An experimental setup for proton irradiation of a murine leg model for radiobiological studies

Figures & data

Figure 1. Experimental setup for a local biological response on the right hindleg of mice. Schematics of the water phantom from a top-down view (A) with three black tubes containing mice positioned on top of a movable plastic plate and from the beam direction (B) with mice feet positioned in the proton field and bodies shielded by brass. (C) Top-down view of the experimental setup with mice and brass and (D) mouse jig with mouse and glued right hindlimb.

Table 1. Categorical analysis tables for 1) acute skin damage scoring table and 2) RILD flexibility scoring table.

1)
Score	Criteria for acute skin damage scoring
0.5	Slight reddening, <25% hair loss
1	Severe reddening, swelling, 25–75% hair loss
1.5	Moist desquamation of one small area, two toes partly stuck together, >75% hair loss
2	Moist desquamation of 25% of skin area, two toes stuck together, general shape unchanged, all toes can be identified
2.5	Moist desquamation of 50% of skin area, toes stuck together, general shape changed, at least three toes can be identified
3	Moist desquamation of 75% of skin area, foot shapeless, 1 or 2 toes can be identified
3.5	Moist desquamation of the entire skin area, foot shapeless
2)*
Score	Criteria for fibrosis scoring
0	Total flexibility (100% flexibility)
1	Mildly reduced flexibility (75% flexibility)
2	Medium reduced flexibility (50% flexibility)
3	Severe reduced flexibility (25% flexibility)
4	Total fixation of joint (0% flexibility)

*For template guideline visualization see Supplementary Figure 1.

Table 2. SHIELD-HIT12A MC calculated relative dose, dose-averaged LET, and track- and dose-averaged Qeff for the eight nominal mouse leg positions.

Position no.	1	2	3	4	5	6	7	8
Depth [cm]	6.7	7.1	7.5	7.9	8.3	8.7	9.1	9.5
Relative mean dose [%]	99.68	100.3	100.0	99.36	98.09	43.58	1.66	0.05
dLET, protons [keV/um]	3.16	3.53	3.99	4.68	6.81	11.23	15.02	9.18
dLET, all [keV/um]	5.09	5.33	5.63	6.04	7.63	11.77	17.89	81.35
dQeff, all [nil]	136.9	138.7	139.9	141.6	163.3	260.3	474.3	3815
tQeff, all [nil]	17.92	20.44	23.99	30.02	47.04	89.59	141.6	118.5

Depths are measured from the phantom surface to the center of the corresponding position.

Figure 2. Dose–response curves for (A) acute skin damage and late-induced late damage (RILD) after (B) 6 months, (C) 9 months, and (D) 12 months for each endpoint severity score where the highest score is the most severe cases. It depicts the percentage of mice (46 Gy, n = 5; 22 Gy, 25 Gy, and 45 Gy, n = 6; 26 Gy, n = 10; 27 Gy, 29 Gy, 31 Gy, 32 Gy, 33 Gy, and 35 Gy, n = 12; 38 Gy and 42 Gy, n = 24) with acute skin damage or RILD as a function of dose. The ED50 (effective dose at 50% responders) with 95% confidence intervals are indicated on each graph. The symbol punctuation on the curves indicates the percentage of mice with a respective score, and the curves are fitted with simple logistic regression.

Figure 3. Development of endpoints as a function of time. (A) Median skin score on mice feet for each radiation dose as a function of days until day 30 after treatment. (B) The median radiation-induced late damage (RILD) scores for 22 Gy (n = 6), 31 Gy and 35 Gy (n = 12), 38 Gy and 42 Gy (n = 24), and 45 Gy (n = 6) were analyzed for 12 months after treatment.

Figure 4. Relative dose measurements compared to SHIELD-HIT12A MC simulations. The measurements are based on absolute dose measurements, as described in the results section, but for this plot, the IC data are normalized to 100% PTV dose (by scaling the Semiflex data by 0.8% and Adv. Markus data by 2.0%). Furthermore, the Semiflex data points are displaced by 1.25 mm upstream to compensate for the shift of the effective measurement point introduced by the cylindrical shape of the air-filled cavity. The eight nominal mice positions are shown as red bars over the SOBP and its distal edge.

Data availability statement

The biological raw data is available on request.

[email protected]

The Monte Carlo Simulations are available on:

https://github.com/APTG/2022_DCPT_MICE

A CAD-file outlining the water phantom dimension in detail is provided.