8th Baltic Congress of Radiology

Radioprotection and management

oral abstract

The relevance of the topic is determined by the growing disease in the world and in Latvia with soft tissue sarcomas in the extremities. Radiation therapy can effectively reduce local and patient mortality. Soft tissue sarcoma is a rare cancer that usually develops in the upper limbs. About 15% of all soft tissue sarcomas are diagnosed in the upper limbs. In Latvia, bone and soft tissue tumours are statistically the least common - about 1% of all cancers, 200 cases per year - and yet this is enough to draw attention to the disease, and the treatment of this type of tumour is very specific. The aim of this work is to elucidate the errors of interfraction in the choice of means of immobilization of soft tissue sarcomas of the extremities. The tasks of the work are to compile and analyze the literature on sarcomas and oncological diseases - soft tissue sarcomas in the extremities, on positioning and immobilization, as well as a practical study on the effect of immobilization agents on interfraction errors in radiotherapy. Hypothesis of work - the choice of the means of immobilization of soft tissue sarcomas of the extremities influences the interfraction errors in radiotherapy .

In this study, 10 patients with soft tissue sarcomas of the extremities were selected and analysed in the Aria radiotherapy system. All patients were similarly prepared for radiotherapy. Patients were positioned on the treatment table in an individually prepared immobilisation device, either a vacuum bag or a thermoplastic mask lying supine. The Latvian Radiotherapy Clinic recorded positional displacement data for each patient in the vertical, longitudinal and lateral directions during each fraction from the Aria radiotherapy system. Patients included in the study were assigned a number in sequence and the investigator recorded the positioning shift data during each fraction. Next, data were recorded on the localisation of the soft tissue sarcoma, which part of the limb, and the immobilisation device used.

Out of 10 patients with soft tissue sarcomas of the extremities, the thermoplastic mask was used in 3 patients and the vacuum bag in 7 patients. It was found that the interfraction errors, the position deviations in the CC,AP and LR directions, are different depending on the immobilization agent used, thermoplastic mask or vacuum bag. In the study, the interfraction error movements are most significant when using the thermoplastic mask immobilizer. The highest interfraction errors were observed using the thermoplastic mask in the LR direction. The lowest inter-fraction errors were observed using the vacuum bag in the CC direction According to the data read from the Aira system on interfraction errors it can be concluded that for soft tissue sarcomas in the extremities it is best to use vacuum bags for immobilisation as it is more comfortable to work with and can be reused for the same patient if necessary if large deviations are found.

In the theoretical part of the work author found out that the interfraction errors, position deviations in the directions CC, AP and LR are different, depending on the thermoplastic mask or vacuum bag of the immobilizing agent used. Research proved that in case of interfraction error of movements, the largest movement occurs using a thermoplastic mask immobilizer. But the least error was in the vertical direction in the CC direction. The largest interfraction errors were observed using thermoplastic masks in the direction of LR, but the smallest interfraction errors were observed using a vacuum bag in the CC direction. From the collected data about interfraction errors from the Aira system, author finds out that vacuum bags for soft tissue sarcomas in the extremities are better to use for immobilization as they are more convenient to handle and can be re-used in case of major abnormalities. Using thermoplastic mask for immobilization, the more times patient gets radiotheraphy, the greater are interfraction errors in the CC, AP, and LR directions , because of changes of body weight and volume, in this case is necessary to form new thermoplastic mask, but a vacuum bag can be used up to end of radiotheraphy with minimal interfraction error deviations in all 3 directions. The research carried correlations with the previous recommendations by the researchers on interfraction errors depending on the immobilization used. The author concludes that it's better to use vacuum bags than thermoplastic masks to gain more accurate tumor irradiation in radiation therapy. The author of the work recommends further research on interfraction errors depending on the immobilizer used in radiotherapy of soft tissue sarcomas in the extremities.

Using thermoplastic mask for immobilization, the more times patient gets radiotheraphy, the greater the interfraction errors in the CC, AP, and LR directions , because of changes of body weight and volume, in this case necessary to form new thermoplastic mask, but a vacuum bag can be used up to the end of radiotheraphy with minimal interfraction error deviations in all directions, it's better to use vacuum bags than thermoplastic masks to gain more accurate tumor irradiation in radiation therapy

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