Journal Thoracic Oncology

Abstracts Journal of Thoracic Oncology • Volume 12 Issue S1 January 2017
PUB045 THE CAPABILITY AND CHARACTERISTIC OF HELICAL
TOMOTHERAPY AT SPARING HIPPOCAMPUS IN PROPHYLACTIC
CRANIAL IRRADIATION
Jian Zhu, Tong Bai, Jiabing Gu, Lu Fu, Yong Yin
Radiation Oncology Physics, Shandong Cancer Hospital & Institute, Jinan/China
Background: Prophylactic cranial irradiation (PCI) is efficient at avoiding lung
cancer intra-cranial metastasis. However, PCI may cause neurocognitive
impairment because of the hippocampal toxicities. It is reported that
hippocampus V7.3Gy > 40% is associated with long-term impairment.
Considering helical tomotherapy (HT) has higher modulation capabilities, we
investigated the capability and characteristic of HT at sparing hippocampus in
PCI. Methods: Six anonymous patients previously treated with whole-brain
radiotherapy with hippocampal sparing were reviewed. Under T1-weighted
MRI, the hippocampus was contoured, and hippocampal avoidance regions
(HAR) were created using a 5-mm volumetric expansion around the
hippocampus. The prescription dose 3.0Gy * 10 fractions was assigned on
planning target volume (PTV) which was defined as whole-brain minus HAR
and bilateral hippocampus. During the HT plan optimization process,
evaluation factors of PTV and other dosimetry factors were recorded
whenever the mean dose of hippocampus decreased by every 2Gy. Results:
The average of six HT plans without hippocampus sparing constraints are as
follow: hippo_Dmean 27.33±2.22Gy, HAR_Dmean 28.62±1.84Gy, PTV_Dmean
30.77±0.74Gy, PTV_D2% 30.93±0.61Gy, PTV_D98% 29.86±0.34Gy, PTV_V30Gy
0.97±0.02% and conformal index (CI) 0.85±0.03, homogeneity index (HI)
0.04±0.01, plan delivery duration 13.70±1.92min. When V7.3Gy of bilateral
hippocampus achieved 40%, the average dosimetry factors are as follow:
hippo_Dmean 8.26±0.24Gy, HAR_Dmean 12.88±1.27Gy, PTV_Dmean
31.00±0.47Gy, PTV_D2% 31.97±0.63Gy, PTV_D98% 21.74±5.44Gy, PTV_V30Gy
0.93±0.02%, CI 0.77±0.08, HI 0.35±0.20, plan delivery duration 21.30±4.97min.
Conclusion: During the process of hippocampus sparing, HAR_Dmean
decreased linearly as well. However, dosimetry variation of PTV presented
three steps: plateau region (> 20Gy), gradient region (~20 to ~10Gy) and falling
region (