Journal of Medical Physics
: 2016  |  Volume : 41  |  Issue : 1  |  Page : 71-

In regard to “Setup error analysis in helical tomotherapy based image-guided radiation therapy treatments”

Slav Yartsev 
 London Regional Cancer Program, London Health Sciences Centre, London, Ontario, Canada

Correspondence Address:
Slav Yartsev
London Regional Cancer Program, London Health Sciences Centre, 790 Commissioners Road East, London, ON

How to cite this article:
Yartsev S. In regard to “Setup error analysis in helical tomotherapy based image-guided radiation therapy treatments”.J Med Phys 2016;41:71-71

How to cite this URL:
Yartsev S. In regard to “Setup error analysis in helical tomotherapy based image-guided radiation therapy treatments”. J Med Phys [serial online] 2016 [cited 2022 Jan 26 ];41:71-71
Available from:

Full Text


I read with interest the paper of Dr. Thondykandy et al. in the latest issue of your journal.[1] The current rapid introduction of pretreatment (tomotherapy megavoltage computed tomography (CT) and cone-beam CT on Varian and Elekta linacs) and in-treatment (CyberKnife, ViewRay) image guidance (IG) needs a careful assessment of these technologies in order to establish their optimal usage. The authors investigated the position correction shifts for 102 patients treated with helical tomotherapy using megavoltage CT for matching the patient position of the day to the planning CT study. There is no information on how planning CT studies were obtained, but for patients with a significant target motion, the usage of fast helical CT studies for planning may be suboptimal for IG purpose, and untagged average studies should be recommended. Systematic and random errors were evaluated and used for treatment margin calculation as per van Herk et al.[2] However, the authors' concluded that the clinical margins used in their hospital were adequate enough for the brain, head and neck, and lung cancer patients while being out of clinical margins for the pelvis and cervical spine injury patients, may be confusing. The margins calculated by Thondykandy et al.[1] correspond only to a part of the total planning target volume (PTV) construction accounting for interfraction motion as explained in BIR publication.[3] These margin values can be used to account for positioning errors if no pretreatment IG is performed.

We need to establish comprehensive recommendations of the PTV margins that include disease site, planning CT parameters, immobilization devices, patient preparation protocols, imaging schedules (no-IG, IG for a limited number of fractions, daily IG), and patient-specific features. The latter is an important factor that can personalize margins. In the case of prostate cancer, Piotrowski et al. have shown that daily IG is needed for obese patients while the patients with body mass index <30 will benefit from IG procedures performed only during a few first treatment fractions.[4] A limited number of pretreatment IG sessions presents as an interesting compromise that allows for savings on labor, time, and imaging dose while taking into account specific information about target motion with the construction of personalized margins for the subsequent fractions without IG.[5]

Compiling a clearly defined instructions for IG procedures and corresponding PTV margins needs a multi-institutional collaboration (task group, workshop, or a special issue of J Med Phys) followed by a careful analysis of clinical outcomes for robust evaluation.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.


1Thondykandy BA, Swamidas JV, Agarwal J, Gupta T, Laskar SG, Mahantshetty U, et al. Setup error analysis in helical tomotherapy based image-guided radiation therapy treatments. J Med Phys 2015;40:233-9.
2van Herk M, Remeijer P, Rasch C, Lebesque JV. The probability of correct target dosage: Dose-population histograms for deriving treatment margins in radiotherapy. Int J Radiat Oncol Biol Phys 2000;47:1121-35.
3BIR Working Party. Geometric Uncertainties in Radiotherapy: Defining the Planning Target Volume. London, UK: British Institute of Radiology; 2003.
4Piotrowski T, Kaczmarek K, Jodda A, Ryczkowski A, Bajon T, Rodrigues G, et al. Image guidance procedures in radiotherapy for prostate cancer and influence of body mass index. J Radiother Pract 2014;13:410-7.
5Yeung TP, Yartsev S, Rodrigues G, Bauman G. Evaluation of image-guidance strategies with helical tomotherapy for localised prostate cancer. J Med Imaging Radiat Oncol 2011;55:220-8.