Radiation Therapy (RT)
RT was previously used to treat Hodgkin lymphoma alone - but is now used to reduce the risk of recurrence in areas of bulky disease at presentation.
Hemoglobin should be kept above 10 gm/dL during RT.
Standard therapy for all intermediate risk category patients (not on protocol) would be to give involved field radiotherapy (21 Gy in 14 fractions of 1.5 Gy per day).
Treatment volumes:
GTV = Gross Tumor Volume = Areas of disease involved at presentation. Includes any lymph node measuring > 1.5 cm in a single axis on CT scan.
CTV = Clinical Target Volume = Anatomical compartment.
PTV = Planning Target Volume = 1.0 cm margin around the CTV to account for patient motion and set-up variability.
Anatomical compartments that are contiguous to involved compartments will also need to be treated if they contain lymph nodes > 1.0 cm on CT.
Definitions of Terms for Historical and Current Radiation Therapy (RT) Volumes:
Term |
Irradiated Regions |
Involved field |
Entire lymph node area |
Extended field |
Involved nodal area and uninvolved contiguous region |
Mantle field |
Cervical, supraclavicular, infraclavicular, axillary and mediastinal, hilar and inferior mediastinal nodes |
Inverted Y |
Paraaortic, pelvic and inguinal nodes ± spleen |
Total nodal |
All involved nodal areas |
Subtotal nodal |
Mantle and paraaortic node |
Liver |
Liver ± paraaortic node |
Preauricular field |
Small volume with preauricular nodes |
Waldeyer’s ring field |
Pre- and postauricular nodes, occipital nodes and lymphoid structures in base of tongue and nasopharynx |
Treatment Technique
Different factors should be taken into account when planning RT for Hodgkin lymphoma to minimize:
- Organ/normal tissue damage
- Impairment of future growth and development
Precise treatment achieved using:
- Immobilization devices
- CT simulation and planning
- Using a compensator or other technique to ensure RT dose homogeneity
- Partial transmission blocks can be used. For example, if treating the liver, this technique can be used as a mechanism to reduce dose that reaches liver but still maintain full dose to adjacent nodes.
- Treatment using a linear accelerator with beam energy of 6mV
- Portal imaging to verify that the actual treatment field matches the planned treatment field
Protection of reproduction organs is important in pediatric patients.
For females:
- Transposition of ovaries to central midline position and then using a pelvic block is possible during pelvic irradiation.
For males:
- Testicular shielding should be used whenever possible.
Techniques for different RT fields:
Technique |
|
Mantle field |
Anterior field simulation:
Posterior field simulation:
Transmission blocks to shield:
|
Waldeyer’s Ring |
For unilateral bulky upper neck disease:
|
Paraaortic field |
Equally weighted anterior and posterior portals 2 cm lateral borders to transverse processes Inferior border – bottom of fourth lumber vertebra Gap placed between mantle and paraaortic field |
Spleen field |
If treated separate from paraaortic field a 1 cm gap on skin is required |
Splenic Hilar nodes |
Needs to be treated if patient had laparotomy – surgeon marks splenic hilum during surgery Can be included in paraaortic field |
Pelvic field |
Iliac crests and midline structures are shielded Fertility preservation:
|
