Histogram reduction method for calculating complication probabilities for three-dimensional treatment planning evaluations

The purpose of this study was to evaluate whether a spacer inserted in the prerectal space could reduce modeled rectal dose and toxicity rates for patients with prostate cancer treated in silico with pencil beam scanning (PBS) proton therapy. A total of 20 patients were included in this study who received photon therapy (12 with rectal spacer (DuraSeal™ gel) and 8 without). Two PBS treatment plans were retrospectively created for each patient using the following beam arrangements: (1) lateral‐opposed (LAT) fields and (2) left and right anterior oblique (LAO/RAO) fields. Dose volume histograms (DVH) were generated for the prostate, rectum, bladder, and right and left femoral heads. The normal tissue complication probability (NTCP) for ≥grade 2 rectal toxicity was calculated using the Lyman–Kutcher–Burman model and compared between patients with and without the rectal spacer. A significantly lower mean rectal DVH was achieved in patients with rectal spacer compared to those without. For LAT plans, the mean rectal V70 with and without rectal spacer was 4.19 and 13.5%, respectively. For LAO/RAO plans, the mean rectal V70 with and without rectal spacer was 5.07 and 13.5%, respectively. No significant differences were found in any rectal dosimetric parameters between the LAT and the LAO/RAO plans generated with the rectal spacers. We found that ≥ 9 mm space resulted in a significant decrease in NTCP modeled for ≥grade 2 rectal toxicity. Rectal spacers can significantly decrease modeled rectal dose and predicted ≥grade 2 rectal toxicity in prostate cancer patients treated in silico with PBS. A minimum of 9 mm separation between the prostate and anterior rectal wall yields the largest benefit.

N T C P = \frac{1}{2 \sqrt{italicπ}} {false\int}_{- \infty}^{t} e^{- \frac{x^{2}}{2}} d x,

where

t = \frac{g E U D - T D_{50}}{m \cdot T D_{50}},

Section: Methodsmentioning

confidence: 99%

“…The LKB model describes the normal tissue complication probability (NTCP) after uniform radiation of a fractional volume ( v ) of normal tissue to a dose ( D ) using the equation:

N T C P = \frac{1}{2 \sqrt{italicπ}} {false\int}_{- \infty}^{t} e^{- \frac{x^{2}}{2}} d x,

where

t = \frac{g E U D - T D_{50}}{m \cdot T D_{50}},

g E U D = {(][, \frac{1}{N_{v o x e l s}}, {false\sum}_{i = 1}^{N_{v o x e l s}}, D_{i}^{1 / n})}^{n},

Section: Methodsmentioning

confidence: 99%

Rectal dose to prostate cancer patients treated with proton therapy with or without rectal spacer

Chung

Polf

Badiyan

et al. 2016

“…( 13 ) The cell survival probability is given by:

S = exp (- E)

where the biological effect of radiation effect E can be expressed as:

E = n \cdot d \cdot (α + β \cdot d)

…”

Section: Methodsmentioning

confidence: 99%

Local tumor control probability to evaluate an applicator‐guided volumetric‐modulated arc therapy solution as alternative of 3D brachytherapy for the treatment of the vaginal vault in patients affected by gynecological cancer

Pedicini¹,

Strigari

Caivano³

et al. 2013

The purpose of this study was to evaluate the applicator‐guided volumetric‐modulated arc therapy (AGVMAT) solution as an alternative to high‐dose‐rate brachytherapy (HDR‐BRT) treatment of the vaginal vault in patients with gynecological cancer (GC). AGVMAT plans for 51 women were developed. The volumetric scans used for plans were obtained with an implanted CT‐compatible vaginal cylinder which provides spatial registration and immobilization of the gynecologic organs. Dosimetric and radiobiological comparisons for planning target volume (PTV) and organs at risk (OARs) were performed by means of a dose‐volume histogram (DVH), equivalent uniform dose (EUD), and local tumor control probability (LTCP). In addition, the integral dose and the overall delivery time, were evaluated. The HDR‐BRT averages of EUD and minimum LTCP were significantly higher than those of AGVMAT. Doses for the OARs were comparable for the bladder and sigmoid, while, although HDR‐BRT was able to better spare the bowel, AGVMAT provided a significant reduction of normald2cc, normald1cc, and dmax (p<0.01) for the rectum. AGVMAT integral doses were higher than HDR‐BRT with low values in both cases. Delivery times were about two or three times higher for HDR‐BRT with respect to the single arc technique (AGVMAT1) and dual arc technique (AGVMAT2), respectively. The applicator‐guided volumetric‐modulated arc therapy seems to have the potential of improving rectum avoidance. However, brachytherapy improves performance in terms of PTV coverage, as demonstrated by a greater EUD and better LTCP curves.PACS number: 87

“…The effective volume method of Kutcher et al (10) was used to generate effective doses and volumes that apply Lyman's (11) theory with Burman et al's (12) parameterization to calculate normal tissue complication probabilities (NTCP). Classically, this model is written as follows:

MJX-TeXAtom-ORD NTCP = MJX-TeXAtom-ORD \frac{1}{\sqrt{2 π}} \int_{- \infty}^{t} exp (\frac{- t^{2}}{2}) d t,

where, for effective volume

v, t = (D - {TD}_{50} (v)) / (m \times {TD}_{50} (v))

and

{TD}_{50} (v) = {TD}_{50} (1) \times v^{- n}

…”

Section: Methodsmentioning

confidence: 99%

Fractionated stereotactic radiotherapy for pediatric patients with retinoblastoma

Higgins

Gerbi

Macedon³

et al. 2006

In this report, we discuss the application of a modified Gill‐Thomas‐Cosman (GTC) relocatable head frame to enable fractionated stereotactic radiotherapy (SRT) of infants under anesthesia. This system has been used to treat two infants, ages 12 and 18 months, for bilateral retinoblastoma on a Varian 6/100 linear accelerator. The GTC head frame was used to reproducibly position and treat the orbits of these children to between 2520 cGy and 3960 cGy in 180‐cGy fractions. A standard head and neck tray, with accompanying thermoplastic mask, was adapted to mount to the head frame to enable these treatments. We found the maximum average deviation in the repeat fixations, as compared with the initial fitting data, to be ±2.2emmm. The overall average difference and standard deviation in measurement was 0.47±0.63.2emmm for the first case and 0.19±0.94.2emmm for the second case, with a combined average of 0.35±0.79.2emmm overall from a total of 381 point measurements. The stereotactic treatment plan (Radionics®) incorporated a single isocenter for each orbit and 3 or 4 arcs per isocenter. An intercomparison has been made between this technique and a standard lateral field technique, designed using the stereotactic radiosurgery (SRS) planning system. Dose‐volume histograms and corresponding normal tissue complication probabilities (NTCP) based on pediatric bone growth inhibition have been calculated for each method for the orbital bone areas. We found that the NTCP is reduced from 95% or more in the standard treatment method to 16% or less with SRT. Use of the modified head frame provides excellent setup reproducibility, facilitates access to patients for anesthesia, and reduces the chances of a poor cosmetic result in these growing children.PACS number: 87.53.Ly