RESUMEN
Inversely planned intensity-modulated radiotherapy (IMRT) and stereotactic small field radiotherapy should be verified before treatment execution. A second verification is carried out for planned treatments in IMRT and 3D conformal radiotherapy (3D-CRT) using a monitor verification commercial dose calculation management software (DCMS). For the same reference point the ion-chamber measured doses are compared for IMRT plans. DCMS (Diamond) computes dose based on modified Clarkson integration, accounting for multi-leaf collimators (MLC) transmission and measured collimator scatter factors. DCMS was validated with treatment planning system (TPS) (Eclipse 6.5 Version, Varian, USA) separately. Treatment plans computed from TPS are exported to DCMS using DICOM interface. Doses are re-calculated at selected points for fields delivered to IMRT phantom (IBA Scanditronix Wellhofer) in high-energy linac (Clinac 2300 CD, Varian). Doses measured at central axis, for the same points using CC13 (0.13 cc) ion chamber with Dose 1 Electrometer (Scanditronix Wellhofer) are compared with calculated data on DCMS and TPS. The data of 53 IMRT patients with fields ranging from 5 to 9 are reported. The computed dose for selected monitor units (MU) by Diamond showed good agreement with planned doses by TPS. DCMS dose prediction matched well in 3D-CRT forward plans (0.8 ± 1.3%, n = 37) and in IMRT inverse plans (-0.1 ± 2.2%, n = 37). Ion chamber measurements agreed well with Eclipse planned doses (-2.1 ± 2.0%, n = 53) and re-calculated DCMS doses (-1.5 ± 2.6%, n = 37) in phantom. DCMS dose validation is in reasonable agreement with TPS. DCMS calculations corroborate well with ionometric measured doses in most of the treatment plans.
RESUMEN
PURPOSE: To start total body irradiation (TBI) treatments, physical parameters are measured for a magna field irradiation. METHODS AND MATERIALS: 6 MV photon beam from Clinac 600 CD linear accelerator (Varian, USA) with fully opened collimator at 45° and gantry at 270° provided a diamond shaped magna field with diagonal dimension 224 cm at 4.0 m source skin distance (SSD). The flatness of the radiation field was measured in the presence of locally designed acrylic beam spoiler and beam flatness filter. Central Axis Depth dose data (CADD), tissue maximum ratios and entrance dose pattern are measured using large phantoms. Methods for clinical dose estimation using semi-conductor diodes and TLD were standardized. RESULTS: PVC beam flattener at the shielding tray position and the presence of acrylic beam spoiler in the radiation field provided a flatness of 100.15% ± 0.44% compared to open beam flatness 101.6 ± 1.5%. A reduction of 2% in percentage depth dose was observed at 10 cm depth in the presence of 15 mm acrylic beam spoiler. However, no changes are observed in the TMRs with presence of beam spoiler. The measured ionization ratios clearly showed change of beam quality with the introduction of beam spoiler. The presence of 15 mm beam spoiler ensured entrance dose 100% at skin and remaining unchanged within 1% upto a depth of 10 mm. Phantom measurements show good agreement between calculated and measured doses. CONCLUSIONS: The paper recommends use of modified CADD parameters for treatment planning, if calibration of output is carried out in the presence of beam spoiler.