Poster — Wed Eve—52: Radiobiological Modeling of a Proposed Dose Escalation in TMI

Abstract

Purpose: To compare the effectiveness of different approaches to total marrow irradiation (TMI) using Helical TomoTherapy. Methods: TMI treatment was planned on a 55 year‐old male patient (87% of the GTV to receive a prescribed dose ([formula omitted]) of 20Gy). Field sizes (fs) of 25 and 50mm were examined. The normal tissue complication probability (NTCP) was calculated using Lyman‐Kutcher‐Burman model. Tumour control probability (TCP) was evaluated using the Poisson model. Dose escalation analysis was performed by linearly escalating the DVHs from the 20Gy‐TMI plan, to any [formula omitted]. Results: There was no substantial difference between TCP using 25mm (40±9%) or 50mm fs (42±9%). For organs of the torso, the difference in the prescribed dose to the GTV that would lead to a normal organ complication of 50% from the TMI ([formula omitted]) between 25 and 50mm was less than 3%. For organs in the head, the [formula omitted] for 50mm fs was consistently lower by up to 15% compared to 25 mm fs. The optimal dose given by maximizing TCP(1‐NTCP), was ∼39Gy for lungs, resulting in 95% (±3%) of tumor control and 3% (0, 16%) rate of pneumonistis. Conclusion: TCP and NTCP were estimated for a TMI patient, originally receiving 20Gy and linearly escalating the DVHs to higher doses. Tissue sparing was seen by using 25mm fs only in the organs of the head. This suggests it would be beneficial to use the small fields in the head only; since using small fields for the whole treatment would lead to long treatment times