Radiotherapy uses high-energy ionising radiation to destroy cancer cells. Radiotherapy treatment planning is usually based on a computed tomography image acquired in the treatment position. The treatment is delivered in daily treatment fractions during several weeks. It is important that the patient is in the exact same position during the treatment fractions compared to the planning image. Otherwise, the dose to the treatment target may be compromised or healthy tissue may be overdosed.
In her doctoral dissertation, Annele Heikkilä aimed to develop methods to minimise setup errors and their dosimetric effects in photon external beam radiotherapy. The focus was on correction of rotational setup errors in breast and pelvic radiotherapy, and inter-isocentre setup errors in craniospinal irradiation.
“Even 1° rotational errors in the patient position may case clinically significant increase in heart and left anterior descending artery doses in left-sided breast radiotherapy. Earlier studies have shown that high doses to the heart and left anterior descending artery increase the risk of ischemic heart disease and major coronary events. Therefore, it is important to correct even small rotational setup errors”, says Heikkilä.
Craniospinal irradiation refers to the radiotherapy of the whole brain and spinal cord. Two to three radiotherapy treatment plans are required for craniospinal irradiation because of the extensive treatment target. The treatment plan junctions must be carefully optimised to avoid dose gap between the plans. The plans must also not overlap, as this will result in harmfully high radiation doses to the junction region. Considering the daily variation in the patient position, setup error correction and treatment field localisation is quite challenging in craniospinal irradiation.
“The human spine shortens by 0.5–2 cm during the day because the gravity compresses the intervertebral discs. Earlier, this effect has not been considered in craniospinal irradiation. In my study, it was demonstrated that the variation of spinal length during the day affects the setup accuracy in craniospinal irradiation. Thus, craniospinal irradiation treatment fractions should be scheduled at the same time of the day as the treatment planning image acquisition”, says Heikkilä.
The research questions of Heikkilä’s dissertation have originated from the practical development areas and problems encountered at the radiotherapy departments of Tampere University Hospital and Hospital Nova of Central Finland. Practical recommendations on minimising and correcting setup errors were formed based on the results. The results of the doctoral research serve to improve the accuracy of radiotherapy treatment delivery and optimise the treatment workflow.
Annele Heikkilä is from Hattula, Southern Finland. She is currently working as a specialising medical physicist at Seinäjoki Central Hospital. Heikkilä will receive the degree of Qualified Medical Physicist upon completion of her doctoral dissertation.
Public defence on Friday 3 October
The doctoral dissertation of MSc Annele Heikkilä in the field of biomedical engineering titled Rotational and inter-isocentre setup errors in external beam radiotherapy will be publicly examined at the Faculty of Medicine and Health Technology at Tampere University at 12 o’clock on Friday 3 October 2025 at Kauppi campus, Arvo-building, Jarmo Visakorpi auditorium (Arvo Ylpön katu 34, Tampere). The Opponent will be Professor Marcel van Herk from University of Manchester. The Custos will be Professor Michiel Postema, Faculty of Medicine and Health Technology, Tampere University.