The first patient was treated on a tumour in the right "loin area" from 22 January 1915. During 12 sessions, the tumour and the four peripheral regions of the target area are alternately irradiated with a medium sized field of 9 cm diameter.
Through the attentiveness of physicist Ben Mijnheer during a flood in the basements of the NKI, the irradiation chart of this first treatment in the AVL could be saved. The primary archive with irradiation data up to 1920 was lost to water damage, although copies of the irradiation charts were found in the patients' medical records.
The irradiation chart shows how dr. Gaarenstroom ensured that a controlled irradiation was administered. The distance of 17 to 18 cm probably indicates the focus-skin distance. The measured beam hardness of 8 - 9 degrees B (Bauer Qualimeter system) on the irradiation chart corresponds to approximately 100 kV tube voltage. The tube current is 2 mA. To make the beam harder, a filter of 5 mm aluminium was used and, behind this, a cushion of sea grass was placed to attenuate the soft secondary scatter radiation from the filter. In the column "Filter etc…" the setting of the apex interrupter is indicated as 50 (half period) or 100 (whole period rectified).
The irradiations last 20 to 30 minutes. Based on dose measurements according to Holzknecht (H) and Kienböck (X), the dose per field per session at the start can be estimated at 60 to 100 röntgen (r); but later in the series, the dose is increased up to as much as 300 r per field.
Neither the hardness of the radiation nor the dose could be accurately determined. Finally, the treatment is stopped due to skin burns.