Goodarzi A H, Nikufar A R, Boluri B, Mahdavi S R, Ghazikhanloo Sani K,
Volume 64, Issue 11 (7 2006)
Abstract
Background: During breast three fields radiotherapy, the problem is that the divergency of the field interferes with matching the edges. So the matching point of these supraclav and tangential field will suffer from over-dose and under-dose. To prevent these these divergency, a half- block is often applied at supracluv field. Also in some techniques like collimator and couch rotation, corner blocks and custom blocks are applied at tangential field which it renders its own problem. Hence, this research employ half-block in all three different radiotherapy scheme to some how radiate the cancerous tissue more appropriately to lessen the over exposure and yet deliver the needed dose to the tissue.
Methods: Ten breast cancer patients of Sohadaye Haftome-Tir hospital were considered for this study. The divegency of the fields at the matching point was blocked by using a half-block application and a slope, under patients. Dosimetery was measured by TLD at desired location on the skin before and after the half-block application. The measurement was carried out at 2 groups under 2 different irradiation methods (SSD, SAD).
Results: Dosimetery showed that the mean over-dose values at SSD method before applying half–block was 151% which reduced to 97% after half–block application, and in the SAD method the under-dose was improved from 41% to 80%.
Conclusion: Half–block can solve adjacent filelds problem efficiently, and since making the half-block at low cost is easily possible at any radiotherapy center, it is suggested to use block more often.
