Dose-fractionation sensitivity of mouse kidney clonogens measured using different interfraction intervals and postirradiation assay times

Dose escalation using twice-daily radiotherapy for nasopharyngeal carcinoma: does heavier dosing result in a happier ending?

PURPOSE

To present our experience using a twice-daily radiotherapy (RT) technique, including hyperfractionated and accelerated-hyperfractionated RT, on nasopharyngeal carcinoma (NPC) patients. The dose to the primary tumor was increased in the hope that local control could be increased without the cost of increased late complications. We analyzed acute and late complications and local control and compared the results with the results of NPC patients treated during the same period using conventional once-daily RT.

METHODS AND MATERIALS

Between October 1991 and July 1998, 222 histologically confirmed, Stage M0, previously unirradiated NPC patients completed RT at our hospital. Most patients had American Joint Committee on Cancer (AJCC) 1992 Stage III and IV disease. Among them, 88 received altered fractionated, twice-daily RT; 76 patients received hyperfractionated RT and 12 accelerated-hyperfractionated RT. The remaining 134 patients received a conventional once-daily regimen. Hyperfractionated RT was delivered using 120 cGy b.i.d. separated by 6-h intervals throughout the course. For the accelerated-hyperfractionated patients, 160 cGy b.i.d. was given, also at 6-h intervals. The median dose in the twice-daily group was 7810 cGy (range 6840-8200). In the once-daily regimen, RT was delivered using 180-200 cGy q.d. The median tumor dose to the primary tumor was 7000 cGy (range 6560-8100) given during about 8 weeks. The median follow-up time was 70.5 and 72 months for the twice-daily and once-daily groups, respectively.

RESULTS

The incidence of acute toxicities was higher in the twice-daily group with more severe mucositis and moist desquamation than in the once-daily group. Both groups had a similar incidence of late complications, except for 3 cases of temporal lobe necrosis in the twice-daily group, all in patients treated with 160 cGy. No difference was noted in recurrence-free local control between the two groups when the individual T stage was compared using AJCC 1992 or 1997 criteria (p = 0.51 and 0.59, respectively). The 5-year local control rate for T1-3 (AJCC 1997) was 93.2% for the twice-daily group and 86.4% for the once-daily group (p = 0.45). In Stage T4 (AJCC 1997) patients, the local control rate dropped drastically to 43.5% and 36.9% for the twice-daily and once-daily groups, respectively. The overall neck control rate at 5 years was 87.3% and 80.3% for the twice-daily and once-daily patients, respectively (p = 0.16). The overall locoregional control rate was 82.7% for the twice-daily group and 66.6% for the once-daily group. The difference was again not statistically significant, but showed a tendency in favor of the twice-daily regimen (p = 0.055). Locoregional failure occurred mainly in Stage T4 patients with central nervous invasion for whom local control was particularly poor, with a failure rate of about 60%.

CONCLUSION

The present data suggest that NPC patients can be safely treated using a 120-cGy twice-daily program with a 6-h interval up to 8000 cGy. The accelerated-hyperfractionated technique is not recommended. A large discrepancy in local control between patients with T1-3 and T4 disease was noted. For T1-3 disease, an excellent local control rate >90% was achieved using the twice-daily regimen. In contrast, failure in the T4 patients was as high as 55% in the twice-daily group and reached 65% in the once-daily group. More rigorous treatment is needed using either additional dose escalation or other strategies for T4 NPC patients. With a dose escalation of 1000 cGy using 120-cGy twice-daily RT, a trend toward better locoregional control and disease-specific survival was noted in the twice-daily group. Whether this difference was truly the result of an increased dose needs additional confirmation in studies with larger patient numbers.

The influence of dose per fraction on the pathogenesis of radiation nephropathy

Both kidneys of male Wistar rats were irradiated with either a 10-Gy single dose or 26 Gy at a rate of 2 Gy per fraction per day. Serum blood urea nitrogen (BUN), creatinine and blood haematocrit levels were assessed prior to radiotherapy and at intervals of 8 weeks thereafter. A subset of animals from each dose group were killed at 4, 8, 16 and 24 weeks and both kidneys of each animal were examined by electron microscopy. In both dose groups a significant increase in BUN and creatinine levels, together with a decrease in haematocrit level, was observed at 16 weeks, and this was followed by an apparent improvement at 24 weeks. There was no statistical difference in these responses between the two groups. The morphological changes in both dose groups were essentially similar, but differed in severity. At 4 weeks after irradiation glomerular and proximal tubular injury were observed in both groups. A marked increase of glomerular and tubular injury in the 10-Gy dose group, without any apparent progression in the 26-Gy dose group, was detected at 8 weeks. By 16 weeks a noticeable improvement in both tubular and glomerular lesions (especially in the 10-Gy dose group) was observed. No apparent difference from the 16th week of evaluation was found at 24 weeks. These findings indicate that there is some recovery in kidney after irradiation, but the extent of the recovery process is somewhat limited.

Single dose versus fractionated total body irradiation before bone marrow transplantation: radiobiological and clinical considerations

PURPOSE

This present review is intended to evaluate the specific influence of fractionation of total body irradiation on the outcome of a subsequent bone marrow transplantation.

METHODS AND MATERIALS

Available experimental and clinical data on the influence of fractionation on leukemia cell killing, immunosuppression, and sparing of normal tissues were analyzed.

RESULTS

Review of available data shows: (a) The role of fractionation on leukemia cell killing may vary with the leukemia type. For acute nonlymphoblastic leukemia, a few experimental and several clinical studies show no or little fractionation effect; a 12-13 Gy fractionated scheme could, therefore, be more efficient than a conventional 10 Gy single dose total body irradiation. For chronic myelogenous leukemia, some sensitivity to fractionation is suggested, so that an increase in total or fractional dose may be necessary in fractionated schemes to equate the efficacy of a 10 Gy single dose. For acute lymphoblastic leukemia, a high fractionation sensitivity was observed for some leukemic cell lines in vitro, without undisputable clinical confirmation for the moment. (b) Numerous experimental studies have demonstrated that the immunosuppressive effect of total body irradiation, a major determinant of engraftment, is highly fractionation sensitive. In humans, high rates of graft failures have been reported when T-cell depletion of the graft was associated to fractionated total body irradiation schedules. (c) A large amount of radiobiological and clinical data have demonstrated that late radiation-induced injuries to normal tissues and organs are highly fractionation sensitive. However, in a context of total body irradiation for bone marrow transplantation, the number of other determinants of normal tissue damage makes it difficult to demonstrate a clear-cut advantage of fractionated over single dose scheme, with a possible exception for children.

CONCLUSIONS

In 1994, available data suggest that very cautious attempts could be made to adapt total body irradiation schedules to the potential normal tissue toxicity, T-cell depletion, and to the type of leukemia.

Two components of repair in irradiated kidney colony forming cells

Data describing the response of mouse kidney colony-forming cells to fractionated X-irradiation using different interfraction intervals were analysed in order to detect the presence of one or more components of repair. A two-component repair model gave a superior fit, with reference to a single-repair rate model, giving distinct repair halftimes of 0.15 (approximate 95% confidence limits: 0.0, 0.40) and 5.03 (1.23, 8.84) h. These values are the first reported for normal cells in vivo, and they are similar to values calculated for tissue responses in skin, lung and the spinal cord. The slow component of repair is important in radiotherapy, in particular regarding novel hyperfractionation regimens when interfraction intervals much less than 1 day are employed.