S. Vigorito

Survey of computed tomography techniques and absorbed dose in Italian hospitals: a comparison between two methods to estimate the dose-length product and the effective dose and to verify fulfilment of the diagnostic reference levels.

The aim of this study was the production of the first Italian survey of radiation dose in computed tomography (CT) prior to the widespread adoption of multislice CT, in order to have a reference point to facilitate later investigation of dose exposure changes brought by this new CT modality. The collected dose data were compared with diagnostic reference levels (DRLs). The agreement between experimental dose evaluation and Monte Carlo (MC) simulations was investigated. The survey was carried out in 29 Italian hospitals, covered 48 CT scanners and 232 examinations. The dose–length product (DLP) and effective dose (E) values were estimated based on MC simulations for seven clinical protocols using the CT-Dose program. Statistical analysis showed a significant difference (p<0.01) in the DLP between the two methods, with MC values being greater than the experimental ones. For E, the MC values were greater in routine head (8.2%), cervical spine (2.7%) and lumbar spine (2.9%) studies. The weighted CT dose index, the DLP and E were always below the DRLs set by the European Community. This dose survey gives a good but incomplete picture of the Italian CT dose situation and may be useful as a reference baseline for defining clinical multislice protocols in the near future.

Validation of a pretreatment delivery quality assurance method for the CyberKnife Synchrony system

PURPOSE To evaluate the geometric and dosimetric accuracies of the CyberKnife Synchrony respiratory tracking system (RTS) and to validate a method for pretreatment patient-specific delivery quality assurance (DQA). METHODS An EasyCube phantom was mounted on the ExacTrac gating phantom, which can move along the superior-inferior (SI) axis of a patient to simulate a moving target. The authors compared dynamic and static measurements. For each case, a Gafchromic EBT3 film was positioned between two slabs of the EasyCube, while a PinPoint ionization chamber was placed in the appropriate space. There were three steps to their evaluation: (1) the field size, the penumbra, and the symmetry of six secondary collimators were measured along the two main orthogonal axes. Dynamic measurements with deliberately simulated errors were also taken. (2) The delivered dose distributions (from step 1) were compared with the planned ones, using the gamma analysis method. The local gamma passing rates were evaluated using three acceptance criteria: 3% local dose difference (LDD)/3 mm, 2%LDD/2 mm, and 3%LDD/1 mm. (3) The DQA plans for six clinical patients were irradiated in different dynamic conditions, to give a total of 19 cases. The measured and planned dose distributions were evaluated with the same gamma-index criteria used in step 2 and the measured chamber doses were compared with the planned mean doses in the sensitive volume of the chamber. RESULTS (1) A very slight enlargement of the field size and of the penumbra was observed in the SI direction (on average <1 mm), in line with the overall average CyberKnife system error for tracking treatments. (2) Comparison between the planned and the correctly delivered dose distributions confirmed the dosimetric accuracy of the RTS for simple plans. The multicriteria gamma analysis was able to detect the simulated errors, proving the robustness of their method of analysis. (3) All of the DQA clinical plans passed the tests, both in static and dynamic conditions. No statistically significant differences were found between static and dynamic cases, confirming the high degree of accuracy of the Synchrony RTS. CONCLUSIONS The presented methods and measurements verified the mechanical and dosimetric accuracy of the Synchrony RTS. Their method confirms the fact that the RTS, if used properly, is able to treat a moving target with great precision. By combining PinPoint ion chamber, EBT3 films, and gamma evaluation of dose distributions, their DQA method robustly validated the effectiveness of CyberKnife and Synchrony system.

Second pelvic recurrence of rectal cancer successfully treated with a re-reirradiation (3rd radiation course)

Introduction: In case of pelvic recurrence of colorectal cancer, reirradiation of previously irradiated patients may increase the rate of salvage radical resection. Due to the high cumulative dose, one of the main concerns is radiation-induced lumbosacral plexopathy. This report describes multiple irradiations of a lesion adjacent to the lumbosacral plexus, using a highly selective technique, which allows optimal sparing of such a critical structure. Case description A 53-year-old woman treated in 2008 for a locally advanced rectal adenocarcinoma with preoperative pelvic irradiation and concomitant chemotherapy followed by surgery had disease recurrence in 2011 and underwent a second course of pelvic radiotherapy. In December 2015, magnetic resonance imaging showed a single local recurrence infiltrating the muscle next to the right lumbosacral plexus and close to the cauda equina. Repeat reirradiation was planned. The total dose deriving from the previous treatment plans was assessed by nonrigid image registration using the dedicated tool implemented in MIM 6.1.7 (MIMvista Corp., Cleveland, OH). The treatment was performed with Cyberknife (Accuray, Sunnyvale, CA) with a schedule of 20 Gy in 5 fractions (4 Gy per fraction). The dose was prescribed to 70% isodose and target coverage was 97%. Two months after the treatment, magnetic resonance imaging showed a decreased signal and stable disease with no change in tumor size. Conclusions This case report suggests that pelvic re-reirradiation might be a possibility in very carefully selected cases of rectal cancer, using high-precision radiation modalities.

CyberKnife radiotherapy for orbital metastases: A single-center experience on 24 lesions

Objectives: To evaluate the feasibility, in terms of acute toxicity and symptom control, of CyberKnife (Accuray, Sunnyvale, CA)-based stereotactic radiotherapy (CyberKnife-SRT) for metastatic orbital lesions. Methods: This retrospective study included patients with symptomatic metastases wholly located within the orbit. Palliative radiation treatment was performed using CyberKnife image-guided technology. Gross tumor volume was defined on a pre-radiotherapy magnetic resonance imaging. Acute and late toxicity was recorded according to Radiation Therapy Oncology Group/European Organization for Research and Treatment of Cancer Scale. Results: Between April 2012 and July 2016, 21 patients underwent CyberKnife-SRT for 24 orbital metastases from different primary tumors. Median treatment dose was 18 Gy (15–24 Gy) given in a median of 3 fractions (2–3 fractions) with a median dose of 6 Gy/fraction (5–10 Gy/fraction). Acute grade 1 toxicity was observed in eight cases. No local recurrence occurred after median follow-up of 6.2 months (1.1–30.0 months) among 16 lesions that underwent post-stereotactic radiotherapy magnetic resonance imaging. All patients reported decreasing pre-stereotactic radiotherapy symptoms without late toxicity. Follow-up >6 months (median 22.8 months) was available for nine lesions; complete and partial radiological response was registered in four and five of them, respectively. Conclusion: In our experience, CyberKnife-SRT is a well-tolerated treatment that offers high local and symptom control in patients with intraocular and periocular malignant lesions.