The study aims to provide a setup for collecting radiotherapy-related toxicity data, loco-regional control, and overall survival data for all Danish cancer patients undergoing reirradiation with high dose intention or with the aim of local tumour control; with the ultimate aim of providing safe reirradiation to a larger group of patients. To build a reirradiation cohort database for future research

Reirradiation of recurrent or new tumours has been associated with high rates of severe and even lethal toxicity in some previous reports [Andratscske2023]. This has led to many patients not being offered high dose reirradiation, even though they may potentially benefit from effective local treatment. Thus, it is extremely important to establish solid evidence of the risk of severe toxicity, to enable radiotherapy to be offered to these patients on an equal footing with patients treated for their first cancer.

This prospective registration study will form the basis of a database enabling us to learn more about which patients are suitable for reirradiation, optimal constraints for organs at risk in reirradiation, overall survival, etc.

Inclusion Criteria:

• High dose reirradiation (reirradiation type I or II or repeat organ irradiation delivered with the aim of local control)

Read Danish (for questionnaires + patient information)

Life expectancy due to age and co-morbidity of ≥6 months.

The general condition must be sufficient to tolerate persistent significant side effects

Histological or imaging verified loco-regional recurrence, solitary oligo metastasis or new primary

Age ≥18 years

Signed informed consent, updated annually

Expected follow up physical, by video, by phone or likely contact at a relevant oncological department

Available dose plan(s) from primary (and prior) radiotherapy course(s) (with 3D reconstruction of previous plans, available port film, or drawings). Multiple re-treatments are allowed (new inclusion and baseline registration)

Exclusion Criteria:

• The primary and reirradiation treatments may not be quasi-simultaneous (i.e. the two treatments should be planned independently)

Inability to attend full course of radiotherapy

Purpose of radiotherapy is ONLY palliation of symptoms

No guidelines are provided on the selection of patients for high dose reirradiation.

All patients are eligible for the database if treated with reirradiation with the aim of local control.

A predefined central data analysis plan has not been established for this study. Instead, data analyses will primarily be undertaken within the framework of individual sub-projects, each of which must be reviewed and approved by the steering committee.