open access

Vol 22, No 5 (2017)
Original research articles
Published online: 2017-09-01
Submitted: 2017-01-24
Get Citation

Setup uncertainties and PTV margins at different anatomical levels in intensity modulated radiotherapy for nasopharyngeal cancer

Milan Anjanappa, Malu Rafi, Saju Bhasi, Rejnish Kumar, Kainickal Cessal Thommachan, Tapesh Bhattacharya, Kunnambath Ramadas
DOI: 10.1016/j.rpor.2017.07.005
·
Rep Pract Oncol Radiother 2017;22(5):396-401.

open access

Vol 22, No 5 (2017)
Original research articles
Published online: 2017-09-01
Submitted: 2017-01-24

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.

Get Citation

Keywords

Nasopharyngeal cancer; PTV margin; Setup error

About this article
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

Vol 22, No 5 (2017)

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

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