Physics Bucharest 2017

Head and neck cancer (historic-conventional)

T2N2(a)M0 SCC of tonsil Issues to consider for matching Ant beam used to treat low neck needs to be matched with sup field (photon- photon) • Solutions Single isocentre technique,

• Ant neck beam and sup field half beam block (asymmetric jaw) • = match at isocentre without pneumbra or beam divergence

Calculate angles required so that both beam edges diverge perpendicular to matched plane, • = slight overlap at depth as width of pneumbra increases

Match beams at 50% (light beam) isodose Gap at skin surface (5-10mm) • =match at one depth but underdose ant to this and overdose post