A Post-Mastectomy Radiation Therapy Dose Distribution Study

Abstract

Purpose: For post-mastectomy radiation therapy, skin dose must be accurately estimated to assess skin reactions, such as: erythema, desquamation, and necrosis. Even with advanced algorithms, planning systems do not always provide accurate dosimetry for target volumes distal to skin. Methods and Materials: In this study, a female anthropomorphic (ART) phantom and the newest generation of optically stimulated luminescence dosimeters (OSLD) (nanoDots, Landauer Inc.) were deployed to measure chest wall dose distribution. Since actual dose to patients' lung and heart cannot be measured using in-vivo dosimetry, film was also used to verify the dose distribution to the left lung and heart. The treatment planning was performed using tolerance limits of 95% to 107% of prescription dose. The ART phantom was irradiated according to 3 three-dimensional (3D) conformal radiotherapy plans for 200 cGy dose per fraction using 6 MV medial and lateral tangential photon beams. The dose distribution provided by treatment planning was studied using nanoDots and film. Results: Results show that the largest surface dose difference between nanoDots measurement and prescribed dose for medial and lateral tangential beams, are 3.8% and 9.8%, respectively. This difference may be due to higher effective point of measurement and angular dependence of the nanoDots. The maximum differences in measured dose compared with prescribed dose, using film for heart and the left lung, were 6.2% and 7.5% respectively. Conclusions: Both nanoDots and film provided reasonable estimation of dose distribution in post-mastectomy radiation therapy.

Verification of treatment planning algorithms using optically stimulated luminescent dosimeters in a breast phantom

“…Several authors have compared TPS calculated surface dose with measured dose and have reported overestimation as well as underestimation of the surface dose by OSLD. [232425] One reason for the variations in estimation is that the measurements were done at the build-up region where the change of a few mm of depth may result in a significant change in dose. Second, OSLD which has a WED of 0.4 mm overestimates the surface dose when compared to detectors which have a lower WED. Positional errors in the placement of OSLD during measurement may also contribute to the variation between TPS calculated dose and measured dose.…”