Lung Cancer

PV QA 4 - Poster Viewing Q&A 4

TU_32_3634 - Effects of Circumferential Bronchial Tree Irradiation on the Development of Radiation Pneumonitis Following Lung SBRT

Tuesday, October 23
2:45 PM - 4:15 PM
Location: Innovation Hub, Exhibit Hall 3

Effects of Circumferential Bronchial Tree Irradiation on the Development of Radiation Pneumonitis Following Lung SBRT
L. Pang1, C. McLaughlin2, N. L. Gagne3, C. Melhus3, and K. E. Huber3; 1Radiation Oncology, Stony Brook University Hospital, Stony Brook, NY, 2VCU Massey Cancer Center, Richmond, VA, 3Tufts University School of Medicine, Boston, MA

Purpose/Objective(s): Stereotactic body radiation therapy (SBRT) may result in the development of serious lung toxicity, including death. There is evidence that increased fractionation, lower daily doses, and non-sequential daily treatments can mitigate this risk. However, a subset of patients will still develop radiation pneumonitis (RP). This study investigated alternative dosimetric parameters beyond those previously reported for lung and proximal bronchial tree (PBT) to test their association with development of RP. We hypothesize that target dose conformity can be adversely affected by tightly constraining dose to an unspecified volume of PBT, which could result in paradoxical adverse lung toxicity.

Materials/Methods: A cohort of 27 consecutively treated patients who underwent static-beam SBRT for lung cancer between 2010 and 2015 were identified at one institution. Clinical RP was coded on a scale from 0-5 using the RTOG Toxicity Criteria version 2 guidelines for late radiation morbidity occurring with a minimum follow-up of 10 months. For analysis, we grouped grades 0-1 and grades 2-3 RP. There was no grade 4-5 RP in this cohort. A treatment planning radiotherapy software was used to collect planning parameter data. Irradiation of the contoured PBT was evaluated by examining abutment or circumferential overlap of fractionation-specific isodose lines, chosen based on the “trachea and large bronchus” section of RTOG dose planning parameters. These reference isodose lines were 15, 16, and 18 Gy, corresponding to the PBT D4cc dose limit for 3x18 Gy, 4x12 Gy, and 5x10 Gy fractionation schemes, respectively. Overlap of the PBT was analyzed for association with RP. Statistical analyses were performed with the chi-square test.

Results: There was a significant association between circumferential radiation of the PBT and RP (p = 0.02) with 81.8% of patients having circumferential radiation classified by grade 2-3 RP versus grade 0-1. Neither PBT D4cc nor abutment of the isodose line with the PBT was significantly associated with RP (p = 0.19). Grade 2-3 RP was observed in 80% of patients with mean lung dose (MLD) > 4 Gy, compared with 33% of patients with MLD ≤ 4 Gy (p = 0.01) and noted in 80% of patients with lung V5 > 20% compared to 33% of patients with V5 ≤ 20% (p = 0.01). There was not a significant association between lung V20, D1000, or D1500 and the RP clinical grade.

Conclusion: Circumferential PBT irradiation beyond the RTOG planning parameters for the D4cc dose limit is significantly associated with RP clinical grade for lung cancer patients treated with SBRT in this cohort. Our results also point to the potential limitations of published RTOG dose parameters as predictors of RP. We suggest establishing a circumferential dose limit for the PBT within ongoing clinical trials investigating the safety of treating centrally located lung tumors with SBRT.

Author Disclosure: L. Pang: None. C. McLaughlin: None. N.L. Gagne: None. C. Melhus: None.

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