MRI detected extaprostatic extension (EPE) in prostate cancer: Do all T3a patients have the same outcomes?

MRI-detected T3a prostate cancer is a heterogeneous disease. This post-hoc analysis of a prospective trial found that patients with T3a disease presenting obliteration of the recto-prostatic angle, contact-asymmetry of neuro-vascular bundle and periprostatic fat invasion, may be at higher risk of biochemical failure and metastases.

A prospective analysis of inter- and intrafractional errors to calculate CTV to PTV margins in head and neck patients

PURPOSE

To evaluate an institute-specific CTV-PTV margin for head and neck (HN) patients according to a 3-mm action level protocol.

METHODS/PATIENTS

Twenty-three HN patients were prospectively analysed. Patients were immobilized with a thermoplastic mask. Inter- and intrafractional set-up errors (in the three dimensions) were assessed from portal images (PI) registration. Digitally reconstructed radiographs (DRRs) were compared with two orthogonal PI by matching bone anatomy landmarks. The isocenter was verified during the first five consecutive days of treatment: if the mean error detected was greater than 2 mm the isocenter position was corrected for the rest of the treatment. Isocenter was checked weekly thereafter. Set-up images were obtained before and after treatment administration on 10, 20 and 30 fractions to quantify the intrafractional displacement. For the set-up errors, systematic (Σ), random (σ), overall standard deviations, and the overall mean displacement (M), were determined. CTV to PTV margin was calculated considering both inter- and intrafractional errors.

RESULTS

A total of 396 portal images was analysed in 23 patients. Systematic interfractional (Σ(inter)) set-up errors ranged between 0.77 and 1.42 mm in the three directions, whereas the random (σ (inter)) errors were around 1-1.31 mm. Systematic intrafractional (Σ(intra)) errors ranged between 0.65 and 1.11 mm, whereas the random (σ (intra)) errors were around 1.13-1.16 mm.

CONCLUSIONS

A verification protocol (3-mm action level) provided by EPIDs improves the set-up accuracy. Intrafractional error is not negligible and contributes to create a larger CTV-PTV margin. The appropriate CTV-PTV margin for our institute is between 3 and 4.5 mm considering both inter- and intrafractional errors.