SBRT of lung cancerOptimizing dose prescription in stereotactic body radiotherapy for lung tumours using Monte Carlo dose calculation
Section snippets
Methods and materials
The four-dimensional planning CT acquired with free un-coached breathing of a patient treated with SBRT for a NSCLC stage T1N0M0 was entered into the planning software (i-plan-RT-dose 4.0, Brainlab, Feldkirchen, Germany). The patient had been positioned frameless in a vacuum-mattress with the arms raised above the head. In the planning CT, GTVs, ITVs en PTVs for two typical T1-tumours (small: diameter 15 mm, and large: diameter 30 mm, respectively) were constructed at three localizations: near
PTV coverage
The numeric planning parameters are displayed in Supplementary Table 1. For small and large lesions planned, coverage of the PTV by the PI (prescription isodose) was 96.5% or higher, and for 16 out of 30 of the plans, PTV coverage was >99%. Conformity indices (CI) were very low at <1.07 in 15 out of 30 plans, the worst three plans yielding conformity indices of 1.22–1.24 (all for PILs of 80%; Supplementary Table 1). In concordance with the steepness of the dose gradient (more rapid dose falloff
Discussion
Stereotactic body radiotherapy is an increasingly used treatment modality for indications including early-stage primary lung cancer and lung metastases. The essence of SBRT consists in administering very high doses per fraction to small target volumes, which in general only comprise gross tumour tissue with tight margins [7]. The tightness of the margin to the PTV in the millimetre range is made possible, firstly, because special methods such as 4D-CT for treatment planning [8], respiratory
Conclusion
In stereotactic radiotherapy for lung-lesions using MC dose calculation and dynamic conformal arc setup, dose prescription at a PIL (prescription isodose level) between 50% and 70% of the dose at the isocenter results in lower dose to surrounding tissues and lungs compared with employing a PIL of 80%. Except for large lesions adjacent to the thoracic wall and for lesions, where normal tissue lies within the PTV, dose should be prescribed at an isodose level considerably lower than 80% when
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Cited by (15)
Frontiers in planning optimization for lung SBRT
2017, Physica MedicaLung stereotactic ablative body radiotherapy: A large scale multi-institutional planning comparison for interpreting results of multi-institutional studies
2016, Physica MedicaCitation Excerpt :One of the main problems when comparing the SABR plans from different institutions is the varied PTV dose prescription. There are two main approaches regarding dose distribution within the target in SABR: (i) to maintain dose homogeneity within the target, which is usually prescribed at the PTV mean value, and (ii) to prescribe dose at PTV boundaries, without considering the dose heterogeneity inside the target [16]. In conventional radiotherapy, the International Commission on Radiation Units and Measurements (ICRU) Report 62 [17] recommended a uniform dose distribution within the target volume with dose prescribed at a reference point (generally the isocenter).
Dose-volume-response analysis in stereotactic radiotherapy for early lung cancer
2014, Radiotherapy and OncologyCitation Excerpt :Others also have shown that the dose at the isocenter – besides the dose at the PTV periphery – predicts local control [8,9]. It should be noted, however, that the isocenter dose may not be the most relevant parameter for a treatment achieving inhomogeneous dose distributions if optimally administered [17]. This comment notwithstanding, the results of that study are nicely compatible with the present study: Applying the assumed alpha/beta ratio of 8.6 Gy to our data, in OM, an isocenter dose of 48 Gy in 4 fractions equals 115 Gy8.6 and resulted in a 84% local control rate at 3 years; in GN, at a mean isocenter dose of 206 Gy8.6, local control was 93% at 3 years.
Monte Carlo simulation approaches to dose distributions for 6 MV photon beams in clinical linear accelerator
2014, Biocybernetics and Biomedical EngineeringStereotactic ablative body radiation therapy with dynamic conformal multiple arc therapy for liver tumors: Optimal isodose line fitting to the planning target volume
2014, Practical Radiation OncologyCitation Excerpt :As a result, we found that a 60% isodose plan provided the most optimal plan for lung tumors.6 Similar to the results of our study, Widder et al 7 reported that a 50%-70% isodose plan resulted in a lower dose to surrounding tissues and lungs compared with an 80% isodose plan using Monte Carlo dose calculations and DCMAT with SABR. Regarding liver tumors, the optimal percentage isodose value may differ from that for the lung because the electron densities of a tumor and normal tissues around the tumor are higher than those for the lung.
Survival and quality of life after stereotactic or 3D-conformal radiotherapy for inoperable early-stage lung cancer
2011, International Journal of Radiation Oncology Biology PhysicsCitation Excerpt :The total dose of 60 Gy was prescribed at the margin of the PTV, constituting 80% of the dose at the isocenter and following the dose-conformity guidelines as used in the Radiation Therapy Oncology Group 0236 trial. Treatment was delivered using four noncoplanar dynamic arcs as previously described (15). The PTV comprising the tumor as seen on a slow 3D-planning CT with a margin of 20 mm (15 mm to CTV; 5 mm to PTV) was treated to 46 Gy, thereafter portals were reduced to tumor plus 5 mm as PTV to the total dose of 70 Gy, which results in a BED of 84 Gy10 for tumor effects.