“Investigation of Potential Skin Toxicity for Patients Receiving Breast IORT using EBT3 Gafchromic® Film.” , Van Heerden, M, African Journal of Medical Physics, Volume 2 (Suppl), 2019, https://globalmedicalphysics.org/wp-content/uploads/2020/05/AJMP-2Supplement-SAAPMB.pdf
M van Heerden - Netcare Hospitals Pty. Ltd
At Netcare Milpark Hospital, intraoperative radiotherapy (IORT) is a treatment option for a select group of early stage breast cancer patients. The Carl Zeiss INTRABEAM® unit is utilized for these procedures. One limitation is the lack of image-guided pre-treatment plans, thus one is unable to anticipate the radiation dose delivered to the overlying skin. EBT3 Gafchromic® film was utilized for this purpose.
Materials and Methods:
EBT3 Gafchromic® film calibration was performed in the INTRABEAM® water phantom using the INTRABEAM® 50 kV x-ray source. Absorbed dose to water could be determined using a PTW TN34013 soft x-ray ionization chamber along with a formalism specified by Zeiss. The irradiated film sections were scanned 42 hours later with an Epson V750 Pro transmission scanner in 48-bit RGB mode and analysis was done using ImageJ. The calibration curve was verified at various dose levels before implementation.
During each breast IORT case, after lumpectomy, one of the spherical treatment applicators (diameters ranging 3-5 cm) are placed into the cavity. The applicator is attached to the probe-like end of the x-ray source. A dose of 20 Gy is prescribed at 0 mm (at the surface of the applicator). During this study, a 1 x 1 cm2 section of film was placed onto the outer skin surface of the breast at a region where the skin-to-applicator distance is minimal. The film was kept sterile by enclosing it with 3M™ Tegaderm™ transparent wound dressing before placement onto the patient. The influence of the Tegaderm™ on the film measurement was also evaluated.
For 83 patients that underwent the procedure, 14 received < 3 Gy as a point dose on the skin surface and 25 received 3-5 Gy. The majority of the patients (34) received skin doses in the 5-10 Gy range, and 10 received doses > 10 Gy. The highest dose being 17 (± 0.3) Gy for two patients. The dose measured by the film could be verified within 3.3 % and the Tegaderm™ had negligible influence on the measurements.
EBT3 has shown to be a useful tool for determining skin doses for breast IORT patients.