Efficacy of brachytherapy with californium-252 neutrons versus cesium-137 photons for eradication of bulky localized cervical cancer: single-institution study

Guidelines by the AAPM and GEC-ESTRO on the use of innovative brachytherapy devices and applications: Report of Task Group 167

Although a multicenter, Phase III, prospective, randomized trial is the gold standard for evidence-based medicine, it is rarely used in the evaluation of innovative devices because of many practical and ethical reasons. It is usually sufficient to compare the dose distributions and dose rates for determining the equivalence of the innovative treatment modality to an existing one. Thus, quantitative evaluation of the dosimetric characteristics of innovative radiotherapy devices or applications is a critical part in which physicists should be actively involved. The physicist's role, along with physician colleagues, in this process is highlighted for innovative brachytherapy devices and applications and includes evaluation of (1) dosimetric considerations for clinical implementation (including calibrations, dose calculations, and radiobiological aspects) to comply with existing societal dosimetric prerequisites for sources in routine clinical use, (2) risks and benefits from a regulatory and safety perspective, and (3) resource assessment and preparedness. Further, it is suggested that any developed calibration methods be traceable to a primary standards dosimetry laboratory (PSDL) such as the National Institute of Standards and Technology in the U.S. or to other PSDLs located elsewhere such as in Europe. Clinical users should follow standards as approved by their country's regulatory agencies that approved such a brachytherapy device. Integration of this system into the medical source calibration infrastructure of secondary standard dosimetry laboratories such as the Accredited Dosimetry Calibration Laboratories in the U.S. is encouraged before a source is introduced into widespread routine clinical use. The American Association of Physicists in Medicine and the Groupe Européen de Curiethérapie-European Society for Radiotherapy and Oncology (GEC-ESTRO) have developed guidelines for the safe and consistent application of brachytherapy using innovative devices and applications. The current report covers regulatory approvals, calibration, dose calculations, radiobiological issues, and overall safety concerns that should be addressed during the commissioning stage preceding clinical use. These guidelines are based on review of requirements of the U.S. Nuclear Regulatory Commission, U.S. Department of Transportation, International Electrotechnical Commission Medical Electrical Equipment Standard 60601, U.S. Food and Drug Administration, European Commission for CE Marking (Conformité Européenne), and institutional review boards and radiation safety committees.

Clinical evaluation of 252Cf neutron intracavitary therapy for primary endometrial adenocarcinoma

BACKGROUND

A pilot feasibility study of the neutron-emitting radioisotope 252Cf was done on patients with uterine adenocarcinoma and medically inoperable disease or unfavorable G3 histologic findings.

METHODS

252Cf intracavitary therapy was combined with 40-45 Gy of fractionated whole-pelvis photon therapy. In select patients, hysterectomy was performed.

RESULTS

Thirty-one patients with Stage I-III adenocarcinoma of the corpus uteri were treated with 252Cf neutron brachytherapy. The patients treated often were in poor general medical condition and had multiple chronic medical illnesses for which conventional radiation and surgery usually would not be recommended. 252Cf allowed short implant treatment time (hours), was usable in a small number of insertions (the average number of insertions was two), and was useful for treating large volume tumors. Stage and grade of the tumor were important determinants of patient survival. The 5-year actuarial survival was 83% for patients with Stage I disease but only 37% for those with Stage II disease (primarily adenosquamous cell carcinomas). The 5-year survival was 100% for patients with Grade 1 tumors, 88% for those with Grade 2 tumors, and 21% for those with Grade 3 tumors.

CONCLUSION

252Cf neutron brachytherapy was found to be an effective and well-tolerated therapy for endometrial carcinoma. The excellent therapeutic efficacy and good patient tolerance make it suitable for additional evaluation in future Phase II-III trials.

A review of californium-252 neutron brachytherapy for cervical cancer

Since 1976 a clinical trial has been conducted to test the feasibility, the potential, and to develop methods for using the neutron-emitting radioactive isotope, californium-252 (Cf-252), for the treatment of cervical cancer. A total of 218 patients were treated in the initial study period from 1976 until 1983. The trials initially treated advanced (Stages III and IV) cervical cancer patients using different doses and schedules; they were extended to include unfavorable presentations of Stages I and II because of favorable results in the initial trials. The authors began to treat patients with Stage IB bulky or barrel-shaped tumors and the majority were treated with both radiation and hysterectomy. Actuarial survival was determined for Stage IB disease and was 87% at 5 years and 82% at 10 years. For those tested with preoperative radiation it was 92% at 5 and 87% at 10 years. For Stage II, it was 62% 5 years and 61% at 10. Survival 5 years after combined radiation and surgical therapy for Stage II disease was 68%. For Stage III, it was 33% at 5 years and 25% at 10. However, 5-year survival using the early neutron implant was 46% versus approximately 19% for delayed Cf-252 or cesium 137. Different schedules and sequences of neutrons and photons greatly altered outcome. Neutron treatment before external photon therapy was better for all stages of disease. Only about 5% of all patients developed complications after neutron therapy. No hematologic or mesenchymal second tumors were observed. Neutron brachytherapy was found to be very effective for producing rapid response and greatly improved local control of bulky, barrel, or advanced cervical cancers. The clinical trial identified and evolved schedules, doses, doses per session, and developed methods different from standard photon therapy but highly effective for local control and cure of cervical cancers of all stages. Clinical and radiobiologic understanding for the use of neutron therapy was greatly advanced by this trial. Future trials will focus on patients with advanced disease and will require evaluation of adjuvant chemotherapy studies and neutron-enhancing chemicals.

Evaluation of time-dose and fractionation for 252Cf neutrons in preoperative bulky/barrel-cervix carcinoma radiotherapy

Time-dose fractionation factors (TDF) were calculated for 252Cf (Cf) neutron therapy versus 137Cs for intracavitary use in the preoperative treatment of bulky/barrel-shaped Stage IB cervix cancers. The endpoint assessed was gross and microscopic tumor eradication from the hysterectomy specimen. We reviewed the data obtained in clinical trials between 1976-1987 at the University of Kentucky Medical Center. Preoperative photon therapy was approximately 45 Gy of whole pelvis irradiation in 5 weeks for both 137Cs and Cf treated patients. 137Cs implant was done after pelvic irradiation x1 to a mean dose of 2104 +/- 36 cGy at point A at a dose rate of 50.5 cGy/h. There were 37.5% positive specimens. Using Cf intracavitary implants, dose varied from 109 to 459 neutron cGy in 1-2 sessions. Specimens were more frequently cleared of tumor (up to 100% at appropriate dose) and showed a dose-response relationship, both by nominal dose and by TDF adjusted analysis of dose, dose-rate, number of sessions, and overall time. Limited understanding of relative biological effectiveness, schedule, effect of implants, and dose rate all made it difficult to use TDF to study neutron effects. Relative biological effectiveness (RBE) was estimated and showed that for Cf, RBE was a complex function of treatment variables. In the pilot clinical studies, a value of 6.0 had been assumed. The present findings of RBE for tumor destruction are larger than those assumed. Cf was effective for cervix tumor therapy and produced control without significant side effects due to the brachytherapy method used. The TDF model was of limited value in the present analysis and more information is still needed for RBE, dose-rate, and fractionation effects for Cf neutrons to develop a more sophisticated and relevant model.

Regeneration in cervix cancer after 252Cf neutron brachytherapy

Regeneration of clonogens in human cervical cancer was assessed by the pathological evaluation of the hysterectomy specimen after intracavitary 252Cf neutron brachytherapy implants separated by varying time intervals followed by extrafascial hysterectomy. In this study, patients with bulky/barrel shaped Stage IB cervical cancers received 252Cf implants plus approximately 45 Gy of whole pelvis linear accelerator radiotherapy in approximately 25 fractions in 5 weeks followed by hysterectomy 4-6 weeks after radiotherapy. The specimens were studied grossly and microscopically for residual tumor. It was found that the fraction of positive specimens increased with elapsed time interval between implants. These findings support the hypothesis that there is repopulation of surviving clonogens with increased time interval between the implants. The observation also supports current concerns that rapid depopulation of tumor can lead to rapid repopulation, that is, rapid shrinkage of tumor can alter the physiological environment such that clonogens can rapidly regenerate.

Clinical study of relative biological effectiveness for cervical carcinoma treated by 252Cf neutrons and assessed by histological tumour eradication

Clinical data of the University of Kentucky trial using californium (252Cf), or caesium (137Cs), are reviewed for dose-response based on the endpoint of tumour eradication estimated from hysterectomy specimens obtained 4-6 weeks after preoperative irradiation. These data are used to assess the relative biological effectiveness (RBE) for 252Cf neutrons compared with 137Cs gamma radiation. Tumours treated were of common stage but were of bulky or barrel shape suitable for "radiosurgical" therapy. Dose-response curves were constructed, and additional data from the literature used to analyse the curve shape. The photon dose-response curve is complex on a logarithmic plot, whereas the 252Cf neutron curve is exponential. This indicates that the RBE can be different depending on the number of implants, schedule and size of dose delivered per session. The RBE values were approximately 8.0 at low doses or for multiple implants but they may rise to approximately 16 at larger doses or for single 252Cf implants.

Dose-response and failure pattern for bulky or barrel-shaped stage IB cervical cancer treated by combined photon irradiation and extrafascial hysterectomy

From 1975 to 1987, 80 patients with bulky or barrel-shaped Stage IB cervical cancer were treated with preoperative irradiation and Cs-137 intracavitary implant therapy, before a planned extrafascial abdominal hysterectomy, using a consistent treatment policy. Of the hysterectomy specimens obtained, 37% were positive histologically at 89 +/- 2.3 days after the start of radiotherapy and at 4 to 6 weeks after the completion of radiation therapy. Sixty-three percent were negative after a total external and internal cervix irradiation dose of 9642 cGy at point T. The average point A dose contributed by intracavitary therapy was 2104 cGy. The survival rate at 5 years was 84%: At 10 years the survival rate was 78%. The failure pattern was analyzed for patients who had positive and negative specimens. The patients with positive specimens failed pelvically or pelvically and distantly. Patients with negative specimens failed in extrapelvic or distant metastatic sites. Preoperative radiotherapy led to excellent local and pelvic control of tumor, and the failures became predominantly distant metastases. The combined radiosurgical therapy was tolerated well and allowed surgical staging of disease. This permitted earlier and selective consideration of adjunctive therapy (i.e., paraaortic irradiation, chemotherapy, or chemoradiotherapy). The dose-response data give insight into the effects of photon radiotherapy on bulky or barrel Stage IB cervical cancers and correlate histologic status with failure pattern, outcome, and long-term survival.