy patients. This issue is detrimental especially for mastectomy patients. With the utilisation of VMAT technique, the accuracy of the arm position is even more crucial to ensure the treatment precision. Our clinical team would like to find out if the use of SGRT technology could improve the supraclavicular fossa position accuracy and reproducibility.

32 mastectomy patients with VMAT (chest-wall and supraclavicular field) technique were aligned using SGRT (AlignRT, Vision RT) workflow. All patients were immobilized with an opened thermoplastic on an all-in-one board. They were firstly aligned base on the skin marking and then fine-tuned using SGRT. The Region of Interest (ROI) was drawn on the ipsilateral chest-wall only. After that, the therapist activated the ‘treatment capture’ function in SGRT system to check on the shoulder and arm position relative to the CT position. Patients’ arms were adjusted accordingly. Lastly, the therapists will check on the ROI again to ensure the overall positioning was near to zero. 142 CBCT images were acquired. During the image registration, chest-wall position (CW) was matched based on sternum, chest-wall contour, and spine. Once the chest-wall was in great position, the supraclavicular fossa positioning discrepancies were calculated based on the acromioclavicular joint (ACJ) matching. All three dimensions x (lateral), y (longitudinal) and z (vertical) were recorded. 

The supraclavicular fossa accuracy in three dimensional were calculated using the formula:  ΔX=｜X-cw－X-acj︱, ΔY =｜Y-cw－Y-acj︱, ΔZ =｜Z-cw－Z-acj︱. The vector is measured using d=√(ΔX² +ΔY² +ΔZ² ). The result showed that the supraclavicular fossa positioning discrepancies were 0.12±0.10cm, 0.10±0.13cm and 0.11±0.12cm in x, y and z directions. The vector, d = 0.16±0.14cm.

‘Treatment capture’ function can provide accurate 3D arm position information. It ensures an accurate and reproducible supraclavicular fossa position which benefits to the dose delivery precision for mastectomy patients and potentially protects the organs at risk such as spinal cord, thyroid gland and brachial plexus.