The fi rst part of this study was about measurement of dosimetric parameters for small photon beams to be used as input data for treatment planning computer system (TPS) and to verify the dose calculated by TPS in Stereotactic Radiosurgery (SRS) procedure. The beam data required were percentage depth dose (PDD), off-axis ratio (OAR) and scattering factor. Small beams of 5 mm to 45 mm diameter from a circular cone collimator in SRS were used for beam data measurements. Measurements were made using pinpoint ionisation chamber (0.016cc). In the second part of this study, we reported the important of carrying out quality assurance (QA) procedures before SRS treatment which were found to infl uence the accuracy of dose delivery. These QA procedures consisted of measurements on the accuracy in target localization and treatment room laser alignment. The calculated TPS dose for treatment was verifi ed using pinpoint ionisation chamber and thermoluminescent detector (TLD) 100H. The deviation mean between measured and calculated dose was -3.28%. The measured dose obtained from pinpoint ionisation chamber is in good agreement with the calculated dose from TPS with deviation mean of 2.17%. In conclusion, pinpoint ionisation chamber gives a better accuracy in dose calculation compared to TLD 100H. The results are acceptable as recommended by International Commission on Radiation Units and Measurements (ICRU) Report No. 50 (1994) that dose delivered to the target volume must be within ± 5% error.
Radiosurgery

This is a retrospective study, the organ doses of the bladder and the rectum were compared between routine PLATO V14.2.3 (Nucletron B.V., Veenendaal, The Netherlands) and newer version software Oncentra MasterPlan (OMP) V4.3 (Nucletron B.V., Veenendaal, The Netherlands) treatment planning systems (TPS). The treatment data of 32 intracavitary brachytherapy patients at Hospital Universiti Sains Malaysia from January 2010 to June 2015 were used. These data sets were used for catheter reconstruction for both PLATO and OMP TPS followed by independent verification using Excel. There was no significant difference in mean doses to organs at risk (OARs) that calculated by both TPS (p>0.05). The mean percentage of doses calculated by PLATO TPS for bladder and rectum were 66.58 ± 27.42% and 46.27 ± 14.47%, respectively. While, the mean percentage of doses for bladder and rectum calculated by OMP TPS were 65.68 ± 24.24% and 46.46 ± 16.66%, respectively. The mean percentage difference in doses comparison between independent verification calculation and PLATO TPS was 1.96 ± 6.00% and then became 6.37 ± 5.17% when it was compared with OMP TPS. Overall, the dose calculation differences for both versions of TPS were within the range recommended by Nuclear Regulatory Commission (NRC). The dose calculations of the two treatment planning systems showed good agreement and both could be used in planning intracavitary brachytherapy for cervical cancer. Whereas, Excel based independent verification is suitable to be implemented as routine dose verification programme prior to treatment delivery.