Optimization of treatment plan for unilateral retinoblastoma patients

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University of Dar es Salaam
Although LINAC is a preferred treatment modality due to its higher dose rate, more uniform dose and gives electron beam of various energies. ORCI is still using 60Co for treatment of all cancer types, since switching to LINAC can be very expensive. The aim of this work was to study the gantry angles, field size and collimator angles of 60Co with the intention to minimize dose to the normal eye of unilateral RB patients. In order to do this, tissue equivalent phantom was constructed. The material used was beeswax with Zeff = 5.58; this was slightly less than that of soft tissue (Zeff = 7.22). Despite this small difference the material was considered to be one of the best because it was easy to insert diodes during determination of dose to the normal eye. Three parameters of 60Co that influence dose to the normal eye were investigated: gantry angle, collimator angle and field size. Gantry angle was varied from 00 to 900 at interval of 100. With the same phantom detector setting, the collimator angle was varied from 00 to ±150 at intervals of 50. Treatment time of 1.21, 1.14 and 1.10 minutes were used for 3 x 3 cm2, 4 x 4 cm2 and 5 x 5 cm2 field sizes. At all three values of field sizes, the doses to the normal eye remained fairly constant for the gantry angle less than 1.0 radian. At this angle, the dose for the 5 x 5 cm2 field started to increase while the increase for the other field sizes delayed till the gantry angle increased to 1.22 radians. For small tumours, field size of 3 x 3 cm2 and gantry angle of 00 were provided the least dose for the normal eye therefore should be used.
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Suleiman, S. A. (2011) Optimization of treatment plan for unilateral retinoblastoma patients, Master dissertation, University of Dar es Salaam. Available at (