J.L. Beach

A comparison of air-cavity inhomogeneity effects for cobalt-60, 6-, and 10-MV x-ray beams.

The inclusion of air-filled spaces in treatment fields creates a potential dosimetric problem due to the loss of charged particle equilibrium near the air-tissue interface. We have used a simulated larynx phantom and a small buildup/extrapolation chamber to compare the magnitude and spatial extent of underdosing and overdosing at the distal surface for two linear accelerators (10- and 6-MV x-rays) and a cobalt-60 machine. Surface doses were compared to doses measured in a similar but homogeneous phantom to give observed/expected ratios (O/E), which were greater than 1.0 for large field sizes and less than 1.0 for small field sizes on all machines. The minimum field sizes which produce no surface underdosing for a simulated 2-cm-diam larynx are roughly 7 X 7 cm for 10-MV x-rays, 6 X 6 cm for 6-MV x-rays, and 5 X 5 cm for cobalt-60. In addition, the depth over which underdosing occurs is seen to increase with increasing energy.

Neutron brachytherapy is better than conventional radiotherapy in advanced cervical cancer

Californium-252 (252Cf), a fast-neutron emitting radioisotope, was used for neutron brachytherapy (NT) of 82 patients with advanced (stage III and IV) cervical cancer. The results were compared with caesium-137 brachytherapy; both isotopes were given in combination with high-dose fractionated pelvic radiotherapy. In patients with stage IIIB disease (ie, tumour to the pelvic side-wall), 252Cf intracavitary therapy resulted in 54% 5-year survival compared with 12% in the caesium group. To be effective, Cf-NT must be given before external beam (photon) therapy.

A precision repeat localization head frame for fractionated stereotactic radiotherapy

An immobilization device was constructed for Fractionated Stereotactic Radiotherapy (FSRT) based on registration of the teeth and facial bones in a single thermoplastic mask system, along with a custom hardened foam pillow for posterior head immobilization relative to the mask. The unit interfaces mechanically with all of our current radiosurgery equipment and can be used with any standard stereotactic planning system. After initial trials to design a reproducible radiographic localization test, we performed a series of daily AP and Lateral port films on 3 patients over five isocenters. Seventy-nine films were reviewed and the maximum deviation in anatomical projection in both sagittal and coronal planes was less than 2 mm, with over 60% of films showing no distinguishable deviations from initial port films. Ninety-three percent of the test films showed a repositioning accuracy of less than 1 mm for all tested structures. We have developed an accurate, non-invasive means of repeat head immobilization that, when properly constructed, can facilitate precise fractionated stereotactic radiation therapy with patient comfort, ease of construction and long term stability.

Phase II clinical trial using californium 252 fast neutron brachytherapy, external pelvic radiation, and extrafascial hysterectomy in the treatment of bulky, barrel-shaped stage IB cervical cancer

From June 1977 to June 1983, 32 patients with bulky (>4 cm diameter), barrel‐shaped Stage IB cervical cancer were treated at the University of Kentucky Medical Center by a combination of outpatient neutron brachytherapy using californium 252 (252Cf) and external pelvic radiation followed by extrafascial hysterectomy. Nineteen patients had cervical tumors 4 to 6 cm in diameter, and 13 patients had lesions in excess of 6 cm in diameter. A dose of 4500 rad external photon therapy was given from a linear accelerator, and one or two 6‐hour 252Cf implants were given during or immediately after external radiation. Extrafascial hysterectomy with bilateral salpingo‐oophorectomy was performed 6 weeks after completion of radiation therapy. Complications during and after radiation were minimal and included vaginal stenosis (three) and proctitis (two). Tumor clearance in the hysterectomy specimen was complete in 23 patients (72%) and residual cervical tumor was present in 9 patients (28%). Two patients developed tumor recurrence and died of disease 15 and 27 months after therapy, respectively. Thirty patients remain free of disease 26 to 96 months (median, 52 months) after treatment, and none have been lost to follow‐up. The actuarial survival of these patients is 97% at 2 years and 94% at 5 years. Intracavitary neutron therapy is well tolerated and is effective when combined with external radiation and hysterectomy in the treatment of bulky, barrel‐shaped Stage IB cervical cancer.

Five-year cure of cervical cancer treated using californium-252 neutron brachytherapy

FEMALE PELVIC CARCINOMA IS ONE OF THE COMMON malignancies seen at the University of Kentucky Medical Center and often presents in an advanced stage. In 1976, we began to test californium-252 neutron brachytherapy (NT) for its efficacy for control of primary and recurrent advanced uterine, cervix, and vaginal cancers. The first protocol used was 5000–5500 rad of whole pelvis irradiation followed by 1–2 Cf-252 insertions using a single tandem placed in the utero-cervico-vaginal region. Of 27 patients with primary carcinomas treated, 10 are alive and well 5 years later (37%) Two of two recurrent tumors were locally controlled but failed later. These patients had advanced cervical, vaginal, or endometrial carcinomas. In 1977, a transitional year, treatment of only unfavorable stages and presentations with NT was initiated. Similar results were obtained with NT as compared to conventional photon therapy (PT). Further improvement in treatment results can be anticipated as NT brachytherapy is used for advanced cancer therapy by more effective treatment schedules and radiation doses. Cf-252 can be used as a radium substitute and achieved similar rates of tumor control and 5-year survivals.

Killing of Human Lung Cancer Cells Using a New [111In]Bleomycin Complex [111In]BLMC

The ability of a [111In]bleomycin complex [( 111In]BLMC) to kill five cell lines of human lung cancer (small cell lung cancer) was investigated. Cells were exposed to either 0.9% NaCl, [111In]Cl3, BLM, [111In]BLMC, nonradioactive InCl3, or In-BLMC for 60 minutes, plated in soft agarose, and assessed for colony formation. [111In]BLMC (40-200 microCi carried by 15-25 micrograms BLM/ml) was more cytotoxic than BLM (15-25 micrograms BLM/ml) by a factor of 1.6-5.3 for five cell lines. The percent survival of N417 cells was 28.4 for [111In]BLMC (40 microCi/15 micrograms BLM/ml) and 54.3 for BLM (15 micrograms/ml); 1.9 for [111In]BLMC (200 microCi/25 micrograms BLM/ml), and 10.0 for BLM (25 micrograms/ml). 111InCl3 (200 microCi/ml) and nonradioactive InCl3 failed to inhibit colony formation. The new [111In]BLMC may be useful for therapy of some lung cancer patients.

Phase I-II clinical trial of Californium-252. Treatment of stage IB carcinoma of the cervix.

Intracavitary Californium‐252 combined with whole‐pelvis photon radiotherapy was tested as the sole form of treatment for 22 patients with Stage IB carcinoma of the cervix. Californium‐252 (Cf) is a fast neutron‐emitting radioisotope currently being tested in trials of neutron brachytherapy (NT). The outcomes of the treated group of patients were traced for local tumor control, survival, patterns of failure, and complications. The Cf intracavitary therapy combined with whole‐pelvis photon radiotherapy resulted in 95% 2‐year and 91% 5‐year actuarial survival. There were 9% Grade II‐III complications by the Stockholm scale and 4% local failures. These results were obtained in an early clinical trial with a group of largely poor‐risk patients with tumors of mean diameter of 4.3 cm.

Treatment of stage IIIB cervical cancer with californium-252 fast-neutron brachytherapy and external photon therapy

From January 1977 to July 1984, 32 patients with Stage IIIB cervical cancer were treated at the University of Kentucky Medical Center by a combination of outpatient neutron brachytherapy and external pelvic radiation. These patients received 4500 to 5000 rad external photon therapy and two or three outpatient Californium‐252 (252Cf) implants, plus sidewall boost irradiation. Treatment results were compared retrospectively to those obtained in a historical control group of patients with Stage IIIB cervical cancer treated with external radiation and conventional photon brachytherapy from 1972 to 1976. Local or regional tumor recurrence developed in 53% of patients treated with neutron therapy and an additional 9% experienced distant metastases. Thirty‐eight percent of patients remain free of disease 12 to 96 months (mean, 51 months) after therapy. The 2‐year and 5‐year survival rates of patients treated with neutron therapy were 53% and 36% which were not significantly different than those obtained with photon brachytherapy (2‐year survival, 61%; 5‐year survival, 34%). Complications of neutron therapy were minimal and included proctitis (19%) and vaginal stenosis (9%). There were no cases of enteric fistulae. Outpatient neutron brachytherapy was cost effective and was well tolerated by patients.

Study of acute 60Co, low dose rate CF-252 and CS-137 radiation on LSA ascites lymphoma In Vivo

Dose response curves were determined for the LSA lymphoma for acute 60Co, low dose rate Cs-137 and Cf-252 radiations using in vivo survival time bioassay. Mean survival times increased with dose with a prominent oxygen effect noted for acute 60Co and Cs-137. OER was lowest for Cf-252 where it was approximately 1.4. The RBEn for oxic LSA cells to Cf-252 neutrons was 3.1 for acute 60Co and 4.2 for Cs-137. It was larger for hypoxic tumor and RBE was 5.3 for 60Co and 5.8 for Cs-137. Survival curves based on survival data used a multitarget dose-response model for photon radiation and exponential dose-response for Cf-252 radiation. When LSA was irradiated in advanced tumor stages in vivo, Cf-252 was much more effective than acute 60Co or LDR Cs-137 for increasing survival time. Tumor response in vivo matched the in vitro irradiated tumor data. No schedule dependence was observed for mixing of 60Co and Cf-252 radiations.

Microdosimetric measurements of radiation quality variations in homogeneous phantoms irradiated by fast neutron beams

The Dual Radiation Action Theory of Kellerer and Rossi (DRA), along with presently available microdosimetric techniques, is applied to the determination of radiation quality variation within tissue equivalent phantoms irradiated by collimated fast neutron beams. The neutron beams investigated were produced by the bombardment of 22.5 and 16 MeV d + on beryllium and by the T(d,n)4He reaction (15-MeV neutrons). Microdosimetric spectra were obtained at points of varying depth and lateral distance from the central axis within a tissue equivalent phantom, including points within the penumbra. From the microdosimetric spectra the parameter RQ, a first approximation to RBE derived from DRA theory, is calculated for each point. All RQ values are calculated for the same level of effect. For these three different beams the results show that the RQ values for the total radiation spectrum of neutron and gamma radiation remain fairly constant with depth and with lateral distance from the beam axis at 2 and 10 cm depths. The largest central axis variation in RQ is 8% for the d(16) + Be beam. The largest variation between a penumbra and an on-axis RQ value is 4% at 2 cm depth in the d(22.5) + Be beam. The results for the d (22.5) + Be beam disagree with previously reported radiological results while the 15 McV beam results are in good agreement.