Optimal treatment margins for radiotherapy of prostate cancer based on interfraction imaging

Target margins in radiotherapy of prostate cancer

“…In other studies, 5-to 10-mm margins (depending on the direction) using skin marks as reference were proposed with IG, allowing a margin reduction to 5 mm. 29,30 Overall, if skin tattoos only are used, the literature would suggest that generous margins (at least 10 mm) are required.…”

Consideration of the likely benefit from implementation of prostate image-guided radiotherapy using current margin sizes: a radiobiological analysis

“…Arnesen et al [22], while modelling translational systematic and random errors that would conventionally be said to require margins of 6.1, 7.0 and 10.4 mm, found no significant difference in TCP between margins of 7.5 and 10.0 mm, and approximately 3% decrease in TCP, corresponding to a reduction of margin from 7.5 to 5.0 mm.…”

“…One measure of the ''correct'' margin to use must be the margin at which further reduction causes a loss in TCP that outweighs the gains related to increased sparing of normal tissue. Such a trade-off between TCP and normal tissue complication probability might be facilitated by use of a composite biological measure such as P+ [22,45,46], the probability of cure without complication at a particular level of severity, but any such measure needs to be carefully chosen to be coincident with clinical concerns.…”

“…Wu et al [21] performed dose reconstructions on repeat CT scans of 28 patients; however, these had been pre-registered based on bony anatomy, meaning that the margins considered were actually between the CTV and the internal target volume. Arnesen et al [22] found no significant effect of IGRT for a CTV-PTV margin of 7.5 mm.…”

Radiobiological Modelling in Radiation Oncology

“…The potential strength of IGRT is that it enables precise target localisation and therefore the possibility of margin reductions, thus decreasing the toxicity to normal tissue and improving the probability of complication free treatment. With regard to the simulation process, the prostate was assumed to be a rigid structure (Arnesen et al 2008) directly correlated in respect of organ motion with rigid OARs. Figure IV.2 depicts the inter-fraction organ motion simulated in this study.…”