Table 5.
CTV to PTV margin recommendations in various series, with image guidance
| Series (number of patients) | Treatment set-up details | CTV - PTV margin requirement (cm) | Comments | ||
|---|---|---|---|---|---|
| R-L | S-I | A-P | |||
| Present series (n = 46) | As in table 4 | 0.36 | 0.37 | 0.37 | As in table 4, with correction of isocenter placement errors 3 mm or greater in size on R-L and S-I axes, 2 mm or greater on A-P axis. No post-correction EPI. |
| van der Heide [5] (n = 453) | Supine, knee cushion. Empty bladder, no bowel instructions. | 0.18 | 0.25 | 0.40 | 2 - 4 fiducial markers. Daily aSi EPI. Correction of all errors prior to treatment. Standard deviations were provided, from which we calculated margins required to give 95% probability of CTV coverage (CTV - PTV margin calculated as SD × 1.65 [6]). |
| Cheung [7] (n = 33) | Supine, vacuum lock bag. Empty bladder and rectum. | 0.30 | 0.30 | 0.40 | 3 fiducial markers. Pre- and post-RT EPI days 1-9 to calculate individualized CTV-PTV margins (averages shown), which were used during the IMRT boost phase, during which daily on-line correction was performed according to fiducial marker position. A 2 mm factor was added in quadrature to the total error, to account for inaccuracies in the on-line correction process. Average individualized CTV to PTV margins are shown, although several patients had margins larger than 0.7 cm along the A-P axis. |
| J Wu [10] (n = 13) | Supine, alpha cradle, soft foam support for lower legs. Empty rectum and partially full bladder (drink 500 mL water 45 mins before) for CT and treatment | ns | 0.53 | 0.60 | 3 fiducial markers. Daily pre-treatment portal images 3× per week over the course of treatment. CTV to PTV margin required to give 99% probability of CTV coverage by 95% isodose line. Margins calculated according to movement of center of mass. |
| Litzenberg [13] (n = 11) | Supine, flat couch, knee support. No bowel or bladder instructions. | 0.18 | 0.70 | 0.58 | As in table 4, with the inclusion of intra-fraction motion. |
| Meijer [20] (n = 30) | As in table 4 | 0.20 | 0.40 sup 0.60 inf | 0.20 | 4 fiducial markers. Simulation study based on 8 CT scans spaced over the course of treatment. Set-up to skin markers then daily on-line imaging, with correction of all set-up errors. Margins calculated using a dose warping technique to give 90% probability of covering the CTV with at least 95% of the prescribed dose. |
| Beltran [21] (n = 40) | As in table 4 | 0.43 | 0.49 | 0.48 | As in table 4, with daily correction of all errors. |
| Nairz [22] (n = 27) | As in table 4 | 0.61 | 0.96 | 1.07 | As in table 4, with daily correction of all errors. |
| Graf [23] (n = 23) | As in table 4 | 0.49 | 0.51 | 0.48 | As in table 4, with daily correction of all errors. |
| Q Wu [24] (n = 28) | Not stated | 0.30 | 0.30 | 0.30 | 15 CT scans obtained during the course of treatment and registered with respect to bony anatomy with planning CT. Evaluation of both image-based and contour-based registration methods. Analysis based on both geometric and dosimetric parameters. Estimated CTV to PTV margins required to allow a dose reduction on the prostate (D99) of not more than 2% for 90% of patients. |
Abbreviations: As in table 4.