Dosimetric impact of source-positioning uncertainty in high-dose-rate balloon brachytherapy of breast cancer

Abstract

PurposeTo evaluate the dosimetric impact of source-positioning uncertainty in high-dose-rate (HDR) balloon brachytherapy of breast cancer.Material and methodsFor 49 HDR balloon patients, each dwell position of catheter(s) was manually shifted distally (+) and proximally (–) with a magnitude from 1 to 4 mm. Total 392 plans were retrospectively generated and compared to corresponding clinical plans using 7 dosimetric parameters: dose (D95) to 95% of planning target volume for evaluation (PTV_EVAL), and volume covered by 100% and 90% of the prescribed dose (PD) (V100 and V90); skin and rib maximum point dose (Dmax); normal breast tissue volume receiving 150% and 200% of PD (V150 and V200).ResultsPTV_EVAL dosimetry deteriorated with larger average/maximum reduction (from ± 1 mm to ± 4 mm) for larger source position uncertainty (p value < 0.0001): from 1.0%/2.5%, 3.3%/5.9%, 6.3%/10.0% to 9.8%/14.5% for D95; from 1.0%/2.6%, 3.1%/5.7%, 5.8%/8.9% to 8.7%/12.3% for V100; from 0.2%/1.5%, 1.0%/4.0%, 2.7%/6.8% to 5.1%/10.3% for V90. ≥ ± 3 mm shift reduced average D95 to < 95% and average V100 to < 90%. While skin and rib Dmax change was case-specific, its absolute change (∣Δ(Value)∣) showed that larger shift and high dose group had larger variation compared to smaller and lower dose group (p value < 0.0001), respectively. Normal breast tissue V150 variation was case-specific and small. Average ∣Δ(V150)∣ was 0.2 cc for the largest shift (± 4 mm) with maximum < 1.7 cc. V200 was increased with higher elevation for larger shift: from 6.4 cc/9.8 cc, 7.0 cc/10.1 cc, 8.0 cc/11.3 cc to 9.2 cc/ 13.0 cc.ConclusionsThe tolerance of ± 2 mm recommended by AAPM TG 56 is clinically acceptable in most clinical cases. However, special attention should be paid to a case where both skin and rib are located proximally to balloon, and the orientation of balloon catheter(s) is vertical to these critical structures. In this case, sufficient dosimetric planning margins are required.

Treatment plan dosimetric impact after catheter stretch during multi-catheter interstitial breast brachytherapy

“…These results may not be directly transferable to our technique due to differences in the type of catheter used. Kim [ 9 ] studied the source-position uncertainty in HDR balloon brachytherapy for breast cancer and concluded that for the balloon applicator, a ± 0.2 cm tolerance for source position accuracy was acceptable in most clinical cases. Again, these results cannot be directly compared to our technique due to differences in applicator and target volume definition.…”

Feasibility of removable balloon implant for simultaneous magnetic nanoparticle heating and HDR brachytherapy of brain tumor resection cavities

“…The primary goal of this effort is to demonstrate feasibility of a novel combination thermobrachytherapy balloon device that should facilitate new clinical trials to investigate simultaneous heat and radiation delivered uniformly and welllocalized in tumor bed immediately after surgery, before tumor cell migration into surrounding normal brain. This initial study focuses on thermal performance of a TBT balloon since the dosimetry of HDR radiation from within an implanted balloon catheter source is already well-characterized in the literature for soft tissue sites including brain and breast [9,29,30]. Subsequent in vivo studies and clinical trials with the proposed thermobrachytherapy device will be required to determine: (a) optimum balloon temperature and penetration depth of therapy for brain; (b) optimum brachytherapy dose for combined therapy; (c) optimum fractionation of heat and brachytherapy; and (d) whether combination strategies of thermobrachytherapy with EBRT, chemotherapy, temozolomide, and/or immunotherapy would be beneficial for GBM and other resected brain tumors.…”