A study of the mantle technique for Hodgkins disease using thermoluminescent dosimetry

A study of the mantle technique for Hodgkins disease patients was embarked upon using thermoluminescent dosimetry (TLD) and a RANDO phantom. There was concern that the technique using Co-60 and turning the patient over for the posterior field may not be optimal as it was felt that the axillary areas of these patients were being under-dosed. A variety of treatment set-ups were performed on a 60-Cobalt unit at extended SSD. The phantom was planned for treatment lying supine for the anterior field and prone for the posterior field. Measurements were made in the neck, hilum and axillae using various combinations of compensators and lead filters. The combination of full field compensators and a lead filter gave the best results in the phantom but did not give satisfactory axillary readings in the patient situation. This was attributed to the difference in shape and AP separation of the patient when lying prone. RANDO, being solid, retains its shape. Treatment was then planned for a 6 MV linear accelerator using a vertical couch extender which enables the patient to remain supine throughout the treatment by increasing the table height to allow the posterior portal to be treated through the couch. Full field compensation was found to give an adequate dose to all the measured areas. This technique has since been performed on 28 patients being treated for Hodgkins disease at the Hillbrow Hospital, and the average axillary dose recorded in these patients is 88.6% of the prescribed dose.