On the transit dose from motorized wedge treatment in Equinox-80 telecobalt unit.

PURPOSE: To estimate the transit dose from motorized wedge (MW) treatment in Equinox-80 telecobalt machine. MATERIALS AND METHODS: Two plans were generated in Eclipse treatment planning system with universal wedge (UW) and MW each for 10 x 10 cm 2 . The transit dose was measured with 0.6 cc cylindrical ion chamber and thermoluminescent dosimeters (TLD) chips at a depth of 5 cm with source to axis distance (SAD) 80 cm. RESULTS: The measured dose with ion chamber was in well agreement with the calculated dose from Eclipse within +/- 2%. The planned dose was 100 cGy while the measured absorbed dose with ion chamber for 15 degrees , 30 degrees , 45 degrees and 60 degrees MW treatment was found to be 100.94, 101.04, 100.72 and 99.33 cGy respectively. For 15 degrees , 30 degrees , 45 degrees and 60 degrees UW treatment, the measured absorbed dose was 99.33, 97.67, 97.77 and 99.57 cGy respectively. Similarly the measured absorbed dose with TLD was within +/- 3% with the planned dose for universal wedge (UW) and MW. From the experimental measurements, it was found that there was no significant contribution of transit dose during MW treatment. CONCLUSION: The actual measurements carried out with ion chamber in Equinox-80 machine for UW and MW revealed no variation between the doses delivered. The doses were comparable for both UW and MW treatments. The results from TLD measurements additionally confirmed no variation between the doses delivered with UW and MW. It was also demonstrated that the observed excess or less transit dose with MW does not have any significant clinical impact. This assured the safe dose delivery with MW.

Design and development of motorized multileaf collimator for telecobalt unit.

A manual multileaf collimator developed for telecobalt unit was motorized to accomplish the easy movement of the leaves. The required field shaping using MLC could be achieved by either using template or display. The beam characteristics were investigated and then compared with those of customized blocks. The maximum interleaf leakage and the percentage of transmission measured at the depth of maximum ionization (0.5cm) were found to be 2.7% and 2.4%, respectively. The field shaping performed by the MLC was verified using film dosimetry. The comparative study of treatment plans of 3DCRT and IMRT between (60)Co beam and 6 MV beams was carried out. This MLC could be used as a substitute for conventional blocks in static fields, there by eliminating the effort and cost of fabricating customized blocks, the need for storage space for blocks and other practical difficulties during the process of the block making. It is also demonstrated that if a provision for IMRT delivery with MLC for (60)Co is made, could be a cost effective alternative to IMRT with 6 MV beam.

Análises de protocolos teleterápicos de controle de qualidade de alguns serviços locais, baseados no TG40 e ARCAL XXX / Routine teletherapy quality control protocols based on TG40 and ARCAL XXX

Considerando a importância da garantia da qualidade nos serviços de radioterapia, este trabalho tem como primeiro objetivo fazer uma avaliação dos testes propostos pelos protocolos oficiais internacionais TG40 e ARCAL XXX para os equipamentos de cobalto, acelerador linear e simulador. O segundo objetivo consistiu em se fazer uma avaliação dos testes que atualmente são realizados por alguns serviços de radioterapia nacionais e da América Latina, comparando-os com os apresentados nos protocolos citados. Dos resultados obtidos, observou-se que embora o TG40 apresente os testes básicos necessários para um controle de qualidade adequado, o ARCAL ainda sugere testes complementares. Dos resultados e discussões, concluiu-se que é necessário que os serviços de radioterapia implementem os testes de controle de qualidade básicos e indispensáveis aos seus equipamentos, e que os demais testes sejam implementados de acordo com as suas necessidades e disponibilidades. Como produto deste estudo, sugestões de protocolos são apresentadas para o trabalho de rotina, provenientes da fusão dos protocolos analisados.

Inter-comparison of absorbed dose to water in a Co-60 therapy beam using IAEA and HPA protocols.

The absorbed dose water in a Co-60 teletherapy beam has been measured with four different standard ionisation chambers applying two codes of practice and also, with a Fricke dosimeter. Measured values agree generally within 2.3%. There is a remarkable agreement of less than 0.3% variation, between ionisation chambers NE 2561 and NE 2481 when the IAEA protocol is applied. The HPA protocol is applicable to only NE 2561 and a variation of about 1.4% was observed between measurements made with this ionisation chamber applying the two protocols. The IAEA protocol shows very accurate results. With a deviation of about 2.2%, the Frickle dosimeter appears to be the least accurate for therapy dose measurement despite its simplicity of application.

Viability of an isocentric cobalt-60 teletherapy unit for stereotactic radiosurgery.

The potential for radiosurgery with an isocentric teletherapy cobalt unit was evaluated in three areas: (1) the physical properties of radiosurgical beams, (2) the quality of radiosurgical dose distributions obtained with four to ten noncoplanar converging arcs, and (3) the accuracy with which the radiosurgical dose can be delivered. In each of these areas the cobalt unit provides a viable alternative to an isocentric linear accelerator (linac) as a radiation source for radiosurgery. A 10 MV x-ray beam from a linac used for radiosurgery served as a standard for comparison. The difference between the 80%-20% penumbras of stationary radiosurgical fields in the nominal diameter range from 10 to 40 mm of the cobalt-60 and 10 MV photon beams is remarkably small, with the cobalt-60 beam penumbras, on average, only about 0.7 mm larger than those of the linac beam. Differences between the cobalt-60 and 10 MV radiosurgical treatment plans in terms of dose homogeneity within the target volume, conformity of the prescribed isodose volume to the target volume, and dose falloffs outside the target volume are also minimal, and therefore of essentially no clinical significance. Moreover, measured isodose distributions for a radiosurgical procedure on our Theratron T-780 cobalt unit agreed with calculated distributions to within the +/- 1 mm spatial and +/- 5% numerical dose tolerances, which are generally specified for radiosurgery. The viability of isocentric cobalt units for radiosurgery will be of particular interest to centers in developing countries where cobalt units, because of their relatively low costs, provide the only megavoltage source of radiation for radiotherapy, and could easily and inexpensively be modified for radiosurgery. Of course, the quality assurance protocols and mechanical condition of a particular teletherapy cobalt unit must meet stringent requirements before the use of the unit for radiosurgery can be advocated.

Quality control in planning and technique of radiotherapy with cobalt-60 for T1 glottic cancer increase local control and organ preservation.

BACKGROUND: In order to evaluate whether individualized technique and dosimetry of radiotherapy increase local control, organ preservation, and survival of patients with T1 glottic cancer, we reviewed 76 cases treated from 1979 to 1993. METHODS: Group A included 32 patients treated from 1979 to 1989 with different techniques, based on clinical aspects. Group B included 44 patients treated from 1990 to 1993 with individualized technique according to tumor extension and patient's anatomy. RESULTS: Five-year local control with radiotherapy alone was achieved in 53% of group A versus 91% of group B (P > 0.005). Survival was similar in both groups with rescue surgery (90% versus 96%). Five-year survival with larynx preservation was 65% in group A versus 88% in group B (P = 0.02). Most recurrences (78%) appeared within 24 months of follow-up. CONCLUSION: Adequate staging, individualized technique, computing planning using simulation and use of immobilization devices during cobalt-60 radiotherapy significantly increase local control and organ preservation in T1 glottic cancer.

[Spiral computed tomography for treatment planning and quality assurance in radiotherapy]. / Spiralcomputertomographie zur Bestrahlungsplanung und Qualitätssicherung in der Strahlentherapie.

BACKGROUND: The possibilities of spiral CT for radiotherapeutic treatment planning and quality assurance have been systematically investigated. PATIENTS AND METHODS: The influence of parameters such as slice thickness, table speed and increment on geometric accuracy was studied. Ring-, spheric-, PMMA- and humanoid Alderson phantoms were used. Furthermore, patients with infradiaphragmatic irradiation of Hodgkin's disease or with mediastinal irradiation were studied using CT-angiography. Patients with carcinomas of the head and neck before HDR- and PDR-brachytherapy were examined as well. RESULTS: Spiral CT offers 3D volume data information with excellent reduction of breath and motion artefacts for virtual simulation. 2D multiplanar reconstructions with excellent local resolution may be obtained. 3D MIP (Maximum Intensity Projection), based on CT-angiographic imaging, is a good tool for infradiaphragmatic treatment planning of Hodgkin's disease, if small numbers for slice thickness, table speed and increment are used. SSD (Surface Shaded Display) offers good 3D visualization and good geometric control of intracavitary and interstitial brachytherapy applicators. High qualitative multiplanar reconstructions are useful for CT-based brachytherapy planning. CONCLUSIONS: Spiral CT is a precious tool for 3D treatment planning and virtual simulation in radiotherapy and superior to conventional CT data acquisition. Quality assurance is improved for dose-volume-histograms and for brachytherapy.

Use of simple quality assurance procedures in the analysis of beam asymmetries on cobalt-60 treatment units.

Recently, the mechanical failure of one of the upper collimator mechanical trimmers on a cobalt-60 unit resulted in large beam asymmetries and unacceptable flatness characteristics. This malfunction was not detected using currently accepted schedules for quality assurance tests. The incident suggests that the frequency of routine beam profile constancy checks should be increased to weekly for cobalt-60 units.

Programa de qualidade em braquiterapia ginecológica / Quality program in gynecological braquitherapy

Este trabalho propõe um Programa de Qualidade em Braquiterapia Ginecológica Low Dose Rate - com a técnica Remote Afterloading visando estabelecer procedimentos operacionais, de forma a assegurar a prescrição do tratamento e garantir a segurança dos pacientes e trabalhadores além de, facilitar o intercâmbio em futuras pesquisas sobre o Tratamento de câncer Ginecológico entre os diversos Centros de Branquiterapia existente no País.

A novel comprehensive quality control instrument for medical accelerators.

A comprehensive quality control instrument for calibration of medical accelerators that use photon, electron, or proton beams in teleradiotherapy is described. It employs a fluorescence screen, mounted on a central stage with four degrees of freedom, monitored by a CCD camera. A single set-up of the instrument enables one to perform mechanical, light laser, and radiation tests, at arbitrary angles of the accelerator gantry. The new device provides for quantitative evaluation of the tests performed and provides for documentation of the test results in real time. The device provides significant time savings with concurrent improvement in accuracy for tests performed during installation and acceptance processes, and the implementation of quality control procedures for medical accelerators.

Intraoperative radiation with external irradiation: an alternative for nonresectable non-small-cell lung cancer?

In 15 patients with nonresectable non-small-cell lung carcinoma (NSCLC) (10 squamous, 1 large cell, 4 adenocarcinomas; T1-T3, N0-N2, all M0), lymph node dissection and intraoperative irradiation of the tumour (IORT) with doses between 10 and 20 Gy (11-20 MeV electron beam) was performed. Four weeks postoperatively 46-56 Gy external irradiation (8 or 23 MeV photons) was delivered to the mediastinum and 46 Gy to the tumour-bearing area. Four weeks postoperatively, 8 minor responses (MR, tumour regression between 4% and 45%) and 6 partial responses (PR, 50%-84%) were found. In 1 case, CT was inconclusive. Eighteen weeks after IORT, volumetry showed 3 CR, 9 PR (62% to 94%) and 1 28% MR. One patient died from intrabronchial hemorrhage 7 weeks after IORT (50% PR). Two others (both CR) died from unrelated causes, 6 and 12 months, respectively, after IORT. One patient (62% PR) died after 14 months from an unknown cause. Another patient died at 15 months from local relapse after CR. The latest CT volume assessment between 7.5 and 21.5 months, respectively, yielded 8 CR, and 1 63% PR. One further case of local CR has developed contralateral pulmonary metastasis after 10 months. All these patients are alive and well. The median time elapsed since IORT is 12.5 months, 10 patients have survived more than 12 months.

[Optimization of combined brachy-teletherapy by the modification technic]. / Zur Optimierung der kombinierten Brachy-/Teletherapie mit Hilfe der Modifikationstechnik.

A method is presented for combined brachy-teletherapy by which the dose distribution of percutaneous irradiation is adapted to the distribution of short-distance irradiation with 192iridium by means of the so-called "field integrated dose modification". Insufficient or excessive doses within the area of superposition of both therapy modalities can so be avoided. Moreover, the therapist can define zones of deviation from the reference dose, if such a dose heterogeneity seems desirable in the individual case. The combined irradiation of prostata and cervix is given as an example to describe in detail the technical, clinical, and radiobiological aspects of this method.

Quality assurance control in the EORTC cooperative group of radiotherapy. 2. Dosimetric intercomparison.

The European Organization for Research on Treatment of Cancer (EORTC) has performed site reviews at 17 institutions participating in clinical trials organized by the Cooperative Group of Radiotherapy. In this paper the dosimetric part of the quality assurance control programme is presented. In a previous paper (part 1) the medical profile of the participating centres was presented. In part 3 an integrated clinical and dosimetric investigation in an anatomical phantom will be presented. The deviations between the absorbed dose values, for specific points along the beam axis in a water phantom, determined by us and reported by the hospitals were within an acceptable level of variation (about +/- 3%) for 85, 70 and 71% of the 60Co gamma, X-ray and electron beams, respectively. In some scanning electron beams, too large deviations were found. The flatness and symmetry of the beams were measured. 73% of the X-ray and 60% of the electron beams were within the acceptable levels of variations. Dosimetric recommendations for institutions participating in EORTC clinical trials are presented.

Development of quality assurance in radiation therapy in North America.

Although diagnostic radiology developed rapidly following Roentgen's discovery, limitations on voltage delayed penetrating external radiation therapy until after World War II. Quality assurance has developed in both the USA and Canada in many different institutions. Tolerances for implementation of the prescribed tumor dose have been established. A series of quality assurance procedures for calibration, three dimensional dose distributions, the treatment planning process, and for treatment delivery have been formulated in protocols and their development is sketched briefly. The importance of computerized tomography in treatment planning and computerized record and verify systems in treatment delivery is emphasized.

Leakage through gaps around shielding windows in radiotherapy treatment rooms.

Radiation streaming down gaps between shielding windows and walls of radiotherapy treatment rooms has been investigated. The calculations were based on a cobalt-60 source and were performed with the computer code RANKERN. The dose rate near the exit of the gap on the cold side of the window was calculated as the sum of contributions from direct line of sight and radiation scattered off the faces of the gap, using albedo data. The RANKERN code employs point kernel equations which are solved by a stochastic integration method. The paper demonstrates that although for a single element window small gaps could lead to significant leakage of radiation, for a double or triple element window, even a gap of ten millimetres would result in a dose rate no greater than that through the surrounding concrete.