Optimizing dosimetric leaf gap parameters for radiation therapy: A comparative study using three diode-array verification tools and an ionization chamber.

BACKGROUND

The dosimetric leaf gap (DLG) value is a key parameter that affects dose calculation accuracy in radiotherapy when using the Eclipse treatment planning system. Diode array dosimeters are used to determine the optimal DLG value because they are convenient and fast, providing instant readout of planar dose distributions rather than a point dose. However, variations in gamma pass rates (GPRs) across devices, even for the same radiotherapy treatment plan, may lead to different DLG determinations.

PURPOSE: To compare the optimal DLG values determined using three -diode array dosimeters with those obtained using an ionization chamber (IC) and to evaluate whether diode array dosimeters can reliably reproduce IC-based DLG values.

METHODS

Optimal DLG values were determined for 6 MV, 10 MV, and flattening filter-free (FFF) beams using ArcCHECK, Delta4, and SRS MapCHECK. The results were compared with the IC-based values across all energies. Radiochromic films validated the IC-based DLG values. Twenty volumetric modulated arc therapy plans were recalculated using ten different DLG values. The results were compared with the measured data. Optimal DLG values were determined using global gamma criteria (3%/2 mm and 2%/2 mm), local gamma (1%/1 mm), and dose difference criteria.

RESULTS

Verification with radiochromic film using IC-based optimal DLG values yielded an average GPR of 98.7 ± 2.3% under the 3%/3 mm criterion. The average DLG difference between the IC and diode array dosimeters was -0.35 ± 0.23 mm (range: -0.80 to 0.26 mm), based on various gamma and dose difference criteria. A DLG difference of -0.35 mm showed dose deviations ranging from 0.27% to 1.05% across all beams. Except for one criterion, no significant differences were observed.

CONCLUSIONS

DLG differences between IC and diode array dosimeters resulted in approximately 1% dose discrepancies, which are within the clinically acceptable range. This finding indicates that ArcCHECK, Delta4, and SRS MapCHECK can determine DLG values comparable to those obtained with IC.