Carmelo Marino

Lung stereotactic ablative body radiotherapy: A large scale multi-institutional planning comparison for interpreting results of multi-institutional studies

PURPOSE A large-scale multi-institutional planning comparison on lung cancer SABR is presented with the aim of investigating possible criticism in carrying out retrospective multicentre data analysis from a dosimetric perspective. METHODS Five CT series were sent to the participants. The dose prescription to PTV was 54Gy in 3 fractions of 18Gy. The plans were compared in terms of PTV-gEUD2 (generalized Equivalent Uniform Dose equivalent to 2Gy), mean dose to PTV, Homogeneity Index (PTV-HI), Conformity Index (PTV-CI) and Gradient Index (PTV-GI). We calculated the maximum dose for each OAR (organ at risk) considered as well as the MLD2 (mean lung dose equivalent to 2Gy). The data were stratified according to expertise and technology. RESULTS Twenty-six centers equipped with Linacs, 3DCRT (4% - 1 center), static IMRT (8% - 2 centers), VMAT (76% - 20 centers), CyberKnife (4% - 1 center), and Tomotherapy (8% - 2 centers) collaborated. Significant PTV-gEUD2 differences were observed (range: 105-161Gy); mean-PTV dose, PTV-HI, PTV-CI, and PTV-GI were, respectively, 56.8±3.4Gy, 14.2±10.1%, 0.70±0.15, and 4.9±1.9. Significant correlations for PTV-gEUD2 versus PTV-HI, and MLD2 versus PTV-GI, were observed. CONCLUSIONS The differences in terms of PTV-gEUD2 may suggest the inclusion of PTV-gEUD2 calculation for retrospective data inter-comparison.

Multicentre treatment planning inter-comparison in a national context: The liver stereotactic ablative radiotherapy case

PURPOSE To compare five liver metastasis stereotactic ablative radiotherapy (SABR) plans optimised in fourteen centres with 3D-Conformal-RT, IMRT, VMAT, CyberKnife and Tomotherapy and identify possible dosimetric differences. METHODS Dose prescription was 75 Gy in 3 fractions, normalised at 67%-95% isodose. RESULTS Excluding few cases, all institutions achieved the planning objectives. Differences up to 40% and 25% in mean dose to liver and PTV were found. No significant correlations between technological factors and DVH for target and OARs were observed; the optimisation strategies selected by the planners played a key role in the planning procedure. CONCLUSIONS The human factor and the constraints imposed to the target volume have a greater dosimetric impact than treatment planning and radiation delivery technology in stereotactic treatment of liver metastases. Significant differences found both in terms of dosimetric target coverage and OAR sparing should be taken into consideration before starting a multi-institutional SARB clinical trial.

Role of the Technical Aspects of Hypofractionated Radiation Therapy Treatment of Prostate Cancer: A Review

The increasing use of moderate (<35 fractions) and extreme (<5 fractions) hypofractionated radiation therapy in prostate cancer is yielding favorable results, both in terms of maintained biochemical response and toxicity. Several hypofractionation (HF) schemes for the treatment of prostate cancer are available, although there is considerable variability in the techniques used to manage intra-/interfraction motion and deliver radiation doses. We performed a review of the published studies on HF regimens as a topic of interest for the Stereotactic Ablative Radiotherapy working group, which is part of the Italian Association of Medical Physics. Aspects of organ motion management (imaging for contouring, target volume definition, and rectum/bladder preparation) and treatment delivery (prostate localization, image guided radiation therapy strategy and frequency) were evaluated and categorized to assess outcome relative to disease control and toxicity. Despite the heterogeneity of the data, some interesting trends that emerged from the review might be useful in identifying an optimum HF strategy.

Small field output factors evaluation with a microDiamond detector over 30 Italian centers

PURPOSE The aim of the study was a multicenter evaluation of MLC&jaws-defined small field output factors (OF) for different linear accelerator manufacturers and for different beam energies using the latest synthetic single crystal diamond detector commercially available. The feasibility of providing an experimental OF data set, useful for on-site measurements validation, was also evaluated. METHODS This work was performed in the framework of the Italian Association of Medical Physics (AIFM) SBRT working group. The project was subdivided in two phases: in the first phase each center measured OFs using their own routine detector for nominal field sizes ranging from 10×10cm2 to 0.6×0.6cm2. In the second phase, the measurements were repeated in all centers using the PTW 60019 microDiamond detector. RESULTS The project enrolled 30 Italian centers. Micro-ion chambers and silicon diodes were used for OF measurements in 24 and 6 centers respectively. Gafchromic films and TLDs were used for very small field OFs in 3 and 1 centers. Regarding the measurements performed with the users detectors, OF standard deviations (SD) for field sizes down to 2×2cm2 were in all cases <2.7%. In the second phase, a reduction of around 50% of the SD was obtained using the microDiamond detector. CONCLUSIONS The measured values presented in this multicenter study provide a consistent dataset for OFs that could be a useful tool for improving dosimetric procedures in centers. The microDiamond data present a small variation among the centers confirming that this detector can contribute to improve overall accuracy in radiotherapy.

Frontiers in planning optimization for lung SBRT

Emerging data are showing the safety and the efficacy of Stereotactic Body Radiation therapy (SBRT) in lung cancer management. In this context, the very high doses delivered to the Planning Target Volume, make the planning phase essential for achieving high dose levels conformed to the shape of the target in order to have a good prognosis for tumor control and to avoid an overdose in relevant healthy adjacent tissue. In this non-systematic review we analyzed the technological and the physics aspects of SBRT planning for lung cancer. In particular, the aims of the study were: (i) to evaluate prescription strategies (homogeneous or inhomogeneous), (ii) to outline possible geometrical solutions by comparing the dosimetric results (iii) to describe the technological possibilities for a safe and effective treatment, (iv) to present the issues concerning radiobiological planning and the automation of the planning process.

A multi-center output factor intercomparison to uncover systematic inaccuracies in small field dosimetry

Large uncertainties in output factor (OF) small fields dosimetry motivated multicentric studies. The focus of the study was the determination of the OFs, for different linacs and radiosurgery units, using new-generation detectors. Intercomparison studies between radiotherapy centers improved quality dosimetry practices. Results confirmed the effectiveness of the studies to uncover large systematic inaccuracies in small field dosimetry.