Intensity-Modulated Radiotherapy With a Simultaneous Integrated Boost in Rectal Cancer

Abstract

Aims: Doseeresponse curves suggest that higher doses of radiotherapy improve the complete response rate in rectal cancer. The UK adopted the EXPERT trial dose and fractionation, 45 Gy in 25 fractions to the pelvis with a sequential 9 Gy in five fractions to the gross tumour, in patients where the aim was to maximise the complete response. In the Oxford University Hospital NHS Foundation Trust (Oxford, UK) we deliver a biological equivalent dose (BED5) in selected patients using intensity-modulated radiotherapy (IMRT) with a simultaneous integrated boost (SIB) in 25 fractions. We carried out a retrospective analysis of our series to: (i) document the toxicity of this protocol; (ii) ascertain whether dose constraints from RTOG 0822 were appropriate; (iii) assess the response. Materials and methods: The demographics and treatment details for all consecutive patients treated with this protocol were collected using electronic systems. Patients received 45 Gy to the elective nodes and 52 Gy using a SIB to the gross tumour with capecitabine chemotherapy using IMRT or RapidArc plans. Acute toxicity was collected prospectively during weekly reviews. For the purpose of this study, a dedicated gastrointestinal radiologist reviewed all baseline and posttreatment magnetic resonance images and assigned a magnetic resonance tumour regression grade (mrTRG). Results: Seventy-one patients were identified. Seventy completed radiotherapy with a median overall treatment time of 34 days (range 32e36 days); 67.6% received full-dose chemotherapy, with 21.2% receiving a reduced dose. There was a 4.2% incidence of grade 3þ non-haematological toxicity and 1.5% grade 3 þ haematological toxicity. 4.2% were admitted during their radiotherapy, with one death due to a pelvic abscess. The RTOG 0822 constraints were achieved in !75% of cases, other than the high-dose bladder constraint. mrTRG 1e2 was seen in 47.8%, with mrTRG 1 seen in 23.9%. Conclusions: We suggest that our protocol shows acceptable acute toxicity, with promising mrTRG results, and could be adopted by centres as an IMRT equivalent dose for EXPERT dose and fractionation.

Intensity-modulated Radiotherapy for Rectal Cancer in the UK in 2020

“…Taking these survey results into account, and in order to maximise the potential resource benefits of IMRT, including reduced planning time and fewer treatment fractions, the guidance working group have suggested using a SIB rather than a sequential boost. In addition, an SIB may improve patient outcomes as shown in other tumour types [ 20 , 21 ]. The optional boost dose in the guidance is 50 Gy.…”

“…Given the evidence for a dose–response relationship in rectal cancer, in selected patients or sites of disease where the aim is complete pathological response (e.g. an organ preservation strategy or where pathologically involved nodes are outside of the TME volume), doses >50 Gy can be considered [ [21] , [22] , [23] ]. Doses >50 Gy have been examined within several phase II studies, which appear to show acceptable acute toxicities and promising pathological complete response rates, although there remains an absence of phase III data [ [24] , [25] , [26] ].…”

“…The guidance states that it is at the discretion of individual centres whether they choose to deliver doses exceeding 50 Gy in clinical scenarios where the goal is complete response. We would suggest a SIB of 52 Gy based on a small series showing minimal acute toxicity [ 21 ]. Rectal protocol …”

1.5 T MR-linac planning study to compare two different strategies of rectal boost irradiation

“…In the framework of a clinical trial various strategies for RT dose escalation for rectal cancer have been studied or have been adopted in on-going clinical trials [32][33][34][35]. The WW3 trial of the Danish group [34] and the APHRODITE trial of the Leeds group [35] investigate a dose-escalation up to 62 Gy in rectal cancer patients using a simultaneous integrated boost (SIB) technique.…”

The benefit of MR‐only radiotherapy treatment planning for anal and rectal cancers: A planning study

“…By comparing MR‐only and CT‐only pathways, we are assessing both the benefit of including MR in the treatment pathway, which is also true of a CT‐MR pathway and the benefit of removing CT‐MR pathway registration uncertainties. We also hypothesize that gross tumor volume (GTV) dose escalation planning 13 , 14 , 15 would enhance the benefit from MR‐only versus CT‐only planning due to the reduced volume of GTVs delineated on MR versus CT.…”