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Radiation therapy for Waldeyer's ring with malignant lymphoma


Medical editor Alexander Fosså MD
Oncologist
Oslo University Hospital

General

Next to the gastrointestinal tract, Waldeyer's ring is is a common localization for extranodal lymphomas. Even though Waldeyer's ring is anatomically not lymph node region, it is considered a region for staging of malignant lymphomas according to the Ann Arbor classification. 

 

Lymphomas in this region are generally DLBCL, but follicular lymphomas also occur relatively often. 

The most common localization is the palatine tonsil followed by the nasopharynx and base of the tongue. Hodgkin's lymphoma rarely occurs in Waldeyer's ring. 

Curative radiation therapy

  • For localized stages of aggressive lymphomas (stage I-II1), consolidative radiation therapy after chemotherapy (CHOP-based or equivalent) to the original tumor-involved area with margin (involved field) is given. 
  • For residual tumor of aggressive lymphomas after full chemotherapy (6–8 CHOP-based cycles or equivalent), consolidative radiation therapy to the residual tumor with margin is considered. 
  • For indolent lymphomas with localized disease (stage I–II1), radiation therapy alone to the involved area with margin is given (involved field).  
  • Ved lokaliserte stadier av klassisk Hodgkin lymfom (stadium IA/IIA) gis strålebehandling mot opprinnelig tumoraffisert område med margin (”involved field”) etter kjemoterapi (ABVD eller tilsvarende).
  • For localized stages of classical Hodgkin's lymphoma (stage IA/IIA), radiation therapy is given to the original area involved with margin (involved field) after chemotherapy (ABVD or equivalent).
  • Special guidelines apply for children and adolescents up to 18 years with Hodgkin's lymphoma.
  • For residual tumor of Hodgkin's lymphoma after full chemotherapy for advanced Hodgkin's lymphoma (6-8 ABVD, 8 BEACOPP or equivalent), consolidative radiation therapy to the residual tumor with margin is considered. 

Palliative radiation therapy

  • As palliative radiation therapy, the method is based on guidelines for curative treatment with individual modifications.

     

 


Definitions

Target Volume

 

 

Definitions of target volumes in accordance with the ICRU (International Commission on Radiation Units and Measurements)

GTV (Gross tumor volume)

Gross palpable or visible/identifiable area of malignant growth.

CTV (Clinical target volume)

Macroscopic tumor volume including any remaining tumor tissue.

ITV (Internal Target Volume)

Volume containing CTV and internal margin to allow for internal movements and changes to CTV.

PTV (Planning Target Volume) Geometric volume containing ITV with set-up margin taking into accound patient movements, variations in patient positioning, and field settings.
OAR (Organ-at-Risk) Normal tissue senstive to radiation that may significantly affect planning and/or dose.

PRV (Planning organ-at-risk volume)

Geometric volume containing risk volume with set-up margin.
TV (Treated Volume) Volume within an isodose surface considered sufficient based on the treatment intention.
IV (Irradiated Volume) Volume-to-receive dose that is of significance with regard to normal tissue tolerance.
CI (Conformity Index) Relationship between the planning target volume and treated volume (PTV/TV).

Field Limits

The field limit is defined as the required course for the 50% isodose curve outside the target volume to give a therapeutic isodose (90% isodose) to the target volume which is intended to be treated. The distance from 90-50% of the isodose (penumbra) depends on multiple conditions and is typically 5-7 mm.

Definition of margins

For radiation therapy of malignant lymphomas, a table is formulated which summarizes standards used for GTV, margins for CTV and ITV, as well as shaping of field limits.

 

 

 

Target volume for radiation therapy
GTV Current tumor for indolent NHL stage I/II1, original tumor (before chemotherapy minus balloon effect) for aggressive NHL stage I/II1 and HL stage I/IIA

Residual tumor for aggressive NHL stage II2/IV and HL stage IIB/IV

CTV GTV + 2 cm craniocaudal for limited disease/short chemotherapy

GTV + 1 cm craniocaudal for residual tumor from extensive disease after full chemotherapy

GTV + 1cm in transverse plane

CTV should always contain the entire lymph node region in the levels to be radiated (limited for lungs and bone, if there is no suspicion of infiltration).

CTV may for indolent NHL stage I/II1 contain the nearest unaffected lymph node region or parts of it.

ITV CTV if internal movement can be ignored (CNS, ENT)

CTV + 1 cm craniocaudal and + 0.5 cm transverse in the mediastinum

CTV + 2–3 cm in mesentery

CTV + 0-0.5 cm transverse retroperitoneally

PTV

Not routinely defined

Field limits ITV + Setup margin and penumbra (1.2 cm)

The field limits should be such that later junctions are simple (on one side of the spine, in vertebral discs etc.)

 

 

Involved node

The radiation field which surrounds the macroscopically involved lymph node only with margin. Thus far, this definition is rarely used in Norway, but increasingly in international studies.

 

Involved field

Radiation field which includes the involved macroscopic lymph node region or organ with margin. After limited chemotherapy for localized lymphomas, the originally affected macroscopic area is used as a basis for field shaping (with the exception of the balloon effect). For residual changes after full chemotherapy in advanced stages, the residual tumor is usually used as a basis (multiple exceptions). What are adequate margins from the macroscopic tumor to the field limit depend on multiple factors. For early stages of NHL and HL without previous chemotherapy or after chemotherapy (3-6 CHOP-based treatments, 2-4 ABVD or equivalent), the margins from the initial extention to the field limit should be 3-4 cm in the vertical direction, from the initial extent and 2 cm in the transversal plane (with the exception of the balloon effect). For residual changes after full chemotherapy for advanced NHL and HL and relatively little internal mobility, then 2 cm from the residual tumor to the field limit is used. Wider margins must be considered in areas of large internal mobility (abdomen, structures near the diaphragm). Regularly, for nodal involvement, the target volume includes the entire lymph node region in the transversal plane for those levels included in the field.

Traditionally, the entire involved lymph node region has been included completely in the craniocaudal direction (direction for lymph drainage). This provides a recognizable geometric field (parts of mantle field or inverted Y-field) which has advantages for standardizing, reproducibility, later junctioning etc. The lymph node regions, as they are defined in the Ann-Arbor classification, represent no functional biological unit and are not intended as a basis for radiation therapy. In this way, it is natural to see the regions as coherent in the vertical direction of the lymph drainage and to use margins to the involved lymph nodes to avoid radiation of entire regions (for example neck/supraclavicular region, mediastinum, and retroperitoneum). Parts of the neighboring regions may be included to compensate for the minimum margins given above. Field shaping should still follow the geometric forms as much as possible, making later field junctioning easier and to avoid border recurrences in areas which are difficult to re-irradiate.

For extranodal lymphomas/organ manifestations, the entire organ is sometimes included (thyroid gland, stomach, brain, spinal cord). Internal mobility must also be taken into consideration here, for example stomach movement, movement of lungs etc. For several organ localizations, it is not possible to give full doses to the entire organ due to the tolerance for ionizing radiation (lungs, liver, kidney), and the fields/doses must be adapted accordingly.

Extended field

This concept is utilized for fields which include macroscopically involved regions/organs and lymph node regions where it is assumed there is microscopic disease. This may be the nearest macroscopic normal region or multiple, more distant areas. The concept was developed for Hodgkin's lymphoma at a time when radiation therapy was the only modality used and was given to large areas with assumed microscopic disease on one or both sides of the diaphragm (mantle field, paraaortal field, inverted Y-field). For today's purposes, the concept is not of much benefit. For localized stages of low-grade NHL, where radiation therapy is given alone with the intention of curing the disease, we have chosen to include the nearest unaffected region in the radiation field, that is, a "minimally extended field." However, this is not practiced at all radiation therapy centers.

 

 


Preparation

  • The patient must be evaluated by a dentist and any dental treatment must be finished before treatment is started.
  • The patient must be immobilized with a mask while the neck is slightly extended as for the mantle field.

  • Implementation

    CT-based simulation

    Dose planning with CT is standard for this treatment.

    • The actual (for curative treatment of localized indolent lymphomas or residual tumor after full chemotherapy for advanved disease) or original tumor volume (for curative treatment after limited chemotherapy for early stages of HL and aggressive NHL) defines GTV.
    • CTV is generated by the margin in the craniocaudal direction 2 cm (for curative treatment of localized indolent lymphomas or after limited chemotherapy for early stages of HL and aggressive NHL) or 1 cm (residual tumor after full chemotherapy). There is a 1 cm margin to CTV in the transversal plane.
    • Previously, the entire Waldeyer's ring was included in CTV the same as all the nodal regions of the neck or axillary groin or equivalent. Waldeyer's ring was then included in CTV from the base of the skull to the lingual tonsils on the base of the tongue and down to os hyoid. Drawing of Waldeyer's ring as CTV follows the mucosa from the lower edge of the base of the skull/sphenoid sinus and forward to the choanae and back to the spine where the retropharyngeal nodes are included. The area of the openining of the eustachian tube is outlined. the platinar tonsils and root of the tongue are included down to os hyoid. Submental, submandibular, and occipital were included in CTV. 
    • For localized stages of Hodgkin's lymphomas or aggressive lymphomas after stage-adapted chemotherapy, it is considered necessary to irradiate the originally involved area of Waldeyer's ring with margin (GTV with margin 1–2 cm to CTV) after chemotherapyy.
    • For localized indolent lymphomas in Waldeyer's ring (Stage I–III), where curative radiotherapy is given, all of Waldeyer's ring is treated (see above) with involved lymph node areas and possibly with the next draining uninvolved lymph node station. Lymph nodes are treated unilaterally on the neck. With lymph node involvement near the midline in Waldeyer's ring they may be treated bilaterally. 
    • Drawing (contouring?) of neck lymph nodes including retropharyngeal, submandibular, and submental nodes is done according to guidelines developed for CT diagnostics. These guidelines appear to cover occipital nodes less effectively, which should be included.
    • Isocentric irradiation with halvblender technique allows irradiation from side to side toward Waldeyer's ring, submandibular, submental, and occipital lymph nodes on the upper neck and anteroposterior beam to the lower part of the neck/supraclavicular region. For unilateral irradiation of parts of Waldeyer's ring, it is often sensible to give a diagonal wedge field to spare the salivary glands of the uninvolved side. 

    CT dose plan, Waldeyer's ring

    Fractionation

    Standard fractionation and total dose for curative treatment is given below. These are also guidelines for palliative treatment, but must be modified individually.

    • For Hodgkin's lymphoma stage I-IIA without risk factors: 2 Gy x 10
    • Otherwise for Hodgkin's lymphoma: 1.75 Gy x 17
    • For curative treatment of indolent non-Hodgkin lymphoma: 2 Gy x 15
    • For aggressive NHL: 2 Gy x 20.

    Follow-up

    Organs at risk

    Mucosa 

    Acute mucositis in the mouth, pharynx, and esophagus, during treatment and shortly after occurs in most patients and may cause some patients significant problems.

    Skin and nails

    Reversible alopecia of irradiated areas of the back of the head and jaw (beard growth) should be expected. 

    Lense, eyes, optic chiasma, pituitary gland

    Fields toward Waldeyer's ring will contribute a dose or radiation to these organs, which is normally under the tolerance dose. It is important to avoid hotspots in these organs.

    Teeth

    Defects should be evaluated before treatment to prevent later osteoradionecrosis. Caution should be used with dental treatment after irradiation of the jaw region. 

    Salivary glands 

    Lasting dry mouth should be expected with fields including both parotid glands. If this can be avoided, problems are often moderate in the long run.

    Blood vessels in the neck

    After irradiation of blood vessels in the neck, there is a slight increase in risk for cerebrovascular complications.


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