Determination of the accuracy of implant reconstruction and dose delivery in brachytherapy in The Netherlands and Belgium.

PURPOSE: To gain insight into the accuracy of brachytherapy treatments, the accuracy of implant reconstruction and dose delivery was investigated in 33 radiotherapy institutions in The Netherlands and Belgium. MATERIALS AND METHODS: The accuracy of the implant reconstruction method was determined using a cubic phantom containing 25 spheres at well-known positions. Reconstruction measurements were obtained on 41 brachytherapy localizers, 33 of which were simulators. The reconstructed distances between the spheres were compared with the true distances. The accuracy of the dose delivery was determined for high dose rate (HDR), pulsed dose rate (PDR) and low dose rate (LDR) afterloading systems using a polymethyl methacrylate cylindrical phantom containing a NE 2571 ionization chamber in its centre. The institutions were asked to deliver a prescribed dose at the centre of the phantom. The measured dose was compared with the prescribed dose. RESULTS: The average reconstruction accuracy was -0.07 mm (+/-0.4 mm, 1 SD) for 41 localizers. The average deviation of the measured dose from the prescribed dose was +0.9% (+/-1.3%, 1 SD) for 21 HDR afterloading systems, +1.0% (+/-2.3%, 1 SD) for 12 PDR afterloaders, and +1.8% (+/-2.5%, 1 SD) for 15 LDR afterloaders. CONCLUSIONS: This comparison showed a good accuracy of brachytherapy implant reconstruction and dose delivery in The Netherlands and Belgium.

Prescribing, recording, and reporting in endovascular brachytherapy. Quality assurance, equipment, personnel and education.

Endovascular brachytherapy is a new, rapidly growing field of interest in radiotherapy for the prevention of neointimal hyperplasia after angioplasty in both coronary and peripheral arteries. Many physics aspects of these treatments have already been addressed in the report of the American Association of Physicists in Medicine task group on 'Intravascular brachytherapy', but up to now there are no generally accepted recommendations for recording and reporting radiation doses and volumes. The terminology to be used by all individuals involved in such treatments (radiation oncologists, physicists, and interventionalists) is not clearly defined. The Endovascular Groupe Européen de Curiethérapie/European Society for Therapeutic Radiology and Oncology Working Group in this document presents recommendations for a common language for general use in endovascular brachytherapy. This proposal addresses general terms and concepts for target and dose specification as well as detailed recommendations for dose prescription, recording and reporting in endovascular brachytherapy for both peripheral and coronary arteries. Additionally, quality assurance and radiation safety aspects are briefly addressed, as are aspects related to equipment, personnel, and training and education related to endovascular brachytherapy.

How long is enough? Defining the treatment length in endovascular brachytherapy.

The International Commission on Radiation Units and Measurement (IRCU) 50 has clearly defined treatment volumes in radiation therapy in the management of neoplasms. These concepts are applied to the field of endovascular brachytherapy (EVBT) for the prevention of postangioplasty restenosis. The following definitions are proposed: gross target length (GTL) is defined as the narrowed segment of the artery that requires intervention. Clinical target length (CTL) is defined as the intervened or injured length, which could be due to angioplasty, stent strut injury, stent deployment, or debulking procedures. Planning target length (PTL) is the CTL plus a margin to account for heart/catheter movement and uncertainty in target localization. The final treatment length (TL) is the PTL plus the effect of penumbra. The accurate specification of treatment length serves several important purposes. Based on an understanding of the different factors constituting the treatment length, adequate margins can be provided beyond the GTL; this will avoid geographic misses and minimize edge failures. These definitions of target length ensure treatment consistency and provide a standard terminology for communication among practitioners of EVBT, something of critical importance in the conduct of multi-institutional trials in this new and multidisciplinary therapy. Finally, since the efficacy of EVBT is critically dependent on the precision of radiation delivery, these guidelines ensure that the benefits of EVBT seen in prospective randomized trials can be translated into daily clinical practice at the community level.

Feasibility and first results of multimodality treatment, combining EBRT, extensive surgery, and IOERT in locally advanced primary rectal cancer.

PURPOSE: To assess the outcome of aggressive multimodality treatment with preoperative external beam radiation therapy (EBRT), extended circumferential margin excision (ECME) and intraoperative electron beam radiation therapy (IOERT) in patients with locally advanced primary rectal cancer. METHODS AND MATERIALS: Thirty-eight patients with primary locally advanced rectal cancer, but without distant metastases, received multimodality treatment. CT-scan showed extension to other structures in 15 patients (39%) and definite infiltration into the surrounding structures in 23 patients (61%). All patients received preoperative EBRT (dose range 25-61 Gy) and 82% received 50.4 Gy. The resection types were: 12 low anterior resections (31%), 14 abdomino-perineal resections (37%), 6 abdomino-transsacral resections (16%), and 6 pelvic exenterations (16%). The IOERT dose ranged from 10 to 17.5 Gy depending on the completeness of the resection. RESULTS: There was no perioperative mortality. The resection margins were microscopically negative in 31 patients (82%), microscopically positive in 4 (10%), and positive with gross residual disease in 3 patients (8%). Pelvic recurrences were observed in 5 patients (13%) including 3 IOERT infield failures. The overall 3-year local control, disease-free survival (DFS), and survival rates were 82%, 65%, and 72%, respectively. Negative resection margins were the most significant prognostic factor with regard to DFS (p = 0.0003) and distant control (p = 0.002) compared with cancer involved surgical margins. CONCLUSION: A high percentage of curative resections can be achieved in this group of patients with locally advanced rectal cancers. Adding IOERT to preoperative EBRT and ECME achieves high local control rates and possibly improves survival.

Intraoperative electron beam radiation therapy for locally recurrent rectal carcinoma.

PURPOSE: Treatment results for locally recurrent rectal cancers are poor. This is a result of the fact that surgery is hampered due to the severance of the anatomical planes during the primary procedure and that radiotherapy is limited by normal tissue tolerance, especially after previous irradiation. This paper describes the results of a combined treatment modality in this patient group. METHODS AND MATERIALS: From 1994 to 1998, 37 patients with locally recurrent rectal cancer, but without distant metastatic disease, received a combined treatment consisting of 50.4 Gy preoperative irradiation or, in case of previous radiotherapy, 30 Gy reirradiation or no irradiation, followed by radical surgery and intraoperative electron beam radiotherapy boost. RESULTS: Fifteen patients received a radical resection (R0), eight a microscopic irradical resection (R1), and 14 a macroscopic irradical resection (R2). The overall 3-year local control (LC), disease-free survival (DFS), and overall survival rates were 60%, 32%, and 58% respectively. Radicality of resection (R0/R1 vs. R2) turned out to be the significant factor for improved survival (p < 0.05), DFS (p = 0.0008), and LC (p = 0.01). Preoperative (re-)irradiation is the other significant factor in survival (p = 0.005) and DFS (p = 0.001) and was almost significant for LC (p = 0.08). After external beam radiation therapy (EBRT) a significantly higher resection rate was obtained (R0/R1 vs. R2 p = 0.001). Symptomatic peripheral local recurrences have a significantly worse prognosis and higher rate of R2-resection (p = 0.0005). CONCLUSION: Centralization of locally recurrent rectal cancer patients enabled the development of an aggressive multimodality treatment, which in turn led to promising results. Distant failure is still a drawback.

Monte Carlo calculated dose distribution for endovascular HDR brachytherapy with Ir-192.

BACKGROUND AND PURPOSE: For endovascular HDR brachytherapy, very thin sources are required and the dose is specified at a short distance to the source centre down to 1.5 mm. The source which is used in the Nucletron HDR Selectron stepping source afterloader is treated by most dose calculation algorithms in clinical use as a point source, although its dimensions are large compared to these dose specification distances. Furthermore, inaccuracies might be introduced because consecutive dwell positions show an overlap of sources if the step size is smaller than the active length of the source. MATERIALS AND METHODS: In order to quantify these inaccuracies, we used the EGS4 Monte Carlo code to generate the dose distribution with 0.5 mm spatial resolution for a single source. From this, translation and superposition were used to calculate dose distributions for multiple dwell positions. The results are compared with those of other Monte Carlo computations and of a commercial brachytherapy planning system. RESULTS AND CONCLUSIONS: Our Monte Carlo calculations showed that secondary electrons have no relevant influence on the dose distribution and that errors up to 25% are made when using the point source approximation for irradiations with a single dwell position. However, when three or more dwell positions are used with equal dwell times, the total error becomes negligibly small because the errors from subsequent dwell positions compensate each other. At distances larger than 5 mm, there is a good match between the Monte Carlo data and those of point source algorithms for all clinical relevant cases.

Measurement and calculation of the dose at large distances from brachytherapy sources: Cs-137, Ir-192, and Co-60.

In a small number of special cases it may be necessary to estimate the radiation dose to organs far away from the target volume of a patient receiving radiotherapy, e.g. the dose to the gonads or to the fetus of a pregnant patient. Previously, for external beam radiotherapy a model was developed, which enabled this estimation with acceptable accuracy for the range of photon beam energies from cobalt-60 to 25 MV, independent of the make of the treatment machines, for generally used techniques and for a wide range of distances from the beam axis and field sizes [Van der Giessen and Hurkmans, Int. J. Radiat. Oncol. Biol. Phys. 27, 717-724 (1993); van der Giessen, ibid. 30, 1239-1246 (1994); to appear in Int. J. Radiat. Oncol. Biol. Phys.]. In this paper, results of measurements and Monte Carlo calculations are reported for evaluation of the dose at large distances from some brachytherapy sources. This has resulted in information on the behavior of the tissue attenuation factor T(r) for commonly used sources: Co-60, Ir-192, and Cs-137, in the range of distances up to 60 cm from the source. The influence of the size of the phantom was investigated. A mathematical model, described earlier by Kornelsen and Young, proved to yield the best fit to the results [Br. J. Radiol. 54, 136 (1981)]. Parameters for this model are derived for these isotopes. A few experiments in a Rando Alderson phantom are presented to support the measurements and the calculations.

Measurements and calculations of the absorbed dose distribution around a 60Co source.

The data from Meisberger et al. [Radiology 90, 953-957 (1968)] are often used as a basis for dose calculations in brachytherapy. In order to describe the absorbed dose in water around a brachytherapy point source, Meisberger provided a polynomial fit for different isotopes taking into account the effect of attenuation and scattering. The validity of the Meisberger coefficients is restricted to distances up to 10 cm from the source, which is regarded to be satisfactory for most brachytherapy applications. However, for more distant organs it may lead to errors in calculated absorbed dose. For this reason dose measurements have been performed in air and in water around a high activity 60Co source used in high dose rate brachytherapy. Measurements were carried out to distances of 20 cm, using ionization chambers. These data show that at a distance of about 15 cm the amount of scattered radiation virtually equals the amount of primary radiation. This emphasizes the contribution of scattered radiation to the dose in healthy tissue far from the target volume, even with relatively high energy photon radiation of 60Co. It is also shown that the Meisberger data as well as the approach of Van Kleffens and Star [Int. J. Radiat. Oncol. Phys. 5, 557-563 (1979)] lead to significant errors in absorbed dose between distances of 10 and 20 cm from the source. In addition to these measurements, the Monte Carlo code has been used to calculate separately primary dose and scattered dose from a cobalt point source. The calculated results agree with the experimental data within 1% for a most distant dose scoring region.