Fractionation in radiotherapy

Comparison of the average surviving fraction model with the integral biologically effective dose model for an optimal irradiation scheme

In this paper, we compare two radiation effect models: the average surviving fraction (ASF) model and the integral biologically effective dose (IBED) model for deriving the optimal irradiation scheme and show the superiority of ASF. Minimizing the effect on an organ at risk (OAR) is important in radiotherapy. The biologically effective dose (BED) model is widely used to estimate the effect on the tumor or on the OAR, for a fixed value of dose. However, this is not always appropriate because the dose is not a single value but is distributed. The IBED and ASF models are proposed under the assumption that the irradiation is distributed. Although the IBED and ASF models are essentially equivalent for deriving the optimal irradiation scheme in the case of uniform distribution, they are not equivalent in the case of non-uniform distribution. We evaluate the differences between them for two types of cancers: high α/β ratio cancer (e.g. lung) and low α/β ratio cancer (e.g. prostate), and for various distributions i.e. various dose-volume histograms. When we adopt the IBED model, the optimal number of fractions for low α/β ratio cancers is reasonable, but for high α/β ratio cancers or for some DVHs it is extremely large. However, for the ASF model, the results keep within the range used in clinical practice for both low and high α/β ratio cancers and for most DVHs. These results indicate that the ASF model is more robust for constructing the optimal irradiation regimen than the IBED model.

Derivation of mean dose tolerances for new fractionation schemes and treatment modalities

Avoiding toxicities in radiotherapy requires the knowledge of tolerable organ doses. For new, experimental fractionation schemes (e.g. hypofractionation) these are typically derived from traditional schedules using the biologically effective dose (BED) model. In this report we investigate the difficulties of establishing mean dose tolerances that arise since the mean BED depends on the entire spatial dose distribution, rather than on the dose level alone. A formula has been derived to establish mean physical dose constraints such that they are mean BED equivalent to a reference treatment scheme. This formula constitutes a modified BED equation where the influence of the spatial dose distribution is summarized in a single parameter, the dose shape factor. To quantify effects we analyzed 24 liver cancer patients for whom both proton and photon IMRT treatment plans were available. The results show that the standard BED equation-neglecting the spatial dose distribution-can overestimate mean dose tolerances for hypofractionated treatments by up to 20%. The shape difference between photon and proton dose distributions can cause 30-40% differences in mean physical dose for plans having identical mean BEDs. Converting hypofractionated, 5/15-fraction proton doses to mean BED equivalent photon doses in traditional 35-fraction regimens resulted in up to 10 Gy higher doses than applying the standard BED formula. The dose shape effect should be accounted for to avoid overestimation of mean dose tolerances, particularly when estimating constraints for hypofractionated regimens. Additionally, tolerances established for one treatment modality cannot necessarily be applied to other modalities with drastically different dose distributions, such as proton therapy. Last, protons may only allow marginal (5-10%) dose escalation if a fraction-size adjusted organ mean dose is constraining instead of a physical dose.

Fraction size in radiation treatment for breast conservation in early breast cancer

BACKGROUND

Shortening the duration of radiation therapy would benefit women with early breast cancer treated with breast conserving surgery. It may also improve access to radiation therapy by improving efficiency in radiation oncology departments globally. This can only happen if the shorter treatment is as effective and safe as conventional radiation therapy. This is an updated version of the original Cochrane Review published in Issue 3, 2008.

OBJECTIVES

To determine the effect of altered radiation fraction size on outcomes for women with early breast cancer who have undergone breast conserving surgery.

SEARCH STRATEGY

We searched the Cochrane Breast Cancer Group Specialised Register, MEDLINE, EMBASE and the WHO ICTRP search portal to June 2009, reference lists of articles and relevant conference proceedings. We applied no language constraints.

SELECTION CRITERIA

Randomised controlled trials of unconventional versus conventional fractionation in women with early breast cancer who had undergone breast conserving surgery.

DATA COLLECTION AND ANALYSIS

The authors performed data extraction independently, with disagreements resolved by discussion. We sought missing data from trial authors.

MAIN RESULTS

Four trials reported on 7095 women. The women were highly selected: tumours were node negative and 89.8% were smaller than 3 cm. Where the breast size was known, 87% had small or medium breasts. The studies were of low to medium quality. Unconventional fractionation (delivering radiation therapy in larger amounts each day but over fewer days than with conventional fractionation) did not affect: (1) local recurrence risk ratio (RR) 0.97 (95% CI 0.76 to 1.22, P = 0.78), (2) breast appearance RR 1.17 (95% CI 0.98 to 1.39, P = 0.09), (3) survival at five years RR 0.89 (95% CI 0.77 to 1.04, P = 0.16). Acute skin toxicity was decreased with unconventional fractionation: RR 0.21 (95% CI 0.07 to 0.64, P = 0.007).

AUTHORS' CONCLUSIONS

Two new studies have been published since the last version of the review, altering our conclusions. We have evidence from four low to medium quality randomised trials that using unconventional fractionation regimens (greater than 2 Gy per fraction) does not affect local recurrence, is associated with decreased acute toxicity and does not seem to affect breast appearance or late toxicity for selected women treated with breast conserving therapy. These are mostly women with node negative tumours smaller than 3 cm and negative pathological margins. Long-term follow up (> 5 years) is available for a small proportion of the patients randomised. Longer follow up is required for a more complete assessment of the effect of altered fractionation.

Fraction size in radiation treatment for breast conservation in early breast cancer

BACKGROUND

Shortening the duration of radiation therapy would benefit women with early breast cancer treated with breast conservation. It may also improve access to radiation therapy by improving efficiency in radiation oncology departments globally. This can only happen if the shorter treatment is as effective and safe as conventional radiation therapy.

OBJECTIVES

To assess the effects of altered fraction size on women with early breast cancer who have undergone breast conserving surgery.

SEARCH STRATEGY

We searched the Cochrane Breast Cancer Group Specialised Register (June 2006), MEDLINE (November 2006), EMBASE (November 2006), reference lists for articles, and relevant conference proceedings. No language constraints were applied.

SELECTION CRITERIA

Randomised controlled trials of unconventional versus conventional fractionation in women with early breast cancer who had undergone breast conserving surgery.

DATA COLLECTION AND ANALYSIS

Data extraction was performed independently by the authors with disagreements resolved by discussion. Missing data was sought by contacting the authors concerned.

MAIN RESULTS

Two trials were included and reported on 2644 women. The women were highly selected with node negative tumours smaller than 5 cm and negative pathological margins; 46% of the women had a cup separation size of less than 25 cm. The studies were of high quality. Data for local recurrence and breast appearance were not available in a form which could be combined. Unconventional fractionation (delivering radiation therapy in larger amounts each day but over fewer days than with conventional fractionation) did not appear to affect: (1) local-recurrence free survival (absolute difference 0.4%, 95% CI -1.5% to 2.4%), (2) breast appearance (risk ratio (RR) 1.01, 95% CI 0.88 to 1.17; P = 0.86), (3) survival at five years (RR 0.97, 95% CI 0.78 to 1.19; P = 0.75), (4) late skin toxicity at five years (RR 0.99, 95% CI 0.44 to 2.22; P = 0.98, or (5) late radiation toxicity in sub-cutaneous tissue (RR 1.0, 95% CI 0.78 to 1.28; P = 0.99).

AUTHORS' CONCLUSIONS

We have evidence from two high quality randomised trials that the use of unconventional fractionation regimes (greater than 2 Gy per fraction) does not affect breast appearance or toxicity and does not seem to affect local recurrence for selected women treated with breast conserving therapy. These are women with node negative tumours smaller than 5 cm and negative pathological margins. Two new trials have been published in March 2008. Their results are consistent with our findings. The results of these trials will be incorporated in the next update of this review.

Hyperfractionated radiation in combination with local hyperthermia in the treatment of advanced squamous cell carcinoma of the head and neck: a phase I-II study

Twenty-seven patients with cervical metastases from squamous cell head and neck tumours were treated with hyperfractionated XRT (total dose 69.60-76.80 Gy, 1.2 Gy b.i.d. five times a week) combined with a total of two to six sessions of superficial external HT. Acute local toxicity was mild; as major acute side effects, only one ulceration was recorded. No severe late side effects were observed. Late toxicity was similar to that observed in our previous studies with the combination of heat and radiation. Nodal complete response was observed in 77% of patients, partial response was observed in 15% of patients and no change was observed in 8% of patients. Five-year actuarial nodal control was 64.5 +/- 19% and 5-year actuarial survival was 24 +/- 10%. The treatment of nodal metastases from head and neck tumours with the combination of HT and hyperfractionated XRT is feasible with an acceptable acute and late toxicity profile.

Anti-tumor effects of local irradiation in combination with peritumoral administration of low doses of recombinant interleukin-2 (rIL-2)

The aim of this work was to improve radiotherapy results by immune stimulation. We tested the effects of a combination of radio- and immunotherapy, i.e., local low dose recombinant interleukin-2 (rIL-2) treatment, in two murine tumor models. Syngeneic tumors (SL2 lymphoma or M8013 mammary carcinoma) were induced subcutaneously on one or both flanks of mice. Irradiation was given either as a single dose (20 Gy) or fractionated (25 Gy) in 2 weeks. One or two cycles of rIL-2 were given concurrent with or subsequent to radiotherapy. One cycle of rIL-2 consisted of peritumoral injections administered on 5 consecutive days. Treatment effects were measured in terms of local tumor response and disease-free survival (DFS). The combined treatment modality was significantly better than treatment with either irradiation alone or rIL-2 alone. When tumors were inoculated on both flanks of the mice, combined radioimmunotherapy of one of the tumors also resulted in regression of the contralateral untreated tumor, indicating that a systemic anti-tumor immune reaction was induced. Additional rIL-2 injections did not enhance radiation toxicity. In conclusion supplementing irradiation with locally administered low doses of rIL-2 results in better local anti-tumor responses and DFS rates than either treatment alone without enhanced treatment toxicity. Furthermore, the local treatment induces a systemic anti-tumor reaction, influencing the growth patterns of a second, untreated tumor.