Seventh interim progress report of the british institute of radiology fractionation study of 3F/week versus 5F/week in radiotherapy of the laryngo-pharynx

Hypofractionnement en radiothérapie : le retour ?

Hypofractionation (i.e. the use of fewer higher fractional doses than usual) is not a new concept. It had actually been proposed in the early year of Radiotherapy by the German and Austrian specialists. In the seventy's, supported by the - wrong - hypotheses which gave birth to the NSD (Nominal Standard Dose), hypofractionation reappears. The consequential increase of late complications which was observed led the radiation oncologists to give up again using large doses per fraction, except for a few specific situations, such as palliative treatments. We are recently facing a new "come-back" of hypofractionation, in particular for breast and prostate cancers. In the case of breast cancer, the aim is clearly to look for more "convenience" for both the patients and the physicians, proposing shorter irradiation schedules including a lesser number of fractions. Some "modestly" hypofractionated schemes have been proposed and used, without apparently altering the efficacy/toxicity ratio, but these results have been seriously questioned. As for prostate cancer, the situation is different, since in that case new radiobiological data are at the origin of the newly proposed hypofractionation schedules. A number of papers actually strongly suggested that the fractionation sensitivity of prostate cancer could be higher than the one of the tissues responsible for late toxicity (i.e the exact opposite of the classical dogma). Based on those data, several hypofractionated schemes have been proposed, with a few preliminary results looking similar to the ones obtained by the classical schedules. However, no randomised study is available so far, and a few recent radiobiological data are now questioning the new dogma of the high fractionation sensitivity of prostate cancer. For those two - frequent - cancers, it seems therefore that prudence should prevail before altering classical irradiation schedules which have proven their efficacy, while staying open to new concepts and proposing well-designed randomised trials in specific cases.

Clinical radiobiology of glottic T1 squamous cell carcinoma

PURPOSE

Radiation therapy is the treatment of choice for early glottic squamous cell cancer in many institutions over the world. Despite a relatively homogenous clinical model of T1 glottic tumors for the fractionation studies, the relationships between dose-time parameters remain unclear. To analyze the influence of fractionation parameters and hemoglobin level on tumor cure, this study has been performed.

MATERIALS AND METHODS

This is a retrospective review of 235 patients with T1N0M0 glottic cancer treated by radiation therapy alone given in a conventional schedule with 5 fractions each week. The individual total dose, dose per fraction, and overall treatment time (OTT) ranged from 51-70 Gy, 1.5-3.0 Gy, and 24-79 days, respectively. The median follow-up was 48 months. Patient data--total dose, dose per fraction, OTT, and hemoglobin level (Hb) measured before the radiation treatment--were fitted by the mixed LQ/log-logistic model.

RESULTS

The 5-year local relapse-free survival rate was 84%. All parameters included in the mixed LQ/log-logistic model improved the fit significantly. The dose-response curve for 235 patients with T1 glottic cancer was well defined and steep, and showed significant decrease in tumor control probability (TCP) when total doses were below 61 Gy. The 10-day prolongation of OTT, from 45 to 55 days, decreased the TCP by 13%. The dose of 0.35 Gy/day, compensated repopulation during the 1 day of prolongation, which indicates a potential doubling time (Tpot) for glottic T1 tumor clonogens of 5.5 days. The drop of Hb level of 1 g/dl (from 13.8 g/dl to 12.8 g/dl) gave a 6% decrease of TCP, provided that OTT was 45 days.

CONCLUSION

The significant correlation between the total dose, overall treatment time, hemoglobin concentration, and tumor control probability has been found for T1 glottic cancer.

The predictive value of histological classification into degrees of differentiation of squamous cell carcinoma of the larynx and hypopharynx compared with the survival of patients

In the course of running two clinical trials between 1966 and 1985, data became available for 1315 patients, 713 in the first trial and 602 patients in the second trial, which has allowed comparison between histological findings in laryngeal and hypopharyngeal carcinoma, the observed survival and the tumour-free rates for these patients who were followed for up to 10 years. Extensive histopathology reviews have revealed over 98% agreement on tumour cell type between the initial report and that of the reviewer. Highly significant differences have been found for squamous cell carcinoma between the observed survival and the tumour-free rates for patients with well-differentiated and with anaplastic lesions. There was a statistically significant greater proportion of patients with well-differentiated tumours at larynx sites and in stage 1 when compared with patients with anaplastic tumours, but even when this was taken into account, multivariate analyses showed that tumour grading still made an independent significant contribution to the prediction of prognosis. For squamous cell carcinoma only very simple and rapidly assessed histopathological features need to be identified to classify tumours into the two grades employed in this study. The analyses have confirmed the prognostic significance of tumour grading in squamous cell carcinoma in the larynx and hypopharynx.

Hypofractionation: lessons from complications

Hypofractionation refers to irradiation schemes with less than 5 fractions per week and larger doses per fraction than 2 Gy. It was initiated around 1960 to ease the burden for patients who had to come to the hospital to be treated every day and to save machine time. In the treatment of breast cancer at the University of Texas M.D. Anderson Cancer Center (UTMDACC) in 1962, the acute reactions of the skin were matched in 3- and 5-day treatment. More severe late sequelae were observed in the 3-day-a-week treatment than in the 5-day treatment. In 1966 the NSD formula was published and from thereon was used to adjust the total dose based on the number of fractions. Later, the TDF and CRE formulae were used. In almost all publications, a high percentage of severe complications after hypofractionation have been reported. There is overwhelming evidence that fraction size of more than 2 Gy produces late unfavorable sequelae, and therefore, despite the inconvenience for patients and the taxing of machine time, hypofractionation should not be used, unless there is a specific rationale concerning the tumor characteristics of doing so. In that case the total dose must be corrected in order not to increase the late morbidity.

Recruitment, follow-up and analysis times in clinical trials of cancer treatment: a case study

A study has been made of the way in which the number of events available for analysis in a clinical trial was dependent on the recruitment period, the maximum follow-up time on individual patients and the length of time between the start of the trial and its analysis. The events considered were deaths, local recurrences and late radiation effects on normal tissue in patients treated for cancer of the laryngo-pharynx by two different fractionation regimes. The relationship is demonstrated between the number of events and the 95% confidence intervals that can be placed on differences between results in the two arms of the trial. It was found, in this particular trial, that no significant improvement in precision was gained by following up patients beyond 5 years or carrying out the analysis later than 2 years after the end of recruitment. The results are discussed in the context of the initial design of clinical trials, particularly those in which the aim is to test therapeutic equivalence.

Final report of the general clinical results of the British Institute of Radiology fractionation study of 3F/wk versus 5F/wk in radiotherapy of carcinoma of the laryngo-pharynx

The 10 year follow-up of a clinical trial involving the comparison of 3F/wk versus 5F/wk in radiotherapy of squamous cell carcinoma of the larynx and hypopharynx has now been completed. The trial involved an intake of 734 patients between 1966 and 1975. The classification of all patients has been revised to conform with the latest TNM publication. A reduction in total dose was made for 3F/wk compared with 5F/wk. This varied between 13% and 11% in centres treating over 3 weeks and 6 weeks, respectively. No statistically significant differences have been found between the two arms (3F/wk versus 5F/wk) of the trial in any of the main group analyses. A number of sub-group analyses relating to survival, tumour-free and laryngectomy-free rates and to the comparison of acute or late normal-tissue radiation damage have also been performed. No differences have been found that could be considered to be statistically significant in relation to the particular sub-group. Previous interim reports suggested minor differences in sub-group analyses between the 3F/wk and 5F/wk regimes in this trial; these have diminished now that the full follow-up data are available. This trial has provided evidence on which clinicians may base their choice between either a 3F/wk fractionation regime or a conventional 5F/wk treatment protocol in the treatment of carcinoma of the laryngo-pharynx.

Radiotherapy alone for oropharyngeal carcinomas: the role of fraction size (2 Gy vs 2.5 Gy) on local control and early and late complications

This retrospective study involved 150 patients treated for oropharyngeal carcinoma by external radiotherapy alone at the Institut Gustave-Roussy. The midplane tumor dose was 70 Gy delivered in 7 weeks. During 1981, 63 patients were treated with 5 fractions (5 F) of 2 Gy per week. The following year, 87 patients, were treated with 4 fractions (4 F) of 2.5 Gy per week. Prognostic factors were equally distributed in both groups. The locoregional tumor control was 83% for the 4 F patients and 83% for the 5 F patients. Degree and incidence of acute reactions with both fractionation regimens were similar. Necrosis of the oropharyngeal mucosa and trismus were significantly more severe and more frequent in the 4 F group (23% and 20% respectively) than in the 5 F group (10% and 5% respectively) (p = 0.03 and p = 0.01). Other late effects such as skin necrosis (6% in the 4 F group versus 0% in the 5 F group) and severe cervical sclerosis (12 vs 5%) were also more frequent in the 4 F group than in the 5 F group but the difference was not significant. The results suggest a greater sensitivity of late compared to early normal tissue effects and of tumor response to an increase in dose per fraction (from 2 Gy to 2.5 Gy) in oropharyngeal carcinoma.

A graphical method for the analysis of decisions in clinical oncology

A technique is proposed for the graphical analysis of clinical decision making. This technique has been applied to two problems in clinical oncology: the respective roles of surgery and radiotherapy in early carcinoma of the larynx; and the assessment of the optimal management policy for patients with clinical Stage I teratoma of the testis. The technique is simple to apply, it could be developed to incorporate patients' preferences and draws attention to the lack of data on treatment-related morbidity.

Large-dose fractionation (hypofractionation)

Fractionation is a radiotherapeutic "modality" that may be manipulated to attempt to improve control of malignant tumors or to decrease effects on normal tissues. In addition, some fractionation regimen must be selected as the basis for addition of any other modality such as radiosensitizers or hyperthermia. Considerable literature derived from clinical experiences with reduced numbers of large fractions has become available in the last 15 years. A review of this literature is focused on tumor control and effects on normal tissues resulting from hypofractionation (fewer than five fractions/week), rapid fractionation (large daily fractions treated five times/week), and rapid split-course regimens that include a rest interval in the course of treatment. The evidence available indicates that a decrease in tumor control is associated with each of these large-dose fractionation approaches. At the same time, late effects on normal tissues are increased as the result of the large-sized fractions. The overall reduction in therapeutic ratio suggests that this avenue of clinical research should no longer be pursued and that such regimens should be adopted with caution for purposes of combining radiosensitizers or hyperthermia. Conversely, clinical research in radiotherapy justifiably can explore the effects of increased numbers of small fractions.

Review: total doses in fractionated radiotherapy--implications of new radiobiological data

The total dose in radiotherapy has been adjusted in the past for different fractionation schedules by the use of empirical formulae such as NSD, TDF and CRE. It is now appropriate to consider fractionation factors which include more biological insight in their formulation than was possible earlier. It has become clear, from both clinical and experimental animal data, that the total dose in multi-fraction irradiations depends more critically on size of dose-per-fraction for late than for early damage to normal tissues. This difference has been interpreted as due to different shapes of the underlying dose-response curves. The late reactions respond with more curvature in the dose-response curve, i.e. with more repair capability at very low doses per fraction, than the early tissue reactions. A linear-quadratic relationship for the dose-response curves has been found to fit experimental data well, with few exceptions. This paper reviews this interpretation and explores some of its implications for radiotherapy and for radiobiology applied to therapy. Of many repair factors that have been suggested, the ratio alpha/beta (of the linear to the quadratic coefficients) is one that should be independent of the level of damage assayed. Values of alpha/beta of about 10 Gy have been reported for a number of early tissue responses but a range of values from about 1 to 5 or 6 Gy for late responses. It is a current challenge to radiobiology to explain why this difference occurs. Once such values are known for different tissues--and the dangers of premature assumptions are emphasized--calculations are possible which might be useful in radiotherapy as an alternative to NSD, TDF, CRE etc. Some data are presented on the magnitude of differences from these previously used empirical formulae, with a discussion about how easily detected the discrepancies might be in clinical practice. Applications to hypofractionation, hyperfractionation and accelerated fractionation are illustrated.