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Roshini Thomas
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P1.14 - Radiotherapy (ID 700)
- Event: WCLC 2017
- Type: Poster Session with Presenters Present
- Track: Radiotherapy
- Presentations: 1
- Moderators:
- Coordinates: 10/16/2017, 09:30 - 16:00, Exhibit Hall (Hall B + C)
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P1.14-017 - Impact of Systematic EBUS-TBNA Mediastinal Staging on Radical Radiotherapy Planning in NSCLC (ID 8497)
09:30 - 09:30 | Author(s): Roshini Thomas
- Abstract
Background:
Radical radiotherapy often relies solely on radiological imaging to determine treatment volumes. Systematic mediastinal staging with endobronchial ultrasound transbronchial needle aspiration (EBUS-TBNA) may identify PET-occult sites of mediastinal disease, or demonstrate benign causes for PET-positive LN. This study evaluated 1) Involved nodal coverage 2) Doses to organs-at-risk when planned based on PET-CT and EBUS-TBNA and 3) Incident dose to mediastinal nodes between 3D-CRT and Intensity-Modulated-Radiotherapy (IMRT).
Method:
Radical radiotherapy plans (60Gy/30 fractions) were created for patients with stage change following EBUS-TBNA from a prospective clinical trial. We compared lung Normal-Tissue-Complication-Probability (NTCP, pneumonitis), oesophageal and heart dose for planning to targets based on PET-CT versus PET-CT+EBUS-TBNA. The incidental dose to PET-negative/EBUS-TBNA-positive nodes from 3DCRT and IMRT was evaluated using volume receiving 35Gy as a surrogate for control of sub-clinical disease (Kepka, IJROBP, 73(5) 2009).
Result:
Of 30 patients enrolled, four were upstaged by EBUS-TBNA; these patients had a significant geographic miss of nodal GTV when planned to PET-positive nodes only (Figure 1). When planned based on PET-CT alone, the incidental dose to PET-negative/EBUS-TBNA-positive nodes was higher with IMRT for two patients (v35Gy increased by 17% & 6%; Figure 1a&b) and lower with IMRT (v35Gy reduced by 16% and 6%; Figure 1c&d) for two, dependent on nodal position relative to the primary. Six patients had negative pathology for PET avid nodal stations; Inclusion of EBUS-negative, PET-positive nodes resulted in an average increased lung NTCP of 5% (range 1%-13%), mean oesophagus dose of 13Gy (range 4-23Gy) and mean heart dose of 4Gy (range -0.1-11Gy) over plans based on EBUS-positive nodes alone. Figure 1
Conclusion:
Systematic EBUS-TBNA has the potential to improve loco-regional control and limit the probability of lung and heart toxicity. The incidental dose to adjacent tissue is inherently related to involved node/tumour position and not solely dictated by the radiation delivery technique.
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P2.14 - Radiotherapy (ID 715)
- Event: WCLC 2017
- Type: Poster Session with Presenters Present
- Track: Radiotherapy
- Presentations: 1
- Moderators:
- Coordinates: 10/17/2017, 09:30 - 16:00, Exhibit Hall (Hall B + C)
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P2.14-001 - Mid-Treatment Perfusion PET/CT Is More Effective Than Ventilation PET/CT in Functionally-Adapted Radiotherapy for NSCLC (ID 8508)
09:30 - 09:30 | Presenting Author(s): Roshini Thomas
- Abstract
Background:
To assess the utility of four-dimensional (4D) ventilation/perfusion (V/Q) PET/CT lung imaging to facilitate mid-radiotherapy treatment adaption with volumetric modulated arc radiotherapy (VMAT).
Method:
In a prospective clinical trial, patients with non-small cell lung cancer (NSCLC) underwent [68]Ga-4D-V/Q PET/CT scanning before and during a six-week (60Gy) course of definitive chemoradiation. Functional lung volumes were delineated on both datasets as ‘highly perfused’ (HPLung) and ‘highly ventilated’ (HVLung), using a 70[th] centile SUV threshold. Three VMAT plans were created on the mid-treatment datatsets: optimised to anatomical lung, HPLung, and HVLung volumes, respectively. Functional dose volumetrics were assessed using the parameters of mean lung dose (MLD), and lung volume receiving 5, 20 or 30Gy, (V5, V20, and V30). Plan quality was assessed for consistency with respect to conformity indices, and doses to critical structures.
Result:
The study cohort consisted of 10 patients resulting in a total of 30 VMAT plans. PTV volumes reduced by a mean of 5.5% between scans. HVLung volume increased between scans by a median value of 39.2%. Subsequent volumetric and spatial changes were reflected in varying DICE similarity coefficients, or DSC (ranging from 0.336-0.923). HPLung decreased by a median value of 4.5% with spatial discrepancy represented by DSC of 0.568-0.805. Increase in ventilated function was most prevalent adjacent to the target, limiting the benefit of adaptive planning (Fig 1). Plan quality was consistent with the median PTV D95 ranging from 60.6-61.3Gy, and mean conformity index ranging from 1.23-1.25. Functional MLD of HPLung decreased by a mean of 7.3%, p=0.02. Plans optimised to HPLung resulted in a reduction of perfused lung V5 by a mean of 13.2%, p<0.01, with HVlung plans yielding a decrease in ventilated lung V5 of 9.6%, p=0.02. Fig 1 Figure 1
Conclusion:
To achieve reduced irradiation of functional lung, radiotherapy adaptation is more effectively facilitated by perfusion rather than ventilation imaging.
