Treatment volume

The treated radiation volume should be determined by the extent of tumor at diagnosis before surgical resection and before chemotherapy, including clinically involved regional lymph nodes. With conformal plans and image-guided RT, a margin of 1 cm to 1.3 cm to a clinical target volume or planning target volume may be used.[12] This clinical tumor volume can be modified on the basis of anatomical constraints, especially in situations where the tumor was pushing, rather than invading, the adjacent normal tissues, or when adjacent normal tissues are functionally critical (e.g., head and neck rhabdomyosarcoma). Thus, while the volume irradiated may be modified because of considerations for normal tissue tolerance, gross residual disease at the time of RT should receive full-dose RT. A reduction in volume after 36 Gy is appropriate in chemoresponsive disease for patients with noninvasive displacement (T1) that has regressed in size, but not for invasive tumors (T2). Gross residual disease still receives the full RT dose (50.4–59.4 Gy, the higher dose if >5 cm at diagnosis).

For involved nodal sites, the treated volume is defined as the extent of nodal involvement at diagnosis, factoring in changes in anatomy, plus a 3-cm margin superiorly and inferiorly in the direction of lymphatic drainage, or inclusion of the entire nodal chain where there is uncertainty.

For metastatic disease, the treated volume is the extent of metastases at diagnosis, with the exception of the lung or extensive brain metastases where the whole organ is irradiated, or diffuse peritoneal metastases where the entire peritoneal cavity is included. The use of novel techniques, such as stereotactic body RT to appropriate sites (e.g., bone or small volume soft tissue metastases), can be considered.