THeragnostic Utilities for Neoplastic DisEases of the Rectum by MRI Guided Radiotherapy (THUNDER2)

Neoadjuvant chemoradiation therapy (nCRT) is the standard treatment modality in locally advanced rectal cancer (LARC) and patients achieving complete response to treatment (CR) usually have a better prognosis in terms of local control (LC), metastases-free survival (MFS) and overall survival (OS).

Since response to radiotherapy is dose dependent in rectal cancer, dose escalation may lead to higher complete response rates. The possibility to predict patients who will achieve CR before surgery or during nCRT is of crucial importance. Recently, an early tumour regression index (ERITCP) was introduced, to predict pathological CR (pCR) after nCRT in LARC patients. In particular, the authors found that the patients with ERITCP <13.1 show a strong response during therapy and have a lower probability to experience distant relapses.

Aim of this clinical trial is to investigate the impact of dose escalation in rectal cancer, identifying the poor responder cases using the ERI index during the course of radiotherapy and increasing the prescribed dose in these patients.

Adopting this boosting protocol, an increase of 10% of CR (clinical and pathological) rate is expected.

For patients enrolled in the trial, chemoradiotherapy (CRT) will be administered using the MRI guided Radiotherapy (MRgRT) machine available in our institution.

The initial radiotherapy treatment will consist in delivering 55 Gy in 25 fractions on Gross Tumor Volume (GTV) plus the corresponding mesorectum of 45Gy in 25 fractions on the whole pelvis. Chemotherapy with 5-fluorouracil(5-FU) or oral capecitabine will be administered continuously.

A 0.35 Tesla Magnetic Resonance image will be acquired at simulation and every day during MRgRT. At fraction 10, ERI will be calculated.

If ERI will be inferior than 13.1 the patient will continue the original treatment. Patients with complete clinical response will go through wait and see approach.

If ERI will be higher than 13.1 the treatment plan will be reoptimized considering the residual tumor at fraction 10 as new therapy volume, where the dose will be intensified to reach 60.1 Gy.

After the end of CRT, the clinical response will be evaluated 8-10 weeks using high tesla MR and CT images or FDGPET-CT image 8-10 weeks after the end of nCRT. Surgery will be performed 12-16 weeks after the end of the CRT in case of partial or stable or progression disease, while in case of major or complete clinical response at restaging imaging, a Watch and Wait (W&W) or local excision (LE) approach should be followed. Late toxicity and quality of life (QoL) will be scored at first follow-up (FUP) and at 1 and 2 years of FUP according to Common Terminology Criteria for Adverse Events (CTCAE) v4.0 scale, functional scales and QoL questionnaires (LARS and SEXUAL questionnaires, at the start of treatment, after surgery and at 1 and 2 years of FUP), respectively.

The number of cases to be enrolled will be 63: all the patients will be treated at Fondazione Policlinico Universitario A. Gemelli IRCCS in Rome. All the cases will be discussed in weekly multidisciplinary tumor board to share the best therapeutic options, both at the diagnosis and at presurgical restaging.

. The primary endpoints will be complete response considered as: ypT0N0 in case of Total Mesorectal Excision (TME), ypT0ycN0 in case of LE, ycT0N0 in case of WW; prospective validation of delta radiomics MR-guide Radiotherapy model.

The secondary endpoints will be:3 years LC, MFS, Disease Free Survival (DFS), OS; R0 resection rate; Tumor Regression Grade (TRG) 1, TRG 2, Neoadjuvant Rectal (NAR) score; Sphincter preservation rate; Organ preservation rate; Rectal and sexual functions.