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C Pla

Publications and source records attributed to C Pla.

At least 19 recordsLinked to original sources
PubMed1997

Electron arc dose distributions as a function of beam energy.

The characteristic angle-beta concept provides a simple semiempirical method for determination of dose distributions in electron arc therapy. Initially, the method required a set of measured radial depth dose distributions for each electron beam energy used for arc therapy. In this paper, we report an extension of the angle-beta concept that enables the determination of arc therapy depth doses for an arbitrary electron energy from the known set of depth dose data at a reference energy. Depth dose distributions of stationary and arc electron beams have been studied in the energy range from 9 to 18 MeV. The stationary electron beams used for electron arc therapy were collimated by photon collimators only, no secondary collimation was used in our experiments. For stationary electron beams and for arc electron beams with a given characteristic angle beta, the depths of dose maximum as well as the depths of a given percentage depth dose beyond the depth of dose maximum are linearly proportional to the mean incident electron energy. This simple geometrical and dosimetric relationship increases the potential usefulness of the angle-beta concept in clinical electron arc therapy.

Electrons↗
PubMed1994

Rectal complications in patients with carcinoma of the cervix treated with concomitant cisplatin and external beam irradiation with high dose rate brachytherapy: a dosimetric analysis.

PURPOSE: This paper reports a dosimetric study of 43 patients treated with a combination of concomitant radiotherapy and chemotherapy (cisplatin) for locally advanced carcinoma of the cervix with the aim of investigating the correlation between the radiation dose to the rectum and the incidence of late rectal complications. METHODS AND MATERIALS: Radiotherapy consisted of 46 Gy external beam irradiation plus three high dose rate intracavitary treatments given weekly, concurrent with the last 3 weeks of external beam therapy, to a total dose of 30 Gy to point A. Cisplatin 30 mg/m2 was given weekly throughout the duration of the external beam irradiation. The brachytherapy irradiated volume was reconstructed from the orthogonal treatment radiographs to accurately locate the reference points defined by the International Commission of Radiation Units and Measurements (ICRU), report 38. The doses calculated at these points were compared to in vivo dose measurements performed immediately prior to treatment. RESULTS: The group of patients who were calculated to have received a dose to the rectal reference point greater than the prescribed point A dose (9/13) had a significantly greater probability of development of late rectal complications compared to the group of patients who were calculated to have received less than the prescribed point A dose at this rectal point (7/30), p = 0.003. There was no correlation of rate of complication with the in vivo measured dose in the rectum, stage of disease, or age. At 40 months post treatment, the group of patients receiving the higher dose to the rectal reference point had an actuarial rate of serious (Grade 3 and 4) rectal complications of 46% compared to a rate of 14% in the remainder. In terms of survival, the group of patients receiving the higher dose to the rectal reference point have all survived, whereas the group of patients receiving the lower dose to the rectal reference point have a significantly different rate of survival of 72%, p = 0.046. CONCLUSION: This investigation has revealed a significant correlation between the dose calculated at the rectal point defined by the ICRU and the incidence of late rectal complications in patients with carcinoma of the cervix undergoing concomitant radiotherapy and chemotherapy. Thus, this rectal reference point appears to be a useful prognostic indicator of late rectal complications in these patients and we recommend that the brachytherapy dose delivered to this rectal point be limited to the dose prescribed to point A for treatment regimens using three fractions of 8-10 Gy each, limiting the total dose to this point, including the external beam component, to 76 Gy. Further study will be required to determine whether this rule should be applied to patients receiving irradiation alone.

Brachytherapy↗
PubMed1993

A technique for fractionated stereotactic radiotherapy in the treatment of intracranial tumors.

PURPOSE: The excellent treatment results obtained with traditional radiosurgery have stimulated attempts to broaden the range of intracranial disorders treated with radiosurgical techniques. For major users of radiosurgery this resulted in a gradual shift from treating vascular diseases in a single session to treating small, well delineated primary tumors on a fractionated basis. In this paper we present the technique currently used in Montreal for the fractionated stereotactic radiotherapy of selected intracranial lesions. METHODS AND MATERIALS: The regimen of six fractions given every other day has been in use for "fractionated stereotactic radiotherapy" in our center for the past 5 years. Our current irradiation technique, however, evolved from our initial method of using the stereotactic frame for target localization and first treatment, and a "halo-ring" with tattoo skin marks for the subsequent treatments. Recently, we developed a more precise irradiation technique, based on an in-house-built stereotactic frame which is left attached to the patient's skull for the duration of the fractionated regimen. Patients are treated with the stereotactic dynamic rotation technique on a 10 MV linear accelerator (linac). RESULTS: In preparation for the first treatment, the stereotactic frame is attached to the patient's skull and the coordinates of the target center are determined. The dose distribution is then calculated, the target coordinates are marked onto a Lucite target localization box, and the patient is placed into the treatment position on the linac with the help of laser positioning devices. The Lucite target localization box is then removed, the target information is tattooed on the patient's skin, and the patient is given the first treatment. The tattoo marks in conjunction with the target information on the Lucite target localization box are used for patient set-up on the linac for the subsequent 5 treatments. The location of the target center is marked with radio-opaque markers on the target localization box and verified with a computerized tomography scanner prior to the second treatment. The same verification is done prior to other treatments when the target center indicated by the target localization box disagrees with that indicated by the tattoo marks. The new position of the target center is then determined and used for treatment positioning. CONCLUSION: The in-house-built frame is inexpensive and easily left attached to the patient's skull for the 12 day duration of the fractionated regimen. Positioning with the Lucite target localization box verified with tattoo marks ensures a high level of precision for individual fractionated treatments.

Brain Neoplasms↗
PubMed1993

Treatment results of high dose rate brachytherapy in patients with carcinoma of the cervix.

PURPOSE: The combination of external beam irradiation and low-dose-rate brachytherapy is known to be an effective form of treatment in carcinoma of the cervix and any change from this well-established therapeutic combination must be able to equal or improve the treatment results. Since 1984 we have been using high dose rate brachytherapy in conjunction with external beam irradiation for patients with carcinoma of the cervix. This paper reports our long term treatment results in terms of local disease control, survival, and complications. METHODS AND MATERIALS: Between January 1984 and December 1989, 187 previously untreated patients with carcinoma of the cervix underwent combined external beam irradiation and high dose rate brachytherapy. The International Federation of Gynecology and Obstetrics stage distribution of patients was as follows: I B = 15, II A = 35, II B = 68, III A = 9, III B = 54, IV A = 6. External beam irradiation to the whole pelvis was delivered by megavoltage irradiation with once-a-day fractionation, to a median dose of 4600 cGy. High dose rate brachytherapy was delivered by a high-dose-rate remote controlled afterloading unit, containing 20 spherical Cobalt 60 sources with a nominal activity of 19 GBq (0.5 Ci) at the time of installation, giving a typical dose rate to point A of 160 cGy/min, decreasing to about 80 cGy/min at the end of the 5-year study. One to 3 high dose rate brachytherapy treatments delivering 800 to 1000 cGy to point A were given weekly concurrently with the last 2 to 3 weeks of radiation therapy, or following its completion. Maximum rectal and bladder doses were routinely measured for each treatment. RESULTS: Overall 5-year actuarial survivals were as follows: I B = 72%, II A = 65%, II B = 66%, III A = 66%, III B = 45%. Five-year actuarial pelvic control rates were as follows: I B = 66%, II A = 83%, II B = 78%, III A = 88%, III B = 40%. At a median follow-up time of 54 months for patients at risk, 23 patients developed 25 complications attributable to radiotherapy (13 rectal, 3 bladder, 8 small bowel, 1 fistula) at a median time of 18 months following completion of treatment. Thirteen complications (7.6%) were grades 3 or 4. Patients with Stage II disease had a higher incidence of complications than patients with Stages I and III disease (p < 0.05). Rectal complications were significantly higher in patients who received a total rectal dose > 5400 cGy (p = 0.045). CONCLUSION: High-dose-rate brachytherapy treatment results are comparable to those obtained with low dose rate brachytherapy techniques. The use of three high dose rate brachytherapy insertions is a practical, economical, and safe treatment for patients with carcinoma of the cervix.

Adult↗
PubMed1993

Clinical experience with electron pseudoarc therapy.

Between November 1986 and June 1990, 24 patients were treated with electron pseudoarc therapy at McGill University. There were 21 females and three males aged 27 to 81 years (median 62 years). 17 patients, nine of whom had received previous conventional locoregional irradiation, were treated palliatively for locally extensive breast carcinoma. Eight of these 17 patients achieved a complete, and six a partial, response to treatment; nine subsequently developed evidence of progressive disease within the treatment field after intervals of one to 27 months (median 5 months) following therapy. Eight patients developed moist desquamation of the treated chest wall, which was extensive in four; one of these patients developed chronic ulceration of the skin. The latter and one additional patient developed radiation pneumonitis. Seven patients were treated with radical intent, two following mastectomy for breast carcinoma, and one each for chest wall lymphoma, chest wall sarcoma, scalp angiosarcoma, scalp lymphoma and posterior cervical soft tissue sarcoma. Local control was achieved in six of these seven patients with minimal toxicity. Electron pseudoarc therapy is a treatment option for selected breast carcinoma patients for palliation of extensive chest wall disease, although morbidity may be considerable. The technique may, however, play a more useful role in other situations where the superficial portion of large curved surfaces is to be treated with curative intent.

Adult↗
PubMed1992

Clinical experience with a single field rotational total skin electron irradiation technique for cutaneous T-cell lymphoma.

Between October 1981 and December 1989, 44 patients with cutaneous T-cell lymphoma (CTCL) were treated with a single field rotational total skin electron irradiation (RTSEI) technique developed in the McGill University, Department of Radiation Oncology. Only 11 (25%) of the 44 patients had received no prior treatment. Three-quarters (33/44) had advanced (T3 or T4) disease. Complete responses were seen in 32/44 (73%) of patients (91% T2, 71% T3 and 58% T4), but only 3/11 (27%) of patients with T2 disease and 3/21 (14%) of patients with T3 disease remain in continuous complete remission in the skin, after median intervals of 58 and 35 months, respectively. Median cause-specific survival for the whole group is 43 months and survival at 5 years is 38%. Survival was significantly better for patients with T2 disease than for patients with T3 disease (relative risk 4.3; 95% CI 1.4-13.2) and patients with T4 disease (relative risk 3.1; 95% CI 0.8-12.1). The RTSEI technique used at McGill has depth-dose characteristics and photon contamination similar to other commonly used TSEI techniques. It is relatively simple and provides a homogenous dose distribution over the entire skin surface in a short treatment time. Results of treatment are similar to those obtained with other techniques. For T2 disease, TSEI is an effective treatment modality with a possibility of long-term tumor control. For more advanced disease, more aggressive treatment, which may include TSEI, is necessary.

Adult↗
PubMed1991

High dose rate afterloading intracavitary therapy in carcinoma of the cervix.

From January 1984 through December 1986, 87 patients with previously untreated carcinoma of the cervix received external beam pelvic irradiation and high dose rate intracavitary therapy (HDRT). There were 18 Stage IIA patients, 39 Stage IIB, and 30 Stage IIIB. The median age was 60 years and the median follow-up time was 42 months for patients at risk. Radiotherapy consisted of external megavoltage irradiation to the whole pelvis (median dose 4600 cGy) combined with one (6 patients), two (51 patients), or three (30 patients) HDRT insertions. A high dose rate remote afterloading unit with 60Co sources was used to deliver the HDRT. The prescribed dose to point A was between 800 and 1000 cGy per treatment. The dose rate at point A initially was approximately 150 cGy/min and dropped to approximately 100 cGy/min during the duration of the study. Treatments with multiple fractions were given at weekly intervals. The overall actuarial survival at 5 years was 88% for Stage IIA, 64% for Stage IIB and 32% for Stage IIIB patients. Pelvic recurrence remained the major cause of failure. Grade III and IV late complications included proctitis and bowel obstruction in six patients each. We conclude that HDRT results are similar to those obtained with conventional low dose rate intracavitary systems. HDRT is cost effective and minimizes exposure to personnel. Several questions, such as the total number of insertions required, dose per HDRT insertion, and optimal HDRT insertion schedule remain unanswered and further experience is needed to better clarify these issues.

Adult↗
PubMed1991

Physical aspects of the angle-beta concept in electron arc therapy.

A technique for the determination of treatment parameters that are required to achieve a desired depth dose distribution in electron arc therapy is discussed and a method for calculating isodose distributions is presented. Both the treatment technique and the dose calculation method rely on the angle beta concept, which uniquely describes the dependence of the radial percentage depth doses in electron arc therapy on the nominal field width, isocenter depth, and virtual source-axis distance. The angle beta concept is discussed in detail and the electron pseudo-arc therapy technique used at McGill is described. Also presented is the method used to achieve dose homogeneity in target volumes treated with the pseudo-arc technique.

Electrons↗
PubMed1990

Three-dimensional isodose distributions in stereotactic radiosurgery.

A personal computer based three-dimensional treatment planning system, which may be used for planning any linear accelerator (Linac) based radiosurgical technique, is presented. The system is used to calculate dose distributions for most of the Linac-based techniques currently in use as well as the theoretically optimum 4 pi geometry. The maximum and minimum dose falloffs are used to compare the various Linac-based radiosurgical techniques. The dynamic rotation technique developed at McGill University is shown to produce distributions with dose falloffs similar to the multiple converging arc techniques used elsewhere and those obtained for the Gamma Unit. Also considered are the effects of beam energy, in the range of 4-25 MV, and beam profiles on the dose distribution.

Brain Neoplasms↗
PubMed1987

Dose distributions around selectron applicators.

Measured and calculated dose distributions around selectron applicators, loaded with 60Co high dose rate pellets, are presented. The effect of the stopping screw, spacers, pellets themselves and the applicator wall on the dose distribution is discussed. The measured dose distribution is in almost perfect agreement with the calculated distribution in planes perpendicular to the applicator axis and containing a source. On the applicator axis directly below the applicator the measured dose amounts to about 75% of the calculated value, when only the stopping screw attenuates the beam from a pellet. When the beam is attenuated by spacers in addition to the stopping screw, the discrepancy between the calculated and measured dose may exceed 50%. Clinically relevant source geometries are also discussed. It is shown that for most regions around the applicator the method of a simple addition of dose contributions from individual point sources is an acceptable approximation for the calculation of dose distributions around the selectron applicators.

Brachytherapy↗
PubMed1987

Stereotactic external beam calculations for radiosurgical treatment of brain lesions.

Radiosurgical techniques are becoming increasingly popular for the selective destruction of brain lesions. To ensure precision in the procedure, set-up and treatment of lesions in this manner, we have adopted standard stereotactic methods to allow one to calculate accurately the absorbed dose and also to preserve accuracy in locating the target site in three dimensions. At McGill University, radiosurgery is performed using the dynamic technique, which utilizes the concurrent rotation of both the 10-MV photon beam linear accelerator (from 30 to 330 degrees) and the patient couch (from 75 to -75 degrees) about a common point centered on the target within the lesion. A three-dimensional treatment planning system for the calculation of dose distributions implemented in conjunction with CT, MRI and DSA stereotactic image analysis systems is presented.

Brain Neoplasms↗
PubMed1984

Clinical aspects of a rotational total skin electron irradiation.

A simple rotational total skin electron irradiation technique utilising a single large field electron beam is presented. Clinical and technical aspects of the technique are discussed and treatment results for the first 10 patients treated for widespread mycosis fungoides reported. The technique is simple and well tolerated by patients, and can easily be implemented in centres utilising electron beam radiotherapy.

Adult↗
PubMedDate not supplied

Physical aspects of a rotational total skin electron irradiation.

A technique for rotational total skin electron irradiation is presented in which the patient stands on a slowly rotating platform (SSD = 285 cm) in a large uniform linear accelerator electron field (Eo = 3.5 MeV). The beam is scattered by the transmission ionization chamber and by a special lead/aluminum scattering filter, and then degraded by a sheet of Lucite. A Farmer chamber is used as a patient dose monitor and a method for absolute dose calibration is presented. The field is uniform to within +/- 5% for dimensions of 180 X 40 cm2. The surface dose for rotational therapy is equal to 45% of the maximum dose in a stationary beam. The rotating beam exhibits a dose maximum on the surface, falls to 80% at 0.5 cm and has an x-ray contamination of approximately 4%. The surface dose rate is about 25 cGy/min for the rotating beam. The rotational beam percentage depth dose distributions, calculated using stationary beam information, agree well with measured data. The stationary beam exhibits a dose maximum at 4 mm in tissue, a surface dose of 93%, 80% dose at a depth of 1 cm, a practical range of 1.75 cm, and an x-ray contamination of 2.5%. The rotational total skin electron irradiation significantly reduces the patient treatment and setup time and solves the problem of beam matching, when compared to standard multiple-beam techniques.

Electrons↗
PubMedDate not supplied

A computerized TLD system.

A computerized thermoluminescent (TL) readout technique is presented which considerably improves the precision of dose readout and facilitates the dose information management and storage. The technique is relatively simple and it involves an interface between a commercially available thermoluminescent dosimetry (TLD) analyzer and a minicomputer. Curve fitting, subtraction of unwanted thermogram peaks, background subtraction, studies of TL decay kinetics, and storage of large number of measured TL data are easily performed with the technique.

Computers↗
PubMedDate not supplied

Calculation of surface dose in rotational total skin electron irradiation.

A single-field rotational total skin electron irradiation technique has recently been developed at the McGill University for treatment of skin malignancies. The dose received by a given surface point during rotation in a uniform large electron field depends on the radius of rotation of the surface point, on the local radius of curvature of the contour in the vicinity of the point of interest, and on the shadows cast by limbs (arms upon trunk or head and neck, and legs upon each other). A method for calculating the surface dose distribution on a patient is presented accounting for the various parameters affecting the dose. A series of measurements were performed with polystyrene and a humanoid phantom, and an excellent agreement between measured and calculated dose distributions was obtained.

Electrons↗