Post-excision RT shows significant reduction in keloid recurrence compared to excision alone. While the recurrence control rates are not statistically different between EBRT and brachytherapy, keloids treated with EBRT recurred significantly later than those treated by HDR brachytherapy by a mean of 2.5 years. Further workup with a randomized control study will help to refine optimal adjuvant RT treatment. LEVEL OF EVIDENCE 3.

The purpose was to report clinical experience of a video‐guided spirometry system in applying deep inhalation breath‐hold (DIBH) radiotherapy for left‐sided breast cancer, and to study the systematic and random uncertainties, intra‐ and interfraction motion and impact on cardiac dose associated with DIBH. The data from 28 left‐sided breast cancer patients treated with spirometer‐guided DIBH radiation were studied. Dosimetric comparisons between free‐breathing (FB) and DIBH plans were performed. The distance between the heart and chest wall measured on the digitally reconstructed radiographs (DRR) and MV portal images, dDRR(DIBH) and dport(DIBH), respectively, was compared as a measure of DIBH setup uncertainty. The difference (Δd) between dDRR(DIBH) and dport(DIBH) was defined as the systematic uncertainty. The standard deviation of Δd for each patient was defined as the random uncertainty. MV cine images during radiation were acquired. Affine registrations of the cine images acquired during one fraction and multiple fractions were performed to study the intra‐ and interfraction motion of the chest wall. The median chest wall motion was used as the metric for intra‐ and interfraction analysis. Breast motions in superior–inferior (SI) direction and “AP” (defined on the DRR or MV portal image as the direction perpendicular to the SI direction) are reported. Systematic and random uncertainties of 3.8 mm and 2 mm, respectively, were found for this spirometer‐guided DIBH treatment. MV cine analysis showed that intrafraction chest wall motions during DIBH were 0.3 mm in “AP” and 0.6 mm in SI. The interfraction chest wall motions were 3.6 mm in “AP” and 3.4 mm in SI. Utilization of DIBH with this spirometry system led to a statistically significant reduction of cardiac dose relative to FB treatment. The DIBH using video‐guided spirometry provided reproducible cardiac sparing with minimal intra‐ and interfraction chest wall motion, and thus is a valuable adjunct to modern breast treatment techniques.PACS number: 87.55.kh, 87.55.ne, 87.55.tg

9011 Background: Stereotactic ablative radiation therapy (SABR) is the standard-of-care for medically inoperable, early stage non-small cell lung cancer (NSCLC), but regional and distant failures remain problematic. Based on our in vivo data showing synergy between radiation and immune checkpoint inhibitors (ICI) and the known efficacy and mild toxicity profile of ICI in NSCLC, we conducted a phase I study to determine the maximum tolerated dose of neoadjuvant, concurrent, and adjuvant atezolizumab with SABR for early stage NSCLC patients (pts). Methods: Eligible pts had histologically confirmed T1-3 NSCLC with at least one feature predictive of increased recurrence risk: diameter ≥1 cm, SUV ≥6.2 on PET, or moderately/poorly differentiated histology, were medically inoperable or refused surgery and had a Zubrod PS ≤2. Patients received 6 cycles of atezolizumab. A 3+3 dose finding design was employed with 3 dose levels: 3 mg/kg, 10 mg/kg, and 1200 mg flat dosing. SABR was delivered starting cycle 3 to 50 Gy over 4-5 fractions. Dose limiting toxicity (DLT) was assessed during the first 9 weeks. Results: 20 pts were enrolled, 15 pts in the dose finding and 5 pts at the recommended phase II dose (RP2D). Patient factors: MedIan age 77; 45% male, 85% smoking history, 85% PS 0-1 and 35% squamous. One pt on dose level 2 had a DLT – a grade 3 rash. Atezolizumab 1200 mg flat dosing was the RP2D. Grade 3 pneumonitis was not observed. Partial responses after 2 cycles were seen in 3/17 evaluable pts (18%) and 1 pt had a minor response. No patient progressed on treatment. PD-L1 expression was 0% 8/13 (62%), >1% - 50% 4/13 (31%), >50% 1/13 (8%) in pts with sufficient tissue. Of 5 pts with PD-L1 expression 3 (60%) were responders and 1 (12.5%) of 8 pts with 0% PD-L1 expression responded. Multi-plex Quantitative Immunofluorescence (QIF) using a T cell activation panel demonstrated to correlate with ICI response was performed on 9 samples (including 2 responders, 1 minor responder). The CD3 QIF score was > two-fold higher in the responders compared to non-responders, and the levels of proliferating and activated T cells were likewise > two-fold higher. Comprehensive stool and serial blood analyses have been completed. Correlative endpoints will be reported along with additional efficacy outcomes. Conclusions: Atezolizumab plus SABR is feasible, safe and shows an efficacy signal in medically inoperable early stage NSCLC. This combination will be tested in a randomized phase III trial SWOG/NRG S1914. Funding: This work was supported by the DOD CDMRP W81XWH-15-2-0063 and Genentech. Clinical trial information: NCT02599454.

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