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We retrospectively reviewed the results of stereotactic body radiotherapy (SBRT) in 46 patients with a total of 136 metastases from primary sarcoma. The purpose of this study was to evaluate the overall response rate and side effects of SBRT in metastatic sarcoma. The patients were treated at Karolinska University Hospital between 1994 and 2005, using 3D conformal multifield technique and a stereotactic body-frame. Prescribed doses ranged from 4 to 20 Gy per fraction in 1–5 fractions, with total doses of 10–48 Gy. All 46 patients were diagnosed with a primary sarcoma. The treated metastases were localized mainly in the lungs. A total number of 136 metastases were treated (1–14 per patient). Overall response rate (local control = CR, PR and SD) for each tumour was 88 % (119/135). Median follow-up was 21.8 months (range 2.7–112.8 months). Thirteen patients (31 %) were long-term survivors (>36 months), and 5 patients are still alive after last follow-up. Two cases of serious non-lethal side effects were seen, one patient had a colon perforation and another patient had contracture of the hip region. SBRT is a safe, convenient and effective non-invasive treatment with high local control for patients with metastatic sarcoma.Electronic supplementary materialThe online version of this article (doi:10.1007/s12032-012-0256-2) contains supplementary material, which is available to authorized users.

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A radiobiologically based 3D model of normal tissue has been developed in which complications are generated when 'irradiated'. The aim is to provide insight into the connection between dose-distribution characteristics, different organ architectures and complication rates beyond that obtainable with simple DVH-based analytical NTCP models. In this model the organ consists of a large number of functional subunits (FSUs), populated by stem cells which are killed according to the LQ model. A complication is triggered if the density of FSUs in any 'critical functioning volume' (CFV) falls below some threshold. The (fractional) CFV determines the organ architecture and can be varied continuously from small (series-like behaviour) to large (parallel-like). A key feature of the model is its ability to account for the spatial dependence of dose distributions. Simulations were carried out to investigate correlations between dose-volume parameters and the incidence of 'complications' using different pseudo-clinical dose distributions. Correlations between dose-volume parameters and outcome depended on characteristics of the dose distributions and on organ architecture. As anticipated, the mean dose and V(20) correlated most strongly with outcome for a parallel organ, and the maximum dose for a serial organ. Interestingly better correlation was obtained between the 3D computer model and the LKB model with dose distributions typical for serial organs than with those typical for parallel organs. This work links the results of dose-volume analyses to dataset characteristics typical for serial and parallel organs and it may help investigators interpret the results from clinical studies.

Objective: This work explores the biological basis of a mechanistic model of radiationinduced lung damage; uniquely, the model makes a connection between the cellular radiobiology involved in lung irradiation and the full three-dimensional distribution of radiation dose. Methods: Local tissue damage and loss of global organ function, in terms of radiation pneumonitis (RP), were modelled as different levels of radiation injury. Parameters relating to the former could be derived from the local dose-response function, and the latter from the volume effect of the organ. The literature was consulted to derive information on a threshold dose and volume-effect mechanisms. Results: Simulations of local tissue damage supported the alveolus as a functional subunit (FSU) which can be regenerated from a single surviving stem cell. A moderate interpatient variation in stem cell radiosensitivity (15%) resulted in a great variation in tissue response between 8 and 20 Gy. The threshold of FSU inactivation within a critical functioning volume leading to RP was found to be approximately 47% and the degree of health status variation (influencing the volume effect) in a population was estimated at 25%. Conclusion: This work has shown that it is possible to make sense of the way the lung responds to radiation by modelling RP mechanistically, from cell death to tissue damage to loss of organ function. Advances in knowledge: Simulations were able to provide parameter values, currently not available in the literature, related to the response of the lung to irradiation. Normal-tissue complication probability (NTCP) modelling is the key to exploiting new planning and treatment technology in radiotherapy to optimal effect. The models help to select the best treatment plan, in terms of total dose, fraction size and beam configuration, for the individual patient's anatomy. Although the potential of current NTCP models for feeding clinical experience into treatment planning is becoming increasingly evident [1][2][3][4][5], they are largely empirically based, providing little or no insight into the underlying processes involved. Moreover, they ignore the spatial distribution of the dose deposited in the organ at risk. By contrast, this work explores the biological basis for a mechanistic model which makes a connection with the real cellular radiobiology involved in lung irradiation and takes into account the full three-dimensional (3D) dose distribution.With conventional fractionation and prescribed radiation dose, lung tumour local control rates are of the order of 40% [6]; potential lung and oesophageal toxicity is generally put forward as the reason for such inadequate dosage. Therefore, it is imperative to understand how the lung responds to radiation, in order not to limit the dose to the tumour unnecessarily. Irradiation of the lungs can lead to radiation pneumonitis (RP), which usually develops around 4-6 weeks after treatment [7]. Patients experience fever, dyspnoea and cough and are treated with oral steroids. Mild or moderate sympto...