{'fraction_non_alphanumeric': 0.05343511450381679, 'fraction_numerical': 0.049872773536895676, 'mean_word_length': 4.476323119777159, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Tumor-to-normal tissue (T/N) dosimetry ratios role in assessment of 90Y selective internal radiation therapy (SIRT).

OBJECTIVE
The purpose of our work is to assess the role of tumor-to-normal tissue (T/N) dosimetry ratios for predicting response in patients undergoing locoregional therapy to the liver with 90Y microspheres.


METHODS
39 patients (seven femal:32 male, mean age 68.3 ± 7.6y), underwent PET/CT imaging after treatment with 90Y microspheres. For attenuation correction and localization of the 90Y microspheres, the low dose, non-diagnostic CT images from PET/CT were used. The acquisition took 15 min and the reconstruction matrix size was 200 × 200×75 mm and voxel size of 4.07 × 4.07×3.00 mm. For dosimetry calculations the local deposition method with known activity of 90Y was used. For each patient, regions-of-interest (ROIs) for tumor(s) and whole liver were manually created; the normal tissue ROI was created automatically. mRECIST criteria on MRI done at a month post treatment and subsequently every three months after90Y treatment, were used to assess response.


RESULTS
For 39 patients, the mean liver, tumor and normal tissue doses (mean ± SD) were, 55.17 ± 26.04 Gy, 911.87 ± 866.54 Gy and 47.79 ± 20.47 Gy respectively. Among these patients, 31 (79%) showed complete response (CR) and 8 (21%) showed progression of disease (PD). For patients with CR, the mean T/N dose ratio obtained was 24.91 (range 3.09-80.12) and for patients with PD, the mean T/N dose ratio was significantly lower, at 6.69 (range 0.36-14.75). Conclusion: Our data shows that patients with CR have a statistically higher T/N dose ratio than those with PD. Because, the number of PD cases was limited and partial volume effect was not considered, further investigation is warranted.


ADVANCES IN KNOWLEDGE
Tumor-to-normal tissue dosimetry ratios can be used for assessing response in patients undergoing locoregional therapy to the liver with 90Y microspheres.