Donald E. Velkley

Build-up region of megavoltage photon radiation sources.

Measurements of surface dose and build-up have been measured for photon radiation sources with maximum energy from 1.2 to 25 MeV. A variable volume ionization chamber was used and the results extrapolated to what would be obtained with a zero volume chamber. The results are found to depend systematically on the plate separation of a parallel plate ionization chamber and an empirical method was derived for correcting measurements made with a fixed volume chamber. The relationship of dose build-up curves with skin reactions in radiation therapy patients is discussed.

The preservation of ovarian function in young women undergoing pelvic radiation therapy

Because cervical carcinoma rarely metastasizes to the ovaries, it became logical to preserve ovarian function by the method of lateral ovarian transposition as part of the management of young women with this disease. This technique prevents castration should subsequent radiation therapy be planned or become necessary. Forty patients with carcinoma of the cervix or vagina underwent unilateral or bilateral ovarian transposition. Eighteen patients received radiation therapy. Of these, 16 had gonadotropin measurements and only 6 (37%) had levels elevated to the postmenopausal range. If patients whose ovaries were not shielded or who received paraaortic radiotherapy are excluded, then only two (17%) had elevated gonadotropin values. It is concluded that, if properly performed, lateral ovarian transposition and ovarian shielding will protect ovarian function in patients receiving pelvic radiotherapy.

Routine clinical estimation of rectal, rectosigmoidal, and bladder doses from intracavitary brachytherapy in the treatment of carcinoma of the cervix☆

Abstract An evaluation of rectal, rectosigmoidal, and bladder doses from intracavitary brachytherapy in carcinoma of the cervix has been initiated on a routine basis in an effort to obtain the optimum radiotherapeutic dose. Contrast radiography on a radiotherapy simulator is used to image the rectum and bladder, and dose rates are determined at predesignated reference points with the aid of computer calculated dose distributions. Forty-three patients have been reviewed in order to ascertain the correlation between radiation injury and dose at reference points in the rectum and bladder. The variability in the incidence of injury and the importance of predisposing factors suggests that a single tolerance dose for the reference points is not satisfactory. However, the reference doses are an important addition to other clinical factors in evaluating the treatment plan. Further, the reference doses can alert the therapist to the presence of hot spots resulting from unusual anatomy or perforation of the uterus. Finally, they serve as documentation of the doses to normal structures within the treatment volume. This is an important aspect of current radiotherapy. In a related study involving 77 patients, the doses at points A and B and the prescription in mghr were analyzed in relation to radiation injury. There was no apparent association between the incidence of radiation injury in either the mghr prescription or the doses at points A or B. Computer calculations were supplemented with in vivo and in vitro thermoluminescent dosimeter (TLD) measurements. The in vivo rectal measurements are of little value on a routine basis because of the difficulties in obtaining the measurements and the uncertainties in the measured values. We conclude that routine contrast radiography of the rectum and the bladder with dose calculations at selected reference points provides important information for optimizing radiotherapy in carcinoma of the cervix without a significant increase in treatment planning effort or patient discomfort.

Sacral plexus injury after radiotherapy for carcinoma of cervix

A 42‐year‐old woman developed lower extremity weakness and sensory loss 1 year after external and intracavitary radiotherapy for Stage IB carcinoma of cervix. She has been followed for 5 years posttreatment, and the neurologic abnormalities have persisted, but no evidence of recurrent carcinoma has been found. We believe this to be a rare case of sacral plexus radiculopathy developing as a late complication after radiotherapy. Suggestions are made for improving the radiotherapy technique to prevent this complication in future cases.

Adjuvant external beam therapy for pathologic stage I and occult stage II endometrial carcinoma

Eighty‐six patients with pathologic Stage I or occult Stage II carcinoma of the endometrium and myometrial invasion and/or Grade 2 or Grade 3 histologic condition received whole‐pelvis external radiation therapy (RT) after extrafascial total abdominal hysterectomy and bilateral salpingo‐oophorectomy. Twenty‐one patients received 4250 cGy in 25 daily fractions for 5 weeks (Group 1), 28 received 4500 cGy in 25 daily fractions for 5 weeks (Group 2), and 37 received 5100 cGy in 30 daily fractions for 6 weeks (Group 3). Seventeen patients had intravaginal brachytherapy after whole‐pelvis RT. Local recurrence developed in two patients (2.3%) (one in Group 1 and one in Group 2). Statistical analysis showed that the depth of myometrial invasion significantly influenced survival (P = 0.016). Tumor grade, pathologic stage, whole‐pelvis radiation dose, and the use of brachytherapy did not influence survival. Complications occurred in 9.5% of patients in Group 1, 24.7% in Group 2, and 40.5% in Group 3. Three patients who received brachytherapy had rectal injuries. The authors conclude that 4250 cGy in 25 fractions for 5 weeks of whole‐pelvis RT appears to induce fewer complications than higher doses, and may be sufficient to prevent local recurrence in most patients who require adjuvant RT. A clinical trial is needed to determine the optimum dose—time—fractionation regimen.

Intracavitary dosimetry: A comparison of MGHR prescription to doses at points a and b in cervical cancer

Abstract This study, involving 77 patients with carcinoma of the cervix, compares the doses at points A and B with the milligram-hour (mg-hr) prescription for the intracavitary use of the Fletcher-Suit afterloading applicators. The doses at points A and B were computer calculated. A linear least-square regression analysis was used to compare the two sets of data. Correlation coefficients between doses at points A and B and the mg-hr prescription are 0.84 (p

Tumor sterilization following high-dose pre-operative irradiation for advanced cancer of the larynx or pyriform sinus.

Twenty-two patients with advanced laryngeal cancer and 5 with advanced pyriform sinus cancer were given 51 Gy (5,100 rad) followed by surgical resection. In 10 (45%) of patients with laryngeal cancer, no tumor was found at the primary site pathologically; 15 (68%) had negative neck specimens. All of those with pyriform sinus cancer had positive specimens. Eighteen patients with laryngeal cancer are free of disease. In contrast, only 1 with pyriform sinus cancer is free of disease; 1 has had a local recurrence and 3 have had metastases. The data suggest that 51 Gy (5,100 rad) are insufficient to sterilize pyriform sinus cancer; higher doses together with adjuvant chemotherapy are needed.

Thin‐walled parallel plate ionization chamber for use with photon and electron beam dosimetry

The design and construction of a thin-walled parallel plate ionization chamber is described. The chamber makes use of a sputtered collecting electrode. The characteristics of this chamber include low leakage (less than 10(-13) A), no stem effect, and reproducibility within 1%. No polarization effects have been seen for electron beams over an energy range 7-25 MeV while for cobalt 60-25 MV photon beams, it is only 10%-15%.

An inexpensive variable‐frequency microwave system for hyperthermia

A microwave hyperthermia system is described which uses surplus communications equipment. The most costly components of the microwave system, the signal generator and amplifier, were obtained through the Federal Surplus Supply System. The cost of the entire system, including 2450 MHz applicator and temperature monitoring system, is under

Evaluation of computed tomography assisted and transit dosimetry treatment planning with thermoluminescent dosimetry measurements

1200. Extensive testing has demonstrated the capability of heating several cm3 mouse tumors to a temperature of 42.5 degrees C. Depth of heating can be varied by adjusting the frequency of the oscillator or by adjusting the output attenuator.