open access
Setup uncertainties and PTV margins at different anatomical levels in intensity modulated radiotherapy for nasopharyngeal cancer
open access
Abstract
Aim
To determine the systematic error (∑), random error (σ) and derive PTV margin at different levels of the target volumes in Nasopharyngeal Cancer (NPC).
Materials and methods
A retrospective offline review was done for patients who underwent IMRT for NPC from June 2015 to May 2016 at our institution.
Alternate day kV images were matched with digitally reconstructed radiographs to know the setup errors. All radiographs were matched at three levels – the clivus, third cervical (C3) and sixth cervical (C6) vertebra. The shifts in positions along the vertical, longitudinal and lateral axes were noted and the ∑ and σ at three levels were calculated. PTV margins were derived using van Herk's formula.
Results
Twenty patients and 300 pairs of orthogonal portal films were reviewed. The ∑ for the clivus, C3 and C6 along vertical, longitudinal and lateral directions were 1.6 vs. 1.8 vs. 2[[ce:hsp sp="0.25"/]]mm; 1.2 vs. 1.4 vs. 1.4[[ce:hsp sp="0.25"/]]mm and 0.9 vs. 1.6 and 2.3[[ce:hsp sp="0.25"/]]mm, respectively. Similarly, the random errors were 1.1 vs. 1.4 vs. 1.8[[ce:hsp sp="0.25"/]]mm; 1.1 vs. 1.2 vs. 1.2[[ce:hsp sp="0.25"/]]mm and 1.2 vs. 1.3 vs. 1.6[[ce:hsp sp="0.25"/]]mm. The PTV margin at the clivus was 4.4[[ce:hsp sp="0.25"/]]mm along the vertical, 4[[ce:hsp sp="0.25"/]]mm along the longitudinal direction and 3.2[[ce:hsp sp="0.25"/]]m in the lateral direction. At the C3 level, it was 5.5[[ce:hsp sp="0.25"/]]mm in the vertical, 5[[ce:hsp sp="0.25"/]]mm in the lateral direction and 4.4[[ce:hsp sp="0.25"/]]mm in the longitudinal direction. At the C6 level, it was 6.4[[ce:hsp sp="0.25"/]]mm in the vertical, 6.9[[ce:hsp sp="0.25"/]]mm in the lateral direction and 4.4[[ce:hsp sp="0.25"/]]mm in the longitudinal direction.
Conclusion
A differential margin along different levels of target may be necessary to adequately cover the target.
Abstract
Aim
To determine the systematic error (∑), random error (σ) and derive PTV margin at different levels of the target volumes in Nasopharyngeal Cancer (NPC).
Materials and methods
A retrospective offline review was done for patients who underwent IMRT for NPC from June 2015 to May 2016 at our institution.
Alternate day kV images were matched with digitally reconstructed radiographs to know the setup errors. All radiographs were matched at three levels – the clivus, third cervical (C3) and sixth cervical (C6) vertebra. The shifts in positions along the vertical, longitudinal and lateral axes were noted and the ∑ and σ at three levels were calculated. PTV margins were derived using van Herk's formula.
Results
Twenty patients and 300 pairs of orthogonal portal films were reviewed. The ∑ for the clivus, C3 and C6 along vertical, longitudinal and lateral directions were 1.6 vs. 1.8 vs. 2[[ce:hsp sp="0.25"/]]mm; 1.2 vs. 1.4 vs. 1.4[[ce:hsp sp="0.25"/]]mm and 0.9 vs. 1.6 and 2.3[[ce:hsp sp="0.25"/]]mm, respectively. Similarly, the random errors were 1.1 vs. 1.4 vs. 1.8[[ce:hsp sp="0.25"/]]mm; 1.1 vs. 1.2 vs. 1.2[[ce:hsp sp="0.25"/]]mm and 1.2 vs. 1.3 vs. 1.6[[ce:hsp sp="0.25"/]]mm. The PTV margin at the clivus was 4.4[[ce:hsp sp="0.25"/]]mm along the vertical, 4[[ce:hsp sp="0.25"/]]mm along the longitudinal direction and 3.2[[ce:hsp sp="0.25"/]]m in the lateral direction. At the C3 level, it was 5.5[[ce:hsp sp="0.25"/]]mm in the vertical, 5[[ce:hsp sp="0.25"/]]mm in the lateral direction and 4.4[[ce:hsp sp="0.25"/]]mm in the longitudinal direction. At the C6 level, it was 6.4[[ce:hsp sp="0.25"/]]mm in the vertical, 6.9[[ce:hsp sp="0.25"/]]mm in the lateral direction and 4.4[[ce:hsp sp="0.25"/]]mm in the longitudinal direction.
Conclusion
A differential margin along different levels of target may be necessary to adequately cover the target.
Keywords
Nasopharyngeal cancer; PTV margin; Setup error


Title
Setup uncertainties and PTV margins at different anatomical levels in intensity modulated radiotherapy for nasopharyngeal cancer
Journal
Reports of Practical Oncology and Radiotherapy
Issue
Pages
396-401
Published online
2017-09-01
DOI
10.1016/j.rpor.2017.07.005
Bibliographic record
Rep Pract Oncol Radiother 2017;22(5):396-401.
Keywords
Nasopharyngeal cancer
PTV margin
Setup error
Authors
Milan Anjanappa
Malu Rafi
Saju Bhasi
Rejnish Kumar
Kainickal Cessal Thommachan
Tapesh Bhattacharya
Kunnambath Ramadas