Tuesday, January 6, 2009

Oncoanatomy - Larynx

TZ presented the resident session of the oncoanatomy: larynx module.  Here are some notes that I culled from the presentation and resulting discussion

Le UCSF n=315, retrospective analysis of T1 Larynx - fx size less than 2.0 Gy were associated with lower local control.  for fx size of 2.25 or greater local control was 94%.  Their standard is 2.25Gy fx to 63Gy.

Several other retrospective series from MDA, and Florida exist with similar findings of inferior results with fx size less than 2Gy..

DB makes the case that in the Duke experience daily fraction doses of 2Gy to 64Gy have led to excellent local control (~94%).  He also comments that due to prescribing to the 95% IDL, the doses may have been closed to 2.1Gy.

Japanese randomized trial:

180 patients with T1N0M0. Randomized to treatment arm A (radiation fraction size 2 Gy, n = 89) or B (2.25 Gy, n = 91). Total Dose was 60 Gy in 30 fxs for tumors ≤  2/3 of vocal cord) or 66 Gy in 33 fractions for tumors > 2/3 cord in Arm A and 56.25 Gy in 25 fractions within 5 weeks for minimal tumor or 63 Gy in 28 fractions within 5.6 weeks for larger than minimal tumors in Arm B. 5yr LC was 77% for Arm A and 92% for Arm B (p = 0.004). 5yr CSS were 97% and 100% (NS). No differences in toxicity.

NOTES for treatment planning:

The figure of 8 refers to the anterior aspect of the thyroid cartilage that is visible on fluoroscopic simulation.  The ‘thin’ part of the cartilage, or the ‘x’ point of the ‘8’  is where the vocal cords attach to the thyroid cartilage and.  This is therefore a useful landmark for simulation and port checks.

For arrangement, parallel opposed can get the job done, but CW comments that CC Wang treated with a four field LAO, RAO, and opposed lats for homogeneity.  DB also remarks that he has been angling his beams slightly more oblique anteriorly to improve posterior coverage.

In regards to wedges, DB also makes the case for using 15deg wedges more than 30deg as he finds that there tends to be a cold spot in  the anterior commisure if the fields are over wedged. 

for T2, retrospective MDACC 180 pt series with improved LC with BID treatment. 

RTOG 95-12 ongoing T2a/b randomized to 70Gy 2Gy/day, HFX 79.2 1.2Gy BID.  Currently no significant differences in arms per report at ASTRO 2006. by Trotti.  5yr LC 70% QD vs 79% BID (p=0.11).  The magnitude of the difference is similar to what is seen in other HFX trials, so DB argues that this is an underpowered study that is probably showing a signal of efficacy.  

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