Purpose:
Radiation therapy is one of the most common treatments in the
fight against prostate cancer, since it is used to control the
tumor
(early stages), to slow its progression, and even to control pain
(metastasis). Although many factors (e.g., tumor oxygenation) are
known to influence treatment efficacy, radiotherapy doses and
fractionation schedules are often prescribed according to the principle
“one-fits-all,” with little personalization. Therefore, the authors aim at
predicting the outcome of radiation therapy a priori starting
from morphologic and functional information to move a step forward in the
treatment customization.
Methods:
The authors propose a two-step protocol to predict the effects of radiation
therapy on individual basis. First, one macroscopic mathematical model of
tumor
evolution was trained on tumor volume progression, measured by caliper, of eighteen
Dunning R3327-AT1 bearing rats. Nine rats inhaled 100% O2 during
irradiation (oxy), while the others were allowed to breathe air. Second, a
supervised learning of the weight and biases of two feedforward neural networks was
performed to predict the radio-sensitivity (target) from the initial volume and
oxygenation-related information (inputs) for each rat group (air and oxygen
breathing). To this purpose, four MRI-based indices related to blood and tissue
oxygenation were computed, namely, the variation of signal intensity
)(normalΔnormalSI in interleaved blood oxygen level dependent and
tissue oxygen level dependent (IBT) sequences as well as changes in longitudinal
)(normalΔR1 and transverse )(normalΔR2* relaxation rates.
Results:
An inverse correlation of the radio-sensitivity parameter, assessed by the
model, was found with respect the normalΔR2* (−0.65) for the oxy group. A further subdivision
according to positive and negative values of normalΔR2* showed a larger average radio-sensitivity for the
oxy rats with normalΔR2*<0 and a significant difference in the two
distributions (p < 0.05). Finally, a leave-one-out procedure
yielded a radio-sensitivity error lower than 20% in both neural networks.
Conclusions:
While preliminary, these specific results suggest that subjects affected by the
same pathology can benefit differently from the same irradiation modalities and
support the usefulness of IBT in discriminating between different responses.