Table 2 Quality of evidence (QoE) modified based on American Society for Radiation Oncology (ASTRO) Clinical Practice Guideline Methodology Guide [28] and strength of recommendation conforming with the same

Level of quality of evidence (QoE)

Level 1

Is based on a systematic review or meta-analysis of at least 2 randomised studies of good quality

Level 2

Is based on at least 2 non-randomised comparative studies

Level 3

Is based on 1 non-randomised comparative study or non-comparative study

Level 4

Is based on the opinion of experts or no evidence referenced in the respective guideline (or not clearly assignable)

Strength of recommendation

Strong

“Benefits clearly outweigh risks and burden, or risks and burden clearly outweigh benefits” [28]

Conditional

“Benefits are finely balanced with risks and burden or appreciable uncertainty exists about the magnitude of benefits and risks.” [28]