Rates of MRI simulator utilisation in a tertiary cancer therapy centre.

Magnetic resonance imaging (MRI) is increasingly being integrated into the radiation oncology workflow, due to its improved soft tissue contrast without additional exposure to ionising radiation. A review of MRI utilisation according to evidence based departmental guidelines was performed. Guideline utilisation rates were calculated to be 50% (true utilisation rate was 46%) of all new cancer patients treated with adjuvant or curative intent, excluding simple skin and breast cancer patients. Guideline utilisation rates were highest in the lower gastrointestinal and gynaecological subsites, with the lowest being in the upper gastrointestinal and thorax subsites. Head and neck (38% vs 45%) and CNS (46% vs 67%) cancers had the largest discrepancy between true and guideline utilisation rates due to unnamed reasons and non-contemporaneous diagnostic imaging respectively. This report outlines approximate MRI utilisation rates in a tertiary radiation oncology service and may help guide planning for future departments contemplating installation of an MRI simulator.

Technical Note: Experimental characterization of the dose deposition in parallel MRI-linacs at various magnetic field strengths.

PURPOSE: Dose deposition measurements for parallel MRI-linacs have previously only shown comparisons between 0 T and a single available magnetic field. The Australian MRI-Linac consists of a magnet coupled with a dual energy linear accelerator and a 120 leaf Multi-Leaf Collimator with the radiation beam parallel to the magnetic field. Two different magnets, with field strengths of 1 and 1.5 T, were used during prototyping. This work aims to characterize the impact of the magnetic field at 1 and 1.5 T on dose deposition, possible by comparing dosimetry measured at both magnetic field strengths to measurements without the magnetic field. METHODS: Dose deposition measurements focused on a comparison of beam quality (TPR20/10 ), PDD, profiles at various depths, surface doses, and field size output factors. Measurements were acquired at 0, 1, and 1.5 T. Beam quality was measured using an ion chamber in solid water at isocenter with appropriate TPR20/10 buildup. PDDs and profiles were acquired via EBT3 film placed in solid water either parallel or perpendicular to the radiation beam. Films at surface were used to determine surface dose. Output factors were measured in solid water using an ion chamber at isocenter with 10 cm solid water buildup. RESULTS: Beam quality was within ±0.5% of the 0 T value for the 1 and 1.5 T magnetic field strengths. PDDs and profiles showed agreement for the three magnetic field strengths at depths beyond 20 mm. Deposited dose increased at shallower depths due to electron focusing. Output factors showed agreement within 1%. CONCLUSION: Dose deposition at depth for a parallel MRI-linac was not significantly impacted by either a 1 or 1.5 T magnetic field. PDDs and profiles at shallow depths and surface dose measurements showed significant differences between 0, 1, and 1.5 T due to electron focusing.

Rapid learning in practice: a lung cancer survival decision support system in routine patient care data.

BACKGROUND AND PURPOSE: A rapid learning approach has been proposed to extract and apply knowledge from routine care data rather than solely relying on clinical trial evidence. To validate this in practice we deployed a previously developed decision support system (DSS) in a typical, busy clinic for non-small cell lung cancer (NSCLC) patients. MATERIAL AND METHODS: Gender, age, performance status, lung function, lymph node status, tumor volume and survival were extracted without review from clinical data sources for lung cancer patients. With these data the DSS was tested to predict overall survival. RESULTS: 3919 lung cancer patients were identified with 159 eligible for inclusion, due to ineligible histology or stage, non-radical dose, missing tumor volume or survival. The DSS successfully identified a good prognosis group and a medium/poor prognosis group (2 year OS 69% vs. 27/30%, p<0.001). Stage was less discriminatory (2 year OS 47% for stage I-II vs. 36% for stage IIIA-IIIB, p=0.12) with most good prognosis patients having higher stage disease. The DSS predicted a large absolute overall survival benefit (∼40%) for a radical dose compared to a non-radical dose in patients with a good prognosis, while no survival benefit of radical radiotherapy was predicted for patients with a poor prognosis. CONCLUSIONS: A rapid learning environment is possible with the quality of clinical data sufficient to validate a DSS. It uses patient and tumor features to identify prognostic groups in whom therapy can be individualized based on predicted outcomes. Especially the survival benefit of a radical versus non-radical dose predicted by the DSS for various prognostic groups has clinical relevance, but needs to be prospectively validated.

Independent calculation-based verification of IMRT plans using a 3D dose-calculation engine.

Independent monitor unit verification of intensity-modulated radiation therapy (IMRT) plans requires detailed 3-dimensional (3D) dose verification. The aim of this study was to investigate using a 3D dose engine in a second commercial treatment planning system (TPS) for this task, facilitated by in-house software. Our department has XiO and Pinnacle TPSs, both with IMRT planning capability and modeled for an Elekta-Synergy 6MV photon beam. These systems allow the transfer of computed tomography (CT) data and RT structures between them but do not allow IMRT plans to be transferred. To provide this connectivity, an in-house computer programme was developed to convert radiation therapy prescription (RTP) files as generated by many planning systems into either XiO or Pinnacle IMRT file formats. Utilization of the technique and software was assessed by transferring 14 IMRT plans from XiO and Pinnacle onto the other system and performing 3D dose verification. The accuracy of the conversion process was checked by comparing the 3D dose matrices and dose volume histograms (DVHs) of structures for the recalculated plan on the same system. The developed software successfully transferred IMRT plans generated by 1 planning system into the other. Comparison of planning target volume (TV) DVHs for the original and recalculated plans showed good agreement; a maximum difference of 2% in mean dose, - 2.5% in D95, and 2.9% in V95 was observed. Similarly, a DVH comparison of organs at risk showed a maximum difference of +7.7% between the original and recalculated plans for structures in both high- and medium-dose regions. However, for structures in low-dose regions (less than 15% of prescription dose) a difference in mean dose up to +21.1% was observed between XiO and Pinnacle calculations. A dose matrix comparison of original and recalculated plans in XiO and Pinnacle TPSs was performed using gamma analysis with 3%/3mm criteria. The mean and standard deviation of pixels passing gamma tolerance for XiO-generated IMRT plans was 96.1 ± 1.3, 96.6 ± 1.2, and 96.0 ± 1.5 in axial, coronal, and sagittal planes respectively. Corresponding results for Pinnacle-generated IMRT plans were 97.1 ± 1.5, 96.4 ± 1.2, and 96.5 ± 1.3 in axial, coronal, and sagittal planes respectively.

Radiation dose and contralateral breast cancer risk associated with megavoltage cone-beam computed tomographic image verification in breast radiation therapy.

PURPOSE: To measure and compare organ doses from a standard tangential breast radiation therapy treatment (50 Gy delivered in 25 fractions) and a megavoltage cone-beam computed tomography (MV-CBCT), taken for weekly image verification, and assess the risk of radiation-induced contralateral breast cancer. METHODS AND MATERIALS: Organ doses were measured with thermoluminescent dosimeters placed strategically within a female anthropomorphic phantom. The risk of radiation-induced secondary cancer of the contralateral breast was estimated from these values using excess absolute risk and excess relative risk models. RESULTS: The effective dose from a MV-CBCT (8-monitor units) was 35.9 ± 0.2 mSv. Weekly MV-CBCT imaging verification contributes 0.5% and 17% to the total ipsilateral and contralateral breast dose, respectively. For a woman irradiated at age 50 years, the 10-year postirradiation excess relative risk was estimated to be 0.8 and 0.9 for treatment alone and treatment plus weekly MV-CBCT imaging, respectively. The 10-year postirradiation excess absolute risk was estimated to be 4.7 and 5.6 per 10,000 women-years. CONCLUSIONS: The increased dose and consequent radiation-induced second cancer risk as calculated by this study introduced by the imaging verification protocols utilizing MV-CBCT in breast radiation therapy must be weighed against the benefits of more accurate treatment. As additional image verification becomes more common, it is important that data be collected in regard to long-term malignancy risk.

Trauma team radiation exposure: the potential need for dosimetry monitoring.

OBJECTIVES: Australian radiation regulations require routine monitoring of health-care workers who might receive a whole-body effective radiation dose in excess of 1 mSv/year. In Australian hospitals, routine monitoring with a dosimeter is recommended for levels beyond 300 microSv/year. We aimed to determine the potential radiation exposure to trauma team members and whether routine personal radiation dosimetry should be recommended. METHOD: An anthropomorphic mannequin with a radiation detector was placed at five locations around the resuscitation bed. Three sets of standard trauma-series X-rays were performed, and the exposure was measured and averaged at each location. These data were then extrapolated to estimate the potential radiation equivalence at the level of the thyroid gland for staff working in each of the locations over a 1 year period with and without personal protective equipment. RESULTS: The total dose ranged from 1.2 to 20.5 microSv for a single trauma patient. The highest recorded dose was at the location of the circulation doctor during pelvic X-ray. Based on these data, it would take only 15 trauma patients per year for a team member to be potentially exposed to the level at which routine dosimetry is usually recommended, should no personal protective equipment be used. The use of a lead gown and a lead gown with a thyroid collar reduced exposure by four- and ninefold, respectively. CONCLUSIONS: We have demonstrated the possibility of significant ionizing radiation exposure for unprotected trauma team members. Dosimeter use by trauma team personnel needs to be reviewed based on local protocols and patient numbers.