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Comparison of geometric uncertainties between alpha cradle and thermoplastic ray cast immobilisation in abdominopelvic radiotherapy: a prospective study

Published online by Cambridge University Press:  09 November 2011

Saikat Das ,
Subhashini John ,
Paul Ravindran ,
Rajesh Isiah ,
Rajesh B ,
Selvamani Backianathan  and
Rabi Raja Singh
Saikat Das*
Affiliation:
Christian Medical College Vellore, India
Subhashini John
Affiliation:
Christian Medical College Vellore, India
Paul Ravindran
Affiliation:
Christian Medical College Vellore, India
Rajesh Isiah
Affiliation:
Christian Medical College Vellore, India
Rajesh B
Affiliation:
Christian Medical College Vellore, India
Selvamani Backianathan
Affiliation:
Christian Medical College Vellore, India
Rabi Raja Singh
Affiliation:
Christian Medical College Vellore, India
*
Correspondence to: Saikat Das, DMRT, MD, DNB, MNAMS, M-Tech, Department of Radiation Oncology, Christian Medical College Vellore, India. Tel: +91-0416-2282046. Fax: +91-0416-2235555. E-mail: drsaikatdas@gmail.com
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Abstract

Context: Setup error significantly affects the accuracy of treatment and outcome in high precision radiotherapy.

Aims: To determine total, systematic, random error and clinical target volume (CTV) to planning target volume (PTV) margin with alpha cradle (VL) and ray cast (RC) immobilisation in abdominopelvic region.

Methods and material: Setup error was compared by using digitally reconstructed radiograph (DRR) as reference image with electronic portal image (EPI) taken during the treatment. Statistical analysis used: The total errors in mediolateral (ML), craniocaudal (CC) and anteroposterior (AP) directions were compared by t-test. For systematic and random errors variance ratio test (F-statistics) was used. Margins were calculated using International Commission of Radiation Units (ICRU), Stroom’s and van Herk’s formula.

Results: A total number of 306 portal images were analysed with 144 images in RC group and 162 images in VL group. For VL, in ML, CC, AP directions systematic errors were, in cm, (0.45, 0.29, 0.41), random errors (0.48, 0.32, 0.58), CTV to PTV margins (1.24, 0.80, 1.25), respectively. For RC, systematic errors were (0.25, 0.37, 0.80), random error (0.46, 0.80, 0.33), CTV to PTV margins (0.82, 1.30, 1.08), respectively. The difference of random error in CC and AP directions were statistically significant.

Conclusions: Geometric errors and CTV to PTV margins are different in different directions. For abdomen and pelvis in VL immobilisation, the margin ranged from 8 mm to 12.4 mm and for RC it was 8.2 mm to 13 mm. Therefore, a margin of 10 mm with online correction would be adequate.

Keywords

CTV to PTV marginpelvic radiotherapyprecision radiotherapyrandom errorsystematic error
Type
Original Article
Information
Journal of Radiotherapy in Practice , Volume 11 , Issue 4 , December 2012 , pp. 239 - 248
Copyright
Copyright © Cambridge University Press 2011

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