Javascript er ikke aktivert i din nettleser. Dette er nødvendig for å bruke Oncolex. Kontakt din systemadministrator for å aktivere JavaScript.

Radiotherapy of parotid gland and submandibula for malignant lymphoma


Medical editor Alexander Fosså MD
Oncologist
Oslo University Hospital

General

Indications

Indolent lymphomas are often present in the salivary glands usually in the form of marginal lesion lymphoma. These lymphomas with underlying Sjøgrens syndrome. Locoregional confined disease is common. Aggressive lymphomas are also observed, but Hodgkin's lymphoma in salivary glands is very rare. 

Curative radiation therapy

  • For localized indolent lymphomas (stage PeI-PeII1), radiation therapy alone is given with the intention of curing the disease. 

  • For localized lymphomas with aggressive histologies (stadium PeI-PeII1), radiation therapy is given as part of curative treatment after chemotherapy (3-6 CHOP-based cycles or equivalent).

  • For residual tumor from aggressive lymphomas after full chemotherapy (6-8 CHOP-based cycles or equivalent), consolidated radiotherapy to the residual tumor with margin is considered. 

Palliative radiation therapy

  • For palliative radiation therapy, guidelines are usually the same as for curative therapy but are adapted individually. 

Definitions

Target Volume

Target volume definitions from ICRU
(International Commission on Radiation Units and Measurements)

GTV (= Gross Tumor Volume)

Tumor volume

Palpable or visible/identifiable area of malignant growth.

CTV (= Clinical Target Volume)

Clinical target volume

Tissue volume containing GTV and subclinical microscopic malignant disease.

ITV (= Internal Target Volume)

Target volume

Volume containing CTV and an internal margin taking into account internal movements and changes in CTV. This is the volume that should receive an optimal dose.

PTV (= Planning Target Volume)

Planning volume

Geometric volume containing ITV and one Setup margin taking into account assumed variation in patient movements, patient positioning, and field alignment.

Planning contour: Beams-Eye-View projection of PTV.

IM (= Inner margin) and SM (= Setup margin)

IM and SM cannot be summed linearly. Total margin must be given specifically for different tumor localizations.

Field limit

The field limit is defined as the area that 50% of the isodose curve outside the target volume must have to give a therapeutic isodose (90% isodose) which encircles the target volume 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

The table below summarizes standards for use of the term GTV, for margins to CTV and ITV, as well as formulation of field limits for radiation therapy of malignant lymphomas.

Target volume for radiotherapy

GTV Tumor in indolent NHL stage I/II1, original tumor (before chemotherapy minus balloon effect) in aggressive NHL stage I/II1 and HL stage I/IIA

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

CTV GTV + 2 cm craniocaudal to confined disease/short chemotherapy

GTV + 1 cm craniocaudal to residual tumor from advanced disease after full chemotherapy

GTV + 1 cm in the transversal plane

CTV should always include the entire lymph node region in the levels to be irradiated (limited in the lungs and bone, unless there is suspicion of infiltration).

CTV may for indolent NHL stage I/II1 include the nearest non-infiltrated lymph node region or parts of it.

ITV CTV if internal movement is negligent (CNS, ENH and others)

CTV + up to 1 cm craniocaudal and up to 0.5 cm transversal in the mediastinum

CTV + 2–3 cm in mesentary and stomach

CTV + up to 0.5 cm transversal retroperitoneally

PTV

Not routinely defined

Field limits

Are set to 1 cm outside ITV for set-up margin and penumbra

Field limits should be arranged so that later junctions are as simple as possible (for example on one side of the spine, in invertebral discs)

Involved node

The field of radiation surrounding macroscopically involved lymph nodes alone with margin. This definition is currently not widely used in Norway, but is emerging in international studies.

Involved field

The involved field is the field of radiation surrounding the macroscopically involved lymph node region or organ with margin. After limited chemotherapy of localized lymphomas, the original macroscopically involved area is used as the foundation for field contouring (with the exception of the balloon effect). For residual lesions after full chemotherapy for advanced stages, the residual tumor is usually used as the foundation (with some exceptions). What determines an adequatemargin from the macrotumor to the field limit depends on multiple factors. For early stages of NHL and HL without previous chemotherapy or after chemotherapy (3–6 CHOP-based cycles, 2–4 ABVD or equivalent), the margins from the initial tumor to the field limit should be 3-4 cmin the direction of lymph drainage lengthwise from initial extent and 2 cm in the transversal plan (exception for balloon effect). With residual lesion have full chemotherapy for advanced NHL and HL and relatively little internal movement, then 2 cm from residualtumor to the field limit is used. Larger margins may be considered in areas for greater internal movement (abdomen, structures near diaphragm). As a general rule with nodal involvement, the target volume includes the entire lymph node region in the transversal plane for the levels included in the field.

Traditionally, the entire inolved lymph node area has been included completely in the craniocaudal direction (direction of lymph drainage). This provides a recognizeable geometric field (parts of mantle or inverted Y field) which is advantageous for standardization, reproduciblity, later junctioning, etc. The lymph node regions as defined in the Ann Arbor classification then do not represent any biologically functional entitites and are not considered a base for radiation therapy. Thus, it is natural to see the regions coherently length-wise inthe direction of lymph drainage and use margins to involved lymph nodes to avoid irradiation of entire regions (for example in the neck, supreclavicular region, mediastinum, and retroperitoneum). Parts of neighboring organs are included to satisfy the minimum margins given above. Field modeling should still be geometric shapes as much as possible to make later joining of fields easier and to avoid border recurrences in areas difficult to irradiate again.

For extranodal lymfomas/organ manifestations, it is sometimes natural to include the entire organ (thyroid gland, stomach, brain, spinal cord). In such cases, it is also necessary to take internal movement into consideration, for example, stomach movement and movement of lung borders etc.. With multiple organ localizations, it is not possible to give full doses to the entire organ due to the tolerance for ionizing radiation (lungs, liver, kidneys) and the fields and doses must be adapted accordingly.

Extended field

This type of field includes macroscopically involved regions/organs and lymph node regions that are assumed to have diseased cells. This may be the nearest macroscopically normal region or multiple, more distant areas. This technique was developed for Hodgkin's lymphoma when radiation therapy was used as the only treatment modality 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). In today's practice, the term 'extended field' is not widely used. For localized stages of low-grade NHL, where radiotherapy is given alone to cure the disease, we have chosen to include the nearest uninvolved regions in the field of radiation, a type of "minimally extended field". This is not, however, practiced by all radiation therapy centers in Norway.



Preparation

Patients must be evaluated by a dentist and treated if necessary before immobilization and start of treatment. 

The patient is immobilized with a mask.


Implementation

The dosage for this radiation therapy should be planned using CT.

CT-based simulation 

  • With isolated involvement of non-Hodgkin lymphoma in salivary gland on one side, CTV is defined as the macrotumor (original tumor before chemotherapy for aggressive lymphomas) with 1 cm margin.

  • For visible tumor growth outside the salivary gland, this is included in the area with 1 cm margin in CTV.

  • The remaining healthy part of the involved salivary gland is also included in CTV. The parotid gland may extend quite deep into the pharynx.

  • In stage Pell1, the involved areas of the neck with 2 cm margin to CTV in the caudal direction are included. For bilateral involvement, the contouring is done equivalent to the contralateral side.

  • In stage PeI of indolent lymphoma, contouring of draining ipsilateral lymph nodes in the upper neck (submandibular, submental, and occipital as well as upper neck region) is considered. 

  • The node region of the neck is included in its entirety in the tranversal plane in slices included in CTV. CTV is chosen such that the field limit on the neck does not involve the spine.

  • Contouring of neck lymph nodes including submandibular and submental nodes can be done according to guidelines developed for CT diagnostics. These appear to include occipital nodes somewhat poorly, and it is important to include these.

  • For unilateral involvement of parotid gland, a field set-up with diagonal wedge field makes it possible to spare the contralateral parotid gland. Isocentric technique with half-beam blocks circumvents joining problems/junctioning issues of anteroposterior irradiation to the neck and supraclavicular fossa. Electron irradiation from the side to the parotid gland is also a possibility. Unilateral involvement of the submandibular gland is likely most effectively covered best with anteroposterior irradiation with sufficient stretching of the neck.

    CT dose plan, parotid gland and submandibula

    Fractionation

    Standard fractionation and total dose for curative treatment is given below. These are also normative for palliative treatment, but should be modified on an individual basis.

    • For curative treatment of indolent NHL: 2 Gy x 15
    • For aggressive NHL: 2 Gy x 20.

     


Follow-up

Risk organs

Salivary glands (especially parotid gland)

Delayed dry mouth should be expected if both parotid glands are irradiated.

Teeth

Defects should be repaired before treatment start to prevent later osteoradionecrosis. Caution should be used with dental treatment after irradiation. 

Eyes and lens

With modern treatment, the doses for these organs should be under the tolerance levels.

Chiasma

With modern treatment, the doses for these organs should be under the tolerance levels. 

Pituitary gland 

With modern treatment, the doses for these organs should be under the tolerance levels.


Oslo University Hospital shall not be liable for any loss whether direct, indirect, incidental or consequential, arising out of access to, use of, or reliance upon any of the content on this website. Oslo University Hospital© 2017