B. Longobardi

Detection of systematic errors in external radiotherapy before treatment delivery

The execution of an independent control of monitor units (MU) and dose distribution calculation, together with a check of the data reported in the treatment chart is an effective tool in strongly reducing the occurrence of systematic errors before treatment delivery. In this paper we report the results of the analysis of 6272 controls (about 5000 patients) registered over more than 5 years; 70 serious errors (producing a deviation larger than 5% from the prescribed daily dose) and 147 minor errors were detected and corrected before the start of the treatment. The error rate was found to be strongly operator-dependent (serious error rate ranging from 0.3 to 2.5% when considering different operators). A time-trend analysis showed a significant reduction of serious errors, i.e. 1.5% in the period from September 1991 to April 1994 compared to 0.9% in the period from April 1994 to November 1996. However, even if the double check was highly effective in revealing human errors, three serious systematic errors (errors occurring during the calculation/planning/transcription phases) escaped the control and were detected by diode in vivo dosimetry during the period October 1994 to November 1996 (in 650 patients controlled).

Application of failure mode and effects analysis (FMEA) to pretreatment phases in tomotherapy

The aim of this paper was the application of the failure mode and effects analysis (FMEA) approach to assess the risks for patients undergoing radiotherapy treatments performed by means of a helical tomotherapy unit. FMEA was applied to the preplanning imaging, volume determination, and treatment planning stages of the tomotherapy process and consisted of three steps: 1) identification of the involved subprocesses; 2) identification and ranking of the potential failure modes, together with their causes and effects, using the risk probability number (RPN) scoring system; and 3) identification of additional safety measures to be proposed for process quality and safety improvement. RPN upper threshold for little concern of risk was set at 125. A total of 74 failure modes were identified: 38 in the stage of preplanning imaging and volume determination, and 36 in the stage of planning. The threshold of 125 for RPN was exceeded in four cases: one case only in the phase of preplanning imaging and volume determination, and three cases in the stage of planning. The most critical failures appeared related to (i) the wrong or missing definition and contouring of the overlapping regions, (ii) the wrong assignment of the overlap priority to each anatomical structure, (iii) the wrong choice of the computed tomography calibration curve for dose calculation, and (iv) the wrong (or not performed) choice of the number of fractions in the planning station. On the basis of these findings, in addition to the safety strategies already adopted in the clinical practice, novel solutions have been proposed for mitigating the risk of these failures and to increase patient safety. PACS number: 87.55.Qr

Exit dose measurements by portal film dosimetry

Abstract Portal in vivo dosimetry is a very attractive tool for patient dose measurements because of the large amount of information that portal film systems can easily collect, once positioned at the exit surface of the patient, The first step in the verification of the reliability of portal films as in vivo dosimeters is the evaluation of the agreement between exit patient dose profiles and optical density profiles measured on the portal film, We checked the possibilities for exit dose measurements of a commercial portal film system (Film Kodak X-Omat V and Localization Kodak Cassette) verifying the agreement between relative exit doses (measured by ionization chamber and film dosimetry, calculated by our treatment planning system (Cadplan Dosetek)) and relative optical densities on portal films in cubic homogeneous and inhomogeneous, cylindrical and humanoid phantoms, In particular, a good agreement (mean difference in absolute value: 2%) between optical densities and calculated exit doses for the Rando phantom were found, once the optical densities values are corrected for an inverse square correction factor, taking into account the variation of the profile of the phantom.

Human errors in the calculation of monitor units in clinical radiotherapy practice

Human mistakes are an important source of error in all steps of radiotherapy planning and their incidence should be investigated. As has been recognized by different authors and by the ICRU [4], the human error rate in the calculation of monitor units (MU) is relatively high. At our institute, we measured the human error rate in the calculation of MU by an independent check of the calculation. From September 1991 to June 1992 we identified and corrected 17 serious errors (deviation from the prescribed dose > or = 5%) over 890 controls (1.9%) (daily dose errors). We also found a serious global dose error rate (i.e. the errors induced on the total reference dose for the complete course of the treatment) of 1.3% (9/685) during the period November 1991-June 1992. These values suggest the importance of human errors in the calculation of MU and also confirm the validity of the independent check of MU calculation as one of the simplest ways of avoiding erroneous dose delivery by incorrect calculation of MU.

Internal target volume defined by contrast-enhanced 4D-CT scan in unresectable pancreatic tumour: Evaluation and reproducibility

We compared customized ITVs obtained with CE-4D-CT imaging (ITV(4D)) with a population-based (ITV(PBC)) in 29 patients (PTs) and evaluated the intra-observer ITV delineation reproducibility in 5 PTs with unresectable pancreatic ductal adenocarcinoma (PDA). The ITV(PBC) was quite different from the ITV(4D), with under/over estimation of volume. Intra-observer volume delineation variability on CE-4D-CT and on a single-phase CE-CT were similar (27.6% vs 24.9%).

Salvage brachytherapy for local recurrence after radical prostatectomy and subsequent external beam radiotherapy

OBJECTIVES To evaluate the technical feasibility, safety, and efficacy of seed implantation for local recurrence after radical prostatectomy and external beam radiotherapy. METHODS Between October 1999 and March 2002, 10 patients with targeted, histologically proven local relapse after surgery and subsequent external beam radiotherapy (only in 8 patients), underwent permanent brachytherapy with palladium-103 and iodine-125 after complete restaging. In all patients, an intraoperative morphovolumetric ultrasound study of the target was performed, with a planning target volume ranging from 5 to 26.7 cm(3). The preimplant prostate-specific antigen values ranged from 1.1 to 6.31 ng/mL. RESULTS Postplan dosimetry was performed to determine the percentage of the target volume that received a dose equal to, or greater than, the prescribed dose (range 84.5% to 95.9%) and the dose that was delivered to the 90% of the target volume (range 85.08% to 129.43%). The urinary scores, measured using the International Prostate Symptom Score, had normalized at 3 months. Only 1 patient had worsened incontinence during the first 2 months, with subsequent restoration of the previous situation. The other patients did not have any changes in their previous clinical condition. One patient experienced occasional gross hematuria that had been present after external beam radiotherapy. No rectal complications were reported. After a median follow-up of 20.6 months, 7 patients showed a decreasing or stable prostate-specific antigen level. CONCLUSIONS This preliminary experience has demonstrated that seed implantation of a neoplastic local recurrence is technically feasible and safe and allows for accurate dosimetry when the area to be treated can be defined by ultrasonography. Longer follow-up, accurate patient selection, and larger series of patients could help to better define the oncologic outcome.

Skin dose measurements for head and neck radiotherapy

The use of immobilization plastic masks in head and neck radiotherapy can partially eliminate skin benefits derived from the utilization of megavoltage photon beams. Filters and blocks between the patient and the accelerator can further increase the skin dose value. In this study, the increase in surface dose due to 2 and 3.2 mm of plastic material utilized for patient immobilization was measured. Then, the effect of blocking trays, wedges, and blocks on skin dose in typical conditions for head and neck irradiation was evaluated. The measurements were obtained with a NE2534 chamber (Markus type) on a perspex phantom for 6 MeV x-rays from an accelerator.

Hypofractionated Image-Guided IMRT in Advanced Pancreatic Cancer With Simultaneous Integrated Boost to Infiltrated Vessels Concomitant With Capecitabine: A Phase I Study

PURPOSE To determine the maximum tolerated radiation dose (MTD) of an integrated boost to the tumor subvolume infiltrating vessels, delivered simultaneously with radical dose to the whole tumor and concomitant capecitabine in patients with pretreated advanced pancreatic adenocarcinoma. METHODS AND MATERIALS Patients with stage III or IV pancreatic adenocarcinoma without progressive disease after induction chemotherapy were eligible. Patients underwent simulated contrast-enhanced four-dimensional computed tomography and fluorodeoxyglucose-labeled positron emission tomography. Gross tumor volume 1 (GTV1), the tumor, and GTV2, the tumor subvolume 1 cm around the infiltrated vessels, were contoured. GTVs were fused to generate Internal Target Volume (ITV)1 and ITV2. Biological tumor volume (BTV) was fused with ITV1 to create the BTV+Internal Target Volume (ITV) 1. A margin of 5/5/7 mm (7 mm in cranium-caudal) was added to BTV+ITV1 and to ITV2 to create Planning Target Volume (PTV) 1 and PTV2, respectively. Radiation therapy was delivered with tomotherapy. PTV1 received a fixed dose of 44.25 Gy in 15 fractions, and PTV2 received a dose escalation from 48 to 58 Gy as simultaneous integrated boost (SIB) in consecutive groups of at least 3 patients. Concomitant chemotherapy was capecitabine, 1250 mg/m(2) daily. Dose-limiting toxicity (DLT) was defined as any treatment-related G3 nonhematological or G4 hematological toxicity occurring during the treatment or within 90 days from its completion. RESULTS From June 2005 to February 2010, 25 patients were enrolled. The dose escalation on the SIB was stopped at 58 Gy without reaching the MTD. One patient in the 2(nd) dose level (50 Gy) had a DLT: G3 acute gastric ulcer. Three patients had G3 late adverse effects associated with gastric and/or duodenal mucosal damage. All patients received the planned dose of radiation. CONCLUSIONS A dose of 44.25 Gy in 15 fractions to the whole tumor with an SIB of 58 Gy to small tumor subvolumes concomitant with capecitabine is feasible in chemotherapy-pretreated patients with advanced pancreatic cancer.