Comparison of Unblocked, Directionally Blocked and Full Blocked Plans in Helical Tomotherapy for Breast Cancer Radiotherapy

Introduction: The doses received by the contralateral breast, lung and heart either directionally or full blocked techniques in Hi-Art Tomotherapy systems in partial or whole breast radiotherapy has been studied. Method: In 20 breast cancer patients 3 plans with non-blocked, directionally blocked and full blocked methods were designed in Hi-Art planning system. In all planning method the dose received by the contralateral breast, the heart volume percentages V5 and V30 and the lung volume percentages V5 and V20 were compared. Results: The mean doses received by contralateral breast were 6.24 Gy (4.50-8.74 Gy) in unblocked group 3.85 Gy (2.08-5.81 Gy) in directionally blocked group and 0.99 Gy (0.69-1.39 Gy) in full blocked group. The mean Lung V5 values were 98% (79-100%) in unblocked group and it was 98% (91-100%) in directionally blocked group while it was 93% (89-97%) in full blocked group. The mean V20 values were 16% (7-23%), 20% (17-24%) and 22% (18-28%) in unblocked, directionally blocked and full blocked groups respectively. The mean Heart V5 value 100% (99-100%) in unblocked group, and it was 99% (85-100%) in directionally blocked group while it was 92% (73- 100%) in full blocked group. The mean V30 values were 11% (2-25%), 6% (0-12%) and 9% (1-22%) in unblocked, directionally blocked and full blocked groups respectively. The mean beam-on time was 261.6 s (237.6-318.2) for unblocked, 277.9 s (237.6-338.5) for directionally blocked and 314.2 s (272.6-429.1) full blocked group. The mean numbers of MUs were 3712 (3353-4536) for unblocked, 3951 (3357-4834) for directionally blocked and 4506 (3866- 6168) for full blocked group. In full blocked group both beam on time and MU values were higher. Conclusion: We propose that further efforts needed to reduce low dose volumes to normal tissues, meanwhile when using directionally and full blocked plans all parameters should be considered together.