Which method is NOT available for correcting surface obliquity?

The photon focusing method is not recognized as a standard technique for correcting surface obliquity in radiation therapy. Surface obliquity refers to the angle at which radiation beam enters the patient's body compared to the perpendicular surface, which can affect dose distribution. Correcting for obliquity is essential to ensure that the prescribed radiation dose adequately covers the target area and spares healthy tissues.

The effective SSD method, TAR method, and isodose shift method are all established techniques used in practice for addressing surface obliquity. The effective SSD method adjusts the source-to-skin distance to account for oblique beams, ensuring that the treatment plan accurately reflects the delivered dose based on patient positioning. The TAR method (tissue-air ratio) quantifies the absorption in different tissues and adjusts the dose calculations accordingly. Similarly, the isodose shift method moves isodose lines to align with surface geometry, optimizing dose distribution to target areas.

In contrast, the photon focusing method is not a recognized approach to addressing obliquity and therefore does not fit within the established practices for correcting surface angles in radiation therapy dosimetry.