Clinical application of SIOPE guidelines in target definition for craniospinal irradiation in children

Objective According to the SIOPE (2018) guidelines, the whole brain target of patients undergoing craniospinal irradiation was delineated and the underdose of sub-structures which were not delineated in original plan was verified, aiming to provide evidence for the risk of whole brain recurrence of craniospinal irradiation and accumulate experience for the clinical application of SIOPE guidelines. Methods Twelve children who underwent craniospinal irradiation were selected. As per the SIOPE guidelines in 2018, the CTVsub (including the superior orbital fissure, foramen rotundum, foramen ovale, jugular foramen, hypoglossal canal, internal auditory meatus and optic nerve) were delineated based on the original CTVold (whole brain plus sieve plate) to form PTVnew. A rough PTV (PTVrough) was formed by giving a margin of 15 mm forward-downward (skull base) and 3 mm in the other directions. CRTold and IMRTold plans were designed based on PTVold. CRTnew and IMRTnew plans were designed based on PTVnew. CRTrough plan was designed based on PTVrough. The omission of sub-structures based on CTVold and the underdose of CTVsub in each plan were evaluated. Results A total of 78.6% of superior orbital fissure, 71.99% of foramen rotundum, 96.76% of foramen ovale, 88.5% of jugular foramen, 97.71% of hypoglossal canal, 99.48% of internal auditory meatus and 100% of optic nerve volume were missed based on CTVold. The target dose coverage of CTVsub based on CRTold and IMRTold was only 91.70% and 89.83%, respectively. The underdose was observed in 16.66%, 3.57%, 20.83%, 1.78% and 1.19% of sub-structures in CRTold, CRTnew, IMRTold, IMRTnew and CRTrough plans, respectively. Of the underdose of all sub-structures, 38.36% and 46.58% occurred in CRTold and IMRTold plans, respectively. Among them, the least and the most significant underdose occurred in foramen rotundum (0%) and foramen ovale (36.66%), respectively. Conclusions As per the SIOPE guidelines, traditional brain tissue delineation (including sieve plate) is likely to omit part of the target during the cranial target definition of craniospinal irradiation. The most significant underdose occurs in foramen ovale, and more obvious in the IMRT plan. The plan based on the delineation of sub-structures can significantly improve the underdose. When AP-PA irradiation is adopted, a rough PTV is recommended to obtain approximate target dose coverage and organ of risk sparing, whereas it requires further clinical verification. Key words: SIOPE guideline; Craniospinal irradiation; Target definition; Sub-structures