Dosimetric study of hippocampus avoidance in multi-center craniospinal irradiation based on volumetric modulated arc therapy with a linear accelerator
Objective To explore the feasibility of multicenter hippocampal-protected craniospinal radiotherapy using volu-metric modulated arc therapy(VMAT)based on a linear accelerator.Methods Nine patients who underwent surgery and chemotherapy at the Cancer Hospital of Affiliated Hospital of Guangdong Medical University from January 1,2022 to De-cember 31,2022,and were required to undergo whole brain and spinal cord radiation therapy without lesion metastasis,were selected as the study subjects.There were 5 females and 4 males.The average age was(12.13±3.91)years old.For each patient,two radiation treatment centers were planned,and standard VMAT(S-VMAT)plans and hippocampal-protected VMAT(HA-VMAT)plans were designed respectively.Plan evaluation and dose analysis were conducted for both types of plans.The t-test was used to evaluate the homogeneity index(HI),conformity index(CI),gradiend index(GI),the planned target volume(PTV)with maximum dose(PTVmax),mean dose(PTVmean),the proportion of 100％prescription dose to body PTV volume(V100％),and the dose to other normal tissues such as the hippocampus.Results The HI,CI,and GI value of the S-VMAT plan were 0.06±0.02,0.97±0.05,and 2.15±0.23,respectively,com-pared with the HA-VMAT plan's values of 0.11±0.12,0.95±0.03,and 3.59±0.67.The differences were statistically significant,with t-values of-3.568,-2.380,and-5.421,and P-values of＜0.001,0.032,and＜0.001,respective-ly.The PTVmax,PTVmean,and V100％values of the S-VMAT plan were(39.07±1.00)Gy,(38.33±1.10)Gy,and(98.33±1.12)％,respectively,compared with the HA-VMAT plan's values of(41.00±0.33)Gy,(37.65±0.88)Gy,and(95.73±0.88)％.The differences were statistically significant,with t-values of-7.439,-2.312,and-2.975,and P-values of 0.003,0.033,and 0.035,respectively.The maximum and average doses to the hippocampus in the S-VMAT plan were(38.51±0.48)and(37.59±0.29)Gy,respectively,while those in the HA-VMAT plan were(14.88±0.34)and(9.74±0.24)Gy.The differences were statistically significant,with the t-values were-4.432 and-4.457,respectively,with all P＜0.001.The average doses to the liver,trachea,throat,and mouth of the S-VMAT plan was lower than those of the HA-VMAT plan.The differences were statistically significant,with the t-values were-3.008,-4.324,-2.901,and-3.325,respectively,with P-values of 0.015,0.001,0.046,and 0.025.The maxi-mum dose and average dose to the eyeball of the S-VMAT plan,as well as the average dose to the right kidney and pan-creas,were higher than those of the HA-VMAT plan.The differences were statistically significant,with the t-values were-1.245,-1.689,1.592,and 5.122,respectively,and the P-values were 0.047,0.049,0.042,and＜0.001.Conclusion The use of linear accelerator VMAT multi center radiotherapy technology can reduce the dose to the hippo-campus while ensuring target coverage,homogeneity,conformability,and high-dose fall-off during whole brain and spinal cord radiotherapy,thereby achieving the protection of cognitive function in patients.
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