Evaluation of Delivered Doses in Proton Beam Therapy for Prostate Cancer Using Positron Emission Tomography/Computed Tomography Imaging

AIMS

Proton beams deposit energy along their paths and stop abruptly without penetrating the opposite side, making it difficult to detect their actual paths. However, confirming the path may lead to evaluating the actual doses to organs at risk in proton therapy for prostate cancer. As proton beams produce positron emitters through nuclear fragmentation reactions, theoretically, proton beam paths can be measured by positron emission tomography/computed tomography (PET/CT). Therefore, this study investigated whether conducting PET/CT examinations immediately after proton beam therapy helps to assess the doses delivered to the rectal and urinary bladder walls, which are the major sites of radiation-related toxicity.

MATERIALS AND METHODS

Between June 2022 and June 2023, 51 consecutive patients with prostate cancer who underwent proton beam therapy were enrolled and imaged with PET/CT to measure these radioactive particles and validate the actual dose delivered to the rectal and urinary bladder walls.

RESULTS

The delivered doses assessed using PET/CT after proton beam therapy strongly correlated with the planned volume for proton beam treatment.

CONCLUSIONS

PET/CT exhibited potential as a valuable tool for validating the irradiated dose to organs at risk.

P5618Coronary flow capacity to identify stenosis associated with coronary flow improvement after coronary revascularization

Background

Coronary flow capacity (CFC) has recently been introduced as a comprehensive assessment of the coronary circulation by combining coronary flow reserve (CFR) and maximal coronary flow velocity to overcome the limitations of using CFR alone, and was reported to provide enhanced risk stratification compared with CFR. However, its potential to identify stenosis that would be associated with clinically relevant flow coronary flow improvement after revascularization has not been investigated.

Aims

The aim of this study is to quantify coronary flow changes after revascularization in relation to CFC and CFR.

Methods and results

Using a combined dataset of DEFINE FLOW and the Amsterdam UMC prospective ComboWire database, a total of 133 patients (135 vessels) with intermediate coronary artery lesions who underwent intracoronary physiologic assessment including intracoronary Doppler flow measurement before and after PCI were analyzed. The median values of fractional flow reserve (FFR) and CFR before PCI were 0.70 (Q1–3: 0.56–0.80) and 1.64 (Q1–3: 1.30–2.06). The number of lesions classified by CFC before PCI were 14 for normal CFC, 40 for mildly reduced CFC, 33 for moderately reduced CFC and 48 for severely reduced CFC. The lesions with larger impairment of CFC showed greater increase in coronary flow, and vice versa (median percent increase in coronary flow by revascularization: 4.2% for normal CFC; 25.9% for mildly reduced; 50.1% for moderately reduced; 145.5% for severely reduced, P<0.0001). Using the same CFR distribution based on CFC criteria showed that only lesions with severely reduced CFR showed a significantly higher coronary flow increase after PCI (−2.6% for CFR in the normal zone; 26.6% for CFR in the mildly reduced zone; 33.3% for CFR in the moderately reduced zone; 81.7% for CFR in the severely reduced zone, P=0.0007). Compared with the established CFR cut-off value of 2.0, moderate to severely reduced CFC showed higher specificity and positive predictive value (PPV) to predict at least 20% increase in coronary flow after PCI (specificity and PPV: 86.4% and 72.5% for ischemic CFC vs. 75.8% and 40% for CFR cut-off value 2.0). Multivariate logistic regression analysis revealed that the lesions with moderately or severely reduced CFC (odd ratio [OR] = 7.606 95%interconfidence interval [CI]: 2.834–20.412, P<0.001) and pre-PCI FFR (OR=0.0002, 95% CI: 0.0002–0.0204, P<0.001) were the independent predictors of coronary flow increase after PCI.

Conclusion

CFC showed a higher diagnostic efficiency for identification of lesions which benefit from revascularization compared to CFR with respect to coronary flow improvement. This study provides the physiological rational of revascularization for the lesions with moderately to severely reduced CFC from the perspective of coronary flow increase.

Acknowledgement/Funding

Philips Volcano

6113Gender differences in long-term outcomes in patients with deferred revascularization following fractional flow reserve assessment: international collaboration registry of physiologic evaluation

Background

Studies of sex differences in fractional flow reserve (FFR) measurements have shown that in comparison with men, angiographic lesions of similar visual severity are less likely to be ischemia producing in women. Gender specific differences may influence revascularization decision making and prognosis after deferred revascularization following FFR measurement.

Purpose

This study sought to investigate the gender difference in long-term prognosis of patients of deferred revascularization following FFR assessment.

Methods

A total of 879 patients (879 vessels) with deferred revascularization with FFR >0.75 who underwent FFR and CFR measurements were enrolled from 3 countries (Korea, Japan, and Spain). Long-term outcomes were assessed in 649 men and 230 women by the patient-oriented composite outcome (POCO, a composite of any death, any myocardial infarction [MI], and any revascularization). We applied inverse-probability weighting (IPW) based on propensity scores to account for differences at baseline between women and men (age, hypertension, hyperlipidemia, diabetes mellitus, lesion location, clinical status, FFR, Reference diameter, Diameter stenosis, lesion length). The median follow-up duration was 1855 days (745–1855 days).

Results

Median FFR values were 0.88 (0.83–0.93) in men and 0.89 (0.85–0.94) in women, respectively. The occurrences of POCO were significantly high in men compared with that in women (10.5% vs 4.2%, P=0.007). Kaplan–Meier analysis revealed that women had a significantly lower risk of POCO (χ2=7.2, P=0.007). Multivariate COX regression analysis revealed that age, male, diabetes mellitus, diameter stenosis, lesion length, and coronary flow reserve were independent predictors of POCO. After applying IPW, the hazard ratio of male for POCO was 2.20 (95% confidence interval: 1.12 to 4.33, P=0.023).

Conclusion

This large multinational study reveals that long-term outcome differs between women and men in favour of women after FFR-guided revascularization deferral.

Acknowledgement/Funding

None