Room: AAPM ePoster Library
Purpose: small skin cancer at the nose (= 2 cm), electron beam has been commonly used. Because of high uncertainty in dose calculation and setup for electron beam therapy, large lateral PTV margin is required. In this study, a new technique using HDR interstitial brachytherapy with 3D-printed bolus is proposed as a simple but more accurate method.
Methods: 6 electron plans, HDR plans were retrospectively generated using 2 or 3 catheters 1 cm apart and 1 cm away from the skin surface. Customized bolus using 3D-printing is under development. Plan comparison was performed between electron and HDR plans. For 2 clinical electron plans, hand-made customized bolus was modified after planning CT scan and no electron plan was available. For 2 patients, eyes and lenses were defined as OARs.
Results: HDR interstitial brachytherapy, average target size was 7.6 mm (ranging from 5.4 to 9 mm) in cranio-caudal dimension, 3.6 mm (from 2.2 to 5 mm) in anterior-posterior dimension, and 11.8 mm (from 7 to 20 mm) in lateral dimension. 40Gy in 10 fractions were prescribed. For electron plans, lateral PTV margin (1-2 cm) was added and 2 dose fractionations were used: 55 Gy in 22 fractions, 50 Gy in 15 fractions. The average target coverage (V100) was 97.01% (from 96.30% to 97.45%) in HDR plan. The average high dose in the target (D0.03cc) was higher with HDR plans: 137.41% (from 129.07% to 153.51%) vs. 113.57% (from 109.72% to 119.00%). The volume enclosed by the prescription dose was much less with HDR plans (0.6 cc vs. 2.42 cc). OAR doses were higher with HDR plans (3.2 Gy vs.0.82 Gy for lenses D2).
Conclusion: a small skin cancer at nose, HDR interstitial brachytherapy approach is feasible by irradiating less volume with less uncertainty compared to conventional electron beams.
Not Applicable / None Entered.