A review on radiotherapy hypofractionation schedules for breast cancer treatment

Breast boost vector: a new metric proposed to optimise isocentre location in an fIMRT–VMAT hybrid technique for a simultaneous integrated boost in breast radiotherapy

Purpose:

Evaluating the improvements of placing the treatment isocentre at the boost centre of mass (CoM) in a hybrid treatment for breast cancer radiotherapy.

Material and methods:

Twenty-two patients were planned in two isocentre locations with two forward intensity-modulated radiation therapy (fIMRT) tangentials to the breast and a volumetric-modulated arc therapy (VMAT) to the boost. A simultaneous integrated boost technique was used. Breast Boost (BB) Vector was investigated as a criterion for selecting an appropriate isocentre placement. Various metrics for boost, breast and hybrid plans were analysed using analysis of variance statistics.

Results:

Comparing hybrid plans at the boost CoM vs. hybrid plans at the breast CoM, no significant differences were found. Analysis of relative variations of planning target volume (PTV) boost coverage vs. BB Vector indicated an upgrade in boost CoM isocentre strategy. Dose to organs at risk was comparable: V5Gy (26·24 vs. 25·69%, p = 0·8), V20Gy (14·66 vs. 14·58%, p = 0·959) and the mean dose (7·37 Gy vs. 7·26 Gy, p = 0·879) to ipsilateral lung; V5Gy (15·60 vs. 15·22%, p = 0·903), and the mean dose (4·91 Gy vs. 4·86 Gy, p = 0·950) to heart and dose to free breast of boost (46·71 Gy vs. 46·62 Gy, p = 0·408).

Findings:

The hybrid fIMRT–VMAT technique centred at the boost CoM resulted equivalent to plans centred at the breast CoM, while benefiting from an enhancement in PTV boost coverage for patients with BB Vector superior to 5.

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.

Impact of tumour bed boost integration on acute and late toxicity in patients with breast cancer: A systematic review

The purpose of this systematic review was to summarise the evidence from studies investigating the integration of tumour bed boosts into whole breast irradiation for patients with Stage 0-III breast cancer, with a focus on its impact on acute and late toxicities. A comprehensive systematic electronic search through the Ovid MEDLINE, EMBASE and PubMed databases from January 2000 to January 2015 was conducted. Studies were considered eligible if they investigated the efficacy of hypo- or normofractionated whole breast irradiation with the inclusion of a daily concurrent boost. The primary outcomes of interest were the degree of observed acute and late toxicity following radiotherapy treatment. Methodological quality assessment was performed on all included studies using either the Newcastle-Ottawa Scale or a previously published investigator-derived quality instrument. The search identified 35 articles, of which 17 satisfied our eligibility criteria. Thirteen and eleven studies reported on acute and late toxicities respectively. Grade 3 acute skin toxicity ranged from 1 to 7% whilst moderate to severe fibrosis and telangiectasia were both limited to 9%. Reported toxicity profiles were comparable to historical data at similar time-points. Studies investigating the delivery of concurrent boosts with whole breast radiotherapy courses report safe short to medium-term toxicity profiles and cosmesis rates. Whilst the quality of evidence and length of follow-up supporting these findings is low, sufficient evidence has been generated to consider concurrent boost techniques as an alternative to conventional sequential techniques.

A unique hypofractionated radiotherapy schedule with 51.3 Gy in 18 fractions three times per week for early breast cancer: outcomes including local control, acute and late skin toxicity

AIM

Evaluation of local control and acute and late toxicity regarding a hypofractionated RT schedule for breast cancer patients.

METHODS AND MATERIALS

Between October 2007 and October 2009, 80 women with early breast cancer were treated by 42.75 Gy in 15 fractions over 5 weeks. This treatment involved three fractions per week (Monday-Wednesday-Friday). All patients received an additional boost dose to the tumor bed of 8.55 Gy in 3 fractions using 6 MV photons. The primary endpoint included any local recurrence in the treated breast. Secondary endpoint included acute and late radiation skin toxicity. The median follow-up time was 63 months (range 60-72). Radiation toxicity was graded according the RTOG/EORTC criteria.

RESULTS

Neither local nor distant recurrence was noted in any patient during this 3-year follow-up. Grade 0, 1, 2 acute skin toxicity was observed in 56/80 (70.0 %), in 19/80 (23.8 %) and in 5/80 (6.3 %), respectively. Three months post-RT, toxicity grades 0, 1, 2 skin toxicity were 64/80 (80 %), 14/80 (17.5 %) and 2/80 (2.5 %), respectively. Late toxicity as grade 0, 1 was observed in 72/80 (90.0 %) and in 8/80 (10.0 %), respectively, 6 months post-RT, whereas after 1 year they were 78/80 (97.5 %) and 2/80 (2.5 %), respectively.

CONCLUSIONS

Preliminary results regarding skin reactions, cosmetic appearance and local control are consistent with published data that support the use of shorter fractionation schedules in early breast cancer patients after breast conservative surgery. Longer follow-up and a randomized prospective study stand in need for the extraction of safe conclusions.