641 / 1542
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