RandomizEd controlled trial for pre-operAtive dose-escaLation BOOST in locally advanced rectal cancer (RECTAL BOOST study): study protocol for a randomized controlled trial

Abstract

Background: Treatment for locally advanced rectal cancer (LARC) consists of chemoradiation therapy (CRT) and surgery. Approximately 15% of patients show a pathological complete response (pCR). Increased pCR-rates can be achieved through dose escalation, thereby increasing the number patients eligible for organ-preservation to improve quality of life (QoL). A randomized comparison of 65 versus 50Gy with external-beam radiation alone has not yet been performed. This trial investigates pCR rate, clinical response, toxicity, QoL and (disease-free) survival in LARC patients treated with 65Gy (boost + chemoradiation) compared with 50Gy standard chemoradiation (sCRT).

Methods/design: This study follows the 'cohort multiple randomized controlled trial' (cmRCT) design: rectal cancer patients are included in a prospective cohort that registers clinical baseline, follow-up, survival and QoL data. At enrollment, patients are asked consent to offer them experimental interventions in the future. Eligible patients-histologically confirmed LARC (T3NxM0 <1 mm from mesorectal fascia, T4NxM0 or TxN2M0) located ≤10 cm from the anorectal transition who provided consent for experimental intervention offers-form a subcohort (n = 120). From this subcohort, a random sample is offered the boost prior to sCRT (n = 60), which they may accept or refuse. Informed consent is signed only after acceptance of the boost. Non-selected patients in the subcohort (n = 60) undergo sCRT alone and are not notified that they participate in the control arm until the trial is completed. sCRT consists of 50Gy (25 × 2Gy) with concomitant capecitabine. The boost (without chemotherapy) is given prior to sCRT and consists of 15 Gy (5 × 3Gy) delivered to the gross tumor volume (GTV). The primary endpoint is pCR (TRG 1). Secondary endpoints include acute grade 3-4 toxicity, good pathologic response (TRG 1-2), clinical response, surgical complications, QoL and (disease-free) survival. Data is analyzed by intention to treat.

Discussion: The boost is delivered prior to sCRT so that GTV adjustment for tumor shrinkage during sCRT is not necessary. Small margins also aim to limit irradiation of healthy tissue. The cmRCT design provides opportunity to overcome common shortcomings of classic RCTs, such as slow recruitment, disappointment-bias in control arm patients and poor generalizability.

Trial registration: The Netherlands Trials Register NL46051.041.13. Registered 22 August 2013. ClinicalTrials.gov NCT01951521 . Registered 18 September 2013.

Figure 1

Study design and flowchart. PICNIC, ProspectIve data CollectioN Initiative on Colorectal cancer; RECTAL BOOST, RandomizEd Controlled Trial for Pre-operAtive Dose-escaLation BOOST in Locally Advanced Rectal Cancer.

Figure 2

Cumulative dose plan of boost plus standard chemoradiation fractions (left) with associated dose volume histogram (right). Delineations of gross tumor volume (GTV) plus planned target volume (PTV_GTV) (red), clinical target volume (CTV) plus PTV (PTV_CTV) (green), bladder (brown) and sigmoid (pink). Areas that receive a total dose of >65 Gy are represented in orange), and those that receive >50 Gy are shown in turquoise.