Top Line: Does the delineation of nasopharyngeal target volumes using the extent of disease after induction chemotherapy reduce toxicity while maintaining locoregional control?
The Study: Induction chemotherapy followed by chemoradiation is a preferred treatment option for locoregionally advanced nasopharyngeal carcinoma (NPC). However, there is controversy about how to delineate target volumes based on pre- and post-induction tumor volume. Consensus guidelines from 2018 recommend that, ideally, pre-IC volumes receive the full therapeutic dose regardless of post-IC shrinkage provided dose to critical OARs is not exceeded. When electing to treat post-induction volumes, those experts recommended at least covering the original extent of disease with the high risk CTV, and not modifying volumes where there is skull base involvement as it is difficult to assess the extent of residual disease. Here we have long term follow up of a prospective, randomized trial comparing the use of pre- or post-IC tumor for target volume delineation. 212 patients with stage III-IVB NPC received 2 cycles of cisplatin and either 5FU or paclitaxel followed by definitive radiation with concurrent weekly cisplatin. Three treatment volumes were used in both arms: 1) gross primary and nodal disease plus a PTV margin received 70 Gy in 33 fractions, 2) a 5-10mm (2-3mm posterior) high risk CTV surrounding gross disease plus a PTV margin received 64 Gy in 33 fractions, and a low risk CTV that included the standard “intermediate risk” landmarks (see above consensus guidelines) and the bilateral neck plus a PTV margin received 54 Gy in 33 fractions. In the pre-IC arm, the high and intermediate dose PTVs were based on the pre-IC extent of gross disease. In the post-IC arm, these PTVs were based on post-IC extent of disease. Two caveats were that any originally involved skull base structures were included based on pre-IC extent of disease, and the intermediate dose volume included all of the original extent of disease. At 5 years, there was no difference between the pre-IC and post-IC arms in the rate of locoregional recurrence free survival (90.2% v 93.5%). Nor were there differences in OS, PFS, or DMFS. Grade 2+ xerostomia (26.8% v 13%) and hearing loss (34% v 20%) were significantly higher in the pre-IC arm. This was likely driven by lower doses to OARs and fewer violations of OAR objectives in the post-IC arm.
TBL: Using the post-induction extent of disease to define target volumes for NPC does not appear to increase the risk of recurrence and may reduce toxicity. | Xiang, Int J Radiat Oncol Biol Phys 2023
The Study: Induction chemotherapy followed by chemoradiation is a preferred treatment option for locoregionally advanced nasopharyngeal carcinoma (NPC). However, there is controversy about how to delineate target volumes based on pre- and post-induction tumor volume. Consensus guidelines from 2018 recommend that, ideally, pre-IC volumes receive the full therapeutic dose regardless of post-IC shrinkage provided dose to critical OARs is not exceeded. When electing to treat post-induction volumes, those experts recommended at least covering the original extent of disease with the high risk CTV, and not modifying volumes where there is skull base involvement as it is difficult to assess the extent of residual disease. Here we have long term follow up of a prospective, randomized trial comparing the use of pre- or post-IC tumor for target volume delineation. 212 patients with stage III-IVB NPC received 2 cycles of cisplatin and either 5FU or paclitaxel followed by definitive radiation with concurrent weekly cisplatin. Three treatment volumes were used in both arms: 1) gross primary and nodal disease plus a PTV margin received 70 Gy in 33 fractions, 2) a 5-10mm (2-3mm posterior) high risk CTV surrounding gross disease plus a PTV margin received 64 Gy in 33 fractions, and a low risk CTV that included the standard “intermediate risk” landmarks (see above consensus guidelines) and the bilateral neck plus a PTV margin received 54 Gy in 33 fractions. In the pre-IC arm, the high and intermediate dose PTVs were based on the pre-IC extent of gross disease. In the post-IC arm, these PTVs were based on post-IC extent of disease. Two caveats were that any originally involved skull base structures were included based on pre-IC extent of disease, and the intermediate dose volume included all of the original extent of disease. At 5 years, there was no difference between the pre-IC and post-IC arms in the rate of locoregional recurrence free survival (90.2% v 93.5%). Nor were there differences in OS, PFS, or DMFS. Grade 2+ xerostomia (26.8% v 13%) and hearing loss (34% v 20%) were significantly higher in the pre-IC arm. This was likely driven by lower doses to OARs and fewer violations of OAR objectives in the post-IC arm.
TBL: Using the post-induction extent of disease to define target volumes for NPC does not appear to increase the risk of recurrence and may reduce toxicity. | Xiang, Int J Radiat Oncol Biol Phys 2023