Experimental study of dosimetry for intra-operative radiotherapy

Objective: To study and compare the dosimetry for intra-operative radiotherapy in three kinds of phantoms; water, solid water and polymethyl ones. Methods: The absorbed dose from electrons of the accelerator with the applicator for intra-operative radiotherapy was measured using an ionization chamber fixed on each phantom. The dose at the specific depth in water on the beam central axis was adjusted to 1 cGy per monitor unit for the reference applicator with SSD at 100 cm for all energy levels of electrons. Then the applicator for intraoperative radiotherapy was used with no other change, i.e. the output factor was measured. The values of MU per cGy absorbed dose for all applicators in water phantom were calculated, and these values were used to calculate the MU value per cGy absorbed dose from the output factors for solid and polymethyl phantoms. Results: The deviation from water phantom was 0.27% and 0.45% for polymethyl and solid water ones, respectively. Conclusion: Using a polymethyl phantom to measure the absorbed dose may be a practical method when no special water tank or solid water is available