IMRT Organ Contraints

The following organ contraints give the UPPER LIMIT that is acceptable, NOT the dose level that should be aimed at. The idea here is AS LOW AS POSSIBLE with acceptable PTV coverage not "mean dose of 26Gy". You should of course realise that acceptable PTV coverage may mean mean dose the same as the PTV. In that case - tough luck! You have to hit the PTV FIRST, then spare the organs, not the other way around. This fact seems to be lost on some prostate planning in the 2000's where the posterior margin on the rectum is 0 mm. You need IGRT working to have any hope of a 0mm margin!

Submandibular glands

Dose-Effect Relationships for the Submandibular Salivary Glands and Implications for Their Sparing by Intensity Modulated Radiotherapy
International Journal of Radiation Oncology Biology Physics, 2008, Volume 72, Issue 2, Pages 373-382
C. Murdoch-Kinch, H. Kim, K. Vineberg, J. Ship, A. Eisbruch

Purpose: Submandibular salivary glands (SMGs) dysfunction contributes to xerostomia after radiotherapy (RT) of head-and-neck (HN) cancer. We assessed SMG dose–response relationships and their implications for sparing these glands by intensity-modulated radiotherapy (IMRT).
Methods and Materials: A total of 148 HN cancer patients underwent unstimulated and stimulated SMG salivary flow rate measurements selectively from Wharton's duct orifices, before RT and periodically through 24 months after RT. Correlations of flow rates and mean SMG doses were modeled throughout all time points. IMRT replanning in 8 patients whose contralateral level I was not a target incorporated the results in a new cost function aiming to spare contralateral SMGs.
Results: Stimulated SMG flow rates decreased exponentially by (1.2%)Gy as mean doses increased up to 39 Gy threshold, and then plateaued near zero. At mean doses ≤39 Gy, but not higher, flow rates recovered over time at 2.2%/month. Similarly, the unstimulated salivary flow rates decreased exponentially by (3%)Gy as mean dose increased and recovered over time if mean dose was <39 Gy. IMRT replanning reduced mean contralateral SMG dose by average 12 Gy, achieving ≤39 Gy in 5 of 8 patients, without target underdosing, increasing the mean doses to the parotid glands and swallowing structures by average 2–3 Gy.
Conclusions: SMG salivary flow rates depended on mean dose with recovery over time up to a threshold of 39 Gy. Substantial SMG dose reduction to below this threshold and without target underdosing is feasible in some patients, at the expense of modestly higher doses to some other organs.

Oral Mucosa

Prospective Evaluation to Establish a Dose Response for Clinical Oral Mucositis in Patients Undergoing Head-and-Neck Conformal Radiotherapy
International Journal of Radiation Oncology Biology Physics, 2008, Volume 72, Issue 3, Pages 756-762
Samir Narayan, Joerg Lehmann, Matthew A. Coleman, Andrew Vaughan, Claus Chunli Yang, Danny Enepekides, Gregory Farwell, James A. Purdy, Grace Laredo, Kerry Nolan, Francesca S. Pearson, Srinivasan Vijayakumar

Purpose: We conducted a clinical study to correlate oral cavity dose with clinical mucositis, perform in vivo dosimetry, and determine the feasibility of obtaining buccal mucosal cell samples in patients undergoing head-and-neck radiation therapy. The main objective is to establish a quantitative dose response for clinical oral mucositis.
Methods and Materials: Twelve patients undergoing radiation therapy for head-and-neck cancer were prospectively studied. Four points were chosen in separate quadrants of the oral cavity. Calculated dose distributions were generated by using AcQPlan and Eclipse treatment planning systems. MOSFET dosimeters were used to measure dose at each sampled point. Each patient underwent buccal sampling for future RNA analysis before and after the first radiation treatment at the four selected points. Clinical and functional mucositis were assessed weekly according to National Cancer Institute Common Toxicity Criteria, Version 3.
Results: Maximum and average doses for sampled sites ranged from 7.4–62.3 and 3.0–54.3 Gy, respectively. A cumulative point dose of 39.1 Gy resulted in mucositis for 3 weeks or longer. Mild severity (Grade ≤ 1) and short duration (≤1 week) of mucositis were found at cumulative point doses less than 32 Gy. Polymerase chain reaction consistently was able to detect basal levels of two known radiation responsive genes.
Conclusions: In our sample, cumulative doses to the oral cavity of less than 32 Gy were associated with minimal acute mucositis. A dose greater than 39 Gy was associated with longer duration of mucositis. Our technique for sampling buccal mucosa yielded sufficient cells for RNA analysis using polymerase chain reaction.

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