Proof of concept for the usability of the IRRAMICE for proton preclinical radiobiological research by a traceable dosimetry evaluation

Abstract

Radiobiology relies on animal studies to demonstrate efficacy and safety of treatments. For proton-based studies in clinical settings, bespoke solutions, enabling animal irradiations without compromising health and safety regulations, need to be developed to facilitate the research. This study aims to demonstrate the usability of the IRRAMICE, a novel system with bespoke collimators to effectively treat small targets, within proton clinical facilities. Following a clinical workflow of planning CT, treatment plan design and delivery, a dosimetric evaluation of the IRRAMICE was conducted. Traceable absorbed dose was determined by measurements with (i) ion chamber, (ii) alanine pellets within a mouse phantom and a bespoke holder in the IRRAMICE, and (iii) Gafchromic film in the holder for a relative evaluation of the collimation system. Dose determined with alanine pellets in the mouse phantom were within 2% of the planned dose. The 2%/2 mm local gamma analysis of the dose distribution of the collimated beam spot determined by the film and the treatment planning system showed an average 98.3% passing rate. Through measurements in mouse phantoms, IRRAMICE demonstrated to be a suitable device for enabling the setup and delivery of treatment plans in a reliable and reproducible manner, to facilitate in vivo preclinical experiments.

Keywords: Dosimetry; IRRAMICE; Preclinical; Proton therapy.

Fig. 1

Summary of tailored approaches used by several research centres.

Fig. 2

3D cross-section view of IRRAMICE (a) and an image of the device with six mouse phantoms, with one compartment showing the collimator and range shifter block positioned on top of the mouse compartment (b).

Fig. 3

IRRAMICE setup in commissioning mode, (a) with phantoms and holders for ionisation chambers and alanine pellet holders, positioned using the lock-bars to ensure reproducibility. (b) Treatment plan with a dose of 12 Gy delivered to an alanine pellet placed in the abdomen compartment within the mouse phantom. (c) kV image taken without the rotating disc part of the collimator to allow for correct alignment of the pellet (lateral and longitudinal). (d) Lasers used to align the rotating collimator to the marker on the mouse phantom.

Fig. 4

Profile comparison of TPS-calculated and EBT3 measured profiles in at (a) 2 cm below the Ta collimator and (b) immediately below the collimator within the alanine-film holder, placed in IRRAMICE.

Fig. 5

Gamma index maps for each respective film, where AH1-3 were at a 2 cm depth and AH4-6 were immediately below the collimator.