The use of improved radiochromic film for in vivo quality assurance of high dose rate brachytherapy

GAFChromic film has become increasingly popular for radiationdosimetry. In this study we explore the use of GAFChromic film as an in vivodosimeter for quality assurance (QA) of fractionated high dose rate 192 Ir treatments. Accuracy of dose distribution is explored for the simple vaginal cylinder geometry for which the dose can be easily calculated for comparison. Source dwell times for several patients were optimized to deliver 500 cGy at 0.5 cm from the surface of the vaginal cylinder applicator using a commercial treatment planning system. GAFChromic film was taped to the vaginal cylinder applicator and was enclosed in a leak proof rubber sleeve prior to its insertion. Optical densities were measured along the film at 2 mm spacing, using a densitometer with filtered red light. Density corrections for transient film darkening effects were made and optical densities were converted to absorbed dose in cGy. In vivo patient dose distribution measured for different patients and different fractions were compared with the calculated values along the applicator surface. The variation between the calculated and measureddose was ±10%. The reproducibility of dosemeasurement for different fractions was within ±5%. This study demonstrates the potential usefulness of the film as an in vivo for brachytherapy QA.