Quantitative Analysis of Extracapsular Extension of Metastatic Lymph Nodes and Its Significance in Radiotherapy Planning in Head and Neck Squamous Cell Carcinoma
Pirus Ghadjar, Heide Schreiber-Facklam, Ruth Grater, Christina Evers, Mathew Simcock, Andreas Geretschlager, Norbert M. Blumstein, Peter Zbaren, Yitzhak Zimmer, Ludwig Wilkens, Daniel M. Aebersold,
International Journal of Radiation Oncology*Biology*Physics, In Press, Corrected Proof, Available online 3 August 2009, ISSN 0360-3016,
Purpose: We performed a histopathologic analysis to assess the extent of the extracapsular extension (ECE) beyond the capsule of metastatic lymph nodes (LN) in head and neck cancer to determine appropriate clinical target volume (CTV) expansions. Methods and Materials: All tumor-positive LN of 98 patients who underwent a neck dissection with evidence of ECE in at least one LN were analyzed by a single pathologist. The largest diameters of all LN, and in the case of ECE, the maximal linear distance, from the capsule to the farthest extent of tumor or tumoral reaction were recorded. Results: A total of 231 LN with ECE and 200 tumor-positive LN without ECE were analyzed. The incidence of ECE was associated with larger LN size (p < 0.001). Of all tumor-positive LN with a diameter of < 10 mm or < 5 mm, 105/220 (48%) nodes or 17/59 (29%) nodes, respectively, showed evidence of ECE. The mean and median extent values of ECE were 2 and 1 mm (range, 1–10 mm) and the ECE was ≤ 5 mm in 97% and ≤ 3 mm in 91% of the LN, respectively. Overall, the extent of ECE was significantly correlated with larger LN size (Spearman's correlation coefficient = 0.21; p = 0.001). Conclusions: The incidence of ECE is associated with larger LN size. However, ECE is found in a substantial number of LN with a diameter of < 10 mm. The use of 10-mm CTV margins around the gross tumor volume seems appropriate to account for ECE in radiotherapy planning of head and neck cancer.
A Comparison of Soft-Tissue Implanted Markers and Bony Anatomy Alignments for Image-Guided Treatments of Head-and-Neck Cancers
Omar A. Zeidan, Adam J. Huddleston, Choonik Lee, Katja M. Langen, Patrick A. Kupelian, Sanford L. Meeks, Rafael R. Manon International Journal of Radiation Oncology * Biology * Physics - 1 March 2010 (Vol. 76, Issue 3, Pages 767-774
Do soft-tissue implanted markers move with respect to bony anatomy?
all markers were placed in or near GTV and centrally, and did not move once placed
a single PTV was used and copied across all scans
soft tissue was constrained with bite blocks/depressors
yes, but a 5mm margin covers 93-95% of fractions (33 of 35 Fx), 8mm margin will cover 100%
If yes, what is the dosimetric consequence on target coverage when using these markers as alignment surrogates compared with the traditional bony anatomy–based alignments?
impossible to tell as the GTV/CTV pair were transferred and then altered by the DIR algorithm, not drawn to match disease risk areas.
Diffusion-Weighted MRI for Nodal Staging of Head and Neck Squamous Cell Carcinoma: Impact on Radiotherapy Planning
Piet Dirix, Vincent Vandecaveye, Frederik De Keyzer, Katya Op de beeck, Vincent Vander Poorten, Pierre Delaere, Eric Verbeken, Robert Hermans, Sandra Nuyts
//International Journal of Radiation Oncology * Biology * Physics - 1 March 2010 (Vol. 76, Issue 3, Pages 761-766
Their rationale is that PET is good when nodes are big but not for small stuff, and its not very anatomical, so this study looks at neck nodes examined in three ways - CT imaging, MRI-DW (diffusion weighted) imaging, pathological imaging - to see if there is a more accurate way to identify involved nodes and to accurately predict their volume. Pains were taken to map the dissected nodes to the correct position on the MRI.
Several anatomical assessments resulted:
CT designation of "LN+" undertaken by a radiologist with identifiable criteria
any node with a minimal axial diameter of >1 cm;
any node with internal central or peripheral attenuation suggestive of necrosis;
extracapsular extension; and/or
obliteration of fat or perivascular soft tissue planes
MRI-DW designation of "LN+" relied on an apparent diffusion coefficient (ADC) of 0.00094mm2/sec.
HISTOPATHOLOGY designation of "LN+" (the gold standard)
CT designation of CTV for treatment
3 CTVs volumes produced according to consensus guidelines
agreed between 2 radiation oncologists
Imaging found only 50% of all LNs in the specimen
Imaging found ALL LN+
~10% were LN+
size of LN+ was 4-30mm
CT correctly staged 9/22
MRI-DW correctly staged 19/22 (both up and down stage and uni<> bilateral estimations) The problems of the RO-defined CTVs are not apparent, that is, did the CTVs adequately cover disease or not.
Radiotherapy Dose–Volume Effects On Salivary Gland Function
J O Deasy, V Moiseenko, L Marks, K S C Chao, J Nam, A Eisbruch
Int. J. Radiation Oncology Biol. Phys. 2010 76_ 3 S58–S63
Publications relating parotid dose–volume characteristics to radiotherapy-induced salivary toxicity were reviewed.
Late salivary dysfunction has been correlated to the mean parotid gland dose, with recovery occurring
with time. Severe xerostomia (defined as long-term salivary function of <25% of baseline) is usually avoided if
at least one parotid gland is spared to a mean dose of less than ~20 Gy or if both glands are spared to less than
~25 Gy (mean dose). For complex, partial-volume RT patterns (e.g., intensity-modulated radiotherapy), each
parotid mean dose should be kept as low as possible, consistent with the desired clinical target volume coverage.
A lower parotid mean dose usually results in better function. Submandibular gland sparing also significantly
decreases the risk of xerostomia. The currently available predictive models are imprecise, and additional study
is required to identify more accurate models of xerostomia risk.
Two things to note - in order of importance:
the requirement for planning is each parotid mean dose should be kept as low as possible, consistent with the desired clinical target volume coverage, that is practice ALARA but get the cancer first!
the function of the parotid follows the following dose constraints, namely Severe xerostomia (defined as long-term salivary function of <25% of baseline) is usually avoided if at least one parotid gland is spared to a mean dose of less than z20 Gy or if both glands are spared to less than z25 Gy (mean dose)
The implications for planning are that the notion that you should plan your parotids to a mean dose of 25Gy is INCORRECT. You plan to give an ALARA dose to the parotids. If you can achieve 10Gy, you achieve 10Gy. How do you do this? Just write "Parotid constraint <10Gy mean" on the prescription and see what can be done. Our mean parotid doses are in the 16-18Gy region, so better than 25Gy is easily achievable.
And the resultant parotid doses will allow you to tell the patient about their likelihood of xerostomia.
A nice summary and review of literature dealing with radiation induced complications in the eye. Click here to access the summary. Summaries of the effect of radiation on various tissue types and their management also included for reference.