Intensity-Modulated Radiation Therapy Techniques and Applications

Primary IMRT Fractionation Techniques

The National Comprehensive Cancer Network recommends Simultaneous Integrated Boost (SIB) for delivering 66-74 Gy to gross disease and 50-60 Gy to subclinical disease in each fraction, using differential "dose painting" throughout the entire treatment course 1, 2, 4
SIB allows for dose escalation to high-risk areas while treating subclinical disease simultaneously in a single daily treatment, and is commonly applied with conventional fractionation and accelerated schedules 1, 2, 4, 5
Sequential (SEQ) IMRT delivers an initial lower-dose phase followed by a high-dose boost volume phase using 2-3 separate dose plans, providing flexibility in adjusting treatment volumes between phases based on tumor response 1, 2
Concomitant Boost Accelerated uses a "modified SEQ" approach, delivering subclinical target doses once daily for 6 weeks, with a separate boost plan as a second daily fraction for the last 12 treatment days, allowing for treatment intensification in the final phase without extending overall treatment time 1, 2, 4, 5

Volumetric Modulated Arc Therapy (VMAT) rotates the radiation source around the patient in one or more arcs while continuously delivering radiation with dynamic multileaf collimator adjustments, reducing treatment delivery time and decreasing monitor units compared to fixed gantry techniques 3
VMAT provides superior high-dose sparing but increases low-dose bath to normal tissues, and is recommended when high-dose organ sparing is the priority, treatment efficiency is important, or contralateral lung sparing is critical 3
The National Comprehensive Cancer Network recommends IMRT for reducing long-term toxicity in oropharyngeal, paranasal sinus, and nasopharyngeal cancers by reducing dose to salivary glands, temporal lobes, auditory structures, and optic structures 1, 2
IMRT may further improve dose distribution and decrease normal tissue dose for thymic malignancies when ASTRO IMRT guidelines are strictly followed 6

The National Comprehensive Cancer Network recommends CT-based planning with scans taken in treatment position, and target delineation requires experience in imaging and thorough understanding of disease spread patterns 1, 2, 6
Close interdisciplinary cooperation is critical for treatment planning, especially in postoperative settings or after induction chemotherapy, and standards for target definition, dose specification, and normal tissue constraints continue to evolve 1, 2