Journal of Medical Physics and Applied Sciences

A Comparative Dosimetric Evaluation in Carcinoma Right Breast for Convex Chest Wall, Post Breast Conservation Surgery using two Distinct Radiotherapy Techniques

Background and purposes: The aim of this research was to compare a six-beam Dynamic Multi Leaf Collimator (DMLC) technique with a restricted Tangential Volumetric Modulate Arc Therapy (tVMAT) technique for convex chest wall after Breast-Conserving Surgery (BCS).

Materials and methods: Twenty patients with carcinoma right-breast whose chest walls were convex or barrel shaped (curvature distance equal to or more than 3 cm) were selected for this study. All the patients were already treated with breast conserving surgery. Patients were prescribed 45 Gy in 25 fractions followed by boost to the tumor bed. They were planned using two different techniques including: 1) Six beam DMLC; and 2) Tangential Volumetric Arc Therapy (tVMAT). All other normal tissues and OAR including ipsilateral lung, contralateral lung, contralateral breast, heart, spinal cord, thyroid, liver and esophagus were contoured according to the RTOG guidelines. The planned volumetric dose of PTV and OARs were compared and analyzed.

Results: Hetrogeneity Index (HI) and Conformity Index (CI) were comparable for both tVMAT and DMLC. PTV volume receiving 95% of prescription dose was better in DMLC (96.41 ± 1.03) as compared to tVMAT (92.24 ± 13.31). V100% was much better in DMLC (83.91 ± 3.25) as compared to tVMAT (70.18 ± 9.74). V107% was reduced in tVMAT (1.93 ± 3.39) than DMLC (2.59 ± 5.08). D95 (Gy) was better in DMLC (96.41 ± 1.03) than tVMAT (92.24 ± 13.31). For ipsilateral lung, V10 and V5 were greatly reduced in DMLC (36.77 ± 2.31, 47.61 ± 2.84) but for tVMAT, V10 was more than the limits (43.95 ± 10.15) but V5 was well within the limit (56.94 ± 18.37). The V20, V30 and mean ipsilateral lung dose was less in DMLC. Mean heart doses in DMLC and tVMAT were 2.61 ± 0.94 and 4.57 ± 2.61. D0.03 of heart was much better in DMLC (24.72±10.70) as compared to tVMAT (32.38 ± 9.65). Mean contralateral breast dose was better in DMLC (2.39 ± 1.28) as compared to tVMAT (4.07 ± 1.70). All other OARs like contralateral lung, Esophagus, Spine, Thyroid and Liver were slightly better in DMLC as compared to tVMAT. Volume of 50% isodose line (3409.63 cc) as well as 20% isodose line (4296.85) was greatly reduced in DMLC as compared to VMAT (3626.70 versus 4750.48 respectively). Total number of monitor units required for delivering both the treatment plans were comparable.

Conclusion: Six beam DMLC treatment planning techniques are best suited for BCS patients with a more convex chest wall. The VMAT plans are more conformal and their treatment time was less but with DMLC technique, various OAR doses and integral dose to normal tissue were less. Similar technique can be applied to Left BCS cases as well.

Author(s):

Harpreet Kaur, Sangeeta Hazarika, Jefy Ninan, Ajay Khatri, Prasobh C, Pooja Handa, Kamal Verma, Sandeep Goel and Subodh Pande

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