ESTRO 2022 - Abstract Book

S330

Abstract book

ESTRO 2022

being the most complex structure to contour. Failure rates and the most common reasons for structures being unacceptable are detailed in Table 1. 40/43 resubmissions were approved, with those still unacceptable being referred to one of the 5 radiation oncologist SABR experts for further training.

Conclusion The outlining benchmark case has highlighted training needs in delineation and interpretation of guidelines. Visual aids may prove useful in future guidance. Detailed feedback was provided to aid with education and ongoing support from mentors is in place. Contouring workshops have also been developed and participation in peer review and clinical trials is recommended going forward.

MO-0393 CPAP ventilator- assisted lung SBRT: is DIBH clinically better than free breathing?

S. appel 1 , J. Goldstein 2 , O. Haisraely 1 , Y.R. Lawrence 1 , Z. Symon 3 , S. Dubinski 4

1 Sheba Medical Center, Radiation Oncology, Ramat Gan, Israel; 2 Soraski Medical Center, Radiation Oncology, Tel Aviv, Israel; 3 SHeba Medical Center, Radiation Oncology, Ramat Gan, Israel; 4 Sheba Medical Center, Radiation Oncology- physics, Ramat Gan, Israel Purpose or Objective Continuous positive airway pressure (CPAP) ventilator to high pressure (15 cm H2O) hyperinflates the lungs and reduces diaphragmatic motion and has been used for motion management at our department. We hypothesized that combining high pressure CPAP with deep inspiratory breath hold (CPAP-DIBH) during lung stereotactic radiotherapy (SBRT) would improve local control, reduce toxicity, and reduce post treatment consolidation compared to high pressure CPAP in free breathing (CPAP-FB).

Materials and Methods

Patients with either stage-I lung cancer or oligometastatic lung metastasis treated with CPAP-assisted SBRT between 6/2014-5/2020 were retrospectively reviewed. Tumor characteristics, treatment variables, local control (LC), respiratory toxicity (measured at 3 months and graded by CTCAEv.5) and radiographic changes 6 and 12-months post SBRT were analyzed.

Results

Eighty patients with 114 lesions were included, of these, 59 (52%) were treated with CPAP-FB and 55 (48%) were treated with CPAP-DIBH. Median radiation dose was 51.8 Gy, median biological effective dose (BED 10 ) was 111Gy. The groups were balanced with respect to age, gross tumor volume (GTV), radiation dose, tumor location and prior lung radiation. Lung volume in CPAP-DIBH group was 5273ml (SD1178), significantly larger than CPAP-FB:3932ml (SD1082) (p=0.001) CPAP-DIBH had smaller planning target volume (PTV) 21 cm 3 (SD30) vs. 33 cm 3 (SD33) in CPAP-FB (p=0.02). With median FU of 21.7months, the LC at 2 years for the entire cohort was 73.5% (95% CI 62-82%); for stage-1 lung cancer 2-yrs LC was 88% (95% CI 59-97%) and for metastatic cancer 70% (95% CI 57-80%). On univariate analysis, LC was improved with GTV ≤ 3cm 3 (HR 4.6, p=0.001), use of CPAP-DIBH (HR 2.5, p=0.04) and non-colon cancers (HR 2.8 p=0.014)(Figure 1A-D). Local control was not affected by location at lower lobes (HR 0.8, p=0.5) and BED (10) <105 Gray (HR 0.54, p=0.24). These associations remained significant for LC using CPAP-DIBH (p<0.0001), GTV ≤ 3cm3 (p=0.001) and non-colon cancer (p=0.0001) on multivariate analysis. Tolerability was favorable: all patients who started also completed treatment, except for one patient who suffered syncope (m/p unrelated). Respiratory toxicity grade 2-3 occurred in 20/110 cases, and was reduced with CPAP-DIBH 6/51 (12%) vs. CPAP-FB 14/59 (24%) (OR 0.43, p=0.1). Respiratory toxicity correlated with larger PTV>35cm 3 (OR 3.3, p=0.025) and PTV/GTV ration>7 (OR 3.1,P=0.036) (table 1).