Dose fractionation and regeneration in radiotherapy for cancer of the oral cavity and oropharynx: tumor dose-response and repopulation

Does tumor control decrease by prolonging overall treatment time or interrupting treatment in laryngeal cancer?

PURPOSE

To evaluate treatment results of radiotherapy in laryngeal cancer and to retrospectively investigate the influence of treatment interruptions on local control rates. A multivariate analysis was performed to investigate the role of overall treatment time on local control rates.

MATERIAL AND METHODS

From 1962 to end 1986, 864 patients with cancer of the larynx were treated with primary radiotherapy, with a variation of doses and treatment times. In 352 patients a systematic interruption of 2 weeks was done after 50 Gy (split-course). Local control rates were calculated by the actuarial method. A multivariate analysis was subsequently performed in order to identify independent variables influencing local control rates.

RESULTS

The univariate analysis showed that in patients treated with a split-course schedule, local control rates were significantly lower in glottic cancer (p < 0.001), with differences of 7% in T1 (p = 0.05) and 11% in T2 (p = 0.11). In node-negative supraglottic cancer a difference of 10% (p = 0.16) was observed. The multivariate analysis showed the following factors to significantly influence local control: site, total dose, total treatment time, T and N stage. Split-course treatment was not an independently significant factor, probably caused by time being a stronger factor. In subgroup analysis, the effect of total treatment time remained statistically significant in T2 glottic cancer.

CONCLUSION

A significant negative influence of treatment interruption was seen in glottic cancer, and a trend toward significance in node-negative supraglottic cancer in univariate analysis. A multivariate analysis showed a negative influence of prolonging treatment time in the total patient group. The effect remained significant in T2 glottic cancer in subsequent subgroup analysis, possibly due to the fact that there is little variation in tumour volume in this group. In larger tumours, where there is substantial variation in tumour volume and a higher probability of heterogeneity in radiosensitivity, the effect of dose-time variations could be more difficult to discern.

Effect of overall treatment time on local control in radical radiotherapy for squamous cell carcinoma of esophagus

PURPOSE

To analyze the effect of overall treatment time on local control in radical radiotherapy for squamous cell carcinoma of esophagus.

METHODS AND MATERIALS

Three hundred and fifty-three patients with inoperable esophageal cancer (tumor length < or = 10 cm in all cases) treated during 1963-1988 by radical radiotherapy alone either as continuous or split-course therapy. The overall treatment time varied from 35 to 55 days and the total dosage from 50 to 71 Gy in the continuous therapy group (n = 138), and in the split-course group (n = 215) with a planned 3-week rest interval in the middle of the treatment from 56 to 70 days and from 55 to 70 Gy, respectively. The logit method of the linear-quadratic formula for local control at 1 year was used to examine the effect of treatment time on local control. All patients were pooled to obtain a wide range of overall treatment times.

RESULTS

The 1-, 2-, and 5-year actuarial survival rates according to the T-stage in the continuous therapy group from the first day of the radiotherapy were: 57%, 32%, and 10% for the T1 tumors and 23%, 8%, and 5% for the T2 tumors. The corresponding figures for the split-course group were: 50%, 19%, and 4% for the T1 tumors and 17%, 6%, and 3% for the T2 tumors. The 1-year local control rate was 56% for the T1 tumors and 15% for the T2 tumors in the continuous therapy group and 48% for the T1 tumors and 10% for the T2 tumors in the split-course group. The results of the logit method did not fit well with the T1 tumors. For the T2 tumors, they showed Dprolif to be about 0.24 Gy/day for local control at 1 year. As a consequence, protraction of overall time by 1 week should be compensated by increasing the total dose by 1.8 Gy for 1 year local control.

CONCLUSIONS

More attention should be focused on repopulation. Shortening of overall treatment time might be beneficial for the treatment of squamous cell carcinoma of esophagus.

Effect of time, dose and fractionation on local control of nasopharyngeal carcinoma

To study the effect of radiation factors on local control of nasopharyngeal carcinoma, 1008 patients with similarly staged T1N03M0 disease (Ho's classification) were retrospectively analyzed. All patients were treated by megavoltage irradiation alone using the same technique. Four different fractionation schedules had been used sequentially during 1976-1985: with total dose ranging from 45.6 to 60 Gy and fractional dose from 2.5 to 4.2 Gy. The median overall time was 39 days (range = 38-75 days). Both for the whole series and 763 patients with nodal control, total dose was the most important radiation factor. The hazard of local failure decreased by 9% per additional Gy (p < 0.01). Biological equivalents expressed in terms of Biologically Effective Dose or Nominal Standard Dose also showed strong correlation. Fractional dose had no significant impact. The effect of overall treatment time was insignificant for the whole series, but almost reached statistical significance for those with nodal control (p = 0.06). Further study is required for elucidation, as 85% of patients completed treatment within a very narrow range (38-42 days), and the possible hazard is clinically too significant to be ignored.

Randomized phase I/II trial of two variants of accelerated fractionated radiotherapy regimens for advanced head and neck cancer: results of RTOG 88-09

PURPOSE

To establish the feasibility of performing split-course accelerated hyperfractionation (AHFX-S) and concomitant boost accelerated fractionation radiotherapy (AFX-C) for advanced head and neck cancer in a multi-institutional cooperative trial setting and to evaluate the tumor clearance rate and acute and late toxicity of these fractionation schedules.

METHODS AND MATERIALS

Between February 1989 and January 1990, 75 patients with Stage III or IV squamous cell carcinoma of the head and neck were randomized to receive: (a) AHFX-S: 1.6 Gy/fraction, twice daily (6-h interval), 5 days/week, to a total dose of 67.2 Gy/42 fractions/6 weeks, with a 2-week rest after 38.4 Gy; or (b) AFX-C: 1.8 Gy/fraction/day, 5 daily fractions/week to 54 Gy/30 fractions/6 weeks to a large field and 1.5 Gy/fraction/day to a boost field, 6 h after large field treatment during the last 11 treatment days, to a total dose of 70.5 Gy/41 fractions/6 weeks. Acute and late toxicities were scored according to the RTOG normal tissue reaction scales and tumor clearance was evaluated at completion of therapy and at regular intervals thereafter.

RESULTS

Of the 70 analyzable patients, 38 received AHFX-S and 32 received AFX-C. The two arms were balanced with respect to sex, age, T-stage, and Karnofsky Performance Status (KPS). However, the AHFX-S arm had a higher proportion of oropharyngeal primaries (63% vs. 44%), and Stage IV disease (82% vs. 50%) and lower proportion of oral cavity lesions (3% vs. 22%) and N0 disease (16% vs. 31%) than the AFX-C arm. The median follow-up was 2 years (range: 0.03-4.87 years). Tolerance of both variants of accelerated fractionated radiotherapy was satisfactory. There was no significant difference in local-regional control, disease-free survival, or survival between the two arms. The 2-year local-regional failure rate, survival, and disease-free survival was 50, 50, and 40%, respectively, for the entire group of patients. Acute radiation mucositis was increased in both arms. There was no significant difference in the incidence of grade 3 acute toxicities (63% vs. 56%) and grade 3 (14% vs. 14%) or grade 4 (6% vs. 17%) late toxicities. Permanent grade 4 late toxicity was observed in 6 and 7% of the patients, respectively.

CONCLUSION

Results of this randomized Phase I/II trial showed that the two accelerated fractionated schedules studied can be successfully given in a multi-institutional cooperative trial. There was no significant difference in acute or late toxicities, local-regional control, disease-free survival, or survival in this small scale study. Therefore, a Phase III trial comparing the relative efficacy of these two accelerated fractionation schedules against standard fractionation and hyperfractionation has been activated.

Fast-neutron therapy in advanced head and neck cancer: a collaborative international randomized trial

PURPOSE

To compare the efficacy of fast-neutron radiotherapy with that of conventionally fractionated photon therapy in the management of patients with locally advanced squamous cell carcinoma of the head and neck.

METHODS AND MATERIALS

Patients with Stage III or IV disease were randomized to receive either 20.4 Gy/12 fractions/4 weeks of neutrons or 70 Gy/35 fractions/7 weeks of photons (control). Between April 1986 and March 1991, 178 patients were entered, 169 of whom were eligible for analysis. The treatment arms were balanced for age, stage, and performance status, but not for primary site of origin.

RESULTS

Complete response occurred in 70 and 52% with neutrons and photons, respectively (p = 0.006). Local regional failure at 3 years for all patients was 63% for neutrons and 68% for photons. Actuarial overall survival curves were virtually identical in both study arms, falling to 27% at 3 years. Acute toxicity was similar in the two arms, but late grade 3-5 toxicity was 40% with neutrons compared to 18% with photons (p = 0.008).

CONCLUSION

Although the initial response rate was higher with neutrons, permanent local control and survival were not improved, and the incidence of late normal tissue toxicity was increased. As a result, fast-neutron therapy for advanced squamous cell carcinoma of the head and neck can only be recommended for patients in whom the logistic benefit of treatment in 12 sessions over 4 weeks outweighs the increased risk of late toxicity.

The decreased influence of overall treatment time on the response of human breast tumor xenografts following prolongation of the potential doubling time (Tpot)

PURPOSE

Repopulation during fractionated radiotherapy has been postulated to result in a significant loss in local control in rapidly proliferating tumors. Clinical data suggest that accelerated fractionation schedules can overcome the influence of repopulation by limiting the overall treatment time. Unfortunately, accelerated therapy frequently leads to increased acute reactions, which may become dose limiting. An alternative to accelerated fractionation would be to decrease the rate of repopulation during therapy. To test the potential efficacy of this alternative, we examined the effect of reducing tumor proliferation rate on the response of MCF-7 human breast carcinoma xenografts treated with a short vs. a long course of fractionated therapy. To reduce the proliferation rate, we deprived nude mice transplanted with MCF-7 xenografts of the growth-stimulating hormone estradiol (E2). We have previously reported that E2 deprivation increases the potential doubling time (Tpot) for MCF-7 xenografts from a mean of 2.6 days to 5.3 days (p < 0.001).

METHODS AND MATERIALS

E2-stimulated and E2-deprived MCF-7 breast carcinoma xenografts were clamped hypoxically and irradiated with four fractions of 5 Gy each, using either a short (3-day) or long (9-day) treatment course. E2 stimulation was restored in all animals at the completion of irradiation. Radiation response was determined by regrowth time and regrowth delay of the irradiated tumors as compared to unirradiated controls.

RESULTS

Prolongation of therapy in rapidly proliferating, E2-stimulated tumors (Tpot approximately 2.6 days) resulted in a significant decrease in regrowth time in two identical experiments. With results pooled for analysis, the regrowth times for the short and long treatments were 62 and 32 days, respectively (combined p < 0.001). The shorter regrowth times suggest that there was less overall tumor damage with the longer fractionated radiotherapy course. No significant difference in regrowth time was observed in the more slowly proliferating, E2-deprived tumors (Tpot approximately 5.3 days) treated with either the short or long regimen. Median regrowth times were 48 and 54.5 days for the short and long treatments, respectively (combined p = 0.14). Similar changes were observed in regrowth delay.

CONCLUSIONS

Reduction in the rate of cell proliferation, induced by E2 deprivation in MCF-7 human breast xenografts during fractionated radiotherapy, resulted in a significantly decreased dependence on overall treatment time in comparison to the more rapidly proliferating E2-stimulated tumors. This model suggests that pharmacologically induced reduction in the rate of tumor cell proliferation during a course of fractionated radiotherapy may be a viable alternative to accelerated fractionation for the treatment of rapidly proliferating tumors.

Repopulation kinetics during fractionated irradiation and the relationship to the potential doubling time, Tpot

PURPOSE

Therapeutic outcome may be adversely affected by repopulation in solid tumors during fractionated irradiation. It has been proposed that the repopulation rate of the surviving cells may be reflected by the pretreatment potential doubling time (Tpot). This concept has been examined by comparing pretreatment Tpot measurements to repopulation monitored in five transplantable murine tumors during fractionated radiation treatment.

METHODS AND MATERIALS

Up to nine fractions of 2 Gy were given to clamped tumors on a 6 h schedule, which allowed adequate time for repair, or on a 24 h schedule, which incorporated more time for repopulation. Tumors were removed from treatment at various times and tumor cell survival was analyzed using an excision assay. The ratio of the cell survival in tumors treated with the same total dose on the two different fractionation schedules (24 h/6 h) was used to calculate an effective doubling time for repopulation during the treatment (Teff). Potential doubling time was assessed in untreated tumors by giving the tumor-bearing animals 5-bromodeoxyuridine (BrdUrd) and, at various times later, removing the tumors for flow cytometric analysis. Tpot values were calculated by two different widely used methods.

RESULTS

For four tumors (RIF-1, KHT-C, KHT-LP1, and B16-F1), the Teff was greater than Tpot indicating that repopulation was not as rapid as suggested by Tpot. For SCC-VII, the only carcinoma tested, Teff was smaller than Tpot indicating that repopulation was more rapid than predicted by Tpot. Individual estimates of Tpot made from single tumor samples taken at different times after BrdUrd administration varied by factors of 2 to 7 for the different tumors.

CONCLUSION

These findings indicate a need for caution in applying measurements of Tpot for prediction of regrowth rates in individual patients' tumors.

Tables of equivalent dose in 2 Gy fractions: a simple application of the linear quadratic formula

PURPOSE

To provide a simple method of showing the equivalent dose in 2 Gy fractions for various treatment regimens using the linear quadratic (LQ) formula.

METHODS AND MATERIALS

Tables of equivalent dose for common total doses and fraction sizes have been calculated using the LQ formula for representative alpha:beta ratios (1, 3, 10). Corrections have not been made for repopulation. Examples are given.

CONCLUSION

The tables offer a simple method of equating one fractionation regimen with another, recognizing the limitation of this method.

Influence of boost technique (external beam radiotherapy or brachytherapy) on the outcome of patients with carcinoma of the base of the tongue

We reviewed 90 patients with squamous cell carcinoma of the base of the tongue. Fifty-three patients were treated with external beam radiotherapy alone (3 T1, 11 T2, 21 T3, and 18 T4 tumors) and thirty-seven patients were treated with external beam radiotherapy plus brachytherapy boost (4 T1, 15 T2, 11 T3, and 7 T4 tumors). For patients with T1, T2 and T3 primaries, the actuarial 3-year local relapse-free survival was 42% following external beam radiotherapy alone and 67% following external beam radiotherapy plus brachytherapy (p < 0.05). The actuarial 3-year cause specific survival for these T-stages was 37% for patients treated with external beam radiotherapy alone and 53% for patients treated with external beam radiotherapy plus brachytherapy (p = 0.1). In the Cox multivariate analyses restricted patients with T1, T2 and T3 staged tumors, treatment modality was the only predictor for local control but no influence on specific survival was found. The trend towards significant differences in specific survival found in the univariate comparison of both treatment modalities was probably due to the significantly higher number of N-positive patients treated with external beam radiotherapy alone. When all stages were included in the Cox analysis, low hemoglobin level, invasion of deep muscle, number of palpable nodes, and history of weight loss significantly influenced the outcome. Soft tissue necrosis occurred more frequently in patients treated with external beam radiotherapy plus brachytherapy (33% vs. 10%, p = 0.52).

T1 nasopharyngeal carcinoma: the effect of waiting time on tumor control

PURPOSE

To study the effect of unperturbed tumor growth on the control of nasopharyngeal carcinoma.

METHODS AND MATERIALS

This is a retrospective analysis of 290 patients with T1N0-3M0 disease (Ho's classification) treated by the same technique and dose schedule to the nasopharyngeal region. The median interval from diagnosis to commencement of irradiation was 26 days (range: 8-68 days). Cox proportional hazards analyses were performed to study the independent effect of waiting time on the probability of failure at various sites. Actuarial failure-free survival of patients with delay < 22 days, 22-28 days and > 28 days were also compared to illustrate the clinical observation.

RESULTS

Both tests showed that waiting time had no significant impact on local failure: The N-stage stratified hazard ratio was 0.985 per day, and the 10-year local failure-free survival for the three groups was 76%, 80%, and 82%, respectively. A similar result was obtained for nodal control in patients with our scheduled neck irradiation. Although the p value of all tests failed to reach statistical significance, the N-stage stratified hazard ratio for distant failure was 1.020 per day, and the corresponding metastasis-free survival in patients with N2-3 disease was 70%, 65%, and 52%, respectively. For node-negative patients without elective neck irradiation, the hazard ratio was 1.019 per day, with the corresponding regional failure-free rates at 57%, 62%, and 33%, respectively.

CONCLUSION

Delay in initiation of treatment to the primary target (within the range observed) did not affect the control rate at irradiated sites, but there was a trend (though statistically insignificant) towards increase in failures at untreated sites that were clinically too serious to be ignored.

Repopulation in mouse oral mucosa: treatment splits

The efficacy of repopulation during treatment splits in conventional radiotherapy (5 fractions/week, 2.5, 3.5, 4.5 Gy/fraction) was studied by delayed top-up treatment of mouse tongue epithelium. Splits of 6 h to 13 days were introduced after 1 or 2 weeks of fractionated irradiation. Following 5 fractions, compensation of about 3 dose fractions was assessed after the first weekend and original tissue tolerance was restored after a split of 4-10 days. About 4.6 dose fractions were repopulated during the second treatment week, followed by a further 1.5 fractions during the first 3 split days; restoration of the initial tolerance required 3-8 days. These results indicate that repopulation was more efficient during fractionated radiotherapy than during a subsequent treatment split. Latent times to complete denudation after the top-up treatment decreased to a dose-dependent minimum after 5 fractions and remained at the decreased level when a second treatment week was added. Original values were restored within 5-8 days after 5 fractions and 6 days after 10 fractions. Epithelial cell density during treatment with 3 or 4 Gy/fraction decreased to a dose-dependent nadir of 63% and 52% of the original number after 5 fractions, and original cell counts were then restored after 5 days. Cellularity remained at 60-70% during the second treatment week and subsequently reached normal values within 4 days. In conclusion, reconstitution of epithelial cellularity precedes restoration of radiation tolerance during treatment splits.

The influence of radiotherapy treatment time on the control of laryngeal cancer: a direct analysis of data from two British Institute of Radiology trials to calculate the lag period and the time factor

This study analyses node-negative laryngeal tumour control data from two clinical trials conducted by the British Institute of Radiology in order to determine the time factors and the presence or absence of a lag period before the time factor takes effect. A direct maximum likelihood approach is used to fit a double-logarithmic model including a repopulation term which commences after an initial lag period, Tk. The analysis yields a time factor of 0.8 Gy per day (95% confidence interval 0.5-1.1 Gy per day) as the extra dose required to counteract the reduction in tumour control probability (TCP) with extension of the treatment time. The latter reduction amounted to between 5 and 12% TCP per week, depending on the stage and time period. With this dataset, where few patients were treated for short times, no statistically significant lag phase can be demonstrated. However, the best estimate of Tk is 21 days (95% confidence interval 0-27 days), which is consistent with estimates from other studies on other datasets. If a lag phase exists, this study would indicate that the duration is less than 27 days. Other studies have used retrospective data and are subject to a number of potential biases. The present study, using data from multicentre prospective randomized clinical trials, is free from some of these sources of bias. The fact that very similar estimates of the radiobiological parameters are obtained lends credence to these other studies and suggests that the potential biases may be small in practice.

Radiobiological considerations in the design of clinical trials

Progress in quantitative clinical radiobiology has improved the possibilities for rational design of new radiotherapy schedules. This paper reviews some general problems in calculating the required number of patients in a trial with a radiobiological rationale. Three such rationales are considered: dose escalation, hyperfractionation, and accelerated fractionation. One crucial factor in calculating the size of a trial is the steepness of the dose-response curve for both tumors and normal tissues, and literature data on this are reviewed. It is concluded that fairly large trials, typically comprising 300 or more patients, are necessary, unless efficient stratification of the patients is possible according to the risk for some specific type of recurrence. Such stratification may be possible either according to clinico-pathological characteristics or to the results from predictive assays.

Influence of radiotherapy treatment time on control of laryngeal cancer: comparisons between centres in Manchester, UK and Toronto, Canada

A comparison has been made of the influence of treatment time on tumour control rates for 496 (T2 and T3) larynx cancer cases in Manchester, UK and 1001 (T1-T4) cases in Toronto, Canada. Both series of patients were treated in fairly short overall times, commonly 3 weeks in Manchester and 4-5 weeks in Toronto. All the tumour control data were analysed using the same method to obtain values of fitted dose, fractionation and time parameters. The analysis showed the following. (a) Differences between the total combined (T2 + T3) data sets from the two centres, fitted using direct analysis and the LQ model incorporating a parameter for overall treatment time, were not significant (p = 0.17) and close similarity in control rates was observed using treatment regimens common to both series. (b) The Manchester series over 9-41 days and the Toronto series over 14-84 days are both consistent in showing for (T2 + T3) tumours the presence of a mean time factor of 0.6-0.8 Gy/day required to abrogate the decrease in tumour control concomitant with an increase in overall treatment time from the minimum the maximum employed in each series. (c) When a parameter was included in the model to test for the possible presence of a lag period before the time factor became operative, the lag was not significant for the Toronto data, in contrast to a significant lag for the Manchester data alone (T2 + T3 data).(ABSTRACT TRUNCATED AT 250 WORDS)

Dose, fractionation and overall treatment time in radiation therapy--the effects on local control for cancer of the larynx

The effect of total tumor dose, split course treatment and overall treatment time on local control was analysed in a retrospective series of 997 patients with carcinoma of the larynx, treated with megavoltage radiotherapy only. Primary tumors were classified by site (glottis and supraglottis) and T-stage. Continuous course (CC, n = 594) treatment was given primarily to small tumors. Split course radiation (SC, n = 403) was generally given to patients with larger field sizes. Total doses of irradiation ranged from 50 to 79 Gy, with a mean of 64 Gy in CC and 66 Gy in SC. Most of the treatments were given with fraction sizes between 2.0 and 2.1 Gy (91%). Overall treatment times ranged between 25 and 60 days in the CC group (mean, 45 days) and between 45 and 120 in the SC group (mean, 76 days). A local recurrence was observed in 256 patients. T-stage was the only tumor characteristic strongly related to local failure. Corrected for T-stage, no difference in local relapse rate was observed between glottic and supraglottic tumors, or between node-negative (n = 886) and node-positive patients (n = 111). After correction for T-stage the local failure rate of SC-treated tumors was 2.1 (95% confidence limits: 1.4-3.1) times higher than of CC-treated tumors. However, this effect could not be explained as an effect of the overall treatment time (OTT) itself, as no effect of OTT was found within the SC and the CC group, even though the variation in OTT's was considerable in the SC group. A higher tumor dose was associated with a lower local failure rate in the CC group (p = 0.005), but not in the SC group (p = 0.56).

Planned and unplanned gaps in radiotherapy: the importance of gap position and gap duration

Local tumour control in 971 patients with squamous carcinoma of the supraglottic larynx has been examined in relation to the occurrence of gaps in radiation therapy. The minimum follow-up time was 3 years. The reasons for a gap in radiotherapy fell into four categories: independent of the patient (national holidays, machine break-down, etc.), planned gaps (split-course therapy), severe normal-tissue reactions, and intercurrent disease. Only 11.7% of patients had no gap at all, 75.5% a single gap, and 2.1% had more than four gaps. The probability of tumour control increased with dose in all patient sub-groups; the average percentage increase for a 1% increase in dose was 4.3. The data were subjected to multivariate analysis, leading to the following conclusions. Patients in whom there was a single gap showed a remarkable trend of local control: if the gap began before day 19 after the start of therapy, the local tumour control was considerably below that in patients who did not suffer a gap in treatment. The local tumour control in patients whose gap began at day 20-29 was indistinguishable from that in patients who had no gap in treatment. A gap further towards the end of treatment was again associated with a severe drop in local control. This trend was independent of the recorded cause of the gap. The mechanism of this phenomenon is not clear. The effect of the timing of a treatment gap appears in this data set to have had a considerable impact on outcome and our observations should stimulate further study of this phenomenon in other clinical settings.

LQ-based model for biological radiotherapy planning

Despite the increasing accumulation of radiobiological data, radiotherapy planning does not take into account the alpha/beta values of normal irradiated tissues. The importance of the fact that the dose per fraction outside the 100% isodose area is not at all identical to the one inside the tumor area is also underestimated. Altered fractionation regimens further complicate the reliability of the conventional radiotherapy plans. In this study we report a theoretical application of the Macejewski's concept of "normalised total dose" that could make feasible the integration of alpha/beta and dose per fraction values in everyday radiotherapy practice. The concept of cumulative normalised total dose permits the preparing of radiotherapy plans with normalised isodose areas (the cumulative isodose area maps) for chosen ranges of radiation normalised doses. The effect of overall treatment time and interfraction interval is also taken into account. The present study suggests some guidelines that could be of value for the elaboration of a computer program for biological radiotherapy planning.

Prognostic factors for local control, regional control and survival in oropharyngeal squamous cell carcinoma

We have performed univariate and multivariate analysis to identify the clinical and treatment-related prognostic factors in a series of 254 patients with newly diagnosed, histologically proven, oropharyngeal squamous cell carcinoma treated with radical radiation therapy. The probabilities of local control, regional control, disease-free survival (DFS) and adjusted survival (AS) were calculated using the Kaplan-Meier method and differences between curves were evaluated by the Mantel-Cox test. The obtained significant variables in the univariate analysis were analysed using the Cox proportional hazards model. In the Cox multivariate analysis, four variables significantly influenced local control probability in the following order: tumour diameter, N stage, alcohol intake and weight loss. N stage significantly influenced the probability of regional control. Five variables influenced both DFS and AS: N stage, tumour diameter, weight loss, alcohol intake and tumour origin within the posterior oropharyngeal wall.

Calculating potential doubling time using monoclonal antibodies specific for two halogenated thymidine analogues

PURPOSE

A new flow cytometric technique that allows for two-incorporated thymidine analogues to be measured simultaneously and independently has been used to improve the accuracy of in vivo cell kinetic estimates, i.e., the length of S-phase (TS) and potential doubling time (Tpot).

METHODS AND MATERIALS

The analogues chlorodeoxyuridine and iododeoxyuridine were injected at different times into mice bearing the mouse mammary tumor MCaK. At different times after labeling, the tumors were harvested and prepared for three color flow cytometric analysis of DNA, chlorodeoxyuridine, and iododeoxyuridine. Control experiments showed that similar estimates of Tpot were obtained from each label when administered singly, or as staggered pulses. Comparisons were made between TS and Tpot calculated from a single label (single point), from the averaged result of the two labels from the same tumor (two point-ave), and from the simultaneous nonlinear fitting of the measured parameters from the two labels, from the same tumor (two point-fit). These estimates of TS and Tpot were then compared to reference values obtained by fitting the pooled measured parameters from all the tumors, that were labeled for different periods of time.

RESULTS

While all of the methods resulted in similar mean estimates of TS and Tpot that were close to the reference values, the fewest assumptions, and the least variability in the results, were obtained using the two point-fit data.

CONCLUSION

The estimation of Tpot using two thymidine analogues is more accurate than that obtained from a single label.

Adjuvant postoperative accelerated hyperfractionated radiotherapy in rectal cancer: a feasibility study

PURPOSE

To assess the acute toxicity and hence feasibility of postoperative hyperfractionated accelerated radiotherapy in rectal cancer.

METHODS AND MATERIALS

Twenty patients were submitted to accelerated hyperfractionated radiotherapy after resection of rectal cancer. A total dose of 48 Gy was given in 3 weeks. Two fractions of 1.6 Gy were used with a mean interfraction interval of at least 6 hours. The pelvic volume was treated by a four-field box technique using a linear accelerator (6-18 MV). Acute toxicity was assessed once per week. Small bowel and skin toxicity were scored according to the criteria of the World Health Organization. Bladder toxicity was scored according to the criteria of the Radiation Therapy Oncology Group.

RESULTS

All the patients underwent the treatment as planned except one. No patient presented grade 3 or 4 bladder toxicity. There was only one patient who complained from grade 3 skin toxicity at the end of the treatment. Fourteen patients had some degree of intestinal toxicity. This was the most frequently occurring acute side-effect. Only two out of the fourteen patients had intestinal toxicity exceeding grade 2.

CONCLUSION

Hyperfractionated accelerated radiotherapy on a pelvic volume is feasible as far as acute toxicity is concerned.

The delay before onset of accelerated tumour cell repopulation during radiotherapy: a direct maximum-likelihood analysis of a collection of worldwide tumour-control data

The worldwide collection of control data for head and neck tumours presented by Withers et al. (Withers, H.R., Taylor, J.M.G. and Maciejewski, B. Acta Oncol. 27: 131-146, 1988) was reanalysed using a model which includes an explicit lag phase before the onset of tumour clonogen repopulation. A direct maximum-likelihood approach was used and the methodology extended to include the computation of profile-likelihood confidence limits. A statistically significant (p = 0.02) lag of 29 days was obtained with 95% confidence limits covering the range 17-31 days. However, the confidence interval was disconnected, and excluded the period 21-23 days. The analysis gave a time factor of 0.66 Gy/day. The mean values confirm the conclusions drawn by the original authors using a two-stage (indirect) method, and the values are similar to those calculated here for another data set comprising 496 patients (lag period = 26 (19-33) days). However, the data set itself is retrospective, and potentially subject to a number of biases. Therefore any clinical conclusions can only be tentative. A new feature of the methodology is the computation of profile-likelihood confidence limits and this will be useful in future direct analyses of clinical data of this type. The more usually computed normal approximation to the confidence limits have been shown to be inadequate in this analysis, and either profile-likelihood limits or likelihood ratio tests must be employed to determine the significance of the model parameters.

A prospective trial of accelerated radiotherapy in the postoperative treatment of high-risk squamous cell carcinoma of the head and neck

PURPOSE

To evaluate the feasibility and toxicity of accelerated fractionation in the postoperative setting in high risk squamous cell carcinoma of the head and neck.

METHODS AND MATERIALS

Thirty-two patients with high risk pathologic features (e.g., extracapsular extension, positive margins, > or = 4 nodes positive, perineural invasion) were enrolled in an accelerated fractionation schedule, using a modification of the M.D. Anderson concomitant boost technique delivering 63 Gy in 5.3 weeks at 1.8 Gy per fraction.

RESULTS

Thirty patients (94%) completed treatment per protocol. Confluent mucositis was seen in 22 (69%) and five patients (22%) required 2 to 4 months for complete healing. Only five patients (16%) lost more than 10% of body weight. At a median follow-up of 32 months (range 22-42 months), the crude infield failure rate is 8/32 (25%). Infield recurrence was significantly associated with the interval from surgery to commencement of radiotherapy; 0/10 (0%) patients beginning radiotherapy within 4 weeks of surgery had infield failures compared to 8/22 (36%) for patients beginning radiotherapy more than 4 weeks after surgery (p = 0.035).

CONCLUSION

While acute side effects appear to be increased compared to conventional radiotherapy, we conclude that postoperative accelerated radiotherapy is feasible and has acceptable toxicity in this population. These results support the concept of rapid tumor repopulation after resection. A randomized multi-institutional trial is currently underway to compare conventional and accelerated fractionation in the postoperative setting.

Capacity and kinetics of SLD repair in mouse tongue epithelium

The effect of dose fractionation on the radiation response of mouse tongue epithelium was quantified in fractionation protocols involving 1, 3, 4, 5 and 10 fractions, separated by at least 4 h. Fractionated irradiation was given either to the whole snout by 300 kV X-rays or locally to the tongue using 25 kV X-rays. Each protocol was terminated by a final local top-up dose (25 kV X-rays) of 5 Gy. The frequency of complete local denudation within the test area was used as the quantal end point. The kinetics of repair of sublethal damage was studied by snout irradiation with four equally spaced fractions, delivered at intervals of 35, 60, 90, 480 or 540 min, again followed by a local top-up dose of 5 Gy. The linear-quadratic model gave a satisfactory fit to the data with the exception of the four fraction/30-h data, suggesting cell cycle effects in this schedule. Analysis of the results with different two-step methods and with direct analysis yielded similar results. The alpha/beta ratio was determined to be approximately 11 GY (direct analysis: 11.6 Gy with 95% confidence limits of 8.1 and 16.4 Gy) and T1/2 was found to be 46 min (35-69 min). Both these values are in the range described for other acutely responding rodent tissues.

Sensitivity of human squamous cell carcinoma of the larynx to fractionated radiotherapy

Data obtained for the response of tumours from two multicentre clinical trials of the British Institute of Radiology have been combined and studied. Both trials involved patients with laryngopharyngeal carcinoma. There were 734 patients in the first trial, recruited between 1965 and 1975, and 611 patients in the second trial, recruited between 1975 and 1985. Observed survival and tumour-free rates for all patients are calculated. T-class and the nodal status of the patient at the start of the treatment were important factors in the determination of both observed survival and tumour-free rates. Overall treatment time was an important factor in determining the recurrence of tumour. The longer the overall treatment time the greater was the chance of tumour recurrence. The linear-quadratic (LQ) model was used in the analysis of the tumour recurrence data for a large group of patients with laryngeal tumours without nodal involvement. A small alpha/beta ratio of 0.94 Gy was obtained for T3 tumours while that of T2 tumours was negative, -10.5 Gy. The value for T1 tumours was higher at 23 Gy. However, use of the LQ model with a time component increased the alpha/beta ratios to 26.0 +/- 27.20 Gy, 18.0 +/- 12.33 Gy and 13.38 +/- 5.40 Gy for T1, T2 and T3 tumours, respectively. The time component, the gamma/alpha ratios, for these tumours were 0.15 +/- 0.27 Gy/day, 0.81 +/- 0.18 Gy/day and 0.76 +/- 0.15 Gy/day, respectively.

Quantitative clinical radiobiology

Based on a series of recent papers, a status is given of our current ability to quantify the radiobiology of human tumors and normal tissues. Progress has been made in the methods of analysis. This includes the introduction of 'direct' (maximum likelihood) analysis, incorporation of latent-time in the analyses, and statistical approaches to allow for the many factors of importance in predicting tumor-control probability or normal-tissue complications. Quantitative clinical radiobiology of normal tissues is reviewed with emphasis on fractionation sensitivity, repair kinetics, regeneration, latency, and the steepness of dose-response curves. In addition, combined modality treatment, functional endpoints, and the search for a correlation between the occurrence of different endpoints in the same individual are discussed. For tumors, quantitative analyses of fractionation sensitivity, repair kinetics, reoxygenation, and regeneration are reviewed. Other factors influencing local control are: tumor volume, histopathologic differentiation and hemoglobin concentration. Also, the steepness of the dose-response curve for tumors is discussed. Radiobiological strategies for improving radiotherapy are discussed with emphasis on non-standard fractionation and individualization of treatment schedules.

The effect of differing radiotherapeutic schedules on the response of glottic carcinoma of the larynx

Laryngeal tumours, especially T1N0M0 and T2N0M0 lesions, are readily controlled by radiotherapy. Studies have shown that control varies with the dose of radiotherapy delivered to the tumour. Other factors, including the dose per fraction and the time over which the treatment schedule is delivered are also important. The varying biological effectiveness of a number of different dose fraction time schedules used in the management of laryngeal tumours of different stages are considered, the end points being tumour control and associated morbidity. Special attention has been given to the length of time over which the schedule is delivered. Of the schedules examined the results would suggest that a dose of 60 Gy given in 25 fractions over a period of 35 days is the best of the six schedules studied for T1, T2, T3 and T4 lesions with minimal associated morbidity. It is possible, however, that the poor results shown on the Kaplan-Meier curves for patients treated with the schedule of 60 Gy in 30 fractions over a period of 42 days could be due to geographical misses of the tumours as 56% were treated without a beam directed shell. The poor result obtained when patients were treated with the schedule of 60 Gy given in 30 fractions over 49+ days may be due to tumour repopulation occurring during the rest period though the possibility of geographical misses may contribute to the poor tumour control results. Mathematical modelling using linear quadratic analysis suggests that the shorter the period of time over which the treatment is given the better chance of achieving tumour control irrespective of the stage of the disease. These models were developed for patients treated with a beam directed shell thus excluding those patients who are most likely to be at risk from a geographic miss of the tumour. Linear quadratic analysis of the treatment data suggests that the ratio alpha/beta for tumour cells is estimated in the region of 13 Gy. For T1 lesions the tumour doubling time is in the order of 6 days, with longer doubling times for the more advanced stages. The analysis provides some support for investigative use of accelerated treatment schedules. This analysis also shows the importance of using beam directed shells when treating small fields especially in the head and neck region.

Is reseeding from the primary a plausible cause of node failure?

In a previous analysis of node failures in 1251 consecutive patients with node positive oropharyngeal and pharyngolaryngeal squamous cell carcinomas treated by external radiotherapy alone at the Institut Curie, the main reasons for patient exclusion were node recurrence associated with primary failure (N+T failures) and doses less than 55 Gy. These exclusions reduced the number of node failures from 399/1251 (32%) to 77/798 (10%). Multivariate analysis of node recurrence indicated that node size and fixity, treatment duration, and T stage of primary were significant (higher probability of isolated node failure for the T1-T2 primaries). In the present analysis, it is noted that 60% of the N+T failures were observed less than 1 month after the completion of the irradiation and, therefore, were not likely the result of reseeding from the primary tumor. When all 1251 patients were included in the analysis, the probability of nodal failure increased for larger nodes, T4 primaries, lower nodal doses, presence of contralateral node metastases, and nodal fixation to the surrounding structures. No influence of the primary site was found. Treatment duration was closely associated with total dose to the nodes. The best description of the data was obtained with a model including total dose and not treatment time. However, as in the previous analysis, the exclusion of low-dose (less than 55 Gy) treatments resulted in the loss of a significant dose-control relationship. We conclude that the majority of node failures is unlikely to result from reseeding from the primary tumor, and therefore should not be excluded from local-control analyses. From a more radiobiological point of view, the exclusion of palliative treatments is questionable when studying the effect of dose on local control.

Treatment acceleration in radiotherapy: the relative time factors and dose-response slopes for tumours and normal tissues

A published collation of data for control of head and neck cancer in over 4500 patients has been subjected to direct analysis to deduce dose-response, fractionation, and time parameters. The analysis confirms the presence of a significant time factor of the order of 0.5-0.6 Gy/day, deduced previously using various assumptions and normalisation procedures. In addition, the dose-response curve was characterised by Da = 29 Gy which contributed to long "effective" doubling times being deduced for tumour clonogens in the patient population as a whole. Some late-reacting normal tissues also show significant time factors, and furthermore, their dose-response curves are in general steeper than for tumours. Hence, care should be taken in accelerating treatments to improve local control, if the treatments are truly at tolerance regarding late-appearing major complications.

The effect of increasing the treatment time beyond three weeks on the control of T2 and T3 laryngeal cancer using radiotherapy

Local control of cancer by radiotherapy may be prejudiced by accelerated tumour clonogen repopulation particularly during protracted treatment schedules. A series of 496 cases of T2 and T3 larynx cancer treated here by radiotherapy has been studied to examine the impact on local control of treatment durations ranging from 9 to 41 days. Data were analysed using a linear-quadratic formulation describing the fractionation sensitivity, with the incorporation of a parameter relating to treatment time. Using combined T2 and T3 data, the increase in dose required to maintain a constant local control (the time factor) was between 0.5 and 0.6 Gy per day. These values are similar to those reported for 4 weeks or more in the literature. Also, the calculated dose to control 50% of tumours, given over the standard Christie duration of 21 days, was on the line projected back from literature data over 28-66 days. The present data are consistent with the presence of such a time factor following a lag phase of not more than 3 weeks after starting radiotherapy. Hence, further consideration should be given to using shorter overall treatment times in radiotherapy for head and neck cancer.

Carcinoma of the nasopharynx: analysis of treatment results in 167 consecutively admitted patients

Radiotherapy with curative intent was administered to 159 of 167 consecutively admitted patients with nasopharyngeal carcinoma. The classification (UICC 1982) gave the staging: stage I 8%, stage II 2%, stage III 28%, and stage IV 61%. The actuarial local tumor control was 54% and correlated to the T-classification. Primary control of neck nodes was 67% but was not correlated to the N-classes. Distant failure occurred in 20% of the patients; this was correlated to the N-classification. The 10-year actuarially corrected survival rate was 37% (stage I+II 60%, stage III 49%, stage IV 27%). Late reactions were seen in 69%, and most patients had mild to moderate xerostomia. Men with high hemoglobin had a better prognosis than men with values in the lower part of the normal range. It is concluded that primary control in the T- and N-positions is the parameter most crucial to success.

The effect of treatment time and treatment interruption on tumour control following radical radiotherapy of laryngeal cancer

A significant effect of overall treatment time on local control was found in a retrospective review of 1012 radically irradiated squamous cell carcinomas of the larynx. The actuarial local relapse free rate (LRFR) at 5 years for the whole group was 59%. The effect of treatment time on local control was modelled to the linear-quadratic equation. Using logistic regression analysis treatment time and dose were significant (p = 0.008 and p = 0.04, respectively). When the analysis was adjusted for the influence of stage and laryngeal subsite treatment time remained a significant prognostic factor (p = 0.02). The derived value of gamma/alpha was 0.7 Gy/day and when adjusted for stage and sub-site 0.8 Gy/day. This equates to a dose increment to maintain iso-effective local control of 0.64 Gy/day and 0.73 Gy/day respectively for daily fractions of 2.5 Gy and an assumed alpha/beta for tumour of 25 Gy. To provide an estimate of the clinical impact of treatment interruptions not compensated for by dose escalation a Cox regression was performed. Significant variables were T stage, N stage, sex, total dose and total length of treatment interruption. Using the proportional hazard model it was calculated that each day of treatment interruption resulted in an increase in the hazard of local relapse by 4.8% (p = 0.006). Based on our data it was calculated that this would result in a decrease in local control of 1.4% for each day of uncompensated treatment interruption.

Accelerated fractionation radiotherapy for laryngeal cancer, acute, and late toxicity

The acute toxicity of an accelerated radiotherapy scheme was compared with a conventional schedule. Eighteen patients with squamous cell carcinoma of the larynx were treated with accelerated fractionation radiotherapy. An average reduction of overall treatment time of 11 days was accomplished by giving 2 fractions a day during the last part of the treatment. Total dose and fraction dose were left unchanged. Acute reactions of skin and mucosa in these patients were compared with those in 40 patients treated with a conventional fractionation scheme, that is, 2 Gy per fraction, 5 fractions per week, to a total dose of 64-70 Gy. Acute reactions were maximal between 5 and 7 weeks after the start of treatment. Complete healing occurred within 3 months in all patients. Mucosal reactions and, as a consequence, dysphagia were clearly increased in those patients treated with accelerated fractionation. For confluent mucositis an ED50 of 66 Gy was calculated compared to 69 Gy for conventional fractionation. To a lesser degree, skin toxicity was also enhanced in the patients treated with the accelerated schedule. Severe edema of the laryngeal mucosa occurred only in patients treated to a total dose of 68 or 70 Gy and was somewhat more frequent with accelerated fractionation (4/10) than with conventional fractionation (4/24). One patient in the accelerated fractionation group underwent laryngectomy for persistent edema and laryngeal necrosis. No severe late skin reactions were observed. It can be concluded that the fractionation schedule tested in this study is feasible. Further shortening of overall treatment time without reduction of total dose will likely lead to unacceptable acute and, possibly, also late toxicity.

Time-dose factors in positive neck nodes treated with irradiation only

This article describes an analysis of time-dose and clinical factors which affect the 2 year rate of control of cervical node metastases from squamous cell carcinoma of the head and neck following external beam radiotherapy in a series of 140 patients. We find that node diameter and normalized total dose are the most important factors, and that overall treatment time is not statistically significant.