Arterial flow redistribution by coil embolization has become common clinical practice during the diagnostic work-up before transarterial radioembolization (RE). However, there is still limited knowledge on how redis- tribution occurs, and debate is ongoing regarding indica- tions, outcomes’ evaluation and optimal time interval between embolization and treatment. The paper by Asultan provides some interesting information in the attempt to answer to some of these open questions [1]. How Should Flow Redistribution be Assessed? Compared to previous studies [2–4], Asultan et al. [1] performed qualitative and quantitative evaluation of flow redistribution, measuring the post-treatment activity dis- tributed to the coil-embolized (dependent) segment relative to the other segments, and demonstrated that qualitative evaluation overestimates the success of redistribution (70%) compared to the quantitative measurements (57% success rated using a cut-off ratio of 0.7). Considering the importance of the tumour radiation-absorbed dose after RE [5], this overestimation may impact treatment results. Thus, qualitative assessment should be recommended and implemented. Are Results Affected by Factors Such as Vascular Anatomy, Tumour Type and Location? Flow redistribution is based on the activation of intraseg- mental and interlobar liver arterial connections following arterial embolization [2]; these connections are variable, depending upon vascular anatomy and tumour type and location. Asultan et al. [1] reported a lower success rate of redistribution when embolizing parasitized arteries (suc- cess rate 0–33%), possibly due to the recruitment of other branches when proximal embolization was performed. Therefore, flow redistribution of parasitized extrahepatic arteries should be performed with caution, it requires distal embolization, as close to the tumour as possible, and it may cause exclusion from RE treatment when redistribution is considered insufficient. Highest success rate of redistribution was reported after embolization of segment IV hepatic artery [1]. As opposite, Ezponda et al. [4] pointed out that in centrally located tumours (segments IV and I), when dealing with vessels in watershed in-between right and left hepatic branches, the success of redistribution is reduced, since it is difficult to predict which collateral vessels are going to re-perfuse the dependent territory. This discrepancy in observations is related to the different population included in these two studies. While Ezponda et al. [4] predominantly included primary tumours requiring unilobar injections, Asultan et al. [1] mainly included metastatic disease and bilobar treatments, in which the final result would not be affected by the fact that redistribution could occur from either right or left side. Asultan et al. [1] also suggested differences in results depending upon the tumour type, reporting lower success rates in patients with neuroendocrine metastases, due to the presence of large and hypervascular lesions in whom flow redistribution could be poor and unpredictable. Since the series was limited, further investigation is needed. Which is the Optimal Time Interval Between Redistribution and RE Treatment? Initially, it was suggested that the recruitment of collaterals after embolization could require several days [2, 3]. More recently, same-day diagnostic work-up has been evaluated, and Ezponda et al. [4] demonstrated that flow redistribution occurs early after embolization and same-day treatment is feasible and effective. The study by Asultan et al. [1] goes one step further, showing that patients treated on the same day had higher activity ratios, compared to patients who underwent treatment two or more days (mean 10 days) after the diagnostic work-up, although the difference was not statistically significant. We may postulate that, partic- ularly in hypervascular disease and for parasitized arteries, a longer interval between embolization and treatment could allow new arterial branches to be recruited, thus reducing the chances for controlling flow redistribution and con- centrating the radiation activity through the same collat- erals that were identified during the diagnostic work-up. Therefore, same-day procedure should not only be con- sidered feasible, but it should be even recommended when flow redistribution is needed. Conclusions Flow redistribution is a safe and effective procedure, able to reduce the number of injection points and avoid non- target extrahepatic radiation. However, it requires a in- depth knowledge of the possible intra- and extrahepatic arterial connections, and it should be performed only when strictly needed, since it may be tricky and unpredictable, particularly in bulky and hypervascular tumours and when parasitized and centrally located arteries are involved.
The Efficacy of Coil Embolization to Obtain Intrahepatic Redistribution in Radioembolization: Qualitative and Quantitative Analyses
Bargellini I.Primo
;Lorenzoni G.;Cervelli R.;Cioni R.
2020-01-01
Abstract
Arterial flow redistribution by coil embolization has become common clinical practice during the diagnostic work-up before transarterial radioembolization (RE). However, there is still limited knowledge on how redis- tribution occurs, and debate is ongoing regarding indica- tions, outcomes’ evaluation and optimal time interval between embolization and treatment. The paper by Asultan provides some interesting information in the attempt to answer to some of these open questions [1]. How Should Flow Redistribution be Assessed? Compared to previous studies [2–4], Asultan et al. [1] performed qualitative and quantitative evaluation of flow redistribution, measuring the post-treatment activity dis- tributed to the coil-embolized (dependent) segment relative to the other segments, and demonstrated that qualitative evaluation overestimates the success of redistribution (70%) compared to the quantitative measurements (57% success rated using a cut-off ratio of 0.7). Considering the importance of the tumour radiation-absorbed dose after RE [5], this overestimation may impact treatment results. Thus, qualitative assessment should be recommended and implemented. Are Results Affected by Factors Such as Vascular Anatomy, Tumour Type and Location? Flow redistribution is based on the activation of intraseg- mental and interlobar liver arterial connections following arterial embolization [2]; these connections are variable, depending upon vascular anatomy and tumour type and location. Asultan et al. [1] reported a lower success rate of redistribution when embolizing parasitized arteries (suc- cess rate 0–33%), possibly due to the recruitment of other branches when proximal embolization was performed. Therefore, flow redistribution of parasitized extrahepatic arteries should be performed with caution, it requires distal embolization, as close to the tumour as possible, and it may cause exclusion from RE treatment when redistribution is considered insufficient. Highest success rate of redistribution was reported after embolization of segment IV hepatic artery [1]. As opposite, Ezponda et al. [4] pointed out that in centrally located tumours (segments IV and I), when dealing with vessels in watershed in-between right and left hepatic branches, the success of redistribution is reduced, since it is difficult to predict which collateral vessels are going to re-perfuse the dependent territory. This discrepancy in observations is related to the different population included in these two studies. While Ezponda et al. [4] predominantly included primary tumours requiring unilobar injections, Asultan et al. [1] mainly included metastatic disease and bilobar treatments, in which the final result would not be affected by the fact that redistribution could occur from either right or left side. Asultan et al. [1] also suggested differences in results depending upon the tumour type, reporting lower success rates in patients with neuroendocrine metastases, due to the presence of large and hypervascular lesions in whom flow redistribution could be poor and unpredictable. Since the series was limited, further investigation is needed. Which is the Optimal Time Interval Between Redistribution and RE Treatment? Initially, it was suggested that the recruitment of collaterals after embolization could require several days [2, 3]. More recently, same-day diagnostic work-up has been evaluated, and Ezponda et al. [4] demonstrated that flow redistribution occurs early after embolization and same-day treatment is feasible and effective. The study by Asultan et al. [1] goes one step further, showing that patients treated on the same day had higher activity ratios, compared to patients who underwent treatment two or more days (mean 10 days) after the diagnostic work-up, although the difference was not statistically significant. We may postulate that, partic- ularly in hypervascular disease and for parasitized arteries, a longer interval between embolization and treatment could allow new arterial branches to be recruited, thus reducing the chances for controlling flow redistribution and con- centrating the radiation activity through the same collat- erals that were identified during the diagnostic work-up. Therefore, same-day procedure should not only be con- sidered feasible, but it should be even recommended when flow redistribution is needed. Conclusions Flow redistribution is a safe and effective procedure, able to reduce the number of injection points and avoid non- target extrahepatic radiation. However, it requires a in- depth knowledge of the possible intra- and extrahepatic arterial connections, and it should be performed only when strictly needed, since it may be tricky and unpredictable, particularly in bulky and hypervascular tumours and when parasitized and centrally located arteries are involved.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
