Objective To explore the ArcCHECK system-based methods for dose verification of ultra-long target for cervical cancer VMAT so as to assure the precision of cervical cancer radiotherapy.Methods A total of 33 patients with ultra-long target(target length≥26 cm)admitted to some hospital for cervical cancer VMAT from 2021 to 2023 were selected retrospectively,and radiotherapy plans were designed for the patients with VMAT technology and verified dosimetrically with different methods.Firstly,the dose distribution data were collected respectively at 5 and 8 cm away from the center of the ArcCHECK system along the bed exit direction,and enrolled into Group Test 1 and Test 2 respectively.Then the ArcCHECK system was flipped 180°,and the dose distribution data were acquired at 8 cm away from the center along the bed exit direction and included into Group Test 3.Dose merging between Group Test 2 and Test 3 with the Merge function was carried out to obtain the dose distribution data which were divided into Group Test 4.The monitor units of Group Test 1,2 and 4 were summarized,and difference analyses were performed on the length of the target area,detection point and irradiation time.Group Test 1,2 and 4 were compared in terms of γ pass rate,normalized dose deviation,confidence limit(CL)of pass rate and acceptance rate(γ pass rate≥95%and γ pass rate≥90%).Spearman's correlation coefficient was used to correlate the parameters such as maximum transverse diameter,length,volume and monitor unit of the target area and expected execution time of the plan.SPSS 19.0 software was used for statistical analysis.Results Group Test 1,2 and 4 had the monitor unit being(758.76±107.63)MU,and had statistically significant differences in length of the target area,detection point and irradiation time(P<0.01).In Group Test 4 γ pass rate under 2%/2 mm criterion did not reach 90%,and in Group Test 1 and 2 γ pass rates under 3%/3 mm and 3%/2 mm criteria both amounted to 95%.Group Test 1,2 and 4 had statistically significant differences in γ pass rate and normalized dose deviation(all P<0.05).In Group Test 1 there were more than 90%of the verification results where γ pass rate≥95%and more than 95%where γ pass rate≥90%under 3%/3 mm criterion.The monitor unit was positively correlated with the maximum transverse diameter,length and volume of the target area,respectively(0.337≤r≤0.568,P<0.05),and the expected execution time of the plan was positively correlated with the volume and monitor unit of the target area,respectively(0.457≤r≤0.517,P<0.01).Conclusion The dose verification method with the target at 5 cm away from the center along the bed exit direction can be applied clinically with high feasibility to the dose verification during the radiotherapy of the cervical cancer VMAT patients with ultra-long target,with the safety of the verification devices ensured effectively.

Objective To explore the ArcCHECK system-based methods for dose verification of ultra-long target for cervical cancer VMAT so as to assure the precision of cervical cancer radiotherapy.Methods A total of 33 patients with ultra-long target(target length≥26 cm)admitted to some hospital for cervical cancer VMAT from 2021 to 2023 were selected retrospectively,and radiotherapy plans were designed for the patients with VMAT technology and verified dosimetrically with different methods.Firstly,the dose distribution data were collected respectively at 5 and 8 cm away from the center of the ArcCHECK system along the bed exit direction,and enrolled into Group Test 1 and Test 2 respectively.Then the ArcCHECK system was flipped 180°,and the dose distribution data were acquired at 8 cm away from the center along the bed exit direction and included into Group Test 3.Dose merging between Group Test 2 and Test 3 with the Merge function was carried out to obtain the dose distribution data which were divided into Group Test 4.The monitor units of Group Test 1,2 and 4 were summarized,and difference analyses were performed on the length of the target area,detection point and irradiation time.Group Test 1,2 and 4 were compared in terms of γ pass rate,normalized dose deviation,confidence limit(CL)of pass rate and acceptance rate(γ pass rate≥95%and γ pass rate≥90%).Spearman's correlation coefficient was used to correlate the parameters such as maximum transverse diameter,length,volume and monitor unit of the target area and expected execution time of the plan.SPSS 19.0 software was used for statistical analysis.Results Group Test 1,2 and 4 had the monitor unit being(758.76±107.63)MU,and had statistically significant differences in length of the target area,detection point and irradiation time(P<0.01).In Group Test 4 γ pass rate under 2%/2 mm criterion did not reach 90%,and in Group Test 1 and 2 γ pass rates under 3%/3 mm and 3%/2 mm criteria both amounted to 95%.Group Test 1,2 and 4 had statistically significant differences in γ pass rate and normalized dose deviation(all P<0.05).In Group Test 1 there were more than 90%of the verification results where γ pass rate≥95%and more than 95%where γ pass rate≥90%under 3%/3 mm criterion.The monitor unit was positively correlated with the maximum transverse diameter,length and volume of the target area,respectively(0.337≤r≤0.568,P<0.05),and the expected execution time of the plan was positively correlated with the volume and monitor unit of the target area,respectively(0.457≤r≤0.517,P<0.01).Conclusion The dose verification method with the target at 5 cm away from the center along the bed exit direction can be applied clinically with high feasibility to the dose verification during the radiotherapy of the cervical cancer VMAT patients with ultra-long target,with the safety of the verification devices ensured effectively.

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