Robert W. Kline

Do prostatic biopsies 12 months or more after external irradiation for adenocarcinoma, stage III, predict long-term survival?

Abstract Serial biopsies of the prostate after high dose external irradiation for adenocarcinoma show a gradual disappearance of the neoplastic cells. With such treatment, results of the biopsies do not have any short term prognostic significance. However, positive biopsies 12 months or more after treatment are reputed to be an unfavorable sign for long-term survival. From August, 1970 through February, 1974, 46 consecutive patients with locally advanced (Stage III, C, or T3 and T4) adenocarcinoma of the prostate underwent external irradiation with 2 MV X rays or cobalt-60 teletherapy. The technique included parallel, opposed, 14 × 14 cm anterior and posterior fields, and a 10 × 14 cm perineal field. The center of the prostate received a total dose of 70 Gy in 30–37 fractions in 43 to 56 days. Details of the dosimetry reveal inhomogeneity of the dose of ±7% within an enlarged prostate. With a median follow-up of 8 years, the actuarial survival rates, uncorrected for death from intercurrent disease, are 69% at 5 years and 49% at 10 years. Biopsies of the prostate 12 months or more after treatment were available from 31 patients: 19 had one or more positive biopsies and 12 had consistently negative biopsies; the survival curves are identical for those with and those without positive biopsies. Prostatic biopsies obtained 24 months or more after treatment were available from 21 patients: 10 had positive and 11 had negative biopsies; the survival curves are identical for those with and without residual cancer cells. Following adequate irradiation of patients with locally advanced adenocarcinoma of the prostate, the results of biopsies obtained one or two years after treatment do not predict long-term survival.

Single and double plane implants: A comparison of the Manchester System with the Paris System

A comparison between the Manchester System and the Paris System of interstitial dosimetry has been made in the case of single and double plane implants. The rules of both systems are reviewed. A brief description of the Paris System is presented in an appendix. Dose distributions for two different examples are presented in two orthogonal planes. The Paris System uses considerably fewer sources than the Manchester System. It results in a larger volume of high dose than the Manchester System. The use of Iridium-192 sources strength and source length can be adjusted represents a significant advantage. The Paris System attempts to adapt the implant configuration to the clinical situation as the target thickness is used to define the source separation and the target length is used to define the source length. The differences in the dose definition are discussed.

The effect of thickness of the waterproofing sheath on the calibration of photon and electron beams

The TG-21 protocol recommends using a thin sheath for waterproofing an ion chamber used in the calibration of photon and electron beams. A thickness of 0.5 mm is suggested for a material having a composition and density close to that of water. This work investigates the effect on the calibration of photon beams ranging from Co60 to 25 MV, and electron beams ranging from nominal energies of 7-18 MeV, for changes in the thickness of the waterproofing sheath from 0.5 to 5.5 mm. For photon beams, a maximum change of 1.2% was found for the 25-MV x-ray beam. For electron beams, a maximum change of 0.5% was found for 10-MeV electrons. It is concluded that the thickness of the waterproofing sheath is not a very sensitive variable, assuming the thickness is between 0.5 and 2.0 mm.

Field separation between lateral and anterior fields on a 6 MV linear accelerator

Field separations of 0, 2.5, 5, and 10 mm between lateral facial-cervical fields and anterior supraclavicular fields have been studied using thermoluminescent dosimeters in the Rando phantom. Measurement points were taken at three different depths in the midsagittal plane and at two locations out of that plane. The resultant radiation distribution for these points was measured at intervals of less than 1 mm. The measured dose distribution was compared to computer generated distributions. The field separation which resulted in the most ideal distribution for routine cases was determined. This agreed well with the field separation determined by the standard calculational approach, which may be used by modifying certain conditions. The application of the results of this data to the clinical situation is discussed.

Carcinoma of the pancreas: Results of irradiation for unresectable lesions

Abstract From 1973 to 1977, 20 patients who had histologically proven unresectable adenocarcinoma of the pancreas with no distant metastases were irradiated at the Medical College of Wisconsin Affiliated Hospitals. The patients received megavoltage external irradiation to minimum tumor doses ranging between 3000 rod in 4 weeks and 5700 rod in 7 weeks (median 4600 rod in 6 weeks their actuarial survival was 54% at 12 months and 21% at 24 months. Fourteen patients who received 4500 rod or more in 6–7 weeks had a median survival of 13 months. Six patients received less than 4500 rod in 3–6 weeks, and their median survival was 7 months. At this writing, three patients are alive and apparently disease free more than 2 years after treatment. Complications were seen in two patients. One died from GI bleeding 2 months after completion of radiation therapy, and the other patient developed pancreatic insufficiency. These results and recent reports in the literature show that aggressive irradiation can result in long-term disease free survival in a small proportion of patients with unresectable pancreatic adenocarcinoma. Further exploitation of this approach alone or combined with chemotherapy is warranted.

Film dosimetry of small electron beams for routine radiotherapy planning

The characteristics of very small fields, 1 X 1 and 2 X 2 cm, of electron beams of nominal energies, 5, 7, 10, 12, 15, and 18 MeV have been studied and compared to a 10 X 10 cm field. A parallel-plate ion chamber and film have been used to obtain various dose parameters. The central axis depth dose measurements, field flatness, uniformity index, and relative output factors are presented. It was found that satisfactory results for determining the relative output factor can be obtained from film data using a scanning densitometer. It is our conclusion that film dosimetry is acceptable in determining the necessary clinical parameters needed to treat patients with fields as small as 2 X 2 cm. For the 1 X 1 cm field size and for the electron energies greater than 10 MeV, there was substantial disagreement between the ion chamber and film data in the buildup region as well as the regions beyond the depth of maximum dose to the depth of 90% dose.

Cranial irradiation in acute leukemia: dose estimate in the lens.

Abstract Cranial irradiation for subclinical arachnoid infiltration is standard treatment in childhood acute lymphocytic leukemia. The incidental dose received by the ocular lens is of potential importance since these children evidence a significant long-term survival rate. Comparison of the lens dose using 6 MV and 4 MV photon beams and a cobalt unit is presented in terms of ion chamber measurements in a water phantom and thermo-luminescent dosimetry (TLD) measurements in a head phantom. TLD measurements on patients treated for acute lymphocytic leukemia (ALL) are examined and used to estimate the dose to the lens. It is demonstrated that the dose to the lens depends strongly on the choice of field margin and on the daily patient set-up. However, using parallel opposed beams in a clinically determined optimal set-up, the dose to the lens is approximately 20–30% of the midline central axis dose. By angling the treatment head to eliminate the geometrical divergence of the beam, it is possible to reduce the lens dose to approximately 15% of the midline dose.

Dose distribution in total skin electron beam irradiation using the six-field technique

Total skin low energy electron beam irradiation is used to treat superficially widespread skin lesions such as cutaneous T-cell lymphoma. Total skin irradiation involves delivering an adequate dose at a depth of 0.25 to 1.0 cm, while sparing underlying tissue. The dose distributions obtained when using a modified Stanford six-field technique depend upon the beam energy, the beam angle, the diameter and shape of the body part, and other variables. The dose distribution uniformity of six pairs of angulated electron beams has been studied as a function of beam energy, the gantry angle, +/- theta, above and below the horizontal and the diameter of a cylindrical polystyrene phantom. Depth doses and dose uniformity for single and multiple fields have been measured as a function of beam energy, phantom diameter and position.

Comparison of measured and calculated dose distributions around an iridium‐192 wire

The relative dose distribution around a 5.0-cm-long piece of 192Ir wire has been measured using LiF chips. Measurements were made at distances of 0.25 to 5.0 cm away from the source and distances of 0.0 to 4.0 cm along the source. In addition, measurements were also made at several distances along the axis of the source. Attention was paid to the errors associated with these measurements. A comparison was made between a commercial software program, ISODOS, an analytical solution to the Sievert integral, and the measurements. Good agreement was obtained at distances along and away from the source. Major disagreements were found at points along the source axis.

Computer dosimetry of 192Ir wire

The dosimetry of 192Ir linear sources with a commercial treatment planning computer system has been evaluated. Reference dose rate data were selected from the literature and normalized in a manner consistent with our clinical and dosimetric terminology. The results of the computer calculations are compared to the reference data and good agreement is shown at distances within about 7 cm from a linear source. The methodology of translating source calibration in terms of exposure rate for use in the treatment planning computer is developed. This may be useful as a practical guideline for users of similar computer calculation programs for iridium as well as other sources.