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

Area of Science:

• Radiation Oncology
• Rectal Cancer Treatment
• Clinical Trials

Background:

• Dose-response relationships indicate higher radiotherapy doses enhance complete response rates in rectal cancer.
• The EXPERT trial established a standard dose and fractionation (45 Gy pelvis, 9 Gy boost) for maximizing complete response.
• Intensity-modulated radiotherapy (IMRT) with a simultaneous integrated boost (SIB) allows for delivering biologically equivalent doses (BED5) in selected rectal cancer patients.

Purpose of the Study:

• To evaluate the toxicity profile of an IMRT/SIB protocol delivering a biologically equivalent dose for rectal cancer.
• To assess the appropriateness of RTOG 0822 dose constraints for this IMRT/SIB approach.
• To determine the treatment response using magnetic resonance tumour regression grade (mrTRG).

Main Methods:

• Retrospective analysis of 71 rectal cancer patients treated with IMRT/SIB and capecitabine chemotherapy.
• Collection of treatment details and acute toxicity data.
• Review of baseline and post-treatment MRI scans by a gastrointestinal radiologist to assign mrTRG.

Main Results:

• Seventy patients completed radiotherapy with a median overall treatment time of 34 days.
• Grade 3+ non-haematological toxicity was 4.2%, and grade 3+ haematological toxicity was 1.5%.
• RTOG 0822 dose constraints were met in most cases, except for the high-dose bladder constraint. Magnetic resonance tumour regression grade 1-2 was observed in 47.8% of patients.

Conclusions:

• The IMRT/SIB protocol demonstrates acceptable acute toxicity in rectal cancer patients.
• Promising magnetic resonance tumour regression grade results suggest potential for improved treatment outcomes.
• This protocol could be considered an intensity-modulated radiotherapy equivalent to the EXPERT trial dose and fractionation.