Table 4.
CTV to PTV margin recommendations in various series, without image guidance
| Series (number of patients) | Treatment set-up details | CTV - PTV margin requirement (cm) | Comments | ||
|---|---|---|---|---|---|
| L - R | S - I | A - P | |||
| Present series (n = 46) | Supine, knee cushion. Comfortably full bladder, empty rectum. | 0.57 | 0.79 | 0.77 | 3 fiducial markers, no correction of isocenter placement errors. Margins required for 95% probability of CTV coverage for any given fraction. |
| van der Heide [5] (n = 453) | Supine, knee cushion. Empty bladder, no bowel instructions. | 0.36 | 0.48 | 0.79 | 2 - 4 fiducial markers. Daily aSi EPI. Results without application of a correction protocol. 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]). |
| Litzenberg [13] (n = 11) | Supine, flat couch, knee support. No bowel or bladder instructions. | 0.82 | 1.25 | 1.02 | 3 implanted Calypso® markers. Real time tracking of transponder position for 8 minutes, to provide information about intra-fraction motion. "Average" CTV to PTV margins, calculated using the method of van Herk [17], to give 90% probability of covering the target with at least 95% of the prescribed dose. |
| Stroom [16] a) Supine (n = 15) | Supine. Knee roll, foot support Suppository prior to planning CT; partially full bladder for all CTs | 0.40 | 0.82 | 0.83 | CT scan in treatment position, repeated at weeks 2, 4 and 6 of treatment. Position of prostate registered with initial treatment planning CT. CTV to PTV margins required to cover target with an unspecified isodose line are calculated using the formula: CTV-PTV = 2Σtot + 0.7σtot, where Σtot and σtot are the quadratically summed contributions of translational set-up uncertainty and internal organ motion. |
| Stroom [16] b) Prone (n = 15) | Prone. Belly board. Otherwise as above | 0.37 | 0.66 | 0.88 | As above. |
| Poli [18] (n = 387) | Supine, foam between knees, ankles in Styrofoam block. Full bladder, no bowel instructions. | 0.77 right 0.66 left | 1.11 sup 0.69 inf | 0.27 ant 1.49 post | Daily localization of target using 2D BAT ultrasound for at least 4 consecutive fractions (average 27 per patient). Margins required for 95% probability of target coverage, including the effect of systematic shift (average 0.61 cm posteriorly). |
| Tinger [19] (n = 8) | Supine, alpha cradle. Urethrogram, rectal probe. Full bladder. No bowel instructions. | 0.53 | 0.73 | 0.66 | Weekly CT, registered to planning CT, to measure center of volume motion of the prostate. Daily EPIs registered to simulator films to measure setup displacement. Data were provided on standard deviation (SD) of total uncertainty of CTV position, from which we calculated margins required to give 95% probability of CTV coverage (CTV-PTV margin calculated as SD × 1.65). |
| Meijer [20] (n = 30) | Position and immobilization not specified. Bladder instructions given. Bowel instructions not specified. | 0.40 | 0.80 sup 1.10 inf | 0.80 ant 1.10 post | 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 no correction of 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) | Position, immobilization, bladder and bowel instructions not specified. | 0.73 | 0.81 | 1.05 | 4 fiducial markers. Set up to skin markers, then daily imaging without correction of set-up errors. Margins were calculated using the method of van Herk [18], to give 90% probability of covering the CTV with at least 95% of the prescribed dose. |
| Nairz [22] (n = 27) | Supine, immobilization not specified, no bowel or bladder instructions | 0.87 | 1.20 | 1.58 | Daily cone beam CT without correction of set-up errors. Margins were calculated using the method of van Herk [17], to give 90% probability of covering the CTV with at least 95% of the prescribed dose. |
| Graf [23] (n = 23) | Supine, no rigid immobilization. Full bladder, no bowel instructions (although scan repeated if excessive rectal filling) | 0.70 | 0.95 | 0.95 | 3 - 5 fiducial markers. Daily EPI without corrections. Margins were calculated using the method of Van Herk [17]. |
Abbreviations: As in table 3. Also, 2D = 2-dimensional; SD = standard deviation; σtot = total random variation; Σtot = total systematic variation.