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WE‐H‐BRA‐02: Radiobiological Modeling of Tumor Control Probability (TCP) and Radiation‐Induced Pneumonitis (RP) for Lung Cancer Patients Treated with Monte Carlo‐Based Lung SBRT
Author(s) -
Pokhrel D,
Sood S,
Shen X,
Badkul R,
McClinton C,
Jiang H,
Mitchell M,
Lominska C,
Wang F
Publication year - 2016
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4957993
Subject(s) - medicine , nuclear medicine , dosimetry , lung , lung cancer , radiation therapy , radiosurgery , parameterized complexity , radiology , mathematics , algorithm
Purpose: To present radiobiological modeling of TCP using tumor size‐adjusted BED(s‐BED)and PTV(D99) to lung SBRT patients treated with X‐ray Voxel Monte Carlo(XVMC) algorithm, apply parameterized Lyman‐NTCP model to predict grade‐2 RP and subsequently, compare with clinical outcomes/observations. Methods: Dosimetric parameters and clinical follow‐up for XVMC‐based lung‐SBRT patients were retrospectively evaluated. Patients were treated at Novalis‐TX with hybrid(2 non‐coplanar partial‐arcs plus 3–6 static‐beams)plan using HD‐MLC/6MV‐SRS‐beam.For TCP,s‐BED modelling was utilized: TCP=EXP[sBED‐TCD50]/k/(1.0+EXP[sBED‐TCD50]/k), where k=31Gy corresponding to TCD50=0Gy and s‐BED was defined as BED10 minus 10 times the tumor diameter(in centimeters)by Ohri et al.(IJROBP,2012). For 2‐yr local‐control, we used more‐realistic MC‐computed PTVD99 as a predictive parameter, s‐BED(D99).Due to relatively shorter median follow‐up interval(12‐months),Kaplan‐Meier curves were generated to estimate 2‐yr observed local‐control and compared to predicted‐rate by TCP modeling. For NTCP, we employed parameterized Lyman‐NTCP model utilizing normal‐lung DVH and α/β=3Gy fitted to predict grade‐2 RP after lung‐SBRT. Results: Total 108 patients (137 tumors) treated for 35–70Gy in 3–5 fractions, either primary‐lung(n=74)or metastatic‐lung(n=53)tumors were included.F or the given prescription dose with MC‐computed MUs, 2‐yr local‐control rates with s‐BED(D99) was 87±8%. Kaplan‐Meier generated observed local‐control rate at 2‐yr was 87.5%,suggesting that PTV(D99) could be a potential predictor (p‐value=0.38). Observed vs predicted TCP for primary‐lung tumors and metastatic tumors were 97% vs 88±7% and 94% vs 86±9%.NTCP model predicted well for symptomatic‐RP with predicted vs observed (3±5% vs 2%). Radiographic and clinically significant RP was observed in 13% and 2% of patients. Higher rates of radiographic change were observed in patients who received >50Gy compared to ≤50Gy(24% vs 10%). Conclusion: Utilizing MC‐computed PTVD99, our TCP results were well correlated with clinical outcome. The predicted grade‐2 RP rate was comparable to clinical observations. Clinical application of these radiobiological models may potentially allow for target dose escalation and/or lung‐toxicity reduction. Further validation of these radiobiological models with longer follow up interval for large cohorts of lung‐SBRT patients is anticipated.