Radiation Physics

PV QA 3 - Poster Viewing Q&A 3

TU_6_3172 - New range margin recommendations based on dose calculation uncertainties

Tuesday, October 23
1:00 PM - 2:30 PM
Location: Innovation Hub, Exhibit Hall 3

New range margin recommendations based on dose calculation uncertainties
J. P. Schuemann1, and H. Paganetti2; 1Massachusetts General Hospital & Harvard Medical School, Boston, MA, 2Department of Radiation Oncology, Massachusetts General Hospital and Harvard Medical School, Boston, MA

Purpose/Objective(s): To recommend new, treatment site specific range margins for proton therapy by re-evaluating the dose-calculation accuracy of analytical dose calculation (ADC) algorithms.

Materials/Methods: We analyze 1920 treatment fields to provide new recommendations for range margins. Six treatment sites (liver, prostate, breast, head-and-neck, lung and medullo) were sub-divided into 12 categories. For each category, the range margins were estimated for target coverage using 2D range profiles of treatment fields in the patients comparing ADC to delivered (as simulated using the TOPAS Monte Carlo tool) fields. The fields were adjusted to ensure a perfect match of dose and range of delivered and ADC fields in water phantoms.

Results: The results for the sub-sites are shown in table 1. Overall, heterogeneous patient geometries are not well described resulting in an average range uncertainty of 4.8%, while homogenous sites could be delivered using a shorter range margin of on average 3.2%.

Conclusion: We find that range margins can be reduced for some treatment fields while the majority of fields require margins slightly higher than currently used. However, when not correcting for loss of dose due to small field sizes, scattering etc. 3.5% should be used. Prostate fields could also use a constant range margin of 2.5 mm. For heterogeneous geometries (see table and figure) generic range margins of 5.3% may be necessary.  

Treatment category

New Margin [%]

Breast upper nodes

5.3

Fields involving nasal/mouth cavity

4.8

Lung

5.2

Neck Nodes

3.8

Medullo (upper spine)

4.8

Breast

4.6

Liver (with lung)

3.7

Medullo (lower spine)

3.5

Whole brain

3.7

Brain boosts / mets

3.2

Liver (no significant lung involvement)

2.9

Prostate

2.5 mm (const.)

Table 1: New recommendations for range margins (without requiring changes to current procedures). Values in % of the range. An additional 1.2 mm for setup uncertainties are the same for all sites and not listed here.  

Author Disclosure: J.P. Schuemann: None. H. Paganetti: Research Grant; National Cancer Institute, General Electric Global Research, INCOM Inc. Honoraria; National Cancer Institute. Travel Expenses; National Cancer Institute. Editorial Board Member; Institute of Physics (IOP).

Harald Paganetti, PhD

Massachusetts General Hospital

Disclosure:
Employment
Massachusetts General Hospital: Academic Hospital: Employee

Compensation
General Electric Global Research: Research Grants; INCOM Inc.: Research Grants; National Cancer Institute: Honoraria, Research Grants, Travel Expenses

Leadership
Institute of Physics (IOP): Editorial Board Member

Presentation(s):

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