From 25 Fractions to Five: How Hypofractionation has Revolutionised Adjuvant Breast Radiotherapy

Early and Intermediate Treatment Outcome After Postoperative External Beam Accelerated Partial Breast Irradiation in Patients With Early-Stage Breast Cancer

PURPOSE

To prospectively evaluate early and intermediate outcome after accelerated partial breast irradiation (APBI) in patients early-with stage breast cancer.

METHODS AND MATERIALS

Inclusion criteria were defined according to the APBI American Society for Radiation Oncology's ASTRO Evidence-Based Consensus Statement. The prescribed dose was 26 to 28 Gy in 5 fractions on 5 consecutive days. Regular follow-up visits with objective and subjective evaluation of treatment tolerance were performed after 0 and 2 weeks, 6 months, and at annual intervals.

RESULTS

Between February 2017 and January 2020, 175 patients with breast conserving surgery met the inclusion criteria for APBI. Mean age was 65.7 years (range, 46-88). Thirteen percent of patients received a diagnosis with carcinoma in situ, 55%, 35%, and 37% with T1a/b/c, and 10% with T2 stages, respectively. The mean volume of planning target volume (PTV) was 119 cc (range, 45-465), the ratio of mean PTV: whole breast volume ratio was 21% (7%-53%). Mean follow-up was 42 months (median, 45, range, 0-67). Acute toxicity after 2 weeks was low with 69%, 26%, and 5% grade 0, 1, and 2. In addition, 1-, 2-, 3-, 4-, and 5-year follow-up data were available from 146, 134, 107, 73, and 25 patients. Patient-reported cosmetic outcomes were assessed excellent or good in 97.9%, 98.5%, 98.1%, 98.6%, and 100%. Regarding grade 2 toxicities, as by now 3%, 2%, 2%, 0%, and 0% G2 fibrosis, 1%, 1%, 0%, 0%, and 0% G2 atrophy, no G2 skin telangiectasia or breast edema occurred. So far, none of the patients have experienced G3 toxicity or higher. The remaining patients had grade 0 or 1 toxicity only. Five ipsilateral breast recurrences (1 marginally to PTV, 4 out-of-field) and 5 distant recurrences were recorded by March 2023. The 4-year in-breast recurrence rate was 2.5%. Eight patients died, with 2 of them from disease. For all patients, the 4-year overall, cancer specific and disease-free survival rates were 97.1%, 99.4%, and 95.3%, respectively.

CONCLUSIONS

We showed high early- and intermediate-term treatment tolerance and disease control of APBI using 26 to 28 Gy in five fractions in one week in carefully selected patients with early breast cancer. APBI is highly appreciated by patients and efficient, as an additional advantage for busy centers.

Dose to Organ at Risk and its Characteristic Variation with the Clinically Used Different Prescription Levels for Early-stage Left-sided Breast Cancer

AIMS

To evaluate the organ at risk (OAR) dose and its characteristic variation with different clinically usable prescription doses (RxD) for breast and chest wall radiotherapy in patients with early-stage left-sided breast cancer.

MATERIALS AND METHODS

In total, 145 patients with early-stage breast cancers (T1N0M0-T2N0M0) on the left side were treated with radiotherapy after a modified radical mastectomy or breast conservation surgery, with a mean age of 45.1 ± 21.6 years. The patient received 4050 cGy of field-in-field (three-dimensional conformal radiotherapy) treatment limited to the breast or chest wall, excluding the supraclavicular node, axillary node and internal mammary chain, over 15 fractions. Additional plans of 5000 cGy/25 fractions, 4500 cGy/20 fractions and 2600 cGy/5 fractions were created with no or minor changes to the original plan. Mathematical modelling was used to study the distinctive change in the dose-volume characteristics for various OARs as a function of the RxD. OAR dosages, both absolute and normalised, were expressed in terms of the RxD. The mathematical (functional) relationship between OAR doses and different prescription levels was deduced by the least squares fit method.

RESULT

The left lung mean dose, V5Gy (%), V10Gy (%) and V20Gy (%) and the heart mean dose, V10Gy (%) and V20Gy (%) were evaluated. The dose-volume parameters showed a parabolic variation (x2) with the RxD. Prescription normalised OAR doses showed a linear relationship with the RxD; relative dose increased with diminishing RxD. Normalised lung and heart mean doses exhibited saturation (linear relationship) with RxD variation. Paired sample t-test results between RxD versus all evaluated parameters were found to be statistically significant (P = 0.004). The Pearson correlation coefficient between different prescription levels for left lung mean dose (range 0.942-1.0), heart mean dose (range 1.0-1.0), left lung V5Gy (%) (range 0.987-1.0), left lung V10Gy (%) (range 0.991-0.999), heart V10Gy (%) (range 0.998-1.0).

CONCLUSION

The functional form of absolute OAR dose-volume parameters versus RxD is parabolic and the RxD normalised OAR dose-volume parameter versus RxD is a straight line with a negative slope as RxD increases. This indicates an increase in the relative OAR dose-volume parameters if the RxD is reduced. This study is the first of its kind to compare the OAR doses as a function of clinically used degenerate prescription levels. These data will help to comprehend the OAR doses while adopting a new dose fractionation regimen and reviewing the radiotherapy treatment plans.

Introduction of ultra-hypofractionation in breast cancer: Implications for costs and resource use

PURPOSE

A shift towards (ultra-)hypofractionated breast irradiation can have important implications for the practice of contemporary radiation oncology. This paper presents a systematic analysis of the impact of different fractionation schedules on multiple key performance indicators, namely resource use, costs, work times, throughput and waiting times.

MATERIALS AND METHODS

Time-driven activity-based costing (TD-ABC) is applied to calculate the costs and resources consumed where the perspective of the radiotherapy department in adopted. Three fractionation regimens are considered: ultra-hypofractionation (5 x 5.2 Gy, UHF), moderate hypofractionation (15 x 2.67 Gy, HF) and conventional fractionation (25 x 2 Gy, CF). Subsequently, a discrete event simulation (DES) model of the radiotherapy care pathway is developed and scenarios are compared in which the following factors are varied: distribution of fractionation regimens, patient volume and operating hours.

RESULTS

The application of (U)HF can permit radiotherapy departments to reduce the use of scarce resources, realise work time and cost savings, increase throughput and reduce waiting times. The financial advantages of (U)HF are, however, reduced in cases of excess capacity and cost savings may therefore be limited in the short-term. Moreover, although an extension of operating hours has favourable effects on throughput and waiting times, it may also reduce cost differences between fractionation schedules by increasing the capacity of resources.

CONCLUSION

By providing an in-depth analysis of the consequences associated with a shift towards (U)HF in breast cancer, the present study demonstrates how a DES model based on TD-ABC costing can assist radiotherapy professionals in making data-driven decisions.

Single Ultra-High Dose Rate Proton Transmission Beam for Whole Breast FLASH-Irradiation: Quantification of FLASH-Dose and Relation with Beam Parameters

Healthy tissue-sparing effects of FLASH (≥40 Gy/s, ≥4-8 Gy/fraction) radiotherapy (RT) make it potentially useful for whole breast irradiation (WBI), since there is often a lot of normal tissue within the planning target volume (PTV). We investigated WBI plan quality and determined FLASH-dose for various machine settings using ultra-high dose rate (UHDR) proton transmission beams (TBs). While five-fraction WBI is commonplace, a potential FLASH-effect might facilitate shorter treatments, so hypothetical 2- and 1-fraction schedules were also analyzed. Using one tangential 250 MeV TB delivering 5 × 5.7 Gy, 2 × 9.74 Gy or 1 × 14.32 Gy, we evaluated: (1) spots with equal monitor units (MUs) in a uniform square grid with variable spacing; (2) spot MUs optimized with a minimum MU-threshold; and (3) splitting the optimized TB into two sub-beams: one delivering spots above an MU-threshold, i.e., at UHDRs; the other delivering the remaining spots necessary to improve plan quality. Scenarios 1-3 were planned for a test case, and scenario 3 was also planned for three other patients. Dose rates were calculated using the pencil beam scanning dose rate and the sliding-window dose rate. Various machine parameters were considered: minimum spot irradiation time (minST): 2 ms/1 ms/0.5 ms; maximum nozzle current (maxN): 200 nA/400 nA/800 nA; two gantry-current (GC) techniques: energy-layer and spot-based. For the test case (PTV = 819 cc) we found: (1) a 7 mm grid achieved the best balance between plan quality and FLASH-dose for equal-MU spots; (2) near the target boundary, lower-MU spots are necessary for homogeneity but decrease FLASH-dose; (3) the non-split beam achieved >95% FLASH for favorable (not clinically available) machine parameters (SB GC, low minST, high maxN), but <5% for clinically available settings (EB GC, minST = 2 ms, maxN = 200 nA); and (4) splitting gave better plan quality and higher FLASH-dose (~50%) for available settings. The clinical cases achieved ~50% (PTV = 1047 cc) or >95% (PTV = 477/677 cc) FLASH after splitting. A single UHDR-TB for WBI can achieve acceptable plan quality. Current machine parameters limit FLASH-dose, which can be partially overcome using beam-splitting. WBI FLASH-RT is technically feasible.

Ultra-Hypofractionation for Whole-Breast Irradiation in Early Breast Cancer: Interim Analysis of a Prospective Study

We report on the early clinical outcomes of a prospective series of early breast cancer (EBC) patients treated with ultra-hypofractionated post-operative whole-breast irradiation (WBI) after breast-conserving surgery (BCS) and axillary management. Primary endpoints were patient's compliance and acute toxicity. Secondary endpoints included physician-rated cosmesis and ipsilateral breast tumour recurrence (IBTR). Acute toxicity was evaluated at the end of WBI, 3 weeks and 6 months thereafter, according to the Common Terminology Criteria for Adverse Events (v. 5.0). Patients were treated between September 2021 and May 2022. The treatment schedule for WBI consisted of either 26 Gy in 5 fractions over one week (standard approach) or 28.5 Gy in 5 fractions over 5 weeks (reserved to elders). Inverse planned intensity-modulated radiation therapy (IMRT) was used employing a static technique. A total of 70 patients were treated. Fifty-nine were treated with the 26 Gy/5 fr/1 w and 11 with the 28.5 Gy/5 fr/5 ws schedule. Median age was 67 and 70 in the two groups. Most of the patients had left-sided tumours (53.2%) in the 26 Gy/5 fr/1 w or right-sided lesions (63.6%) in the 28.5 Gy/5 fr/5 ws group. Most of the patients had a clinical T1N0 disease and a pathological pT1pN0(sn) after surgery. Ductal invasive carcinoma was the most frequent histology. Luminal A intrinsic subtyping was most frequent. Most of the patients underwent BCS and sentinel lymph node biopsy and adjuvant endocrine therapy. All patients completed the treatment program as planned. Maximum detected acute skin toxicities were grade 2 erythema (6.7%), grade 2 induration (4.4%), and grade 2 skin colour changes. No early IBTR was observed. Ultra-hypofractionated WBI provides favourable compliance and early clinical outcomes in EBC after BCS in a real-world setting.

HYPORT adjuvant acute toxicity and patient dosimetry quality assurance results - Interim analysis

BACKGROUND

HYPORT adjuvant trial is a randomised phase III open-label noninferiority trial comparing standard moderately hypofractionated 3 week adjuvant radiation therapy in breast cancer with a novel 1-week schedule. The trial was initiated in March 2019 and is open to recruitment with a total sample size of 2100. We report the results of dosimetric quality assurance, acute toxicity and pre planned first interim safety analysis in the first 271 patients.

METHODS

Stage I-III breast cancer planned for adjuvant radiation therapy to the breast/chest-wall (along with regional nodes as indicated) were randomised to receive 40 Gy/15 fractions/3 weeks or 26 Gy/5 fractions/1 week. For simultaneous integrated boost, the patients in the control arm received 8 Gy/15 fractions/3 weeks, while those in the experimental arm received 6 Gy/5 fractions/1 week (to the tumour bed). For sequential boost, the prescribed dose was 12 Gy/4 fractions/4 days in both arms. Compliance to pre specified dosimetric parameters and acute toxicities were evaluated.

RESULT

Data of the first 271 patients was analysed of whom 104 patients received tumour bed boost using SIB. All mandatory dosimetric criteria were met apart from one patient with a higher contralateral breast dose due to optimal internal mammary nodal coverage. Overall three patients (1.1%) experienced grade 3 radiation dermatitis (none received SIB), no other Grade 3 or higher toxicities reported.

CONCLUSION

This acute toxicity interim analysis demonstrates that hypofractionated adjuvant radiotherapy with SIB for patients with breast cancer is feasible, and associated with minimal severe acute toxicities.