TriangleHEALTH PROFESSIONAL · SOURCE READING
ISRT or INRT treatment planning
Source: Childhood Hodgkin Lymphoma Treatment (PDQ®)–Health Professional Version, National Cancer Institute.
Source updated: April 16, 2025 · Captured 2026-09-09.
Selected source text with whitespace normalised. This Triangle page is not an NCI PDQ summary.
Radiation therapy planning that uses CT scans obtained during the simulation procedure is a requirement for contemporary INRT or ISRT. Fusion of staging imaging (CT or PET-CT) with the planning CT dataset can facilitate delineation of the treatment volume. Radiation therapy planning scans that encompass the full extent of organs at risk (e.g., lungs) are important so that normal tissue exposures can be calculated accurately.
Definitions that are important in planning radiation therapy include the following:
Prechemotherapy or presurgery gross tumor volume (GTV): Imaging abnormalities of nodal or non-nodal tissues at initially involved sites.
Postchemotherapy GTV: Imaging abnormalities at initially involved sites that remain abnormal after chemotherapy.
Postchemotherapy clinical target volume (CTV): Abnormal tissues originally involved with lymphoma but taking into account the reduction in the axial (transverse) diameter that has occurred with chemotherapy. This delineation requires consideration of the expected routes of disease spread and the quality of pretreatment imaging.
Internal target volume (ITV): Encompasses the CTV, with an added margin to account for variation in shape and motion within the patient (e.g., breathing).
Planning target volume (PTV): Encompasses the ITV or CTV and accounts for variation in daily setup for radiation; generally, 0.5 cm to 1 cm.
Boost radiation therapy: Some protocols, such as the EuroNet-PHL-C1 protocol, give additional radiation therapy (a boost) to sites with a poor response and/or bulky residual disease after initial chemotherapy. These volumes were determined after completion of all chemotherapy. This approach is sometimes used for patients with residual areas of PET avidity after chemotherapy.
Organ at risk determination and dose constraints: Because of the importance of long-term tissue injury after radiation, the dose to normal tissues is kept as low as reasonably achievable while adequately treating the PTV. Some specific organ radiation dose tolerances guide these decisions, and these organs are considered organs at risk.
The treatment volume for unfavorable or advanced disease is somewhat variable and often protocol-specific. Large-volume radiation therapy may compromise organ function and limit the intensity of second-line therapy if relapse occurs. In patients with intermediate or advanced disease, who often have multifocal/extranodal disease, the current standard of therapy includes postchemotherapy ISRT that limits radiation exposure to large portions of the body.[45,50] For example, in the AHOD0031 trial, radiation therapy was given to involved sites at diagnosis,[20] but in the AHOD1331 trial, it was given to bulky mediastinal disease and to slow responding disease sites (based on interim PET scan).[53] There is emerging evidence for omitting radiation therapy entirely in patients who have a complete, PET-based response. Thus, in the S1826 trial, radiation therapy was given only to patients with residual, metabolically active posttherapy sites as defined on PET.[30]
Publication references
Read the original reference and check its publication notices.
Preserved source evidence · Not medical advice