Proceedings of the 38th Annual ASTRO Meeting 359

2166 THE EFFECTS OF VASCULARISED TISSUE TRANSFER ON RE-IRRADIATION.

‘K Narayan, *M W Ashton and rG I Taylor.

‘Peter MacCallum Cancer Institute, Melbourne, Australia * Royal Melbourne Hospital, Melbourne, Australia

Purpose: Nowadays, radical re-irradiation of locally recurrent squamous cell carcinoma is being increasingly tried. The process usually involves some form of surgical excision and vascularised tissue transfer followed by r&radiation. The aim of this study was to examine the extent of protection from the effects of re-irradiation provided by vascularised tissue transfer.

Methods and Materials: One hundred Sprague Dawley rats had their left thighs irradiated to a total dose of 72Gy in 8 fractions, one fraction per day, 5 days per week.

The rats were then divided into two groups: At 4 months, one half of the rats had 50% of their quadriceps musculature excised and replaced with a vascularised non-irradiated rectus abdominous myocutaneous flap. The other group served as the control. Six months following the initial radiotherapy all rats were then re- irradiated with either 75 or 90% of the original dose. Incidence of necrosis and the extent of necrosis was measured. Microvasculature of control, transplanted muscle and recipient site was studied by micro-corrosion cast technique and histology of cast specimen. tissues were sampled at pre-irradiation and at 2, 6 and 12 months post re-irradiation. Microvascular surface area was measured from the histology of cast specimen.

Results: Necrosis in the control group was clinically evident at 6 weeks post re irradiation and by 10 months all rats developed necrosis. Forty per cent of the thigh that received 75% of the original dose on m&radiation did not develop any necrosis by 13 months. other groups developed necrosis to variable extents, however a rim of tissue around the grail always survived. The average thickness of surviving tissue was 9mm. (range being 4-25 mm). None of the transferred flap nor re-irradiated recipient quadriceps developed necrosis.

Conelusion: 1. Transplanted rectus abdominus myocutaneous flap and undisturbed muscle have similar radiation tolerance. 2. Vascularised myocutaneous flap offers considerable protection against re radiation of the tissue in its proximity 3. Such protected zone may not be sufficient for external beam radiotherapy but could be useful in a single plane interstitial radiotherapy.

2167 CAUDA EQUINA TOLERANCE TO RADIATION THERAPY

l&2 2 3 2 2 Pi&m, R.S. ; O’Farrell, D. ;Fullerton, B. ; Efird, J. ; Munzenrfder, J.

1 Department of Radiation Oncology, Boston University School of Medicine, 2 Department of Radiation Oncology, 3 Department of Anatomy, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114 and Harvard Cyclotron Laboratory, Cambridge, MA

Purpose: To report neurologic sequelae and clinical outcome for local recurrence free-survival and overall survival of patients treated with high-dose fractionated radiation therapy utilizing 3D treatment planning and combined proton and photon beams to portions of the cauda equina (L2-Coccyx), and to reassess tolerance of this structure to therapeutic radiation.

Materials & Methods: From 1974 through 1994 , 62 patients were treated to fields encompassing portions of the cauda equina, of whom 55 were evaluable; this cohort is the study group. Pathology included 37 sarcomas, 17 chordomas, 3 desmoid tumors, 2 ependymomas, 2 adrenocortical carcinomas and 1 squamous cell carcinoma of the cervix. 29 patients were male; 26 were female. Median prescribed dose was 66.59 CGE (Cobalt Gray Equivalent: proton Gy x RBEl .l + photon Gy), ranging from 42.00-82.00 CGE. 30 CT treatment planning has been used in all patients treated since 1980. Median follow up was 44 months (range 1.5168 months). Neurologic status was assessed by retrospective chart review. Dose volume histograms are available and will be compared with risk of neurologic side effects.

Results: Treatment outcome was evaluated for local recurrence, radiation complication-free survival (both assessed at last living follow up)and absolute survival. 98 patients expired, 37 were alive at last follow up. Overall survival at 3 years was 81% and at 5 years 70 %. At last living follow up, 29 patients were NED, 5 had local failure, 7 distant metastases, 7 local failure 8 distant metastases, 5 local symptoms, recurrence possible, and 2 were alive, disease status undetenined. Neurologic status at last living follow up: 3 patients had probable radiation complications, 5 had pain, which may represent radiation complications, and 8 were neurologically impaired secondary to their disease. Including the 5 pain patients as RT complications, the radiation complication-free survival of evaluable patients at 3 years was 95% and at 5 years was 76%.

Conclusion: These data suggest that the tolerance of the cauda equina to radiation therapy may be greater than has been generally accepted. Local failure remains a significant problem in these diseases, as does metastatic spread.