title: Radiobiologic comparison of helical tomotherapy, intensity modulated radiotherapy, and conformal radiotherapy in treating lung cancer accounting for secondary malignancy risks.
abstract: The aim of the present study is to examine the importance of using measures to predict the risk of inducing secondary malignancies in association with the clinical effectiveness of treatment plans in terms of tumor control and normal tissue complication probabilities. This is achieved by using radiobiologic parameters and measures, which may provide a closer association between clinical outcome and treatment delivery. Overall, 4 patients having been treated for lung cancer were examined. For each of them, 3 treatment plans were developed based on the helical tomotherapy (HT), multileaf collimator-based intensity modulated radiation therapy (IMRT), and 3-dimensional conformal radiation therapy (CRT) modalities. The different plans were evaluated using the complication-free tumor control probability (p+), the overall probability of injury (pI), the overall probability of control/benefit (pB), and the biologically effective uniform dose (D¯¯). These radiobiologic measures were used to develop dose-response curves (p-D¯¯ diagram), which can help to evaluate different treatment plans when used in conjunction with standard dosimetric criteria. The risks for secondary malignancies in the heart and the contralateral lung were calculated for the 3 radiation modalities based on the corresponding dose-volume histograms (DVHs) of each patient. Regarding the overall evaluation of the different radiation modalities based on the p+ index, the average values of the HT, IMRT, and CRT are 67.3%, 61.2%, and 68.2%, respectively. The corresponding average values of pB are 75.6%, 70.5%, and 71.0%, respectively, whereas the average values of pI are 8.3%, 9.3%, and 2.8%, respectively. Among the organs at risk (OARs), lungs show the highest probabilities for complications, which are 7.1%, 8.0%, and 1.3% for the HT, IMRT, and CRT modalities, respectively. Similarly, the biologically effective prescription doses (DB¯¯) for the HT, IMRT, and CRT modalities are 64.0, 60.9, and 60.8Gy, respectively. Regarding the risk for secondary cancer, for the heart, the lowest average risk is produced by IMRT (0.10%) compared with the HT (0.17%) and CRT (0.12%) modalities, whereas the 3 radiation modalities show almost equivalent results regarding the contralateral lung (0.8% for HT, 0.9% for IMRT, and 0.9% for CRT). The use of radiobiologic parameters in the evaluation of different treatment plans and estimation of their expected clinical outcome is shown to provide very useful clinical information. The radiobiologic analysis of the response probabilities showed that different radiation modalities appear to be more effective in different patient geometries and target sizes and locations. Furthermore, there is not a clear pattern between the plans that appear to be more effective for the treatment and the risk of secondary malignancy. It seems that radiobiologically based treatment planning taking into account the risk of secondary cancer can be established as an effective clinical tool for a more clinically relevant treatment optimization.
authors.affiliation: Department of Medical Physics, Medical School, University of Patras, Patras, Greece.
authors.forename: Georgios
authors.initials: G
authors.lastname: Komisopoulos
authors.affiliation: Department of Radiation Oncology, University of Texas Health Sciences Center at San Antonio, San Antonio, TX; Department of Medical Radiation Physics, Karolinska Institutet & Stockholm University, Stockholm, Sweden. Electronic address: mavroidis@uthscsa.edu.
authors.forename: Panayiotis
authors.initials: P
authors.lastname: Mavroidis
authors.affiliation: Department of Radiation Oncology, University of Texas Health Sciences Center at San Antonio, San Antonio, TX.
authors.forename: Salvador
authors.initials: S
authors.lastname: Rodriguez
authors.affiliation: Department of Radiation Oncology, University of Texas Health Sciences Center at San Antonio, San Antonio, TX.
authors.forename: Sotirios
authors.initials: S
authors.lastname: Stathakis
authors.affiliation: Department of Radiation Oncology, University of Texas Health Sciences Center at San Antonio, San Antonio, TX.
authors.forename: Nikos
authors.initials: N
authors.lastname: Papanikolaou
authors.affiliation: Department of Medical Physics, Medical School, University of Patras, Patras, Greece.
authors.forename: Georgios C
authors.initials: GC
authors.lastname: Nikiforidis
authors.affiliation: Department of Medical Physics, Medical School, University of Patras, Patras, Greece.
authors.forename: Georgios C
authors.initials: GC
authors.lastname: Sakellaropoulos
mesh_terms: D005260:Female; D006801:Humans; D008175:Lung Neoplasms / Q000532:radiotherapy*; D008297:Male; D009381:Neoplasms, Radiation-Induced / Q000175:diagnosis / Q000209:etiology*; D059351:Organ Sparing Treatments / Q000379:methods*; D058958:Organs at Risk / Q000528:radiation effects*; D011874:Radiometry; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D020266:Radiotherapy, Conformal / Q000009:adverse effects* / Q000379:methods*; D018570:Risk Assessment / Q000379:methods; D016896:Treatment Outcome
keywords: Biologically effective uniform dose; CRT; Helical tomotherapy; IMRT; Radiobiologic measures; Risk for secondary cancer