Fig 1.
Illustration of the SFRT spatial fractionation study design.
A very large range of radiation spatial fractionation scale was used to derive the impact of radiation spatial fractionation. Four arms share the same 20 Gy volume-average dose. The high dose 50GySFRT arm is added because 20GySFRT is not known to have tumor control. The dosimetric parameters studied and number of animals per study arm are listed in Table 1.
Table 1.
Summary of nine SFRT dosimetric parameter specifications in the six-arm study.
Fig 2.
Animal irradiation setup and treatment alignment and verification.
(A—B) The treatment setup components include (1) X-ray source, (2) endoscopic camera (lens shielded), (3) field shaping collimator for all treated arms (20GySFRT shown), (4) animal and tumor, and the (5) 3-axial heated animal positioning stage. (C) Photo of the built-in irradiator light shines through the 50GySFRT collimator and onto the outlined tumor as seen from the beams-eye view camera (live feed used to position tumor within the treatment fields). (D) EBT-3 treatment verification films with a cutout in the tumor region. The films were reviewed for all treated animals for treatment targeting verification.
Fig 3.
Phantom dosimetry measurement.
EBT-3 films were calibrated by ion chamber under large field conditions. All beam profiles and corresponding percentage depth dose were measured using two films as shown: one is on the surface perpendicular to radiation beam (A) and one sandwiched between two small phantom blocks parallel to radiation beam (B). The circles indicate the film areas used for volume-average dose calculation estimates. The following assumption was made for volume-averaged tumor dose and EUD calculations: dose value does not vary +/-1cm along the direction parallel to the same valleys/peaks.
Fig 4.
Measured dose beam profiles and percentage depth doses for all treatment arms.
(A-D) Figures display the percentage depth doses for each of the 20 Gy volume-averaged treatment arms. (E-H) Figures display the corresponding SFRT beam profiles for each of the 20 Gy volume-averaged treatment arms. Note that the 20GySFRT and 50GySFRT arms share the same SFRT collimator and thus the same relative dosimetry. The large non-uniformity of the peak doses in the SFRT radiation is due to the finite x-ray target size and the nondivergence of the SFRT collimator. However, the actual peak dose non-uniformity in the treated tumor (diameter of ~10mm) is within 10%.
Fig 5.
Illustration of 3D ultrasound imaging-based tumor volume measurement.
Figure (A) is an illustration of the 3D ultrasound imaging setup with anesthetized animal (23). Two-dimensional transverse image slices (B) are acquired along the elevational direction and are then reconstructed into 3D images [30] (C). Tumors are visually identified on the ultrasound images. Resulting 3D images (C) are used to measure the tumor dimensions and calculate tumor volume. Imaging data is acquired pre-treatment (D) and every ~third day thereafter (E-G). In images D-G the tumor (yellow dotted line) and corresponding tumor volume grow over time following a 20GyHalfSFRT treatment.
Fig 6.
Animal survival, tumor volume change, and body weight change post-treatment.
Animal survival (A), normalized averaged tumor volume (B), and normalized averaged body weight (C) are shown for all six study arms. In plots (B) and (C), the error bars at each time point represent one standard deviation from the mean for each treatment arm. The statistical significance values for each pair of survival curves are shown in S2 Table.
Table 2.
Pearson Correlation coefficient matrix for the eight SFRT dosimetric parameters relevant for tumor treatment response.
Fig 7.
Associations between Percentage Survival (Day 17) and eight dosimetric parameters.
The percentage survival at Day 17 for each treatment arm is plotted against their corresponding (A) Tumor EUD, (B) valley dose, (C) percentage volume irradiated, (D) valley width, (E) peak width, (F) volume-averaged dose, (G) peak dose, (H) and PVDR. In addition, their corresponding regression lines and R2 values are presented. Eight linear regression models with single covariates, one for each dosimetric parameter, were used to calculate the R2 value and corresponding statistics.
Table 3.
Table of coefficients for univariate Cox Proportional Hazards analysis of survival.
Fig 8.
Associations between body weight change (Day 17) and eight dosimetric parameters.
Individual animal body weight change are plotted against each of the 8 treatment dosimetric parameters: valley dose (A), valley width (B), peak width (C), percentage volume irradiated (D), normal tissue EUD (E), PVDR (F), volume-averaged dose (G), and peak dose (H) vs % Body Weight at Day 17 and their corresponding regression lines and R2 values are shown. Eight linear regression models with single covariates, one for each dosimetric parameter, were used to calculate the R2 value and corresponding statistics. The body weight change averages for each of the treatment arms are also shown (black bars).
Table 4.
Table of coefficients for univariate linear regression analysis of Body Weight (Day 17).