title: Inclined head position improves dose distribution during hippocampal-sparing whole brain radiotherapy using VMAT.
abstract: OBJECTIVE
  Hippocampal-sparing whole brain radiotherapy (HS-WBRT) aims to preserve neurocognitive functions in patients undergoing brain radiotherapy (RT). Volumetric modulated arc therapy (VMAT) involves intensity-modulated RT using a coplanar arc. An inclined head position might improve dose distribution during HS-WBRT using VMAT.
  
  
  METHODS
  This study analyzed 8 patients receiving brain RT with inclined head positioning. A comparable set of CT images simulating a non-inclined head position was obtained by rotating the original CT set. HS-WBRT plans of coplanar VMAT for each CT set were generated with a prescribed dose of 30 Gy in 10 fractions. Maximum dose to the hippocampi was limited to 16 Gy; to the optic nerve, optic chiasm, and eyeballs this was confined to less than 37.5 Gy; for the lenses to 8 Gy. Dosimetric parameters of the two different plans of 8 patients were compared with paired t-test.
  
  
  RESULTS
  Mean inclined head angle was 11.09 ± 0.73°. The homogeneity (HI) and conformity (CI) indexes demonstrated improved results, with an average 8.4 ± 10.0 % (p = 0.041) and 5.3 ± 3.9 % (p = 0.005) reduction, respectively, in the inclined vs. non-inclined position. The inclined head position had lower hippocampi Dmin (10.45 ± 0.36 Gy), Dmax (13.70 ± 0.25 Gy), and Dmean (12.01 ± 0.38 Gy) values vs. the non-inclined head position (Dmin = 12.07 ± 1.07 Gy; Dmax = 15.70 ± 1.25 Gy; Dmean = 13.91 ± 1.01 Gy), with 12.8 ± 8.9 % (p = 0.007), 12.2 ± 6.8 % (p = 0.003), and 13.2 ± 7.2 % (p = 0.002) reductions, respectively. Mean Dmax for the lenses was 6.34 ± 0.72 Gy and 7.60 ± 0.46 Gy, respectively, with a 16.3 ± 10.8 % reduction in the inclined position (p = 0.004). Dmax for the optic nerve and Dmean for the eyeballs also decreased by 7.0 ± 5.9 % (p = 0.015) and 8.4 ± 7.2 % (p = 0.015), respectively.
  
  
  CONCLUSIONS
  Inclining the head position to approximately 11° during HS-WBRT using VMAT improved dose distribution in the planning target volume and allowed lower doses to the hippocampi and optic apparatus.
authors.affiliation: Departments of Radiation Oncology, Seoul National University College of Medicine, Seoul, Republic of Korea.
authors.forename: Kyung Su
authors.initials: KS
authors.lastname: Kim
authors.affiliation: Departments of Radiation Oncology, Seoul National University College of Medicine, Seoul, Republic of Korea.
authors.forename: Suk-Jin
authors.initials: SJ
authors.lastname: Seo
authors.affiliation: Departments of Radiation Oncology, Seoul National University College of Medicine, Seoul, Republic of Korea.
authors.forename: Jaegi
authors.initials: J
authors.lastname: Lee
authors.affiliation: Department of Radiation Oncology, Seoul National University Bundang Hospital, 166 Gumiro, 13620, Seongnamsi, Kyeonggido, Republic of Korea.
authors.forename: Jin-Yong
authors.initials: JY
authors.lastname: Seok
authors.affiliation: Department of Radiation Oncology, Seoul National University Bundang Hospital, 166 Gumiro, 13620, Seongnamsi, Kyeonggido, Republic of Korea.
authors.forename: Joo Wan
authors.initials: JW
authors.lastname: Hong
authors.affiliation: Department of Radiation Oncology, Seoul National University Bundang Hospital, 166 Gumiro, 13620, Seongnamsi, Kyeonggido, Republic of Korea.
authors.forename: Jin-Beom
authors.initials: JB
authors.lastname: Chung
authors.affiliation: Departments of Radiation Oncology, Seoul National University College of Medicine, Seoul, Republic of Korea.
authors.forename: Eunji
authors.initials: E
authors.lastname: Kim
authors.affiliation: Departments of Radiation Oncology, Seoul National University College of Medicine, Seoul, Republic of Korea.
authors.forename: Noorie
authors.initials: N
authors.lastname: Choi
authors.affiliation: Departments of Radiation Oncology, Seoul National University College of Medicine, Seoul, Republic of Korea.|Department of Radiation Oncology, Seoul National University Bundang Hospital, 166 Gumiro, 13620, Seongnamsi, Kyeonggido, Republic of Korea.
authors.forename: Keun-Yong
authors.initials: KY
authors.lastname: Eom
authors.affiliation: Departments of Radiation Oncology, Seoul National University College of Medicine, Seoul, Republic of Korea.|Department of Radiation Oncology, Seoul National University Bundang Hospital, 166 Gumiro, 13620, Seongnamsi, Kyeonggido, Republic of Korea.
authors.forename: Jae-Sung
authors.initials: JS
authors.lastname: Kim
authors.affiliation: Departments of Radiation Oncology, Seoul National University College of Medicine, Seoul, Republic of Korea. inah228@snu.ac.kr.|Department of Radiation Oncology, Seoul National University Bundang Hospital, 166 Gumiro, 13620, Seongnamsi, Kyeonggido, Republic of Korea. inah228@snu.ac.kr.
authors.forename: In Ah
authors.initials: IA
authors.lastname: Kim
mesh_terms: D000328:Adult; D000368:Aged; D001932:Brain Neoplasms / Q000150:complications / Q000175:diagnosis / Q000532:radiotherapy*; D016371:Cranial Irradiation / Q000009:adverse effects / Q000379:methods*; D005131:Eye Injuries / Q000175:diagnosis / Q000209:etiology / Q000517:prevention & control*; D005260:Female; D006257:Head / Q000528:radiation effects; D006624:Hippocampus / Q000528:radiation effects*; D006801:Humans; D008297:Male; D008875:Middle Aged; D059351:Organ Sparing Treatments / Q000379:methods*; D056888:Patient Positioning / Q000379:methods*; D000069079:Radiation Exposure / Q000032:analysis / Q000517:prevention & control; D011832:Radiation Injuries / Q000175:diagnosis / Q000209:etiology / Q000517:prevention & control*; D011879:Radiotherapy Dosage; D050397:Radiotherapy, Intensity-Modulated / Q000009:adverse effects / Q000379:methods; D016896:Treatment Outcome
keywords: Cognitive function; Intensity-modulated radiotherapy; Metastases; Organs at risk; Survival