Solberg, Timothy D.

TPS9082 Background: Limited stage small cell lung cancer (LS-SCLC) is treated with standard of care platinum/etoposide (EP) and thoracic radiation therapy (TRT) with curative intent, however the majority of patients are not cured and median overall survival is approximately 30 months. Addition of atezolizumab to chemotherapy in extensive stage SCLC has improved progression free and overall survival in a non-curative setting leading to hope that addition of an immune checkpoint inhibitor to standard chemoradiotherapy could benefit LS-SCLC patients. LU005 is a randomized phase II/III trial of standard concurrent chemoradiation with or without atezolizumab for patients with LS-SCLC. Methods: Patients are randomly assigned in a 1:1 ratio to standard EP chemotherapy with concurrent TRT (45 Gy BID or 66 Gy QD) with or without atezolizumab beginning concurrently with TRT, and continued every 3 weeks for up to 12 months. Eligible patients have LS-SCLC, PS 0-2, adequate organ function, no concerning comorbidities (including no active autoimmune disease) and are eligible for TRT. Patients are randomized prior to their second cycle of EP and thoracic radiation begins with the second overall cycle of chemotherapy (first cycle of study therapy) in both treatment arms. Prophylactic cranial radiation (PCI) is recommended for patients who respond to treatment. The phase II/III primary endpoints are progression free (PFS) and overall survival (OS) respectively. Secondary endpoints include objective response rates, local and distant disease control, and quality of life/patient reported outcomes assessment. Translational science component includes blood and tissue based immune related assays. This study activated in May 2019. 50 of 506 planned patients have been accrued as of 2/1/2020. Supported by grants U10CA180868 (NRG Oncology Operations), U10CA180822 (NRG Oncology SDMC), U23CA180803 (IROC) from the National Cancer Institute (NCI) and Genentech. *Authors Ross and Higgins are co-first authors and contributed equally to this work. Clinical trial information: NCT03811002.

Because treatment planning systems (TPSs) generally do not provide monitor units (MUs) for double‐scattered proton plans, models to predict MUs as a function of the range and the nominal modulation width requested of the beam delivery system, such as the one developed by the MGH group, have been proposed. For a given nominal modulation width, however, the measured modulation width depends on the accuracy of the vendor's calibration process and may differ from this nominal value, and also from one beamline to the next. Although such a difference can be replicated in our TPS, the output dependence on range and modulation width for each beam option or suboption has to be modeled separately for each beamline in order to achieve maximal 3% inaccuracy. As a consequence, the MGH output model may not be directly transferable. This work, therefore, serves to extend the model to more general clinic situations. In this paper, a parameterized linear‐quadratic transformation is introduced to convert the nominal modulation width to the measured modulation width for each beam option or suboption on a per‐beamline basis. Fit parameters are derived for each beamline from measurements of 60 reference beams spanning the minimum and maximum ranges, and modulation widths from 2 cm to full range per option or suboption. Using the modeled modulation width, we extract the MGH parameters for the output dependence on range and modulation width. Our method has been tested with 1784 patient‐specific fields delivered across three different beamlines at our facility. For these fields, all measured outputs fall within 3%, and 64.4% fall within 1%, of our model. Using a parameterized linear‐quadratic modulation width, MU calculation models can be established on a per‐beamline basis for each double scattering beam option or suboption.PACS number: 87.53.Qc