**1. Introduction**

Radiation therapy is the core treatment strategy with curative intent and organ preservation for many inoperable cancer types. The main aim of radiation therapy is the local control of the tumor.

With open field conventional 2D RT, both healthy tissue and tumors are irradiated with a similar dose per fraction of 1.8–2 Gy. Now, the 3D-CRT is the new standardized procedure. The target volumes are defined on CT or PET-CT or other high-definition imaging such as

the MRI. During the treatment planning, a 3-D projection of the area of interest provides the opportunity to match the high-dose radiation region to the target volume while minimizing the radiation dose to the surrounding healthy tissue. More refined radiation techniques, which lead to enhanced conformity, can be performed with the use of these generation machines. 3-D techniques have given way to IMRT or volumetric modulated arc therapy (V-MAT) [1–4].

High conformity is generally accepted as a way to reduce toxicity and allows dose escalation to produce better results and long-term tumor control. This is only possible through IGRT, which involves real-time imaging of the treatment target and normal organs during each treatment, in order to avoid uncertainty about patient positioning and tumor targeting and to also reduce the irradiated volumes without missing any of the targets [5].

Trials have investigated different fractionation schedules to also increase local control, which has become of high importance in clinical oncology patient management. Randomized clinical trials have established equivalent outcomes between radical surgery and organ-preservation treatment with an RT backbone for appropriately selected patients.

The radiation oncologist's main concern is local recurrence after definitive radiation therapy. The combined chemo-radiation protocols have led to the increased tumor control and survival rates, but the results have remained unchanged for a long time. All eyes are now on radiation therapy for a more targeted improvement of local tumor control and diminishment of the odds of local recurrence [6].

The newly developed approach of applying different radiation doses to different areas in one single session is called SIB or simultaneous integrated boost-intensity-modulated radiotherapy (SIB-IMRT). By increasing the dose per fraction focally to the tumor itself while maintaining lower dose to the elective areas of interest, a more accurate dose distribution can be achieved, in order to improve local tumor control without putting the neighboring organs at risk. The advances, improvements and clinical usage of this technique will be expanded in full detail [7].
