Impact of SPECT/CT lymphoscintigraphy-based radiotherapy planning for reducing incidental dose to arm draining lymph nodal region vs standard planning on lymphedema incidence in early breast cancer patients post BCS: A double blind randomized controlled trial.

Abstract

TPS67 Background: Breast cancer-related lymphedema (BCRL) affects approximately 20-25% of patients after breast-conserving surgery and adjuvant radiotherapy, significantly impacting quality of life. Incidental radiation dose to arm-draining lymph nodes contributes to lymphedema development. SPECT/CT lymphoscintigraphy can identify these critical lymphatic structures, potentially enabling dose reduction through modified radiotherapy planning while maintaining target coverage. Methods: This double-blind randomized controlled trial will enroll 110 early breast cancer patients with unilateral disease post breast-conserving surgery and adequate axillary dissection planned only for whole-breast irradiation with or without boost and no regional nodal irradiation. All patients undergo SPECT/CT lymphoscintigraphy with intradermal technetium-99m sulfur colloid injection (250 μCi each in the third interdigital web space and medial ulnar condyle) to identify arm-draining lymph nodes. CT simulation will be done in identical position with wing board and thermoplastic immobilization. For each patient, standard and modified plans are generated; modified plan incorporates arm-draining nodal dose constraint (<50% of prescribed dose, i.e., Dmean <20 Gy for 40 Gy prescription) without compromising target coverage (D98% >95%) or organ-at-risk constraints. Patients with achievable modified plan constraints are randomized (computer-generated sequence with stratification by risk groups; SNOSE allocation concealment) to receive either standard or modified plan of hypo fractionated radiotherapy (40.5 Gy/15 fractions to whole breast with or without simultaneous integrated boost 48 Gy/15 fractions to tumor bed). Primary objective is lymphedema incidence (arm circumference difference >2 cm at 10 cm above or 5 cm below olecranon) at 6 months post-radiotherapy. Secondary outcomes include quality of life (LyQLI questionnaire domains) at baseline and 6 months, lymphedema at 1 and 3 years and locoregional/distant recurrence rates. Blinded observers perform all assessments; significance set at p < 0.05 (two-tailed). Expected outcomes: Modified SPECT/CT-based planning is hypothesized to reduce lymphedema incidence from 28% to 8% at 6 months (80% power, α=0.05), with improved quality of life scores and maintained locoregional control at 3-year follow-up. Clinical trial information: CTRI/2025/09/094117 .