Analysis of Planning Target Volume Margin on Different Immobilization Devices for Radiotherapy in Carcinoma Breast

Abstract

Aim: This study was conducted to analyze and compare the Planning Target Volume (PTV) margin from different immobilization devices using different formulae in carcinoma breast radiotherapy.
Methodology: Patients with carcinoma breast who underwent adjuvant radiotherapy with four different immobilization devices were identified, and positional errors were assessed during pre-radiotherapy verification, using CBCT. Based on these errors, PTV margins were calculated using Van Herk, Stroom and ICRU 62 formulae.
Results: The calculated PTV margin for mould using van Herk, Stroom and ICRU formulae was (9.0, 7.6 and 4.8mm) ML direction, (12.0, 10.0 and 7.0mm) CC direction, (7.7, 6.5 and 4.2mm) AP direction, and for vacloc (9.2,7.8,5.0), (6.5,5.6,3.9) and (8.2,7,4.5) mm for ML, CC, and AP respectively. The lowest margins were noted with ABC (5.5,4.5,3.6) in ML, (7.0,6.0, 4) in CC, (5.3,4.4, 2.7) mm in AP. Whereas breast board the margin was little large with (10.6,9.1, 6.1) ML, (12.7,10.8,7.0) CC, and AP (6.3,5.3, 3.3) mm.
Conclusion: It is found that the systematic and random errors are less with gating, so the margin. In all immobilization devices large margin was observed in cranial-caudal direction mm (12.7 max and 6.5 min). Along with Van Herk, Stroom formula also be considered for margin calculation.