Table 1.
Definitions, regions of interest and location of recurrences.
| Region of interest (ROI) |
Definition | Dose* | No. of recurrences inside the ROI** |
Recurrences specific to the ROI***/ recurrences available for analysis (%) |
Median target volume cm3 (range) |
|---|---|---|---|---|---|
| GTV-PET | The FDG-PET positive volume, delineated by a nuclear medicine physician. | 66/68 Gy | 22 | 22/41 (54) | 22 (1–167) |
| GTV | The gross tumour volume, based on all available diagnostic imaging as well as the results of the clinical examination. | 36 | 14/44 (32) | 60 (7–245) | |
| CTV-t | The clinical target volume includes the GTV with a 1 cm margin to account for delineation uncertainty, adjusted for unaffected bone and with a 3 mm margin to the skin. | 46 | 10/48 (21) | 244 (28–617) | |
| CTVE-h | The high-risk elective clinical target volume includes areas at high risk of microscopic disease. It is constructed by adding a 2 mm margin to the CTV-t and including lymph node levels with a high risk of sub clinical disease. | 60 Gy | 47 | 1/48 (2) | 598 (257–1444) |
| CTVE-l | The low-risk elective clinical target volume includes areas at low but still significant risk of microscopic disease. It is constructed by adding a 2 mm margin to CTVE-h and including lymph node levels with a low risk of sub clinical disease. | 50 Gy | 47 | 0/48 (0) | 739 (413–1470) |
| Out-of-field | Anatomical regions outside of CTVE-l | - | 48 | 1/48 (2) | - |
| GTV-PET 90%-SUVmax | GTV-PET sub-volumes defined by iso-SUV-curves constructed as percentages of the maximum SUV. | 3 | 3/41 (7) | 0.4 (0–2.6) | |
| GTV-PET 80%-SUVmax | 6 | 3/41 (7) | 1.6 (0.1–11.7) | ||
| GTV-PET 70%-SUVmax | 7 | 1/41 (2) | 3.4 (0.4–26.2) | ||
| GTV-PET 60%-SUVmax | 11 | 4/41 (10) | 6.1 (0.7–43.1) | ||
| GTV-PET 50%-SUVmax | 14 | 3/41 (7) | 9.2 (0.8–63.5) | ||
| Other | |||||
| Recurrence volume | Delineated by the radiologist and radiation oncologist with access to all previous imaging and clinical examinations available at the time of recurrence volume. | ||||
| Nidus | Estimated point of origin within the recurrence volume minimizing the maximum distance to the recurrence boundary. |
*
According to the DAHANCA guidelines the prescribed total radiation dose to the CTV-t was 66 Gy, whereas tumors with a diameter > 4 cm and nasopharyngeal tumors were prescribed 68 Gy.
**
The number of recurrences inside a ROI also includes the recurrences located in the target volumes encompassed by the ROI in question.
***
The number of recurrences for which the estimated point of origin is specific to a ROI is the number of recurrences within that ROI but excluding recurrences located in target volumes contained inside the ROI in question.