Developing delineation guidelines for the lymphatic target volumes in ‘prone crawl’ radiotherapy treatment position for breast cancer patients

This project focuses on the promising new 'prone crawl' position for breast cancer radiotherapy. This position places the patient in prone, with the arm on the treated side alongside the body. The other arm is extended above the head, resembling a phase from crawl swimming. In prone position, the breast can hang free, away from organs at risk and by placing the arm alongside the body, the radiation beam can still reach the axillary lymph nodes. Preliminary data showed reduced radiation dosages in lungs, non-treated breast, thyroid and oesophagus, compared to the regularly used supine position. After proving the potential of this new position, it is important to optimize it for widespread clinical use. An important part of radiation therapy is the delineation of the target tissue (the tumour or the lymphatic system, if cancer cells have infiltrated the lymphatics) and the organs at risk. The goal of radiotherapy is to kill tumour cells by hitting them with a high energy beam. This beam is guided by the delineations and it is therefore really important that delineations are performed accurately, since the beam will also kill healthy cells and it could cause damage to organs at risk (like the heart and lungs) if it misses the target area. To ensure that delineations are performed according to a universal standard and to guarantee that every patient gets the same quality of treatment across different centres, delineation guidelines exist to guide the radiation oncologist when performing delineations. Since the prone crawl position is still very new, no position specific guidelines existed and as such, making these position specific guidelines was the goal of the PhD. Since the lymphatics are in the submillimetre size range and they are soft tissues, they cannot directly be visualised on the CT scans used for treatment planning. Instead, the current delineation guidelines contain reference structures like muscles and blood vessels, that are visible on patient CT scans. Since nobody ever completely visualised the lymphatic system in the target area, complete with spatial relations with the reference structures that are used on CT, it seemed very interesting to try and provide a map of the lymphatic system and base the new delineation guidelines for the prone crawl position on the actual location of these lymphatics. Therefore, the PhD was divided into 2 parts. The first part focused on finding a methodology to visualise the lymphatics on CT images by injecting radiographic contrast agents. The second part of the PhD focused on setting up the actual delineation guidelines and developing a methodology specifically for this purpose. The experiments performed during the PhD yielded 3 papers for the first part and another 3 papers for the second part. Position specific delineations were developed and they are currently being used at the radiotherapy department. Apart from this, the methodologies that were developed during this PhD will also be useful for future guideline development studies and future lymphatic mapping efforts. This thesis may to date even be the only document that thoroughly discusses the possibility of retrograde lymphatic injection